Abstract: Lithosphere delamination is an important way for compositional and structural evolution of collisional orogens. Geotectonic research, geophysical survey and geochemical analysis have revealed that the lithosphere of East Qinling-Dabie Mountains had delaminated intensively in Mesozoic. However, the extensive Mesozoic metamorphism and magmatism have been weakly related to lithosphere delamination. Based on a comprehensive review on research results of metamorphic rocks, the authors argue that the formation and exhumation of UHPM (ultra-high pressure metamorphite) experienced two stages, i.e., cold slab subduction and exhumation during 240～200Ma, and lithosphere delamination and thermal exhumation during 196～163Ma. The rapid thermal exhumation, co-occurred with extensive regional metamorphism and intermediate-acidic magmatism, implied that the subducted slabs had broken off and delaminated. The p-T-t path of UHPM consists of two curves, i.e., a barrette-like curve reflecting the process of cold slab subduction and exhumation (cold overthrusting), and a crescent curve representing the thermal exhumation after slab breakoff. By statistically analyzing of isotopic ages for granitoids and commenting on previous studies, the authors preliminarily determine that a large volume of granitoids developed during 200～100Ma, predominately formed in the period of 150～100Ma, with the peak age at about 130Ma. The inferred lithosphere delamination from the development of granitoids occurred slightly later than that deduced from researches on metamorphic rocks. Distant effect of Jurassic collisions of Qiangtang terrane, Lasa terrane and Paleo-Pacific land onto the Eurasian land made East Qinling-Dabie Mountains in a compressional circumstance for a long time, and suppressed its orogenic extension; whereas, Cretaceous late-collisional extension and appearance of West Pacific trench-arc-basin system relieved East Qinling-Dabie Mountains of external compression, instantly result in violent orogenic lithosphere delamination-extension and depressurized-calefactive melting, and consequently, led to the formation of large scale Early Cretaceous granitoids and intermediate-acidic volcanic rocks. In conclusion the magmatism caused by lithosphere delamination in East Qinling-Dabie Mountains occurred in the transition from compression to extension in the period of J₃-K₂.

Key words: east Qinling-Dabie Mountains, lithosphere delamination, granitoid, UHPM(ultra-high pressure metamorphite), p-T-t path, transition from compression to extension

摘要： 岩石圈拆沉是碰撞造山带物质成分调整和构造演化的重要方式之一。构造地质研究、地球物理探测和地球化学分析等都已揭示东秦岭-大别造山带曾在中生代发生岩石圈拆沉，但有关中生代变质作用和岩浆活动与岩石圈拆沉的内在联系研究却较为薄弱。通过全面评述该区变质岩研究成果，作者认为：超高压变质岩的形成和剥露经历了240～200Ma的板片冷俯冲冷折返和196～163Ma的岩石圈拆沉热折返；热折返伴随了广泛而强烈的区域变质作用和中酸性岩浆活动，指示板片断离拆沉的发生；超高压变质岩p-T-t轨迹由两部分组成，即反映板片冷俯冲冷折返过程的发夹状曲线和指示板片断离拆沉热折返过程的新月形曲线。通过对花岗岩类同位素年龄统计和前人研究成果的评述，初步确定在200～100Ma之间发育大量花岗岩类，并集中在150～100Ma为主(即侏罗纪—白垩纪之交)，高峰时间为130Ma左右；花岗岩类大量发育指示了岩石圈拆沉的存在，且滞后于根据变质岩研究所揭示的拆沉时间。羌塘地体、拉萨地体和西太平洋古陆在侏罗纪与欧亚大陆拼贴碰撞的远距离效应使东秦岭—大别造山带长期处于挤压环境，伸展作用被抑制；白垩纪的碰撞晚期伸展和西太平洋沟弧盆体系的远距离效应使东秦岭—大别地区的外部挤压消失，导致造山带岩石圈迅速强烈拆沉伸展和减压增温熔融，从而形成大规模早白垩世花岗岩类和中酸性火山岩。总之，东秦岭—大别地区岩石圈拆沉所导致的岩浆活动主要发生在J₃—K₁的挤压伸展转变期。

关键词: 东秦岭—大别造山带, 岩石圈拆沉, 花岗岩类, 超高压变质岩, p-T-t轨迹, 挤压伸展转