Available online at www.sciencedirect.com Gondwana Research 13 (2008) 126–138 www.elsevier.com/locate/gr Age and origin of high Ba–Sr appinite–granites at the northwestern margin of the Tibet Plateau: Implications for early Paleozoic tectonic evolution of the Western Kunlun orogenic belt ⁎ Hai-Min Ye a, Xian-Hua Li b, Zheng-Xiang Li c, Chuan-Lin Zhang a, a Nanjing Institute of Geology and Mineral Resources, China Geological Survey, Nanjing 210016, China b Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China c Institute of Geoscience Research (TIGeR), Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth WA 6845, Australia Received 10 May 2007; received in revised form 3 August 2007; accepted 5 August 2007 Available online 7 September 2007 Abstract The Buya appinite–granite is a typical high Ba–Sr granite emplaced at the northern West Kunlun orogenic belt along the northwestern margin of the Tibetan Plateau. The granite is dated at ca. 430 Ma using the SHRIMP U–Pb zircon method. It consists of alkaline feldspar granites with coeval appinite enclaves. The granite possesses high SiO2 (69.77–72.69%), K2O (4.44–5.10%) and total alkalinity (K2O+Na2O=8.80–9.92%), Sr (655–1100 ppm), Ba (1036–1433 ppm) and LREE, and low HREE and HFSE contents and insignificant negative Eu anomalies. Consequently, # the samples have very high Sr/Y (74–141) and (La/Yb)N (37–96) ratios. On the other hand, they have low MgO (or Mg ), Cr and Ni contents and low radiogenic Nd isotopes (ɛNd(T)=−8.4 to −10.4). The high Ba–Sr and other geochemical signatures of the granite also appear in the appinite enclaves except that the appinite enclaves have relatively higher abundances in these elements and higher ɛNd(T) values (−5.7 to −6.7). Elemental and isotope compositions suggest that the appinites were derived from partial melting of an enriched lithospheric mantle source probably induced by upwelling of the asthenosphere due to the delamination of a subducted slab. The granite was likely derived from partial melting of the mafic lower crust (with residual garnet), associated with involvement of minor LILE-enriched appinitic magma, followed by crystal fractionation of hornblende, biotite, apatite and allanite. In combination with previous investigations on the evolution of the Western Kunlun, we suggest that the Buya high Ba–Sr plutons represent the end of an early Paleozoic crust thickening event after a terrane accretion on southern Tarim craton, and the beginning of a post-orogenic collapse phase in the Paleozoic West Kunlun orogenic belt. © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Buya high Ba–Sr appinite–granite; Geochronology; Geochemistry; Petrogenesis; Tectonic implications; West Kunlun orogenic belt 1. Introduction The geologic and tectonic evolution of the North China Craton and surrounding crustal blocks have been the focus of various important investigations and debates on the structural, magmatic and metamorphic histories and supercontinent genesis (Santosh et al., 2006; Kusky et al., 2007 and references therein). While many of the studies focused on the Paleoproterozoic evolution of the North China Craton, the Paleozoic and Mesozoic evolution of the region is also critical to the under- standing the evolution of the East and Southeast Asian conti- nental lithosphere (cf. Metcalfe, 2006). In this context, the ⁎ Corresponding author. Tel.: +86 25 84897946; fax: +86 25 84600446. Fig. 1. Major tectonic units of the Tibet Plateau. The West Kunlun orogen is on E-mail address: [email protected] (C.-L. Zhang). the northern periphery of the Tibet Plateau. 1342-937X/$ - see front matter © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2007.08.005 H.