Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and h...Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58-1.12 μW/m3 with a median of 0.85 μW/m3. Accordingly, the contents of U, Th and K20 in China crust are in ranges of 0.83-1.76 μg/g, 3.16-6.69 μg/g, and 1.0%-2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China＇s continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain （1995）, Rudnick and Gao （2003）, Weaver and Tarney （1984）, Shaw et al. （1986）, and Wedepohl （1995） overestimate the abundance of incompatible elements such as U, Th and K of continental crust.展开更多
The ratio of P- to S-wave velocities （Vp/Vs） is regarded as one of the most diagnostic properties of natural rocks. It has been used as a discriminant of composition for the continental crust and provides valuable c...The ratio of P- to S-wave velocities （Vp/Vs） is regarded as one of the most diagnostic properties of natural rocks. It has been used as a discriminant of composition for the continental crust and provides valuable constraints on its formation and evolution processes. Furthermore, the spatial and temporal changes in Vp/Vs before and after earthquakes are probably the most promising avenue to understanding the source mechanics and possibly predicting earthquakes. Here we calibrate the variations in Vp/Vs in dry, anisotropic crustal rocks and provide a set of basic information for the interpretation of future seismic data from the Wenchuan earthquake Fault zone Scientific Drilling （WFSD） project and other surveys. Vp/Vs is a constant （Ф0） for an isotropic rock. However, most of crustal rocks are anisotropic due to lattice-preferred orientations of anisotropic minerals （e.g., mica, amphibole, plagioclase and pyroxene） and cracks as well as thin compositional layering. The Vp/Vs ratio of an anisotropic rock measured along a selected pair of propagation-vibration directions is an apparent value （Фy） that is significantly different from the value for its isotropic counterpart （Ф0）. The usefulness of apparent Vp/Vs ratios as a diagnostic of crustal composition depends largely on rock seismic anisotropy. A 5% of P- and S-wave velocity anisotropy is sufficient to make it impossible to determine the crustal composition using the conventional criteria （Vp/Vs≤1.756 for felsic rocks, 1.756〈Vp/Vs≤1.809 for intermediate rocks, 1.809〈Vp/Vs≤1.944 for mafic rocks, and Vp/V2〉1.944 fluidfilled porous/fractured or partially molten rocks） if the information about the wave propagation-polarization directions with respect to the tectonic framework is unknown. However, the variations in Vp/Vs measured from borehole seismic experiments can be readily interpreted according to the orientations of the ray path and the polarization of the shear waves with respect to the present-day principal stress directions （i.e., the orientation of cracks） and the frozen fabric （i.e., foliation and lineation）.展开更多
The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(...The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(Qingzang)Plateau and adjacent blocks,plateau uplift,and strong earthquake mechanisms.P-wave velocity and crustal composition provide key constraints on the properties of distinct tectonic units and their evolutionary modification processes.Based on the results of 8 Deep Seismic Sounding(DSS)profiles completed in the Bayan Har block and surrounding areas over the past 20 years,We constructed one-dimensional P-wave velocity models for the crust of Bayan Har block,Qilian fold belt,Qinling fold belt,Alxa block,Ordos block and Sichuan basin.Furthermore,crustal composition models for different tectonic units were established based on these results.The results reveal that the crustal thickness of the Bayan Har block gradually decreases towards the NNE,NE,and SE directions,while the average crustal velocity increases correspondingly.The felsic layer in the crust accounts for more than half of the total crustal thickness.The mafic content within the crust of different tectonic units exhibits notable variations,which may reflect that the Bayan Har block,Qilian fold belt,and Qinling fold belt have experienced more intensive lithospheric evolution processes compared to Ordos basin and Sichuan basin.The seismicity distribution in this region is significantly controlled by crustal velocity and composition heterogeneity across the Bayan Har block and adjacent areas,which demonstrates that earthquakes within and around the Bayan Har block exhibit both high frequency and larger magnitudes.These seismic characteristics primarily result from intense crustal stress accumulation and release during the outward expansion of the Qingzang Plateau.展开更多
On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geother...On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geotherms for each grid is established for P-T correction on P-wave velocities. The average depths of sub-crustal layers and their average P-wave velocities of 18 tectonic units in eastern China are exhibited. Our result presents a 32-34 km thick crust beneath eastern China, which is thinner than previous studies, with an average velocity of 6.54 km/s, corresponding to a 5 kg/m3 variation in crustal mean density. The thicker upper but thinner middle and lower crust results in a lower average seismic velocity of eastern China. An intermediate crustal composition with a SiO2 content of 59.7 wt% has been estimated. However, there exists a significant lateral variation in the crustal structures among the tectonic units of eastern China. The structure and composition features of some regions in eastern China indicate that extension has played an important role in the continental crust evolution of eastern China.展开更多
