A great amount of new S-wave data has been combined to image the mantle structure down to lower mantle depth near the southeastern margin of Eurasia and understand the tectonics in South China since the Mesozoic.Our r...A great amount of new S-wave data has been combined to image the mantle structure down to lower mantle depth near the southeastern margin of Eurasia and understand the tectonics in South China since the Mesozoic.Our results reveal a large-scale structure beneath the South China Sea,with a prominent,broad low-velocity feature of at least 1500-km wide in and below the mantle transition zone(MTZ)and a pronounced low-velocity feature of nearly 500-km wide in the lowermost mantle.Together these features may represent the head-and-tail of an upwelling mantle plume that has interacted with and deformed by the subducting plates in the region.The Andaman-Sumatra plate is seen subducting steeply without stagnation in the MTZ over the large-scale low-velocity structure,suggesting that the upwelling mantle may have exerted significant influence on the overlying plate tectonics.Our results suggest a long-term extensional regime near the southeastern margin of Eurasia,which may help to understand the formation of the large-scale intra-plate magmatism and mineralization with accumulation of huge amount of rare metal elements in South China during the Mesozoic,and the continental breakup,the southeastward extrusion of Indochina,and the opening of the South China Sea during the Cenozoic.展开更多
Despite extensive efforts to understand the tectonic evolution of the Jiangnan Orogen in South China,the orogenic process and its mechanism remain a matter of dispute.Previous geodynamic studies have mostly focused on...Despite extensive efforts to understand the tectonic evolution of the Jiangnan Orogen in South China,the orogenic process and its mechanism remain a matter of dispute.Previous geodynamic studies have mostly focused on collisional orogeny,which is commonly invoked to explain the Jiangnan Orogen.However,it is difficult for such hypotheses to reconcile all the geological and geophysical data,especially the absence of ultrahigh-pressure metamorphic rocks.Based on the magnetotelluric data,we present a group of resistivity models produced through the combination of two-dimensional and three-dimensional inversions,revealing the geo-electrical structures of Jiangnan and a typical collisional orogen.In our models,the resistive crust is separated into three parts by a prominent conductive layer with opposite dipping directions on both sides.A special thrust-nappe system,which is different from that developed in a typical collisional process,is revealed in the Jiangnan Orogen.This structure suggests a process different from the simple collisional orogeny.To interpret our observations,an'intra-continental orogeny'is proposed to address the development of the Jiangnan Orogen in the Mesozoic.Furthermore,this'reworked'process may contain at least two stages caused by the decoupling of the lithosphere,which is revealed by an extra conductive layer beneath Jiangnan.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0600201)National Natural Science Foundation of China(Grant Nos.42174109,41674099,41974100,and 42174169)+1 种基金China Geological Survey(Grant No.DD20221829)U.S.NSF(Grant No.1927133)。
文摘A great amount of new S-wave data has been combined to image the mantle structure down to lower mantle depth near the southeastern margin of Eurasia and understand the tectonics in South China since the Mesozoic.Our results reveal a large-scale structure beneath the South China Sea,with a prominent,broad low-velocity feature of at least 1500-km wide in and below the mantle transition zone(MTZ)and a pronounced low-velocity feature of nearly 500-km wide in the lowermost mantle.Together these features may represent the head-and-tail of an upwelling mantle plume that has interacted with and deformed by the subducting plates in the region.The Andaman-Sumatra plate is seen subducting steeply without stagnation in the MTZ over the large-scale low-velocity structure,suggesting that the upwelling mantle may have exerted significant influence on the overlying plate tectonics.Our results suggest a long-term extensional regime near the southeastern margin of Eurasia,which may help to understand the formation of the large-scale intra-plate magmatism and mineralization with accumulation of huge amount of rare metal elements in South China during the Mesozoic,and the continental breakup,the southeastward extrusion of Indochina,and the opening of the South China Sea during the Cenozoic.
基金funded by the Anhui Province Science Program(2018-g-1-4)the National Science Program(Nos.41630320,42174087)the National Key R&D Program of China(No.2016YFC0600201)。
文摘Despite extensive efforts to understand the tectonic evolution of the Jiangnan Orogen in South China,the orogenic process and its mechanism remain a matter of dispute.Previous geodynamic studies have mostly focused on collisional orogeny,which is commonly invoked to explain the Jiangnan Orogen.However,it is difficult for such hypotheses to reconcile all the geological and geophysical data,especially the absence of ultrahigh-pressure metamorphic rocks.Based on the magnetotelluric data,we present a group of resistivity models produced through the combination of two-dimensional and three-dimensional inversions,revealing the geo-electrical structures of Jiangnan and a typical collisional orogen.In our models,the resistive crust is separated into three parts by a prominent conductive layer with opposite dipping directions on both sides.A special thrust-nappe system,which is different from that developed in a typical collisional process,is revealed in the Jiangnan Orogen.This structure suggests a process different from the simple collisional orogeny.To interpret our observations,an'intra-continental orogeny'is proposed to address the development of the Jiangnan Orogen in the Mesozoic.Furthermore,this'reworked'process may contain at least two stages caused by the decoupling of the lithosphere,which is revealed by an extra conductive layer beneath Jiangnan.
