a petrologic, geochemical and sr–nd isotopic study on...
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ORIGINAL PAPER
A petrologic, geochemical and Sr–Nd isotopic study on contactmetamorphism and degassing of Devonian evaporitesin the Norilsk aureoles, Siberia
Kwan-Nang Pang • Nicholas Arndt • Henrik Svensen •
Sverre Planke • Alexander Polozov • Stephane Polteau •
Yoshiyuki Iizuka • Sun-Lin Chung
Received: 19 May 2012 / Accepted: 3 November 2012
� Springer-Verlag Berlin Heidelberg 2012
Abstract Devonian evaporites and associated sedimen-
tary rocks in the Norilsk region were contact metamor-
phosed during emplacement of mafic sills that form part of
the end-Permian (*252 Ma) Siberian Traps. We present
mineralogical, geochemical and Sr–Nd isotopic data on
sedimentary rocks unaffected by metamorphism, and meta-
sedimentary rocks from selected contact aureoles at
Norilsk, to examine the mechanisms responsible for
magma-evaporite interaction and its relation to the end-
Permian environmental crisis. The sedimentary rocks
include massive anhydrite, rock salt, dolostone, calcareous
siltstones and shale, and the meta-sedimentary rocks
comprise calcareous hornfels, siliceous hornfels and minor
meta-anhydrite and meta-sandstone. Contact metamor-
phism took place at low pressure and at maximum
temperatures corresponding to the phlogopite-diopside
stability field. Calcareous hornfels have high CaO, MgO,
CO2, SO3, low SiO2 and initial Sr isotopic ratios of
0.7079–0.7092, features indicative of calcareous siltstone
protoliths. Siliceous hornfels, in contrast, have high SiO2,
Al2O3, Na2O, low in other major element oxides and initial
Sr isotopic ratios of 0.7083–0.7152, consistent with pelitic
or shaley protoliths. Loss of CO2 in a subset of calcareous
hornfels can be explained by decarbonation reactions dur-
ing metamorphism, but release of SO2 from evaporites
cannot be accounted for by a similar mechanism. Occur-
rences of wollastonite and a variety of hydrous minerals in
the calcareous hornfels are consistent with equilibration
with hydrous fluid, which was capable of leaching large
quantities of anhydrite in the presence of dissolved NaCl.
In this way, substantial sediment-derived sulfur could have
been mobilized, incorporated into the magmatic system
and released to the atmosphere. The release of CO2 and
SO2 from Siberian evaporites added to the variety of toxic
gases generated during metamorphism of organic matter,
coal and rock salt, contributing to the end-Permian envi-
ronmental crisis.
Keywords Contact aureole � Metamorphism �End-Permian � Evaporite � Norilsk � Siberian Traps
Introduction
Extensive Paleozoic evaporites, marls, organic-rich shales
and coal formations in the Tunguska Basin, East Siberia,
were intruded by sills related to the plumbing system of the
Communicated by T. L. Grove.
Electronic supplementary material The online version of thisarticle (doi:10.1007/s00410-012-0830-9) contains supplementarymaterial, which is available to authorized users.
K.-N. Pang � N. Arndt
Institut des Sciences de la Terre, Universite Joseph Fourier,
1381 rue de la Piscine, 38401 Grenoble, France
K.-N. Pang (&) � S.-L. Chung
Department of Geosciences, National Taiwan University,
P.O. Box 13-318, Taipei 10699, Taiwan
e-mail: [email protected]
H. Svensen � S. Planke � S. Polteau
Physics of Geological Processes (PGP), University of Oslo,
PO Box 1048, Blindern, 0316 Oslo, Norway
A. Polozov
Institute of Geology of Ore Deposits, Petrography,
Mineralogy and Geochemistry, Russian Academy of Sciences,
119017 Moscow, Russia
Y. Iizuka
Institute of Earth Science, Academia Sinica, 128 Academia Road
Section 2, Nankang Taipei 11529, Taiwan
123
Contrib Mineral Petrol
DOI 10.1007/s00410-012-0830-9
end-Permian Siberian Traps (Naldrett et al. 1995; Kont-
orovich et al. 1997; Naldrett and Lightfoot 1999; Arndt
et al. 2003). The Siberian flood basaltic volcanism was
associated with the largest known environmental crisis in
the Earth’s history, causing up to 70 % of terrestrial and
95 % of marine species to become extinct (Sharma 1997;
Wignall 2001). Recent studies propose that the crisis was
triggered by emission of sediment-derived greenhouse and
toxic gases during emplacement of the sills (Retallack and
Jahren 2008; Svensen et al. 2004, 2009a; Ganino and Arndt
2009). Other authors, however, suggest that the extinction
might have predated the main phase of volcanism and
propose that its trigger was degassing of magmatic CO2
and HCl from altered oceanic crust (Sobolev et al. 2011).
While the arguments for these competing hypotheses are
still debatable, new data and observations in this context
are important in understanding the relations between flood
basaltic volcanism and mass extinctions.
In the Norilsk region, northern Siberia, available data
and observations point to extensive magma-evaporite
interaction, including (1) development of extensive contact
aureoles surrounding the intrusions related to the Siberian
Traps (Likhachev 1994; Turovtsev 2002; Naldrett 2004),
(2) occurrence of magmatic anhydrite in the intrusions
(Li et al. 2009a; Ripley et al. 2010), (3) high 87Sr/86Sr in
the intrusions (Arndt et al. 2003), (4) high 34S in sulfides in
Ni–Cu–(PGE) sulfide ore-bearing intrusions (Gorbachev
and Grinenko 1973; Grinenko 1985; Li et al. 2003) and (5)
high Cl contents of olivine-hosted melt inclusions in the
Gudchikhinsky picrites (Sobolev et al. 2009). However,
most previous studies have focused mainly on the intru-
sions; systematic studies of the evaporitic host rocks by
modern methods have not been carried out, except for
earlier comprehensive petrographic studies in Russian that
are not generally available (e.g., Turovtsev 2002). In par-
ticular, Turovtsev (2002) focused on metamorphism of
terrigenous and carbonate rocks but did not investigate
evaporite metamorphism in detail. Further, as noted by
Walker et al. (1994) and Naldrett (2004), good Sr isotopic
analyses of anhydrite at Norilsk are not generally available
but important to evaluate magma-evaporite interaction.
Here, we present a comparative mineralogical, geochemi-
cal and Sr–Nd isotopic study on sedimentary rocks unaf-
fected by contact metamorphism, and meta-sedimentary
rocks from selected contact aureoles from boreholes and
outcrops in the Norilsk region.
Geological background
The Tunguska Basin is situated on the Siberian craton and
contains one of the oldest known petroleum systems in the
world (Frolov et al. 2011). The Precambrian basement
consists of granitoids, granitic gneisses, schists and am-
phibolites. The sedimentary rocks are Neoproterozoic to
Permian in age with total thicknesses ranging from 3 to
12.5 km (Kontorovich et al. 1997). The Neoproterozoic
strata are dominated by carbonates with minor shale,
sandstone and evaporites, overlain by thick (up to
*2.5 km) Cambrian marine evaporite deposits composed
of salt, anhydrite and carbonates in the southern parts of the
basin. In the Norilsk region, rock salt is generally absent in
the Cambrian succession, but is present locally within
Devonian sediments. The Ordovician to Devonian sequen-
ces are also dominated by the evaporitic facies consisting of
carbonates, marls, anhydrites with minor salt layers. The
Carboniferous to Lower Permian strata comprise terrige-
nous sedimentary rocks including conglomerates, sand-
stones, siltstones and coals, collectively referred to as the
Tunguska series. Sedimentation terminated in the Upper
Permian with the onset of flood basalt volcanism of the
Siberian Traps (Surkov et al. 1991; Ulmishek 2001).
The end-Permian (*252 Ma) Siberian Traps is the
world’s largest continental large igneous province (LIP)
covering an area of at least 4.5 9 106 km2 with a total
volume of *4 9 106 km3 in the northwestern part of the
Siberian craton and widespread sub-surface extension in
the West Siberian Basin (Sharma 1997; Czamanske et al.
2002; Reichow et al. 2002; Saunders et al. 2005). The
on-craton exposure of the province encompasses a central
region of flood basalts and basaltic pyroclastic rocks sug-
gested to have erupted in less than one million years (Kamo
et al. 2003). The lava pile, typically [3 km-thick in the
northwest, thinner to the southeast and absent in the south,
comprises dominantly tholeiite basalt and minor picrite
with minor alkaline rocks of more diverse compositions
(from trachyte to meimechite). The intrusive facies of the
province crop out mainly at the margins of the volcanic
pile but are penetrated by boreholes throughout the basin.
Phreatomagmatic pipes with hydrothermal magnetite
mineralization, likely rooted in Cambrian evaporites, are
abundant in the southern part of the province (Von der
Flaass and Naumov 1995; Svensen et al. 2009a, b). Basaltic
pipes are known from the northern part of the province (see
Fig. 1) but have not been subjected to detailed studies.
Norilsk lies between the Yenisey-Khatanga trough and
the West Siberian Basin in northern Siberia (Fig. 1). It is
located near the northwestern boundary of the Siberian
Traps where both extrusive and intrusive facies crop out.
The extrusive facies consists of thick piles of basaltic lavas
that erupted onto the Tunguska Basin sedimentary rocks.
