喜马拉雅造山带东、西构造结的地质特征与对比

喜马拉雅造山带的东、西两端分别有一个构造急剧转向的地区——构造结，这里是探讨喜马拉雅造山带构造演化的重要场所．区域地质调查资料对比显示这2个构造结有：(1)相似的地貌景观；(2)相似的地质特征和演化历史，即都缺失喜马拉雅沉积岩(寒武纪—第三纪)；(3)结晶岩系中都有高压变质岩，且在10Ma以来均发生过深熔与混合岩化作用；(4)25Ma以来，特别是10Ma以来两地都经历了快速剥露和隆升作用；(5)印度板块一欧亚板块的碰撞时间接近，分别为75Ma和65Ma，均早于喜马拉雅造山带的其他地区．这些相似性表明：伸展拆离和以河流作用为主的地表过程是喜马拉雅造山带的东、西构造结快速剥露的主导因素；因强烈剥露减压所致的地壳部分熔融作用形成的岩浆向地表减压处的流动在构造结的演化过程中起着重要作用。

A Geological Comparison between the Eastern and Western Himalayan Syntaxes

There are two syntaxes, where orogenic structures turn sharply. They occurred in the eastern and western ends of the Himalayan belt respectively, and are the ideal places to discuss the evolution of the belt. The comparison of geological data from the eastern and the western syntaxes shows that they have: (1) similar geography; (2) geological features and evolution (both lost the Himalayan sediments of Cambrian-Tertiary); (3) similar high-pressure metamorphic rocks which overprinted by the re-melting of crust and migmatization younger than 10 Ma; (4) similar rapid uplifting experience since 25 Ma, especially since 10 Ma; (5) similar ages of the collision between India and Eurasia (75 Ma and 65 Ma in eastern and western syntaxes respectively) and much earlier than other places within the belt. The similarities suggest that: (1) detachment and surface processes (especially river process) would be the main reasons resulted in rapid denudation; and (2) the melts derived from the partial melting rocks in middle to low crust due to the denudation flowed and focused would play important roles on the evolutions of the syntaxes.