Origin of Middle Triassic high-K calc-alkaline granitoids and their potassic microgranular enclaves from the western Kunlun orogen, northwest China: A record of the closure of Paleo-Tethys

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• 作者：Yao-Hui Jiang ; ^{yhj186@hotmail.com} ; Ru-Ya Jia ; Zheng Liu ; Shi-Yong Liao ; Peng Zhao ; Qing Zhou
• 关键词：High-K calc-alkaline ; Granitoids ; Microgranular enclaves ; Paleo-Tethys ; Western Kunlun orogen ; China
• 刊名：Lithos
• 出版年：2013
• 出版时间：January, 2013
• 年：2013
• 卷：156-159
• 期：Complete
• 页码：13-30
• 全文大小：3289 K

文摘

The western Kunlun orogen, the northwest Tibet Plateau, occupies a key tectonic position at the junction between the Pan-Asia and the Tethyan tectonic domains. It is related to subduction of Proto- and Paleo-Tethys and terrane collision from early Paleozoic to early Mesozoic. This paper presents the first detailed SHRIMP zircon U-Pb chronology, mineral chemistry, major and trace element, and Sr-Nd-Hf isotope geochemistry of three Middle Triassic plutons (Yuqikapa, Muztaga and Taer) and their microgranular enclaves in the western Kunlun orogen. SHRIMP zircon U-Pb dating shows that the Yuqikapa pluton was emplaced in the Anisian (~ 243 Ma) and the Muztaga and Taer plutons that contain microgranular enclaves were emplaced in the Ladinian (234-227 Ma). The Yuqikapa pluton is composed of peraluminous high-K calc-alkaline two-mica granites (monzogranite-syenogranite-alkali-feldspar granite), with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7071-0.7077, ¦Å_Nd (T) of ? 4.4 to ? 6.3 and ¦Å_Hf (T) (in-situ zircon) of ? 3.3. Elemental and isotopic data suggest that they were formed by ¡°wet¡± anatexis of the Precambrian metasedimentary and metaigneous rocks in the continental collision (overthrust) zone. The Muztaga and Taer plutons consist of metaluminous to weakly peraluminous high-K calc-alkaline granitoids (granodiorite-monzogranite), with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7052 ? 0.7104, ¦Å_Nd (T) of ? 3.6 to ? 7.3 and ¦Å_Hf (T) (in-situ zircon) of ? 3.1 to ? 1.0. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metasedimentary and metaigneous rocks in the normal lower-crust (< 40 km) for the Muztaga pluton and in the thickened lower-crust (~ 40-50 km) for the Taer pluton, triggered by underplating of coeval (233-226 Ma) mantle-derived enclave-forming magmas. The enclaves are basic (SiO₂ 48.0-51.6 wt. % ) to intermediate (SiO₂ 53.0-54.6 wt. % ) with high K₂O (1.4-4.2 wt. % ). They generally have lower initial ⁸⁷Sr/⁸⁶Sr ratios (0.7034-0.7084) and high initial ¦Å_Hf (? 1.1 to + 1.2) than their respective host granitoids. The enclave magmas are considered to have been derived from the partial melting of subduction-modified mantle in the spinel stability field (< 60 km) (enclaves in the Muztaga pluton) and the spinel-garnet transition zone (~ 60-80 km) (enclaves in the Taer pluton). Final closure of the Paleo-Tethys occurred in the Middle Triassic Anisian (~ 243 Ma). The Middle Triassic Ladinian (234-227 Ma) dates the post-collisional regime caused by Paleo-Tethyan oceanic slab break-off.