青藏高原新生代火山作用与构造演化  

Cenozoic Yolcanism and Tectonic Evolution on the Tibetan Plateau

作　　者：夏林圻[1] 李向民[1] 马中平[1] 徐学义[1] 夏祖春[1] 

机构地区：[1]中国地质调查局西安地质矿产研究所,陕西西安710054

出　　处：《西北地质》2010年第1期1-25,共25页Northwestern Geology

基　　金：中国地质调查局综合研究项目(1212010611804)

摘　　要：青藏高原的新生代火山作用是印度-亚洲大陆碰撞的火山响应,它显示了系统的时、空变化。随着印度-亚洲大陆碰撞从－65 Ma的接触-碰撞（即＂软碰撞＂）转变到－45 Ma的全面碰撞（即＂硬碰撞＂）,火山作用也逐渐从钠质＋钾质变为钾质-超钾质＋埃达克质。65－40 Ma的钾质和钠质熔岩主要分布于藏南的拉萨地块,少量分布于藏中的羌塘地块。从45－26 Ma,在藏中的羌塘地块中广泛发育钾质-超钾质熔岩和少量埃达克岩。随后的碰撞后火山作用向南迁移,在拉萨地块中产生－26－10 Ma间的同时代超钾质和埃达克质熔岩。尔后,从－18 Ma始,钾质和少量埃达克质火山作用重新向北,在西羌塘和松潘-甘孜地块中呈广泛和半连续状分布。此种时-空变异对形成青藏高原的深部地球动力学过程提供了重要约束。该过程包括：已消减的新特提斯大洋板片的回转、断离及随后增厚拉萨岩石圈根的去根作用,及因此而造成的印度岩石圈向北下插。青藏高原的隆升是自南向北穿时发生的。高原南部被创建于渐新世晚期,并保持至今;直到中新世中期,由于下插印度岩石圈的持续向北推挤,西羌塘和松潘-甘孜岩石圈的下部开始塌陷和拆离,高原北部才达到其现今的高度和规模。Cenozoic volcanism on the Tibetan plateau,which shows systematic variations in space and time,is the volcanic response to the India-Asia continental collision.The volcanism gradually changed from Na-rich ＋ K-rich to potassic-ultrapotassic ＋ adakitic compositions along with the India-Asia collision shifting from contact-collision of-65 Ma（i.e.,＂soft collision＂） to all-sided collision of-45 Ma（i.e.,＂hard collision＂）.The sodium-rich and potassium-rich lavas with ages of 65～40 Ma distribute mainly in the Lhasa terrane of southern Tibet and subordinately in the Qiangtang terrane of central Tibet.The widespread potassic-ultrapotassic lavas and subordinate adakites were generated from -45 to 26 Ma in the Qiangtang terrane of central Tibet.Subsequent post-collisional volcanism migrated southwards,producing ultrapotassic and adakitic lavas coevally between-26 and 10 Ma in the Lhasa terrane.And then the potassic and minor adakitic volcanism was renewed to the north and become extensive and semicontinuous since -18 Ma in the western Qiangtang and Songpan-Ganze terranes.Such spatial-temporal variations provide important constraints in the geodynamic processes that evolved at depth to form the Tibetan plateau.These processes include rollback and breakoff of the subducted Neo-Tethyan slab followed by removal of the thickened Lhasa lithospheric root,and consequently northward underthrust of the Indian lithosphere.The Tibetan plateau is suggested to have risen diachronously from south to north.Whereas the southern part of the plateau may have been created and maintained since the Late Oligocene,the northern plateau would have not attained its present-day elevation and size until the mid-Miocene when the lower part of the western Qiangtang and Songpan-Ganze lithospheres began to collapse and detach owing to the persistently northward push of the underthrust Indian lithosphere.

关 键 词：青藏高原 印度-亚洲碰撞 新生代火山作用 地球化学 构造演化 

分 类 号：P588.14[天文地球—岩石学]