作　　者： (易治宇）; (李忠海）; (许志琴）; (黄宝春）;

机构地区： 大陆构造与动力学实验室,中国地质科学院地质研究所,北京100037

出　　处： 《地球物理学进展》 2017年第4期1510-1520,共11页

摘　　要： 印度-亚洲的初始碰撞问题是当今地球科学研究的热点.印度-亚洲碰撞带西段经历了从弧陆碰撞到陆陆碰撞的复杂演化过程,重建这一过程有利于更为全面地揭示和理解陆陆碰撞及造山的动力学机制.本文对西构造结附近各个地体(西拉萨-喀喇昆仑、科西斯坦-拉达克及喜马拉雅地体)白垩纪以来的古地磁数据(6个原生及35个次生分量)进行了回顾和总结,古地磁原生分量指示亚洲大陆南缘和科西斯坦岛弧在碰撞前分别位于约14°N和赤道附近,很可能代表了陆陆及弧陆初始碰撞发生的位置;统计分析表明重磁化分量对应的古纬度在分布上存在3个显著的峰值(分别为约3°S^2°N、12°N及22°N),前两个峰值与原生分量指示的古纬度重叠,暗示重磁化可能与弧陆及陆陆初始碰撞伴随的造山作用有关;现有层析成像资料业已表明印度-亚洲碰撞带之下的地幔中存在两条带状分布的新特提斯洋残留洋壳,本文进一步通过初步的动力学数值模拟,表明现今残留洋壳的位置能够大致代表洋壳断离时古缝合带的位置,而该位置又与古地磁数据所揭示的初始碰撞位置基本一致.上述结果一致地表明印度-科西斯坦-亚洲之间弧陆及陆陆初始碰撞分别发生于近赤道及北半球低纬度地区(约14°N)附近,结合最新印度板块的运动轨迹及不同的大印度模型,推测上述弧-陆及陆-陆初始碰撞时间分别不晚于约62 Ma和约48 Ma. The initial collision between India and Asia is a hot spot of geoscience.The western segment of the collision zone,involved in complicated continent-arc-continent collision,is hence a key for understanding the process and mechanism of continent-continent collision.In this study,a comprehensive analysis was applied to the available paleomagnetic data（including 6 primary and 35 secondary components） obtained from the area near the western syntaxis（including the western Lhasa-Karakorum,Kohistan-Ladakh and Himalaya terranes）.The primary remanences of this compilation indicate that the Kohistan arc and the southern margin of Asia near the western syntaxis were originally located near the paleo-equator and about 14° N,respectively,and most probably represented the initial positions for the continent-arc and continent-continent collisions.Statistical analysis of paleolatitudes calculated from the secondary components defines 3 notable peaks at about 3° S～2° N,12° N and 22° N,respectively.The former two peaks overlap the paleolatitudes defined by the primary components,implying that the overprints were possibly associated with the orogenic processes accompanied by the initial collisions.Former studies based on global seismic tomography distinguished two remanent oceanic slabs of the Neo-Tethys from the mantle beneath the India-Asia collision zone,the positions of which are proposed,by a primary numerical modeling designed in this study,to have roughly represented the paleopositions of the paleo-sutures of the continent-arc-continent collision.The inferred paleopositions of the paleo-sutures are also compatible with the ones inferred from paleomagnetic data.The above analysis consistently supports that the initial contacts between India-Kohistan-Asia should have occurred near the paleo-Equator and low latitude of the northern Hemisphere（about 14° N）.Together with the trajectory of continent India since about 100 Ma and the assumption of different sizes of Greater India,the timing of initial contacts be

关 键 词： 印度 亚洲碰撞 古地理重建 古地磁 地震层析成像 数值模拟