Lithos 123 (2011) 145–157

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Crustally-derived granites in the Panzhihua region, SW China: Implications for felsicmagmatism in the Emeishan large igneous province

J. Gregory Shellnutt a,⁎, Bor-Ming Jahn a, Mei-Fu Zhou b

a Academia Sinica, Institute of Earth Science, 128 Academia Road Sec. 2, Nankang Taipei 11529, Taiwanb Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China

⁎ Corresponding author. Tel.: +886 2 2783 9910x618E-mail address: jgshelln@earth.sinica.edu.tw (J.G. Sh

0024-4937/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.lithos.2010.10.016

a b s t r a c t

a r t i c l e i n f o

Article history:Received 17 May 2010Accepted 27 October 2010Available online 4 November 2010

Keywords:Late PermianEmeishan large igneous provinceGraniteCrustal meltingAluminum saturation indexZr saturation thermometry

In the Panxi region of the Late Permian (~260 Ma) Emeishan large igneous province (ELIP) there is a bimodalassemblage of mafic and felsic plutonic rocks. Most Emeishan granitic rocks were derived by differentiation ofbasaltic magmas (i.e. mantle-derived) or by mixing between crustal melts and primary basaltic magmas (i.e.hybrid). The Yingpanliangzi granitic pluton within the city of Panzhihua intrudes Sinian (~600 Ma) marblesand is unlike the mantle-derived or hybrid granitic rocks. The SHRIMP zircon U–Pb ages of the Yingpanliangzipluton range from 259±8 Ma to 882±22 Ma. Younger ages are found on the zircon rims whereas older agesare found within the cores. Field relationships and petrography indicate that the Yingpanliangzi pluton mustbe b600 Ma, therefore the older zircons are interpreted to represent the protolith age whereas the youngeranalyses represent zircon re-crystallization during emplacement. The Yingpanliangzi granites are metalu-minous and have negative Ta–NbPM anomalies, low εNd(260 Ma) values (−3.9 to −4.4), and high ISr (0.71074to 0.71507) consistent with a crustal origin. The recognition of a crustally-derived pluton along with mantle-derived and mantle–crust hybrid plutons within the Panxi region of the ELIP is evidence for a completespectrum of sources. As a consequence, the types of Panxi granitoids can be distinguished according to theirASI, Eu/Eu*, εNd(T), εHf(T), TZr(°C) and Nb–TaPM values. The diverse granitic magmatism during the evolutionof the ELIP from ~260 Ma to ~252 Ma demonstrates the complexity of crustal growth associated with LIPs.

; fax: +886 2 2783 9871.ellnutt).

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© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Large igneous provinces (LIPs) are voluminous (N104 km3),rapidly emplaced, regions of new crust which appear regularlythroughout geologic time (Bryan and Ernst, 2008; Coffin and Eldholm,1994; Ernst et al., 2005). They are found at constructive plate margins,passive continental margins and within-plate settings, both conti-nental and oceanic (Courtillot et al., 1999). The secular variation ofLIPs appears to be on the order of 1 per ~10 million years during thepast 150 Ma. However based on the known record of continental LIPs,it is probably closer to 1 per ~20 million years (Ernst et al., 2005). It isuncertain if LIP genesis is cyclical but since many continental LIPs (e.g.Central Atlantic Magmatic Province, Siberian Traps, Parana–Etendeka,Ferrar–Karoo, Emeishan) are associated with break-up or amalgam-ation of supercontinents it stands to reason that more LIPs will formduring these events and that there should be a concentration ofcontinental LIPs every 300–500 Ma (e.g. the supercontinent cycle;Coffin and Eldholm, 1994; Nance et al., 1988). Furthermore, many LIPsshow internal secular variations which correspond tomagmatic peaks

occurring for a few million years at different intervals during theirformation (Bryan and Ernst, 2008).

The study of LIPs is important because they contain diverseigneous rock assemblages, are associated with important mineraldeposits, are major crust building episodes and, are correlated withmass extinctions (Courtillot et al., 1999; Ernst et al., 2005; Richardset al., 1989). The mantle plume model is one explanation for thepetrogenesis of some LIPs, however, it is not universally accepted(Campbell and Griffths, 1990; Foulger and Anderson, 2005; Foulgerand Natland, 2003; Griffiths and Campbell, 1990, 1991; King andAnderson, 1995; Morgan, 1971, 1972; Richards et al., 1989;White andMckenzie, 1989, 1995; Wolfe et al., 2009). The anomalously high-temperature conditions required to generate thick piles of basalticrocks have implications for crustal recycling, as the injection of maficmagmas can induce melting of the overriding lithosphere, andgenerate plutonic rocks of crustal affinity in addition to thosegenerated by differentiation of basaltic magmas (Annen and Sparks,2002; Annen et al., 2006; Bergantz, 1989; Hill et al., 1992; Huppertand Sparks, 1988; White and McKenzie, 1989). However, identifyingthe compositional differences between crust-derived and mantle-derived granitic rocks is somewhat problematic because assimilationof crustal material is common when mantle-derived magmas areemplaced within continental crust.

146 J.G. Shellnutt et al. / Lithos 123 (2010) 145–157

The Late Permian (260 Ma) Emeishan large igneous province (ELIP)of SW China is primarily located within the western part of the YangtzeBlock, very near the boundary with the Tibetan Plateau (Ali et al., 2005;Li and McCulloch, 1996; Qiu et al., 2000). There are many publishedstudies which have focused on the genesis of the flood basalts howeverthere are comparatively few studies which focus on the contempora-neous felsic plutonic rocks. Although the majority of Emeishanmagmatism occurred between ~260 Ma and ~257 Ma there wassporadic magmatism in the region until ~240 Ma (He et al., 2007;Shellnutt et al., 2008). Lying between the cities of Panzhihua andXichang (Panxi region), SichuanProvince, there is a bimodal assemblageof felsic plutonic rocks and mineralized gabbroic intrusions (ShellnuttandZhou, 2007). The composition, age and geological associationsof thePanxi granitic rocks indicate that they have variable origins, anobservation having a bearing on the formation of the ELIP and thecrust in general. Emeishan granitic rocks are identified as originatingeither by 1) differentiation of mantle-derived basaltic rocks, henceforthknown as mantle-derived granites (Shellnutt and Jahn, 2010; Shellnuttand Zhou, 2007, 2008; Shellnutt et al., 2009a,b; Zhong et al., 2007,2009); 2)melting of the crust (Shellnutt and Zhou, 2007; Xu et al., 2008;Zhong et al., 2007) or; 3) a mixture of crust- and mantle-derivedmagmas (i.e. hybrid) (Luo et al., 2007; Xu et al., 2008). Furthermore thegranitoids appear to correspond to two separate periods of magmatismat ~260 Ma and ~252 Ma, respectively (Shellnutt et al., 2008). Previousstudies have focused on themantle-derived granitoids because they areassociated with layered gabbroic rocks that host giant Fe–Ti-oxidedeposits, whereas, comparatively, very little is known about thecrustally-derived and hybrid granitic rocks.

