【摘要】 氦同位素研究确定,大别山榴辉岩等超高压岩石矿物并非来自地幔,而是生成于岩石圈地幔顶部。结合深部地球物理,提出一个岩石圈地幔顶部形成超高压矿物的模型。即表壳岩石俯冲到岩石圈地幔顶部,形成超高压变质岩,然后由于地壳隆升、剥蚀,出露到地表。冲入大别山地区岩石圈地幔顶部的表壳岩石之所以会形成超高压变质岩是因为它同时受到板块会聚的强大压力和蘑菇云地幔产生的高温。沿六安—黄石综合地球物理、地球化学剖面实测的热流剖面显示,南大别构造带的莫霍面温度达到1307℃,超高压变质作用所需要的高温条件至今依然存在。已有文献表明黏塑性的大陆板块在碰撞俯冲时,岩石圈地幔的变形远比通常认定的那种刚性板块俯冲要复杂。俯冲呈对冲形式,方向大都向下,在岩石圈地幔中,俯冲板块和制动板块像麻花一样相互楔入,在深部甚至改变俯冲方向,制动板块反而向俯冲板块俯冲。当岩石圈地幔顶部局部熔融时,无疑俯冲物质将向局部熔融层扩散,在高温高压下发生超高压变质作用。大别山变形晚期,在核部形成"背形穹隆"。将形成于岩石圈地幔顶部的超高压变质岩带到地表,接受剥蚀而出露地表。已有资料表明,全球主要超高压变质岩的分布带与古特提斯洋分布有关,古特提斯洋碰撞带是全球最长的一条陆内碰撞俯冲带。它们是否均为黏塑性板块之间的软碰撞、在邻近碰撞带的岩石圈地幔顶部是否都有高温的区域则尚待验证。更多还原

【Abstract】 Study of helium isotrope of UHP rocks in the Dabie area shows that minerals of UHP rocks such as eclogite in the Dabie area were not derived from the mantle but formed at top of the lithospheric mantle (LID). According to the deep geophysical data, the authors propose a new model for the formation of UHP minerals at the lithospheric mantle lid, i.e. when supracrustal rocks were subducted to the LID, UHP metamorphic rocks were formed at strong pressures caused by convergence of plates and high temperatures produced by the mushroom cloud mantle, and then were exposed at the surface due to doming and erosion of the crust. The available literature indicates that when visco-plastic continental plates collided and were subducted the deformation of the LID was much more complex than the deformation due to subduction of a rigid plate. The direction of subduction was mostly vertically downward, and the subducted plate and retro-side wedged each other like fried dough twist and the subducting direction might change at depth. When the LID partially melted, subducted materials would spread in the locally molten layer and formed UHP metamorphic rocks at high pressures and temperatures. The global distribution of main UHP metamorphic rocks is associated with the distribution of the Paleo-Tethys Ocean. However, it is not certain whether both of them were soft collision between visco-plastic continental plates and whether there were high-temperature regions at the LID near the collision zone.更多还原