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Sveconorwegian Mid-crustal Ultrahigh-temperature Metamorphism in Rogaland,Norway: U^Pb LA-ICP-MS Geochronologyand Pseudosections of Sapphirine Granulitesand Associated Paragneisses
KIRSTEN DRU« PPEL1,2*, LIZ ELSA« �ER1, SO« NKE BRANDT3 ANDAXEL GERDES4
1TECHNICAL UNIVERSITY BERLIN, INSTITUTE FOR APPLIED GEOSCIENCES, ACKERSTR. 71^76, D-13355 BERLIN,
GERMANY2KIT KARLSRUHE, INSTITUTE FOR APPLIED GEOSCIENCES, ADENAUERRING 20B, D-76131 KARLSRUHE, GERMANY3UNIVERSITY OF KIEL, INSTITUTE FOR GEOSCIENCES, LUDEWIG-MEYN-STR. 10, D-24118 KIEL, GERMANY4GOETHE-UNIVERSITY FRANKFURT, INSTITUTE FOR GEOSCIENCES, ALTENHO« FERALLEE 1, D-60438 FRANKFURT AM
MAIN, GERMANY
RECEIVEDJANUARY 13, 2011; ACCEPTED SEPTEMBER 12, 2012ADVANCE ACCESS PUBLICATION NOVEMBER 5, 2012
MgAl-rich sapphirine granulites (bulk XMg 0·71^0·75) occur as
boudinaged layers in migmatitic garnet^orthopyroxene^cordierite^
spinel gneisses and migmatitic garnet^sillimanite metapelites in the
vicinity of the c. 930^920 Ma Rogaland anorthosite^mangerite^
charnockite complex, SW Norway. Investigation of the mineral
reaction history of the sapphirine granulites and the surrounding
paragneisses, combined with geothermobarometric calculations and
constraints from pseudosections calculated in the Na2O^CaO^
K2O^FeO^MgO^Al2O3^SiO2^H2O^TiO2 (NCKFMASHT)
system, indicates a clockwise P^T path that reached peak-
metamorphic ultrahigh-temperature (UHT) conditions of c.10008C at c. 7·5 kbar by prograde heating. UHT peak metamorph-
ism is followed by near-isothermal (ultra)high-temperature decom-
pression to P55·5 kbar at 900^10008C and subsequent
near-isobaric cooling to5750^8008C at c. 5 kbar. In situ U^Pb
laser ablation inductively coupled plasma mass spectrometry dating
of metamorphic zircon within the sapphirine granulites yields con-
cordant ages of 1010� 7Ma and 1006� 4Ma for zircon
presumably formed during prograde breakdown of garnet at
T4850^9408C as estimated fromTi-in-zircon thermometry, sug-
gesting that UHT metamorphism and the deduced clockwise P^Tevolution is linked to regional Sveconorwegian metamorphism at c.1010 Ma. Most of the metamorphic zircon surrounds largely resorbed
inherited oscillatory zoned zircon cores (207Pb/206Pb apparent ages
1220^1841 Ma), testifying to the sedimentary origin of the sapphir-
ine granulites. Epitactic growth of xenotime on metamorphic zircon
at 933� 5Ma is suggested to be related to crystallization of anatec-
tic melt during post-decompressional cooling. The clockwise P^Tpath culminating at mid-crustal UHTconditions at c. 1010Ma fol-
lowed by (U)HTdecompression is interpreted to result from colli-
sional tectonics during the early stages of the Sveconorwegian
Orogeny, followed by gravitational collapse of the mountain plateau.
KEY WORDS: anorthosite; isograds; pseudosection; sapphirine; U^Pb
dating; UHT metamorphism
*Corresponding author. E-mail: kirsten.drueppel@kit.edu
� The Author 2012. Published by Oxford University Press. Allrights reserved. For Permissions, please e-mail: journals.permissions@oup.com
JOURNALOFPETROLOGY VOLUME 54 NUMBER 2 PAGES 305^350 2013 doi:10.1093/petrology/egs070
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I NTRODUCTIONRocks of highly magnesian and aluminous bulk compos-ition are highly sensitive to P^Tchanges and often preservewell-developed reaction textures that provide informationabout P^T conditions. Such MgAl-granulites are increas-ingly being used to elucidate the P^T paths of granulite-facies terranes (e.g. Bertrand et al., 1992; Harley, 1998;Kriegsman & Schumacher, 1999; Baba, 2003; Martignole& Martelat, 2003; Goncalves et al., 2004; Sajeev et al.,2004; Brandt et al., 2007, 2011).We report new petrological and geochronological data
for sapphirine-bearing MgAl-granulites from Rogaland(SW Norway). The sapphirine granulites of Rogalandoccur as boudinaged lenses in migmatitic metasedimen-tary gneisses (Grt^Opx^Crd^Spl gneisses and Grt^Silmetapelites; mineral abbreviations after Kretz, 1983)enclosed by migmatitic charnockite. They are exposed inthe vicinity of the 930^920Ma anorthosite^mangerite^charnockite (AMC) plutonic suite of Rogaland, SWNorway, some 8 km from the actual contact. This region isaffected by ultrahigh-temperature (UHT) granulite-faciesmetamorphism and an interference exists between regionalSveconorwegian metamorphism (M1 between c. 1035 and970 Ma) and contact metamorphism related to intrusionof the anorthosite plutons (M2 between 930 and 920 Ma;Tobi et al., 1985). Considering alignment of part of the sap-phirine crystals, Jansen & Tobi (reported by Maijer &Padget,1987) inferred that their formation might be relatedto the regional metamorphism. Detailed petrological andgeochronological investigations are, however, thus far lack-ing for these rocks.In this study, we combine petrographic investigations of
reaction textures, mineral chemistry, bulk geochemistryand geothermobarometric data with calculated P^T pseu-dosections of sapphirine granulites and the surroundingmigmatitic Grt^Opx^Crd^Spl paragneisses and Grt^Silmetapelites to constrain both their peak-metamorphicconditions and retrograde P^Tevolution. In situ laser abla-tion inductively coupled plasma mass spectrometry(LA-ICP-MS) dating of zircon and xenotime in thin sec-tions of the sapphirine granulites links their metamorphicevolution to the main metamorphic events reportedfrom the Rogaland area; that is, regional Sveconorwegianmetamorphism (M1) versus contact metamorphism relatedto intrusion of the Rogaland Complex during thepost-collisional stage of the Sveconorwegian Orogeny(M2). Results are discussed in a regional context, especiallyconsidering the close spatial association of the UHTgranu-lites with the anorthositic^noritic Rogaland Complex.Our results place new constraints on the tectonothermalevolution of the Rogaland Sector during Late Proterozoiccrust-forming processes and on the generation of contactmetamorphic envelopes surrounding large Proterozoicanorthosite massifs.
GEOLOGICAL SETT INGThe study area forms part of the SveconorwegianRogaland^Vest Agder terrane of southwestern Norway.The high-grade metamorphic basement exposed in thispart of the Baltic Shield mainly comprises large bodies ofmigmatitic charnockites and charnockitic gneisses. Attheir margins, the large charnockitic plutons are inter-layered with mafic to ultramafic, and metasedimentarylenses (Fig. 1). The latter are mainly composed of migmati-tic metagreywackes and metapelites referred to as ‘garneti-ferous migmatites’ (Huijsman et al., 1981), as well assubordinate quartzites, calcsilicates, and marbles of theso-called ‘Faurefjell formation’ (Hermans et al., 1975).Deposition ages of c. 1·5 Ga have been suggested for theserocks (e.g. Verschure, 1985). The whole area underwenthigh-grade regional metamorphism during the Sveconor-wegian Orogeny (M1) at c. 1035^970Ma (U^Pb monazite:Bingen & van Breemen, 1998; Bingen et al., 2008a; U^Pbzircon:Wielens et al.,1981; Mo« ller et al., 2002, 2003; Tomkinset al., 2005; Re^Os molybdenite: Bingen & Stein, 2003;Bingen et al., 2006, 2008b; Table 1). This metamorphicevent was associated with strong deformation of the rocksand is suggested to record crustal thickening of the Roga-land^Vest Agder terrane (Bingen et al., 2008c). Corre-sponding amphibolite-facies peak-metamorphic conditionsof 600^7008C and 6^8 kbar, increasing from NE to SW(Tobi et al., 1985), have been calculated for garnet-bearingmigmatites (Jansen et al., 1985; Tobi et al., 1985; Tomkinset al., 2005). Zircon included in cordierite coronas formedby garnet breakdown of metasediments of the Oltedalarea (Fig. 1), near the orthopyroxene isograd, dates re-gional decompression following the M1 event at955�8Ma (Tomkins et al., 2005).The high-grade metamorphic basement was subse-
quently intruded by the Rogaland Complex (Fig. 1), a1200 km2 anorthosite^mangerite^charnockite suite at930^920Ma (Scha« rer et al., 1996), presumably duringpostorogenic exhumation of the Rogaland^Vest Agder ter-rane (Versteeve, 1975). The Rogaland Complex comprisesthree main massif-type anorthosite bodies that are them-selves intruded by the layered mafic series of theBjerkreim^Sokndal lopolith, comprising anorthosite,norite, gabbronorite, mangerite, and charnockite layers(Michot, 1960). Thermal ionization mass spectrometry(TIMS) U^Pb-dating of zircon and baddeleyite inclusionsin orthopyroxene megacrysts in the anorthosites hasyielded ages of 931^926Ma (Scha« rer et al., 1996). Theend of the igneous activity is dated at 920�3Ma byzircon from ilmenite-rich norite from Tellness (Scha« reret al., 1996). Low pressures of c. 4 kbar are postulatedfor the emplacement depth of the Rogaland Complexbased on barometric estimates for garnet^orthopyroxene^plagioclase^sillimanite equilibria in osumilite-bearinggneisses (Jansen et al., 1985;Westphal, 1998;Westphal et al.,
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2003) in the surrounding metamorphic basement andexperiments on the stability of osumilite in metapelites(i.e. 5·5�0·2 kbar for the stability of an osumilite^garnet^orthopyroxene assemblage at 800^8508C; Hollandet al., 1996). Melting experiments on jotunite from thelate-stage Bjerkreim^Sokndal layered intrusion supportthese relatively low M2 pressures of 55 kbar (VanderAuwera & Longhi, 1994).The intrusion of the Rogaland Complex is suggested
to be responsible for a multi-stage contact-metamorphicoverprint of the surrounding basement, comprising anearly, high-temperature to UHT granulite-facies stage(M2; 49008C, c. 5 kbar), followed by a retrogradeamphibolite-facies overprint (M3; 550^7008C, 3^5 kbar)attributed to isobaric cooling of the intrusive bodies(Hermans et al., 1975; Maijer et al., 1981; Maijer, 1987).According to Jansen et al. (1985) and Maijer (1987), thecontact-thermal M2 metamorphism was a very intenseevent, erasing most of the regional metamorphic M1 para-geneses during static recrystallization, with undeformed,high-grade contact-metamorphic M2 assemblages beingpreserved in a 10^30 km wide aureole around theRogaland Complex. More recently, Bingen et al. (2006)were able to show that the post-collisional anorthositeplutonism is associated with significant ductile deform-ation in the surrounding basement at least 10 km awayfrom the plutons.
Following Jansen et al. (1985) and Maijer (1987), contact-metamorphism is reflected by several mineral isograds;that is (with increasing distance from the contact): (1) the(inverted) pigeonite-in isograd in metabasites c. 5 km fromthe contact; (2) the osumilite-in isograd in metapelites c.10^13 km from the intrusive contact; (3) the orthopy-roxene-in isograd in leucocratic ortho- and paragneisses, c.20 km from the contact; (4) the clinopyroxene-in isograd ingranitic gneisses further east (Fig. 1). Whereas the first twoisograds wrap around the western lobe of the RogalandComplex, the last two run subparallel to the southeasternigneous contact, but diverge from it in the north.According to Jansen et al. (1985) and Westphal et al. (2003)contact-metamorphic temperatures during the M2 event de-crease from 9008C close to the contact, judging from the oc-currence of pigeonite (now inverted) and estimates for theosumilite-bearing assemblage, to c. 7508C at 15 km distancefrom the igneous complex at the orthopyroxene isograd. Incontrast to the pigeonite-in and osumilite-in isograds, forwhich a genetic relation with the emplacement of theRogaland Complex is generally accepted, the origin ofthe Opx-in and Cpx-isograds is still debated. They areeither discussed in terms of the anorthosite emplacement(M2; Tobi et al., 1985; Maijer, 1987; Westphal et al., 2003) orsuggested to represent transitions in the regional meta-morphic grade during the Sveconorwegian Orogeny(M1; e.g. Bingen & van Breemen,1998; Bingen et al., 2008a).
Fig. 1. Geology of the Rogaland^Vest Agder metamorphic terrane, modified after Falkum (1982). Isograds after Tobi et al. (1985). Location ofstudy area (Fig. 2) is indicated by the rectangle.
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Table 1: Compilation of published geochronological data on igneous and metamorphic events in the Rogaland area
Igneous/metamorphic stage Reference Lithology Mineral and method Age (Ma)
Igneous (pre- to syn-M1) Pasteels & Michot (1975) Granitic gneiss U–Pb zircon c. 1486
Zhou et al. (1995) Charnockitic gneiss U–Pb zircon 1159� 5
Bingen & van Bremen (1998) Augen gneiss U–Pb zircon 1049 þ2/–8, 1051 þ2/–8, 1051 þ2/–4
Andersen et al. (2002) Granite U–Pb zircon 1036 þ23/–22
Moller et al. (2002) Pigeonite charnockite U–Pb zircon 1588� 10 (inherited), 1033� 20, 1056� 10
Pigeonite charnockite U–Pb zircon 1520� 7 (inherited), 1035� 6
Augen gneiss U–Pb zircon 1034� 7
Moller et al. (2003) Pegmatitic leucosome U–Pb zircon 1039� 11
Migmatitic garnet gneiss U–Pb zircon 1046� 12
Tomkins et al. (2005) Metapelitic migmatite U–Pb zircon 1233� 67 to 3053� 67
Metamorphic (syn-M1) Pasteels & Michot (1975) Garnet gneiss U–Pb zircon c. 1018–951
Augen gneiss U–Pb zircon 1001–1041
Bingen & van Bremen (1998) Augen gneiss U–Pb monazite 1006� 3, 975� 2, 1010� 2, 1000� 1,
1012� 1, 1008� 1, 990� 1, 974� 2
Charnockitic gneiss U–Pb monazite 1019� 1, 1005� 1, 1004� 1, 1001� 1
Augen gneiss U–Pb monazite 1024� 1, 1009� 1, 987� 2, 986� 2,
970� 5, 971� 2, 951� 6
Charnockitic gneiss U–Pb monazite 997� 1, 986� 2, 985� 1, 972� 1,
1004� 1, 950� 1, 943� 1
Augen gneiss U–Pb monazite 1007� 2, 979� 1
Moller et al. (2002) Augen gneiss U–Pb zircon 1020� 7 to 980� 7
Pigeonite charnockite U–Pb zircon 1013� 8, 1014� 11, 1017� 12 to
992� 14, 972� 20
Tomkins et al. (2005) Metapelitic migmatite (peak) U–Pb zircon 1035� 9, 989� 11
Metapelitic migmatite
(decompression)
U–Pb zircon 955� 8
Bingen et al. (2008b) Granitic gneiss U–Pb monazite 1002� 7
Augen gneiss Th–Pb monazite 999� 5, 997� 5
Charnockitic gneiss Th–Pb monazite 1013� 5, 980� 5
Felsic granulite U–Pb monazite 1032� 5, 990� 8
Metamorphic
(post-M1 decompression)
Bingen & Stein (2003) Qtz–Pl–Kfs-Leucosome
in Grt–Opx-gneiss
Re–Os molybdenite 974� 3 to 969� 3
Tomkins et al. (2005) Metapelitic migmatite
(decompression)
U–Pb zircon 955� 8
Bingen et al. (2006) Granitic gneiss Re–Os molybdenite 982� 4 to 974� 3; 959� 3, 956� 3
to 947� 3, 946� 3 to 939� 3
Augen gneiss Re–Os molybdenite 953� 3 to 931� 3
Igneous (syn-M2) Pasteels et al. (1979) Pegmatite U–Pb zircon 914� 6
Charnockite U–Pb zircon 931� 10
Scharer et al. (1996) Anorthosite U–Pb baddeleyite 915� 4, 929� 2, 932� 3, 932� 3
Norite U–Pb zircon 920� 3
Quartz mangerite U–Pb zircon 931� 5
Metamorphic (M2 to M3) Pasteels & Michot (1975) Garnet gneiss U–Pb zircon 910� 30
Bingen & van Bremen (1998) Augen gneiss U–Pb monazite 928� 3, 927� 1, 925� 2, 912� 3,
907� 5, 930� 1, 928� 1, 904� 5, 904� 8
Charnockitic gneiss U–Pb monazite 932� 1
Moller et al. (2002) Pigeonite charnockite U–Pb zircon 931� 22, 920� 5, 911� 6
Bingen et al. (2008b) Augen gneiss Th–Pb monazite 927� 5, 924� 5, 922� 5, 914� 4, 910� 9
Bingen et al. (2006) Qtz vein Re–Os molybdenite 918� 3 to 917� 3
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F I ELD RELATIONS OF THEV IKESDALEN AREAThe occurrence of sapphirine-bearing rocks in the vicinityof the Rogaland Complex was first decribed by Hermanset al. (1976). The exposure is situated c. 7 km north of theintrusive contact with the anorthosite massif adjacent tothe osumilite-in isograd and north of Vikes� (Fig. 1). Thearea is dominated by banded to massive, partially garnet-bearing, migmatitic charnockite, interlayered withmigmatitic metasedimentary units and metabasites. Meta-sediments mainly comprise Grt^Opx^Crd^Spl gneissesintercalated with subordinate metapelites (Fig. 2). Garnet-rich granite forms single, concordant layers, which weinterpret as leucosomes of the metasedimentary units. Thesapphirine granulites are exposed as concordant, discon-tinuous and folded layers within the Grt^Opx^Crd^Spl-gneisses (Fig. 3a^c). They form either sharplybounded, decimetre- to metre-thick boudins (Fig. 3a) ordiffuse schlieren (Fig. 3b), which grade into the surround-ing gneisses. Prismatic sapphirine crystals of up to 2 cm inlength display a weak alignment, oriented subparallel to
the regional foliation (Fig. 3c). The surrounding stronglymigmatitic Grt^Opx^Crd^Spl gneisses are banded on acentimetre to metre scale and display a foliation that wassubsequently folded (Fig. 3d). Leucosomes form irregularpatches or concordant layers, mainly composed of quartz,alkali feldspar, plagioclase and garnet. Restitic domainsare rich in orthopyroxene, spinel, plagioclase and garnet,the last of which forms large crystals of up to 5 cm in diam-eter largely replaced by symplectitic orthopyroxene,spinel, cordierite, and plagioclase (Fig. 3d). Rare migmati-tic Grt^Sil metapelites form narrow, concordant layers inthe Grt^Opx^Crd^Spl gneisses and contain broad con-cordant garnet-rich leucosomes of granitic composition.
ANALYT ICAL METHODSMajor and trace element contents of bulk-rock sampleswere analysed with a PHILIPS PW 1404 wavelength-dispersive X-ray fluorescence (XRF) spectrometer at theInstitute of Applied Geosciences, Technical UniversityBerlin, Germany, using fused glass discs.
Fig. 2. Geological map of the Ivesdalen area (see Fig.1 for location), showing the sample locations of the sapphirine granulite, migmatitic meta-pelite and migmatitic Grt^Opx^Crd^Spl gneiss.
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Electron microprobe (EMP) analyses of minerals wereperformed on a Cameca Camebax instrument at theZentraleinrichtung fu« r Elektronenmikroskopie (ZELMI),Technical University Berlin, Germany. Natural and syn-thetic standards were used for instrument calibration.Mineral analyses were performed with an accelerating volt-age of 15 kV, a beam current of 20 nA and an electronbeam of 2·5 mm in diameter. Exsolved feldspar wasadditionally analysed with a defocused beam of 20 mm indiameter. EMP profiles across minerals were analysedusing a Cameca SX100 instrument at the GeoForschungs-Zentrum (Helmholtz Centre) Potsdam, Germany. Analyseswere performed with an accelerating voltage of 15 kV, abeam current of 20 nA and a beam diameter of 2mm.In situ trace element analyses of the major phases in both
the sapphirine granulites and the surrounding gneisseswere performed on polished �100 mm thick sectionsby LA-ICP-MS at the Institute for Geodynamicsand Geomaterials, University of Wu« rzburg, Germany.
A Merchantek 266 LUV laser coupled with an Agilent7500i ICP-MS device was used [plasma power 1250W, car-rier gas (Ar) 1·28 lmin^1, plasma gas (Ar) 14·9 lmin^1,auxiliary gas (Ar) 0·9 lmin^1]. The diameter of the laserbeam was 50 mm and the laser repetition rate was 10Hzfor all analyses. We measured background and sample at20 s each. Si in silicates and Mn in ilmenite and magnetitewere used as internal standards. The glass reference mater-ials NIST 612 [values given by Pearce et al. (1997)] andNIST 614 [values given by Horn et al. (1997)] were usedfor external instrument calibration and for control of theresults. Data processing was conducted using GLITTER3.0 software (On-line Interactive Data Reduction for theLA-ICP-MS, Macquarie Research Ltd., 2000). The preci-sion is approximately �7% for element concentrations410 ppm, �10% for concentrations 45 ppm, �15% forconcentrations 41ppm and �20% for concentrations51ppm. The minimum detection limits were in the rangeof 0·02^0·5 ppm.
Fig. 3. Outcrop photographs. (a) Sharply bounded and weakly foliated sapphirine granulite boudin surrounded by foliated Grt^Opx^Crd^Splgneiss. (b) Folded schlieren of sapphirine granulite with diffuse contacts to the bordering Grt^Opx^Crd^Spl gneiss. (c) Weakly aligned, pris-matic crystals of deep blue sapphirine in the sapphirine granulite, visible on a macroscopic scale. (d) Porphyroblastic garnet of the Grt^Opx^Crd^Spl gneiss largely replaced by an orthopyroxene^spinel^plagioclase intergrowth and set in a foliated Kfs^Pl^Qtz^Bt matrix.