Fig. 1. Simplified geological map showing the distribution of ELIP-relate

The Yingpanliangzi granitic pluton has intruded Neoproterozoicgranitic gneisses and marble. The marble was deposited during theLate Neoproterozoic and indicates that the Yingpanliangzi plutonmust be younger than ~600 Ma. Magmatism in the western YangtzeBlock is primarily concentrated during the Neoproterozoic (~850 to~750 Ma) and the Late Permian (~260 Ma) (Ali et al., 2005; Zhao andZhou, 2007; Zhou et al., 2002a,b). The geological relationshipstherefore suggest that the Yingpanliangzi pluton may be related tothe ELIP, however, it is compositionally dissimilar to other ELIPgranitic rocks (Shellnutt and Zhou, 2007; Xu et al., 2008; Zhong et al.,2007). We present new zircon U–Pb ages, whole-rock major and traceelement abundances and Sr–Nd isotopic compositions of theYingpanliangzi pluton in order to determine its likely origin andassess its association with the other ELIP-related granitoids.

2. Geological overview

Southwestern China comprises the western margin of the YangtzeBlock to the east and the easternmost part of the Tibetan Plateau to thewest (Fig. 1). The Yangtze Block consists of Mesoproterozoic graniticgneisses and metasedimentary rocks that have been intruded byNeoproterozoic granites (Li et al., 1999; Zhao et al., 2008; Zhou et al.,2002b). The Neoproterozoic granites, gneisses and gabbros are foundalong the western and northernmargin of the Yangtze Block, and rangein age from ca. 850 Ma to ca. 750 Ma and have continental-arcgeochemical characteristics (Zhao and Zhou, 2007; Zhou et al.,2002b). The Neoproterozoic rocks are overlain by a nearly continuous

d granitic intrusions within the Panxi (Panzhihua-Xichang) region.

147J.G. Shellnutt et al. / Lithos 123 (2011) 145–157

sequence of marine and terrestrial strata from the Late Neoproterozoic(~600 Ma) to the Early Mesozoic (He et al., 2006; Yan et al., 2003).

The Late Permian (~260 Ma) ELIP is a ~0.3×106 km2, fragmented,wedge shaped, region of flood basalts and related intrusive rockslocated within the Yangtze Block (Chung et al., 1998; He et al., 2010).The volcanic rocks include picrites, basaltic andesites, trachytes andbasalts which are subdivided into high- and low-Ti groups (Shellnuttand Jahn, 2010; Xu et al., 2001; Zhang et al., 2006). The basalticsequences range in thickness from 1.0 to 5.0 km in the western halfand 0.2 to 2.6 km in the eastern half and were subsequently affectedby younger regional scale deformation associated with the Indo-Eurasian collision (Chung et al., 1997; Lo et al., 2002; Zhou et al.,2002a). The Red-River and Longmenshan–Jinhe fault zones, activeduring the Indo-Eurasian collision, mark the western boundary of theELIP and are partially responsible for exhuming the plutonic rocks.There are also many mafic–ultramafic intrusions that host Fe–Ti–V orNi–Cu–PGE deposits, making the ELIP an important target for mineralexploration. A mantle plume model has been used to explain thegeological, geochemical and geophysical features of the ELIP (Chungand Jahn, 1995; Chung et al., 1998; He et al., 2003; Song et al., 2001;Xu et al., 2004).

The felsic plutonic rocks of the ELIP are spatially associated withlayered gabbroic Fe–Ti–V oxide bearing intrusions and Neoproterozoiccontinental arc-related granites and gneisses (Fig. 1). The plutonic rockscan be divided in to three types (i.e. peralkaline, metaluminous,peraluminous) according to their aluminum saturation index(ASI=Al/Ca−1.67P+Na+K; Frost et al., 2001). The peralkalinerocks are proposed to be the products of fractional crystallization ofEmeishan basaltic magmas, whereas the metaluminous rocks areconsidered to be derived by partial melting of basaltic rocks (Shellnuttand Zhou, 2007; Shellnutt et al., 2009a; Zhong et al., 2009). In contrastthere is only one example of a peraluminous granite (e.g. Ailanghepluton; Fig. 1) that is considered to be derived by melting of the crust(Shellnutt and Zhou, 2007; Zhong et al., 2007).

Fig. 2. Sample locations of the Yingpanliangzi gModified from Ma et al. (1999).

2.1. Local geology of Panzhihua

Panzhihua is underlain by Precambrian basement rocks that areintruded by Permian gabbros and granites which are collectivelyoverlain by a Triassic conglomerate unit (Fig. 2). To the south, east andwest of the city are Neoproterozoic and possibly older gabbroic,granitic and sedimentary rocks (Ma et al., 1999; Zhao and Zhou,2007). Overlying these rocks is marble of the Sinian (~600 Ma)Dengying Formation which was intruded by the Late PermianPanzhihua gabbro–granite complex (Shellnutt and Jahn, 2010). TheEmeishan flood basalts are found to the west and northwest of thecity; the basalts tend to be rare in the Panxi area compared to otherparts of the ELIP. All of the Permian rocks in Panzhihua are related,either directly or indirectly, to the ELIP.

The Yingpanliangzi pluton is located south of the Jinsha River andintrudes Proterozoic granitic gneisses. The pluton is exposed along aroad cut revealing fresh, albeit sporadic outcrops that containellipsoidal microgranular enclaves. East of the main outcropping is agranitic dyke that intrudes the Denying (~600 Ma) marble. Samplesfrom the dyke and pluton were collected from two outcrops located at26°33′36″ N, 101°42′53″ E and 26°34′10″N, 101°42′36″ E.

3. Petrography

Rocks from the Yingpanliangzi pluton are fresh, granular, medium-to coarse-grained and consist of quartz (~55%), perthitic alkali feldspar(~20%), plagioclase (~15%) and biotite (~10%). Interstitial to the coarsecrystals of quartz, alkali feldspar and plagioclase are minor (b5%) toaccessory (b1%) amounts of medium-grained, granular titanite,hornblende, muscovite and zircon. Within the matrix are plagioclasecrystals with 120° triple junction boundaries. Quartz, alkali feldspar,plagioclase and hornblende are sub-hedral to anhedral, whereasmuscovite, biotite and titanite are sub-hedral to euhedral. There is notextural evidence of deformation or hydrothermal alteration.

ranite within the city of Panzhihua.

