The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigat...The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study,the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso-Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900-1100℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from "cold mantle and hot crust" before the Cretaceous to "hot mantle and cold crust" after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events.Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.展开更多
Mid-ocean ridge and oceanic transforms are among the most prominent features on the seafloor surface and are crucial for understanding seafloor spreading and plate tectonic dynamics,but the deep structure of the ocean...Mid-ocean ridge and oceanic transforms are among the most prominent features on the seafloor surface and are crucial for understanding seafloor spreading and plate tectonic dynamics,but the deep structure of the oceanic lithosphere remains poorly understood.The large number of microearthquakes occurring along ridges and transforms provide valuable information for gaining an indepth view of the underlying detailed seismic structures,contributing to understanding geodynamic processes within the oceanic lithosphere.Previous studies have indicated that the maximum depth of microseismicity is controlled by the 600-℃isotherm.However,this perspective is being challenged due to increasing observations of deep earthquakes that far exceed this suggested isotherm along mid-ocean ridges and oceanic transform faults.Several mechanisms have been proposed to explain these deep events,and we suggest that local geodynamic processes(e.g.,magma supply,mylonite shear zone,longlived faults,hydrothermal vents,etc.)likely play a more important role than previously thought.展开更多
Thermal structures of three deep seismic profiles in the continental margin in the northern South China Sea are calculated, their 'thermal' lithospheric thicknesses are evaluated based on the basalt dry solidu...Thermal structures of three deep seismic profiles in the continental margin in the northern South China Sea are calculated, their 'thermal' lithospheric thicknesses are evaluated based on the basalt dry solidus, and their rheological structures are evaluated with linear frictional failure criterion and power-law creep equation. 'Thermal' lithosphere is about 90 km in thickness in shelf area, and thins toward the slope, lowers to 60-65 km in the lower slope, ocean crust and Xisha Trough. In the mid-west of the studied area, the lithospheric rheological structure in shelf area and Xisha Islands is of four layers: brittle, ductile, brittle and ductile. Because of uprising of heat mantle and thinning of crust and lithosphere in Xisha Trough, the bottom of the upper brittle layer is only buried at 16 km. In the eastern area, the bottom of the upper brittle layer in the north is buried at 20 km or so, while in lower slope and ocean crust, the rheological structure is of two layers of brittle and ductile, and展开更多
The detailed lithospheric structure of South China is the basis for the understanding of tectonic processes of eastern China.Specifically,two essential issues in the study of lithospheric structure are the thermal and...The detailed lithospheric structure of South China is the basis for the understanding of tectonic processes of eastern China.Specifically,two essential issues in the study of lithospheric structure are the thermal and compositional structures,which are usually derived from either geophysical or geochemical observations.However,inversions from single geophysical or geochemical datasets have certain limitations,making it necessary to develop joint inversions of geophysical,geochemical and petrological datasets.In this paper,through thermodynamic simulation and probabilistic inversion,we inverted multiple datasets including topography,geoid height,surface heat flow and surface wave dispersion curves for the 3D lithospheric thermal and compositional structure of South China.The results reveal a thin(<100 km)and flat LAB beneath the South China Fold System Block and the lower Yangtze Craton.Also,we found that the lithospheric mantle is primarily composed of saturated peridotite,indicating that the ancient refractory lithospheric mantle has been replaced by new materials.The dominant dynamic mechanism for lithospheric thinning in eastern South China may be the flat subduction of ancient Pacific slab,while thermal erosion may have also played a significant role.In contrast,the LAB depth beneath the Sichuan Basin is much thicker(>200 km),suggesting that the thick and cold craton lithospheric roots are retained.There may exist a discontinuous interface beneath the Sichuan Basin,with the saturated lower layer thicker than the refractory upper layer.As a result,the lithospheric mantle of the Sichuan Basin and surrounding regions is mainly composed of saturated and transitional peridotite.展开更多