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For the in situ U^Pb LA-ICP-MS analyses, two selectedsapphirine granulite samples were prepared as polishedthick sections (c. 80^100 mm thick). The internal structuresof zircon and xenotime were characterized via back-scattered electron (BSE) images on a high-resolution scan-ning electron microscope at ZELMI, Technical UniversityBerlin, Germany, and under cathodoluminescence (CL)using a JEOL JSM-6400 electron microprobe at theGoethe-University Frankfurt (GUF). U^Pb analyses werecarried out by LA-ICP-MS at GUF using a Thermo-Finnigan Element II sector field ICP-MS system coupledto a New Wave UP213 ultraviolet laser with a teardroplow-volume cell following the method described byGerdes & Zeh (2006, 2009) and Frei & Gerdes (2009). Thelaser was fired with 5Hz repetition rate and an energydensity of about 3 J cm^2 over 18 s of ablation. The spotsize was adjusted to the grain size and varied between 8and 20 mm for zircon and between 8 and 18 mm for xeno-time. The estimated depth penetration was about10^20 mm. Signal was tuned for maximum sensitivitywhile keeping the oxide formation rate below 0·2%(UO/U). All data were corrected for common-Pb basedon the background and interference-corrected 204Pbsignal (daily 204Hg¼170�20 c.p.s) and a model Pb com-position (Stacey & Kramers, 1975). Within-run Pb/Ufractionation was corrected for each analysis using alinear regression through all ratios. Subsequently instru-mental mass bias and drift were corrected by normaliza-tion to reference zircon GJ-1. Previous studies at GUFhave shown that LA-ICP-MS with non-matrix matchedstandardization can yield precise and accurate results(e.g. Meier et al., 2006; Dill et al., 2007; Millonig et al.,2008). Reported uncertainties (�2s) were propagated byquadratic addition of the external reproducibility (SD,standard deviation) of the GJ-1 reference standard (1·3%for 206Pb/238U; n¼19) of the day and the within-run statis-tics of each analysis (2 SE, standard error). Accuracy andprecision of the non-matrix matched standardization waschecked by repeated analyses (n¼ 5) of Moacir monaziteand Ples› ocive zircon. Moacir analyses yielded a weightedmean 207Pb/235U age of 502·4�5·5Ma (MSWD¼ 0·7;SD¼ 2·2%) and Ples› ocive analyses a concordia age of336·4�2·8Ma (MSWD¼1·5). This is in perfect agree-ment with recent isotope dilution (ID)-TIMS analyses ofthese reference minerals (i.e. 511·2�0·4Ma and337·13�0·37, respectively; Slama et al., 2008; Gasquetet al., 2010).
RESULTSPetrographySapphirine granulites
The sapphirine granulites preserve peak-metamorphicassemblages of coarse porphyroblastic sapphirine
(15^25 vol. %) and orthopyroxene (15^20 vol. %) that areset in a fine-grained matrix of alkali feldspar (10^15vol. %), plagioclase (10^15 vol. %) and biotite (15^25vol. %; Fig. 4a) and are partly replaced by fine-grainedspinel^cordierite(^biotite) intergrowths (21^28 vol. %).The minerals mostly display a homogeneous distributionwith a weak foliation being defined by slightly aligned sap-phirine and biotite (Fig. 4a).Sapphirine forms subhedral prismatic crystals (mostly
1mm to 2 cm in length) with a strong colourless to laven-der blue pleochroism (Fig. 4b). They preserve rare inclu-sions of biotite. Porphyroblastic, subhedral orthopyroxene(mostly 1mm to 1·5 cm in diameter) with fine-grained,exsolved ilmenite platelets, displays strong greenish tobrownish pleochroism (Fig. 4b) and also contains rarebiotite inclusions. Granoblastic alkali feldspar and plagio-clase of the equigranular, fine-grained matrix (grain sizesof 0·2^0·5mm) are generally anhedral and display strongmicroperthitic and antiperthitic exsolution, respectively,indicating their formation at high temperatures. Alongthe albite exsolution lamellae, alkali feldspar is stronglysericitized, whereas plagioclase displays only minoralteration.Commonly, porphyroblastic sapphirine is replaced by a
fine-grained symplectite composed of cordierite and greenspinel (Fig. 4a, b and d) whereby its original shape is pre-served. A granoblastic cordierite^spinel reaction rim, onthe other hand, occurs between porphyroblastic sapphirineand orthopyroxene (Fig. 4b and c). Sapphirine (includingthe pseudomorphous cordierite^spinel symplectites) is sub-sequently mantled by an almost monomineralic rim ofgranoblastic spinel, followed by cordierite towards theneighbouring orthopyroxene (Fig. 4b). Spinel of both reac-tion textures displays exsolution of magnetite and platyreddish brown ilmenite. In places, spinel also containsexsolved corundum. Brownish biotite mainly replaces cor-dierite of the cordierite^spinel intergrowths (Fig. 4b^d)but also occurs as corona around porphyroblastic ortho-pyroxene. In addition, biotite is an abundant replacementproduct of matrix alkali feldspar.Accessory phases include zircon, xenotime, magnetite,
and ilmenite. Subhedral zircon (50^100 mm in diameter)occurs in the feldspar^biotite matrix, as inclusions in sap-phirine and orthopyroxene and as inclusions in cordieritewithin the cordierite^spinel reaction textures (Fig. 4d).
Migmatitic Grt^Sil metapelites
Migmatitic metapelites are made up of greyish^bluishlayers rich in garnet (up to 10 vol. %), cordierite (8^30vol. %), sillimanite (up to 5 vol. %), and spinel (up to 10vol. %); they contain minor plagioclase, quartz, ilmenite,sulphides, and alkali feldspar, as well as accessory zircon,alternating with felsic leucosomes mainly consisting ofmedium-grained, granoblastic quartz, plagioclase and
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minor microperthitic orthoclase, as well as accessoryspinel.Anhedral, medium-grained garnet 1^3mm in diameter
within the melanocratic layers contains abundant inclu-sions of sillimanite, quartz and minor biotite (Fig. 5a).Garnet is associated with anhedral, porphyroblastic spineland ilmenite (both 1^2mm in diameter) and porphyro-blastic quartz (0·5^3mm in diameter; Fig. 5a). Porphyro-blastic spinel and quartz occur in direct contact or areseparated from each other by retrograde coronas (Fig. 5b,d and e; see below). Spinel preserves inclusions of silliman-ite and quartz whereas porphyroblastic quartz enclosessillimanite, biotite and spinel (Fig. 5b). Matrix sillimaniteoccurs as euhedral, fine-grained prisms of up to 0·2mmin length that are associated with garnet-rich, foliation-parallel stringers (Fig. 5a). Minor plagioclase, alkali feld-spar and quartz in the matrix form anhedral, granoblasticgrains 0·1^0·2mm in diameter.
Garnet is separated from prismatic sillimanite and/orquartz by narrow plagioclase coronas, which are followedby broad cordierite moats (Fig. 5a and c). Porphyroblasticspinel and quartz are locally separated by a fine-grainedintergrowth of quartz and hercynitic spinel (Fig. 5a).More often porphyroblastic spinel is separated from por-phyroblastic quartz by a broad moat of cordierite (Fig. 5dand e). Locally, this cordierite forms symplectites withquartz (Fig. 5d and e), which occasionally containK-feldspar. A second generation of fine-grained (50·1mm)garnet forms a corona around porphyroblastic spinel(Fig. 5a, b, e and f). Coronitic garnet also forms rimsaround sulfides, ilmenite (Fig. 5e) and spinel of thespinel^quartz intergrowths (Fig. 5a). Locally, coroniticgarnet replaces cordierite of the cordierite^quartz sym-plectites around spinel, as evident from vermicularquartz, which is preserved as inclusions in the newlyformed garnet (Fig. 5e and f). Rarely cordierite is partly
Fig. 4. Mineral assemblages and reaction textures of the sapphirine granulites (a, thin-section scan; b^d, thin-section photomicrographs). (a)Sapphirine and orthopyroxene porphyroblasts are set in a medium-grained Kfs^Pl^Bt matrix. (b) At the contact with orthopyroxene, por-phyroblastic sapphirine is subsequently mantled by granoblastic spinel and cordierite. (c) Sapphirine itself is replaced by spinel^cordierite sym-plectites, the latter of which is preferentially replaced by biotite. (d) Zircon is most abundant in granoblastic cordierite of the cordierite^spinelreaction rims.
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Fig. 5. Mineral assemblages and reaction textures of the Grt^Sil metapelites (thin-section photomicrographs). (a) The porphyroblastic assem-blage of spinel, quartz, and garnet, intergrown with sillimanite, constitutes the melanocratic layers of the migmatitic Grt^Sil metapelite.Garnet is surrounded by a broad cordierite rim. A spinel^quartz intergrowth occurs between porphyroblastic spinel and quartz. Spinel of theintergrowth is surrounded by a narrow garnet corona. (b) Porphyroblastic spinel is in direct contact with quartz, which also occurs as an inclu-sion in spinel. Quartz preserves a small biotite inclusion. Coronas of garnet and cordierite locally separate porphyroblastic spinel and quartz.(c) A narrow plagioclase rim followed by a broad cordierite corona separates porphyroblastic garnet from sillimanite. (d) Porphyroblasticquartz and spinel are separated by a broad cordierite corona, which also occurs around sillimanite and ilmenite. Locally, cordierite forms asymplectitic intergrowth with quartz. Spinel is partly replaced by corundum, retrogressed to Al-hydroxides. (e) Spinel and ilmenite are sur-rounded by a cordierite^quartz symplectite, partly overgrown by garnet, with the vermicular quartz being preserved as inclusions in thenewly formed garnet. (f) Biotite formed at the expense of cordierite and porphyroblastic spinel is rimmed by a garnet corona. In addition, bio-tite overgrows the margins of the garnet (upper left).
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replaced by biotite, which, in turn, is surrounded by a rimof garnet, comprising abundant quartz inclusions (Fig. 5f).Locally, euhedral garnet, which forms around spinel, coex-ists with biotite^quartz intergrowths that have grownalong cordierite margins.
Migmatitic Grt^Opx^Crd^Spl gneisses
The Grt^Opx^Crd^Spl gneisses are inhomogeneous intexture and mainly comprise equigranular, medium-grained leucocratic zones composed of alkali feldspar(30^50 vol. %), plagioclase (30^50 vol. %), and quartz(10^20 vol. %), together with minor biotite (0^10 vol. %),orthopyroxene (0^5 vol. %), spinel (0^5 vol. %), and ac-cessory cordierite, zircon, and ilmenite (Fig. 6a). Maficschlieren of up to 10 cm in width and up to several metresin length are irregularly distributed in the outcrops, butmay also alternate with quartz^feldspar-rich zones ona thin-section scale defining a compositional layering(Fig. 6a). These melanocratic zones are mainly composedof relics of porphyroblastic orthopyroxene and garnet, thelatter of which is largely replaced by complex intergrowthsof orthopyroxene (50^70 vol. %), hercynite spinel/magnet-ite (10^20 vol. %), plagioclase (�10 vol. %) biotite (5^10vol. %), cordierite (5^15 vol. %), and minor alkali feldspar(510 vol. %; Fig. 6a^d).Garnet forms coarse porphyroblastic grains of up to
6 cm in diameter, locally associated with porphyroblasticorthopyroxene (1^3 cm in diameter) intergrown with fine-grained, greenish spinel (1^2mm in diameter; Fig. 6a, band e). The orthopyroxene porphyroblasts frequently dis-play exsolution of greenish spinel (Fig. 6c and e). Porphyro-blastic garnet and orthopyroxene are surrounded by afine- to medium-grained (grain sizes of 0·1^1·2mm), leuco-cratic matrix composed of anhedral, micro- to mesoperthi-tic alkali feldspar, subhedral, antiperthitic plagioclase,weakly aligned biotite, quartz, and minor fine-grained, an-hedral ilmenite (Fig. 6a and b).Porphyroblastic garnet (1^6 cm in diameter) is largely to
completely replaced by a fine-grained intergrowth ofmedium-grained, anhedral, antiperthitic plagioclase,brownish, anhedral orthopyroxene with vermicular spinelexsolution, and isometric greenish spinel (Fig. 6b and c)associated with magnetite. Plagioclase mainly occurs indirect contact with the garnet relicts, separating it fromthe replacing orthopyroxene (Fig. 6c). Fine-grained anhe-dral cordierite, in places together with biotite, occurs as anarrow reaction rim between orthopyroxene and exsolvedspinel in the Opx^Spl^Pl intergrowth replacing porphyro-blastic garnet (Fig. 6d and e). Alkali feldspar and biotiteare preserved only in the outermost zones of the pseudo-morphs after garnet. Biotite also forms coronas aroundporphyroblastic orthopyroxene and garnet (Fig. 6e). Asecond generation of garnet overgrows coronitic biotite assub- to euhedral grains (Fig. 6f). In addition, fine-grainedsecondary garnet of up to 0·1mm in diameter is intergrown
with orthopyroxene, replacing orthopyroxene of the Opx^Spl^Pl intergrowth as garnet^orthopyroxene symplectites,or forms monomineralic rims around spinel.
Mineral chemistrySelected samples of both the sapphirine granulites and thesurrounding migmatitic Grt^Opx^Crd^Spl gneisses andmigmatitic Grt^Sil metapelites were analysed for themajor and trace element composition of their majorphases by EMP and LA-ICP-MS (only sapphirine granu-lites), respectively.The XMg of Fe^Mg silicates is calculatedas molar Mg/(MgþFe2þ). Representative analyses arelisted inTables 2^9.
Garnet
Garnet formulae were calculated on a 24-oxygen basis. Forthe estimation of the Fe3þ contents of garnet a calculationmodus on the basis of 16 cations was chosen. End-membercalculation followed the sequence andradite, grossular, al-mandine, spessartine and pyrope. Resorbed porphyro-blastic garnet of the Grt^Opx^Crd^Spl gneisses is analmandine^pyrope solid solution with minor proportionsof spessartine (�10mol %) and grossular (�3mol %)and an average composition of Prp41Alm46Sps10Grs3 (XMg
0·46^0·48; Table 2). Core^rim zoning is not developed(Fig. 7). Rims of secondary garnet around spinel, late sym-plectitic garnet intergrown with orthopyroxene, andregrown euhedral garnet on biotite (average compositionPrp35Alm53Sps11Grs1; XMg 0·38^0·40) are always less mag-nesian than porphyroblastic garnet (Fig. 7).Porphyroblastic garnet of the migmatitic metapelite is a
Ca- and Mn-poor pyrope^almandine solid solution(Prp38^35Alm58^61Sps1Grs2^0; XMg 0·36^0·40; Table 2). Thepyrope content slightly increases towards the rim (Fig. 7).Secondary garnet (Prp33^29Alm67^63Sps2Grs2; XMg 0·30^0·34; Table 2, Fig. 7) rimming spinel is also Ca- andMn-poor but less magnesian than porphyroblastic garnet.
Orthopyroxene
Orthopyroxenes of the sapphirine granulite and Grt^Opx^Crd^Spl gneiss show only minor differences in their com-positions (Table 3; Fig. 7). Porphyroblastic orthopyroxeneof the sapphirine granulites is characterized by higherXMg values (0·69^0·75), when compared with porphyro-blastic matrix orthopyroxene of the Grt^Opx^Crd^Splgneisses (XMg 0·63^0·67).The Al2O3 contents of porphyro-blastic orthopyroxene from the sapphirine granulite andthe Grt^Opx^Crd^Spl gneiss, on the other hand, are simi-lar (8·1^8·9wt %), with the highest values being preservedin the cores of large grains. Orthopyroxene replacing por-phyroblastic garnet in the Grt^Opx^Crd^Spl gneiss hassimilar XMg (0·63^0·68) and Al2O3 contents (7·3^9·3wt%). Symplectitic orthopyroxene intergrown with lategarnet is characterized by higher XMg values (0·70^0·77)and the lowest Al2O3 contents (5·5^6·3wt %).
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Regarding its trace element composition, orthopyroxeneof the sapphirine granulite is characterized by high andrimward increasing Ti (860^2500 ppm) and Mn (1250^2150 ppm), and minor contents of Sc (40^90 ppm),V (60^105 ppm),Y (10^80 ppm), and Zr (5^15 ppm).
Spinel
Spinel of the Spl^Crd symplectites replacing sapphirine inthe sapphirine granulites is essentially a hercynite^spinelsolid solution and always less magnesian (XMg 0·48^0·56)than the coexisting cordierite and associated sapphirine
Fig. 6. Mineral assemblages and reaction textures of the Grt^Opx^Crd^Spl gneisses (a, b, thin-section scans; c^f, thin-section photomicro-graphs). (a) The Grt^Opx^Crd^Spl gneisses are characterized by a heterogeneous texture with melanocratic Grt^Opx^Spl^Pl^Crd-richzones alternating with Akfs^Pl^Qtz leucosomes. (b) Porphyroblastic garnet is partially to completely replaced by a pseudomorphic,fine-grained Opx^Spl^Pl^Crd intergrowth. (c) Relicts of garnet are preserved and subsequently mantled by plagioclase and spinel/orthopyrox-ene. (d) Texturally late cordierite, in places associated with biotite, separates orthopyroxene from spinel. (e) Late biotite also replaces garnetand orthopyroxene. Orthopyroxene may also preserve early biotite inclusions. (f) Late garnet overgrows biotite and spinel.
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(Table 4). Contents of Fe2O3, as calculated from ideal stoi-chiometry, are low (3^6wt %), and ZnO and Cr2O3 con-tents are always 50·2wt %. Regarding the traceelements, the spinel contains minor Ti (17^140 ppm), V(60^230 ppm), and Mn (290^1050 ppm), whereas theamounts of the REE, Y, and Zr (50·1ppm) are mostlybelow the detection limit.Spinel intergrown with orthopyroxene in Opx^Spl^Pl
symplectites replacing garnet in the Grt^Opx^Crd^Splgneisses is also an unzoned hercynite^spinel solid solution,but significantly less magnesian (XMg 0·33^0·43) than
that of the sapphirine granulites. It contains only minorCr2O3, NiO, and ZnO of50·1wt % and shows low valuesof Fe2O3 (3^5wt %) and MnO (0·6^0·9wt %).Magnetite exsolution lamellae of spinel have an almostpure end-member composition.Green spinel intergrown with quartz, as well as the
matrix spinel of the metapelites is an almost pure, unzoned,hercynite^spinel solid solution with negligible Cr2O3
(50·4wt %) and ZnO (50·3wt %) contents and very lowFe2O3 (1·4^2·0wt %) as calculated from ideal stoichiom-etry. The XMg of symplectitic spinel (XMg 0·39^0·40)
Table 2: Representative electron microprobe analyses of garnet in the migmatitic Grt^Opx^Crd^Spl gneiss and the migma-
titic metapelite
Rock type: Grt–Opx–Crd–Spl-gneiss Metapelite
Sample: Ro-IV-05-07 Ro-IV-05-07 Ro-IV-07-03
Texture: porph. porph. porph. porph. porph. porph. porph. secondary garnet porphyroblastic secondary
around Spl
Grt Grt Grt Grt Grt Grt Grt around Spl with Opx
SiO2 39·2 39·4 39·2 39·2 39·2 39·3 39·2 39·5 39·7 38·3 38·3
TiO2 0·02 0·03 0·01 0·02 0·02 0·01 0·03 0·02 0·00 0·04 0·07
Al2O3 21·8 21·8 21·8 21·8 21·7 21·8 21·8 22·2 22·4 22·4 22·0
Cr2O3 0·03 0·00 0·00 0·00 0·01 0·03 0·03 0·00 0·00 0·00 0·00
Fe2O3 1·70 0·05 0·08 0·00 0·00 0·00 0·00 0·54 0·32 0·61 0·68
FeO 22·7 22·1 22·0 21·9 21·6 21·7 21·6 25·1 24·7 26·7 29·8
MnO 4·60 4·31 4·36 4·37 4·46 4·33 4·49 5·00 4·81 0·94 0·81
MgO 11·1 10·9 10·8 10·8 10·9 11·0 10·9 8·94 9·39 9·66 7·84
CaO 0·88 0·95 0·99 0·94 1·00 1·01 1·03 0·87 0·92 0·69 0·77
Sum 100 99·5 99·2 99·1 99·0 99·1 99·1 102 102 99·4 100
Formula (O¼ 24)
Si 5·95 6·03 6·02 6·03 6·03 6·03 6·03 5·98 5·99 5·93 5·95
Ti 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01
Al 3·90 3·94 3·95 3·95 3·94 3·94 3·95 3·97 3·99 4·07 4·03
Cr 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Fe3þ 0·20 0·01 0·01 0·00 0·00 0·00 0·00 0·06 0·04 0·07 0·08
Fe2þ 2·69 2·83 2·83 2·82 2·78 2·78 2·78 3·18 3·11 3·45 3·88
Mn 0·59 0·56 0·57 0·57 0·58 0·56 0·58 0·64 0·61 0·12 0·11
Mg 2·51 2·49 2·47 2·48 2·50 2·51 2·49 2·02 2·11 2·23 1·82
Ca 0·14 0·16 0·16 0·15 0·17 0·17 0·17 0·14 0·15 0·11 0·13
Sum 16·0 16·0 16·0 16·0 16·0 16·0 16·0 16·0 16·0 16·0 16·0
XMg 0·48 0·47 0·47 0·47 0·47 0·47 0·47 0·39 0·40 0·39 0·32
andradite 0·00 0·13 0·22 0·00 0·00 0·00 0·00 1·54 0·92 1·8 2·0
grossular 2·41 2·45 2·48 2·56 2·74 2·76 2·82 0·81 1·56 0·1 0·2
almandine 45·4 46·9 46·9 46·8 46·2 46·2 46·1 53·2 52·0 58·4 65·4
spessartine 9·91 9·25 9·42 9·45 9·63 9·34 9·71 10·7 10·3 2·1 1·8
pyrope 42·3 41·3 41·0 41·2 41·5 41·7 41·4 33·8 35·3 37·6 30·6
porph., porphyroblastic.
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resembles that of the resorbed porphyroblastic garnet (XMg
0·36^0·40), whereas matrix spinel is less magnesian (XMg
0·28^0·29; Table 4).