148 J.G. Shellnutt et al. / Lithos 123 (2010) 145–157

4. Analytical methods

4.1. SHRIMP zircon U–Pb dating

Zircon grains were separated using conventional heavy liquid andmagnetic techniques, mounted in epoxy, polished and photographedin transmitted and reflected light to identify grains for analysis. U–Pbisotopic ratios of zircons were measured using remote access of theSHRIMP II, Chinese Academy of Geological Sciences, Beijing fromAcademia Sinica in Taipei. The measured isotopic ratios were reducedoff-line using standard techniques (c.f. Claoue-Long et al., 1995) andthe U–Pb ages were normalized to a value of 417 Ma determined byU–Pb analysis of zircon standard Temora 1 (Black et al., 2003).Common Pb was corrected using the methods of Compston et al.(1984). The 206Pb/238U and 207Pb/235U data were corrected foruncertainties associated with the measurements of the Temora 1standard. The 207Pb/206Pb ages given in Table 1 are independent of thestandard analyses.

Table 1SHRIMP zircon analytical data of sample GS07-070.

Spot U Th 206Pbc 206Pb* (1)

206Pb/238U(ppm) (ppm) (%) (ppm)

Age

GS04-070.1 89 95 0.77 9.72 763 ±GS04-070.2 571 604 0.01 46.9 588 ±GS04-070.3 492 495 0.00 54.6 783 ±GS04-070.4 446 367 0.00 39.6 634 ±GS04-070.5 490 217 0.25 37.7 552 ±GS04-070.6 366 324 0.13 41.2 794 ±GS04-070.7 228 154 0.50 14.8 467 ±GS04-070.8 152 93 1.57 7.98 376 ±GS04-070.9 178 128 3.93 6.55 260 ±GS04-070.10 542 392 0.21 59.8 778 ±GS04-070.11 487 740 0.18 49.1 714 ±GS04-070.12 208 347 0.52 23.3 784 ±GS04-070.13 376 313 0.49 25.5 487 ±GS04-070.14 811 296 0.31 36.9 332 ±GS04-070.15 617 617 1.85 40.9 471 ±GS04-070.16a 261 340 0.32 28.8 775 ±GS04-070.16b 252 97 0.38 14.5 416 ±GS04-070.17 121 57 1.62 13.6 780 ±GS04-070.18 79 64 1.01 9.46 830 ±GS04-070.19 122 46 2.39 6.90 403 ±GS04-070.20 160 214 0.95 16.9 742 ±GS04-070.21 294 366 0.46 25.6 620 ±GS04-070.22 523 448 0.17 44.8 612 ±GS04-070.23 151 109 1.56 16.5 762 ±GS04-070.24 211 108 0.33 15.7 535 ±GS04-070.25 121 200 0.71 13.3 775 ±GS04-070.26 200 262 0.17 19.3 686 ±GS04-070.27 73 128 1.83 8.60 811 ±GS04-070.28 669 549 0.33 50.0 536 ±GS04-070.29 48 29 2.76 5.90 845 ±GS04-070.30 109 107 28.53 15.3 712 ±GS04-070.31 231 153 0.48 14.3 446 ±GS04-070.32 185 286 0.67 23.4 883 ±GS04-070.33 198 162 0.80 21.8 772 ±GS04-070.34 74 52 1.39 6.94 657 ±GS04-070.38 311 243 0.30 23.0 530 ±GS04-070.39 319 308 0.47 29.9 664 ±GS04-070.40 1082 758 1.16 43.7 293 ±GS04-070.41 320 215 – 32.5 721 ±GS04-070.42 218 186 0.64 18.9 616 ±GS04-070.43 685 384 1.16 26.5 281 ±GS04-070.44 531 879 1.67 51.8 682 ±GS04-070.45 167 97 0.96 6.09 266 ±

Errors are 1-sigma; Pbc and Pb⁎ indicate the common and radiogenic portions, respectivelyError in Standard calibration was 0.65%( not included in above errors but required when co(1) Common Pb corrected using measured 204Pb.(2) Common Pb corrected by assuming 206Pb/238U–207Pb/235U age-concordance.(3) Common Pb corrected by assuming 206Pb/238U–208Pb/232Th age-concordance.

4.2. Whole-rock geochemical analyses

Major oxides were determined by wavelength-dispersive X-rayfluorescence spectrometry (WD-XRFS) on fused glass beads using aPhilips PW2400 spectrometer at the University of Hong Kong. Thesamples were processed by cutting with a diamond-bonded steel sawinto small pieces which were then crushed in a steel jaw crusher. Thecrusher was extensively cleaned after each sample with de-ionizedwater. The crushed samples were pulverized in an agate mill until thesuitable particle size was obtained. Trace elements, including REE,were determined by inductively-coupled plasma mass spectrometry(ICP-MS) of nebulized solutions using a VG Plasma-Quad Excell ICP-MS at the University of Hong Kong after a 2-day closed-beakerdigestion using a mixture of HF and HNO3 acids in high-pressurebombs (Qi et al., 2000). Pure elemental standard solutions were usedfor external calibration and AMH-1, GBP-1 and OU-6 were used asreference materials (c.f. Shellnutt and Zhou, 2007). The precisions ofthe XRF analyses are estimated to be ±2% (relative) for major oxides

(2) (3) (1)

206Pb/238U 206Pb/238U 208Pb/232Th

Age Age Age

20 765 ±21 765 ±24 704 ±15014 586 ±14 594 ±17 712 ±3918 784 ±19 780 ±22 748 ±3616 632 ±16 630 ±18 733 ±6215 549 ±15 550 ±16 705 ±7419 793 ±19 791 ±22 833 ±4712 463 ±12 456 ±14 700 ±709.9 375.4 ±9.8 382 ±11 408 ±2108.0 266.5 ±7.5 267.5 ±8.5 −1180 ±120018 779 ±19 783 ±20 719 ±3617 716 ±17 709 ±22 637 ±3719 786 ±20 780 ±26 721 ±6212 485 ±12 482 ±14 612 ±687.9 331.2 ±8.0 329 ±8.5 392 ±4311 471 ±11 479 ±14 491 ±15018 775 ±19 772 ±23 789 ±4610 415 ±10 417 ±11 476 ±7820 790 ±20 788 ±21 372 ±21022 829 ±22 832 ±25 844 ±11011 406 ±11 407 ±12 173 ±43018 743 ±19 730 ±23 716 ±9615 619 ±15 602 ±19 676 ±5414 610 ±15 606 ±17 705 ±3120 770 ±20 774 ±22 462 ±19013 532 ±14 529 ±15 714 ±7720 778 ±20 762 ±27 657 ±10017 685 ±17 699 ±21 726 ±5922 817 ±22 816 ±30 607 ±26013 535 ±13 535 ±15 608 ±5525 857 ±26 858 ±28 409 ±24029 705 ±19 705 ±44 963 ±84011 442 ±11 442 ±12 688 ±9422 888 ±23 879 ±29 720 ±10019 777 ±19 777 ±21 585 ±12018 659 ±18 658 ±21 559 ±14013 528 ±13 526 ±15 616 ±5616 664 ±16 672 ±19 669 ±747.1 292.6 ±7.1 290.5 ±8.1 343 ±13017 717 ±17 717 ±19 852 ±3915 616 ±16 619 ±18 633 ±1107 281.1 ±6.9 281.3 ±7.6 249 ±15019 690 ±19 701 ±26 322 ±1607.3 265.6 ±7.2 263.7 ±8.0 282 ±250

.mparing data from different mounts).

