东昆仑祁漫塔格晚古生代末期幔源岩浆活动成因及地质意义:以鹰爪沟岩体为例

幔源岩浆活动的成因研究，对约束区域构造演化历史具有重要意义.东昆仑祁漫塔格鹰爪沟镁铁-超镁铁质层状岩体由橄榄辉长苏长岩、含长橄榄二辉岩及橄榄二辉岩组成.获得橄榄辉长苏长岩的LA-ICP-MS锆石U-Pb年龄为263±4 Ma，指示岩体形成于中二叠世晚期.岩石地球化学特征显示，鹰爪沟岩体具有低SiO₂、高MgO、FeO_t含量，富集LREE、LILE，亏损HREE以及Th、U、Nb、Ta、Ti等不相容元素等特征.全岩ε_Nd（t）=0.73~0.92，锆石ε_Hf（t）=8.33~13.50.综合区域地质背景资料，认为其形成于古特提斯洋俯冲作用下的活动大陆边缘裂谷，源自于受软流圈熔体和俯冲流体交代的岩石圈地幔.结合同期具有壳幔混源特征的花岗岩资料，认为东昆仑地区在中二叠世已有幔源岩浆底侵活动，主要形成于古特提斯洋俯冲体制下局部的伸展背景. 

Genesis and Geological Significance of Late Paleozoic Mantle-Derived Magmatism in Qimantag,East Kunlun: A Case Study of Intrusion in Yingzhuagou

The study of the origin of mantle-derived magmatism is of great significance to the tectonic evolution history. Located in the Yingzhuagou area of Qimantag, East Kunlun, the mafic-ultramafic layered intrusion consists of olivine gabbro-norite, feldspar-olivine websterite and olivine websterite.The LA-ICP-MS zircon U-Pb dating results suggest that the olivine gabbro-norite intruded at 263±4 Ma, belonging to late Middle Permian. All the rocks are characterized by low SiO₂, high MgO and FeO_t, enrichment of LREE and LILE, depletion of HREE and incompatible elements (e.g.Th, U, Nb, Ta, Ti). ε_Nd(t)=0.73-0.92, ε_Hf(t)=8.33-13.50. Based on the regional geological background, it is suggested that the rocks were formed in an active continental margin rift setting with the subduction of Paleo-Tethys Ocean. The magma came from the lithospheric mantle metasomatized by subduction fluid and asthenosphere melt. Combining the data of granite that originated from mixing of crustal and mantle materials in the same period, it is concluded that underplating of mantle-derived magmas should have started before Middle Permian in East Kunlun area and should have been controlled by the regional extensional setting in the subduction of Paleo-Tethys Ocean.