The Tian Shan is a vast range that spans several countries in Asia.Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics.In this study,we explored the crustal cha...The Tian Shan is a vast range that spans several countries in Asia.Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics.In this study,we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region.A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P-to S-wave velocities(Vp/Vs)for 91 broadband seismic stations in the central and western Tian Shan.Our results revealed significant lateral variations in crustal thickness and Vp/Vs.A—45-km-thick crust and an intermediate-high Vp/Vs(-1.74-1.84)were found in the Kazakh Shield and Tarim Basin,which we interpreted to indicate a mafic crystalline basement and lower crust.The central Tian Shan varied greatly in crustal thickness(40-64 km)and Vp/Vs ratio(1.65-2.00).which may be due to crustal shortening,mafic underplating,and crustal melting.In contrast,we observed a relatively thin crust(42-50 km)with an intermediate Vp/Vs ratio(-1.78)in the western Tian Shan.The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric.展开更多
Based on Moho and Curie depth,heat flow,and upper mantle S-wave velocity anomaly,we infer the thermo-chemical structure of the lithospheres in Africa and surrounding oceans.The Moho depth is derived from gravity anoma...Based on Moho and Curie depth,heat flow,and upper mantle S-wave velocity anomaly,we infer the thermo-chemical structure of the lithospheres in Africa and surrounding oceans.The Moho depth is derived from gravity anomaly using the Parker-Oldenburg method,with constraints from seismic Moho.Crustal stratification defined by Curie-Moho depth difference shows that thermal and strong compositional processes may have shaped the lithospheric architecture of the African continental plate.Moho and Curie depths indicate the southern and eastern African cratons have thermochemical structures different from the West African Craton.Large Curie-Moho depth difference in southern and eastern Africa aligns with the low velocity anomaly originated from the core-mantle boundary.Mantle upwelling from the African low-velocity anomaly presumably induced partial melting at great depth,and the release of mineral-rich fluid and large amounts of volatile components facilitates a regional metasomatism,and results in a depleted,predominantly felsic,low-density paramagnetic crust.Mantle xenolith in kimberlites and volcanic rocks supports metasomatism by melts transmitted through narrow conduits as an intermittent or continuous upward flux of mineral-rich fluid.Alignment of the Curie-Moho depth difference at the intra-plate volcanic province correlates with weak lithospheric strength along the corridor connecting the intra-plate volcanic province with the Ethiopian plateau,suggesting a pathway for thermochemical asthenospheric flow.Crustal stratification and compositional-driven density layering support crustal buoyancy and uplift in the Hoggar,and southern and eastern Africa.A magnetized uppermost mantle is prevalent in the entire oceanic region,except at large igneous provinces(LIPs),volcanic seamounts,and oceanic plateaus,which have partial paramagnetic crusts.Our results support thermochemical upwelling related to the low velocity anomaly beneath the African plate.展开更多
Crustal thickness and composition are closely related to geology and tectonic evolution of the region.Studying the differences in the crustal thickness and composition of the South China Block(SCB)is important to gain...Crustal thickness and composition are closely related to geology and tectonic evolution of the region.Studying the differences in the crustal thickness and composition of the South China Block(SCB)is important to gain a comprehensive understanding of multi-phase amalgamation,breakup,reworking,and regional geodynamic processes.In this study,teleseismic data from 135 high-density portable broadband stations from Sino Probe were processed using Common Conversion Point(CCP)stacking and H-κstacking methods.The Moho depth and P-wave and S-wave velocity ratio(V_(p)/V_(s))were studied.Our results revealed several insights about the tectonic processes in the SCB.First,the crustal structure and V_(p)/V_(s)ratios of the Cathaysia Block,Jiangnan Orogenic Belt,and Yangtze Block were significantly different.The average depth of the Moho in the Cathaysia Block was approximately 31 km,and the V_(p)/V_(s)ratios increased from the inland area(1.66)to the coastal area(1.78),indicating the oceanward increase of mafic proportion in the lower crust,which is related to the influence of the Paleo-Pacific Plate westward subduction.Second,the crustal thickness of Jiangnan Orogenic Belt deepens from east ca.31 to the west ca.42 km and the V_(p)/V_(s)ratios varied from 1.75 to 1.64,illustrating a relatively felsic crust,which could have been related to the Mesozoic upper crustal thickening under compression followed by the lower crust removal under the extensional background.Third,the average crustal thickness of the Yangtze Block was 42 km,and the V_(p)/V_(s)ratios ranged from 1.64 to 1.84,presenting a positive correlation between the Moho depth and the V_(p)/V_(s)ratio,which is explained by the relatively thick mafic lower crust.Based on the variations in the crustal structure and V_(p)/V_(s)ratios of the profile,we inferred that the central part of the Jiangnan Orogenic Belt was bounded by the Jiangshan-Shaoxing-Hengyang in the east and the Jiujiang-Shitai-Jishou in the west.The small-scale Moho depth undulations at the intersection of the Cathaysia Block and the Jiangnan Orogenic Belt could be related to the Mesozoic compression-extension geodynamic transformation.展开更多
基金supported by the National Natural Science Foundation of China (Grants Nos. 40376013, 40572128, and 40104003)
文摘Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58-1.12 μW/m3 with a median of 0.85 μW/m3. Accordingly, the contents of U, Th and K20 in China crust are in ranges of 0.83-1.76 μg/g, 3.16-6.69 μg/g, and 1.0%-2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China＇s continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain （1995）, Rudnick and Gao （2003）, Weaver and Tarney （1984）, Shaw et al. （1986）, and Wedepohl （1995） overestimate the abundance of incompatible elements such as U, Th and K of continental crust.
