造山带岩石圈去根作用的地震层析证据及其构造意义

TOMOGRAPHIC EVIDENCES FOR SLAB BREA KOFF IN OROGENIC BELTS AND ITS TECTONIC IMPLICATIONS

造山带岩石圈去根作用作为碰撞后或造山后阶段构造-岩浆活动的重要机制,是研究造山带大地构造演化不可或缺的环节。近年来通过地震层析成像技术获得的一系列成果表明俯冲板片发生断离/拆离作用残留在对流地幔中,表现为高导低阻而冷的高速体;这些被断离/拆离的板片直接记录了造山带巨厚岩石圈去根作用。板片断离/拆离作用导致岩石圈深部伸展-减薄作用和热的软流圈地幔上隆,从而引起强烈的交代岩石圈地幔部分熔融作用和断陷盆地的形成。

Removal of the thickened lithosphere contributes to the post-collisio nal /post-orogenic tectono-magmatic activities in oro genic belts.As an important stage in the understanding of the evoution of orogenic belts,it is nec essary to find where these subducted slabs had been and how they were removed at mantle depths after c ontinent-continent collision or ocean-continent collision.Re-cent results from seismic tomograph y demonstrate that subducted oceani c lithosphere can be observed globally as slabs of relatively high seismic velocity in the upper as well as lower mantle.These detached /separated slabs has direc tly recorded the unrooting history o f the thickened lithosphere beneath collisional belts and their removal would certainly resulted in the thinning of mantle litho-sphere,triggering partial melting of pre-existent metasomatized upper mantle peridotites.As a consequence,it brings about the extensive magmatism and formation of fa ult-rifting basins around orogenic belts.