The intrusive facies occurs as sills within Devonian to
Permian strata and, to a lesser extent, within the Pre-
cambrian basement. Exposure of the intrusions is con-
trolled by deep crustal faults trending in northeasterly
directions (Zen’ko and Czamanske 1994). Some intrusions
Contrib Mineral Petrol
123
(i.e., Norilsk I, Talnakh and Kharaelakh) host large Ni–Cu–
(PGE) sulfide deposits, representing one of the largest
accumulations of magmatic sulfides in the world. One
unusual feature of the ore-bearing intrusions is the devel-
opment of intense metamorphic and metasomatic aureoles,
which are in many cases as thick as, or thicker than, the
intrusions (Likhachev 1994; Naldrett 2004). Sulfur isotopic
studies of the ore sulfides indicate that ore formation
involved isotopically heavy crustal S derived from the
evaporitic country rocks (Grinenko 1985; Li et al. 2003).
The presence in the Kharaelakh intrusion of magmatic
anhydrite, a rare mineral in intra-plate magmatic rocks, has
been taken as evidence of evaporite assimilation by the
ascending magma (Li et al. 2009a; Ripley et al. 2010).
Sample descriptions
During a 2006 field campaign to the Norilsk region, dia-
mond drill-cores stored at the Talnakh mine site were
investigated. Figure 1 shows the locations of boreholes.
The on-site work included borehole logging and sampling
at representative intervals (Fig. 2). The drill-cores intersect
Silurian to Permian strata almost unaffected by contact
metamorphism (MD56), meta-sedimentary rocks in the
Mikchangda area (MD48) and those occurring in the upper
aureole of the ore-bearing Talnakh intrusion (TG21).
Table 1 shows the lithology of the samples and the geo-
logical formations that they belong to. Additional samples
were collected from outcrops and underground mine
exposure in the Norilsk region.
Drill-core MD56 contains Devonian and Silurian
evaporitic strata with thicknesses of *600 and *400 m,
respectively. The Upper Devonian Nakokhoz and Lower
Devonian Zubov Formations represent sulfate-bearing
sequences, and the Middle Devonian Manturov Formation
consists of halite-bearing sequences (Zharkov 1984).
These sequences are overlain by a *200 m-thick
sequence of Carboniferous to Permian sandstone, silt-
stone, shale and coal seams intruded by minor sills. The
evaporitic strata are largely free of sills and show no
petrographic evidence of metamorphism. Most samples
appear homogeneous at the scale of hand specimen or
polished thin section; laminations or veins in some
heterogeneous samples are separated to become a sub-
sample if possible. The rocks have variable relative
abundance between chemical sedimentary and clastic
fractions and include massive anhydrite, dolostone, rock
salt, calcareous siltstones and shale (Table 2). Anhydrite,
dolomite, calcite and halite in the rocks are fine-grained
Fig. 1 Simplified geological
map of the Norilsk region,
Siberia (after Malitch et al.
1999)
Contrib Mineral Petrol
123
and granular. The clastic fraction of the rocks, if present,
is composed of fine-grained mixture of quartz and clay
minerals with or without chlorite and muscovite. Sample
MD56-36 is an organic-rich shale belonging to the
Carboniferous-Permian Tunguska series. It contains rutile
and pyrite apart from the aforementioned silicate phases.
Fig. 2 Logs of drill-cores from which the majority of samples in this
study were taken, based on our logging and available logs. Note that
drill-cores MD56 and MD48 were reduced in size by 50 % compared
to TG21. Areas bounded by the green line denote portions of the
contact aureole illustrated in Fig. 9. asl above sea level
Contrib Mineral Petrol
123
Drill-core MD48 was aimed for prospecting of Ni-Cu
mineralization and intersects multiple sills and the meta-
sedimentary rocks occurring between them in the
Mikchangda area. The cumulative thickness of the sills,
which are intercalated with meta-sedimentary rocks, is
*550 m (Fig. 2). The samples are taken from an interval
corresponding to the Devonian evaporitic strata of drill-
core MD56, including the high-temperature zones between
sills (MD48-1 to MD48-6) and the lower aureole of the
sills (MD48-11 to MD48-24) (Fig. 2). Samples from the
high-temperature zones occur close to the sills and some of
them even contain parts of the sills (Fig. 3a), which are
separated to become a sub-sample if possible. The meta-
sedimentary rocks (or portions of the rocks) display
heterogranular textures typical of contact metamorphic
rocks, including the development of porphyroblasts and
mineral clusters in a fine-grained matrix. The porphyro-
blasts include clinopyroxene, amphibole, phlogopite,
chlorite and anhydrite. Titanite, pyrite, calcite, Fe–Ti
oxides, Cr-spinel and Mg–Al spinel occur as accessory
minerals. The matrix contains mainly microcrystals of
similar mineralogy as the porphyroblasts and minor fine-
grained portions whose mineralogy cannot be identified
under optical microscope. Samples from the lower aureole
in general show low degrees of recrystallization hence
higher portion of the fine-grained matrix compared to those
from the high-temperature zones. They also show fine
laminations presumably corresponding to the original
bedding prior to metamorphism. Sample MD48-11, taken
at *5.2 m from the intrusive contact, is mineralogically
similar to samples present in the high-temperature zones
mentioned above, except in addition containing small
amount of apatite. Layers of massive, fine-grained gray
anhydrite are present in the aureole at *7.9 m and 18.6 m
from the sill contact (Table 2). Sample MD48-14 further
from the contact contains K-feldspar instead of phlogopite
as the major K-bearing phase. Sample MD48-17 contains
actinolite but is clinopyroxene-free. Sample MD48-23a,
taken at *69.3 m from the intrusive contact, shows no
signs of recrystallization and resembles sample MD56-22
in terms of textures. Therefore, the total thickness of the
lower Mikchangda aureole might be less than *70 m as
defined by textures and mineralogy.
Drill-core TG21 intersects the *160 m-thick Talnakh
intrusion and its contact aureole. The samples, taken along
a *230 m-thick interval from the upper aureole, are het-
erogranular meta-sedimentary rocks. Metamorphic nod-
ules, in the scale of several millimeters, and mineral
clusters occur in a finer-grained matrix in these rocks.
Chlorite, muscovite and quartz are major matrix phases;
albite is concentrated in the rims of the metamorphic
nodules. Apatite, calcite, anhydrite, K-feldspar, monazite,
Fe–Ti oxides, phlogopite, pyrite and rutile occur as
accessory minerals. Sulfide and magnetite mineralization,
and veins of calcite and gypsum are noted in some places
along this drill-core.
Additional samples were collected from underground
exposure of the Kharaelakh intrusion in the Oktyabysky
mine and outcrops of the Chernogorsk intrusion. Sample
NOR-2a and NOR-3 are fine-grained siliceous hornfels
adjacent to massive sulfide ore in the Kharaelakh intrusion.
They have a mineral assemblage consisting of albite,
chlorite, muscovite and quartz with or without amphibole
and garnet. Samples NOR-5, NOR-6, NOR-7a to NOR-7e
are meta-sedimentary rocks that are texturally similar to
those from the high-temperature zones of drill-core MD48.
A major difference is the presence of wollastonite and
garnet in these samples indicative of a relatively high
metamorphic grade. Samples NOR-14a, NOR-14b and
NOR-16 are enclaves of meta-sandstone in the Cherno-
gorsk intrusion. They contain equigranular quartz and
feldspar with minor muscovite. Samples NOR-15 and
NOR-17 are fine-grained siliceous hornfels close to the
contact of the intrusion. The texture and mineralogy of
these rocks are similar to meta-sedimentary rocks in drill-
core TG21.