Sapphirine
Regarding its major element composition, the por-phyroblastic sapphirine of the sapphirine granulites isunzoned and does not vary in composition between sam-ples. With high XMg values of 0·81^0·78, sapphirine ismore magnesian than the coexisting orthopyroxene. Allanalyses are mixtures between the ideal 7:9:3 and 2:2:1
end-members (Fig. 8). Significant amounts of ferric iron(0·21^0·33 a.p.f.u.) are calculated from ideal stoichiometry(Table 5).In terms of its trace element composition, sapphirine
contains minor Ti (350^1450 ppm), Mn (500^900 ppm),Be (3^15 ppm), Sc (5^13 ppm), Y (1^13 ppm), and Zr(0·1^0·2 ppm), which strongly decrease towards the grainmargins and cracks (especially Ti and Mn), whereasLi (30^110 ppm) increases in the same direction. Likeorthopyroxene, sapphirine displays enrichment of theheavy REE (HREE)4Gd (Yb 1^4 ppm) with respect to
Fig. 7. Zoning profiles of garnet in the Grt^Opx^Crd^Spl gneisses and migmatitic metapelite and of orthopyroxene in the Grt^Opx^Crd^Splgneiss, and sapphirine granulite. Profiles always extend from rim to rim, through the core.
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the light REE (LREE), which are always below the detec-tion limit.
Cordierite
Late cordierite separating orthopyroxene from spinel ofthe Grt^Opx^Crd^Spl gneiss is Mg-rich (XMg 0·88^0·92).High totals of c. 100wt % indicate the absence of H2O orCO2 fluids in the structural channels.Cordierite of the Crd^Spl reaction rims around sapphir-
ine in the sapphirine granulite shows no systematic com-positional variation depending on its textural position;
that is, as granoblastic reaction product of sapphirine andorthopxyroxene or as a symplectitic phase formed duringthe breakdown of sapphirine alone (Table 6). With XMg
values of 0·86^0·88 cordierite is always more magnesianthan both the associated spinel and sapphirine. It showshigh totals of around 100wt %, K2O contents at or belowthe detection limit and low Na2O contents (50·9wt %).Regarding its major element composition, cordierite ofthe sapphirine granulites is unzoned. Minor concentriczoning is revealed by the trace elementsTi (15^3000 ppm),Mn (270^1100 ppm), V (0·5^340 ppm), Rb (3^100 ppm),
Table 3: Representative electron microprobe analyses of orthopyroxene in the migmatitic Grt^Opx^Crd^Spl gneiss and the
sapphirine granulite
Rock type: Sapphirine granulite Grt–Opx–Crd–Spl gneiss
Sample: Ro-05-16b Ro-05-15 Ro-05-33B Ro-IV-05-07
Texture: porph. porph. porph. porph. porph. porph. Matrix Opx repl. Opx repl. Opx repl. Opx repl. Opx repl. Opx repl. Opx
Opx Opx Opx Opx Opx Opx Opx Grt Grt Grt Grt Grt Grt smpl.
SiO2 48·7 49·4 48·7 49·9 49·8 50·0 47·1 47·8 48·1 47·9 48·6 48·8 48·0 50·8
TiO2 0·19 0·19 0·13 0·14 0·13 0·14 0·08 0·11 0·06 0·06 0·05 0·05 0·04 0·02
Al2O3 9·10 8·91 9·15 8·11 8·23 8·80 8·79 8·78 8·76 8·82 9·27 8·89 8·48 6·34
Cr2O3 0·04 0·01 0·01 0·01 0·01 0·01 0·02 0·00 0·00 0·02 0·00 0·00 0·01 0·00
Fe2O3 1·60 0·72 3·14 1·78 1·99 1·41 4·09 3·27 1·75 2·59 3·73 2·85 2·52 2·59
FeO 16·4 16·6 14·7 15·8 15·4 16·5 17·8 18·5 19·3 19·1 17·4 18·3 19·2 18·0
MnO 0·34 0·28 0·21 0·35 0·35 0·28 1·43 1·26 1·28 1·30 1·04 0·95 1·28 0·93
MgO 22·6 23·7 23·9 24·4 24·5 24·1 20·7 21·0 20·7 20·6 22·1 21·8 20·7 23·3
CaO 0·58 0·11 0·28 0·05 0·09 0·05 0·06 0·06 0·07 0·09 0·06 0·07 0·05 0·05
Na2O 0·13 0·02 0·10 0·01 0·02 0·02 0·02 0·00 0·00 0·02 0·04 0·02 0·01 0·03
K2O 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·00
Sum 99·8 99·9 100 101 101 101 100 101 100 100 102 102 100 102
Formula (O¼ 6)
Si 1·78 1·80 1·76 1·80 1·80 1·79 1·75 1·76 1·78 1·77 1·75 1·77 1·78 1·83
Al(4) 0·22 0·20 0·24 0·20 0·20 0·21 0·25 0·24 0·22 0·23 0·25 0·23 0·22 0·17
Al(6) 0·17 0·18 0·15 0·14 0·15 0·16 0·13 0·14 0·17 0·16 0·15 0·15 0·15 0·10
Ti 0·01 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Cr 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Fe3þ 0·04 0·02 0·09 0·05 0·05 0·04 0·11 0·09 0·05 0·07 0·10 0·08 0·07 0·07
Fe2þ 0·50 0·50 0·44 0·48 0·47 0·49 0·55 0·57 0·60 0·59 0·52 0·55 0·59 0·54
Mn 0·01 0·01 0·01 0·01 0·01 0·01 0·04 0·04 0·04 0·04 0·03 0·03 0·04 0·03
Mg 1·23 1·28 1·29 1·31 1·31 1·29 1·15 1·15 1·14 1·14 1·19 1·18 1·14 1·25
Ca 0·02 0·00 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Na 0·01 0·00 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
K 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Sum 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00
XMg 0·71 0·72 0·74 0·73 0·74 0·72 0·67 0·67 0·66 0·66 0·69 0·68 0·66 0·70
Al p.f.u. 0·39 0·38 0·39 0·35 0·35 0·37 0·38 0·38 0·38 0·38 0·39 0·38 0·37 0·27
p.f.u., per formula unit; porph., porphyroblastic; smpl., symplectitic; repl., replacing.
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Be (4·5^12 ppm), Sc (0·5^4 ppm), and Nb (0·1^5 ppm),which decrease towards the margins of the larger cordier-ite grains forming the reaction rims between sapphirineand spinel. The amounts of Zr (50·1 to 0·5 ppm) and Y(50·1 to 8 ppm) are very low. Symplectitic cordieritegrown exclusively at the expense of sapphirine is unzonedand has the lowest overall trace element contents.Cordierite separating garnet and sillimanite in the
metapelite has the lowest Mg/Fe ratios in all the rocktypes investigated (XMg 0·77^0·81; Table 6). According to
high totals of up to 99·1wt %, cordierite contains onlyminor structurally bound H2O or CO2.
Feldspar
Alkali feldspar is a major constituent of the leucocraticmatrix of both the sapphirine granulite and theGrt^Opx^Crd^Spl gneiss. The original composition of themicroperthitic alkali feldspar of the Grt^Opx^Crd^Splgneiss, composed of orthoclase (average Or89Ab10An1)with plagioclase exsolution lamellae (average Or2Ab75
Table 4: Representative electron microprobe analyses of spinel in the migmatitic Grt^Opx^Crd^Spl gneiss, the migmatitic
metapelite and the sapphirine granulite
Rock type: Sapphirine granulite Grt–Opx–Crd–Spl gneiss Metapelite
Sample: Ro-05-16b Ro-05-15 Ro-05-14 Ro-Iv-05-07 Ro-Iv-07-03
Texture: Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl intergr. Spl–Qz matrix
w Crd w Crd w Crd w Crd w Crd w Crd w Opx w Opx w Opx w Opx sympl
SiO2 0·03 0·03 0·01 0·04 0·14 0·01 0·01 0·05 0·03 0·03 0·00 0·00
TiO2 0·00 0·02 0·02 0·02 0·01 0·01 0·03 0·00 0·00 0·01 0·00 0·01
Al2O3 60·8 61·5 62·3 60·6 59·9 60·6 58·7 60·6 59·9 60·3 61·7 59·7
Cr2O3 0·06 0·06 0·04 0·13 0·08 0·05 0·22 0·04 0·04 0·06 0·10 0·46
MgO 12·0 12·7 13·5 12·9 13·4 14·0 7·80 10·1 10·4 10·2 9·94 7·10
MnO 0·18 0·10 0·16 0·15 0·17 0·23 0·87 0·72 0·72 0·72 0·05 0·15
FeO 22·9 22·1 20·9 21·4 20·2 19·4 28·2 25·4 24·8 25·1 26·4 30·4
Fe2O3 4·11 3·54 3·11 5·32 6·02 5·69 3·63 2·64 4·22 3·23 1·47 2·04
NiO 0·03 0·02 0·02 0·00 0·02 0·02 0·00 0·00 0·03 0·01 0·00 0·00
ZnO 0·16 0·16 0·19 0·19 0·14 0·05 0·17 0·09 0·04 0·02 0·26 0·31
Sum 99·8 99·9 100 100 99·5 99·4 99·3 99·3 99·6 99·4 99·9 100
Formula (O¼ 4)
Si 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Ti 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Al 1·92 1·93 1·94 1·90 1·88 1·90 1·92 1·94 1·91 1·93 1·97 1·95
Cr 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01
Mg 0·48 0·50 0·53 0·51 0·53 0·55 0·32 0·41 0·42 0·41 0·40 0·29
Mn 0·00 0·00 0·00 0·00 0·00 0·01 0·02 0·02 0·02 0·02 0·00 0·00
Fe3þ 0·08 0·07 0·06 0·10 0·11 0·10 0·08 0·05 0·08 0·07 0·03 0·04
Fe2þ 0·52 0·49 0·46 0·48 0·46 0·44 0·65 0·58 0·56 0·57 0·60 0·70
Ni 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Zn 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·01
Sum 3·00 3·00 3·00 3·00 3·00 3·00 3·00 3·00 3·00 3·00 3·00 3·00
XMg 0·48 0·50 0·53 0·51 0·54 0·56 0·33 0·41 0·43 0·42 0·40 0·29
hercynite 47·7 45·9 43·4 43·6 40·9 39·1 61·9 54·8 52·3 53·8 58·0 67·9
spinel 47·9 50·4 53·2 51·1 53·3 55·3 32·3 40·8 41·9 41·3 40·2 29·4
magnetite 3·99 3·46 3·04 4·92 5·43 5·13 3·78 2·74 4·17 3·28 1·67 2·34
galaxite 0·40 0·23 0·36 0·34 0·38 0·51 2·04 1·65 1·65 1·66 0·11 0·35
intergr. w, intergrown with.
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An23), was measured with a broadened beam of 25 mm andranges between Or35Ab49An16 and Or46Ab40An16 (Table7; Fig. 9). The composition of micro- to mesoperthiticalkali feldspar of the sapphirine granulite, on the otherhand, was both measured with a broadened beam (c.25 mm) and recalculated from the volumetric proportionsof the alkali feldspar host (average Or78Ab20An2) andplagioclase exsolution lamellae (average Or3Ab70An27) asOr52Ab36An11.Matrix andesine (Ab67^70) of the sapphirine granulites
shows minor orthoclase contents of 53·5mol % and ismore Ca-rich than the oligoclase (Ab70^75; Or 52·5mol%) of the Grt^Opx^Crd^Spl gneisses (Table 7; Fig. 9).The latter shows only minor compositional variations,which are unrelated to its textural position; that is, asmatrix feldspar and as a replacement product of garnet,associated with orthopyroxene and spinel.Matrix plagioclase (Ab65^68) and coronitic plagioclase
resorbing garnet (Ab67^70) of the migmatitic metapeliteare unzoned and characterized by low orthoclase contentsof51mol % (Table 7; Fig. 9).
Biotite
Biotite of the sapphirine granulite was observed indifferent textural positions. Biotite replacing cordierite of
the Spl^Crd symplectites displays the highest XMg of0·77^0·83, whereas biotite replacing orthopyroxene andalkali feldspar (XMg 0·73^0·79) is always less magnesian(Table 8). Biotite inclusions in the peak-metamorphicphases were too small to gain reliable results. Highamounts of F (up to 1·9wt %) and TiO2 (4·3^6·0wt %)in biotite from all textural settings suggest its growth athigh temperatures.The lowest XMg values of 0·66^0·67 are recorded by
matrix biotite and biotite of the Opx^Pl^Spl intergrowthsreplacing porphyroblastic garnet in the Grt^Opx^Crd^Splgneisses, corresponding to lower values of F (up to 1·2wt%) but similar, highTiO2 contents (5·6^5·9wt %). Biotiteof single samples from both rock types is compositionallyuniform and shows no significant chemical zoning.Biotite inclusions in peak-metamorphic garnet of the
migmatitic metapelite display XMg values of 0·69^0·75and variable but high TiO2 contents (4·6^6·3wt %;Table 8). Rare late biotite replacing garnet and cordieriteshows similar XMg values of 0·68^0·74 but trends to lowerTiO2 (3·7^5·1wt %).
Fe^Ti oxides
Matrix ilmenite in the sapphirine granulites is charac-terized by high hematite contents of up to 27mol %,
Table 5: Representative electron microprobe analyses of sapphirine in the sapphirine granulite
Sample: Ro-05-16b Ro-05-16b Ro-05-16b Ro-05-16b Ro-05-15 Ro-05-15 Ro-05-15 Ro-05-15 Ro-05-33B Ro-05-33B
SiO2 14·5 14·2 14·4 14·3 14·3 14·4 15·0 14·2 14·7 14·4
MgO 16·3 16·5 16·1 16·1 16·3 16·6 16·4 16·4 16·5 16·5
Al2O3 58·6 58·8 58·4 58·7 59·2 58·9 58·8 59·2 57·8 59·4
Cr2O3 0·04 0·05 0·03 0·02 0·03 0·03 0·05 0·02 0·04 0·05
FeOtot 10·9 10·9 11·0 10·7 10·1 10·2 10·0 10·0 10·3 10·1
NiO 0·00 0·01 0·00 0·01 0·00 0·00 0·03 0·00 0·00 0·01
ZnO 0·00 0·00 0·00 0·01 0·00 0·04 0·00 0·02 0·00 0·01
MnO 0·05 0·06 0·10 0·08 0·14 0·14 0·14 0·07 0·08 0·09
Sum 100 100 100 99·9 100 100 100 99·9 99·5 101
Formula (O¼ 20)
Si 1·73 1·70 1·73 1·72 1·71 1·72 1·79 1·71 1·77 1·72
Al(4) 4·27 4·30 4·27 4·28 4·29 4·28 4·21 4·29 4·23 4·28
Al(6) 3·99 3·98 4·00 4·03 4·06 4·01 4·07 4·06 3·99 4·06
Fe3þ 0·27 0·32 0·27 0·24 0·22 0·27 0·13 0·23 0·24 0·21
Cr 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Fe2þ 0·82 0·76 0·83 0·83 0·79 0·75 0·86 0·77 0·80 0·79
Mn 0·00 0·01 0·01 0·01 0·01 0·01 0·01 0·01 0·01 0·01
Mg 2·91 2·93 2·89 2·88 2·91 2·95 2·91 2·93 2·96 2·92
Zn 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Ni 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Sum 14·0 14·0 14·0 14·0 14·0 14·0 14·0 14·0 14·0 14·0
XMg 0·78 0·79 0·78 0·78 0·79 0·80 0·77 0·79 0·79 0·79
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suggesting late re-equilibration during retrogression of therocks. Magnetite is a common constituent of the leuco-cratic domains of the Grt^Opx^Crd^Spl gneisses, whereit forms subhedral grains or exsolution lamellae in hercyni-tic spinel, displaying an almost pure end-membercomposition.
Whole-rock geochemistrySapphirine granulites and the hosting Grt^Opx^Crd^Splgneisses and migmatitic Grt^Sil metapelites were analyzedfor their bulk composition, using the rock chips left overfrom thin-section preparation. The sapphirine granulitesare characterized by high MgO (10^12wt %; XMg 0·70^0^75) and Al2O3 (23^25wt %), whereas SiO2 (45^50wt
%), Na2O, K2O and CaO are low (Fig. 10, Table 10). Thecomposition of the hosting Grt^Opx^Crd^Spl gneisses ismore variable owing to their heterogeneous texture butalways less magnesian (XMg¼ 0·51^0·69) and slightly lessAl-rich (Al2O3 21^22wt %) than that of the sapphirinegranulite (Table 10). Melanocratic layers of the surround-ing Grt^Opx^Crd^Spl gneisses, composed mainly oforthopyroxene and spinel, are characterized by very lowSiO2 contents (43wt %), moderate XMg values (0·51) andhigh Al2O3 (22wt %), whereas the Grt^Opx-rich melano-cratic zones display strong compositional similarities tothe sapphirine granulites, with almost identical values forXMg (0·69) and Al2O3 (22wt %), but higher SiO2 (54wt%) and CaO. When compared with the hosting Grt^
Table 6: Representative electron microprobe analyses of cordierite in the migmatitic Grt^Opx^Crd^Spl gneiss, the migmati-
tic metapelite and the sapphirine granulite
Rock type: Sapphirine granulite Grt–Opx–Crd–Spl gneiss Metapelite
Sample: Ro-05-16b Ro-05-15 Ro-05-33 Ro-IV-07-03
Texture: Crd Crd Crd Crd Crd sep. Crd sep. Crd sep. rim on sympl.
intergr. intergr. intergr. intergr. Opx and Opx and Opx and Grt–Sill with Kfs
with Spl with Spl with Spl with Spl Spl Spl Spl
Na2O 0·13 0·16 0·26 0·93 0·07 0·07 0·03 0·22 0·36
SiO2 50·7 50·6 50·4 50·7 50·9 51·1 50·6 49·1 49·9
MgO 12·2 12·1 11·8 11·4 12·2 12·3 12·1 10·6 10·5
Al2O3 34·0 34·0 34·1 34·0 34·3 34·2 34·0 33·0 33·5
K2O 0·03 0·02 0·01 0·01 0·03 0·01 0·00 0·01 0·01
CaO 0·02 0·02 0·04 0·02 0·03 0·01 0·02 0·01 0·01
FeO 2·84 3·07 3·11 2·22 2·90 2·01 2·98 4·68 4·71
TiO2 0·00 0·00 0·00 0·00 0·02 0·05 0·00 0·02 0·05
Cr2O3 0·01 0·01 0·00 0·00 0·00 0·00 0·00 0·04 0·00
MnO 0·05 0·03 0·03 0·02 0·05 0·06 0·05 0·05 0·08
Sum 100 100 99·8 99·3 100 99·8 99·7 97·7 99·1
Formula (O¼ 18)
Na 0·03 0·03 0·05 0·18 0·01 0·01 0·01 0·04 0·07
Si 5·00 5·00 4·99 5·04 5·00 5·03 5·00 5·01 5·02
Mg 1·80 1·78 1·74 1·68 1·78 1·81 1·78 1·60 1·57
Al 3·96 3·96 3·98 3·98 3·98 3·97 3·98 3·96 3·97
K 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Ca 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Fetot 0·23 0·25 0·26 0·18 0·24 0·17 0·24 0·40 0·40
Ti 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Cr 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Mn 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·00 0·01
Sum 11·0 11·0 11·0 11·1 11·0 11·0 11·0 11·0 11·0
XMg 0·88 0·88 0·87 0·90 0·88 0·92 0·88 0·80 0·80
intergr., intergrown; sep., separating.
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Opx^Crd^Spl gneisses, the sapphirine granulites alwaysshow higher K2O and LOI (loss of ignition) values, reflect-ing the abundance of texturally late biotite.The metapeliteshows high SiO2, Al2O3 (19wt %) and Fe2O3 (10wt %),minor amounts of CaO, K2O, Na2O, and TiO2 of52wt%, as well as a comparably low XMg value of 0·36.Relationships between the bulk composition and the
observed mineral assemblages of the sapphirine granulitesand the associated gneisses and metapelites are illustratedin a schematic Al2O3^FeO^MgO (AFM) diagram pro-jected from K-feldspar and plagioclase (Fig. 10). The pres-ence of peak-metamorphic Opx^Spr assemblages is inagreement with the high XMg of the sapphirine granulites.In contrast, the hosting and less magnesian sapphirine-freegneisses preserve the peak-metamorphic assemblage oforthopyroxene^spinel^plagioclase, replacing early garnet,therefore plotting in the Opx^Spl stability field. TheFe^Al-rich migmatitic metapelite is situated in the stability
field of Grt^Sil, consistent with the observed mineralassemblage.
P^T^X EVOLUTIONGeothermobarometryGeothermobarometric calculations were performed for thesapphirine granulites, the Grt^Opx^Crd^Spl gneisses andthe migmatitic metapelites to constrain the peak andretrograde P^T conditions. Results and applied geother-mobarometer calibrations are summarized inTable 11.