The asthenosphere upwelled on a large scale in the western Pacific and South China Sea during the Cenozoic, which formed strong upward throughflow and caused the thermal structure to be changed obviously. The mathemat...The asthenosphere upwelled on a large scale in the western Pacific and South China Sea during the Cenozoic, which formed strong upward throughflow and caused the thermal structure to be changed obviously. The mathematical analysis has demonstrated that the upward throughflow velocity may have varied from 3×10^11 to 6×10^12 m/s. From the relationship between the lithospheric thickness and the conductive heat flux, the lithospheric heat flux in the western Pacific should be above 30 mW/m^2, which is consistent with the observed data. The huge low-speed zone within the upper mantle of the marginal sea in the western Pacific reflects that the upper mantle melts partially, flows regionally in the regional stress field, forms the upward heat flux at its bottom, and causes the change of the lithospheric thermal structure in the region. The numerical simulation result of the expansion and evolution in the South China Sea has demonstrated that in the early expansion, the upward throughflow velocity was relatively fast, and the effect that it had on the thickness of the lithosphere was relatively great,resulting in the mid-ocean basin expanding rapidly. After the formation of the ocean basin in the South China Sea, the upward throughflow velocity decreased, but the conductive heat flux was relatively high, which is close to the actual situation. Therefore, from the heat transfer point of view, this article discusses how the upward heat flux affects the lithospheric thermal structure in the western Pacific and South China Sea. The conclusions show that the upward heat throughflow at the bottom of the lithospheric mantle resulted in the tectonic deformation at the shallow crust. The intensive uplifts and rifts at the crust led to the continent cracks and the expansion in the South China Sea.展开更多
Based on the data of geo-temperature and thermophysical parameters of rocks in the Kuqa Depression and the Tabei Uplift, northern flank of the Tarim Basin, in terms of the analytical solution of 1-D heat transfer equa...Based on the data of geo-temperature and thermophysical parameters of rocks in the Kuqa Depression and the Tabei Uplift, northern flank of the Tarim Basin, in terms of the analytical solution of 1-D heat transfer equation, the thermal structure of the lithosphere under this region is determined. Our results show that the average surface heat flow of the northern flank of the Tarim Basin is 45 mW/m2, and the mantle heat flow is between 20 and 23 mW/m2; the temperature at crust-mantle boundary (Moho) ranges from 514°C to 603°C and the thermal lithosphere where the heat conduction dominates is 138–182 km thick. Furthermore, in combination with the P wave velocity structure resulting from the deep seismic sounding profile across this region and rheological modeling, we have studied the local composition of the lithosphere and its rheological profile, as well as the strength distribution. We find that the rheological stratification of the lithosphere in this region is apparent. The lowermost of the lower crust is ductile; however, the uppermost of the mantle and the upper and middle parts of the crust are both brittle layers, which is typically the so-called sandwich-like structure. Lithospheric strength is also characterized by the lateral variation, and the uplift region is stronger than the depression region. The lithospheric strength of the northern flank of the Tarim Basin decreases gradually from south to north; the Kuqa Depression has the lowest strength and the south of the Tabei Uplift is strongest. The total lithospheric strength of this region is4.77×1012–5.03×1013 N/m under extension, and 6.5×1012–9.4×1013 N/m under compression. The lithospheric brittleductile transition depth is between 20 km and 33 km. In conclusion, the lithosphere of the northern flank of the Tarim Basin is relatively cold with higher strength, so it behaves rigidly and deforms as a whole, which is also supported by the seismic activity in this region. This rigidity of the Tarim lithosphere makes it little deform interior, but only into flexure under the sedimentation and tectonic loading associated with the rapid uplift of the Tianshan at its northern margin during the Indian-Eurasian continental collision following the Late Eocene. Finally, the influences of factors, such as heat flow, temperature, crustal thickness, and especially basin sediment thickness, on the lithospheric strength are discussed here.展开更多
Determination of the physical and chemical structures of the inaccessible continental lithosphere by comprehensive geophysical and geochemical studies can provide valuable information on its formation and evolution.Ex...Determination of the physical and chemical structures of the inaccessible continental lithosphere by comprehensive geophysical and geochemical studies can provide valuable information on its formation and evolution.Extensive studies from various disciplines have revealed complex lithospheric modification of the North China Craton(NCC),but less attention has been paid to an integrated study from different fields.Here we provide an integrated constraint on the lithospheric mantle structure of the NCC by comprehensive semiology,gravity and thermal studies with xenolith data involving depth(levels in the lithosphere),property(chemical and physical),and timing(formation and reworking ages).Our results suggest that the NCC has a relatively heterogeneous lithospheric mantle.Its margins and internal weak zones,especially in the eastern NCC,are generally underlain by the fertile,weakly metasomatized mantle with generally young formation ages.In contrast,its core tends to preserve the refractory,strongly metasomatized mantle with ages roughly coupled to the overlying Archean crust.Such a lithospheric structure shows the preferential modification of the lithospheric mantle in the eastern NCC and in the peripheral regions of the western NCC.The interior of the craton,especially most of the western NCC,remains stable and has been weakly modified.展开更多
