碰撞后岩浆作用与陆壳生长:以柴北缘超高压变质带为例  

Post-Collision Magmatism and Continental Crust Growth in Continental Orogenic Belt:An Example from North Qaidam Ultrahigh-Pressure Metamorphic Belt

作　　者：周辰傲 宋述光[1] Zhou Chen’ao;Song Shuguang(Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《地球科学》2023年第12期4481-4494,共14页Earth Science

基　　金：国家自然科学基金(No.91955202)。

摘　　要：碰撞后岩浆活动对于了解造山带垮塌和去根过程及陆壳生长具有重要意义.总结了柴北缘超高压变质带中形成于400~360 Ma的碰撞后花岗岩-辉长岩侵入体和镁铁质岩脉的年代学和地球化学特征.其中,花岗岩侵入体具有典型的I-型花岗岩特征,形成于壳幔相互作用的岩浆混合.来自地幔的镁铁质岩脉可以划分为两组:(1)392~375 Ma中基性岩脉;(2)约360Ma超基性岩脉.其地球化学特征表明,镁铁质岩脉的微量元素和同位素随形成时间的变新而逐渐亏损,地幔源区从岩石圈地幔变为软流圈地幔.这种源自地幔的镁铁质岩浆活动是碰撞后岩浆活动开始和造山带垮塌的关键指标.结合碰撞后岩浆作用的特征,提出了一个地球动力学模型来解释柴北缘约35百万年(Ma)的造山带垮塌去根过程,在395~375 Ma发生缓慢的岩石圈地幔侵蚀,360 Ma前岩石圈发生拆沉作用,岩石圈地幔垮塌,同时软流圈地幔上升.地幔岩浆的加入表明碰撞后阶段是大陆生长的重要时期.The post-collision magmatic activity is of great significance to understand the orogenic collapse,delamination and continental crust growth.In this paper it summarizes the geochronological and geochemical characteristics of post-collisional magmatism at 400-360 Ma in the North Qaidam ultrahigh-pressure metamorphic belt.The granite intrusions have I-type characteristics and were formed by the crust-mantle magmatic mixing.Mafic dykes can be divided into two groups:(1)Intermediate-basic dykes at 392-375 Ma;(2)Ultrabasic dykes about 360 Ma.The geochemical characteristics show that the trace elements and isotopes of mafic dyke are gradually depleted with time,and the mantle source changes from lithospheric mantle to asthenosphere mantle.The mafic magmatic activity is the key of post-collision magmatic activity and orogen collapse.Combining the feature of magmatism after the collision,it proposes a geodynamic model to explain the activities of lithosphere and asthenosphere mantle in post-collision stage about 35 million years(Ma),the unrooting process of orogeny began at slow lithospheric mantle erosion in 395-375 Ma,and ended up with lithosphere delamination and asthenosphere upwelling at 360 Ma.The addition of mantle magma indicates that the post-collision stage is an important period for continental growth in earth history.

关 键 词：大陆碰撞 碰撞后岩浆作用 造山带垮塌 拆沉作用 陆壳生长 岩石学 地球化学 

分 类 号：P597[天文地球—地球化学]