The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deforma...The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.展开更多
We used twodimensional numerical simulations to investigate smallscale convection in the upper mantlelithosphere system with depth and temperaturedependent viscosity. Our aim was to examine the mechanism of craton thi...We used twodimensional numerical simulations to investigate smallscale convection in the upper mantlelithosphere system with depth and temperaturedependent viscosity. Our aim was to examine the mechanism of craton thinning by thermal con vection. The model domain is 700 km deep and 700 km wide with a resolution of 71x71 nodes and 160000 markers. The ve locity boundary conditions are freeslip along all the boundaries. A thermal insulation condition was applied at the two side walls, with constant temperatures for the top and bottom boundaries. We assumed an initial temperature of 273 K at the upper boundary and 1673 K at the lower boundary, and 1573 K at the bottom of the lithosphere （200 km depth） for the thick, cold, and stable North China Craton （NCC）. We calculated the thermal evolution in the upper mantle when the temperature at its bottom is raised because of lower mantle convection or plumes. The temperature at the bottom of the upper mantle was set at 1773, 1873, 1973, and 2073 K for different models to study the temperature effect on the lithospheric thinning processes. Our endmember calculations show that with the bottom boundary raising the lithosphere can be thinned from a depth of 200 km to a depth of between 100 and 126.25 km. The thinning rates are at mm/y order of magnitude, and the thinning timescale is about 10 Ma.展开更多
文摘The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 90814014 & 40971226)Sino-Probe 09-03 (YOQ0360032)Sino-Probe 07
文摘We used twodimensional numerical simulations to investigate smallscale convection in the upper mantlelithosphere system with depth and temperaturedependent viscosity. Our aim was to examine the mechanism of craton thinning by thermal con vection. The model domain is 700 km deep and 700 km wide with a resolution of 71x71 nodes and 160000 markers. The ve locity boundary conditions are freeslip along all the boundaries. A thermal insulation condition was applied at the two side walls, with constant temperatures for the top and bottom boundaries. We assumed an initial temperature of 273 K at the upper boundary and 1673 K at the lower boundary, and 1573 K at the bottom of the lithosphere （200 km depth） for the thick, cold, and stable North China Craton （NCC）. We calculated the thermal evolution in the upper mantle when the temperature at its bottom is raised because of lower mantle convection or plumes. The temperature at the bottom of the upper mantle was set at 1773, 1873, 1973, and 2073 K for different models to study the temperature effect on the lithospheric thinning processes. Our endmember calculations show that with the bottom boundary raising the lithosphere can be thinned from a depth of 200 km to a depth of between 100 and 126.25 km. The thinning rates are at mm/y order of magnitude, and the thinning timescale is about 10 Ma.
