The intraplate uplift of the Qinghai-Tibet Plateau took place on the basis of breakup and assembly of the Precambrian supercontinent, and southward ocean-continent transition of the Proto-, Paleo-, Meso- and Neo-Tethy...The intraplate uplift of the Qinghai-Tibet Plateau took place on the basis of breakup and assembly of the Precambrian supercontinent, and southward ocean-continent transition of the Proto-, Paleo-, Meso- and Neo-Tethys during the Caledonian, Indosinian, Yanshanian and Early Himalayan movements. The intraplate tectonic evolution of the Qinghai-Tibet Plateau underwent the early stage of intraplate orogeny characterized by migrational tectonic uplift, horizontal movement and geological processes during 180-7 Ma, and the late stage of isostatic mountain building characterized by pulsative rapid uplift, vertical movement and geographical processes since 3.6 Ma. The spatial-temporal evolution of the intraplate orogeny within the Qinghai-Tibet Plateau shows a regular transition from the northern part through the central part to the southern part during 180-120 Ma, 65-35 Ma, and 25-7 Ma respectively, with extensive intraplate faulting, folding, block movement, magmatism and metallogenesis. Simultaneous intraplate orogeny and basin formation resulted from crustal rheological stratification and basin-orogen coupling that was induced by lateral viscous flow in the lower crust. This continental dynamic process was controlled by lateral flow of hot and soft materials within the lower crust because of slab dehydration and melted mantle upwelling above the subducted plates during the southward Tethyan ocean-continent transition processes or asthenosphere diapirism. Intraplate orogeny and basin formation were irrelevant to plate collision. The Qinghai-Tibet Plateau as a whole was actually formed by the isostatic mountain building processes since 3.6 Ma that were characterized by crust-scale vertical movement, and integral rapid uplift of the plateau, accompanied by isostatic subsidence of peripheral basins and depressions, and great changes in topography and environment. A series of pulsative mountain building events, associated with gravity equilibrium and isostatic adjustment of crustal materials, at 3.6 Ma, 2.5 Ma, 1.8-1.2 Ma展开更多
We present results from a 484 km wide-angle seismic profilie acquired in the northwest part of the South China Sea （SCS） during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic li...We present results from a 484 km wide-angle seismic profilie acquired in the northwest part of the South China Sea （SCS） during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic line （SO49-18） crosses the continental slope of the northern margin, the Northwest Subbasin （NWSB） of the South China Sea, the Zhongsha Massif and partly the oceanic basin of the South China Sea. Seismic sections recorded on 13 ocean-bottom seismometers were used to identify refracted phases from the crustal layer and also reflected phases from the crust-mantle boundary （Moho）. Inversion of the traveltimes using a simple start model reveals crustal images in the study area. The velocity model shows that crustal thickness below the continental slope is between 14 and 23 kin. The continental part of the line is characterized by gentle landward mantle uplift and an abrupt oeeanward one. The velocities in the lower crust do not exceed 6.9 km/s. With the new data we can exclude a high-velocity lower crustal body （velocities above 7.0 kin/s） at the location of the line. We conclude that this part of the South China Sea margin developed by a magma-poor rifting. Both, the NWSB and the Southwest Sub-basin （SWSB） reveal velocities typical for oceanic crust with crustal thickness between 5 and 7 kin. The Zhongsha Massif in between is extremely stretched with only 6-10 km continental crust left. Crustal velocity is below 6.5 kin/s; possibly indicating the absence of the lower crust. Multi-channel seismic profile shows that the Yitongansha Uplift in the slope area and the Zhongsha Massif are only mildly deformed. We considered them as rigid continent blocks which acted as rift shoulders of the main rift subsequently resulting in the formation of the Northwest Sub-basin. The extension was mainly accommodated by a ductile lower crustal flows, which might have been extremely attenuated and flow into the oceanic basin during the spreading stage. We compared the crustal structures along the norther展开更多
The crustal thicknesses and the Poisson’s ratios under the seismic stations can be calculated by receiver function method with H-κ stacking effectively. But the stacking results are affected to some extent by the av...The crustal thicknesses and the Poisson’s ratios under the seismic stations can be calculated by receiver function method with H-κ stacking effectively. But the stacking results are affected to some extent by the average crustal P-wave velocity. To eliminate this effect and get more accurate crustal structure along the Zhenkang-Luxi deep seismic sounding profile which lies in Yunnan Province, we calculate the receiver functions from the teleseismic events recorded by 11 temporary stations as well as 5 permanent ones along the profile and carry out the stacking with Vp obtained from the profile in this study. Our study shows that the crustal thicknesses along the Zhenkang-Luxi profile range from 34.8 km to 41.8 km with an average of 39 km. The crust is thicker in the middle part of the profile and thinner in both sides in general. Dramatic changes of crustal thickness about 3 km are detected across both the Lancangjiang fault and the Xiaojiang fault, which implies that these faults cut through the Moho. The lowest Poisson’s ratio under the stations is 0.22 and the highest is 0.27 with the mean of 0.25, which is lower than the global average value 0.27 in the continental crust. It suggests that most of the crust along the profile lacks mafic component, but contains more felsic substance. The low Poisson’s ratio also indicates that there is no satisfying condition for partial melting. We deduce that the material flow in the middle-lower crust in the southeastern margin of the Tibetan plateau may occur only in the north region of 24°N.展开更多
