印度与欧亚大陆碰撞时限的古地磁研究进展与问题  

Paleomagnetic constraints on the onset of India—Eurasia collision: a synthesis

作　　者：张大文 颜茂都[2,3] ZHANG Dawen;YAN Maodu(College of Tourism and Environmental Resource,Zaozhuang University,Zaozhuang,Shandong,277160;Key Laboratory of Continental Collision and Plateau Uplift,Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing,100101;Center for Excellence in Tibetan Plateau Earth Sciences,Chinese Academy of Sciences,Beijing,100101)

机构地区：[1]枣庄学院旅游与资源环境学院,山东枣庄277160 [2]中国科学院青藏高原研究所大陆碰撞与高原隆升重点实验室,北京100101 [3]中国科学院青藏高原地球科学卓越创新中心,北京100101

出　　处：《地质论评》2019年第5期1251-1268,共18页Geological Review

基　　金：第二次青藏大科考基金资助项目(编号:2019QZKK0707);中国科学院战略性先导科技专项资助项目(编号:XDA20070201);中国科学院大陆碰撞与高原隆升重点实验室开放—合作基金项目(编号:LCPU201905)的成果;枣庄学院博士科研基金项目(编号:2018BS064)~~

摘　　要：古地磁学在限定印度—欧亚板块碰撞时限的研究中扮演着重要的角色。然而受磁倾角浅化、地球磁场长期变以及重磁化等诸多因素影响,不同时期获得的古地磁数据质量参差不齐,造成其限定的印度—欧亚大陆碰撞时限从65到20多百万年不等。本文针对这一现状,通过对拉萨陆块和特提斯喜马拉雅已有的晚白垩世—古近纪古地磁数据开展严格的可靠性评判,共筛选出10条有效数据(其中拉萨陆块9条、特提斯喜马拉雅1条),获得以下认识:①拉萨陆块晚白垩世期间基本稳定在10°~16°N,在始新世晚期—渐新世早期位于21.8+2.5/-2.3°N;②特提斯喜马拉雅在晚白垩世中期位于约34.2+4.4/-5.0°S,并与印度板块有基本一致的古纬度;③对于用来限定碰撞时限的晚白垩世晚期—始新世早期的古地磁结果,经评判分析,认为至少到目前为止,在明确磁倾角浅化及浅化程度、地球磁场长期变是否被平均掉和剩磁的原生性及重磁化程度等问题之前,还缺乏真正有效的古地磁数据。因此,总体来说,现有的古地磁数据在限定拉萨陆块与特提斯喜马拉雅碰撞时限的精确度方面,还有很大的提升空间,亟待针对存在争议的岩石地层单元开展更详细的磁学和非磁学相结合的综合研究进行验证,并在更多地区获得高质量的古地磁数据(尤其是晚白垩世晚期—古近纪)。此外,考虑到两个陆块呈近东西向的巨型狭长条带,其地质时期的展布方向会显著影响东、西部的古纬度,今后的相关古地磁研究应尽量分东、西部不同区域开展。Paleomagnetism played key roles in understanding the onset of India—Eurasia collision.However,the quality of the existing paleomagnetic data varies tremendously,such as due to inclination-shallowing,paleosecular variation and remagnetization issues,etc.,yielding controversial India—Eurasia collision time ranging from 65 to 20 Ma.In this paper,we carried out strict reliability assessments on the available Late Cretaceous—Paleogene paleomagnetic data from the Lhasa Block and Tethyan—Himalaya and obtained 10 pieces of reliable paleomagnetic data.The results suggested that:(1)the Lhasa Block has been stabilized at^10°to 16°N during Late Cretaceous and was located at^21.8+2.5/-2.3°N in the late Eocene—early Oligocene;(2)the Tethyan—Himalaya was located at^34.2+4.4/-5.0°S during the middle Late Cretaceous,similar to that of the India Plate,indicating that the Tethyan—Himalaya might have belonged to the northern part of the India Plate at least during between the Early Cretaceous and middle Late Cretaceous;(3)the present late Late Cretaceous—early Oligocene paleomagnetic data can only be regarded as references and are not qualified enough to constrain India—Asia collision before the inclination shallowing,paleosecular variation and remagnetization issues have been fully addressed.It is urgent to carry out further comprehensive magnetic and non-magnetic researches on the disputed rock units to check and validate the above factors and to acquire more reliable paleomagnetic data(especially the late Late Cretaceous—Paleogene)from wider areas around the Lhasa Block and Tethyan—Himalaya(especially the middle and western parts).Additionally,given the huge E—W trending long and narrow shape of the two blocks,slight rotation might cause significant difference in paleolatitudes between the east and west parts,future paleomagnetic analyses should be carried out on both the east and west parts of the region.

关 键 词：拉萨陆块 特提斯喜马拉雅 晚白垩世—古近纪 碰撞时限 古地磁 可靠性评判 

分 类 号：P318.44[天文地球—固体地球物理学]