地幔通道流:青藏高原大规模生长的深部机制  

Mantle flow:The deep mechanism of large-scale growth in Tibetan Plateau

作　　者：侯增谦[1] 许博 郑远川[2] 郑洪伟[1] 张洪瑞[1] Zengqian Hou;Bo Xu;Yuanchuan Zheng;Hongwei Zheng;Hongrui Zhang(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学(北京),地质过程与矿产资源国家重点实验室,北京100083

出　　处：《科学通报》2021年第21期2671-2690,共20页Chinese Science Bulletin

基　　金：国家重点研发计划(2016YFC0600310);中国科学院战略性先导科技专项(XDA20070304)资助。

摘　　要：地处喜马拉雅造山带后陆区的青藏高原,其成因与生长一直存在争议.基于前人资料和我们的综合研究发现,西起西昆仑,东经北羌塘和昆仑山口,向南折向芒康-大理,直抵红河-哀牢山,发育一条跨越青藏高原不同构造单元的长达数千公里的巨型高热流带,并显示由高原内部向东北部边缘迁移之势.沿此巨型高热流带,岩石圈地幔部分熔融产生的钾质镁铁质岩-煌斑岩群(42~32 Ma)和钾质碱性岩-碳酸岩(27~7 Ma)、软流圈减压熔融产生的洋岛玄武岩(ocean island basalts, OIB)(16~1 Ma),以及中下地壳熔融产生的钾质长英质岩(40~0.3 Ma)呈群聚式断续展布;以峰期麻粒岩相变质为特征的高温深变质带与大型走滑断裂带(40~17 Ma)相伴发育;下地壳麻粒岩包体具有高达800°C的变质温度,地幔橄榄岩包体显示地幔垂直流动特征;地球物理探测所揭示的6个大型低速异常体呈群聚式、等间距、断续式展布.我们提出:印度大陆岩石圈地幔俯冲触发了亚洲大陆软流圈涌动,后者沿后陆区若干地幔通道垂直上涌,热蚀并吞噬地幔岩石圈,直抵地壳底部.这些"地幔通道流"源于400 km深处,形成于晚(硬)碰撞以来(≤40 Ma),不仅为维持青藏高原隆升提供了深部热能,而且为高原地壳生长输送了新生幔源物质,同时引发中下地壳塑性流变和侧向流动,并驱动青藏高原向北东方向侧向生长.The origin and growth of the Tibetan Plateau,located in the back lands of the Himalayan orogenic belt,have always been considered controversial.Based on data from previous studies and our own comprehensive research,we found that a giant high-heat flow zone thousands of kilometres long developed,spanning different tectonic units of the Qinghai-Tibet Plateau,encompassing the Kunlun,Qiangtang,Mangkang-Dali and Honghe-Ailao Mountain ranges.All these tectonic units show a tendency to have migrated from the inner plateau towards the northeast edge.Several rock groups are distributed along this giant high-heat flow zone in a continuous pattern:The potassic mafic rock-lamprophyre group(42–32 Ma)and potassic alkaline rock-carbonate rock(27–7 Ma)from partial melting of lithosphere and mantle,the ocean island basalt(16–1 Ma)from decompression melting of the asthenosphere,and the potassic feldspathic rock(40–0.3 Ma)from the melting of the middle-lower crust.The high temperature deep metamorphic zone,characterized by granulite facies metamorphism in the peak period,was accompanied by a large strike-slip fault zone(40–17 Ma).The metamorphic temperatures of the lower crust granulite xenoliths rose to 800°C.However,the mantle peridotite xenoliths show characteristics of vertical mantle flow.The six large low-speed anomalous bodies revealed by geophysical exploration are clustered,equidistant,and intermittently distributed.Our research proposes that the Indian continental lithospheric-mantle subduction triggered the Asian continental asthenosphere surge,which caused vertical upwelling along a number of mantle channels in the posterior continental region,thermally corroding and engulfing the mantle-lithosphere and reaching as far as the bottom of the crust.These"mantle flow channels"came from depths around 400 km.They began forming after the late(hard)collision 40 Ma,and not only provided deep heat to sustain the Tibetan Plateau uplift but also prepared new mantle source material for the plateau’s crustal growth.At th

关 键 词：青藏高原 碰撞造山 地壳生长 软流圈上涌 地幔通道流 

分 类 号：P542.5[天文地球—构造地质学]