Table 1 Lithology and geological formations of samples in this study
Formation Evaporites and
carbonates
Clastic rocks Calcareous hornfels
and meta-anhydrite
Siliceous
hornfels
Carboniferous-Permian Tunguska MD56-36
Upper Devonian Kalargon (D3kl) MD56-34 MD48-1, 2, 4, 6b
Upper Devonian Nakokhoz (D3nk) MD56-31
Middle Devonian Manturov (D2mt) MD56-26
Lower Devonian Razvedochnaya (D1rz) TG21-1 to 5, 7 to 10
Lower Devonian Zubov (D1zb) MD56-19, 22, 23 MD48-16,
17, 23a, 24
MD48-11 to 14
Lower Silurian Tanymen (S1tm) MD56-9a
Contrib Mineral Petrol
123
Table 2 Texture and mineralogy of samples in this study
Sample Depth (m) Rock type Texture Mineral phases1 Remarks
Drill-core MD56
MD56-9a 1,178.0 Calcareous siltstone Finely laminated Cc, Qtz, Kfs Cc vein (as MD56-9b)
MD56-19 815.0 Rock salt Coarse crystalline Hl
MD56-22 744.6 Calcareous siltstone Fine granular Qtz, Kfs, Cc, Anh, Anh-Cls vein
MD56-23 742.7 Calcareous siltstone Fine granular Qtz, Kfs
MD56-26 504.5 Massive anhydrite Fine crystalline Anh
MD56-31 382.6 Massive anhydrite Fine crystalline Anh
MD56-34 323.6 Dolostone Massive Cc2
MD56-36 231.3 Shale Finely laminated, deformed Ms, Chl, Qtz, Kfs, Rt
Drill-core MD48
MD48-1 704.6 Calcareous hornfels Heterogranular crystalline Cpx, Phl, Amp, Chl,
Anh, Cc, Opa, Ttn
MD48-2 717.7 Calcareous hornfels Heterogranular crystalline Cpx, Phl, Chl, Ep, Anh,
Ttn, Py
MD48-4 735.0 Calcareous hornfels Heterogranular crystalline Cpx, Phl, Chl, Anh, Cc, Opa
MD48-6b 742.8 Calcareous hornfels Heterogranular crystalline Cpx, Phl, Chl, Anh, Cc,
Opa, Ap, Spn
MD48-11 1,257.8 Calcareous hornfels Finely laminated Cpx, Phl, Amp, Chl, Anh,
Cc, Opa, Ap
MD48-12 1,260.0 Calcareous hornfels Fine granular, spotted Cpx, Phl, Anh, Cc
MD48-13 1,260.5 Meta-anhydrite Fine crystalline Anh
MD48-14 1,262.0 Calcareous hornfels Finely laminated Cpx, Kfs, Cc, Ttn, Ap
MD48-16 1,271.2 Meta-anhydrite Fine crystalline Anh
MD48-17 1,275.2 Calcareous hornfels Finely laminated, spotted Amp, Chl, Kfs, Ab,
Cc, Ttn, Ap
MD48-23a 1,321.9 Calcareous hornfels Fine granular Qtz, Kfs, Cc, Opa, Ap Anh-Cls vein
(as MD48-23b)
MD48-24 1,338.1 Calcareous hornfels Fine granular Ms, Chl, Qtz, Cc, Kfs
Drill-core TG21
TG21-1 981.0 Siliceous hornfels Heterogranular crystalline, spotted Qtz, Chl, Ms, Ab, Cc, Ap
TG21-2 992.6 Siliceous hornfels Heterogranular crystalline Qtz, Chl, Ms, Ab, Ap
TG21-3 1,005.6 Siliceous hornfels Heterogranular crystalline, spotted Qtz, Chl, Ms, Ab, Opa,
Mnz, Rt, Cr-Spn
TG21-4 1,010.5 Siliceous hornfels Heterogranular crystalline, spotted Qtz, Chl, Ms, Opa, Mnz,
Ap, Rt, Py, Cr-Spn
TG21-5 1,070.5 Siliceous hornfels Coarsely crystalline Qtz, Chl, Ms, Ab Cc-sulfide vein
TG21-7 1,143.6 Siliceous hornfels Heterogranular crystalline Qtz, Chl, Ms, Ab, Ap
TG21-8 1,159.1 Siliceous hornfels Coarsely crystalline Qtz, Chl, Ms, Ab, Ap
TG21-9 1,165.1 Siliceous hornfels Coarsely crystalline Qtz, Chl, Ms, Ab, Ap
TG21-10 1,197.0 Siliceous hornfels Heterogranular crystalline Qtz, Chl, Ms, Ap, Rt, Cr-Spn
Samples from mine exposures
NOR-2a – Siliceous hornfels Fine crystalline Amp, Chl, Ms, Ab, Ap, Cp
NOR-3 – Siliceous hornfels Fine crystalline Grt, Chl, Ms, Ab
NOR-5 – Calcareous hornfels Heterogranular crystalline Cpx, Grt, Anh, Cc, Cp Anh vein
NOR-6 – Calcareous hornfels Heterogranular crystalline Cpx, Grt, Wo, Anh, Cc Anh vein
NOR-7a – Massive anhydrite Fine crystalline Anh
NOR-7b – Calcareous hornfels Heterogranular crystalline Cpx, Wo, Anh, Cc, Cp
NOR-7c – Calcareous hornfels Coarse crystalline Cpx, Grt, Wo, Anh, Cc, Cp
NOR-7d – Calcareous hornfels Heterogranular crystalline Cpx, Wo, Anh, Cc, Cp
NOR-7e – Calcareous hornfels Heterogranular crystalline Cpx, Grt, Wo, Anh, Cc, Cp
Contrib Mineral Petrol
123
Analytical methods
Forty-three samples (8 sedimentary rocks and 35 meta-
sedimentary rocks) were collected for this study, forming a
representative collection of available sediment and hornfels
types. Rock powders for geochemical and Sr–Nd isotopic
analyses were prepared by crushing of rock slabs on a steel
plate and pulverization in an agate mill. Polished thin
sections were prepared for petrographic observation and
electron microprobe analysis.
Electron microprobe analysis
The samples were analyzed with a JEOL JXA-8500F
electron probe microanalyzer at Institute of Earth
Sciences, Academia Sinica, Taiwan. The analyses were
performed using wavelength-dispersive method at an
accelerating voltage of 12 kV, a beam current of 3 nA, a
beam diameter of 2 lm and a peak counting time of 10 s.
Accuracy of the analyses was monitored using mineral
standards, and precision was generally better than 1 % for
most elements.
Major and trace element analyses
Major element oxides and trace element abundances were
measured using routine methods by inductively coupled
plasma-atomic emission spectrometry (ICP-AES) and
inductively coupled plasma-mass spectrometry (ICP-MS),
respectively, at the University of Grenoble, France.
Analytical procedures for the trace element analysis follow
Chauvel et al. (2010), with accuracy and precision gener-
ally better than ±5 % (relative) for most trace elements as
shown by statistics of duplicate analyses of samples and of
reference material BE-N, BHVO-2, BR-24, RGM-1 and
JSd-2 (see electronic supplementary material). Loss on
ignition (LOI) was obtained by routine methods.
Light element analyses
Measurements of total organic carbon and total inorganic
carbon were conducted by a Carbon Analyzer LECO
(CR-412) instrument at the Department of Geosciences,
University of Oslo. Sample powders weighing 350 mg
were loaded into combustible crucible boats. Aliquots of
inorganic carbon were released by addition of HCl at
40–50 �C. All crucibles with samples were washed, dried
and combusted in pure oxygen at 1,350 �C in the LECO
instrument. Analyses for H and S were performed at OEA
Laboratories Limited, Callington, UK. Sample powders
and V2O5 were loaded into tin capsules using a Mettler
ultra-microbalance. The sample capsules were dropped
sequentially into a reaction furnace packed with pure
tungsten oxide and Cu held at 1,000 �C with He as a carrier
gas. They were then flash combusted by a pulse of oxygen
at *1,700 �C. The resultant gases were purified and
separated on a packed GC column before flowing to the
detector for quantification on a CE instruments (Thermo)
EA1110 elemental analyzer. The light element data were
expressed as total organic C (TOC), CO2 (carbonates), H2O
and SO3 for the ease of comparison with other major
element data.
Sr–Nd isotopic analyses
Measurements of Sr–Nd isotopes were performed by a
ThermoFinnigan Neptune Multi-collector ICP-MS at
Department of Geosciences, National Taiwan University,
Taiwan. Analytical procedures are the same as in Lee et al.
(2012). Within-run isotopic fractionation was corrected for88Sr/86Sr = 8.375209 and 146Nd/144Nd = 0.7219. The87Sr/86Sr ratio of the Sr standard SRM987 was
0.71029 ± 1, and the 143Nd/144Nd ratio of the La Jolla
standard JNdi-1 was 0.512122 ± 7 through the course of
the measurements. The data were calculated as initial87Sr/86Sr and eNd values relative to an age of 251 Ma,
Table 2 continued
Sample Depth (m) Rock type Texture Mineral phases1 Remarks
NOR-14a – Meta-sandstone Nodular Qtz, Chl, Ab
NOR-14b – Meta-sandstone Nodular Qtz, Chl, Ab
NOR-15 – Siliceous hornfels Finely laminated Qtz, Chl, Ms, Ab, Opa
NOR-16 – Meta-sandstone Nodular Qtz, Chl, Ab
NOR-17 – Siliceous hornfels Finely laminated Qtz, Chl, Ms, Ab
1 Ab albite, Amp amphibole, Anh anhydrite, Ap apatite, Cc calcite-dolomite, Chl chlorite, Cls celestine, Cp chalcopyrite, Cpx clinopyroxene, Cr-
Spn chrome spinel, Ep epidote, Grt garnet, Hl halite, Kfs K-feldspar, Mnz monazite, Ms muscovite, Opa opaque Fe–Ti oxides, Phl phlogopite, Pypyrite, Qtz quartz, Rt rutile, Spn spinel, Ttn titanite, Wo wollastonite
Contrib Mineral Petrol
123
Fig. 3 Scans of thin sections, photomicrographs and backscattered
electron images of representative samples from the Norilsk contact
aureoles, Siberia. a Contact between dolerite and calcareous hornfels
(sample MD48-1); the grain size of the hornfels is coarsened toward
the contact as a result of contact metamorphism. b Metamorphic
nodules rich in albite in a fine-grained matrix in siliceous hornfels
(sample TG21-3). c Chlorite and clinopyroxene crystals surrounded
by anhydrite porphyroblast in calcareous hornfels (sample NOR-7c,
crossed polars). d Fine crystals of muscovite and albite, and fibrous
chlorite in siliceous hornfels (sample NOR-2a, crossed polars).
e Chlorite, either fibrous or crystalline, and fine clinopyroxene grains
surrounded by coarse anhydrite and phlogopite crystals in calcareous
hornfels (sample MD48-4). f Fibrous chlorite and muscovite, and fine
quartz grains in siliceous hornfels (sample TG21-10). Ab albite, Anhanhydrite, Chl(c/f) chlorite (crystalline/fibrous), Cpx clinopyroxene,
Ms muscovite, Qtz quartz
Contrib Mineral Petrol
123
decay constants of 1.42 9 10-11 year-1 for 87Rb, 6.54 9
10-12 year-1 for 147Sm, and present day chondritic values
of 143Nd/144Nd = 0.512638, 147Sm/144Nd = 0.1967,87Sr/86Sr = 0.7045 and 87Rb/86Sr = 0.0827 (Faure and
Mensing 2005).
Results
Mineral compositions
Representative analyses of minerals from the Norilsk
aureoles are listed in Table 3. The full dataset, together
with mineral chemical data presented by Turovtsev (2002),
is provided as an electronic supplement. Data for clino-
pyroxene, phlogopite and amphibole are calculated using
the programs PYROX (Yavuz 2001), MICA ? (Yavuz
2003) and WinAmphcal (Yavuz 2007), respectively. Min-
erals indicative of peak metamorphic conditions of the
Mikchangda aureole include clinopyroxene and phlogopite.
