青藏高原东部地壳、上地幔速度精细结构研究

The India-Eurasia collision (50Ma) initiates serial enigmatic and interesting scientific questions, such as, in the Songpan-Ganzi and Yidun terranes which are on the eastern edge of the Tibetan Plateau, Sinian-Lower Permian (610Ma-270Ma) strata are lithologically similar to Sinian-Lower Permian rocks of the western part of the Yangtze block, and Upper Permian metabasalts are part of the Emeishan large igneous province which is believed to have formed from the Emeishan mantle plume (260Ma). All of above phenomenon indicates that Songpan-Ganzi terrane, Yidun terrane and Yangtze block were contiguous at least until Late Permian time. Why there is a very steep topographic gradients exist between Songpan-Ganzi, Yidun terrane and Yangtze block at present? Even the steep topographic margin is steeper than that of the collision zone (South edge of the Tibetan Plateau). When did the Songpan-Ganzi, Yidun terrane uplift, before or after India-Erasia collision? If uplift happened before collision, is this responded to the activity of Emeishan ancient mantle plume? And is there some geologic “footprint” left in the stable Yangtze block? We plan to image the fine velocity structures (Vp, Vs and Vp/Vs) of crust and upper mantle by using the body wave traveltime tomography on the basis of high density stations data, and provide new seismology constraints on the interaction between different blocks and lithosphere deformation mechanism.

印－欧板块之间的碰撞现象（50Ma）引起了一系列值得关注和深入思考的科学问题，如在青藏高原东缘的松潘－甘孜、义敦地块内，震旦界至下二叠系（610Ma-270Ma）的地层岩性相似于扬子块体西部相应年代的地层岩性，上二叠系的玄武岩和峨眉山大火成岩省的玄武岩都是由260Ma的峨眉山古地幔柱活动所形成，以上表明，松潘－甘孜、义敦地块和扬子块体西部在晚二叠系前应属于同一整体，为何现今它们之间有非常陡峭的地势高度？其陡峭程度甚至超过了碰撞接触带（南缘区域）；松潘－甘孜、义敦地块是在印－欧板块碰撞后产生的隆升还是在碰撞前就已经隆升?若在碰撞前就已隆升，是否与峨眉山古地幔柱活动有关，在扬子稳定的陆核中是否会留存相关的地质活动“遗迹”？我们拟利用高密度的台站数据通过体波走时层析成像方法开展Vp，Vs和Vp/Vs的结构研究，获取地壳和上地幔的精细结构，揭示不同块体间的相互作用过程以及岩石圈变形隆升的深部原因。

印－欧板块之间的碰撞现象（50Ma）引起了一系列值得关注和深入思考的科学问题。已有研究表明松潘－甘孜、义敦地块和扬子块体西部在晚二叠系前应属于同一整体，为何现今它们之间有非常明显的地势高度变化差异？与青藏高东缘陡峭的地势相比，青藏高原东北缘和东南缘的地势变化较为平缓，前人已经提出很多模型来解释这一现象，但仍未达成统一意见。针对这一主要问题，使用中国地震科学台阵和川西流动台站的数据，本项目在青藏高东部开展高分辨的壳幔速度结构研究。研究结果表明：青藏高原下方是以低速异常为代表的低强度岩石圈，青藏高原周边区域（鄂尔多斯和四川盆地等块体）下方，则是以高速异常为代表的高强度岩石圈。根据研究结果，本项目提出一个推挤变形导致地势隆升的地球动力学模型：在以印度板块为代表的高强度岩石圈的推挤和阻挡作用下，低强度岩石圈产生挤压变形，其中水平缩短吸收印度板块的推挤作用，垂直向伸展导致高原的隆升。使用以上模型，可以解释青藏高原东部陡峭和平缓地势产生的深部原因。