Abstract Permian-Triassic granitoids are widespread in the East Kunlun Orogen (EKO) and are influential in the re-construction of Paleo-Tethyan tectono-magmatic activities. In this contribution, zircon U Pb dating and Lu Hf isotopic as well as whole rock major and trace elements analysis have been conducted on a series of syenogranite plutons from the eastern segment of EKO to constrain their petrogenesis and tectonic implication. The syenogranites are characterized by dominant mineral assemblages of K-feldspars and minor plagioclase and biotite, in contrast to the coexisting granodiorites that are rich in amphibole and plagioclase. Zircon U Pb dating reveals that the studied syenogranites represent a two-stage magmatism from Middle Permian to Late Triassic (ca. 265 Ma and 235–232 Ma). Geochemical and mineralogical evidences show that the syenogranites are classified as high-K calc-alkaline, weakly peraluminous, highly fractionated (DI = 93–95) and moderately fractionated (DI = 82–91) I-type granites. They yield negative ɛHf (t) values (−13.25 to −0.11), which, together with their high Th/Nb (0.73–4.88), Th/La (0.29–2.65) and La/Nb (1.07–4.48) ratios and moderate pressure conditions (7–10 kbar) imply magma generation through partial melting of the normal-thickened lower crust. The magma underwent extensive plagioclase and subordinate K-feldspar fractionation during evolution. Given the old two-stage Hf model ages (TDM2 = 1270–2100 Ma), we interpret the ancient lower crust as their dominant source rocks with limited contribution from the juvenile lower crust. Our new data, in tandem with published data show that the Middle-Permian (ca. 265 Ma) Jialuhe syenogranites were formed during a period of local extension concomitant with the northward subduction of the Paleo-Tethyan ocean. In contrast, the Late-Triassic Qingshuihe (235 Ma), Keri (234 Ma), Wutuo (232 Ma) and Balong syenogranite plutons were generated in response to asthenospheric upwelling, lower crust delamination and subsequent continental rifting in a post-collisional extension stage along the convergent plate margins.

中文翻译：

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东昆仑造山带东段二叠系-三叠系正长花岗岩的成因及构造意义

摘要 二叠纪-三叠纪花岗岩广泛分布于东昆仑造山带（EKO），对古特提斯构造岩浆活动的重建具有重要影响。在这项贡献中，对来自 EKO 东段的一系列正长花岗岩进行了锆石 U Pb 定年和 Lu Hf 同位素以及全岩主微量元素分析，以限制其岩石成因和构造意义。正长花岗岩的特征是钾长石和少量斜长石和黑云母的主要矿物组合，与富含角闪石和斜长石的共存花岗闪长岩形成对比。锆石 U Pb 测年表明，所研究的正长花岗岩代表了从中二叠世到晚三叠世（约 265 Ma 和 235-232 Ma）的两阶段岩浆作用。地球化学和矿物学证据表明，正长花岗岩分为高钾钙碱性、弱过铝质、高度分异（DI = 93-95）和中等分异（DI = 82-91）I型花岗岩。它们产生负的 ɛHf (t) 值（-13.25 到 -0.11），连同它们的高 Th/Nb (0.73–4.88)、Th/La (0.29–2.65) 和 La/Nb (1.07–4.48) 比率和中等压力条件（7-10 kbar）意味着岩浆是通过正常增厚的下地壳的部分熔融产生的。岩浆在演化过程中经历了广泛的斜长石和次级钾长石分馏。鉴于旧的两阶段 Hf 模型年龄（TDM2 = 1270-2100 Ma），我们将古老的下地壳解释为它们的主要烃源岩，而年轻的下地壳贡献有限。我们的新数据，与已发表的数据相结合，表明中二叠纪（约 265 Ma）加鲁河正长花岗岩形成于与古特提斯洋向北俯冲相伴的局部伸展时期。相比之下，晚三叠世清水河（235 Ma）、克里（234 Ma）、乌托（232 Ma）和巴龙正长花岗岩是在碰撞后伸展阶段响应软流圈上涌、下地壳分层和随后的大陆裂谷产生的沿着会聚的板块边缘。