-M. Ye et al. / Gondwana Research 13 (2008) 126–138 127 Fig. 2. (a) Tectonic units of the West Kunlun orogen in which the Paleozoic and Mesozoic granites are shown (NKT: the North Kunlun Terrane, SKT: the South Kunlun Terrane, KTT: the Karakorum–Tianshuihai Terrane; ①: the ca. 470 Ma Yierba I-type granodiorite pluton (Yuan et al., 2002); ② the Yixiekegou volcanic series, a member of the Kudi ophiolite; ③ the ca. 405 Ma North Kudi A-type granite (Yuan et al., 2002); ④ the Kudi gneiss (Xiao et al., 2005); ⑤ ultramafic–mafic complex, a member of the Kudi ophiolite; ⑥ the ca. 505 Ma Kangxiwa gneissic granodiorite pluton (Zhang et al., 2007a,b); ⑦ the Kangxiwa gneiss (Zhang et al., 2007a,b). (b) Geological map of the Buya appinite–granites consisting more than ten stocks along an east–west-trending zone, sharing similar color, texture and petrography; Pt2kl—the Mesoproterozoic Kalakashi Group; Pt2al—the Mesoproterozoic Ailiankate Group; Pz2–Mz—lower Paleozoic to Mesozoic strata. (c) A detailed map showing the structure of one pluton from the Buya appinite–granites (the appinite enclaves are not shown in scale). Western Kunlun Orogen (WKO), a 1000 km long early temporal framework of the early Paleozoic tectonic evolution in Paleozoic mountain belt located along the northern periphery the WKO. of the Tibetan plateau, connected with the Pamir syntaxis to the west and the Altyn-East Kunlun Orogen to the east (Fig. 1)isof 2. Regional geology and petrography considerable importance in understanding the reconstruction of paleo-Asia because it occupies a key tectonic position between The WKO was formed by multiple stages of terrane accretions the Tarim block to the north and the Tethyan domain to the south along the southwestern margin of the Tarim craton (Dewey et al., (Gao and Reiner, 2000; Xiao et al., 2001; Wang et al., 2001; Xiao et al., 2005; Yang et al., 2007). Previous studies have identified three types of the early Paleozoic granites in the WKO, i.e., the oceanic ridge granites (e.g., the Aoyitake granites, Jiang et al., 1999), subduction-related granites (e.g., the ca. 471 Ma Yierba granites, Yuan et al., 2002) and the post-orogenic A-type granites (e.g., the ca. 405 Ma north Kudi A-type granites) (Yuan et al., 2002). However, the petrotectonic in the WKO needs further investigations because little is known for the magmatic rocks during much of the Ordovician and Silurian time (Yuan et al., 1999; Jiang et al., 1999; Xiao et al., 1999; Yuan et al., 2002; Jiang et al., 2002; Xiao et al., 2002, 2005). In this contribution we report the petrography, age, elemental and Nd isotopic geochemistry of the early Paleozoic Buya high Ba–Sr granites in the WKO along the northern periphery of the Tibet Plateau, with the aims of (1) characterizing its Fig. 3. Photo of an appinite enclave in the Buya granite indicating magma mingling petrogenesis and (2) reconstructing a more detailed spatio- between the appinite and the granite. The diameter of the coin is about 2 cm. 128 H.-M. Ye et al. / Gondwana Research 13 (2008) 126–138 Table 1 SHRIMP U–Pb zircon data for the Buya granite (sample KL018) Spots U (ppm) Th (ppm) Th/U f 206 206Pb 238U± 207Pb/235U± 207Pb/206Pb± Age Age 206Pb/238U± 207Pb/206Pb± 18-3.1 1344 165 0.12 1.1 0.1144 0.0031 1.087 0.033 0.0689 0.0008 698 18 896 23 18-5.1 3594 739 0.21 1.2 0.0730 0.0031 0.546 0.029 0.0542 0.0015 454 18 380 62 18-6.1 3876 587 0.15 1.2 0.0619 0.0023 0.510 0.027 0.0597 0.0019 387 14 592 72 18-8.1 2496 427 0.17 1.1 0.0723 0.0041 0.546 0.037 0.0548 0.0017 450 25 402 69 18-8.2 1975 168 0.08 1.8 0.0969 0.0043 0.813 0.082 0.0608 0.0052 596 25 633 194 18-9.1 3962 767 0.19 3.9 0.0631 0.0023 0.472 0.020 0.0542 0.0009 395 14 380 39 18-11.2 1047 299 0.29 1.1 0.1468 0.0069 1.320 0.095 0.0652 0.0032 883 39 781 107 18-14.1 2542 729 0.29 1.4 0.0691 0.0020 0.591 0.094 0.0620 0.0095 430 12 675 365 18-15.1 683 161 0.24 3.5 0.1131 0.0047 0.835 0.240 0.0535 0.0150 691 27 351 796 18-16.1 769 554 0.72 1.0 0.1596 0.0044 1.497 0.055 0.0680 0.0015 955 24 869 46 18-20.1 1278 269 0.21 2.0 0.0710 0.0024 0.549 0.023 0.0561 0.0011 442 14 456 44 18-22.1 1152 322 0.28 1.0 0.0658 0.0031 0.426 0.050 0.0470 0.0048 411 19 48 227 18-23.1 1199 436 0.36 7.0 0.0695 0.0045 0.536 0.121 0.0559 0.0113 433 27 449 449 18-26.1 1245 279 0.22 1.0 0.0691 0.0053 0.549 0.117 0.0562 0.0123 431 29 452 461 18-27.1 2195 534 0.24 2.1 0.0699 0.0041 0.529 0.241 0.0631 0.0037 437 21 684 175 f 206: percentage of common 206Pb in total 206Pb. 1988; Pan and Wang, 1994; Xiao et al., 1999, 2002, 2005; Zhang minor amount of biotite (2–5%) and hornblende (b1%). et al., 2007a)(Fig. 1), i.e., the late Mesoproterozoic to early Accessory minerals include apatite, zircon, titanite, allanite, and Neoproterozoic orogenic belt in northern Kunlun (also known as Ti–Fe oxides.