Clinopyroxene has compositions between augite and
diopside with variable degrees of Tschermak substitution
(Fig. 4a). This is reflected in the highly variable Al2O3
content of clinopyroxene ranging from less than 1 to *13
wt% (see supplementary material). Within-sample differ-
ence of several weight percent is common. The Mg# of
clinopyroxene ranges from 61 to 97 with the majority
between 78 and 85. Its TiO2 content is generally low
(\1 wt%), and Cr is mostly below detection limit. Some
analyses plot outside the pyroxene quadrilateral toward the
wollastonite apex, compared to those from the sills that are
dominated by augite (Fig. 4a). Phlogopite in the aureole
has low TiO2 (\0.5 wt%) and high Mg# (73–97, with the
majority [85). It contains H2O as the dominant volatile
species (3.5–4.5 wt%) and minor F (below detection limit
to 2 wt%) (see electronic supplementary material). Other
minerals from the aureole include chlorite (clinochlore-
chamosite solid solution), amphibole (magnesiotaramite),
albite, orthoclase (Fig. 4b), titanite and apatite (Table 3).
The major minerals from the Talnakh aureole include
muscovite, chlorite, albite and apatite (Table 3). The
muscovite has high Al2O3 (*28 to 35 wt%) and moderate
Mg# (38–80). Biotite containing up to *7 wt% F occurs as
patches associated with apatite, chlorite, rutile and pyrite in
sample TG21-4 (Table 3). Apatite contains F as the dom-
inant volatile species (4.1–5.4 wt%, see supplementary
material), in contrast with that in the Mikchangda aureole
containing substantial Cl apart from F (Fig. 4c).
Major, trace and light elements
Major, trace and light element data for sedimentary rocks
in the Norilsk region and meta-sedimentary rocks from the
Norilsk aureoles are given as an electronic supplementary
material. Sedimentary rocks from drill-core MD56 display
wide compositional variations indicative of the relative
abundance of a chemical sedimentary and a detrital,
silty fraction (Figs. 5, 6). In a SiO2–(CaO ? MgO)–
(Al2O3 ? Na2O ? K2O) ternary diagram (Fig. 5), these
rocks fall on a linear trend between massive anhydrite and
dolostone near the (MgO ? CaO) apex and the shale
sample near the SiO2–(Al2O3 ? Na2O ? K2O) line. The
only exception is sample MD56-19, an impure rock salt
containing *6.3 wt% SiO2 and *30 wt% Na2O. Its Na2O
content implies *56 % halite by weight. Positive trends of
Al2O3, TiO2, Na2O, Cr, La, Zr and H2O with SiO2 suggest
that these components are controlled primarily by the
detrital fraction in the rocks (Figs. 6a, b, d–g, 7a). The
negative trend of (CaO ? MgO) versus SiO2 is consistent
with control by anhydrite and carbonates (Fig. 6c). The
lack of systematic variation between TOC and SiO2 indi-
cates that the distribution of organic carbon is mostly
random (Fig. 7b). No correlations between CO2 or SO3 and
SiO2 suggest the relative abundance between anhydrite and
carbonates is variable in the chemical sedimentary fraction
(Fig. 7c, d). The sedimentary rocks display modest frac-
tionation between light and heavy REE (e.g., La/Yb =
5.7–27.3). In mantle-normalized trace element diagrams,
they show consistent patterns marked by negative Ba, Nb,
Ta and Ti anomalies (Fig. 8a).
Samples from drill-core MD48 consist of massive
anhydrite and calcareous hornfels. The massive anhydrite
is compositionally similar to those from the nearby drill-
core MD56, except for higher absolute abundance of most
trace elements (Fig. 8b). Calcareous hornfels have SiO2
(22.9–46.8 wt%), Al2O3 (5.0–13.9 wt%), Fe2O3 (3.0–6.1
wt%), CaO (9.4–28.8 wt%), MgO (6.6–22.8 wt%), CO2
(0.2–20.5 wt%), H2O (1.7–10.0 wt%) and SO3 (0.1–20.8
wt%) as major element oxides. The calcareous hornfels
tend to follow the major element trends shown by the
sedimentary rocks (Figs. 5, 6), except H2O extending to
much higher values (Fig. 7a). Like the sedimentary rocks,
massive anhydrite and calcareous hornfels from drill-core
MD48 also show negative Ba, Nb, Ta and Ti anomalies
(Fig. 8b). In addition, these rocks exhibit marked negative
Eu anomaly. Samples taken close to the intrusive contact
have low TOC and CO2 compared to those occurring at
distances greater than *60 m from the contact (Fig. 9a).
Drill-core TG21 consists entirely of siliceous hornfels
that have SiO2 (53.3–75.2 wt%), Al2O3 (13.8–24.9 wt%),
Fe2O3 (0.8–10.6 wt%), CaO (0.2–5.3 wt%), MgO (0.1–4.0
wt%), Na2O (0.4–10.8 wt%) and K2O (below detection
limit to 4.8 wt%) as major element oxides. The siliceous
hornfels do not follow the major element trends shown
by the sedimentary rocks (Figs. 5, 6). They display
slight fractionation between light and heavy REE (e.g.,
Contrib Mineral Petrol
123
Table 3 Representative electron microprobe analyses of minerals from the Norilsk contact aureoles, Siberia
Sample Lab ID SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO
Mikchangda aureole
Clinopyroxene
MD48-1 ES-10 50.10 1.01 3.30 0.30 10.57 0.14 14.16
MD48-2 Cs-2 46.44 0.00 10.25 0.00 5.89 0.00 12.26
MD48-4 C48 44.84 1.18 13.14 0.03 2.12 0.00 13.32
MD48-6 E97 48.84 0.41 6.36 0.13 4.30 0.16 14.74
MD48-11 Bs-7 46.50 1.18 7.91 0.11 5.64 0.26 13.03
Phlogopite
MD48-1 C-20 38.10 0.21 20.84 bdl3 4.66 0.00 21.94
MD48-2 A16 36.52 0.08 21.02 bdl 6.56 0.00 23.26
MD48-4 A11 40.08 0.15 17.68 bdl 2.25 0.00 25.44
MD48-6 E91 39.32 0.17 16.26 bdl 2.56 0.03 25.57
MD48-11 C28 38.59 0.00 18.52 bdl 5.16 0.00 23.38
Chlorite
MD48-2 B46 28.83 0.17 20.25 bdl 16.89 0.00 21.93
MD48-4 C58 32.02 bdl 19.60 bdl 1.88 0.13 32.71
MD48-11 C35 40.96 0.02 10.41 bdl 4.78 0.08 29.60
MD48-17 F68 31.66 0.09 19.55 bdl 10.09 0.14 25.57
Amphibole
MD48-1 D-37 37.80 0.59 21.76 bdl 6.41 0.00 14.68
MD48-11 C24 40.66 0.69 15.74 bdl 8.28 0.00 16.12
MD48-11 D42 41.61 0.11 15.78 bdl 7.58 0.25 16.49
MD48-17 A5 54.18 0.09 6.14 bdl 5.21 0.02 18.48
Feldspar
MD48-14 A2-31 65.40 bdl 17.60 bdl 0.13 bdl bdl
MD48-17 F73 65.06 bdl 18.17 bdl 0.30 bdl bdl
MD48-17 D42 68.88 bdl 19.88 bdl 0.02 bdl bdl
MD48-23 C6 65.41 bdl 18.21 bdl 0.01 bdl bdl
Titanite
MD48-1 A-5 31.49 32.02 3.95 bdl 2.36 bdl 0.16
MD48-2 A11 31.33 33.41 2.68 bdl 1.12 0.01 0.14
MD48-14 A2-4 31.22 36.44 1.64 bdl 1.33 0.21 bdl
Apatite
MD48-11 C40 0.86 bdl bdl bdl 0.43 0.05 0.16
MD48-14 A2-22 0.41 bdl bdl bdl 0.32 0.00 0.08
MD48-17 C27 0.24 bdl bdl bdl 0.49 0.21 0.35
Talnakh aureole
Muscovite
TG21-3 A2-13 44.42 0.49 29.51 bdl 7.31 0.04 3.79
TG21-4 B-19 49.34 0.34 32.63 bdl 3.59 bdl 1.07
TG21-10 RR-24 46.84 bdl 32.57 bdl 4.41 0.04 1.78
TG21-10 Map1-59 46.03 0.06 32.51 bdl 4.15 0.15 1.91
Phlogopite
TG21-4 A-83 43.41 0.57 14.25 bdl 7.96 bdl 16.86
TG21-4 A-85 44.35 0.44 16.59 bdl 7.15 0.00 14.22
Chlorite
TG21-3 A2-15 28.60 0.18 24.25 bdl 25.72 0.13 8.32
TG21-3 Mat-54 24.87 0.19 23.58 bdl 29.23 0.38 10.24
TG21-4 A-90 25.56 0.72 18.00 bdl 41.55 0.03 3.04