基金中国地质调查局资助的基础研究项目(编号:12120113093800)的成果supported by the U.S. Department of Energy through contract DE-AC52-06NA25396 to Los Alamos National Laboratory~~
基金supported by the China National Science Foundation (Grant No: 40572113)China national key basic research program for earlier stage study (Grant No: 2005CCA05600)
文摘The intraplate uplift of the Qinghai-Tibet Plateau took place on the basis of breakup and assembly of the Precambrian supercontinent, and southward ocean-continent transition of the Proto-, Paleo-, Meso- and Neo-Tethys during the Caledonian, Indosinian, Yanshanian and Early Himalayan movements. The intraplate tectonic evolution of the Qinghai-Tibet Plateau underwent the early stage of intraplate orogeny characterized by migrational tectonic uplift, horizontal movement and geological processes during 180-7 Ma, and the late stage of isostatic mountain building characterized by pulsative rapid uplift, vertical movement and geographical processes since 3.6 Ma. The spatial-temporal evolution of the intraplate orogeny within the Qinghai-Tibet Plateau shows a regular transition from the northern part through the central part to the southern part during 180-120 Ma, 65-35 Ma, and 25-7 Ma respectively, with extensive intraplate faulting, folding, block movement, magmatism and metallogenesis. Simultaneous intraplate orogeny and basin formation resulted from crustal rheological stratification and basin-orogen coupling that was induced by lateral viscous flow in the lower crust. This continental dynamic process was controlled by lateral flow of hot and soft materials within the lower crust because of slab dehydration and melted mantle upwelling above the subducted plates during the southward Tethyan ocean-continent transition processes or asthenosphere diapirism. Intraplate orogeny and basin formation were irrelevant to plate collision. The Qinghai-Tibet Plateau as a whole was actually formed by the isostatic mountain building processes since 3.6 Ma that were characterized by crust-scale vertical movement, and integral rapid uplift of the plateau, accompanied by isostatic subsidence of peripheral basins and depressions, and great changes in topography and environment. A series of pulsative mountain building events, associated with gravity equilibrium and isostatic adjustment of crustal materials, at 3.6 Ma, 2.5 Ma, 1.8-1.2 Ma
基金financially supported by the National Basic Research Program(973) of China(No. 2007CB41170403)the National Natural Science Foundation of China(No.91028006 and 41074066)
文摘We present results from a 484 km wide-angle seismic profilie acquired in the northwest part of the South China Sea （SCS） during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic line （SO49-18） crosses the continental slope of the northern margin, the Northwest Subbasin （NWSB） of the South China Sea, the Zhongsha Massif and partly the oceanic basin of the South China Sea. Seismic sections recorded on 13 ocean-bottom seismometers were used to identify refracted phases from the crustal layer and also reflected phases from the crust-mantle boundary （Moho）. Inversion of the traveltimes using a simple start model reveals crustal images in the study area. The velocity model shows that crustal thickness below the continental slope is between 14 and 23 kin. The continental part of the line is characterized by gentle landward mantle uplift and an abrupt oeeanward one. The velocities in the lower crust do not exceed 6.9 km/s. With the new data we can exclude a high-velocity lower crustal body （velocities above 7.0 kin/s） at the location of the line. We conclude that this part of the South China Sea margin developed by a magma-poor rifting. Both, the NWSB and the Southwest Sub-basin （SWSB） reveal velocities typical for oceanic crust with crustal thickness between 5 and 7 kin. The Zhongsha Massif in between is extremely stretched with only 6-10 km continental crust left. Crustal velocity is below 6.5 kin/s; possibly indicating the absence of the lower crust. Multi-channel seismic profile shows that the Yitongansha Uplift in the slope area and the Zhongsha Massif are only mildly deformed. We considered them as rigid continent blocks which acted as rift shoulders of the main rift subsequently resulting in the formation of the Northwest Sub-basin. The extension was mainly accommodated by a ductile lower crustal flows, which might have been extremely attenuated and flow into the oceanic basin during the spreading stage. We compared the crustal structures along the norther
基金supported by the Seismic Youth Funding of Geophysical Exploration Center,China Earthquake Administration (YFGEC2016003)the National Natural Science Foundation of China (41774070 and 41404049)
文摘The crustal thicknesses and the Poisson’s ratios under the seismic stations can be calculated by receiver function method with H-κ stacking effectively. But the stacking results are affected to some extent by the average crustal P-wave velocity. To eliminate this effect and get more accurate crustal structure along the Zhenkang-Luxi deep seismic sounding profile which lies in Yunnan Province, we calculate the receiver functions from the teleseismic events recorded by 11 temporary stations as well as 5 permanent ones along the profile and carry out the stacking with Vp obtained from the profile in this study. Our study shows that the crustal thicknesses along the Zhenkang-Luxi profile range from 34.8 km to 41.8 km with an average of 39 km. The crust is thicker in the middle part of the profile and thinner in both sides in general. Dramatic changes of crustal thickness about 3 km are detected across both the Lancangjiang fault and the Xiaojiang fault, which implies that these faults cut through the Moho. The lowest Poisson’s ratio under the stations is 0.22 and the highest is 0.27 with the mean of 0.25, which is lower than the global average value 0.27 in the continental crust. It suggests that most of the crust along the profile lacks mafic component, but contains more felsic substance. The low Poisson’s ratio also indicates that there is no satisfying condition for partial melting. We deduce that the material flow in the middle-lower crust in the southeastern margin of the Tibetan plateau may occur only in the north region of 24°N.
