The latest Cretaceous magmatic activity in the eastern segment of Lhasa terrane provides important insights for tracking the magma source and the geodynamic setting of the eastern Gangdese batholith (eastward of eastern Himalayan Syntaxis). Here, we present a detailed petrological, geochemical and geochronological study of intrusive rocks (monzodiorites and granodiorites) of the eastern Gangdese batholith. The studied monzodiorites and granodiorites give zircon U–Pb crystallization ages of 70–66 Ma and 71–66 Ma with ε_Hf(t) values of –4.8 to +6.2 and –1.9 to +5.3, respectively. These rocks are metaluminous to weakly peraluminous I-type granites showing geochemically arc-related features of enrichment in LREEs and some LILEs (e.g., Rb, Th, and U) and depletion in HREEs and some HFSEs (e.g., Nb, Ta, and Ti). They were interpreted to be derived from partial melting of mantle material and juvenile crust, respectively, which were proposed to be triggered by the Neo-Tethyan slab rollback during the northward subduction, and both experienced ancient crustal contamination. They formed in a transitional geodynamic setting from Neo-Tethyan oceanic flat subduction to slab rollback beneath the eastern Gangdese during the latest Cretaceous.

中文翻译：

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藏东南冈底斯带东部最新白垩纪侵入岩成因及构造意义

拉萨地体东段白垩纪最新的岩浆活动为追踪冈底斯岩基东部（喜马拉雅东侧）岩浆源和地球动力学背景提供了重要的启示。在这里，我们对冈底斯东部岩基的侵入岩（二长闪长岩和花岗闪长岩）进行了详细的岩石学、地球化学和地质年代学研究。研究的二长闪长岩和花岗闪长岩给出的锆石 U-Pb 结晶年龄分别为 70-66 Ma 和 71-66 Ma，ε _Hf ( t) 值分别为 –4.8 至 +6.2 和 –1.9 至 +5.3。这些岩石是超铝质至弱过铝质 I 型花岗岩，在地球化学上显示出 LREEs 和一些 LILEs（例如，Rb、Th 和 U）的富集和 HREEs 和一些 HFSEs（例如，Nb、Ta 和 Ti）的贫化的地球化学弧相关特征）。它们被解释为分别来自地幔物质和幼年地壳的部分熔融，被认为是由新特提斯板块向北俯冲过程中的回滚引发的，并且都经历了古地壳的污染。它们形成于一个过渡的地球动力学环境，从新特提斯洋平面俯冲到最近白垩纪东部冈底斯下方的板片回滚。