拉萨地块西北部早白垩世岩浆岩地球化学特征及其对高原南部早期地壳生长的指示  

Geochemical characteristics of Early Cretaceous magmatic rocks in the northwestern part of the Lhasa Block and indications of early crustal growth of the southern plateau

作　　者：黄思华 陈建林[1] 曾云川[1,2] 谈荣钰 黄童童 刘希军 HUANG Si-hua;CHEN Jian-lin;ZENG Yun-chuan;TAN Rong-yu;HUANG Tong-tong;LIU Xi-jun(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China;Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,College of Earth Sciences,Guilin University of Technology,Guilin 541004,China)

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]桂林理工大学地球科学学院广西隐伏金属矿产勘查重点实验室,广西桂林541004

出　　处：《地球化学》2020年第1期21-35,共15页Geochimica

基　　金：国家重点研发计划(2016YFC0600305);国家自然科学基金(41573024,41873037);广西隐伏金属矿产勘查重点实验室开放基金(17-140-27-K01)。

摘　　要：青藏高原巨厚的地壳被认为是印度与欧亚大陆碰撞挤压和幔源镁铁质物质底侵共同作用的结果。青藏高原南部不仅广泛发育新生代侵入岩,同时也发育大量的中生代花岗质岩浆岩,特别是早白垩世时期岩浆作用最为发育。本次研究对拉萨地块西北部日松地区早白垩世花岗闪长岩及其细粒闪长质包体进行了岩石学、地球化学和年代学研究,结果表明,花岗闪长岩及其细粒闪长质包体具有相同的形成年龄(约106~105 Ma),它们可能为壳幔岩浆混合作用的产物。在上述研究的基础上,结合前人对拉萨地块西北部大量白垩纪中酸性岩浆岩的研究结果,运用简单的全岩微量元素比值(如(La/Yb)N)推算地壳厚度,显示拉萨地块西北部从白垩纪早期到晚期地壳厚度有不断增加的趋势,并且指示在早白垩世很可能已经发生了明显增厚。结合区域构造演化特征,初步认为拉萨地块西北部在早白垩世时期地壳增厚方式以岩浆底侵为主,暗示青藏高原南部可能在早白垩世地壳已经开始生长,而晚白垩世地壳加厚则很可能是拉萨与羌塘地块陆-陆碰撞构造挤压的结果。It is generally believed that the double-thick crust of Tibet resulted from collision of the Indian and Eurasian continents and underplating of mafic magma from the mantle.Mesozoic and Cenozoic igneous rocks(especially from the early Cretaceous),are widely distributed in the southern part of the Tibetan Plateau.The geochemical characteristics of the Early Cretaceous(106–105 Ma)Risum granodiorites and related diorite enclaves,indicate that they resulted from mixing of the crust-mantle magma in the northwestern(NW)Lhasa terrane.The above results,combined with those from previous research on th e Cretaceous intermediate-acid magmatic rocks in the NW Lhasa terrane,indicate that the crustal thickness in the studied region increased from the early to late Cretaceous(based on the whole-rock trace element ratio,for example,of(La/Yb)N).In particular,this shows that there was an obviously thickened crust in the study area during the early Cretaceous.Combined with the characteristics of regional tectonic evolution,the thickened crust of the NW Lhasa terrane was related to underplating by mafic magmas in the early Cretaceous and then collision of the Qiangtang and Lhasa terranes in the late Cretaceous.

关 键 词：早白垩世 岩浆作用 地球化学 地壳厚度 拉萨地块 

分 类 号：P597[天文地球—地球化学]