The East Kunlun Orogenic Belt (E-KOB) evolved into an extensional tectonic setting with plenty of mafic magmatism after the closure of the Paleo-Tethys Ocean. However, the deep tectonic system and geodynamic processes in this context still need further clarification. The detailed field geological, petrological, geochronological and geochemical works carried out on the Yeniugou gabbros in this study could provide key evidence for clarifying this issue. The gabbros are predominantly composed of clinopyroxene, orthopyroxene, plagioclase, olivine and ilmenite. Zircon U–Pb dating results suggest that their formation at ca. 209–207 Ma. Characterized by a relatively low SiO2 content and a moderate total alkaline content, these rocks are classified as alkalic to subalkaline series. High values of Mg# (42.2–59.4) and high concentrations of compatible elements (V, Cr, Co, Ni) suggest that their parent magma was generated through high partial melting of a lithospheric mantle source. The left-leaning rare earth element distribution patterns, combined with the characteristic spikes of Nb-Ta, indicate that they were originated from the lithospheric mantle metasomatized by subducting components. The positive zircon εHf(t) values (0.1–5.7), along with elevated Nb/La ratios (0.45–0.67), further confirm a small amount of asthenosphere mantle contribution. Elevated Zr/Y ratios, plus a slightly positive correlation between Alz and TiO2 in clinopyroxene, imply that they formed within an extensional setting, where the upwelling of the asthenospheric mantle provided heat for partial melting of the metasomatic lithospheric mantle. Combined with previous data, we suggest that E-KOB underwent delamination of thickened lithosphere in the late Triassic, following the closure of the Paleo-Tethys Ocean.

中文翻译：

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青藏高原北部东昆仑造山带加厚岩石圈晚三叠世延伸：来自镁铁质岩浆作用地球化学和地质年代学的证据


东昆仑造山带 （E-KOB） 在古特提斯洋关闭后演变成一个伸展的构造环境，具有大量的镁铁质岩浆作用。然而，在这种情况下，深层构造系统和地球动力学过程仍需要进一步澄清。本研究对叶牛沟辉长岩进行了详细的野外地质、岩石学、地质年代学和地球化学工作，可为澄清这一问题提供关键证据。辉长岩主要由斜辉石、斜辉石、斜长石、橄榄石和钛铁矿组成。锆石 U-Pb 测年结果表明，它们形成于约 209-207 马。这些岩石的特点是 SiO2 含量相对较低，总碱性含量适中，被归类为碱性到亚碱性系列。高值的 Mg# （42.2–59.4） 和高浓度的相容元素 （V、Cr、Co、Ni） 表明它们的母体岩浆是通过岩石圈地幔源的高度部分熔化产生的。左倾的稀土元素分布模式，结合 Nb-Ta 的特征尖峰，表明它们起源于俯冲成分交代的岩石圈地幔。正的锆石 εHf（t） 值 （0.1-5.7） 以及升高的 Nb/La 比率 （0.45-0.67） 进一步证实了少量的软流圈地幔贡献。升高的 Zr/Y 比值，加上斜辉石中 Alz 和 TiO2 之间的略微正相关，意味着它们在伸展环境中形成，其中软流圈地幔的上升流为交代岩石圈地幔的部分熔化提供了热量。 结合以前的数据，我们认为 E-KOB 在古特提斯洋关闭后，在晚三叠世经历了加厚岩石圈的分层。