First Identification of Mafic Igneous Enclaves in Miocene Lavas of Southern Tibet With Implications for Indian Continental Subduction
First Identification of Mafic Igneous Enclaves in Miocene Lavas of Southern Tibet With Implications for Indian Continental Subduction
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首次识别藏南中新世熔岩中的镁铁质火成岩包体，对印度大陆俯冲具有重要意义
DOI：
10.1029/2018gl079061
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发表时间：
2018-08
影响因子：
5.2
通讯作者：
Ou Quan
中科院分区：
文献类型：
--
作者：
Hao Lu-Lu;Wang Qiang;Wyman Derek A.;Qi Yue;Ma Lin;Huang Fang;Zhang Le;Xia Xiao Ping;Ou Quan
印度大陆俯冲到亚洲板块之下的历史仍不清楚。藏南中新世超钾质岩石具有极高的同位素丰度，常被用来追踪与印度大陆俯冲有关的地幔交代作用和地球动力学过程。然而，这些岩石可能受到了拉萨古壳的污染。原生超钾质岩浆的不确定性掩盖了它们的地幔来源。本文报道了藏南新生代熔岩中的第一个镁铁质火成岩。它们主要由单斜辉石、金云母和辉长岩组成，其锆石U-Pb年龄为21.5±0.3 Ma。矿物和块状岩石的地球化学特征表明它们来自原生超钾质岩浆的结晶。块状岩石的锶-钕、单斜辉石和锆石氧同位素显示出其同位素富集性。结合碰撞前玄武岩，我们认为包体的地幔来源来自于俯冲的印度大陆。这一研究表明，印度大陆不晚于中新世早期俯冲到拉萨中部以下。
The history of Indian continental subduction beneath Asian plate remains unclear. Miocene ultrapotassic rocks in southern Tibet, with extremely enriched isotopes, have often been used to trace mantle metasomatism and geodynamic processes associated with Indian continental subduction. These rocks, however, may have been contaminated by Lhasa ancient crust. Uncertainties on primary ultrapotassic magmas obscure their mantle sources. Here we report on first mafic igneous enclaves in Cenozoic lavas of southern Tibet. They consist principally of clinopyroxene, phlogopite, and sanidine and have a zircon U‐Pb age of 21.5 ± 0.3 Ma. Mineral and bulk‐rock geochemical characteristics indicate their crystallization from primary ultrapotassic magmas. Bulk‐rock Sr‐Nd, clinopyroxene Sr, and zircon O isotopes demonstrate their isotopically enriched character. Combined with precollisional basalts, we suggest that the mantle source of the enclaves was enriched by the subducted Indian continent. This study implies that the Indian continent had subducted beneath central Lhasa no later than early Miocene.
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