青藏高原东缘构造演化的SHRIMP锆石U-Pb年代学框架

Eastern Margin of the Tibetan Plateau: A Window to Probe the Complex Geological History from the Proterozoic to the Cenozoic Revealed by SHRIMP Analyses

青藏高原东缘一直被普遍认为是一个吸收印度一欧亚大陆碰撞变形的调节带。本文所获得的最新SHRIMP锆石U～Pb测年结果显示：青藏高原东缘具有更加复杂的地质历史。测年结果表明，高原东缘最古老的前寒武纪结晶基底形成于古元古代（2401～1912Ma）。这一古老基底首先受到中元古代构造热事件（1361～1040Ma）的影响，随后受到新元古代与弧岩浆活动有关构造热事件（791～817Ma）的强烈改造。松潘一甘孜复理石杂岩的基底是亲洋壳型的，形成于晚新元古代的大陆裂解作用（681～655Ma）。高原东缘的前寒武纪微地块可能是由这次裂解作用从扬子或青藏地块拉裂出去形成的。这些微陆块先增生拼贴于东冈瓦纳大陆、然后又从中裂离，并最终卷入高原东缘的特提斯构造演化过程中。伴随东冈瓦纳大陆裂解，高原东缘古特提斯洋于石炭纪至二叠纪早期拉开（328～292Ma），经早中生代弧一陆碰撞作用闭合（224-213Ma）。中侏罗世这一地区发育显著的构造岩浆活动（175Ma），但其动力学背景仍不十分清楚。晚白垩世岩浆活动（97Ma）可能是印度板块初始俯冲阶段的产物。新生代岩浆作用（18Ma）与陆陆碰导致的大规模走滑断层作用所引起的同熔作用有关。

The eastern margin of the Tibetan plateau （EMTP） has been traditionally considered as an adjustment for absorbing the deformation caused by India--Asia collision. However, SHRIMP analyses showed that the EMTP has a complex geologic history. The oldest Precambrian basement in the EMTP formed in the Paleoproterozoic （2401-1912 Ma）, was affected first by Mesoproterozoic tectonothermal events （1361-1040 Ma ） and then by the strongly arc-related magmatic events in the Neoporterozoic （791 - 817 Ma）. The basement of the Songpan--Ganzi block is of affinity with oceanic crust derived from the Neoproterozoic rifting （681-655 Ma）, and by which the Precambrian blocks in the EMTP might be split off from the basement of the Yangtze block and / or the Tibetan plateau. Those blocks assembled with and then were disintegrated from the east Gondwanaland and finally involved in the Tethys evolution in the EMTP. Tethys in eastern Tibet opened in the Carboniferous to the early Permian （328- 292 Ma） followed with breakup of the east Gondwanaland, and then closed in the early Mesozoic magmatism occurred in the middle Jurassic （175 Ma） by arc-continent collision （224- 213 Ma）. Significant in this area, but its dynamics still remains unclear. The timing of magmatism at the beginning of the late Cretaceous （97 Ma） might represent the initial subduction of India. Cenozoic magmatism in the EMTP （18 Ma） was related to syntexis caused by large-scale strike-slip faulting.