西昆仑康西瓦地幔包体的研究及其对碰撞造山带深部地幔动力学过程的制约

The Pamir-west Kunlun is a textbook example of collisional orogen formed by collision between the Indian and Tarim plates during Ceonzoic. However, the mantle geodynamic processes beneath this orogeneic belt during Cenozoic remain hotly debated. Mantle xenoliths entrained in volcanic rocks are directly from deep mantle and could provide important information on the nature of the sub-continental lithospheric mantle, which provides new insights for above disputes. In central and northern Tibet, the mantle peridotite xenoliths from the Cenozoic potassic rocks are only found in the Kangxiwa area. This study will conduct a comprehensive study including petrographic, geochemical as well as petrogenesis studies using systematic Nd-Sr-Os-O isotopes for Pliocene Kangxiwa potassic rock and mantle xenoliths and nearby Late Miocene Dahongliutan potassic rock. This study will answer three key questions: (1) the nature of the lithospheric mantle of the Pamir-west Kunlun during Cenozoic;(2) the mantle sources and petrogenesis of the potassic rocks and (3)the mantle geodynamic process of the Pamir-west Kunlun collisional orogen during Cenozoic.

帕米尔-西昆仑是印度-塔里木板块碰撞形成的新生代典型陆陆碰撞造山带，但目前对其新生代以来的深部地幔动力学过程存在广泛的争论。直接来源于岩石圈地幔的岩石-地幔包体，为解决上述争论提供了新的制约。康西瓦新生代钾质岩中的地幔橄榄岩包体是该区迄今为止在青藏高原中北部发现的唯一有地幔橄榄岩包体的出露点。本项目以康西瓦上新世钾质岩中的地幔包体及寄主岩为重点研究对象，并与邻区大红柳滩晚中新世火山岩对比，在详细岩石学研究的基础上，开展矿物学、元素与Nd-Sr-Os-O同位素示踪在内的地球化学研究。回答三个关键的科学问题：（1）帕米尔-西昆仑新生代地幔性质；（2）钾质岩的地幔源区和成因机制；（3）帕米尔-西昆仑碰撞造山带新生代深部地幔动力学过程。

青藏高原广泛分布新生代钾质岩，少量钾质岩含有地幔包体。但是，目前对于钾质岩的地幔源区，岩石成因及其深部动力学过程，和高原富集地幔的形成过程仍然存在争议。本项目通过对西昆仑地区新生代钾质岩和其中的地幔包体开展了详细的岩石学、年代学、矿物和全岩元素和同位素地球化学的研究，揭示了西昆仑新生代钾质岩的地幔源区和岩石成因，及其与印度和欧亚板块大陆俯冲作用和高原隆升的关系；探讨了西昆仑新生代地幔富集过程。首次系统定量估算了中亚造山带（北疆）地壳生长速率，提出了增生造山过程中大陆地壳生长的非均匀性。发现洋内弧大陆地壳成熟新机制，提出了洋内弧地壳自身的化学风化和地壳循环作用可以导致其地壳成熟。