Table 2Whole rock chemical analyses of the Yingpanliangzi granite.

Sample GS03-063 GS03-064 GS03-065 GS03-066 GS03-068 GS04-070 GS04-076 AMH-1 GBP-1 OU-6

SiO2 (%) 70.99 69.33 71.66 70.88 69.89 71.34 73.82TiO2 0.26 0.30 0.27 0.28 0.29 0.23 0.24Al2O3 14.59 15.02 14.47 14.88 14.81 14.89 14.33Fe2O3t 2.15 2.56 2.17 2.14 2.41 1.83 1.78MnO 0.06 0.07 0.06 0.07 0.06 0.05 0.05MgO 0.62 0.83 0.63 0.72 0.77 0.91 0.66CaO 1.88 2.31 1.98 2.16 2.27 2.43 1.86Na2O 4.29 4.36 4.28 4.42 4.39 5.10 3.99K2O 3.99 3.65 3.47 3.47 3.05 2.64 4.06P2O5 0.06 0.07 0.06 0.07 0.08 0.08 0.06LOI 0.70 0.51 0.71 0.64 1.11 1.27 0.47Total 99.59 99.03 99.76 99.73 99.13 100.76 101.33

ASI 0.99 0.99 1.01 1.00 1.02 0.96 1.00Na+K/Al 0.78 0.74 0.75 0.74 0.71 0.76 0.76Sc (ppm) 13 15 13 12 10 16 14 14 17 23V 21 29 23 29 29 24 21 104 106 133Cr 5 7 5 3 5 5 3 42 182 81Co 4 5 4 4 4 3 3 19 19 29Ni 1 2 1 4 5 5 4 35 58 44Cu 4 3 8 4 3 6 3 35 33 41Zn 44 51 50 64 49 30 32 68 79 122Ga 16.6 17.6 17.0 17.4 17.7 14.6 13.8 20 21 26Rb 106 93 88 83 70 46 92 18 56 119Sr 231 287 230 303 285 342 252 540 362 135Y 20 24 25 23 19 18 18 15 17 27Zr 157 179 182 176 161 103 137 151 213 180Nb 8 9 10 7 7 5 7 8 10 14Cs 0.5 0.5 0.4 0.4 0.3 0.2 0.6 0.30 0.34 8.2Ba 1000 1163 757 1199 844 1141 1418 316 903 497La 30.6 37.8 41.7 40.0 33.2 27.8 33.5 15.9 49.8 34.2Ce 60.4 72.1 79.5 72.2 62.7 54.7 63.6 33.1 96.2 77.3Pr 6.8 8.2 8.4 7.9 6.7 5.9 6.9 4.3 11.1 8.3Nd 23.5 28.4 28.3 27.7 23.8 21.4 23.3 17.0 40.2 31.3Sm 4.2 5.2 5.1 4.9 4.2 4.0 3.9 3.6 6.3 6.2Eu 0.86 1.08 0.95 1.26 1.17 1.02 0.79 1.2 1.8 1.4Gd 3.89 4.78 4.69 4.90 4.29 4.13 4.45 3.3 5.1 5.5Tb 0.58 0.68 0.68 0.71 0.58 0.62 0.60 0.5 0.6 0.8Dy 3.36 4.20 4.05 3.81 3.10 3.49 3.27 2.8 3.0 5.1Ho 0.74 0.89 0.90 0.81 0.67 0.75 0.67 0.6 0.6 1.0Er 2.35 2.85 2.85 2.54 2.03 2.32 2.38 1.5 2.0 3.1Tm 0.37 0.45 0.44 0.39 0.31 0.33 0.35 0.2 0.3 0.5Yb 2.61 3.09 3.16 2.68 2.12 2.24 2.38 1.4 2.0 3.1Lu 0.39 0.47 0.48 0.39 0.33 0.33 0.37 0.2 0.3 .05Hf 4.6 5.4 5.4 4.9 4.5 3.4 4.5 3.7 5.2 4.8Ta 0.7 0.8 0.8 0.4 0.5 0.6 0.7 0.9 0.5 1.1Th 16.0 15.7 13.8 12.1 8.6 8.2 10.3 2.6 10.8 11.7U 2.5 2.6 2.0 1.7 1.1 1.0 2.2 0.9 0.8 2.0Eu/Eu* 0.64 0.65 0.59 0.78 0.84 0.76 0.58TZr(°C) 770 774 783 777 769 726 768

LOI=loss on ignition; ASI=Al/Ca−1.67P+Na+K; Eu/Eu*=[2*EuN/(SmN+GdN)]. TZr(°C) results from zirconium saturation thermometry (Hanchar and Watson, 2003). Measurevalues for standards (AMH-1, GBP-1 and OU-6).

149J.G. Shellnutt et al. / Lithos 123 (2011) 145–157

present in concentrations greater than 0.5 wt.% and±5% (relative) forminor oxides present in concentrations greater than 0.1% (Table 2).The precision of the ICP-MS analyses are estimated to be better than±5% (relative) for most elements.

Strontium and Nd isotopic analyses were performed on a VG-354thermal ionization magnetic sector mass spectrometer at the Instituteof Geology and Geophysics, Chinese Academy of Sciences, Beijing. Thechemical separation and isotopic measurement procedures aredescribed in Zhang et al. (2001). Mass fractionation corrections forSr and Nd isotopic ratios were based on values of 86Sr/88Sr=0.1194and 146Nd/144Nd=0.7219. Uncertainties in Rb/Sr and Sm/Nd ratiosare less than ±2% and ±0.5% (relative), respectively.

5. Results

5.1. Zircon U–Pb SHRIMP data

The zircon crystals are typically euhedral, 70 to 200 μm in lengthand have oscillary igneous zonation and re-crystallized rims (Fig. 3).

In some cases the re-crystallization rims cut the zonation of the olderportion of the zircon and appearmore diffuse (Griffin et al., 2006). TheTh/U ratios range from 0.26 to 1.75, have an average value of 0.89with1σ standard deviation of 0.39. The 45 individual zircon analyses donot yield a coherent mean 206U/238Pb age instead they produce arange of generally concordant ages between 260±8 Ma and 882±22 Ma (Fig. 4) (Table 1). The zircon rims yield the youngest, whereasthe cores tend to have the oldest age. The younger analyses havelower Th/U (b0.7) than the older zircons (~1.0 to ~1.7). Inmany cases,however, the beam spot size was larger than an individual zircongrowth ring and therefore some analyses undoubtedly covered two ormore crystal growth zones.