The lithosphere of the North China Craton(NCC)has experienced significant destruction and deformation since the Mesozoic,a notable feature of which is the widespread extensional structure and lithospheric thinning in ...The lithosphere of the North China Craton(NCC)has experienced significant destruction and deformation since the Mesozoic,a notable feature of which is the widespread extensional structure and lithospheric thinning in the eastern NCC.Since the thermo-rheological structure of the lithosphere is one of the main factors controlling these dynamic processes,a threedimensional thermo-rheological model of the present lithosphere in the NCC was developed based on a geophysical-petrological method using a variety of data,and its relationship with the extensional structures and the formation of rifts was further analyzed.Our results show that the western NCC is characterized by thick lithosphere,low Moho temperature(TMoho<600°C),as well as high lithospheric strength and mantle-crust strength ratio(Sm/Sc>1).The deformation of the western narrow rift is consistent with the localized deformation dominated by the strength of lithospheric mantle.On the other hand,the lithosphere in the eastern NCC is characterized by extensive thinning(with lithospheric thickness of about 80–110 km).However,the decrease of lithospheric strength is not uniform,with high strength(10×1012 Pa m)observed in some areas(such as the Bohai Bay Basin and Hehuai Basin).Most of the eastern lithosphere is characterized by high TMoho(600–750°C)and low Sm/Sc(<1),which is inconsistent with the widespread extensional structure in the eastern NCC.Incorporating results from palaeo-geothermal and petrological studies,we developed a thermo-rheological structure model of the lithosphere at different evolutionary stages of the NCC,and suggested that the eastern NCC had a significantly thinned and weakened lithosphere in the early stages of the formation of the rift,leading to a regional distributed extension deformation dominated by crustal strength,which eventually evolved into a series of wide rifts.However,the cooling and accretion of the lithosphere in the subsequent stages significantly increased the strength of the lithospheric mantle,resulting in the inconsistency between the present thermo-rheological structure of the lithosphere and the extensional structure formed in the past.展开更多
基金funded by the National Natural Science Foundation of China (Grant Nos.41402219, 41302202,41125010,41302202,and 91114202)
文摘The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study,the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso-Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900-1100℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from "cold mantle and hot crust" before the Cretaceous to "hot mantle and cold crust" after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events.Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.
基金Supported by the State Key Program of National Natural Science of China(No.42330308)the Project of Donghai Laboratory(No.DH-2022ZY0005)+4 种基金the Scientific Research Fund of the Second Institute of OceanographyMinistry of Natural Resources(No.QHXZ2301)the National Science Foundation for Distinguished Young Scholars of China(No.42025601)for Young Scientists of China(No.41906064)the Zhejiang Provincial Natural Science Foundation of China(No.LDQ24D060001)。
文摘Mid-ocean ridge and oceanic transforms are among the most prominent features on the seafloor surface and are crucial for understanding seafloor spreading and plate tectonic dynamics,but the deep structure of the oceanic lithosphere remains poorly understood.The large number of microearthquakes occurring along ridges and transforms provide valuable information for gaining an indepth view of the underlying detailed seismic structures,contributing to understanding geodynamic processes within the oceanic lithosphere.Previous studies have indicated that the maximum depth of microseismicity is controlled by the 600-℃isotherm.However,this perspective is being challenged due to increasing observations of deep earthquakes that far exceed this suggested isotherm along mid-ocean ridges and oceanic transform faults.Several mechanisms have been proposed to explain these deep events,and we suggest that local geodynamic processes(e.g.,magma supply,mylonite shear zone,longlived faults,hydrothermal vents,etc.)likely play a more important role than previously thought.