Migmatitic Grt^Opx^Crd^Spl gneisses
The P^T conditions during the formation of the peak-metamorphic Grt^Opx^Pl^Qtz assemblage preserved inrare leucocratic domains of the Grt^Opx^Crd^Splgneisses were calculated by combining analyses fromporphyroblastic garnet cores (XMg 0·48; XGrs 0·02) with
Table 7: Representative electron microprobe analyses of plagioclase and alkali feldspar in the migmatitic Grt^Opx^Crd^Spl
gneiss, the migmatitic metapelite and the sapphirine granulite
Sample: Grt–Opx–Spl–Crd gneiss Ro-IV-05-07 Sapphirine granulite Ro-05-16b Meta-pelite
Ro-IV-07-03
Texture: matrix matrix matrix Kfs Kfs Pl Pl matrix Pl repl Pl repl Pl repl Kfs Kfs Pl Pl matrix matrix matrix matrix
Akfs Akfs Akfs host host lam. lam. Pl Grt Grt Grt host host lam. lam. Pl Pl Pl Pl
BB BB BB
SiO2 62·8 63·3 62·8 64·5 64·4 62·4 62·6 61·3 61·2 60·9 62·4 65·7 65·3 61·3 61·1 60·8 60·8 60·5 60·0
MgO 0·01 0·00 0·04 0·00 0·01 0·00 0·00 0·00 0·02 0·00 0·00 0·00 0·00 0·11 0·00 0·10 0·00 0·26 0·00
Al2O3 21·8 22·0 21·6 18·5 18·7 23·9 23·7 24·4 24·4 24·4 23·8 19·2 19·2 25·4 25·3 25·3 25·4 25·3 24·8
K2O 6·91 6·67 7·05 14·90 14·69 0·31 0·40 0·40 0·39 0·45 0·39 13·23 13·75 0·89 0·45 0·62 0·13 0·19 0·14
CaO 3·31 3·27 3·12 0·18 0·19 5·26 5·00 5·79 6·09 5·91 5·06 0·48 0·39 5·61 5·98 5·77 6·82 6·61 6·35
Na2O 5·35 5·49 5·26 1·04 1·10 9·11 9·09 8·27 8·42 8·54 9·16 2·24 1·86 8·30 8·41 8·42 8·26 8·06 7·85
FeO 0·03 0·04 0·09 0·03 0·08 0·04 0·02 0·03 0·06 0·08 0·04 0·07 0·03 0·19 0·05 0·20 0·05 0·34 0·19
TiO2 0·03 0·03 0·01 0·00 0·00 0·00 0·03 0·02 0·00 0·00 0·04 0·04 0·03 0·01 0·03 0·01 0·00 0·00 0·00
BaO 0·07 0·02 0·00 0·06 0·05 0·00 0·02 0·00 0·02 0·00 0·02 0·06 0·06 0·00 0·00 0·00 0·02 0·01 0·00
SrO 0·05 0·04 0·07 0·12 0·15 0·00 0·00 0·00 0·00 0·00 0·00 0·03 0·07 0·01 0·00 0·00 0·00 0·00 0·00
Sum 100 101 100 99·3 99·4 101 101 100 101 100 101 101 101 102 101 101 101 101 99·3
Formula (O¼ 8)
Si 2·83 2·83 2·84 2·99 2·98 2·75 2·76 2·72 2·71 2·71 2·75 2·98 2·97 2·69 2·69 2·68 2·67 2·67 2·69
Mg 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·01 0·00 0·02 0·00
Al 1·16 1·16 1·15 1·01 1·02 1·24 1·23 1·28 1·28 1·28 1·24 1·02 1·03 1·31 1·31 1·31 1·32 1·31 1·31
K 0·40 0·38 0·41 0·88 0·87 0·02 0·02 0·02 0·02 0·03 0·02 0·76 0·80 0·05 0·02 0·03 0·01 0·01 0·01
Ca 0·16 0·16 0·15 0·01 0·01 0·25 0·24 0·28 0·29 0·28 0·24 0·02 0·02 0·26 0·28 0·27 0·32 0·31 0·31
Na 0·47 0·48 0·46 0·09 0·10 0·78 0·78 0·71 0·72 0·74 0·78 0·20 0·16 0·71 0·72 0·72 0·70 0·69 0·68
Fe 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·01 0·00 0·01 0·01
Ti 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Ba 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Sr 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Sum 5·02 5·01 5·02 4·99 4·99 5·03 5·02 5·01 5·02 5·03 5·03 4·99 4·99 5·03 5·03 5·04 5·02 5·02 5·00
orthoclase 38·7 37·6 39·8 89·6 88·8 1·66 2·17 2·24 2·15 2·46 2·10 77·7 81·3 4·87 2·44 3·35 0·73 1·02 0·80
albite 45·6 47·0 45·1 9·51 10·12 74·5 75·0 70·5 69·8 70·6 75·0 20·0 16·8 68·7 70·0 69·6 68·2 67·0 68·5
anorthite 15·6 15·5 15·1 0·90 1·03 23·8 22·8 27·3 28·0 27·0 22·9 2·35 1·97 26·4 27·5 27·0 31·1 32·0 30·7
BB, measured with broadened beam; Akfs, alkali feldspar; lam., lamellae.
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those of unzoned porphyroblastic matrix orthopyroxene(XMg 0·63; Alpfu/2¼0·195), and associated matrix plagio-clase (An27). Very high temperatures of 1000^10608C arecalculated for a reference pressure of 7·5 kbar, using theGrt^Opx Fe^Mg exchange thermometer calibrations ofLee & Ganguly (1988), Carswell & Harley (1990) and Bhat-tacharya et al. (1991). Similar temperatures of c. 10008C areconstrained with the Al-in-Opx thermometer of Aranovich& Berman (1997), indicating that the porphyroblastic as-semblage in leucocratic domains formed at UHTconditionsof 1020�308C. Uniform, high pressures of 7·5�1 kbar arecalculated for a reference temperature of 10008C, usingthe Grt^Opx^Pl^Qtz barometer calibrations of Newton &
Perkins (1982), Powell & Holland (1988) and Bhattacharyaet al (1991), which are, within error, consistent with pressuresestimated by Al-in-Opx barometry (i.e. 8·2 kbar, calibra-tion of Harley & Green, 1982). Feldspar thermometry ofternary matrix feldspar of the Grt^Opx^Crd^Spl gneisses,using the thermodynamic dataset of Elkins & Grove(1990) and the computer software SolvCalc by Wen &Nekvasil (1994), yields high temperatures of 1060�708C(Fig. 9) for a reference pressure of 7 kbar and thus corrobor-ates the extreme Grt^Opx temperatures. For the calcula-tion of the P^T conditions during garnet replacementthrough Opx^Spl^Pl intergrowths in the melanocratic do-mains of the same samples, analyses from margins of
Table 8: Representative electron microprobe analyses of biotite in the migmatitic Grt^Opx^Crd^Spl gneiss, the migmatitic
metapelite and the sapphirine granulite
Rock type: Grt–Opx–Crd–Spl gneiss Sapphirine granulite Metapelite
Sample: Ro-IV-05-07 Ro-05-14 Ro-05-15 Ro-05-16 Ro-IV-07-03
Texture: matrix matrix matrix repl. repl. Bt repl. Bt repl. Bt repl. Bt repl. repl. Bt repl. Bt repl. Bt repl. Bt repl. Bt repl. Bt repl. incl. in repl.
Bt Bt Bt Grt Grt Kfs Kfs Crd Crd Opx Kfs Kfs Crd Crd Opx Opx Grt Crd
SiO2 37·1 37·4 37·1 37·2 37·2 38·1 38·0 38·2 38·9 38·7 37·9 37·1 38·5 38·9 38·6 38·5 38·51 37·87
Al2O3 15·7 15·3 15·4 15·6 15·4 14·8 14·8 15·6 15·9 15·2 14·9 14·7 15·7 15·6 15·8 15·7 13·29 13·58
TiO2 5·62 5·93 5·89 5·81 5·77 4·93 4·67 4·42 3·94 4·92 5·88 5·24 4·26 4·52 5·88 5·59 6·25 3·74
FeO 12·6 13·2 13·2 13·2 13·0 9·80 9·17 8·61 7·50 8·99 10·43 10·79 8·82 8·41 9·31 10·2 12·21 11·34
MnO 0·18 0·13 0·12 0·14 0·16 0·03 0·00 0·01 0·01 0·01 0·01 0·00 0·05 0·04 0·02 0·05 0·08 0·02
MgO 14·6 14·4 14·6 14·4 14·4 17·7 18·0 19·4 20·5 18·6 16·7 16·6 19·6 19·6 17·6 17·0 15·12 17·38
BaO 0·01 0·05 0·05 0·05 0·11 0·04 0·02 0·06 0·00 0·07 0·03 0·02 0·08 0·01 0·04 0·08 0·02 0·01
CaO 0·03 0·07 0·00 0·01 0·03 0·02 0·02 0·02 0·01 0·00 0·00 0·01 0·10 0·05 0·08 0·06 0·00 0·00
Na2O 0·12 0·12 0·10 0·10 0·11 0·14 0·21 0·07 0·15 0·16 0·15 0·12 0·19 0·22 0·21 0·18 0·07 0·13
K2O 9·68 9·54 9·66 9·74 9·68 9·88 9·80 9·60 9·73 9·98 9·83 9·59 9·23 9·79 9·76 9·35 10·30 10·33
F 1·13 1·18 1·19 1·14 1·13 1·77 1·75 1·52 1·71 1·74 1·22 1·25 1·30 1·51 1·18 1·08 n.d. n.d.
Cl 0·02 0·01 0·02 0·00 0·02 0·02 0·02 0·01 0·00 0·00 0·02 0·03 0·03 0·01 0·01 0·01 n.d. n.d.
Sum 95·6 96·2 96·1 96·3 95·9 95·4 94·7 96·0 96·6 96·5 95·7 94·1 96·6 97·2 97·3 96·6 95·9 94·4
Formula (O¼ 22)
Si 5·45 5·48 5·44 5·45 5·47 5·54 5·55 5·48 5·51 5·53 5·50 5·49 5·49 5·51 5·48 5·50 5·67 5·65
Al(4) 2·55 2·52 2·56 2·55 2·53 2·46 2·45 2·52 2·49 2·47 2·50 2·51 2·51 2·49 2·52 2·50 2·31 2·35
Al(6) 0·17 0·11 0·11 0·13 0·14 0·07 0·09 0·11 0·16 0·09 0·04 0·06 0·12 0·12 0·12 0·15 0·00 0·04
Ti 0·66 0·70 0·69 0·68 0·68 0·58 0·55 0·51 0·45 0·57 0·69 0·62 0·49 0·51 0·67 0·64 0·69 0·42
Fe 1·55 1·62 1·62 1·62 1·60 1·19 1·12 1·03 0·89 1·08 1·27 1·34 1·05 1·00 1·10 1·22 1·50 1·41
Mn 0·02 0·02 0·01 0·02 0·02 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·00 0·01 0·01 0·00
Mg 3·19 3·14 3·18 3·14 3·15 3·84 3·92 4·15 4·32 3·95 3·61 3·66 4·17 4·12 3·71 3·63 3·32 3·86
Ba 0·00 0·00 0·00 0·00 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00
Ca 0·00 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·02 0·01 0·01 0·01 0·00 0·00
Na 0·03 0·03 0·03 0·03 0·03 0·04 0·06 0·02 0·04 0·04 0·04 0·03 0·05 0·06 0·06 0·05 0·02 0·04
K 1·81 1·78 1·81 1·82 1·81 1·83 1·83 1·76 1·76 1·82 1·82 1·81 1·67 1·77 1·76 1·71 1·93 1·97
Sum 15·5 15·4 15·4 15·4 15·4 15·6 15·6 15·6 15·6 15·6 15·5 15·5 15·6 15·6 15·4 15·4 15·5 15·7
OH 3·47 3·45 3·45 3·47 3·47 3·18 3·19 3·31 3·24 3·21 3·44 3·41 3·41 3·32 3·47 3·51 n.d. n.d.
F 0·53 0·55 0·55 0·53 0·53 0·82 0·81 0·69 0·76 0·79 0·56 0·59 0·58 0·68 0·53 0·49 n.d. n.d.
Cl 0·00 0·00 0·00 0·00 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·01 0·00 0·00 0·00 n.d. n.d.
XMg 0·67 0·66 0·66 0·66 0·66 0·76 0·78 0·80 0·83 0·79 0·74 0·73 0·80 0·81 0·77 0·75 0·69 0·73
n.d., not detected.
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Table9:
RepresentativeLA-ICP-M
Straceelementdataofselected
mineralsinsapphirinegranulite
Sam
ple:
Ro-IV-05-16
Ro-IV-05-15
Ro-IV-05-16
Ro-IV-05-15
Ro-IV-05-16
Ro-IV-05-15
Ro-IV-05-16
Ro-IV-05-15
Ro-IV-05-15
Mineral:
Orthopyroxene
Orthopyroxene
Sap
phirine
Sap
phirine
Spinel
Spinel
Cordierite
Cordierite
Zirco
n
Point:
2324
815
31
22
68
1415
1016
1221
core
3co
re13
rim
16rim
9rim
15
Analysis
(ppm)
Li
15·5
18·8
18·7
22·5
35·1
36·6
31·5
50·9
53·8
14·9
125
72·6
539
344
485
414
14·8
17·0
22·1
36·8
34·7
Be
50·33
0·444
50·11
50·32
12·9
7·80
8·22
6·45
50·25
50·20
0·988
0·827
12·1
6·09
4·60
5·64
51·9
51·6
51·4
1·95
51·3
Sc
68·1
57·2
51·7
77·1
11·3
13·3
11·2
13·0
50·28
50·30
0·421
0·376
1·26
0·783
0·631
0·437
n.a.
n.a.
n.a.
n.a.
n.a.
Ti
878
1223
917
1679
1190
1135
1111
956
56·7
69·9
139
59·2
35·3
377
38·1
69·5
510·0
14·3
10·4
10·3
55·4
V68·1
73·1
105
103
151
190
185
208
168
184
230
222
77·9
5·66
23·4
2·71
1·84
50·23
50·27
0·188
2·61
Mn
1550
1632
2148
1868
688
747
795
842
852
921
1029
775
724
358
519
492
7·32
29·1
2·94
9·66
53·8
Rb
3·94
15·3
0·100
17·4
50·06
50·09
50·07
0·384
1·03
0·301
6·19
4·92
13·1
20·1
34·2
21·0
50·12
0·390
0·512
0·134
2·37
Sr
0·391
0·762
0·184
0·490
0·275
0·274
50·08
0·642
0·439
0·053
0·477
0·393
1·79
1·73
6·30
3·64
0·258
3·41
0·457
0·525
2·22
Y14·6
14·4
57·6
38·5
6 ·90
9·86
9·37
12·4
0·050
50·03
0·088
0·101
0·306
0·099
0·176
50·10
744
913
1558
2767
1008
Zr
5·92
5·01
8·91
10·7
0·221
0·199
0·231
0·232
50·03
50·06
50·05
50·05
50·10
50·05
50·07
50·13
n.a.
n.a.
n.a.
n.a.
n.a.
Nb
0·218
0·643
50·02
1·40
50·05
50·04
50·05
50·05
50·03
0·066
50·03
50·03
50·06
0·584
50·03
0·256
1·52
1·24
1·51
1·50
1·37
Ba
0·844
4·24
50·18
4·87
0·347
50·27
50·29
50·31
1·24
0·388
0·534
0·745
0·704
4·03
11·8
2·99
50·51
1·93
1·32
50·32
18·0
La
50·05
0·021
50·02
50·08
50·03
50·04
50·05
50·04
50·02
50·04
50·02
50·03
50·02
50·03
50·03
50·06
50·07
50·08
50·07
50·05
0·09
Ce
50·06
50·03
50·02
50·03
50·02
50·03
50 ·03
50·03
50·02
50·03
50·01
50·02
50·04
50·02
50·02
50·04
4·40
4·74
3·62
1·55
5·12
Pr
50·06
50·02
50·02
50·05
50·01
50·03
50·05
50·02
50·02
50·02
50·02
50·01
50·02
50·01
50·01
50·05
0·071
0·090
50·05
0·077
0·088
Nd
50·15
50·12
50·07
50·38
50·11
50·19
50·20
50·16
50·10
50·06
50·09
50·16
50·17
50·09
50·09
50·24
0·945
1·69
0·393
0·583
0·781
Sm
50·21
50·10
50·14
50·38
50·22
50·25
50·33
50·23
50·12
50·18
50·06
50·08
50·20
50·16
50·17
50·45
1·68
2·16
3·17
2·12
3·22
Eu
50·08
50·04
50·04
50·13
50·05
50·06
50·04
50·06
50·02
50·04
50·03
50·03
50·08
50·03
50·05
50·07
50·12
0·234
0·150
0·126
0·778
Gd
50·13
50·13
0·948
1·03
50·20
0·275
0·415
0·219
50·16
50·17
50·11
50·15
50·12
50·05
50·13
50·30
9·67
12·0
17·7
19·0
16·3
Tb
0·069
0·090
0·379
0·282
0·031
0·072
0·060
0·043
50·02
50·03
50·02
50·02
50·03
50·01
50·03
50·08
3·78
5·41
8·41
10·8
5·99
Dy
1·43
1·25
5·90
4·58
0·468
0·998
0·907
0·869
50·07
50·09
50·09
50·06
50·10
50·08
50·05
50·25
52·1
69·4
124
158
81·7
Ho
0·568
0·540
1·72
1·36
0·221
0·372
0·280
0·368
50·02
50·03
50·02
50·02
50·03
50·06
50·02
50·07
23·3
29·1
48·3
66·1
33·5
Er
3·09
2·87
8·38
8·69
1·28
1·32
1·25
2·04
50·05
50·07
50·08
50·07
50·10
50·06
50·06
50·13
118
141
235
300
171
Tm
0·802
0·832
1·59
1·90
0·231
0·385
0·303
0·391
50·02
50·02
50·02
50·03
50·05
50·01
50·02
50·06
27·0
30·8
54·6
59·9
35·7
Yb
7·03
6·37
13·4
15·5
2 ·22
3·19
2·93
4·08
50·11
50·11
50·09
50·12
50·18
50·09
50·11
50·25
279
319
541
539
359
Lu
1·16
1·17
1·99
2·99
0·356
0·490
0·552
0·713
50·03
50·03
50·03
50·02
50·04
50·02
50·02
50·06
n.a.
n.a.
n.a.
n.a.
n.a.
Hf
0·862
0·601
0·886
1·75
50·11
50·13
50·13
0·105
50·07
50·09
50·08
50·08
50·09
50·05
50·06
50·28
12017
14237
12986
16233
9288
Ta
50·04
0·036
0·045
50·08
50·04
50·05
50·06
50·04
50·03
0·036
50·02
50·02
50·05
0·075
50·04
50·09
0·816
1·41
1·27
1·50
0·912
Ca
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
5178
5177
5165
5106
5195
Cr
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
54·3
50·42
53·6
52·7
50·6
Co
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
0·509
0·543
50·19
0·248
0·964
Ni
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
1·21
51·2
50·89
50·69
5·47
Cu
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
50·92
50·89
4·28
50·57
93·3
Zn
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
56·6
56·7
56·1
54·4
58·1
Ga
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
0·589
50·23
50·19
0·744
1·89
Sn
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
50·58
50·61
0·856
0·390
6·02
Cs
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
50·07
50·07
50·06
50·04
0·159
n.a.notan
alysed
.
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resorbed garnet (XMg 0·47; XGrs 0·03^0·02) are combinedwith those of the replacing, adjacent Al-rich orthopyroxene(XMg 0·63; Al
pfu/2¼0·20), and associated unzoned plagio-clase (An28). Pressures of 7·5�1 kbar are calculated usingthe Grt^Opx^Pl^Qtz barometer (calibrations as above),which are identical to the pressures calculated for the por-phyroblastic assemblage but represent maximum values, asquartz is absent in the reaction texture. Remarkably, how-ever, the Grt^Opx^Pl pressures are close to the Al-in-Opx
pressures (i.e. 8·1 kbar, calibration of Harley & Green,1982). Corresponding temperatures, calculated from Grt^Opx Fe^Mg and Al-in-Opx thermometry (calibrations asabove and for a reference pressure of 7·5 kbar) range be-tween 980 and 10308C (1000�308C), and hence are similarto those calculated for the peak-metamorphic Grt^Opxpairs of the leucocratic domains.Symplectitic late-stage garnet (XMg 0·40^0·43) inter-
grown with low-Al-orthopyroxene (XMg 0·67^0·68; Alpfu/2
Fig. 8. Ternary SiO2^(Mg,Fe2þ)O^(Al,Fe3þ,Cr)2O3 diagram illustrating the compositional variation of sapphirine in the sapphirine granu-lites. Positions of the 2:2:1 and 7:9:3 endmembers are marked. The compositional trend runs almost parallel to theTschermaks substitution line.
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up to 0·14), on the other hand, formed at lower P^Tcondi-tions of 760�308C (both Grt^Opx Fe^Mg exchange andAl-in-Opx thermometry with calibrations as above) and 3^5 kbar (Al-in-Opx barometry of Harley & Green,1982).
Migmatitic Grt^Sil metapelites
Peak pressures experienced by the garnet^sillimanite-bearing migmatitic metapelite were estimated for plagio-clase (An31) and coexisting garnet (XMg 0·38; Grs0-2)from the Grt^Sil^Pl^Qz (GASP) equilibrium (calibrationsof Newton & Haselton, 1981; Koziol & Newton, 1988;Powell & Holland, 1988) yielding a pressure of 7·5�0·5kbar (for a reference temperature of 10008C), which is in
agreement with the pressure estimates for the associatedGrt^Opx^Crd^Spl gneisses. Pressure calculations for theformation of coronitic plagioclase resorbing garnetthrough the GASP equilibrium have been performed bycombining garnet rim compositions (XMg 0·38; Grs0-2)with coronitic plagioclase (An30). The results (for a refer-ence temperature of 10008C) are about 1 kbar lower(6·5�0·7 kbar) than the peak pressures.
Sapphirine granulites
Peak temperatures of 1075�1108C were estimated fromthe Fe^Mg exchange thermometer of Kawasaki & Sato(2002) using the compositions of coexisting unzoned
Fig. 9. Compositions of alkali feldspar and plagioclase in the sapphirine granulites and Grt^Opx^Crd^Spl gneisses, plotted in the ternary feld-spar diagram. Solvi at 7 kbar were calculated with the software SOLVCALC (Wen & Nekvasil, 1994) using the feldspar activity model ofElkins & Grove (1990).
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porphyroblastic Al-rich orthopyroxene (XMg 0·69^0·75;Alpfu/2 up to 0·20) and coexisting sapphirine (XMg 0·81^0·78). Similar extreme temperatures of 1090�508C8Cwere estimated for a reference pressure of 7 kbar for theformation of ternary feldspar from feldspar solvus therm-ometry (Elkins & Grove, 1990; Fig. 9).
