| 青藏高原南部岩脉分布及其研究意义 |
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| 引用本文： | 赵志丹,唐演,朱弟成,刘栋,王青,董国臣,周肃,莫宣学.青藏高原南部岩脉分布及其研究意义[J].岩石学报,2021,37(11):3399-3412. |
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| 作者姓名： | 赵志丹 唐演 朱弟成 刘栋 王青 董国臣 周肃 莫宣学 |
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| 作者单位： | 中国地质大学地质过程与矿产资源国家重点实验室, 地球科学与资源学院, 北京 100083 |
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| 基金项目： | 本文受国家自然科学基金项目（9206220026、42073035）、第二次青藏高原综合科学考察研究项目（2019QZKK0702）和国家重点研发计划项目（2016YFC0600304）联合资助. |
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| 摘 要： | 青藏高原是面积大、海拔高、时代最新的经典碰撞造山带,其演化过程被记录在各类地质作用中,包括各类岩浆作用。岩脉是与其他类型岩浆作用具有相似矿物成分的小规模侵入体,德国人Harry Rosenbusch早在1877年对其开展了系统研究。区域上大规模产出的基性岩墙群经常发育在伸展构造环境,并被认为代表地质历史时期发生的大陆裂解作用,其深部则与地幔柱或者热点存在相关。在青藏高原的羌塘地体、拉萨地体和喜马拉雅造山带发育了不同类型的岩脉或岩墙群。在羌塘地体中部出露面积约为40000km2的早二叠世（约283Ma）基性岩墙群属于大火成岩省（LIP）岩浆作用,与二叠纪中特提斯洋的初始打开有关。在西藏南部的特提斯喜马拉雅带产出的时代约为132Ma的白垩纪措美-班伯里大火成岩省岩浆作用,覆盖面积超过50000km2,其最早的岩浆作用可能代表了特提斯喜马拉雅之下大陆裂解之前孕育克格伦地幔柱头部的相关岩石圈伸展作用,并继续裂解导致了印度与澳洲大陆的裂解分离。本文着重讨论了高原南部的白垩纪以来的岩脉,它们主要发育在拉萨地体南部,蕴含了岩浆作用与构造作用的双重信息。它们具有不同的产状、成分、年龄和成因,对于揭示冈底斯弧演化、印度与亚洲大陆的碰撞过程,以及碰撞导致的高原应力状态变化等都具有重要的意义。高原南部岩脉主要分为三期：（1）时代约为90Ma的岩脉,具有玄武质到中酸性的成分,主要侵位在日喀则白垩纪弧后盆地,例如在南木林县南部出现的基性-酸性双峰式岩浆作用,可能代表了冈底斯岩浆弧之上发育的伸展作用。（2）时代约为50Ma的同碰撞期岩脉,主要侵入到林子宗火山岩、冈底斯岩基或者白垩世设兴组/昂仁组沉积地层等单元中,它们发育时间为60~41Ma,其峰期作用时间与冈底斯岩浆大爆发的时间一致,可能受控于深部俯冲的特提斯洋洋壳的断裂作用。（3）碰撞后中新世岩脉,多具有埃达克质岩石的地球化学性质,与区域上钾质-超钾质火山岩和埃达克质侵入岩的时代一致,它们是高原南部加厚下地壳部分熔融作用的产物,可能受控于下地壳拆沉作用或者与南北向裂谷带密切相关的板片撕裂有关。这些岩脉的延伸方向既有南北向,也有东西向,在构造上可能代表了高原隆升到最大高度后深部拆沉作用导致的山体垮塌伴生的伸展构造有关。
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| 关 键 词： | 岩脉 岩墙群 地幔柱 伸展作用 拉萨地体 青藏高原 |
| 收稿时间： | 2021/9/1 0:00:00 |
| 修稿时间： | 2021/10/28 0:00:00 |
Distribution and its significance of dikes in southern Tibetan Plateau |
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| ZHAO ZhiDan,TANG Yan,ZHU DiCheng,LIU Dong,WANG Qing,DONG GuoChen,ZHOU Su,MO XuanXue.Distribution and its significance of dikes in southern Tibetan Plateau[J].Acta Petrologica Sinica,2021,37(11):3399-3412. |
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| Authors: | ZHAO ZhiDan TANG Yan ZHU DiCheng LIU Dong WANG Qing DONG GuoChen ZHOU Su MO XuanXue |
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| Institution: | State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China |
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| Abstract: | The Tibetan Plateau is a typica collisional orogenic belt, with the biggest area, highest average altitude, and the youngest age on the world. Its evolutional processes were recorded in different geological events, including different type of magmatism. Dikes, which represent minor intrusions with mineral compositions corresponding to most other igneous rock types, has been studied since 1877 by Harry Rosenbusch. Large scale regional mafic dike swarms are often intruded in extensional tectonic environment, and are trend to represent continental break-up in geological history, and were linked to mantle plume or hot spots coming from below. Multiple type dikes emplaced on the Tibetan Plateau, including Qiangtang terrane, Lhasa terrane, and the Himalayan orogenic belt. The Early Permian (ca. 283Ma) mafic dike swarms which areal extent of ~40000km2 in the middle of the Qiangtang terrane suggest a Large Igneous Province (LIP), which has been linked to the initial opening of the Meso-Tethys Ocean during the Permian. The dike swarms outcropped on the Tethyan Himalaya in southern Tibet, which were named ~132Ma Comei-Bunbury LIP covering area more than 50000km2, are possibly related to the incubation of the Kerguelen plume head beneath the Tethyan Himalaya during pre-breakup lithospheric extension, and finally led to the break-up of India and Australia. This paper introduces mainly the dikes in the southern part of the plateau, which intruded in the southern Lhasa terrane since Cretaceous, which contain double information of magmatism and tectonism. These dikes show varies occurrence, composition, age, and petrogenesis, and play important role in revealing the tectonic evolution of the Gangdese arc, collisional processes between Indian and Asian continents, and the plateau stress regime in response to the collision. The dikes in southern plateau, focus mainly in three periods:(1) The ~90Ma dikes with basaltic to intermediate composition emplaced mainly in the Xigaze Cretaceous back arc basin. These dikes, such as with bimodal composition in Namling area, may suggest the extension processes on the Gangdese magmatic arc. (2) The ~50Ma syn-collisional dikes intruded into the Linzizong volcanic succession, Gangdese batholith, or the sedimentary strata of Cretaceous Shexing Formation/Angren Formation. These dikes emplaced during the times from 60Ma to 41Ma, with the same time span with the magmatic "flare-up", which explained to be related to the break-up of subducted Tethyan oceanic crust. (3) The post-collisional Miocene dikes showing geochemically adakitic composition, occurred within the age span of the potassic and ultrapotassic volcanics, and adakitic intrusions. They were generated from the partial melting of thickened lower crust caused by delamination or detachment related to N-S normal fault system. These dikes trending N-S or E-W directions also represent the extension that possibly indicate the uplift or collapse of the plateau thereafter it achieved the highest attitude. |
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| Keywords: | Dike Dike swarm Mantle plume Extension Tibetan Plateau |
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