大别山超高压变质杂岩的折返

作为世界上规模最大的一个超高压变质带，大别山超高压变质杂岩是扬子板块 与中朝板块在三叠纪碰撞造山的产物，表现为扬子板块呈北北东向斜向俯冲到中朝板块之下。 超高压变质杂岩的折返机制是个复杂的动力学过程，折返速率也随时间推移而变慢。早期阶段 （三叠纪－早侏罗纪）同碰撞期浮力驱动下高压－超高压变质杂岩在俯冲带内沿道冲－韧性剪 切断裂快速挤侵（ｅｘｔｒｕｓｉｏ）到地壳层位，折返速率高达４ｍｍ／年；中期伴随着巨厚造山带山根的 拆沉，上部发生拉张塌陷，使超高压变质杂岩进一步减压，但折返速率缓慢，～(４０)Ａｒ／~(３９)Ａｒ年代学显 示１１７Ｍａ前它们仍处在地壳的较深部；晚期伴随着晚侏罗－早白垩纪花岗质岩浆的上升侵位， 超高压变质杂岩进一步抬升，同时低角度正断层发育，此阶段的折返机制类似于变质核杂岩模 型。整个折返过程中剥蚀一直在起作用。

EXHUMATION OF THE DABIE SHAN ULTRAHIGH PRESSURE METAMORPHIC COMPLEX

As a largest-scale ultrahigh-pressure zone in the world, the Dabie Shan ultrahigh-pressure metamorphic complex was the product of collision orogenics between Yangtze craton and Sino Korean craton in Triassic, in which the Yangtze plate was obliquely subducted at NNE direction beneath Sino-Korean plate. The exhumation mechanism of the UHP rocks is a complex dynamic process, exhumation rate dropping down with time. In early stage(from T to J_1 ), syncollision extrusion of UHP rocks move fast upward the crust along the obduction-ductile shear fault in the subduction belt drived by moved buoyancy force with the exhumation rate up to 4mm/year. In middle stage, with the delamination of the root of the thickened orogene belt, extension developed upper part, which caused the UHP rocks decompression, but the rate was slower, 40Ar/ 39Ar geochronology shows that the UHP rocks were still in lower part of the crust before 117Ma; In late stage, with the intrusion of the granitic magma in Cretaceous, the UHP rocks were lifted further, and low-angle normal faults developed simultaneously. The exhumation mechanism in this stage is similar to metamorphic core comples model. The erosion was existence throughout the extrusion processes.