P^T pseudosectionsTo constrain detailed P^T paths of the migmatitic metape-lites, the sapphirine granulites, and hosting migmatiticGrt^Opx^Crd^Spl gneisses pseudosections were calcu-lated in the NCKFMASHT system, using theTHERIAK-DOMINO software (v. 20/03/07) of DeCapitani & Brown (1987), with the internally consistentthermodynamic dataset of Holland & Powell (1998;THERIAK-DOMINO filename tcdb55c2d.txt) and themineral activity models of Baldwin et al. (2005) for feld-spar,White et al. (2007) for garnet, biotite, spinel, ilmenite,orthopyroxene and liquid, Holland & Powell (1998) forcordierite, and Kelsey et al. (2004) for sapphirine.To ensure a close correspondence between the observed
mineral assemblages and the calculated pseudosections,sample compositions were determined on the rock chipsleft over from the thin-section preparation. The chemistryof the sapphirine granulites and the migmatitic Grt^Silmetapelites is adequately expressed in the systemNCKFMASHT and that of the hosting, partly Ti-freeGrt^Opx^Crd^Spl gneisses in the NCKFMASH system,as additional components (e.g. Zn, Cr in spinel) are
present at only trace element level and will thus not signifi-cantly affect the topology of the pseudosections. Absence(in garnet and orthopyroxene) or low amounts (in sapphir-ine and spinel) of (calculated) Fe3þ suggests reducingconditions of metamorphism. For the dry and weaklyretrogressed Grt^Opx^Crd^Spl gneisses, water contentsare directly taken from the determined LOI. Sapphirinegranulites and migmatitic Grt^Sil metapelites, on theother hand, always show variably elevated water contents,owing to the formation of biotite during retrogression indi-cating post-peak H2O influx. As the present study focuseson the reconstruction of the peak-metamorphic conditionswe have calculated the pseudosections for the least retro-graded sapphirine granulite sample and the migmatitcGrt^Sil metapelite sample for a reduced water content.Based on a comparison with the water contents of theleast retrogressed samples of the associated Grt^Opx-Spl^Crd granulites, containing �1mol % H, we performedcalculations assuming a low water content of 1mol %H. These low H2O values are realistic for the formation ofthe ‘dry’ peak-metamorphic mineral assemblages of boththe sapphirine granulite and the Grt^Sil metapelite andmoreover in accordance with the generally assumed ordetermined low H2O content of such UHT rocks(e.g. Kelsey et al., 2004; Brandt et al., 2011). As a conse-quence the retrograde segment of the P^T evolutioninferred for these samples is only semi-quantitative.Temperatures constrained for the crystallization of the par-tial melt at the solidus and for the regrowth of biotite
Fig. 10. Relationship between bulk-rock composition and mineral assemblages of the sapphirine granulite, migmatitic metapelite, and migma-titic Grt^Opx^Crd^Spl gneiss, illustrated in a schematic Al2O3^FeO^MgO diagram projected from H2O, plagioclase, and K-feldspar.
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represent maximum and minimum values, respectively, ashigher H2O contents would shift the solidus towardslower temperatures and would expand the biotite stabilityfield towards higher temperatures. The studied samplesare migmatites or restitic domains of migmatites thatunderwent significant melt and H2O loss and hence adramatic change of the bulk-rock composition near or atpeak-metamorphic conditions. Therefore, the prograde
segment of the inferred P^T path, as inferred from min-eral inclusions in the porphyroblastic minerals combinedwith calculated pseudosections, must be regarded as onlysemi-quantitative. To refine the estimation of the peak con-ditions we have calculated isopleths for the aluminiumcontents (calculated as XMg-Tschermaks component¼Alpfu/2)of orthopyroxene, which is robust against post-peakFe^Mg exchange, and the XMg [calculated as molar
Table 10: Bulk-rock geochemistry of representative samples of the sapphirine granulites and associated migmatitic metape-
lites and Grt^Opx^Crd^Spl gneisses
Rock type: Sapphirine granulite Grt–Opx–Crd–Spl gneiss Metapelite
Sample: RO-IV-05-16 RO-IV-05-15 RO-IV-05-14 RO-05-33B RO-IV-05-09 RO-IV-05-07 RO-05-33B2 RO-IV-07-03
Opx–Spl rich Grt–Opx rich
wt %
SiO2 48·9 45·2 47·5 49·7 52·6 42·5 53·6 61·1
Al2O3 24·0 24·8 23·3 24·3 21·9 21·5 21·2 19·1
Fe2O3 6·86 8·17 8·71 8·77 7·23 19·5 8·83 9·79
MnO 0·06 0·08 0·08 b.d.l. 0·1 0·91 b.d.l. 0·05
MgO 9·00 12·1 10·8 10·2 5·76 10·1 9·71 2·83
CaO 1·31 0·85 1·09 2·07 3·17 1·46 2·05 0·94
Na2O 2·32 1·21 1·68 2·13 3·75 2·27 2·49 1·29
K2O 4·39 4·25 4·16 3·28 3·95 1·22 2·82 1·88
TiO2 0·74 0·98 0·82 0·89 0·71 50·10 0·60 1·14
P2O5 0·07 0·05 0·06 0·06 0·07 0·08 0·07 0·03
LOI 3·13 3·41 2·44 0·80 0·95 0·04 0·72 2·06
Sum 101 101 101 102 100 99·6 102 100
XMg 0·72 0·75 0·71 0·70 0·61 0·51 0·69 0·36
ppm
Ba 269 208 251 212 256 176 238 457
Ce n.a. n.a. n.a. 530 n.a. n.a. 530 n.a.
Co n.a. n.a. n.a. 67 n.a. n.a. 78 n.a.
Cr 49·8 66·5 54·2 45 52·6 49·3 36 122
Ga 23·2 29·1 23·0 24 22·0 515 27 23
Hf n.a. n.a. n.a. 10·7 n.a. n.a. 9·1 n.a.
La n.a. n.a. n.a. 540 n.a. n.a. 50 n.a.
Nb 13·1 16·2 12·9 18 15·1 50·0 14 17
Nd n.a. n.a. n.a. 22 n.a. n.a. 510 n.a.
Pb 510 510 510 b.d.l. 10·2 510 510 13
Rb 140 153 149 110 218 20·5 111 64
Sc n.a. n.a. n.a. 21 n.a. n.a. 19 n.a.
Sr 90·1 62·6 71·2 115 284 99·3 130 127
Th 13·5 510 510 b.d.l. 24·8 510 520 520
V n.a. n.a. n.a. 90 n.a. n.a. 67 n.a.
Y 38·5 41·5 31·7 137 23·1 771 40 43
Zn 76·6 72·1 80·3 114 87·7 43·8 108 145
Zr 251 268 234 270 219 394 217 245
b.d.l., below detection limit; n.a., not analysed.
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Mg/(MgþFe)] and XGrs [calculated as molar Ca/(CaþMgþFeþMn)] of garnet. Peak P^Tconditions were con-strained by comparing the contours with the analysedXMg and XGrs of garnet (calculated as above) and the Alcontent of orthopyroxene (calculated as Alpfu/2).
Migmatitic Grt^Sil metapelite
The pseudosection for the Si- and Fe-rich migmatitic meta-pelite (bulk rock XMg 0·36) is characterized by the stabilityof Grt^Sil assemblages (þ ilmenite, quartz, plagioclase andK-feldspar) over a very large P^T range (Fig. 11a). Owingto the low H2O content used for the calculations the solidusis situated at high temperatures of 800^9108C. At subsolidusconditions,58008C and pressures45·5 kbar, Grt^Sil coex-ists with biotite. At temperatures above the solidus and
pressures46·5^7 kbar biotite is replaced by melt. At lowerpressures Grt^Sil coexists with cordierite. Towards tempera-tures 41020^10508C Grt^Sil is progressively replaced bySpr^Qtz assemblages at pressures 46·5^7 kbar and bySpl^Qtz assemblages at pressures56·5^7 kbar. A clockwiseP^T path is constrained for the migmatitic Grt^Sil metape-lite, based on the following criteria (Fig. 11a).
(1) Prograde inclusions of biotite and sillimanite in coarsegarnet and quartz indicate that the early mineral as-semblage Grt^Bt^Sil^Kfs^Pl^Qtz^Ilm was partiallyconsumed by melting reactions during prograde heat-ing to T48008C (maximum temperature owing toprograde H2O and melt loss), thereby crossing the sol-idus at P47 kbar.
Table 11: Results of geothermobarometric calculations for the sapphirine granulites and the migmatitic metapelites and Grt^
Opx^Crd^Spl gneisses
Sample Texture Temperature (8C) Pressure (kbar)
Grt–Opx Fe–Mg Al in Spr–Opx Feldspar Grt–Opx–Pl–Qtz Al in GASP
Opx Opx
Pref LG CH B AB KS EG Tref NP PH B (Mg) HG PH NH KN
Migmatitic Grt–Sil metapelite
Peak
Ro-IV-07-03 Grt(core)–Sil–
Pl(matrix)–Qtz
950 — — — — 6·4 6·8 7·5
1000 — — — — 7·1 7·5 8·1
Garnet replacement
Ro-IV-07-03 Grt(rim)–Sil–
Pl(corona)–Qtz
950 — — — — 5·5 5·9 6·6
1000 — — — — 6·1 6·5 7·2
Sapphirine granulite
Peak
Ro-IV-05-14 Spr–Opx–Fsp 7·0 — — — — 1075� 110 1090� 50
Grt–Opx–Crd–Spl gneiss
Porphyroblastic
Ro-IV-05-07 Grt(core)-Opx(porph.)–
Pl(matrix)–Qtz
7·5 1054 999 1009 994 — 1060� 70 980 7·7 7·1 6·7 7·6 — — —
8·0 1058 1003 1016 1004 — — 1000 7·8 7·2 6·8 8·2 — — —
Garnet replacement
Ro-IV-05-07 Grt(margin)–
Opx(repl.)–Pl(repl.)
7·5 1033 979 989 990 — — 980 7·8 7·1 6·8 7·5 — — —
(maximum pressure!) 8·0 1037 983 996 1001 — — 1000 7·9 7·2 6·9 8·1 — — —
Symplectitic
Ro-IV-05-07 Grt(sympl.)–
Opx(sympl.)
3·5 789 744 751 753 — — 760 — — — 3·4 — — —
4·0 792 747 757 762 — — 800 — — — 4·8 — — —
AB, Aranovich & Berman (1997); B, Bhattacharya et al. (1991); B (Mg), Bhattacharya et al. (1991), Mg-exchange; CH,Carswell & Harley (1990); EG, Elkins & Grove (1990); HG, Harley & Green (1982); KN, Koziol & Newton (1988); KS,Kawasaki & Sato (2002); LG, Lee & Ganguly (1988); NH, Newton & Haselton (1981); NP, Newton & Perkins (1982); PH,Powell & Holland (1988).
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(2) The absence of early cordierite suggests that the fur-ther evolution proceeded through the large trivariantfield Grt^Sil^Kfs^Pl^Ilm^Qtz^melt at P46·5^7·2kbar andT48008C.
(3) The studied Grt^Sil metapelite displays the peak-metamorphic assemblage of Grt^Spl^Sil^Kfs^Pl^Ilm^Qtz^melt, which is stable in a narrow divariant
field at 6·6^7·2 kbar and 990^10408C.The upper tem-perature limit for the peak conditions is given by theabsence of sapphirine, which is stable at T410208C.Based on the composition of porphyroblastic garnet(XMg up to 0·40; XGrs 0·015^0·020) P^Tconditions of10008C and 6·6 kbar are estimated for the formationof the peak assemblage, broadly consistent with the
Fig. 11. P^T pseudosections for (a) the migmatitic metapelite, (b) the migmatitic Grt^Opx^Crd^Spl gneiss, and (c) the sapphirine granulite,contoured for the XAlpfu/2 of orthopyroxene (migmatitic Grt^Opx^Crd^Spl gneiss and sapphirine granulite) and the XMg and XGrs of garnet(migmatitic Grt^Opx^Crd^Spl gneiss and metapelite). The bulk compositions are given as normalized mole proportions of theNCKFMASH(T) components. P^T paths are derived from mineral reaction textures and compositions. Deduced peak P^Tconditions overlapwith results from the thermobarometric calculations (c. 10008C, 7·5 kbar; Table 11). Bold dashed line marks the solidus. (See text for discussionof proposed P^T paths.)
(continued)
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results of the GASP barometry and indicating slightlydecreasing pressures during heating to UHT condi-tions. The formation of spinel^quartz intergrowthsbetween porphyroblastic spinel and quartz probablyoccurred in the same stability field.
(4) The growth of cordierite between spinel and quartz isconsistent with entry into the divariant field Grt^Spl^Sil^Kfs^Pl^Ilm^Qtz^melt through decompres-sion still at UHTconditions.
(5) Subsequent entry into the divariant field Grt^Crd^Sil^Kfs^Pl^Ilm^Qtz^melt through decompression^cooling is evident from the growth of cordierite
coronas between garnet, sillimanite and quartz,which was accompanied by the formation of plagio-clase coronas around garnet that formed through theGASP equilibrium.
(6) Regrowth of garnet (XMg 0·30^0·35), which forms ascoronas around ilmenite and spinel, thereby replacingpost-peak cordierite, is not clearly evident from thepseudosection. However, calculated isopleths for themode of garnet abundance have a positive slope inthe trivariant Grt^Crd^Sil^Kfs^Pl^Ilm^Qtz field(not shown) and indicate garnet growth with decreas-ing temperature, suggesting that late garnet forms in
Fig. 11. Continued
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response to post-decompressional near-isobaric cool-ing at sub-solidus conditions.
(7) The limited growth of late biotite, which forms at theexpense of retrograde cordierite, suggests cooling toT57008C. Biotite regrowth was accompanied bycontinued garnet regrowth, as indicated by garnetrims around late biotite, consistent with cooling.Biotite formation is most probably related to reactionwith crystallizing melt.This is apparently inconsistentwith the position of the solidus at 8008C. However,the high solidus temperature is an artefact of the low-ered water content used for the pseudosection
calculations. Applying the analysed water content ofc. 11mol % H (taken from the LOI), representativefor the retrograde evolution, the solidus is shifted toT57008C, consistent with inferred biotite formationthrough interaction with melt.
Migmatitic Grt^Opx^Crd^Spl gneisses
The calculated pseudosections for several samples of theGrt^Opx^Crd^Spl gneiss are rather similar and thereforeare illustrated for only the least altered sampleRo-IV-05-07 (Fig. 11b). Because sample Ro-IV-05-07
Fig. 11. Continued
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contains Ti below the detection limit, consistent with theabsence of Ti phases, the pseudosection was calculated inthe NCKFMASH system. The topology of the pseudosec-tion is characterized by the large stability field of orthopyr-oxene and the absence of quartz over the wholeinvestigated P^T range (700^11008C, 4^8 kbar). Quartz ispresent in the thin section, but only in rare leucocratic sub-domains, which are not represented by the overall Si-poorbulk chemistry. Owing to the low H2O content and thehigh bulk XMg, the solidus is located at high temperaturesof 850^9508C. At sub-solidus conditions, orthopyroxenecoexists with spinel^K-feldspar^plagioclase^biotite.Additional cordierite is stable at low pressures (5 c. 4·5^5·5 kbar) and is replaced by garnet at higher pressures (4c. 5^5·5 kbar). At elevated pressures 46·5 kbar garnet isprogressively replaced with increasing temperature byorthopyroxene and spinel (þ feldspar, liquid), which arestable in a large pentavariant stability field. Garnet finallydisappears at T4900^10008C. Contours of XMg indicatethat garnet becomes less magnesian with deceasing P andT, whereas Al-in-Opx isopleths demonstrate that theamount of Al in orthopyroxene increases withtemperature.We have constrained a clockwise P^T path for the mela-
nocratic domains of the Grt^Opx^Crd^Spl gneiss(bulk-rock XMg 0·51), which is based on the following ob-servations (Fig. 11b).
(1) Biotite and spinel inclusions in porphyroblastic garnetand orthopyroxene, respectively, suggest an early stagesubsolidus assemblage of Grt^Opx^Bt^Spl^Kfs^Pl,which is stable in a large trivariant field at P45·5kbar and T58508C. Owing to prograde H2O andmelt loss experienced by the Grt^Opx^Crd^Spl gneis-ses these temperatures must be regarded as maximumvalues.
(2) During heating to T49008C biotite was completelyconsumed via melt-producing reactions. The resultingassemblage garnet^orthopyroxene^spinel^plagioclasecoexisting with melt, representing the observed por-phyroblastic assemblage of the melanocratic sample,is stable at P46·7 kbar and 910^9908C.
(3) At higher temperatures garnet becomes unstable andthe observed decomposition of porphyroblasticgarnet (XMg up to 0·47) to form orthopyroxene^spinel^plagioclase intergrowths coexisting with meltis in agreement with continued heating toT4910^9908C and entry into the pentavariant Opx^Spl^Fsp^Liq field. Based on the composition of ortho-pyroxene from the Opx^Spl^Pl domains (Alpfu/2 upto 0·20), combined with a peak pressure of 7·5�1kbar, as calculated by barometry for the rare quartz-bearing subdomains, UHTconditions of c. 9908C areconstrained for the formation of the Opx^Spl^Plintergrowths (Fig. 11b), which are consistent with the
maximum thermal stability of garnet at a pressure of7·5 kbar in the pseudosection (c. 9608C) and are ingood agreement with results of Grt^Opx thermom-etry for the garnet replacement (1000�308C).
(4) The occurrence of symplectitic alkali-feldspar andbiotite in the outermost zones of the Opx^Pl^Splpseudomorphs after garnet testifies to mineral^meltreactions during cooling into the trivariant Opx^Spl^Bt^Kfs^Pl^Liq field atT58758C.
(5) The reappearance of biotite is locally accompanied bythe growth of cordierite as a narrow reaction rim be-tween orthopyroxene and spinel. Cordierite forma-tion, plus continued biotite growth, is consistent withentry into the trivariant Opx^Spl^Crd^Bt^Kfs^Plfield, which occurs at subsolidus conditions and lowpressures of 55·5 kbar. Hence cordierite formationproves marked decompression of the order of c. 2kbar from peak pressures at still high temperatures ofc. 800^8508C (Fig. 11b).
(6) The formation of euhedral garnet (XMg 0·39^0·40;XGrs 0·02) in association with Al-poor orthopyroxene(XMg 0·67^0·68; Al pfu/2 up to 0·14) overgrowing boththe Opx^Spl^Pl symplectites and Al-rich porphyro-blastic orthopyroxene is consistent with re-entry intothe Grt^Opx^Bt^Spl^Kfs^Pl trivariant field throughcontinued cooling to �800^7508C at a pressure of c.5·5^5 kbar (Fig. 11b), broadly in agreement with thethermobarometric data for this stage (760�308C, 3^5kbar). Regrowth of euhedral garnet formed at theexpense of late biotite also indicates cooling.
Sapphirine granulites
The topology of all pseudosections for the sapphirinegranulites is rather similar and therefore is illustrated foronly sample Ro-05-16 (Fig. 11c). Orthopyroxene is stableover the entire P^Twindow (700^11008C, 4^8 kbar). Thesolidus is situated at a high temperature of 9008C. At sub-solidus conditions orthopyroxene coexists with biotite(plus other phases). Coexisting sapphirine and orthopyrox-ene are stable at temperatures both above and below thesolidus. The following P^T path was established for thesapphirine granulites based on the observed mineral reac-tion sequence (Fig. 11c).
(1) Biotite inclusions in orthopyroxene and sapphirineindicate initial temperature conditions 59008C.The lack of spinel, corundum, garnet or cordieriteinclusions, which are stable together with biotite atsubsolidus conditions in various assemblages,might be explained by either their complete con-sumption during the melting reaction or by a differ-ent, less aluminous bulk composition prior to partialmelting.
(2) During heating biotite was consumed through ortho-pyroxene- and sapphirine-producing melt reactions,
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which initiate at temperatures49008C. The inferredhighest-grade assemblage Spr^Opx^Pl^Kfs^melt isstable together with ilmenite and rutile in a large sta-bility field at UHT conditions of 900^9908C andP46 kbar and is limited towards higher temperaturesby the incoming of spinel coexisting with sapphirine.Based on the composition of Al-rich porphyroblasticorthopyroxene (Alpfu/2 up to 0·20) coexisting withsapphirine, peak-metamorphic P^T conditions of950^10008C at 7^8 kbar are constrained from theAl-in-Opx isopleths, which are slightly lower than thethermometric data for the sample (Opx^Spr therm-ometry and Fsp thermometry: c. 1050^11008C), butare consistent with the P^T data estimated from theGrt^Sil metapelites and the Grt^Opx^Crd^Splgneisses. Both rutile and ilmenite are inferred phasesin the melt-present Pl^Kfs^Opx^Spr peak assemblageof the pseudosections, but rutile is not observed in thesamples. The lack of rutile can be explained by the in-corporation of high amounts of Ti in orthopyroxeneat peak conditions, which is evidenced by ilmeniteplatelets exsolved from orthopyroxene during cooling.However, Ti is not included in the available orthopyr-oxene mixing models. This explains the mismatch be-tween the calculated and observed occurrence ofrutile.
(3) Peak metamorphism is followed by decompression of1·5^2 kbar, as documented by the formation of cor-dierite^spinel symplectites between porphyroblasticsapphirine and orthopyroxene; this indicates entryinto the narrow 2Fsp^Opx^Crd^Spl^Rt^Ilm^Liqfield at a pressure of55·7 kbar and still UHT tem-peratures of 910^9508C.
(4) Subsequent regrowth of biotite at the expense oforthopyroxene, sapphirine, and symplectitic cordier-ite reflects interactions between peak-metamorphic aswell as early retrograde mineral assemblages withcrystallizing melt during cooling to subsolidus tem-peratures59008C. This comparably high solidus tem-perature must be regarded as a maximum value aspseudosection modelling for this sample was per-formed with a reduced H2O content.
(5) The late formation of corundum in the sapphirinegranulites is in agreement with continued cooling toT57508C at c. 5 kbar.
U^PB LA- ICP-MS DAT ING OFZ IRCON AND XENOTIME ANDTI- I N-Z IRCON THERMOMETRYU^Pb zircon datingTwo sapphirine granulite samples (i.e. Ro-IV-05-14 andRo-05-33B) were selected for U^Pb LA-ICP-MS analysis.