Contrib Mineral Petrol
123
Table 3 continued
Sample Lab ID SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO
TG21-4 B-14 39.67 0.28 19.18 bdl 22.23 bdl 5.56
TG21-10 R-17 24.88 bdl 22.89 bdl 35.30 0.04 5.35
Feldspar
TG21-3 Mat-60 68.28 bdl 20.00 bdl 0.22 bdl bdl
TG21-3 Mat-63 67.95 bdl 20.39 bdl 0.00 bdl bdl
Apatite
TG21-4 A-5 0.20 bdl bdl bdl 0.78 0.06 0.02
TG21-4 A-87 0.35 bdl bdl bdl 0.72 bdl 0.03
Sample Lab ID CaO Na2O K2O P2O5 F Cl H2O1 Total Mg#2
Mikchangda aureole
Clinopyroxene
MD48-1 ES-10 20.47 0.31 0.02 – – – – 100.38 70.5
MD48-2 Cs-2 25.87 0.05 0.01 – – – – 100.77 78.8
MD48-4 C48 24.98 0.76 0.12 – – – – 100.49 91.8
MD48-6 E97 25.37 0.04 0.13 – – – – 100.48 86.0
MD48-11 Bs-7 24.91 0.15 0.06 – – – – 99.73 80.5
Phlogopite
MD48-1 C-20 0.00 0.25 9.60 – 0.23 0.03 4.15 100.01 89.3
MD48-2 A16 0.20 0.44 7.49 – 0.00 0.02 4.24 99.83 86.3
MD48-4 A11 0.02 0.82 9.24 – 1.20 0.02 3.79 100.69 95.3
MD48-6 E91 0.00 0.36 10.38 – 1.13 0.05 3.72 99.54 94.7
MD48-11 C28 0.08 0.97 9.56 – 0.08 0.07 4.20 100.60 89.0
Chlorite
MD48-2 B46 0.16 0.00 0.13 – 0.05 0.00 12.03 100.43 69.8
MD48-4 C58 0.82 0.08 bdl – 0.05 0.37 12.76 100.41 96.9
MD48-11 C35 1.32 0.01 0.12 – 0.12 0.23 12.76 100.41 91.7
MD48-17 F68 0.24 0.04 0.07 – 0.06 0.01 12.39 99.91 81.9
Amphibole
MD48-1 D-37 13.68 2.38 1.37 – 0.42 0.05 1.88 101.02 80.3
MD48-11 C24 12.67 2.77 1.05 – 0.26 0.18 1.90 100.31 77.6
MD48-11 D42 13.04 2.88 0.64 – 0.00 0.14 2.05 100.56 79.5
MD48-17 A5 11.90 0.47 1.44 – 0.11 0.04 2.09 100.18 86.3
Feldspar
MD48-14 A2-31 0.76 0.09 16.75 – – – – 100.73 –
MD48-17 F73 0.16 0.13 16.33 – – – – 100.15 –
MD48-17 D42 0.32 10.92 0.10 – – – – 100.12 –
MD48-23 C6 0.06 0.17 16.32 – – – – 100.18 –
Titanite
MD48-1 A-5 28.34 0.06 bdl – 0.23 0.02 1.02 99.66 –
MD48-2 A11 28.27 0.06 0.03 – 0.00 0.04 1.11 98.19 –
MD48-14 A2-4 27.80 bdl 0.24 – bdl bdl 1.13 100.00 –
Apatite
MD48-11 C40 53.50 0.10 0.00 39.60 0.89 3.66 0.42 99.66 –
MD48-14 A2-22 54.14 0.12 0.15 41.31 2.33 2.51 0.09 101.45 –
MD48-17 C27 54.72 0.00 0.07 42.08 3.15 0.15 0.32 101.78 –
Talnakh aureole
Muscovite
TG21-3 A2-13 0.00 0.26 10.22 – 0.22 0.28 4.21 100.75 48.0
Contrib Mineral Petrol
123
Table 3 continued
Sample Lab ID CaO Na2O K2O P2O5 F Cl H2O1 Total Mg#2
TG21-4 B-19 0.37 0.07 8.58 – bdl 0.02 4.55 100.56 34.7
TG21-10 RR-24 0.04 0.23 9.51 – 0.18 0.15 4.35 100.11 41.9
TG21-10 Map1-59 0.08 0.42 9.70 – bdl 0.23 4.38 99.60 45.1
Phlogopite
TG21-4 A-83 0.51 0.22 9.72 – 7.31 0.29 0.91 102.02 79.0
TG21-4 A-85 0.70 0.20 9.85 – 4.65 0.26 2.11 98.76 78.0
Chlorite
TG21-3 A2-15 0.14 0.14 1.39 – bdl 0.03 11.60 100.50 36.6
TG21-3 Mat-54 0.05 0.02 0.01 – 0.02 bdl 11.27 99.87 38.4
TG21-4 A-90 0.33 0.00 0.19 – 0.00 0.00 10.60 100.03 11.5
TG21-4 B-14 0.25 0.08 0.67 – 0.04 0.10 12.06 100.12 30.8
TG21-10 R-17 0.09 bdl 0.19 – bdl 0.05 10.94 99.73 21.3
Feldspar
TG21-3 Mat-60 0.54 10.99 0.07 – – – – 100.10 –
TG21-3 Mat-63 0.82 10.68 0.10 – – – – 99.94 –
Apatite
TG21-4 A-5 54.98 0.12 0.07 41.03 5.37 0.13 – 102.76 –
TG21-4 A-87 53.61 0.29 0.09 41.38 5.12 0.12 – 101.69 –
1 H2O calculated on the basis of ideal mineral formulae2 Mg# = molar 100 9 Mg/(Mg ? Fe2?)3 bdl = below detection limit
AnAb
Or
Cpx from sills
Plagioclasefrom sills
Fs
Wo
En
a
b
Sanidine
Anorthoclase
AlbiteOligoclase
Andesine Labradorite Bytownite Anorthite
Diopside
Augite
Pigeonite
Hedenbergite
HedenbergiteEnstatite
OHCl
Fc
Apatite fromlayered intrusions
Drill-core MD56 (sedimentary rocks)Drill-core MD48 (calcareous hornfelsand meta-evaporites)Drill-core TG21 (siliceous hornfels)
Fig. 4 Compositions of
a clinopyroxene, b feldspars and
c apatite in Paleozoic
sedimentary rocks and in meta-
sedimentary rocks from the
Norilsk contact aureoles,
Siberia. Gray fields in a and
b denote our unpublished data
from the sills, whereas in
c denotes compositions of
igneous apatite in major layered
intrusions (after Boudreau et al.
1995)
Contrib Mineral Petrol
123
La/Yb = 3.6–8.1). In mantle-normalized trace element
diagrams, most siliceous hornfels show negative Ba, Nb,
Pb, Sr anomalies (Fig. 8c). Also, a subset of samples is
much richer in large ion lithophile elements (LILE) than
the others. Concentrations of TOC, CO2 and SO3 are low at
intervals *200 m from the intrusive contact (Fig. 9b).
Sample TG21-1 collected at *230 m from the contact has
*1 wt% TOC.
Samples from mine exposure comprise massive anhy-
drite, calcareous hornfels, siliceous hornfels and meta-
sandstone. The former three rock types are geochemically
similar to their counterparts in drill-cores MD48 and TG21
(Figs. 5, 6, 7, 8d, e). Meta-sandstones have SiO2
(86.1–89.0 wt%), Al2O3 (6.8–7.6 wt%) and Na2O (3.2–3.6
wt%) as the only major element oxides. Their trace element
patterns are marked by negative Ba and Ti anomalies and
positive Pb, Zr and Hf anomalies (Fig. 8f).
Sr–Nd isotopes
Sr–Nd isotopic data for sedimentary rocks in the Norilsk
region and meta-sedimentary rocks from the Norilsk
aureoles are listed in Table 4. All samples are character-
ized by high initial Sr isotopic ratios ranging from 0.7079
to 0.7154 (Table 4). The lowest value of 0.7079 for mas-
sive anhydrite from drill-core MD56 is similar to that of
Devonian seawater (Veizer et al. 1999). The calcareous
hornfels have a relatively restricted range of (87Sr/86Sr)i
(0.7079–0.7092), whereas siliceous hornfels have a slightly
higher and wider range of (87Sr/86Sr)i (0.7083–0.7152). In
the Mikchangda aureole, (87Sr/86Sr)i tends to increase with
increasing distance away from the intrusive contact
(Fig. 9a). The meta-sandstone (sample NOR-14a) has
(87Sr/86Sr)i of 0.7088. The Nd isotopic compositions of the
samples are highly variable, with eNd(t) from -8.0 to ?4.3
for sedimentary rocks, -1.1 to ?9.6 for calcareous
hornfels and -4.8 to ?10.2 for siliceous hornfels
(Table 4). The meta-sandstone has eNd(t) of -6.4.
On the (87Sr/86Sr)i–eNd(t) diagram, the samples have
high initial Sr isotopic ratios compared to flood basalts and
the related intrusive rocks of the Siberian Traps (Fig. 10a).
The isotopic variations of the intrusive rocks can be
explained in terms of two end-members: shale (sample
MD56-36) and impure evaporites (see Arndt et al. 2003).
Some samples have exceptionally high eNd(t) (?8.8 to
?10.2), even higher than the highest value of ?7 reported
for the flood basalts (Sharma 1997). However, there is no
evidence that these samples formed from mafic and isoto-
pically depleted protoliths. We thus speculate that the high
eNd(t) values are due to disturbance of the Sm–Nd isotopic
system during contact metamorphism (see Polat et al.
2008). On a (87Sr/86Sr)i–Sr diagram, the data of the intru-
sive rocks fall roughly on trends toward contamination by
either shale or impure evaporites, but not toward that by
pure anhydrite (Fig. 10b).