5.2. Major and trace elements and radiogenic isotope geochemistry

Granitoid rocks of the Yingpanliangzi pluton belong to themagnesian alkali-calcic group of granitic rocks (Frost et al., 2001).They are metaluminous to peraluminous in character and have lowFe* (FeOt/(FeOt+MgO)) values (Fe*=0.65 to 0.76) andmoreover they

Fig. 4. Results of zircon SHRIMP dating of sample GS04-070. (a) Concordia plot showingerror ellipses and (b) frequency distribution of ages.

150 J.G. Shellnutt et al. / Lithos 123 (2010) 145–157

have lowMgO(0.62 to0.91 wt.%) and Fe2O3 between1.78 and2.56 wt.%(Fig. 5a, b, c). The rocks are slightly sodic as indicated by their low K2O/Na2O ratios (Fig. 5d). SiO2 contents range from 69.3 to 73.8 wt.% withlow TiO2 (≤0.30 wt.%), MnO (b0.08 wt.%) and P2O5 (b0.09 wt.%). Thereare weak negative covariate trends of TiO2, Al2O3, Fe2O3 and MnOagainst SiO2, but no obvious correlation of Na2O, K2O, CaO and MgOversus SiO2. Loss on ignition (LOI) is lowwith values ranging from0.51%to 1.27% indicating low volatile contents and minor alteration. Ga/Alratios and transitional normative compositions (i.e. either a smallamount of hyperstheneor corundum) suggest the granites are similar toI-type granitoids (Chappell and White, 1974; Whalen et al., 1987).

The granites from Yingpanliangzi have low concentrations of Ni,Co, Cr and Cu (b10 ppm) and moderate concentration of Sc (10–16 ppm) and V (21–29 ppm). Rb (46–106 ppm), Sr (230–342 ppm),Zr (103–182 ppm) and Ba (757–1418 ppm) contents are variablyhigh. The granites have light rare earth element (REE) enrichedprofiles with moderate La/SmN (4.5–5.5; N=normalized to chondritevalues of Sun andMcDonough, 1989), and negative Eu-anomalies (Eu/Eu*=0.58–0.84) and weakly inclined heavy REEs (Gd/LuN=1.2–1.6;Fig. 6a). The primitive-mantle normalized incompatible elementdiagram shows distinct depletions in Cs, Nb–Ta, Ti and Sr (Fig. 6b).

The initial Sr–Nd isotopic analyses have been calculated using theyoungest zircon U–Pb SHRIMP age of 260 Ma (Table 3). The ISr(ISr=87Sr/86Sr initial ratio) values are high and variable, and rangefrom 0.71074 to 0.71507. In contrast, the initial 143Nd/144Nd ratioshave a narrow range from 0.51208 to 0.51210, and εNd(260) valuesbetween −3.9 and −4.4 (Fig. 7).

6. Discussion

6.1. Emplacement ages of the Yingpanliangzi pluton

SHRIMP zircon U–Pb ages for the pluton cover a range of nearly600 million years from the Neoproterozoic to the Late Permian(Fig. 4). The two end-member zircon ages of ~780 Ma and ~260 Macorrespond to two major crust building episodes in the Yangtze Block(Zhou et al., 2002a,b). The rocks from the Yingpanliangzi pluton donot have any evidence of metamorphism or migmatization and thepresence of ellipsoid enclaves suggests that the rocks are notmetamorphosed and represent an intrusive body. As sample GS04-070 was collected from a dyke that cross-cuts the Denying marble(~600 Ma) it precludes the possibility that the Yingpanliangzi pluton

Fig. 3. Cathodoluminescence photo of zircons from Yingpanliangzi granite sampleGS04-070. The location of the spot analysis (white circle) is located on the sketch (notto scale) to the right. The sketches show different visible structural domains in thezircons and are not necessarily correlative between the individual zircons. The blackandwhite domains are the oldest domains (e.g. core), orange are intermediate domainsand the green represents the youngest domain.

could be older than ~600 Ma, therefore, we interpret the emplace-ment age to be ca. 260 Ma and, that the older ages from the zirconcores represent the protolith ages (e.g. Yangtze Block).

6.2. Origin of the Yingpanliangzi pluton

The interpreted 260±8 Ma emplacement age of the Yingpanliangzipluton suggests that it is temporally related to Emeishan magmatism.Granitic rocks derived by melting of the crust commonly have negativeprimitive-mantle normalized Nb–Ta anomalies, εNd(T) and ISr valuesand enrichment of Th and U for example (Barbarin, 1999; Green, 1995;Hamilton et al., 1980). The rocks of the Yingpanliangzi pluton havenegative primitive-mantle normalized Ta–Nb anomalies and εNd(260)values (−3.9 to −4.4), and ISr values (0.71074 to 0.71507), similar tocrustally-derived granites and distinct from granitic rocks derivedby differentiation of Emeishan basaltic magmas (Figs. 5f, 6 and 7;Batchelor and Bowden, 1985; Chen and Jahn, 1998; Shellnutt and Zhou,2007). In comparison, the Yingpanliangzi granites are similar to theNeoproterozoic Kangding granitoids and the Late Permian Ailanghepluton (Figs. 5 and 6).

Selected large ion lithophile element-high field strength elementratios (e.g. Rb/Nb, Th/Ta, La/Ta, Rb/Zr) can be used as indicators forpotential crustal source reservoirs. It is thought that these ratios canremain unchanged, or are enriched, in melts produced from anatexis.

Fig. 5. Major and trace element plots of the Yingpanliangzi granites. (a) and (b) Classification of the granites according to scheme of Frost et al. (2001). (c) Alkali index (Na+K/Al)versus aluminum saturation index (ASI=Al/Ca−1.67P+Na+K; Frost et al., 2001). (d) K2O/Na2O versus SiO2. (e) Ba/Rb versus Al2O3 wt.%. (f) Tectonomagmatic discrimination ofgranitic rocks by Batchelor and Bowden (1985) (R1=4Si−11(Na+K)−2(Fe+Ti) and R2=6Ca+2 Mg+Al). Granitoid data from Shellnutt and Zhou (2007), Zhong et al. (2007)and Zhou et al. (2002b). UC = upper crust, LC = lower crust (Rudnick and Gao, 2003).

151J.G. Shellnutt et al. / Lithos 123 (2011) 145–157

The trace element ratios of the Yingpanliangzi granite are similar tothe peraluminous granitic rocks from the Yangtze Block (Kangdinggranitoids) and the average crustal values of Rudnick and Gao (2003)(Fig. 8). The LILE/HFSE ratios (e.g. Rb/Nb, Th/Ta) of Yingpanliangzigranites overlap with those of the Neoproterozoic granites, thePermian Ailanghe pluton and average crustal values, suggestingderivation frommelting of crustal sources rather than fractionation ofEmeishan mafic magmas.