文摘Thermal structures of three deep seismic profiles in the continental margin in the northern South China Sea are calculated, their 'thermal' lithospheric thicknesses are evaluated based on the basalt dry solidus, and their rheological structures are evaluated with linear frictional failure criterion and power-law creep equation. 'Thermal' lithosphere is about 90 km in thickness in shelf area, and thins toward the slope, lowers to 60-65 km in the lower slope, ocean crust and Xisha Trough. In the mid-west of the studied area, the lithospheric rheological structure in shelf area and Xisha Islands is of four layers: brittle, ductile, brittle and ductile. Because of uprising of heat mantle and thinning of crust and lithosphere in Xisha Trough, the bottom of the upper brittle layer is only buried at 16 km. In the eastern area, the bottom of the upper brittle layer in the north is buried at 20 km or so, while in lower slope and ocean crust, the rheological structure is of two layers of brittle and ductile, and
基金supported by the National Natural Science Foundation of China(Grant No.41674106)the National Key Research and Development Program of China(Grant No.201YFC1500302)。
文摘The detailed lithospheric structure of South China is the basis for the understanding of tectonic processes of eastern China.Specifically,two essential issues in the study of lithospheric structure are the thermal and compositional structures,which are usually derived from either geophysical or geochemical observations.However,inversions from single geophysical or geochemical datasets have certain limitations,making it necessary to develop joint inversions of geophysical,geochemical and petrological datasets.In this paper,through thermodynamic simulation and probabilistic inversion,we inverted multiple datasets including topography,geoid height,surface heat flow and surface wave dispersion curves for the 3D lithospheric thermal and compositional structure of South China.The results reveal a thin(<100 km)and flat LAB beneath the South China Fold System Block and the lower Yangtze Craton.Also,we found that the lithospheric mantle is primarily composed of saturated peridotite,indicating that the ancient refractory lithospheric mantle has been replaced by new materials.The dominant dynamic mechanism for lithospheric thinning in eastern South China may be the flat subduction of ancient Pacific slab,while thermal erosion may have also played a significant role.In contrast,the LAB depth beneath the Sichuan Basin is much thicker(>200 km),suggesting that the thick and cold craton lithospheric roots are retained.There may exist a discontinuous interface beneath the Sichuan Basin,with the saturated lower layer thicker than the refractory upper layer.As a result,the lithospheric mantle of the Sichuan Basin and surrounding regions is mainly composed of saturated and transitional peridotite.
基金supported jointly by the Important Direction Project of the CAS Knowledge Innovation Program (Nos. KZCX2-YW-203-01, KZCX2-YW-128-4)the Program of Key Laboratory of Marginal Sea Geology (No. MSGL04-8)
文摘The asthenosphere upwelled on a large scale in the western Pacific and South China Sea during the Cenozoic, which formed strong upward throughflow and caused the thermal structure to be changed obviously. The mathematical analysis has demonstrated that the upward throughflow velocity may have varied from 3×10^11 to 6×10^12 m/s. From the relationship between the lithospheric thickness and the conductive heat flux, the lithospheric heat flux in the western Pacific should be above 30 mW/m^2, which is consistent with the observed data. The huge low-speed zone within the upper mantle of the marginal sea in the western Pacific reflects that the upper mantle melts partially, flows regionally in the regional stress field, forms the upward heat flux at its bottom, and causes the change of the lithospheric thermal structure in the region. The numerical simulation result of the expansion and evolution in the South China Sea has demonstrated that in the early expansion, the upward throughflow velocity was relatively fast, and the effect that it had on the thickness of the lithosphere was relatively great,resulting in the mid-ocean basin expanding rapidly. After the formation of the ocean basin in the South China Sea, the upward throughflow velocity decreased, but the conductive heat flux was relatively high, which is close to the actual situation. Therefore, from the heat transfer point of view, this article discusses how the upward heat flux affects the lithospheric thermal structure in the western Pacific and South China Sea. The conclusions show that the upward heat throughflow at the bottom of the lithospheric mantle resulted in the tectonic deformation at the shallow crust. The intensive uplifts and rifts at the crust led to the continent cracks and the expansion in the South China Sea.
基金This work was jointly supported by the National Natural Science Foundation of China (Grant No. 49832040) the State Key Program for Basic Sciences of China (Grant No. 1999043302)the National 9th Five-Year Plan Special Research Programs of China (Grant No. 99-111).