Discussion
Protoliths and metamorphic conditions
Four types of meta-sedimentary rocks are recognized in
this study, that is, calcareous hornfels, siliceous hornfels,
meta-anhydrite and meta-sandstones. The fact that they
have different mineralogical, geochemical and Sr–Nd iso-
topic compositions, as illustrated above, is best understood
in terms of different protoliths. The relatively low SiO2,
Al2O3, Na2O and high CaO, MgO, CO2 and SO3 in cal-
careous hornfels are indicative of impure evaporite proto-
liths, such as the calcareous siltstone in drill-core MD56.
This interpretation is supported by the fact that these rocks
are intermediate between massive anhydrite (or dolostone)
Sills
Al O +2 3
SiO2
MgO +OK+OaNCaO 2 2
Drill-core MD56 (sedimentary rocks)Drill-core MD48 (calcareous hornfelsand meta-evaporites)
Samples from mine exposure(calcareous and siliceous hornfels,and meta-sandstone)
Drill-core TG21 (siliceous hornfels)
Fig. 5 A ternary diagram
SiO2–(CaO ? MgO)–
(Al2O3 ? Na2O ? K2O) of
bulk-rock compositions for
Paleozoic sedimentary rocks
and meta-sedimentary rocks
from the Norilsk contact
aureoles, Siberia. Gray fielddenotes our unpublished data
from the sills
Contrib Mineral Petrol
123
and shale for most major elements (Figs. 7, 8) and Sr
isotopic ratios (Fig. 10). In contrast, siliceous hornfels have
high SiO2, Al2O3, Na2O and low CaO, MgO, CO2 and SO3
(Figs. 7, 8), features consistent with pelitic or shaley pro-
toliths. The different protoliths suggested for calcareous
and siliceous hornfels are also consistent with their dif-
ferent mineral compositions. Meta-anhydrite has very
similar composition as and thus likely formed from mas-
sive anhydrite protoliths. The very high SiO2, Al2O3 and
Na2O in meta-sandstones are indicative of quartzo-feld-
spathic protoliths.
The lithostatic pressure during contact metamorphism in
the Norilsk aureoles can be deduced from depths at which
the intrusions emplaced. The trace element and isotopic
compositions of the ore-bearing sills can be matched with
those of distinctive units in the volcanic sequence (Arndt
et al. 2003), and the vertical distance between the intrusive
and volcanic units is *1.5 km. Assuming the overburden
has an average density similar to the continental crust
(2.7 g cm-3), the pressure at which the intrusions were
emplaced was likely to be *0.4 kbar or less.
The peak temperature of metamorphism can be esti-
mated by mineral assemblages of rocks in the aureoles. The
peak metamorphic assemblage consists of phlogopite and
clinopyroxene indicated by the samples in the high-tem-
perature zones in the Mikchangda intrusion (Fig. 2). In the
Talnakh intrusion, the peak assemblage might have been
obscured by retrograde metamorphism resulting in an
30
Al
O(w
t.%)
23
20
10
0
b
a
0.8
0.4
40
Mg
O+
Ca
O(w
t.%
)
1.2T
iO(w
t.%
)2
0
60
20
0
ed
Cr
(pp
m)
102
Na
O(w
t.%
)2
0
100
50
10
40
150
200
250
101
100
10-1
10-2
gf
SiO (wt.%)2 SiO (wt.%)2
Zr
(pp
m)
50
La
(pp
m)
400 60
600
0 20 6020 80
30
20
0
400
040 80
200
c
Drill-core MD56 (sedimentary rocks)Drill-core MD48 (calcareous hornfelsand meta-evaporites)
Samples from mine exposure(calcareous and siliceous hornfels)
Drill-core TG21 (siliceous hornfels)
Fig. 6 Binary plots of bulk-
rock concentrations of selected
major and trace elements versus
SiO2 for Paleozoic sedimentary
rocks and meta-sedimentary
rocks from the Norilsk contact
aureoles, Siberia. a Al2O3.
b TiO2. c MgO ? CaO.
d Na2O. e Cr. f La. g Zr. Data
for meta-sandstone are not
plotted
Contrib Mineral Petrol
123
assemblage of quartz, chlorite, muscovite and alkali feld-
spars (Turovtsev 2002; this study). Aarnes et al. (2010)
modeled the mineral assemblages of an average pelite with
increasing grade of metamorphism. Their results indicate
that phlogopite is stable at temperatures \750 �C and
muscovite at temperatures \500 �C. As pointed out by
these authors and Aarnes et al. (2011), the maximum
temperature that can be attained in contact aureoles is a
function of (1) the size of the intrusion, (2) the temperature
of magma, (3) the distance away from the intrusive contact,
(4) the geothermal gradient and (5) the lithology of host
rocks. In general, the temperature of wallrocks adjacent to
the intrusive contact is roughly half of the liquidus tem-
perature of the magma and decreases exponentially with
increasing distance from the contact. Assuming a liquidus
of *1,200 �C for the sills, their contact aureoles probably
attained maximum temperatures of \600 �C (Carlsaw and
Jaeger 1959). This is generally in line with the absence of
very high-grade metamorphic assemblages in the Norilsk
aureoles.
Mechanisms of magma-evaporite interaction
The evaporite country rocks at Norilsk might interact with
the intruding magmas in various ways: (1) wholesale or
partial melting, (2) elemental transfer via hydrous fluid
(Li et al. 2003, 2009b; Ripley et al. 2003) and (3) meta-
morphic devolatilization (Ganino and Arndt 2009). In this
section, these mechanisms are examined in light of our
new data.
Melting of evaporites theoretically produces sulfate-rich
melts that are readily incorporated into the magmatic sys-
tem, in a way similar to crustal contamination of mantle-
derived magmas. The melting point of anhydrite is
*1,450 �C (http://www.mindat.org/min-234.html), which
led Li et al. (2003) and Ripley et al. (2003) to suggest that
evaporite melting probably did not take place at Norilsk
due to the lack of potential agents that may lower its
melting point. Experiments indicate that partial melting of
anhydrite-dolomite mixtures occurs at *900 to 1,000 �C
(van der Sluis 2010) and probably at lower temperatures in
the presence of impurities such as silt horizons or frag-
ments. Our findings confirm the presence of carbonates and
siliceous impurities in Devonian evaporites at Norilsk.
Assuming the basaltic magma intruding the evaporites has
a liquidus of *1,200 �C, their assimilation through partial
melting may not be completed precluded. However, this
should occur locally along the contacts against the country
rocks, and its role in causing extensive magma-evaporite
interaction is uncertain.
ba
)%.t
w(C
OT
)%.t
w(O
H2
0 0
30
2
4
6
1
2
3
4
5
40
60dc
2SiO (wt.%) SiO (wt.%)2
)%.t
w(O
S3
40
)%.t
w(O
C2
40 060 0 20 600802
20
10
0 040 80
20
Fig. 7 Binary plots of bulk-rock concentrations of light elements versus SiO2 for Paleozoic sedimentary rocks and meta-sedimentary rocks from
the Norilsk contact aureoles, Siberia. a H2O. b TOC. c CO2. d SO3. Data for meta-sandstone are not plotted. Legend is the same as in Fig. 6
Contrib Mineral Petrol
123
Transfer of elements from evaporites to magma via
circulating hydrothermal fluid merits consideration in
shallow magmatic systems like Norilsk. In this study,
several observations from the aureoles are consistent
with the presence of hydrous fluid during contact meta-
morphism: (1) the abundance of hydrothermal veins of
carbonates and/or sulfates in drill-cores of aureole rocks in
this study, (2) the occurrence of wollastonite in calcareous
hornfels (Li et al. 2009b; this study) indicating equilibra-
tion with hydrous fluid (Greenwood 1967; Ferry et al.
2001), (3) the abundance of hydrous phases in the aureoles,
including chlorite, hydrogrossular, muscovite, pectolite,
phengite, phlogopite, thomsonite and xonotlite (Li et al.
2009b; this study). Dehydration of chlorite, muscovite and
clay minerals in sedimentary rocks during contact meta-
morphism likely result in a hydrous fluid, percolating and
reacting with evaporites in the aureoles. Experiments by
Newton and Manning (2005) demonstrated that the solu-
bility of anhydrite increases enormously with NaCl activity
in hydrothermal solutions at *600 to 800 �C. In view of
this, the presence of salt horizons in the Tunguska sedi-
mentary sequence is noteworthy (Matukhin 1978; Zharkov
1984; Svensen et al. 2009a). There are two observations
consistent with participation of the salt horizons during
metamorphism: (1) most siliceous hornfels in this study
contain high Na2O (0.42–10.8 wt%; with the majority
[3 wt%), a feature that, according to van de Kamp and
Leake (1996), is best explained by addition of Na from
salts or brines, and (2) high Cl in apatite from the aureole
(Fig. 4c) and in melt inclusions in some Siberian magmatic
rocks (Sobolev et al. 2009) points to formation of a Cl-rich
fluid and addition of Cl derived from the salt horizons,
respectively. Based on the above arguments, we suggest
that elemental transfer via a hydrous fluid, together with
the presence of dissolved salts, likely contributed to
extensive magma-evaporite interaction at Norilsk.
Devolatilization of calcareous sedimentary rocks during
metamorphism directly generates fluids of CO2 (i.e.,
decarbonation) and SO2 (i.e., desulfatation), which in the-
ory are able to enter the magmatic system. For example,
the release of CO2 by decarbonation reactions during
progressive metamorphism of siliceous dolomites is well
known (Bowen 1940). Degassing of SO2 from anhydrite in
an analogous manner was proposed by Gorman et al.