The nearly flat HREE patterns shown in Fig. 6a indicate that thesource did not retain a HREE sequestering garnet-rich residue. ManyHREE and Y have high partition coefficients for garnet and it is clearfrom the Gd/LuN ratio (Gd/LuN=1.2 to 1.6) that the source ofYingpanliangzi granites did not contain garnet because there is little

or no depletion in these elements. Therefore, the granites fromYingpanliangzi likely originated from middle to upper crustal levels.The isotopic values of the Yingpanliangzi granite show long termdepletion of radiogenic 143Nd and enrichment of 87Sr producing lowεNd(T) values and high ISr values, which resemble the range of valuesfor the upper crust of the Yangtze Block (Chen and Jahn, 1998; Fig. 7).

Injection of basaltic magmas into the crust is capable of inducingcrustal melting (Annen and Sparks, 2002; Annen et al., 2006; Huppertand Sparks, 1988). Within the city of Panzhihua there are numerousoccurrences of ELIP-related plutonic mafic rocks including the ~3 kmthick, 19 km long, sill-like Panzhihua gabbroic intrusion (Shellnuttand Jahn, 2010; Zhou et al., 2005). The large volume of magmatism inthe region was likely sufficient to create the necessary thermal

Fig. 6. (a) Chondrite normalized rare-earth element and (b) Primitive-mantlenormalized incompatible element plots of the Yingpanliangzi granites, Ailanghegranites, Kangding granitoids and upper crust. Granitoid and crust data from Rudnickand Gao (2003), Shellnutt and Zhou (2007), Zhong et al. (2007) and Zhou et al. (2002b).Element order and normalizing values of Sun and McDonough (1989).

Fig. 7. εNd(260) versus ISr isotopic plot for the granitic rocks of the Yingpanliangzipluton. Mixing line was calculated assuming a pure crustal melt from the Yangtze uppercrust with either Neoproterozoic granitoids from the northwestern Yangtze Block orEmeishan basaltic rocks that have positive εNd(T) values. Yangtze upper and lower crustvalues and Neoproterozoic granitoids values are taken from Chen and Jahn (1998), Linget al. (2001) andMa et al. (2000). εNd(T) is calculated using an approximate equation ofεNd(T)=εNd(0)−Q*f*T; in which Q=25.1 Ga−1, f=f(Sm/Nd), T=age (in Ga).ISr=87Sr/86Sr initial ratio at 260 Ma. Range of Emeishan basaltic rocks are shown forreference (Ali et al., 2005).

152 J.G. Shellnutt et al. / Lithos 123 (2010) 145–157

conditions to generate crustal melts. The average zircon saturationtemperature estimate of the Yingpanliangzi pluton (767±14 °C 2σ;M=1.63±0.7 2σ) is within the temperature range that is expectedduring the injection of basaltic magmas into a granodioritic uppercrust (Annen and Sparks, 2002; Hanchar and Watson, 2003; Miller etal., 2003; Watson and Harrison, 1983). It is likely that this TZr(°C)estimate is a maximum due to the presence of inherited zircons.Partial melting of the upper Yangtze Block crust (εNd(T)=−8.0 to−22), however, cannot explain the concentration of some traceelements (e.g. Ba, Nb) or εNd(T) values of the Yingpanliangzi pluton(εNd(T)=−3.9 to −4.4) suggesting there must be a mixture of atleast two components. It is possible that, given their isotopic range,Emeishan basaltic magmas, in addition to heat, contributed material

Table 3Whole-rock Sr and Nd isotopic data for the Yingpanliangzi granite.

Sample Rock Rb Sr 87Rb/86Sr

87Sr/86Sr ±2σm87Sr/86Sr Model Age

(ppm) (ppm) (260 Ma) (Ma)I=0.704

GS03-063 Granite 106 231 1.33 0.719749 13 0.71483 830GS03-064 Granite 93 287 0.938 0.715414 14 0.71194 852GS03-065 Granite 88 230 1.11 0.718460 14 0.71436 913GS03-066 Granite 83 303 0.793 0.713646 14 0.71071 851GS03-070 Granite 46 342 0.389 0.714358 8 0.71292 1851GS03-076 Granite 92 252 1.06 0.715920 8 0.71201 790

Note:(1) Rb, Sr, Sm and Nd concentrations were obtained by ICP-MS and have precision less tha(2) The results of isotopic measurements for Sr and Nd reference materials are: NBS-987 (

(i.e. the enclaves) which then mixed with crustal melts producing theεNd(T) values of the Yingpanliangzi pluton.

6.3. Genesis of ELIP-granitoids from 260 Ma to 252 Ma

The Yingpanliangzi pluton was primarily produced by melting ofthe crust and that it represents the first evidence of crustal meltingdirectly associated with the eruption and emplacement of Emeishanmafic magmas at ~260 Ma. Previously only one pluton (i.e. Ailanghe)associated with the ELIP was identified as being derived from thecrust, however, known zircon ages reveal that it is between 251 Maand 255 Ma and therefore its precise relationship to ELIP magmatismremains uncertain (Fig. 9; He et al., 2007; Shellnutt and Zhou, 2007;Zhong et al., 2007; Xu et al., 2008). The recognition of a crustally-derived pluton along with mantle-derived and mantle–crust hybridplutons at that time is evidence for a broad spectrum of magmasources. In this regard, the Yingpanliangzi pluton is important as itsuggests there is a link between the eruption of flood basalts andmelting of the crust, and its petrogenesis therefore sheds light on therole that LIPs may play in crust building processes. The range ofgranitic compositions testifies to the diversity of granitic rocksexpected to be found within other LIPs or continental within-platesettings. Below, we summarize the salient petrogenetic characteristics

Sm Nd 147Sm/144Nd

143Nd/144Nd

±2σm εNd(0) εNd f TDM-1(ppm) (ppm) (260 Ma) (Sm/Nd)

4.15 23.47 0.1069 0.512278 12 −7.0 −4.0 −0.46 12435.23 28.42 0.1113 0.512269 13 −7.2 −4.4 −0.43 13095.06 28.31 0.1081 0.51227 12 −7.2 −4.2 −0.45 12684.85 27.71 0.1058 0.51226 13 −7.4 −4.4 −0.46 12563.97 21.35 0.1124 0.512282 8 −6.9 −4.1 −0.43 13053.92 23.28 0.1018 0.512287 18 −6.8 −3.7 −0.48 1175

n ±2%.Sr)=0.710248±3 (2 σm). JMC (Nd)=0.511813±10 (2σm).

Fig. 8. Comparison of the of the Rb/Nb and Th/Ta ratios of the Panxi granitoids. Lowercrust (LC) and upper crust (UC) values of Rudnick and Gao (2003).Data from Luo et al. (2007), Shellnutt and Zhou (2007, 2008), Shellnutt et al. (2009a),Xu et al. (2008), Zhong et al. (2007, 2009), and Zhou et al. (2002b).

Fig. 9. Summary of zircon U–Pb ages of the granitic plutons, mafic dyke and tuff fromthe Panxi region.Data from Luo et al. (2007), Shellnutt and Zhou (2007, 2008), Shellnutt et al. (2008,2009a), Xu et al. (2008) and Zhong et al. (2007, 2009).