In both samples, large, well-rounded zircon grains of50^100 mm diameter are randomly distributed throughoutthe feldspar^biotite matrix (Fig. 12a) or occur as raretiny inclusions in sapphirine and orthopyroxene. In add-ition, zircon is especially abundant within the decompres-sional cordierite^spinel reaction textures replacingporphyroblastic sapphirine and orthopyroxene (Fig. 12b).CL and BSE images of zircons from all textural settingsreveal a complex internal structure for most grains(Fig. 12c^f). They exhibit corroded cores with an internalfine-scale oscillatory zoning (Fig. 12c and d) that is inter-preted to reflect magmatic zircon growth. In most grains,the oscillatory zoned core is surrounded by a thinrim (525 mm), which is not zoned and occurs apparentlyrandomly relative to the core. These rims, which we inter-pret as metamorphic overgrowths, are characterized bya slightly higher BSE brightness than the oscillatoryzoned cores and display a very weak, homogeneous CLwith sharp boundaries against the magmatic zones(Fig. 12c^f). The textural relationships indicate that theoscillatory zoned zircon cores are older than the rims.Rare internally featureless and anhedral zircon occursin the cordierite^spinel reaction rims between orthopyr-oxene and sapphirine as very small (515 mm) grainsthat display a similar homogeneous luminescence tothe overgrowth rims on corroded zircon cores. Basedon the lack of any zoning and similarity to the meta-morphic rims they are interpreted as completely newlygrown.Oscillatory zoned zircon cores have variable contents of
Y (740^2600 ppm) and Ti (up to 25 ppm; Table 9) as wellas variable U (130^1800 ppm) and Th/U ratios (0·11^0·90;Fig. 13; Table 12). The U, Y and Ti contents of the meta-morphic zircon rims and small single grains are alsovariable and partly even higher (U 280^2600 ppm, Y960^2800 ppm, Ti up to 55 ppm; Tables 9 and 12), whereastheir Th/U ratios are, with only three exceptions, very low(0·02^0·19; Table 12), consistent with their inferred meta-morphic growth (Fig. 13). When compared with the cor-roded zircon cores, they display stronger enrichment ofLREE over HREE (Table 9).In sample Ro-05-33B, a total of 45 U^Pb analyses were
performed in 25 large oscillatory zoned cores with a beam8^20 mm in diameter. Forty-two of these analyses have adiscordance lower than 5%. Their 207Pb/206Pb ages rangefrom 1841�26 to 1220� 40Ma with a clear cluster be-tween 1495 and 1470Ma (21 analyses, Fig. 14a). This distri-bution strongly suggests a detrital origin for the zirconcores, representing various igneous source rocks. In add-ition, 20 analyses were acquired with a 8^12 mm beam onnarrow metamorphic rims in 12 zircon crystals. Fourteenconcordant analyses (discordance 52%) collected onhomogeneous metamorphic rims wider than 15 mm, to-gether with four concordant analyses of xenotime
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Fig. 12. Photomicrographs of representative zircon grains in sapphirine granulite Ro-IV-05-14 (a, b, e, f, BSE images; c, d, CL images). (a)Zircon occurs as inclusions in biotite and perthitic alkali feldspar of the leucocratic matrix. (b) Zircon is abundant in granoblastic cordieriteof the Crd^Spl reaction rims. (c, d) Zircon inclusions in cordierite of the Crd^Spl intergrowth showing oscillatory zoned cores and broad meta-morphic rims of up to 20 mm with a very weak and homogeneous CL. (e, f) Broad, homogeneous BSE-bright metamorphic rims surroundingoscillatory zoned cores are partly overgrown by anhedral BSE-bright xenotime. Images are taken after LA-ICP-MS analysis (note small diam-eter of LA-ICP-MS craters in zircon cores and rims of c. 20 mm and c. 10 mm, respectively). LA-ICP-MS U^Pb results are indicated as207Pb/206Pb ages with 2s errors.
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(discordance 52%) displaying a similar age range (seebelow), define a concordia age of 1006�4Ma (Fig. 14a).In sample Ro-IV-05-14, 35 analyses were performed on
21 crystals, comprising 24 analyses of oscillatory zonedcores, eight analyses of metamorphic rims and three ana-lyses of metamorphic zircon grains in cordierite^spinelsymplectites that are large enough to be measured. Thebeam diameter was changed between 8 and 16 mm toremain smaller than the target. The 207Pb/206Pb ages ofthe oscillatory zoned cores vary between 1501�21 and1265�54Ma with a cluster of the concordant data at1501^1455Ma (Fig. 14b and Table 12). Although youngerand/or older core ages are not detected in sampleRo-IV-05-14, a detrital origin of the magmatic coresseems very likely, based on data for the associated sapphir-ine granulite Ro-05-33B. Metamorphic zircon rims andtwo newly formed metamorphic zircon grains in Crd^Splreactions rims around sapphirine yield very similar207Pb/206Pb ages of 989� 49 to 1064�38Ma and of993�23 to 1029�32 Ma, respectively (Table 12). Ten con-cordant analyses (discordance 54%) of metamorphiczircon grains and rims define a concordia age of1010�7Ma (Fig. 14b), very similar to that of sampleRo-05-33B (1006�4 Ma) and pointing to metamorphicgrowth of zircon during regional Sveconorwegian meta-morphism M1 in both samples.
U^Pb xenotime datingSingle grains of xenotime, as well as xenotime intergrownwith the zircon margins (U 1210^5950 ppm, Th/U 0·9^6·3), occur in sample Ro-05-33B. They show a strong,homogeneous BSE response and, like the metamorphiczircon rims, define similar Sveconorwegian concordant207Pb/206Pb ages of 1001^979Ma (five analyses).
In contrast, small, BSE-bright anhedral xenotime(520 mm; U 970^3490 ppm, Th/U 0·8^4·2), epitacticallygrown on the margins of zircon in samples Ro-05-33Band Ro-IV-05-14 (Fig. 12f), yields younger concordia agesof 933�5Ma (eight spots) and 928�10Ma (three spots),respectively (Fig. 14a and b).
Ti-in-zircon thermometryTemperatures during metamorphic zircon formation in thesapphirine granulites at c. 1000Ma were calculated fromthe titanium concentration in zircon, using the revisedTi-in-zircon thermometer calibration of Ferry & Watson(2007), based on the original version of the thermometerby Watson et al. (2006). In their modified Ti-in-zirconthermometer, Ferry & Watson (2007) took into accountthatTi could take the place of either Zr or Si in zircon, fol-lowing reaction (1) ZrSiO4þTiO2¼ZrTiO4þ SiO2 or(2) SiO2þTiO2¼TiSiO4. Experimental data demon-strate that the Ti content in zircon increases with decreas-ing aSiO2 and increasing aTiO2. Following this, the revisedthermometer of Ferry & Watson (2007) involves theactivities of both TiO2 and SiO2 in the rock system. Attemperatures of 400^10008C the thermometer returnstemperatures with an estimated uncertainty of �108 orbetter. Using unconstrained aSiO2 and aTiO2 additionalmaximum uncertainties are estimated as 60^708C at7508C.In the case of the sapphirine granulites of Rogaland,
rutile was not identified but minor ilmenite is present in-stead as Ti-rich phase, suggesting that the activity of titan-ium is almost equal to unity or only slightly lower in theserocks. Quartz, on the other hand, is absent from oursamples, providing evidence for a certain amount ofsilica undersaturation in the rock system and indicatingsilica activities �0·5 and51. Following this, temperatures
Fig. 13. Th/U vs 207Pb/206Pb age diagram for the analysed zircon of the sapphirine granulites. Magmatic cores generally show higher Th/Uratios than metamorphic zircon rims (core^rim mixture analyses are excluded from the diagram).
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Table12:U^PbLA-ICP-M
SanalysesforsapphirinegranulitesamplesRo-05-33B
andRo-IV-05-14
Analysis
Spot
Calc.
Texture
Position
207Pb*
Uy
Pby
Thy/
206Pb/
206Pbz/
�2s
207Pbz/
�2s
207Pbz/
�2s
rho§
Age(M
a).
Disc
(mm)
(c.p.s.)
(ppm)
(ppm)
U204Pb
238U
(%)
235U
(%)
206Pb
(%)
207Pb/
�2s
206Pb/
�2s
207Pb/
�2s
(%)
235U
238U
206Pb
Zirco
nin
matrixmineralsofRo-05-33b
16-1_1
20detritalco
rein
Bt
30771
481
121
0·27
34536
0·2424
2·0
2·998
2·3
0·08968
1·2
0·85
1399
251407
181419
231
16-1_2
20detritalco
rein
Bt
55745
705
188
0·26
18393
0·2572
2·6
3·268
2·8
0·09215
1·0
0·93
1475
351473
221471
190
16-1_3
20detritalco
rein
Bt
56120
746
192
0·38
10587
0·2437
2·0
2·996
2·2
0·08917
1·0
0·90
1406
251407
171408
180
13-2_1
16co
re–rim
mixture
inOpx
17469
338
710·23
1042
0·2032
2·5
2·243
3·2
0·08006
2·1
0·76
1192
271195
231198
410
13-2_2
16detritalco
rein
Opx
16825
462
133
0·57
6041
0·2628
2·3
3·348
2·9
0·09240
1·8
0·78
1504
301492
231476
341
13-3_1
16detritalco
rein
Opx
22446
515
143
0·41
11563
0·2590
1·9
3·321
2·5
0·09302
1·6
0·76
1485
251486
201488
300
13-3_2
16co
re–rim
mixture
inOpx
29806
1000
207
0·16
11080
0·2064
3·0
2·443
3·2
0·08587
1·2
0·93
1209
331256
231335
236
14-1_1
16co
re–rim
mixture
inSpr
13079
355
820·22
14964
0·2281
2·4
2·732
2·9
0·08685
1·7
0·81
1325
281337
221357
331
14-1_2
16co
re–rim
mixture
inSpr
15250
373
930·21
3786
0·2470
2·2
3·004
2·4
0·08822
1·0
0·91
1423
281409
181387
192
14-1_3
16detritalco
rein
Spr
11962
280
690·25
13184
0·2383
2·0
2·990
2·4
0·09097
1·4
0·81
1378
251405
191446
273
11c-1_
18
xmetam
orphic
rim
inKfs
7721
837
141
0·05
2456
0·1715
2·5
1·722
3·1
0·07283
1·8
0·81
1020
241017
201009
371
11c-1_
216
detritalco
rein
Kfs
25398
607
164
0·18
27691
0·2645
2·6
3·363
2·9
0·09221
1·3
0·90
1513
351496
231472
252
11c-1_
316
detritalco
rein
Kfs
31605
778
207
0·19
20370
0·2587
3·6
3·290
4·0
0·09225
1·6
0·92
1483
481479
311473
300
11c-1_
416
detritalco
rein
Kfs
39950
882
240
0·18
42541
0·2640
2·5
3·397
2·6
0·09332
0·8
0·95
1510
341504
211494
151
11a-1_
18
xmetam
orphic
rim
inOpx
4617
634
105
0·08
4708
0·1676
2·0
1·685
2·7
0·07292
1·9
0·72
999
181003
181012
381
11a-1_
28
xmetam
orphic
rim
inOpx
3105
561
920·02
3130
0·1715
2·6
1·733
3·5
0·07331
2·4
0·75
1020
251021
231022
480
11a-1_
312
detritalco
rein
Opx
25688
1160
307
0·27
18723
0·2565
2·7
3·246
3·1
0·09177
1·5
0·87
1472
361468
251463
290
11a-1_
412
xmetam
orphic
rim
inOpx
19122
1548
300
0·45
26494
0·1717
2·6
1·719
2·9
0·07261
1·3
0·90
1022
251016
191003
261
2-1_
18
detritalco
rein
Kfs
3968
339
880·14
1006
0·2479
3·3
3·121
4·2
0·09132
2·6
0·79
1427
431438
331453
491
2-1_
216
detritalco
rein
Kfs
45318
1083
311
0·25
47754
0·2721
2·5
3·566
2·6
0·09505
0·7
0·96
1552
341542
211529
131
6-1_
216
detritalco
rein
Kfs
16784
424
112
0·14
2501
0·2582
2·5
3·322
2·8
0·09333
1·2
0·91
1481
331486
221495
221
6-1_
316
detritalco
rein
Kfs
49021
1320
357
0·18
13932
0·2638
2·1
3·383
2·4
0·09302
1·0
0·90
1509
291501
191488
201
8-1_
416
detritalco
rein
Opx
22652
531
146
0·21
12599
0·2638
2·4
3·442
2·8
0·09464
1·3
0·88
1509
331514
221521
250
8-1_
516
detritalco
rein
Opx
36270
1239
273
0·13
16648
0·2194
2·4
2·666
2·7
0 ·08813
1·1
0·91
1279
281319
201385
215
Zirco
nin
Crd–S
pl(–B
t)zones
ofRo-05-33B
17-1_1
20detritalco
rein
Crd
32086
461
121
0·13
7619
0·2653
2·0
3·410
2·6
0·09320
1·6
0·77
1517
271507
211492
311
17-1_2
12detritalco
rein
Crd
14286
493
129
0·19
2678
0·2584
2·5
3·311
3·0
0·09294
1·6
0·84
1482
331484
231487
300
18-2_1
16detritalco
rein
Crd
16914
362
970·24
18191
0·2626
1·9
3·342
2·6
0·09232
1·7
0·75
1503
261491
201474
321
18-2_2
16detritalco
rein
Crd
15451
363
880·20
17153
0·2393
2·7
3·010
2·9
0·09123
1·2
0·91
1383
331410
231451
233
18-1_1
16detritalco
rein
Crd
10034
240
610·26
3755
0·2558
2·5
3·242
2·9
0·09191
1·6
0·84
1468
321467
231466
310
18-1_2
16detritalco
rein
Crd
16882
358
101
0·45
18194
0·2589
2·4
3·317
2·8
0·09294
1·4
0·87
1484
321485
221487
270
18-1_3
16detritalco
rein
Crd
18262
383
105
0·34
19771
0·2555
2·5
3·253
2·8
0·09235
1·2
0·91
1467
331470
221475
220
18-4_1
16detritalco
rein
Crd
14953
348
900·28
8971
0·2472
2·6
3·052
3·2
0·08955
1·8
0·83
1424
341421
241416
340
18-4_2
16detritalco
rein
Crd
16624
380
101
0·33
3618
0·2542
2·2
3·233
2·5
0·09225
1·2
0·87
1460
281465
191472
230
18-6_1
16detritalco
rein
Crd
20441
446
117
0·25
21906
0·2553
2·4
3·260
2·8
0·09260
1·5
0·85
1466
321472
221480
291
(continued
)
DRU« PPEL et al. UHT METAMORPHISM, ROGALAND, NORWAY
337Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
Table12:Continued
Analysis
Spot
Calc.
Texture
Position
207Pb*
Uy
Pby
Thy/
206Pb/
206Pbz/
�2s
207Pbz/
�2s
207Pbz/
�2s
rho§
Age(M
a).
Disc
(mm)
(c.p.s.)
(ppm)
(ppm)
U204Pb
238U
(%)
235U
(%)
206Pb
(%)
207Pb/
�2s
206Pb/
�2s
207Pb/
�2s
(%)
235U
238U
206Pb
18-6_2
12x
metam
orphic
rim
inCrd
5747
400
670·11
4508
0·1708
2·1
1·701
2·9
0·07224
1·9
0·74
1016
201009
19993
392
18-6_3
16detritalco
rein
Crd
26967
552
154
0·36
8241
0·2614
2·3
3·351
2·5
0·09297
1·0
0·91
1497
301493
201487
190
15-1_1
16detritalco
rein
Crd
15684
470
101
0·16
5864
0·2137
2·9
2·386
3·5
0·08095
2·0
0·82
1249
321238
251220
401
14-2_1
16detritalco
rein
Crd
9635
134
540·82
4104
0·3280
2·4
5·089
2·8
0·11253
1·4
0·86
1829
391834
241841
260
14–2_2
16detritalco
rein
Crd
10224
158
560·56
9384
0·3124
2·4
4·766
3·2
0·11064
2·2
0·74
1753
361779
271810
402
14-2_3
12co
re–rim
mixture
inCrd
6533
241
590·30
6123
0·2297
2·3
2·882
3·7
0·09099
2·9
0·61
1333
271377
281446
565
14-3_1
12x
metam
orphic
rim
inCrd
6887
538
880·10
9669
0·1690
2·1
1·675
2·7
0·07190
1·7
0·78
1007
19999
17983
342
14-3_2
16detritalco
rein
Crd
21813
718
180
0·59
2913
0·2344
2·0
2·769
2·4
0·08569
1·5
0·80
1357
241347
181331
281
14-3_3
12detritalco
rein
Crd
15480
904
192
0·21
5965
0·2078
2·9
2·454
3·7
0·08565
2·3
0·78
1217
321259
271330
455
11b-3_1
12x
metam
orphic
rim
inBt
12888
921
155
0·10
2098
0·1711
2·4
1·704
2·7
0·07223
1·3
0·88
1018
231010
18993
272
Analysis
Spot
Calc.
Texture
Position
207Pb*
Uy
Pby
Thy/
206Pb/
206Pbz/�2s
207Pbz/�2s
207Pbz/�2s
rho§
Age(M
a)Disc.
(mm)
(c.p.s.)
(ppm)
(ppm)
U204Pb
238U
(%)
235U
(%)
206Pb
(%)
207Pb/�2s
206Pb/�2s
207Pb/�2s
(%)
235U
238U
206Pb
Zirco
nin
Crd–S
pl(–B
t)zones
ofRo-05-33B
11b-3_2
8x
metam
orphic
rim
inBt
4714
569
960·14
2071
0·1671
1·8
1·679
2·6
0·07287
1·8
0·70
996
171001
171010
371
11b-3_3
12detritalco
rein
Bt
32477
1096
242
0·18
4562
0·2164
2·1
2·519
2·5
0·08443
1·3
0·84
1263
241278
181302
262
11b-3_4
12detritalco
rein
Bt
23811
1774
372
0·23
2978
0·2036
1·8
2·321
2·1
0·08267
1·0
0·87
1195
201219
151261
203
11b-5_1
16detritalco
rein
Crd
19007
665
160
0·13
7668
0·2409
1·5
2·901
2·3
0·08734
1·7
0·65
1392
191382
181368
341
11b-1_1
12detritalco
rein
Crd
8807
389
105
0·15
2622
0·2630
2·9
3·355
3·5
0·09252
2·0
0·83
1505
401494
281478
371
11b-1_2
8detritalco
rein
Crd
4251
409
109
0·13
1455
0·2592
4·4
3·248
4·8
0·09090
2·0
0·91
1486
591469
381445
382
11b-1_3
12detritalco
rein
Crd
16130
651
179
0·20
17130
0·2611
3·8
3·354
4·1
0·09316
1·6
0·93
1495
511494
331491
300
11b-1_4
12detritalco
rein
Crd
7019
292
790·26
7502
0·2677
2·1
3·433
2·9
0·09300
1·9
0·75
1529
291512
231488
362
11b-3_1
8x
metam
orphic
rim
inBt
5387
946
156
0·02
956
0·1698
2·5
1·717
2·9
0·07333
1·6
0·85
1011
231015
191023
311
11b-3_2
8x
metam
orphic
rim
inBt
7655
1442
236
0·03
4986
0·1668
2·0
1·676
3·1
0·07290
2·4
0·63
994
181000
201011
491
11b-3_3
16detritalco
rein
Bt
28594
770
203
0·17
4322
0·2559
2·9
3·195
3·2
0·09054
1·2
0·92
1469
381456
251437
241
11b-3_4
16detritalco
rein
Bt
66076
938
309
0·63
13218
0·2644
1·7
3·422
1·9
0·09385
1·0
0·87
1513
231509
151505
180
9-4_
18
xmetam
orphic
rim
inBt
1962
403
670·10
1069
0·1683
2·4
1·695
3·4
0·07304
2·4
0·71
1003
221007
221015
481
9-4_
212
xmetam
orphic
rim
inBt
28408
2082
441
0·83
12061
0·1687
2·3
1·674
2·8
0·07194
1·5
0·84
1005
22999
18984
301
9-4_
38
xmetam
orphic
rim
inBt
2306
518
850·05
3307
0·1700
2·9
1·709
3·6
0·07290
2·1
0·81
1012
281012
231011
420
9-4_
412
detritalco
rein
Bt
7367
490
117
0·43
1704
0·2182
2·3
2·712
3·4
0·09016
2·5
0·68
1272
261332
251429
477
9-2_
28
xmetam
orphic
rim
inCrd
7151
1362
224
0·06
9167
0·1703
2·5
1·712
3·1
0·07288
1·7
0·83
1014
241013
201011
340
9-2_
38
core–rim
mixture
inCrd
12082
1934
369
0·11
5374
0·1925
2·9
2·227
3·2
0·08389
1·3
0·91
1135
301189
221290
268
9-2_
412
detritalco
rein
Crd
24571
922
257
0·22
26272
0·2631
2·6
3·381
3·1
0·09318
1·7
0·84
1506
351500
251492
321
(continued
)
JOURNAL OF PETROLOGY VOLUME 54 NUMBER 2 FEBRUARY 2013
338Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
Table12:Continued
Analysis
Spot
Calc.
Texture
Position
207Pb*
Uy
Pby
Thy/
206Pb/
206Pbz/�2s
207Pbz/�2s
207Pbz/�2s
rho§
Age(M
a)Disc.
(mm)
(c.p.s.)
(ppm)
(ppm)
U204Pb
238U
(%)
235U
(%)
206Pb
(%)
207Pb/�2s
206Pb/�2s
207Pb/�2s
(%)
235U
238U
206Pb
1-1_
112
detritalgrain
inSpl
28021
3424
603
0·10
33097
0·1791
2·4
1·892
4·1
0·07662
3·2
0·60
1062
241078
271111
653
5-2_
312
detritalco
rein
Crd
62536
1809
522
0·90
17376
0·2130
2·2
2·605
2·6
0·08868
1·5
0·82
1245
251302
191397
297
5-1_
112
detritalco
rein
Crd
17519
885
217
0·28
20043
0·2293
2·3
2·758
2·6
0·08726
1·3
0·88
1331
281344
201366
242
3-2_
116
detritalco
rein
Crd
24324
555
149
0·19
12564
0·2584
2·4
3·337
2·5
0·09365
0·8
0·95
1482
321490
201501
151
Xen
otimein
matrixmineralsofRo-05-33b
11-c
xt_1
12x
metam
orphic
grain
inBt
56863
2776
1001
3·15
7690
0·1703
2·1
1·702
2·3
0·07250
0·9
0·91
1014
191009
151000
191
11-c
xt_2
8x
metam
orphic
grain
inBt
45472
5946
1436
0·88
7444
0·1709
2·2
1·708
2·5
0·07246
1·3
0·85
1017
201011
16999
271
11-c
xt_3
8x
metam
orphic
grain
inBt
8056
1839
636
3·29
2771
0·1682
1·8
1·664
2·5
0·07176
1·7
0·72
1002
17995
16979
352
11-c
xt_4
8metam
orphic
grain
inBt
6892
1564
465
2·39
9490
0·1641
1·8
1·637
2·7
0·07235
2·0
0·68
980
17985
17996
401
6-1_
18
xmetam
orphic
grain
inKfs
10804
2795
847
2·95
4375
0·1550
1·9
1·487
2·6
0·06959
1·8
0·73
929
17925
16916
371
8-1_
18
xmetam
orphic
grain
inOpx
6184
1583
579
4·20
3948
0·1562
2·3
1·512
3·2
0·07020
2·3
0·70
936
20935
20934
470
8-1_
212
xmetam
orphic
grain
inOpx
91362
2190
506
1·61
45551
0·1564
1·7
1·531
2·1
0·07099
1·3
0·80
937
15943
13957
261
8-1_
38
xmetam
orphic
grain
inOpx
13263
3487
754
1·35
6666
0·1548
2·1
1·491
2·8
0·06985
1·8
0·77
928
19927
17924
360
Xen
otimein
Crd–S
pl(–B
t)zones
ofRo-05-33B
18-6_0
12x
metam
orphic
grain
inCrd
18480
1836
449
2·21
9794
0·1559
1·8
1·493
2·0
0·06947
0·9
0·89
934
15928
12913
182
9-2_
112
xmetam
orphic
grain
inCrd
72042
2700
876
3·13
53940
0·1558
1·6
1·512
1·9
0·07042
1·1
0·81
933
14935
12941
231
5-2_
112
xmetam
orphic
grain
inCrd
8992
972
254
2·06
3321
0·1572
1·8
1·522
2·3
0·07024
1·5
0·76
941
16939
14935
310
5-2_
218
xmetam
orphic
grain
inCrd
7572
1846
512
2·46
2873
0·1545
2·2
1·493
2·7
0·07005
1·5
0·83
926
19927
16930
310
3-1_
116
xmetam
orphic
grain
inCrd
116364
1212
610
6·29
31104
0·1677
1·8
1·677
1·9
0·07254
0·7
0·92
999
161000
121001
150
Analysis
Spot
Calc.