(1984). Figure 11 is a plot of (CO2 ? SO3) versus CaO of
samples in this study illustrating devolatilization. Pure
Calcareous siltstone
Rock salt
Shale
Dolostone
d Mine exposure(calcareous hornfels)
c TG21
103
10-1
102
100
eltn
am
evit imir
P/el
pm
aS
100
a MD56
101
10-1
CsRb Er
f Mine exposure(meta-sandstone)
e Mine exposure(siliceous hornfels)
b MD48eltn
am
evitimir
P/el
pm
aS
CsRb
Ba U Ta Ce Sr Zr Sm Ti Tb Y LuTh Nb La Pb Nd Hf Eu Gd Dy
Ba U Ta Ce Sr Zr Sm Ti Tb Y LuTh Nb La Pb Nd Hf Eu Gd Dy Er
101
102
102
100
101
10-1
eltn
am
evitimi r
P/el
pm
aS
Fig. 8 Primitive mantle-
normalized trace element
diagram for Paleozoic
sedimentary rocks and meta-
sedimentary rocks from the
Norilsk contact aureoles,
Siberia. a Samples in drill-core
MD56. b Samples in drill-core
MD48. c Samples in drill-
core TG21. d Calcareous
hornfels from mine exposure.
e Siliceous hornfels from mine
exposure. f Meta-sandstone
from mine exposure.
Normalizing values are after
McDonough and Sun (1995)
Contrib Mineral Petrol
123
Ta
ble
4R
b-S
ran
dS
m–
Nd
iso
top
icd
ata
for
un
met
amo
rph
ose
dse
dim
enta
ryro
cks
and
met
a-se
dim
enta
ryro
cks
fro
mth
eN
ori
lsk
con
tact
aure
ole
s,S
iber
ia
Sam
ple
Rb
(pp
m)
Sr
(pp
m)
87R
b/8
6S
r87S
r/86S
r2r
(87S
r/86S
r)i1
Sm
(pp
m)
Nd
(pp
m)
147S
m/1
44N
d143N
d/1
44N
d2r
(143N
d/1
44N
d) i
eNd
(t)
Dri
ll-c
ore
MD
56
MD
56
-9a
11
41
64
0.2
40
0.7
18
17
30
.000
01
70
.711
04
.12
18
.30
.136
0.5
12
75
70
.000
00
40
.512
54
.3
MD
56
-9b
16
.85
63
0.0
86
0.7
08
89
40
.000
01
00
.708
68
.50
28
.70
.179
0.5
12
68
40
.000
00
50
.512
41
.5
MD
56
-19
19
.03
89
0.1
41
0.7
09
35
60
.000
00
50
.708
91
.03
4.0
20
.155
0.5
12
50
30
.000
00
90
.512
2-
1.3
MD
56
-22
94
.14
54
0.6
00
0.7
11
17
40
.000
01
20
.709
02
.65
13
.00
.123
0.5
12
52
40
.000
00
60
.512
30
.1
MD
56
-23
56
.02
69
60
.00
70
.70
89
58
0.0
00
00
50
.708
71
.86
8.6
50
.130
0.5
12
48
90
.000
00
30
.512
3-
0.8
MD
56
-23
(du
p)
56
.02
,696
0.0
07
0.7
08
93
70
.000
00
30
.708
71
.86
8.6
50
.130
0.5
12
48
90
.000
00
80
.512
3-0
.8
MD
56
-26
20
.30
1,4
49
0.0
00
0.7
07
86
60
.000
00
60
.707
9–
––
––
––
MD
56
-31
0.1
01
82
90
.00
00
.70
78
72
0.0
00
00
70
.707
9–
––
––
––
MD
56
-34
3.4
01
08
0.0
11
0.7
08
70
70
.000
00
80
.708
40
.26
1.3
90
.113
0.5
12
16
30
.000
00
60
.512
0-
6.6
MD
56
-36
12
09
1.0
0.4
55
0.7
28
97
20
.000
00
70
.715
43
.27
22
.10
.089
0.5
12
05
10
.000
00
10
.511
9-
8.0
Dri
ll-c
ore
MD
48
MD
48
-14
0.6
47
80
.02
90
.70
87
34
0.0
00
00
70
.707
97
.01
27
.50
.154
0.5
12
53
00
.000
00
70
.512
3-
0.8
MD
48
-20
.90
39
60
.00
10
.70
81
14
0.0
00
00
50
.708
15
.79
26
.60
.132
0.5
12
47
50
.000
00
40
.512
3-
1.1
MD
48
-43
1.0
22
60
.04
70
.70
93
09
0.0
00
00
80
.707
94
.63
24
.00
.117
0.5
12
52
10
.000
00
20
.512
30
.3
MD
48
-12
34
.36
90
0.0
17
0.7
08
95
50
.000
00
60
.708
42
.38
9.5
30
.151
0.5
13
01
50
.000
00
50
.512
88
.8
MD
48
-13
6.4
02
49
80
.00
10
.70
85
85
0.0
00
00
80
.708
6–
––
––
––
MD
48
-17
72
.57
64
0.0
33
0.7
09
74
30
.000
00
70
.708
83
.01
12
.20
.149
0.5
12
71
60
.000
00
30
.512
53
.0
MD
48
-23
a7
5.9
24
00
.10
90
.71
23
53
0.0
00
01
00
.709
13
.40
16
.10
.128
0.5
13
01
90
.000
00
90
.512
89
.6
MD
48
-23
b0
.90
27
96
0.0
01
0.7
08
65
50
.000
00
50
.708
7–
––
––
––
MD
48
-24
48
.61
97
0.7
14
0.7
11
77
50
.000
00
60
.709
22
.33
9.4
60
.149
0.5
12
65
70
.000
00
30
.512
41
.9
Dri
ll-c
ore
TG
21
TG
21-1
0.3
06
1.0
0.0
02
0.7
09
78
60
.000
00
60
.709
76
.26
25
.80
.147
0.5
12
48
10
.000
00
20
.512
2-
1.5
TG
21-2
56
.52
46
0.6
65
0.7
11
94
70
.000
00
90
.709
62
.69
12
.50
.130
0.5
12
51
30
.000
00
20
.512
3-
0.3
TG
21-3
93
.91
30
0.2
49
0.7
16
20
30
.000
00
80
.708
77
.37
35
.00
.127
0.5
13
04
40
.000
00
60
.512
81
0.2
TG
21-4
94
.16
2.0
0.5
24
0.7
30
86
80
.000
00
40
.715
23
.73
17
.90
.126
0.5
12
57
40
.000
00
30
.512
41
.0
TG
21-7
56
.53
49
0.4
69
0.7
10
96
40
.000
01
00
.709
31
2.0
43
.20
.168
0.5
12
63
30
.000
00
30
.512
40
.8
TG
21-8
1.7
01
06
0.0
06
0.7
09
88
40
.000
00
80
.709
72
.50
11
.70
.129
0.5
12
48
40
.000
00
20
.512
3-
0.8
TG
21-1
01
27
89
.00
.49
30
.72
62
32
0.0
00
00
30
.711
55
.62
35
.20
.097
0.5
12
54
60
.000
00
20
.512
41
.4
Sam
ple
sfr
om
min
eex
po
sure
NO
R-3
88
.52
80
0.9
15
0.7
14
38
30
.000
00
90
.711
14
.69
22
.10
0.1
28
0.5
12
60
60
.000
00
10
.512
41
.6
NO
R-5
5.2
03
33
0.0
45
0.7
08
41
60
.000
01
00
.708
32
.50
9.9
90
.151
0.5
12
52
40
.000
00
40
.512
3-
0.8
NO
R-7
b1
.00
27
30
.01
10
.70
86
30
0.0
00
00
20
.708
63
.52
15
.10
0.1
41
0.5
12
51
70
.000
00
20
.512
3-
0.6
NO
R-1
4a
2.7
05
6.0
0.0
17
0.7
09
28
90
.000
00
90
.708
80
.67
2.5
80
.157
0.5
12
24
60
.000
00
80
.512
0-
6.4
NO
R-1
51
71
23
92
.07
20
.71
56
47
0.0
00
00
40
.708
35
.71
34
.60
0.1
00
0.5
12
31
20
.000
00
50
.512
1-
3.2
NO
R-1
74
1.4
50
20
.02
80
.70
94
84
0.0
00
00
90
.708
64
.69
22
.30
.127
0.5
12
27
90
.000
00
20
.512
1-
4.8
1(8
7S
r/86S
r)i
and
eNd
(t)
val
ues
wer
eca
lcula
ted
bas
edon
anag
eof
251
Ma,
k(87R
b)
=1
.42
91
0-
11
yea
r-1,
k(1
47S
m)
=6
.54
91
0-
12
yea
r-1,
and
pre
sen
td
aych
on
dri
tic
val
ues
of
143N
d/1
44N
d=
0.5
12
63
8,
147S
m/1
44N
d=
0.1
96
7,
87S
r/86S
r=
0.7
04
5an
d87R
b/8
6S
r=
0.0
82
7(F
aure
and
Men
sin
g2
00
5)
2S
amp
les
MD
56-2
6,
MD
56-3
1an
dM
D4
8-1
3w
ere
no
tan
aly
zed
for
Nd
iso
top
esd
ue
tolo
wN
dco
nte
nts
Contrib Mineral Petrol
123
evaporites composed of anhydrite, dolomite and calcite plot
in the shaded area and shale plot near the origin. Calcareous
siltstones (i.e., impure evaporites) and any metamorphic
rocks that do not undergo extensive devolatilization should
plot in arrays between the origin and the shaded area. Here,
two assumptions are relevant: (1) Ca in the protoliths is
present exclusively in anhydrite and carbonates and (2) Ca is
neither added nor removed to the aureole rocks during
metamorphism. Rocks that plot below these arrays indicate
significant devolatilization due to preferential loss of CO2
and/or SO3 relative to CaO. Figure 11 shows that a subset of
calcareous hornfels exhibits devolatilization in various
degrees. The majority of them have less than *2.5 wt%
CO2 but *4.5–21 wt% SO3. As a result, we argue that
devolatilization is mainly brought about by loss of CO2 and
sulfate minerals are largely unaffected by this process. The
decarbonation reactions likely caused the formation of
clinopyroxene and phlogopite in calcareous hornfels at the
expense of dolomite (Rice 1977; Tracy and Frost 1991):
5 CaMg CO3ð Þ2 dolomiteð Þ þ 8SiO2 þ H2O
¼ Ca2Mg5Si8O22 OHð Þ2 tremoliteð Þ þ 3 CaCO3 calciteð Þþ 7 CO2
Ca2Mg5Si8O22 OHð Þ2 tremoliteð Þþ KAlSi3O8 K-feldsparð Þ þ 2 CaMg CO3ð Þ2 dolomiteð Þ¼ 4 CaMgSi2O6 diopsideð Þþ KMg3AlSi3O10 OHð Þ2 phlogopiteð Þ þ 4 CO2
The latter reaction occurs at *460 to 500 �C for a wide
range of mole fractions of CO2 in the fluid (Tracy and Frost
1991), temperatures that can be reached according to our
temperature estimates based on mineral assemblage.
