大别-苏鲁区超高压变质岩的多期构造变质演化

Polyphase tectonometamorphic evolution of UHP metamorphic rocks in the Dabie-Sulu region,east-central China.

对大别-苏鲁地区超高压(UHP)变质岩的详细构造和岩石学研究揭示了其复杂的构造变质演化历史。除前超高压事件外,至少可识别出5个相继发育的构造变质事件或阶段(D_1-D_5)。D_1和 D_2同超高压事件与三叠纪(250～230Ma)中朝克拉通和扬子克拉通间的大陆深俯冲及碰撞有关,而超高压后的 D_3和 D_4韧性变形及其伴生的减压部分熔融作用和退变质作用事件,则是超高压岩石向中上地壳折返过程中(230～140Ma)发生的。碰撞后形成的 D_4构造,主导了大别-苏鲁超高压和高压变质带区域尺度的构造格架。第5阶段的构造以摩擦或摩擦-粘性过渡性变形机制为主,并伴随有大规模的未变形的花岗质岩体就位,该期构造热事控制了现今大别-苏鲁地区的地貌学特征。新的构造和岩石学资料并结合可利用的地质年代学和地球化学等资料,提出一个涉及中朝与扬子克拉通间三叠纪大陆深俯冲、碰撞及相继超高压变质岩石向地表的多期折返构造变质演化模式。

A structural and petrological study of UHP metamorphic rocks in the Dabie-Sulu region, east-central China, revealed their polyphase tectonometamorphic evolution. Excluding pre-peak UHP event, five major, at least, sequential tectonometamorphic events （D1-D5） are recognized. Syn-UHP D1 and D2 events are related to Triassic （250 -230Ma） deep subduction and collision between the Sino-Korean and Yangtze cratons, while post-UHP D3 and 94 ductile deformations in association with decompressianal partial melting and retrogressive metamorphism took place during exhumetion （230 - 140Ma ） of the UHP rocks to the upper crust. The 94 structures formed during post-collisional extension dominate in some degree the map pattern of the Dabie-Sulu UHP and HP metamorphic belts. The final event （ D5 ） is characterized by a fractional or fractional-viscous transition deformation mechanism, and associated with the emplacement of large volumes of undeformed granite plotons, which controls the present-day geomorphology of the Dabie-Sulu region. The new presented structural and petrological data, combined with available geochronological and geochemical constraints are used to assess a speculative tectonometamorphic evolution model involving deep continental subduction and collision between the Sino-Korean and Yangtze cratons leading to UHP metamorphism, subsequent polyphase exhumation of the UHP metamorphic rocks toward the surface.