153J.G. Shellnutt et al. / Lithos 123 (2011) 145–157

that support the differences between the ELIP-granitic rocks andcontextualize those rocks within the temporal and petrologicaldevelopment of the ELIP as a whole.

The Emeishan basalts erupted during a short interval between~260 Ma and ~257 Ma (He et al., 2007). The injection of ultramafic

Table 4Summary of chemical characteristics of ELIP granitic rocks.Data is compiled from Luo et al. (2007); Shellnutt et al. (2009a,b); Shellnutt and Zhou (200

Type Genesis Age ASI Eu/Eu* εNd(T)(Ma)

Mantle Fractionalcrystallization

~260 Weakly peralkaline b1.0 +1.5 to +

Partial Melting ~260 to~251

Metaluminous N1.0 +1.3 to +

Crust Crust ~260 to~251

Peraluminous toMetaluminous

b1.0 −6.7 to−

Hybrid Crust+Mantle ~260 Metaluminous ≈ 1.0 −0.7 to +

ASI is the alumina saturation index (Al/Ca−1.67P+Na+K); Eu/Eu*=[2*EuN/(SmN+GdN)]thermometry; BaPM and Nb–TaPM indicate the presence of anomalous primitive-mantle nor

and mafic magmas began at ~260 Ma at which time, some likelyaccumulated in the middle crust, whereas others reached progres-sively shallower depths and ultimately breached the surface. Magmascompositionally similar to high-Ti basalt formed shallow-levelchambers where fractional crystallization produced Fe–Ti oxide-bearing layered gabbros and peralkaline granitoids (Shellnutt andJahn, 2009, 2010; Shellnutt et al., 2009a). The peralkaline graniticrocks have chemical characteristics including: Eu/Eu*b1.0, εNd(T)N+1.5; positive zircon εHf(T) values and negative BaPM anomalies. TheBaima (860 °C±17 2σ, M=1.9±0.04 2σ), Panzhihua (940 °C±212σ, M=1.7±0.09 2σ) and Taihe (897 °C±14 2σ, M=1.7±0.05 2σ)plutons have M values within the calibration range of Watson andHarrison (1983) suggesting their average zircon saturation temper-ature estimates may be reasonable (Table 4; Figs. 10 and 11). Thecalculated magmatic temperatures are consistent with experimentalmodeling and previous studies of A-type granites (Clemens et al.,1986).

The Cida pluton, located just to the north of the Baima pluton, hassimilar bulk rock composition (e.g. Eu/Eu*b1, ISr=0.7030 to 0.7053),TZr(°C) estimates (TZr=953 °C±62 2σ; M=1.55±0.2 2σ) andprimitive-mantle normalized incompatible element patterns as theperalkaline rocks, however, it is metaluminous and has εNd(T) valuesof−0.3 to +0.2 (Fig. 10). The compositional similarities between theCida pluton and the other peralkaline plutons suggests it may haveformed by the same process (e.g. fractional crystallization of maficmagmas) but assimilated a significant amount of crustal material(Fig. 11; Zhong et al., 2007).

The second type ofmantle-derived granitoids aremetaluminous andrange in age from ~260 Ma to ~252 Ma and are characterized by thefollowing: Eu/Eu*N1.0 (Woshui=1.45±0.1 2σ; Huangcao=1.30±0.12σ), εNd(T) valuesN+1.5; positive zircon εHf(T) values, and havedepleted Th–UPM and Zr–HfPM anomalies and positive BaPM anomalies(Table 4; Figs. 10 and 11). The average zircon saturation temperatureestimate for theWoshui syenites is 723 °C±18 2σ (M=1.9±0.04 2σ)however the Huangcao and Daheishan plutons fall outside of thecalibration range ofWatson andHarrison (1983) (Fig. 10c). It is thoughtthat those Emeishan mafic magmas which stalled at mid-crustal levelsserved as source material for the Woshui pluton at 260 Ma and lateracted as the source material for the ~252 Ma Huangcao and Daheishanplutons (Shellnutt and Zhou, 2007, 2008; Shellnutt et al., 2009b; Zhonget al., 2009). Although the origin of the mantle-derived metaluminousrocks is debated, the positive εNd(T) and εHf(T) values indicate theyoriginated from a similar mantle source as the peralkaline rocks. Thecontrasting Eu/Eu* values between the metaluminous and peralkalinerocks suggest that plagioclase did not fractionate. Furthermore thecontrasting BaPM anomalies suggest the peralkaline rocks likelyexperienced alkali feldspar fractionation whereas the metaluminousrocks did not, implying that the rocks evolved differently.

The injection of Emeishan basalticmagmas likely inducedmelting ofthe Yangtze Block basement rocks and produced the Yingpanliangzi

7, 2008); Xu et al. (2008); Zhong et al. (2007, 2009).

εHf(T) TZr(°C) BaPM Nb–TaPM Examples

3.4 +8.7±0.4to +9.2±1.0

860 °C±17 −ve None Baima, Taihe, Panzhihua(Dianchang), Cida?897 °C±14

940 °C±21953 °C±62

3.2 +5.8±0.3to +8.6±0.2

723 °C±18 +ve None Woshui, Huangcao andDaheishan

3.9 −2.6±0.4 767 °C±14 +ve or−ve −ve Ailanghe,Yingpanliangzi

1.4 +1.4±0.9 +ve None Maomaogou, Salian

normalized to C1 chondrites of Sun andMcDonough (1989); TZr is the zircon saturationmalized values.

0.0 0.5 1.0 1.5 2.0-8

-7

-6

-5

-4

-3

-2

-1

0

+1

+2

+3

+4

εNd (

T)

Eu/Eu*

Cru

stH

ybri

dM

antle

Fractionation Partial Melting?

b

c

700 740 780 820 860 900 940 980 1020

TZr(oC)

Woshui

Ailanghe

Baima

Taihe

Panzhihua

Cida

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.40.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3N

a+K

/Al

ASI

Metaluminous

Peralkaline

Peraluminous

TaiheBaimaPanzhihuaAilangheKangdingYingpanliangzi

WoshuiHuangcaoDaheishanCidaMaomaogou

a

Fig. 10. Chemical subdivision of the Panxi granitic rocks. (a) Alkali index (Na+K/Al)versus aluminum saturation index (ASI=Al/Ca−1.67P+Na+K). (b) εNd(T) versusEu/Eu* (Eu/Eu*=2*EuN/SmN+GdN). Dashed lines represent general divisions betweenmantle-derived, hybrid and crust-derived ELIP-granitoids. (c) Zr saturation thermom-etry of the Panxi granitic rocks with M=1.3 to 1.9.

Fig. 11. Primitive-mantle normalized incompatible element diagrams of the Panxiregion granitoids. Rocks are normalized to values of Sun and McDonough (1989).