Gas release and the end-Permian environmental crisis
As mentioned above, the release of CO2 and SO2 from the
aureoles during contact metamorphism most likely
involves hydrothermal leaching of evaporites and decar-
bonation of impure evaporites, respectively. Here, we
estimate the generation potentials of these gases in a LIP
context.
We estimate CO2 production potential using decarbon-
ation reactions and the volume of the aureole rocks that
underwent partial degassing. Based on molar volume, the
aforementioned clinopyroxene- and phlogopite-forming
20
40
60
80
200
150
100
50
0
a Mikchangda
b Talnakh
(wt.%) (wt.%) (wt.%)
morf
ya
wa
ecn
atsiD
)m(tc
atn
ocevis
urtni
CO2 SO3
Cpx Phl Kfs Chl AnhCc+
0.5 1 1.5 0 1 4Qtz Chl Mus Ab Ap
20
TOC
20 40
0 3 1
0m
orfy
aw
aec
natsi
D)
m(tcat
noc
e visurt
niAnhydritelayers
Sill
Hornfels
Sediments
(?)
Sill
Hornfels
Sills (minor)
Metasomatichornfels
0 1 2 3 100 30 0 60 0.709 0.710
( Sr/ Sr)87 86i
0 0.5 1.5 0.710 0.7142
Fig. 9 Simplified column sections of the Mikchangda and Talnakh aureoles showing variations of mineralogy, TOC, CO2, SO3 and (87Sr/86Sr)i
with distance away from the intrusive contact. The color scheme of the sections is the same as in Fig. 2
Contrib Mineral Petrol
123
reactions produce 375–430 g CO2 per kilogram of dolo-
mite, or 188–215 g CO2 per kilogram of impure evaporite
with 50 % dolomite. If we assume the volume of the
metamorphosed rock in the lower Mikchangda aureole to
be 0.5 km3 [5 km (length) 9 500 m (breadth) 9 200 m
(aureole thickness)], a density of 2,500 kg m-3 and 80 %
of dolomite was transformed to clinopyroxene and phlog-
opite, the total amount of CO2 produced is about 0.4 Gt.
With reference to estimates of CO2 released from the
Deccan volcanism (Self et al. 2006), the amount of mag-
matic CO2 released from the Mikchangda intrusion [5 km
(length) 9 500 m (breadth) 9 550 m (sill thickness)]
would be *0.015 Gt, much less than the above estimate of
metamorphic CO2. Scaling the above estimates to a LIP
scale is somewhat speculative, but the present day out-
cropping area of the intrusions is at least 1.6 9 106 km2
and they most frequently intruded Paleozoic sedimentary
rocks (Kontorovich et al. 1997). These values imply that
the total amount of metamorphic CO2 generated by
decarbonation would be in the order of several tens of
thousand Gt or above and is not trivial compared to esti-
mates in earlier studies (Table 5).
The SO2 production potential cannot be estimated using
the above method because it was not released directly from
heating of evaporites as for CO2 (see earlier discussion). In
the Norilsk region, the source of sulfides in the Ni-Cu-
(PGE) deposits is generally considered to be the reduced
form of sulfates in evaporites (Li et al. 2003, 2009a, b;
Ripley et al. 2003; Arndt et al. 2003; Naldrett 2004),
providing an indirect means to estimate SO2 release. These
deposits contain *1,300 mT of ore (Naldrett 2004) sug-
gested to have formed from immiscible sulfide melts
equilibrated with basaltic magma belonging to the intrusive
portion of the Siberian Traps. Assuming magma/sulfide
mass ratios (R factors) of 100–400 (Li et al. 2009b), the
mass of magma was *130 to 520 Gt. The maximum
concentration of S dissolved in a basaltic magma at
1,300 �C, and 1 GPa is *0.18 wt% under reducing con-
ditions and *1.8 wt% under oxidizing conditions (Jugo
et al. 2005). If 70 % of the S was degassed, the total
amount of SO2 produced ranges from 0.03 to 1.3 Gt. This is
a minimum estimate because it only accounts for the S
dissolved in the magma and neglects any SO2 potentially
occurring as a separate fluid phase in the magmatic system.
In addition, total amount of metamorphic SO2 on a LIP
scale would be in the order of several hundreds or thou-
sands Gt (Table 5).
Recent studies emphasize the role of volatile release in
triggering the end-Permian environmental crisis (Berner
2002; Self et al. 2006; Beerling et al. 2007; Retallack and
Jahren 2008; Svensen et al. 2009a; Li et al. 2009a; Sobolev
et al. 2011; Black et al. 2012; Tang et al. 2012). However,
diverse opinions still exist about the source of volatiles
15
10
5
0
-10
-150.704 0.708 0.712
)(
dN
t
( Sr/ Sr)87 86i
0.716
a
b
101 102 104
)rS
/rS
(6
87
8i
Sr (ppm)103
0.716
0.712
0.708
0.704
-5
Disturbanceof Nd isotopes(?)
Crustalcontamination
Evaporitecontamination
Crustalcontamination
Evaporitecontamination
Fig. 10 Binary plots of Sr–Nd isotopic compositions for Paleozoic
sedimentary rocks and meta-sedimentary rocks from the Norilsk
contact aureoles, Siberia. a eNd(t) versus (87Sr/86Sr)i. b (87Sr/86Sr)i
versus Sr concentrations. The isotopic data were calculated at
t = 252 Ma. Gray fields and white diamonds denote flood basalts
and intrusive rocks, respectively, from the Siberian Traps after
Sharma et al. (1992), Lightfoot et al. (1993), Hawkesworth et al.
(1995) and Arndt et al. (2003). Legend is the same as in Fig. 6
60
060200
)%.t
w(O
S+
OC
32
CaO (wt.%)
40
40
20
Cc
Anh
Dol
80
60
40
20
80
60
40
20
80
60
40
20
Degassing
Ca-poorsulfate
Assimilation
Fig. 11 A binary plot of (CO2 ? SO3) versus CaO for Paleozoic
sedimentary rocks and meta-sedimentary rocks from the Norilsk
contact aureoles, Siberia (see text for discussion). Data for samples in
drill-core TG21 are not plotted. Legend is the same as in Fig. 6
Contrib Mineral Petrol
123
(e.g., magmatic vs. sediment-derived, mantle vs. crust).
Our results show that contact metamorphism of impure
evaporites could have generated abundant CO2 in addition
to that of organic matter and coal (Svensen et al. 2009a)
which, when emitted to the atmosphere, can be one of the
main contributor to the end-Permian global warming. We
also note that anhydrite can be mobilized by leaching
associated with magmatic-hydrothermal activity, releasing
SO2 to the magmatic system and eventually the atmo-
sphere. The SO2 has harmful effects on respiratory systems
of organisms and it might form acid rain. These gases,
together with other greenhouse gases like CH4 or toxic
gases of halocarbons released by magmatic or sediment
degassing (Table 5), likely contributed to the end-Permian
crisis.
Concluding remarks
Contact metamorphism in the Norilsk aureoles occurs at
low pressure and moderate peak metamorphic tempera-
tures. Calcareous hornfels from the Mikchangda aureole
formed by calcareous siltstone protoliths, whereas siliceous
hornfels from the Talnakh aureole formed by pelitic or
shaley protoliths. Decarbonation during metamorphism
resulted in loss of CO2 from the aureole rocks. Hydro-
thermal leaching of sulfates from evaporites produced SO2
that subsequently enters the magmatic system. The release
of these gases into the atmosphere provides a viable
explanation for the end-Permian environmental crisis and
mass extinctions.
Acknowledgments We thank Francis Coeur for assistance in sam-
ple preparation, Catherine Chauvel, Sarah Bureau and Christele Poggi
in major and trace element analyses, and Hao-Yang Lee and Chiu-
Hong Chu for Sr–Nd isotopic analyses. We acknowledge funding
granted to NTA from the French ANR (BEGDy project) and the
American NSF (continental geodynamics program) and to HS and
others from PGP and the Norwegian Research Council (YFF and SFF
grants). Logistic support and access to drill-cores provided by Norilsk
Nickel are gratefully acknowledged. We express special thanks to
Valery Fedorenko, former Norilsk Nickel chief geologist, for the
assistance in the field trip and sample delivery. Comments by two
anonymous reviewers and the editor Tim Grove improved the quality
of the manuscript.
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