Paleozoic post-collisional magmatism and high-temperature granulite-facies metamorphism coupling with lithospheric delamination of the East Kunlun Orogenic Belt,NW China

• 作者: Qian Wang Jiao Zhao Chuanlin Zhang Shengyao Yu Xiantao Ye Xiaoqiang Liu
• 来源期刊: 地学前缘（英文版）
• 年，卷（期）: 2022,（1）
• 所属期刊栏目: Research Paper
• 页码范围: 96-113
• 页数: 18页
• 语种: 英文

摘要

Lithosphere extension and upwelling of asthenosphere at post-collisional stage of an orogenic cycle gen-erally induce diverse magmatism and/or associated high-temperature metamorphism.Nevertheless,the intimate coexistence of post-collisional magmatic activity and high-temperature metamorphism is rare.In this contribution,a lithological assemblage composing of diverse magmatic rocks deriving from dis-tinct magma sources and coeval high-temperature metamorphism was identified in eastern Kunlun.Petrography,ages,mineral chemistry and whole-rock geochemistry demonstrated that those intimately coexistent diverse rocks were genetically related to post-collisional extension.The garnet-bearing mafic granulites in Jinshuikou area interior of the East Kunlun Orogenic Belt are mainly composed of garnet,orthopyroxene,and plagioclase,with peak metamorphic P-T conditions of ～ 701-756 ℃ and 5.6-7.0 kbar,representing a granulite-facies metamorphism at 409.7 ± 1.7 Ma.The diverse contemporaneous mag-matic rocks including hornblendites,gabbros and granites yield zircon U-Pb ages of 408.6 ± 2.5 Ma,413.4 ± 4.6 Ma,and 387-407 Ma,respectively.The hornblendites show N-MORB-like REE patterns with(La/Sm)N values of 0.85-0.94.They have positive zircon εHf(t) values of 0.1-4.9 and whole-rock εNd(t) val-ues of 3.9-4.7 but relatively high (87Sr/86Sr)i values of 0.7081 to 0.7088.These features demonstrate that the hornblendites derived from a depleted asthenospheric mantle source with minor continental crustal materials in source.As for the gabbros,they exhibit arc-like elemental signatures,low zircon εHf(t) values(-4.3 to 2.5) and variable whole-rock eNd(t) values (-4.9 to 1.2) as well as high (87Sr/86Sr)i values (0.7068 to 0.7126),arguing for that they were originated from partial melting of heterogeneous lithospheric man-tle anteriorly metasomatized by subducted-sediment released melts.Geochemistry of the granites defines their strongly peraluminous S-type signatures.Zircons from the granites yield a large range of εHf(t) values ranging from-30.8 to-5.1,while the whole-rock samples yield consistent (87Sr/86Sr)i values(0.7301 to 0.7342) and negative εNd(t) values (-10.1 to-12.4).These features indicate that the S-type granites could be generated by reworking of an ancient crust.Taken together,the penecontemporaneous magmatism and metamorphic event,demonstrated the early-middle Devonian transition from crustal thickening to extensional collapse.The post-collisional mantle-derived magmas serve as an essential driving force for the high-temperature granulite-facies metamorphism and anataxis of the crust associ-ated with formation of S-type granite.This study not only constructs a more detail Proto-Tethys evolution process of the eastern Kunlun,but also sheds new light on better understanding the intimate relationship between magmatism and metamorphism during post-collisional extensional collapse.