154 J.G. Shellnutt et al. / Lithos 123 (2010) 145–157

pluton. However, the Ailanghe pluton is also considered to be a crustalmelt but it is younger than the main period of ELIP-magmatism(Shellnutt and Zhou, 2007; Xu et al., 2008; Zhong et al., 2007). The twoplutonshave differingASI, Ailanghe is peraluminous andYingpanliangziis metaluminous, however they share some geochemical characteristics

such as Eu/Eu*b1.0, negative εNd(T) values, negative Nb–Ta primitive-mantle normalized anomalies, and LREE enrichment with flat HREEchondrite normalized patterns (Table 4; Figs. 6, 10 and 11). The majorand trace element compositional differences may reflect heterogeneityof the Yangtze Block which is composed of Paleoproterozoic toNeoproterozoic granitic and gneissic rocks. Therefore, the compositionof crustalmelts could reflect amultitude of reservoirs, potentially givingeach pluton a distinct composition. The average zircon saturationtemperatures estimates of the Yingpanliangzi granites are within therange ofmodeledwall-rock temperature estimates after the injection ofbasaltic magmas into the crust (Annen and Sparks, 2002; Huppert andSparks, 1988) and therefore the Yingpanliangzi pluton and possibly theAilangheplutonmaybe consideredas indirectly related to theEmeishanmagmatism.

Fig. 12. Tectonomagmatic interpretation of the Panxi granitic rocks. Mantle-derived(1) peralkaline and (2) metaluminous granitic rocks formed by differentiation (e.g.fractional crystallization and partial melting) of Emeishan mafic magmas. (3) Hybridgranitic rocks formed by homogenization between Emeishan magmas and crustalmaterial. (4) Crustally-derived granitic rocks formed by partial melting of upper crust.

155J.G. Shellnutt et al. / Lithos 123 (2011) 145–157

The Maomaogou syenite and Salian diorite are currently the onlyknown examples of plutons which have chemical characteristics ofmantle–crust hybrids (Xu et al., 2008). The hybrid granitoids are~260 Ma, are metaluminous and have Eu/Eu*≈1.0, εNd(T)=−0.7 to+1.4 and zircon εHf(T)=+1.4 (Figs. 10 and 11; Luo et al., 2007; Xuet al., 2008). Currently, little is known about the hybrid granitoids, andtherefore, it is difficult to constrain their geochemical characteristics(Table 4).

Fig. 12 conceptualizes the tectonomagmatic types of granitoidsfound within the Panxi region. The mantle-derived (1) peralkalineand (2) metaluminous granitic rocks formed by differentiation (e.g.fractional crystallization or partial melting) of Emeishan maficmagmas. The (3) hybrid granitic rocks were produced by homoge-nization between Emeishan magmas and crustal material and the (4)crustally-derived granitic rocks were formed by partial melting of theupper crust due to injection of Emeishan magmas.

ELIP volcanism is contemporaneous with the Baima (259±5;258±4 Ma), Taihe (261±2 Ma), Panzhihua, Cida (261±4 Ma),Maomaogou (262±4 Ma), Salian (260±4 Ma), Yingpanliangzi andWoshui (260±2 Ma) plutons. However, the Ailanghe (255±4 Ma;251±6 Ma), Huangcao (252±3 Ma) and Daheishan (253±2 Ma)plutons have mean ages younger than the main phase of Emeishanmagmatism (i.e. ≤ 257 Ma). Middle Triassic ages have also beenreported from a mafic alkaline dyke (242±2 Ma) and rhyolitic tuff(238±3 Ma) in the Panxi region (Fig. 9; Shellnutt et al., 2008; Xuet al., 2008). The tuff is interpreted to represent the eruption ofcrustal melts generated by conductive heat transfer and lithosphericthinning associated with the Emeishan mantle plume and thus the~252 Ma granitoids may signal a continuation of magmatism post-257 Ma. However, He et al. (2007) suggested that Emeishan basalticvolcanism ended at ~257 Ma. Furthermore heat incubation modelssuggest that high temperatures will last ≤2 Ma after the cessation ofbasalt injection (Annen and Sparks, 2002). The discrepancy betweenthe end of ELIP volcanism and the emplacement of the ~252 Maplutons (e.g. Daheishan, Huangcao, Ailanghe?) creates a temporalconundrum. Either a second, mutually exclusive, melting eventoccurred at ~252 Ma or, Emeishan magmatism was continuous untilat least ~252 Ma. One possible explanation for the post-257 Mamagmatism is lithospheric thinning related to the collision betweenthe Indochina Block and the South China Block during the LatePermian/Early Triassic (LePvrier et al., 2004). The initial stages ofcollision may have been a crucial factor for creating conditionssuitable for generating melts from the middle/lower crust (i.e.Emeishan underplated material) of the South China Block and thusthe emplacement of the younger granitoids (Shellnutt et al., 2008).After ELIP magmatism, the region again became a stable platformwith the deposition of clastic and carbonate rocks until ~230 Ma

when the North China Block and South China Blocks collided (Heet al., 2006; Shellnutt et al., 2008).

7. Conclusion

The Yingpanliangzi granites contain zircons which record an olderage (~780 Ma), likely the igneous protolith, and a younger, inferredmagmatic age (~260±8 Ma). The whole-rock composition, negativeprimitive-mantle normalized Ta–Nb anomalies, low εNd(260 Ma)

values (−3.9 to −4.4), and high ISr values (0.71074 to 0.71507) areconsistent with a crustal origin for the granites of the Yingpanliangzipluton. We suggest that the Yingpanliangzi pluton was formed bymelting of the upper Yangtze Block during the emplacement ofEmeishan basaltic magmas at ~260 Ma. The Yingpanliangzi pluton isthe first entirely crust-derived pluton that is contemporaneous withthemain phase of Emeishanmagmatism. The granitic rocks of the ELIPmay be subdivided into three distinct groups (e.g. mantle-derived,mantle-crust hybrid and crust-derived) on the basis of their whole-rock and trace element geochemistry, whole-rock Nd isotopes, zirconHf isotopes and their zircon saturation thermometry estimates. Theca. 10 m.y. temporal range of the granitoids may be related to eithercontinuous ELIP magmatism or to changes in the thermal structurebeneath the Yangtze Block from a mantle plume regime tolithospheric thinning associated the collision between the IndochinaBlock and the South China Block.

Acknowledgements

We thank G.N. Eby, J.D. Greenough and H.A. Sandeman for theirconstructive reviews and Drs. G.F. Zellmer and T.-F Yui for theircomments on an earlier version of this manuscript. The authors wouldlike to thank Professor Ma Yuxiao and Mr. Zhao Hao both fromChengdu University of Science and Technology for their field supportand Mr. Liang Qi and Ms. Xiao Fu for their analytical support at theUniversity of Hong Kong. This study is supported by a 973 matchinggrant from HKU and Academia Sinica post-doctoral fellowship to JGS.

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