Texture
Position
207Pby
Uy
Pby
Thy/
206Pb/
206Pbz/�2s
207Pbz/�2s
207Pbz/�2s
rho§
Age(M
a)Disc.
(mm)
(c.p.s.)
(ppm)
(ppm)
U204Pb
238U
(%)
235U
(%)
206Pb
(%)
207Pb/�2s
206Pb/�2s
207Pb/�2s
(%)
235U
238U
206Pb
Zirco
nin
matrixmineralsofRo-IV-05-14
14-9-2_1
12x
meta.
rim
matrixBt
21233
836
139
0·10
52276
0·1695
2·1
1·725
2·6
0·07378
1·6
0·78
1010
191018
171035
332
14-9-2_2
16detritalco
rematrixBt
17567
257
630·33
5339
0·2353
2·4
2·928
2·8
0·09028
1·4
0·86
1362
301389
221431
273
14-9-3_1
12meta.
rim
matrixKfs
31474
1259
220
0·19
23065
0·1780
1·9
1·813
2·3
0·07385
1·3
0·83
1056
181050
151037
261
14-9-3_2
12detritalco
rematrixKfs
19441
489
137
0·42
21544
0·2598
1·9
3·298
2·5
0·09208
1·6
0·77
1489
261481
201469
311
14-9-1_1
8detritalco
rematrixKfs
8605
493
121
0·87
7035
0·2410
4·3
2·970
4·8
0·08939
2·0
0·91
1392
541400
371412
381
14-9-1_2
8x
meta.
rim
matrixKfs
2474
284
480·14
5619
0·1674
1·9
1·665
3·1
0·07212
2·4
0·61
998
19995
20989
491
14-9-1_3
16detritalco
rematrixKfs
28785
394
102
0·21
61655
0·2530
2·0
3·240
2·4
0·09289
1·2
0·85
1454
261467
181486
241
14-10-1_
18
detritalco
rematrixKfs
6424
303
800·23
7758
0·2559
2·9
3·298
3·9
0·09345
2·7
0·73
1469
381480
311497
501
14-10-1_
216
detritalco
rematrixKfs
16615
216
500·34
36114
0·2287
2·3
2·854
3·0
0·09053
1·8
0·79
1327
281370
231437
355
14-7-1_1
8detritalco
rematrixKfs
4471
289
750·48
9737
0·2580
4·0
3·325
4·6
0·09349
2·3
0·87
1479
531487
371498
441
(continued
)
DRU« PPEL et al. UHT METAMORPHISM, ROGALAND, NORWAY
339Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
Table12:Continued
Analysis
Spot
Calc.
Texture
Position
207Pby
Uy
Pby
Thy/
206Pb/
206Pbz/�2s
207Pbz/�2s
207Pbz/�2s
rho§
Age(M
a)Disc.
(mm)
(c.p.s.)
(ppm)
(ppm)
U204Pb
238U
(%)
235U
(%)
206Pb
(%)
207Pb/�2s
206Pb/�2s
207Pb/�2s
(%)
235U
238U
206Pb
14-7-1_2
8x
meta.
rim
matrixKfs
4689
464
740·02
12686
0·1670
2·2
1·669
3·0
0·07247
2·0
0·74
996
21997
19999
410
14-7-1_3
16detritalco
rematrixKfs
38322
516
146
0·49
7492
0·2519
2·5
3·210
2·7
0·09242
1·0
0·93
1448
321460
211476
191
14-7-2_3
16detritalco
rematrixOpx
16583
225
590·23
4457
0·2534
3·3
3·229
3·7
0·09243
1·7
0·89
1456
431464
291476
321
14-1-1_2
16grain
matrixKfs
30813
431
116
0·29
67883
0·2595
3·9
3·350
4·4
0·09363
2·0
0·89
1487
521493
351501
381
Zirco
nin
Crd–S
pl(–B
t)reactionzones
ofRo-IV-05-14
14-8-1_3
8x
meta.
rim
Crd–S
pl
4930
568
990·19
13731
0·1711
2·0
1·711
2·8
0·07254
2·0
0·70
1018
191013
181001
411
14-8-1_4
16detritalco
reCrd–S
pl
40410
594
152
0·33
11724
0·2452
2·1
3·087
2·6
0·09131
1·5
0·81
1414
261429
201453
292
14-6-1_1
16detritalgrain
Crd–S
pl
64919
806
234
0·50
10375
0·2622
2·8
3·385
3·0
0·09363
1·1
0·93
1501
381501
241501
210
14-4-7_1
16detritalgrain
Crd–S
pl
29108
476
109
0·33
67953
0·2263
3·2
2·716
3·5
0·08705
1·4
0·91
1315
381333
261362
272
14-4-2_1
12x
meta.
grain
Crd–S
pl
19062
893
150
0·12
8499
0·1724
2·1
1·737
2·7
0·07306
1·7
0·77
1025
201022
171016
351
14-4-2_2
16x
meta.
grain
Crd–S
pl
12525
309
540·15
33860
0·1708
2·0
1·732
2·5
0·07354
1·6
0·78
1017
181021
161029
321
14-4-1_1
16x
meta.
grain
Crd–S
pl
22052
572
980·16
59983
0·1717
1·6
1·710
1·9
0·07225
1·1
0·82
1021
151012
13993
232
14-4-3_1
12detritalco
reCrd–S
pl
16791
531
108
0·11
4118
0·2075
4·5
2·369
5·3
0·08281
2·8
0·85
1216
501233
381265
542
14-4-3_2
12detritalco
reCrd–S
pl
17361
525
116
0·12
40978
0·2234
2·3
2·650
3·1
0·08601
2·0
0·75
1300
271315
231338
392
14-4-3_3
16detritalco
reCrd–S
pl
19299
314
720·15
44996
0·2283
2·8
2·704
4·1
0·08591
3·0
0·68
1325
331330
301336
570
14-4-5_1
8detritalco
reCrd–S
pl
4538
238
560·16
4956
0·2285
6·5
2·812
7·8
0·08927
4·4
0·83
1326
781359
601410
844
14-4-5_2
12rim–core
mixture
Crd–S
pl
13591
533
990·31
6790
0·1791
4·8
1·961
5·3
0·07941
2·3
0·90
1062
471102
371182
467
14-4-5_3
8x
meta.
rim
Crd–S
pl
29148
2594
433
0·18
7773
0·1678
2·0
1·731
2·7
0·07484
1·9
0·73
1000
181020
181064
384
14-4-6_1
16detritalco
reCrd–S
pl
37885
492
132
0·31
82178
0·2548
1·8
3·230
2·2
0·09196
1·2
0·85
1463
241464
171467
220
14-4-8_1
16rim–core
mixture
Crd–S
pl
40651
765
172
0·31
26020
0·2165
2·0
2·471
2·3
0·08280
1·0
0·89
1263
231264
171264
200
14-4-4_1
8x
meta.
rim
Crd–S
pl
5092
361
610·08
3530
0·1693
2·1
1·722
3·3
0·07377
2·6
0·64
1008
201017
221035
522
14-4-4_2
16detritalco
reCrd–S
pl
17495
239
630·21
10064
0·2545
2·1
3·217
2·5
0·09169
1·3
0·85
1462
281461
191461
250
14-4-5_1
8x
meta.
rim
Crd–S
pl
3121
310
550·30
3896
0·1668
2·3
1·663
3·3
0·07231
2·4
0·69
994
21994
21995
490
14-4-5_2
8rim–core
mixture
Crd–S
pl
6093
299
760·17
13107
0·2479
6·8
3·123
7·4
0·09138
2·9
0·92
1428
881438
591455
561
14-4-5_3
12detritalco
reCrd–S
pl
36202
804
217
0·27
14625
0·2583
2·5
3·304
2·8
0·09278
1·3
0·88
1481
331482
221483
250
14-4-5_4
12detritalco
reCrd–S
pl
29510
770
202
0·24
66557
0·2558
2·6
3·238
3·0
0·09181
1·5
0·87
1468
351466
241464
280
Xen
otimein
matrixmineralsofRo-IV-05-14
14-7-2_1
8x
meta.
grain
inOpx
18766
2163
456
1·69
52225
0·1544
1·9
1·507
2·4
0·07076
1·5
0·78
926
16933
15950
302
14-7-2_2
8x
meta.
grain
inOpx
10981
1455
246
1·08
31882
0·1555
1·8
1·488
2·9
0·06955
2·2
0·64
930
16925
18915
461
Xen
otimein
Crd–S
pl(–B
t)reactionzones
ofRo-IV-05-14
14-8-1_2
8x
meta.
grain
inCrd
2942
1216
181
0·76
5982
0·1539
2·2
1·499
3·5
0·07064
2·7
0·64
923
19930
21947
542
Spotsize
8,12,16
or20
mm;dep
thofcrater�20
mm.206Pb/2
38U
erroristhequad
raticad
ditionofthewithin-runprecision(2
SE)an
dtheexternal
reproducibility
(2SD)ofthereference
zircon.207Pb/2
06Pberrorpropag
ation(207Pbsignal
dep
enden
t)followingGerdes
&Zeh
(2009).207Pb/2
35U
erroristhequad
raticad
ditionofthe
207Pb/2
06Pban
d206Pb/2
38U
uncertainty.Calc.,datausedforco
nco
rdia
agecalculation;Disc.,disco
rdan
ce;meta.,metam
orphic.
*Within-runbackg
round-correctedmean
207Pbsignal
inc.p.s.(counts
per
seco
nd).
yU
andPbco
ntentan
dTh/U
ratiowerecalculatedrelative
toGJ-1
reference
zircon.
zTim
e-resolved
datawereco
rrectedforbackg
round,within-runPb/U
fractionationan
dco
mmonPbusingStacey&
Kramers(1975)
model
Pbco
mpositionan
dsubsequen
tlynorm
alized
toGJ-1
(ID-TIM
Svalue/measuredvalue);207Pb/2
35U
calculatedusing
207Pb/2
06Pb/(
238U/2
06Pb�1/137·88).
§Rhois
the
206Pb/2
38U/2
07Pb/2
35U
errorco
rrelationco
efficien
t.
JOURNAL OF PETROLOGY VOLUME 54 NUMBER 2 FEBRUARY 2013
340Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
Fig. 14. U^Pb concordia diagrams for LA-ICP-MS analysis of zircon and xenotime from two sapphirine granulite samples. (a) Sapphirinegranulite sample Ro-05-33B; (b) sapphirine granulite sample Ro-IV-05-14. Insets illustrate concordia diagrams for the growth of metamorphiczircon and xenotime during the regional Sveconorwegian metamorphism (M1) and of xenotime during post-collisional decompression and in-trusion of the anorthosite^mangerite^charnockite suite (M2). Xenotime analyses are marked as bold grey lines in the upper inset of (a). conc,concordance; MSWD (CþE), concordance and equivalence.
DRU« PPEL et al. UHT METAMORPHISM, ROGALAND, NORWAY
341Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
were calculated using determining factors of (1)aSiO2¼ aTiO2¼1 and (2) aSiO2¼0·5 and aTiO2¼1.Titanium concentrations in the oscillatory zoned zirconcores (11 spots) range from 11·6 to 25·1ppm Ti (Table 9),yielding temperatures of 760^840�508C, assuming silicaand titanium saturation in the rock system, and minimumtemperatures of 760^840�508C using a reduced Siactivity of 0·5. The Ti contents of the homogeneousmetamorphic zircon rims (six spots) are 10·3^55·4 ppm(Table 9), yielding temperatures of 750^940�508C and690^850�508C, for aSiO2¼1 and 0·5, respectively.Following this, maximum temperatures of c. 850^9408Care constrained for metamorphic zircon growth at1006�4Ma during M1, consistent with (U)HTconditions.
DISCUSS IONOrigin of the sapphirine granulitesMagnesium^aluminium-rich sapphirine granulites havebeen regarded as the product of several possible processes,including metamorphism of hydrothermally altered maficto ultramafic rocks or high-Mg clays (e.g. Sheraton, 1980;Harley et al., 1990), syn-metamorphic metasomatism (e.g.Herd et al., 1969; Vry & Cartwright, 1994; Dunkley et al.,1999) or formation of restitic MgAl-rich domains in meta-sedimentary rocks via partial melting (e.g. Clifford et al.,1981; Baba, 2003; Brandt et al., 2007). For the sapphirinegranulites of Ivesdalen (XMg 0·70^0·75) a metasedimen-tary origin is evidenced by their apparent structural andcompositional resemblance to the Grt^Opx-rich melano-cratic layers of the surrounding banded Grt^Opx^Spl^Crd gneisses and their partly diffuse contact relationshipsto the latter. A metasedimentary origin is also supportedby the abundance of inherited detrital igneous zircon inthe sapphirine granulites. The major part of the oscillatoryzoned zircon cores displays nearly concordant 207Pb/206Pbapparent ages ranging from 1841 to 1220 Ma, consistentwith a sedimentary origin derived from different igneoussources and deposition at51220 Ma. The large populationof 1501^1455Ma igneous zircon suggests emplacement ofthe igneous protoliths during the Telemarkian igneousevent at 1520^1480 Ma, defined by Bingen et al. (2008a,2008b). Magmatic zircon with preserved oscillatoryzoning has also been identified by Mo« ller et al. (2002,2003) in a number of ortho- and paragneiss samples fromthe same area, yielding significantly younger ages of c.1035Ma and c. 1050 Ma. The lack of such detrital zirconin our samples is consistent with sedimentation of theirprotoliths prior to these igneous events. An alternative pro-tolith could be metasomatically altered S-type granite, aspostulated for the formation of Grt^Opx-bearing alumin-ous migmatitic gneisses from Rogaland by Mo« ller et al.(2003). Regarding the close association of the sapphirinegranulites with Grt^Opx-rich metasedimentary units andthe large range of almost concordant ages of the oscillatory
zoned zircon in our samples, this scenario is rather un-likely. Most probably, these rocks represent Grt(^Opx)-rich metasedimentary layers that were metamorphosed tosapphirine^orthopyroxene granulites and Grt^Opx^Crd^Spl gneisses during heating to UHTconditions.
P^T^t evolutionBased on the observation of sequential reaction texturesand stable mineral assemblages, combined with constraintsfrom pseudosections in the NCKFMASH(T) system andthermobarometric calculations, a clockwise P^T path isinferred for the sapphirine granulites, the host Grt^Opx^Spl^Crd gneisses and associated Grt^Sil metapelites ofIvesdalen, SW Norway (Fig. 15). This P^T path comprisesheating to MP^UHTconditions (c. 7·5 kbar, 10008C) fol-lowed by near-isothermal (U)HT decompression toP55·5 kbar at 900^10008C and subsequent near-isobariccooling toT5750^8008C at c. 5 kbar. Observed reactiontextures and results of the thermobarometric calculationsmostly correlate well with predictions from pseudosectionsin the NCKFMASH(T) system.The P^T path can be sub-divided into the following stages (Fig. 15).
Peak metamorphism
Relics of porphyroblastic prograde garnet and orthopyrox-ene associated with matrix plagioclase and quartz in leu-cocratic domains of the Grt^Opx^Spl^Crd gneisses testifyto peak metamorphism at temperatures of c. 10208Cand pressures of c. 7·5 kbar. In the melanocraticdomains, porphyroblastic garnet was replaced by a peak-metamorphic orthopyroxene^spinel^plagioclase inter-growth during prograde heating to temperatures of c.10008C. Similar UHTconditions of c. 10508C are calculatedby feldspar thermometry and Opx^Spr thermometry forthe peak-metamorphic sapphirine^orthopyroxene^feld-spar assemblage of the associated sapphirine granulites.These inferred ultrahigh temperatures are consistent withthe high Al2O3 contents of orthopyroxene in both rocktypes (up to 9·7wt %). Corresponding mid-crustalpressures of c. 7·5 kbar, determined by Grt^Opx^Pl^Qtzbarometry of the Grt^Opx^Spl^Crd gneisses, are in agree-ment with GASP pressures of 7·5�0·5 kbar, calculatedfor a spatially associated migmatitic Grt^Sil metapelite,and generally correlate well with the stability of thepeak-metamorphic assemblages as predicted by thepseudosections.
UHTdecompression
Post-peak decompression to pressures56 kbar at still ultra-high temperatures of c. 900-10008C is documented by vari-ous decompression textures, which frequently occur in allrock types investigated: (1) formation of cordierite^spinelreaction rims between porphyroblastic sapphirine andorthopyroxene of the sapphirine granulites; (2) growth ofcordierite as narrow reaction rims between orthopyroxene
JOURNAL OF PETROLOGY VOLUME 54 NUMBER 2 FEBRUARY 2013
342Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
and spinel in the migmatitic Grt^Opx-Spl^Crd gneisses;(3) formation of spinel^quartz symplectites at the expenseof garnet^sillimanite in the migmatitic metapelite; (4) for-mation of a cordierite corona between spinel and quartzin the migmatitic metapelite; (5) formation of a cordieritecorona between garnet, sillimanite, and quartz in the mig-matitic metapelite; (6) formation of a plagioclase coronaaround garnet (GASP reaction) in the migmatitic metape-lite.The interpretation of the post-peak path of the samplesheavily relies on cordierite-bearing symplectites and
corona textures. These textures are traditionally inter-preted in terms of decompression (e.g. Harley, 1998), asalso evidenced by the pseudosections of this study. Inmore recent years, however, it has been demonstrated thatcordierite corona structures may also form owing to an in-crease of the water activity, whereby cordierite becomesstable towards higher pressures (e.g. Harley & Thompson,2004; Kelsey et al., 2004; Baldwin et al., 2005). The gener-ally anhydrous peak-metamorphic and early retrogradeassemblages of our samples indicate low water activities
Fig. 15. Suggested P^T^t paths (grey, literature; black, this study) of metamorphism in high-grade metamorphic basement rocks intruded bythe Rogaland Complex at 920^930 Ma. Regional amphibolite-facies conditions of 6^8 kbar, 600^7008C are suggested for M1 metamorphismduring regional Sveconorwegian metamorphism at c. 1035^970 Ma (Jansen et al., 1985; Tomkins et al., 2005). Estimates for the maximum tem-peratures reached during later contact-related metamorphism M2 within the proposed contact aureole range from 7608C (Jansen et al., 1985)to49008C at the contact at low pressures of c. 5 kbar (Westphal et al., 2003). Ages of the metamorphic stages were determined by U^Pbzircon dating (i.e. Mo« ller et al., 2003; Tomkins et al., 2005; see text for discussion). Metamorphic zircon growth in sapphirine granulites of thisstudy occurred at 1006�4 Ma following prograde garnet breakdown during heating toT49008C. Sapphirine granulites and related rocks ofthis study are characterized by subsequent mid-crustal UHT metamorphism (c. 10008C, 7·5 kbar) followed by decompression to P55·5 kbarat 900^10008C. Growth of texturally late xenotime at 933�5 Ma is presumably related to cooling below the solidus and crystallization of leuco-some melt during M3.
DRU« PPEL et al. UHT METAMORPHISM, ROGALAND, NORWAY
343Downloaded from https://academic.oup.com/petrology/article-abstract/54/2/305/1485547by gueston 13 February 2018
during these stages of the metamorphic evolution. In add-ition, decompression to P55·5 kbar of these samples isalso evidenced by a number of cordierite-free,‘dry’ reactiontextures (i.e. quartz^spinel- and plagioclase-producing re-action textures in the metapelites and garnet^orthopyrox-ene regrowth in Grt^Opx^Crd^Spl gneisses), whoseformation is independent of the water activity.
Cooling
Subsequent cooling toT5750^8008C at c. 5 kbar is docu-mented by (1) the regrowth of biotite at the expense of thecordierite, spinel and orthopyroxene in the sapphirinegranulites and the Grt^Opx^Crd^Spl gneisses, reflectinginteractions between high-grade and early retrograde min-eral assemblages with crystallizing melt, (2) the late forma-tion of corundum at the expense of symplectitic spinel inthe sapphirine granulites, (3) the decomposition ofpeak-metamorphic Al-rich orthopyroxene into Al-poororthopyroxene^garnet symplectites in the Grt^Opx^Crd^Spl gneisses, (4) regrowth of garnet at the expense of cor-dierite in the migmatitic metapelite, and (5) regrowth ofgarnet as coronas around spinel in the migmatitic metape-lite. These predictions from the pseudosections are inagreement with P^T conditions of 760�308C and 3^5kbar as calculated by Grt^Opx Fe^Mg exchange andAl-in-Opx barometry of texturally late symplectitic assem-blages in the Grt^Opx^Spl^Crd gneisses. As a note of cau-tion, the cooling history of the sapphirine granulites andmigmatitic metapelites is not perfectly estimated by thepseudosections in Fig. 11, as these were calculated for areduced water content. Low water contents lead to a shiftof the biotite stability and solidus towards higher tempera-tures. Pseudosections for the comparably ‘dry’ Grt^Opx^Crd^Spl gneisses, on the other hand, were calculated forthe original water content but still document cooling toT58508C at pressures of c. 5 kbar. The late formation of agarnet corona around late biotite in the metapelite andregrowth of euhedral garnet at the expense of biotite inthe Grt^Opx^Crd^Spl gneisses provides possible evidencefor reheating of the samples. However, because of the lackof any significant zoning pattern in the newly formedgarnet a definite discrimination between prograde andretrograde garnet regrowth is difficult.
