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 northern margin and found an east-west thicken trend of the crust below the continent slope. This might be contributed by the east-west sea-floor spreading along the continental margin.展开更多
Continental rifting is one of the fundamental components in the Wilson cycle,and its comprehensive investigation is essential for understanding the geodynamic mechanisms of plate tectonics.Furthermore,continental rift...Continental rifting is one of the fundamental components in the Wilson cycle,and its comprehensive investigation is essential for understanding the geodynamic mechanisms of plate tectonics.Furthermore,continental rifts host significant mineral and hydrocarbon resources and also preserve valuable records of climatic environmental evolution.This study presents a systematic synthesis of their classification and magmatism after reviewing the research history of continental rifts.The formation and evolution of continental rifts are spatiotemporally associated with magmatic activity.Based on magmatic productivity,rifted margins that develop from successful continental rifts are categorized into different types,including magma-rich and magmapoor,with the intermediate category encompassing margins developed in active continental margin settings.Previous studies and systematically compiled data in this study indicate that distinct magmatic rock assemblages are characteristic of different rift types.Magma-rich rifts and rifted margins typically exhibit bimodal magmatism,including highly alkaline–silica poor alkaline rocks during the early rifting stage,alkalic basalt–trachyandesite–peralkaline rhyolite,transitional basalt and rhyolite during the evolutionary stage,and predominantly tholeiitic basalt during the final stage.Magma-poor rifted margins primarily consist of mafic rocks,including carbonatite and alkaline rocks during the initial rifting stage,followed by alkalic and tholeiitic basalts during the evolutionary stage.The lithospheric mantle in magma-poor rifted margins experienced extensive melt-induced metasomatism,making it an important research target for understanding continental rifting processes and magmatic evolution.In active continental margin rifts,magmatic rocks are dominated by bimodal magmatism,primarily encompassing the entire calcalkaline suite from basalt to rhyolite,along with minor alkalic basalt.During continental rifting,these magmatic processes effectively weaken the lithosphere,localize deformation,and ultimately facilitate the rifting progression to continental breakup.Further questions meriting attention include:(1)petrogenesis and geodynamics of magmatic rocks in continental rifts;(2)controlling factors for success or failure of continental rifting;(3)the nature of the ocean-continent transition and the process of transitioning from continental rifting to seafloor spreading;(4)controlling factors for the generation of magma-rich versus magma-poor rifted margins;and(5)the impact of continental rifting on climate change.Addressing these questions necessitates integrated approaches combining systematic geological,geochemical,and geophysical investigations of both modern and ancient rift systems with advanced techniques of numerical geodynamic modeling.展开更多
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 northern margin and found an east-west thicken trend of the crust below the continent slope. This might be contributed by the east-west sea-floor spreading along the continental margin.
基金supported by the Strategic Priority Research Program(A)of the Chinese Academy of Sciences(Grant No.XDA0430102)the Deep Earth Probe and Mineral Resources Exploration(Grant No.2024ZD1001103)。
文摘Continental rifting is one of the fundamental components in the Wilson cycle,and its comprehensive investigation is essential for understanding the geodynamic mechanisms of plate tectonics.Furthermore,continental rifts host significant mineral and hydrocarbon resources and also preserve valuable records of climatic environmental evolution.This study presents a systematic synthesis of their classification and magmatism after reviewing the research history of continental rifts.The formation and evolution of continental rifts are spatiotemporally associated with magmatic activity.Based on magmatic productivity,rifted margins that develop from successful continental rifts are categorized into different types,including magma-rich and magmapoor,with the intermediate category encompassing margins developed in active continental margin settings.Previous studies and systematically compiled data in this study indicate that distinct magmatic rock assemblages are characteristic of different rift types.Magma-rich rifts and rifted margins typically exhibit bimodal magmatism,including highly alkaline–silica poor alkaline rocks during the early rifting stage,alkalic basalt–trachyandesite–peralkaline rhyolite,transitional basalt and rhyolite during the evolutionary stage,and predominantly tholeiitic basalt during the final stage.Magma-poor rifted margins primarily consist of mafic rocks,including carbonatite and alkaline rocks during the initial rifting stage,followed by alkalic and tholeiitic basalts during the evolutionary stage.The lithospheric mantle in magma-poor rifted margins experienced extensive melt-induced metasomatism,making it an important research target for understanding continental rifting processes and magmatic evolution.In active continental margin rifts,magmatic rocks are dominated by bimodal magmatism,primarily encompassing the entire calcalkaline suite from basalt to rhyolite,along with minor alkalic basalt.During continental rifting,these magmatic processes effectively weaken the lithosphere,localize deformation,and ultimately facilitate the rifting progression to continental breakup.Further questions meriting attention include:(1)petrogenesis and geodynamics of magmatic rocks in continental rifts;(2)controlling factors for success or failure of continental rifting;(3)the nature of the ocean-continent transition and the process of transitioning from continental rifting to seafloor spreading;(4)controlling factors for the generation of magma-rich versus magma-poor rifted margins;and(5)the impact of continental rifting on climate change.Addressing these questions necessitates integrated approaches combining systematic geological,geochemical,and geophysical investigations of both modern and ancient rift systems with advanced techniques of numerical geodynamic modeling.