文摘Based on the data of geo-temperature and thermophysical parameters of rocks in the Kuqa Depression and the Tabei Uplift, northern flank of the Tarim Basin, in terms of the analytical solution of 1-D heat transfer equation, the thermal structure of the lithosphere under this region is determined. Our results show that the average surface heat flow of the northern flank of the Tarim Basin is 45 mW/m2, and the mantle heat flow is between 20 and 23 mW/m2; the temperature at crust-mantle boundary (Moho) ranges from 514°C to 603°C and the thermal lithosphere where the heat conduction dominates is 138–182 km thick. Furthermore, in combination with the P wave velocity structure resulting from the deep seismic sounding profile across this region and rheological modeling, we have studied the local composition of the lithosphere and its rheological profile, as well as the strength distribution. We find that the rheological stratification of the lithosphere in this region is apparent. The lowermost of the lower crust is ductile; however, the uppermost of the mantle and the upper and middle parts of the crust are both brittle layers, which is typically the so-called sandwich-like structure. Lithospheric strength is also characterized by the lateral variation, and the uplift region is stronger than the depression region. The lithospheric strength of the northern flank of the Tarim Basin decreases gradually from south to north; the Kuqa Depression has the lowest strength and the south of the Tabei Uplift is strongest. The total lithospheric strength of this region is4.77×1012–5.03×1013 N/m under extension, and 6.5×1012–9.4×1013 N/m under compression. The lithospheric brittleductile transition depth is between 20 km and 33 km. In conclusion, the lithosphere of the northern flank of the Tarim Basin is relatively cold with higher strength, so it behaves rigidly and deforms as a whole, which is also supported by the seismic activity in this region. This rigidity of the Tarim lithosphere makes it little deform interior, but only into flexure under the sedimentation and tectonic loading associated with the rapid uplift of the Tianshan at its northern margin during the Indian-Eurasian continental collision following the Late Eocene. Finally, the influences of factors, such as heat flow, temperature, crustal thickness, and especially basin sediment thickness, on the lithospheric strength are discussed here.
基金supported by the National Natural Science Foundation of China(Grant No.41930215)the National Key R&D Program of China(Grant No.2016YFC0600403)。
文摘Determination of the physical and chemical structures of the inaccessible continental lithosphere by comprehensive geophysical and geochemical studies can provide valuable information on its formation and evolution.Extensive studies from various disciplines have revealed complex lithospheric modification of the North China Craton(NCC),but less attention has been paid to an integrated study from different fields.Here we provide an integrated constraint on the lithospheric mantle structure of the NCC by comprehensive semiology,gravity and thermal studies with xenolith data involving depth(levels in the lithosphere),property(chemical and physical),and timing(formation and reworking ages).Our results suggest that the NCC has a relatively heterogeneous lithospheric mantle.Its margins and internal weak zones,especially in the eastern NCC,are generally underlain by the fertile,weakly metasomatized mantle with generally young formation ages.In contrast,its core tends to preserve the refractory,strongly metasomatized mantle with ages roughly coupled to the overlying Archean crust.Such a lithospheric structure shows the preferential modification of the lithospheric mantle in the eastern NCC and in the peripheral regions of the western NCC.The interior of the craton,especially most of the western NCC,remains stable and has been weakly modified.
基金supported by the National Natural Science Foundation of China(Grant Nos.41731072,41574095)the National Key R&D Program of China(Grant No.2017YFC1500305)Most figures were prepared with the Generic Mapping Tools(Wessel and Smith,1998)。
文摘The lithosphere of the North China Craton(NCC)has experienced significant destruction and deformation since the Mesozoic,a notable feature of which is the widespread extensional structure and lithospheric thinning in the eastern NCC.Since the thermo-rheological structure of the lithosphere is one of the main factors controlling these dynamic processes,a threedimensional thermo-rheological model of the present lithosphere in the NCC was developed based on a geophysical-petrological method using a variety of data,and its relationship with the extensional structures and the formation of rifts was further analyzed.Our results show that the western NCC is characterized by thick lithosphere,low Moho temperature(TMoho<600°C),as well as high lithospheric strength and mantle-crust strength ratio(Sm/Sc>1).The deformation of the western narrow rift is consistent with the localized deformation dominated by the strength of lithospheric mantle.On the other hand,the lithosphere in the eastern NCC is characterized by extensive thinning(with lithospheric thickness of about 80–110 km).However,the decrease of lithospheric strength is not uniform,with high strength(10×1012 Pa m)observed in some areas(such as the Bohai Bay Basin and Hehuai Basin).Most of the eastern lithosphere is characterized by high TMoho(600–750°C)and low Sm/Sc(<1),which is inconsistent with the widespread extensional structure in the eastern NCC.Incorporating results from palaeo-geothermal and petrological studies,we developed a thermo-rheological structure model of the lithosphere at different evolutionary stages of the NCC,and suggested that the eastern NCC had a significantly thinned and weakened lithosphere in the early stages of the formation of the rift,leading to a regional distributed extension deformation dominated by crustal strength,which eventually evolved into a series of wide rifts.However,the cooling and accretion of the lithosphere in the subsequent stages significantly increased the strength of the lithospheric mantle,resulting in the inconsistency between the present thermo-rheological structure of the lithosphere and the extensional structure formed in the past.