Timing of UHT metamorphismIn the sapphirine granulites, both oscillatory zoned,rounded zircon cores as well as broad, homogeneous,metamorphic zircon rims and single grains of meta-morphic zircon are observed. Concordia ages of1010�7Ma and 1006�4Ma demonstrate that meta-morphic zircon in the sapphirine granulites (both as over-growth rims on detrital zircon cores and as small singlegrains) formed during the regional Sveconorwegian meta-morphism between 1035 and 970Ma (Pasteels & Michot,1975; Bingen et al., 1993, 2008a, 2008b; Mo« ller et al., 2002,
2003; Tomkins et al., 2005). In contrast to Tomkins et al.(2005) and Mo« ller et al. (2002, 2003), we record no zircongrowth related to regional decompression after 970Ma orcontact metamorphism at around 930Ma (M2).Remarkably, metamorphic zircon in the sapphirine granu-lites, which is locally intergrown with xenotime, is charac-terized by high Ycontents of up to 2800 ppm and usuallylow Th/U ratios of 0·02^0·19, a feature also observed byMo« ller et al. (2003) for their metamorphic zircon grownduring M2 and M3, which also co-precipitated with xeno-time. According to Mo« ller et al. (2003) these highYcontentsobserved in their zircon are related to breakdown ofgarnet during M2. Even though garnet relicts are not pre-served in the sapphirine granulites, its previous existenceduring the prograde evolution of these samples is predictedby the calculated pseudosections (Fig. 11c). Therefore, for-mation of zircon and co-precipitating xenotime might berelated to prograde garnet breakdown during M1.Maximum temperatures of c. 840^9508C, attained duringmetamorphic zircon growth in the sapphirine granulitesat c. 1010 Ma, as calculated fromTi-in-zircon thermometry(Ferry & Watson, 2007), support the interpretation ofzircon formation during prograde garnet breakdown atHT to UHT conditions and are furthermore consistentwith constraints from the P^T pseudosections for the sap-phirine granulites (Fig. 11c), indicating garnet breakdownat temperatures 49008C. The fact that rims of meta-morphic zircon grown during M2 are not observed in oursamples does not necessarily mean that the sapphirinegranulites were not affected by this event. The generallack of zircon rims related to both post-M1 decompressionand contact metamorphism M2 in our samples may berelated to (1) the absence of peak-metamorphic garnet inthe sapphirine granulites releasing Zr during retrogradebreakdown, (2) the comparably low Zr contents of re-sorbed peak-metamorphic and early retrograde phases(510 ppm), which cannot provide enough Zr to producezircon during retrogression, and (3) the ‘dry’ mineralogyof the samples owing to previous extensive melt lossduring M1, hampering prograde dissolution^regrowth ofzircon as well as retrograde growth of zircon related tomelt crystallization during M2 (Kelsey et al., 2008).Evidence for M2 metamorphism of the sapphirine
granulites is restricted to the presence of late anhedralxenotime, epitactically grown on the metamorphic zirconand defining concordia ages of 928�10Ma and 933�5Ma. In garnet-absent samples such as the sapphirinegranulites, however, xenotime has a wide P^T stabilityrange and may persist throughout all metamorphicgrades (e.g. Bea & Montero, 1999; Pyle & Spear, 1999;Spear & Pyle, 2002). Nevertheless, we were unable to iden-tify an unambiguous source for the Y and P needed forxenotime crystallization, as the main phases of the sap-phirine granulites contain only minor Y,
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generally515 ppm (except Opx with up to 75 ppm;Table 9). Most probably, xenotime formation at c. 930Main these samples is related to leucosome crystallizationduring cooling below the solidus. Late biotite crystalliza-tion in the sapphirine granulites implies introduction offluid, possibly leading to recrystallization of xenotime bya dissolution^reprecipitation process.In summary, our data indicate that garnet breakdown in
the sapphirine granulites during prograde heating toUHTconditions of49008C was responsible for the forma-tion of metamorphic zircon at 1006�4Ma during theSveconorwegian Orogeny M1 (Fig. 15). Consequently, theUHT metamorphism at c. 10008C,7·5 kbar and subsequentdecompression to pressures55·5 kbar at still high tempera-tures documented by our samples is probably related tothe same metamorphic event. This interpretation is sup-ported by the coincidence in the clockwise P evolution ofour samples and those of Degeling et al. (2001); the latterare unaffected by M2 metamorphism and yield post-M1 re-gional decompression ages of 955�8Ma (Degeling et al.,2001; Tomkins et al., 2005). Alternative formation of theUHTassemblages in the sapphirine granulites, Grt^Opx^Crd^Spl gneisses and Grt^Sil metapelites duringcontact-thermal M2 metamorphism cannot be definitelyexcluded, even though we find no petrological evidencefor a second UHT overprint of our samples. Subsequentpost-decompressional cooling into the amphibolite facies,on the other hand, most probably occurred during M2 toM3, judging from (1) xenotime formation at c. 930 Ma,probably related to leucosome crystallization during cool-ing, (2) similarities between the cooling-related reactiontextures of our samples and those observed by Westphalet al. (2003) in samples from the same area, which havebeen dated at 908�9Ma (Mo« ller et al., 2003), and (3) thecoincidence of pressures estimated for cooling of oursamples (i.e. c. 5 kbar) and those proposed for the anortho-site^norite-related contact metamorphism M2 and subse-quent cooling M3 (c. 3^5 kbar; Jansen et al., 1985; VanderAuwera & Longhi, 1994; Westphal, 1998; Westphal et al.,2003).
Links with regional metamorphic phasesOne of the main goals of this study was to link the variousstages of the metamorphic evolution of our samples to oneor more of the main metamorphic events established forthis area; that is: (1) the regional Sveconorwegian meta-morphism M1 bracketed between c. 1035 and 970 Ma;(2) contact metamorphism M2 related to intrusion of theanorthosite^mangerite^charnockite suite at c. 930 Ma;(3) retrograde metamorphism M3 associated with progres-sive re-equilibration of the basement rocks during coolingof the anorthosite^ mangerite^charnockite massif. To datethere is only limited information on the P^T paths experi-enced by the basement rocks from both inside and outsidethe osumilite-in isograd, although P^T estimates have
been made for the subsequent metamorphic stages M1,M2, and M3 (Jansen et al., 1985; Degeling et al., 2001),linked with growth episodes of zircon as determined fromin situ U^Pb dating (Degeling et al., 2001; Mo« ller et al.,2002, 2003; Tomkins et al., 2005).Based on phase equilibria for texturally early,
garnet-bearing, M1 assemblages in the migmatitic gneissessurrounding the Rogaland Complex, Jansen et al. (1985)concluded that the highest-grade conditions during theregional Sveconorwegian metamorphism M1 peaked atamphibolite-facies conditions of 600^7008C and 6^8 kbar.Similar conditions were proposed by Degeling et al. (2001)for peak metamorphism and prograde wet partial meltingof a migmatitic Grt^Sil metapelite exposed at the Opx-inisograd some c. 25 km from the Rogaland Complex andapparently unaffected by a later prograde overprintduring M2. In situ U^Pb dating combined with investiga-tion of the trace element composition of metamorphiczircon from this sample link metamorphic zircon growthat 1035�9Ma with incipient prograde migmatization ofthe metapelite (Tomkins et al., 2005). This interpretation issupported by U^Pb dating of metamorphic monazite in afelsic granulite from the same area, yielding ages of1032�5 and 990�8Ma (Bingen et al., 2008b). Recent de-tailed investigation of the peak-metamorphic conditionsand P^T paths experienced by the migmatitic Grt^Opxgneisses and Grt^Sil metapelites from the same area dem-onstrate that regional metamorphism M1 culminated atsignificantly higher overall temperatures of 900�1008C(Grt^Opx Fe^Mg equilibria, Al-in-Opx thermometry)than those previously proposed, whereas calculated pres-sures of 6�1 kbar (Grt^Opx^Pl^Qtz and GASP equili-bria) are comparable (Franke & Dru« ppel, 2007).Post-peak decompression following the M1 event andpre-dating anorthosite emplacement is evident fromcommon decompression textures (Degeling et al., 2001;Tomkins et al., 2005), with conditions of 5·6 kbar,7108C being estimated for the replacement of the peak-metamorphic garnet^sillimanite assemblage by cordierite(Tomkins et al., 2005). Zircon formed during this reactiondates the regional decompression at 955�8Ma (Degelinget al., 2001; Tomkins et al., 2005), hence pre-datinganorthosite^norite emplacement. Remarkably, similarpeak-metamorphic mid-crustal pressures of 7·5�0·5 kbarfollowed by post-peak decompression by about 2 kbar alsocharacterize the P evolution of the sapphirine granulitesand related rocks of this study, whereas the peak-metamorphic temperatures are at least 1308 higher thanthe granulite-faciesTcalculated for M1.For the subsequent contact metamorphism M2 induced
by the emplacement of the Rogaland Complex thermom-etry supports UHT peak-metamorphic conditions of c.9008C, calculated for osumilite-bearing gneisses in thevicinity of the igneous massif and our study area
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(Westphal, 1998; Westphal et al., 2003). Low pressures of c.4^5 kbar are postulated for the emplacement depth ofthe Rogaland Complex and associated contactmetamorphism M2 based on barometric estimates forgarnet^orthopyroxene^plagioclase^sillimanite equilibriain osumilite-bearing gneisses (Jansen et al., 1985;Westphal,1998;Westphal et al., 2003) and experiments on the stabilityof osumilite in metapelites (Holland et al., 1996). Meltingexperiments on jotunite from the late-stage Bjerkreim^Sokndal layered intrusion support these relatively low M2
pressures of 55 kbar (Vander Auwera & Longhi, 1994),which are moreover consistent with the regional decom-pression to c. 5·6 kbar at 7108C postdating M1 andpre-dating anorthosite emplacement (Degeling et al., 2001;Tomkins et al., 2005). In situ U^Pb zircon dating of meta-morphic zircon grains or rims on inherited cores, over-grown by or intergrown with M2 minerals such asmagnetite, spinel and orthopyroxene, in migmatiticgneisses surrounding the Rogaland Complex yields agesof 927�7 Ma, hence directly linking UHT metamorph-ism with the intrusion of the anorthosite^norite massif(Mo« ller et al., 2002, 2003).Even though the UHT temperatures of c. 9008C previ-
ously proposed for M2 contact metamorphism are broadlyconsistent with those constrained for the sapphirine granu-lites and associated rocks of this study (i.e. c. 10008C), ourobserved P evolution with mid-crustal UHT metamorph-ism at c. 7·5 kbar being followed by decompression toP� 5·5 kbar is incompatible with the previously proposedupper crustal simple heating^cooling path at c. 5 kbar.The observed discrepancy between our pressure estimates(c. 7·5 kbar) and those proposed byWestphal et al. (2003)for Grt^Opx-bearing gneisses inside the osumilite-in iso-grad (c. 5 kbar) is probably related to the selection of refer-ence temperatures of only 700^8508C for the pressurecalculations of Westphal et al. (2003). Resetting of theFe^Mg system of garnet^orthopyroxene pairs used for thetemperature calculation of Westphal et al. (2003) is evidentfrom the partially extreme Al2O3 contents of orthopyrox-ene (up to 9·7wt %), which is more robust against retro-grade exchange and indicates temperatures in excess of9508C (using Al-in-Opx thermometry for P� 5 kbar), con-sistent with our data. Given these higherTestimates as ref-erence temperature, the resulting pressures are shifted tosignificantly higher, mid-crustal pressure values. Followingthis, the osumilite isograd could be an M1 isograd deflectedduring intrusion of the anorthosite plutons and associateddoming of the crust.A number of subsequent, retrograde, low-temperature,
low-pressure reaction textures are observed in the base-ment rocks in the vicinity of the igneous contacts and areinterpreted to overprint the high-grade M2 assemblages atP^Tconditions of c. 550^7008C, 3^5 kbar during slow cool-ing of the anorthosite^norite pluton from M2 to M3
(Maijer, 1987; Westphal, 1998; Wesphal et al., 2003). In situ
U^Pb dating of zircon overgrown by retrograde mineralassemblages in a migmatitic orthogneiss (i.e. zircon inclu-sions in coronitic garnet and in garnet^orthopyroxenesymplectites replacing orthopyroxene) yields an age of908�9Ma (Mo« ller et al., 2003), supporting this interpret-ation. The latter reaction textures strongly resemble thoseobserved in our migmatitic Grt^Sil metapelite and Grt^Opx^Crd^Spl gneisses (garnet regrowth around spineland cordierite, and decomposition of peak-metamorphichigh-Al orthopyroxene to low-Al orthopyroxene^garnetsymplectites), which occur in our samples at c. 3^5 kbar,700^8008C and are likewise interpreted to result from con-tinued cooling from UHTconditions into the amphibolitefacies.
Geodynamic implicationsThe sapphirine granulites and associated rocks of thisstudy are exposed at c. 7 km distance from the igneouscontact of the Rogaland anorthosite complex, within theproposed contact thermal aureole and next to theosumilite-in isograd. A typical regional metamorphicclockwise P^T path is deduced for the sapphirine granu-lites and the surrounding Grt^Opx^Crd^Spl gneisses andGrt^Sil metapelites studied here, with peak-UHT meta-morphism at 10008C and 7·5 kbar being followed bynear-isothermal decompression to55·5 kbar at still UHTconditions of 900^10008C and subsequent, near-isobariccooling to T5750^8508C. Syn-metamorphic ductiledeformation is common in the sapphirine granulites,marked by an alignment of the peak-metamorphic sap-phirine and retrograde biotite in the sapphirine granulites;this runs subparallel to the regional foliation and bandingdefined by the migmatitic Grt^Opx^Crd^Spl gneisses andGrt^Sil metapelites, as well as the surrounding migmatiticcharnockites. Our data demonstrate that temperatures ofat least 850^9408C were already reached during theSveconorwegian Orogeny M1 at c. 1010 Ma, recorded byzircon grown during prograde garnet breakdown in thesapphirine granulites.It remains uncertain whether the UHT peak meta-
morphism at c. 10008C, 7·5 kbar and early UHT decom-pression to P55·5 kbar at 900^10008C recorded by thesamples of the present study document continuous heatingto even higher temperatures during M1 and subsequentpre-M2 decompression or heating and decompressionduring contact-thermal M2 metamorphism.We prefer thefirst scenario as calculated regional P conditions attainedduring M1 (6^8 kbar) and the proposed post-peak decom-pression are almost identical to those of the sapphirinegranulites and associated rocks of this study. After decom-pression to P55·5 kbar at still UHT conditions of 900^10008C the sapphirine granulites and associated rockscould have formed the country-rocks for the intrudingRogaland Complex. In this case, elevated temperatures
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still in excess of 9008C would have hindered the rocks fromattaining new low-pressure UHTassemblages during M2.Cooling of the samples below the solidus and crystalliza-tion of the leucosome, on the other hand, presumablyoccurred during emplacement and cooling of the anortho-site^norite massif at 930^908Ma (M2^M3) at low pres-sures of c. 5 kbar. Alternatively, the mid-crustal peakassemblages of the sapphirine granulites and their hostrocks and the post-peak decompression might haveformed during M2 metamorphism, with metamorphiczircon remaining completely unaffected. In that case, thelow pressures of c. 5 kbar postulated for the emplacementof the Rogaland Complex and associated contact-metamorphism (Jansen et al., 1985; Vander Auwera &Longhi, 1994; Westphal et al., 2003) require further atten-tion. Our interpretation that the UHT metamorphism re-corded by the studied rocks from the vicinity to theRogaland Complex is related to regional M1 metamorph-ism is consistent with the recent finding that ortho- andparagneisses exposed at 425 km distance from the an-orthosite complex at the Opx-in isograd, which are henceclearly unaffected by the contact^metamorphic M2 eventat 930^920 Ma, experienced medium-pressure near-UHTconditions at 900�1008C, 6�1 kbar (Franke & Dru« ppel,2007), indicating the widespread occurrence of granulite-facies rocks formed during regional Sveconorwegian meta-morphism. Our data suggest that UHT metamorphism inRogaland is not exclusive to M2 metamorphism during an-orthosite^norite emplacement but already occurredduring the regional Sveconorwegian metamorphism M1 atc. 1010 Ma, reaching temperatures4850^9408C (presum-ably c. 10008C). According to Bingen et al. (2006, 2008c)high-grade metamorphism during M1 is related to the col-lision between Fennoscandia and an unknown craton, pos-sibly Amazonia, at the end of the Mesoproterozoic,leading to formation of the Sveconorwegian orogenexposed over a total width of c. 500 km. This event wasmainly characterized by crustal thickening associatedwith tectonic imbrication and voluminous syn-collisionalgranite magmatism at c. 1050Ma (Bingen et al., 2008a),consistent with our constrained clockwise P^T paths,documenting granulite-facies metamorphism at mid-crustal levels, followed by decompression and cooling. Theextreme temperatures in excess of c. 10008C at mid-crustalpressures attained by our samples, however, imply a zoneof very high heat flow, which is difficult to explain by aconventional collisional model. Based on numerical model-ing, Clark et al. (2011) suggested that crustal thickening toform a wide and long-lived mountain plateau, which atthe same time displays high internal concentrations ofheat-producing elements to substantially raise the crustaltemperatures and low erosion rates, is the most likely geo-dynamic scenario to reach UHTconditions at mid-crustallevels. Preferential thickening of crust that has previously
undergone pre-heating in an extensional back-arc settingor mechanical heating in shear zones, on the other hand,contributes to elevated temperatures, but will not usuallylead to ultrahigh temperatures (Clark et al., 2011). In theRogaland Sector, a direct heat source, for example volu-minous, coeval, mafic plutons, is not observed.Accordingly, a collisional scenario is appealing, consistentwith our reconstructed clockwise P^T paths. The wholeRogaland area underwent high-grade regional meta-morphism from c. 1035 to 970Ma (Wielens et al., 1981;Bingen & van Breemen, 1998; Mo« ller et al., 2002, 2003;Bingen & Stein, 2003; Tomkins et al., 2005; Bingen et al.,2006, 2008a, 2008b) that peaked in granulite-facies condi-tions at c. 1010Ma (Degeling et al., 2001; Mo« ller et al., 2002,2003; Tomkins et al., 2005; Bingen et al., 2006, 2008b).Investigation of reaction textures combined with geochron-ology demonstrate that the high-grade lithologies of theRogaland^Vest Agder Sector resided at high-grade condi-tions for at least 60 Myr until c. 970 Ma, when decompres-sion commenced (Tomkins et al., 2005; Bingen et al., 2006,2008b). Following this, both the P^T conditions and dur-ation of high-grade metamorphism recorded by the crustalbasement of the Rogaland Sector, including our samples,are in agreement with its formation as a collision-related,long-lived, high-grade metamorphic mountain plateau. Inthis context, the retrograde decompression still at veryhigh temperatures, as recorded by our samples, is finallyassociated with melting of mafic lower crust giving rise tovoluminous anorthosite plutonism at 930^920 Ma; thiscan be interpreted as gravitational collapse of the moun-tain plateau.
CONCLUSIONSWe have documented a single-phase clockwise P^Tevolu-tion for regional MP^UHT granulite-facies MgAl-richsapphirine granulites and associated paragneisses of theRogaland Sector (South Norway), which are exposedclose to the 930^920Ma anorthosite^mangerite^charnock-ite suite of the Rogaland Complex. Our data, in combin-ation with U^Pb ages of zircon and xenotime measuredin thin sections, provide new insights into the crustal evolu-tion of the Rogaland Sector during latest Mesoproterozoicto early Neoproterozoic times, as follows.
(1) The metasedimentary protoliths of the sapphirinegranulites were deposited between 1220 and 1050Maand mainly incorporate zircon from early Mesopro-terozoic igneous rocks.
(2) The rocks record a clockwise P^Tevolution culminat-ing at UHT conditions of c. 10008C at a mid-crustallevel (c. 7·5 kbar). Retrograde decompression to pres-sures of c. 5 kbar, initially at prevailing UHTcondi-tions, was followed by near-isobaric cooling.
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(3) In situ U^Pb zircon and xenotime age data combinedwith Ti-in-zircon thermometry indicate that regionalMP^UHT metamorphism occurred during regionalSveconorwegian metamorphism M1 at c. 1010 Ma,prior to the emplacement of the Rogaland Complex(930^920 Ma). In the sapphirine granulites, theformation of texturally late xenotime is related to theemplacement and cooling of the anorthosite^manger-ite^charnockite suite (M2^M3) at low pressures of c. 5kbar.
(4) The clockwise P^T path of the regional, c. 1010MaMP^UHT metamorphism is interpreted to be relatedto collisional tectonics during the early stages of theSveconorwegian Orogeny, followed by gravitationalcollapse of the mountain plateau.
ACKNOWLEDGEMENTSWe wish to thank Christa Zecha (TU Berlin) for carefulsample preparation, and Petra Marsiske (TU Berlin) forhelp with the XRFmeasurements. The assistance of OonaAppelt (GFZ Potsdam) and Francois Galbert (TU Berlin)during EMP analysis is greatly appreciated.We are grate-ful to Helene Bra« tz and Reiner Klemd (University ofErlangen) for their help and advice with the LA-ICP-MSmeasurements. We also wish to thank Astrid Kowitz(Humboldt University Berlin) for her companionshipduring the field investigations. The manuscript benefitedfrom discussions with Bernard Bingen, Mogens Marker,and Trond Slagstad (NGU Trondheim). Thoughtful com-ments on an earlier version of the paper by Chris Clarkand Andreas Mo« ller, and on the final version by BernardBingen, Chris Clark and Jacqueline Halpin helped toimprove the paper. The logistical support by theGeological Survey of Norway (NGU Trondheim), espe-cially the introduction to the regional geology of theRogaland area by Mogens Marker and Peter Ihlen, isgratefully acknowledged.
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