Since the Cenozoic,a series of extensional south-north normal faults and gneiss-granite domes evolved in the southern Tibetan Plateau,the formation mechanism of which is of scientific interest and which has implicatio...Since the Cenozoic,a series of extensional south-north normal faults and gneiss-granite domes evolved in the southern Tibetan Plateau,the formation mechanism of which is of scientific interest and which has implications for the tectonic dynamics of the plateau.Typical of such features are the Xainza-Dinggye rift and the Mabja gneiss dome,which are located in the Xainza-Xietongmen-Dinggye region in the central Tibetan Plateau.In this study,Magnetotelluric measurements across this region are used to generate a high-resolution 3-D electrical resistivity model of the subsurface and to analyze the cause of the conductive zones.The large-scale conductive zones identified in the middle-lower crust may result from aqueous melt partial melting,whereas the smaller-scale conductive zones in the upper-middle crust may result from saline fluids,possibly with varying minor volumes of melts.Subsequently,based on the electrical resistivity model and combined with the spatiotemporal coupling of the geological,geochemical,and geophysical data,the state and migration features of crustal materials are discussed.The results show that the upwelling of mantle materials along subduction channels and slab-windows related to the tearing of the Indian lithospheric plate contributed to the partial melting of the middle-lower crust in the Lhasa terrane.Furthermore,partial melting of the upper-middle crust in the Tethys-Himalaya terrane resulted from southern extrusion of crustal materials in the Lhasa terrane.These two mechanisms can significantly reduce the effective viscosity.We speculate that the deformation of the brittle upper crust that is controlled by large-scale ductile layers characterized by weak rheology is the main dynamic mechanism of rift evolution.Meanwhile,the metamorphism and anatexis in the upper-middle crust of the Tethys-Himalaya terrane related to the southern extrusion of materials contributed to the evolution of the Mabja gneiss dome.During the middle Miocene,the southern extrusion of crustal materials may have been influenced by the cooling events beneath the Mabja gneiss dome,which can explain why the deep areas beneath the Mabja gneiss dome have middle-high resistivity.In addition,our study region is located in the Mediterranean-Himalayan seismic belt,and mainly includes shallow-focus earthquakes and intermediate-depth earthquakes.In the north,shallow-focus earthquakes are mainly controlled by the accumulation of stress in the brittle layer of the overlying crust related to the ductile layer of the middle and lower crust.In the south,shallow-focus earthquakes(e.g.,Dingri MS6.8 earthquake)mainly occur in the rigid,resistive block,which is surrounded by conductive zones,possibly because fluid migration may be hindered by these resistive blocks.The intermediate-depth earthquakes are mainly controlled by the response in the subsurface area,which is related to the detachment of the Indian lithospheric mantle from the Indian crust.展开更多
基金supported by the High-performance Computing Platform of China University of Geosciences,Beijingsupported by the National Natural Science Foundation of China(Grant No.42304087)+1 种基金the National Key R&D Program of China(Grant No.2022YFF0800901)the Fundamental Research Funds for the Central Universities(Grant No.29-2023-202)。
文摘Since the Cenozoic,a series of extensional south-north normal faults and gneiss-granite domes evolved in the southern Tibetan Plateau,the formation mechanism of which is of scientific interest and which has implications for the tectonic dynamics of the plateau.Typical of such features are the Xainza-Dinggye rift and the Mabja gneiss dome,which are located in the Xainza-Xietongmen-Dinggye region in the central Tibetan Plateau.In this study,Magnetotelluric measurements across this region are used to generate a high-resolution 3-D electrical resistivity model of the subsurface and to analyze the cause of the conductive zones.The large-scale conductive zones identified in the middle-lower crust may result from aqueous melt partial melting,whereas the smaller-scale conductive zones in the upper-middle crust may result from saline fluids,possibly with varying minor volumes of melts.Subsequently,based on the electrical resistivity model and combined with the spatiotemporal coupling of the geological,geochemical,and geophysical data,the state and migration features of crustal materials are discussed.The results show that the upwelling of mantle materials along subduction channels and slab-windows related to the tearing of the Indian lithospheric plate contributed to the partial melting of the middle-lower crust in the Lhasa terrane.Furthermore,partial melting of the upper-middle crust in the Tethys-Himalaya terrane resulted from southern extrusion of crustal materials in the Lhasa terrane.These two mechanisms can significantly reduce the effective viscosity.We speculate that the deformation of the brittle upper crust that is controlled by large-scale ductile layers characterized by weak rheology is the main dynamic mechanism of rift evolution.Meanwhile,the metamorphism and anatexis in the upper-middle crust of the Tethys-Himalaya terrane related to the southern extrusion of materials contributed to the evolution of the Mabja gneiss dome.During the middle Miocene,the southern extrusion of crustal materials may have been influenced by the cooling events beneath the Mabja gneiss dome,which can explain why the deep areas beneath the Mabja gneiss dome have middle-high resistivity.In addition,our study region is located in the Mediterranean-Himalayan seismic belt,and mainly includes shallow-focus earthquakes and intermediate-depth earthquakes.In the north,shallow-focus earthquakes are mainly controlled by the accumulation of stress in the brittle layer of the overlying crust related to the ductile layer of the middle and lower crust.In the south,shallow-focus earthquakes(e.g.,Dingri MS6.8 earthquake)mainly occur in the rigid,resistive block,which is surrounded by conductive zones,possibly because fluid migration may be hindered by these resistive blocks.The intermediate-depth earthquakes are mainly controlled by the response in the subsurface area,which is related to the detachment of the Indian lithospheric mantle from the Indian crust.
