全球典型大陆造山带中榴辉岩的折返机制:来自变质岩和地球物理的限制

The exhumation mechanism of eclogites in continental orogenic belts:Metamorphic petrology and geophysical constraints

大陆岩石圈深俯冲作用是地球科学领域的前沿热点,榴辉岩的折返机制是板块构造及动力学的关键科学问题。全球著名的大陆造山带中榴辉岩的p-T轨迹呈现差异性折返特征,为了揭示榴辉岩的折返机制,本文结合变质岩石学和地球物理学研究,选取3个典型大陆造山带——中生代—新生代的阿尔卑斯造山带、中生代的苏鲁—大别造山带和新生代的喜马拉雅造山带中的榴辉岩进行阐述。在阿尔卑斯造山带地区,地球物理研究结果发现,欧洲板块的俯冲造成了Adria地区下方的岩石圈存在明显厚度差异。同时,阿尔卑斯造山带Doria Maria和Pohorje地区以及Pohorje地区内部,榴辉岩折返历史也不尽相同,原因可能是亚德里亚大洋岩石圈断离后不同期次的逆冲推覆作用使其差异性斜向挤出。苏鲁—大别造山带中榴辉岩的快速折返,原因可能是华南板块与华北板块碰撞后岩石圈的拆沉或断离作用。在喜马拉雅造山带,西构造结和中喜马拉雅榴辉岩的折返存在差异性。在西构造结,那让和卡甘榴辉岩呈现不同的p-T轨迹和折返速率,变质岩石学和地球物理研究结果都表明它们的差异性折返很可能与印度-欧亚大陆碰撞过程中的构造挤压作用以及印度大陆岩石圈的断离作用有关。喜马拉雅造山带是年轻的正在进行造山活动的造山带,相较于古老的苏鲁-大别造山带,它更适合变质岩石学和地球物理学的综合研究。因此西构造结高压/超高压榴辉岩的折返机制——构造挤压和俯冲板块断离可应用于全球造山带。

The deep subduction of the continental lithosphere is a frontier hotspot in the field of earth science,and the exhumation mechanism of eclogite is a key scientific issue in plate tectonics and continental dynamics.The p-T paths of eclogites from the world-famous continental orogenic belts show differential exhumation characteristics.To explore the exhumation mechanism in this study,metamorphic petrology and geophysical investigations were conducted on eclogites from three typical continental orogenic belts-Mesozoic-Cenozoic Alps,Mesozoic Sulu-Dabie,and Cenozoic Himalayas.The geophysical investigation found that,in the Alpine orogenic belt,subduction of the European plate resulted in large variations in lithospheric thickness beneath the Adria area.At the same time,the exhumation histories of eclogites are not the same in the Doria Maria and Pohorje areas of the Alpine orogenic belt versus in the greater Pohorje area,which,then,is probably due to the differential oblique extrusion of thrusting nappes from different periods after the break-off of the Adriatic ocean lithosphere.In the Sulu-Dabie orogenic belt,rapid exhumation of eclogites is likely be caused by the delamination or break-off of the lithosphere after the collision of the South and North China blocks.In the Himalayan orogenic belt,there are differences in the exhumation histories of eclogites in the middle Himalayas,and so are the differences in the p-T path and exhumation rate of eclogites from Naran versus from the Upper Kaghan Valley in the Western Himalayan Syntaxis.The differential exhumation,according to both metamorphic petrology and geophysical studies,is likely related to the tectonic extrusion and the break-off of the Indian continental lithosphere during the collision of the Indian and European plates.The Himalayan Orogen is a young and ongoing orogeny,thus it is more suitable for comprehensive metamorphic petrology and geophysical studies compared to the ancient Sulu-Dabie Orogen.Therefore,the exhumation mechanism of(ultra)-high-pressure eclogites in the Western Himalayan Syntaxis,i.e.,tectonic compression and the break-off of subducting plate,can be applied to global orogenic belts.