基金funded by the Natural Sciences and Engineering Council of Canada and the Geological Survey of China
文摘The ratio of P- to S-wave velocities （Vp/Vs） is regarded as one of the most diagnostic properties of natural rocks. It has been used as a discriminant of composition for the continental crust and provides valuable constraints on its formation and evolution processes. Furthermore, the spatial and temporal changes in Vp/Vs before and after earthquakes are probably the most promising avenue to understanding the source mechanics and possibly predicting earthquakes. Here we calibrate the variations in Vp/Vs in dry, anisotropic crustal rocks and provide a set of basic information for the interpretation of future seismic data from the Wenchuan earthquake Fault zone Scientific Drilling （WFSD） project and other surveys. Vp/Vs is a constant （Ф0） for an isotropic rock. However, most of crustal rocks are anisotropic due to lattice-preferred orientations of anisotropic minerals （e.g., mica, amphibole, plagioclase and pyroxene） and cracks as well as thin compositional layering. The Vp/Vs ratio of an anisotropic rock measured along a selected pair of propagation-vibration directions is an apparent value （Фy） that is significantly different from the value for its isotropic counterpart （Ф0）. The usefulness of apparent Vp/Vs ratios as a diagnostic of crustal composition depends largely on rock seismic anisotropy. A 5% of P- and S-wave velocity anisotropy is sufficient to make it impossible to determine the crustal composition using the conventional criteria （Vp/Vs≤1.756 for felsic rocks, 1.756〈Vp/Vs≤1.809 for intermediate rocks, 1.809〈Vp/Vs≤1.944 for mafic rocks, and Vp/V2〉1.944 fluidfilled porous/fractured or partially molten rocks） if the information about the wave propagation-polarization directions with respect to the tectonic framework is unknown. However, the variations in Vp/Vs measured from borehole seismic experiments can be readily interpreted according to the orientations of the ray path and the polarization of the shear waves with respect to the present-day principal stress directions （i.e., the orientation of cracks） and the frozen fabric （i.e., foliation and lineation）.
基金supported by the National Key R&D Program of China(No.2023YFC3012002)the National Natural Science Foundation of China(42374073)。
文摘The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(Qingzang)Plateau and adjacent blocks,plateau uplift,and strong earthquake mechanisms.P-wave velocity and crustal composition provide key constraints on the properties of distinct tectonic units and their evolutionary modification processes.Based on the results of 8 Deep Seismic Sounding(DSS)profiles completed in the Bayan Har block and surrounding areas over the past 20 years,We constructed one-dimensional P-wave velocity models for the crust of Bayan Har block,Qilian fold belt,Qinling fold belt,Alxa block,Ordos block and Sichuan basin.Furthermore,crustal composition models for different tectonic units were established based on these results.The results reveal that the crustal thickness of the Bayan Har block gradually decreases towards the NNE,NE,and SE directions,while the average crustal velocity increases correspondingly.The felsic layer in the crust accounts for more than half of the total crustal thickness.The mafic content within the crust of different tectonic units exhibits notable variations,which may reflect that the Bayan Har block,Qilian fold belt,and Qinling fold belt have experienced more intensive lithospheric evolution processes compared to Ordos basin and Sichuan basin.The seismicity distribution in this region is significantly controlled by crustal velocity and composition heterogeneity across the Bayan Har block and adjacent areas,which demonstrates that earthquakes within and around the Bayan Har block exhibit both high frequency and larger magnitudes.These seismic characteristics primarily result from intense crustal stress accumulation and release during the outward expansion of the Qingzang Plateau.
基金supported by grants from the National Natural Science Foundation of China(No.40104003)China Post-doctoral Science Foundationthe Chinese Academy of Sciences K.C.Wong Post-doctoral Research Award
文摘On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geotherms for each grid is established for P-T correction on P-wave velocities. The average depths of sub-crustal layers and their average P-wave velocities of 18 tectonic units in eastern China are exhibited. Our result presents a 32-34 km thick crust beneath eastern China, which is thinner than previous studies, with an average velocity of 6.54 km/s, corresponding to a 5 kg/m3 variation in crustal mean density. The thicker upper but thinner middle and lower crust results in a lower average seismic velocity of eastern China. An intermediate crustal composition with a SiO2 content of 59.7 wt% has been estimated. However, there exists a significant lateral variation in the crustal structures among the tectonic units of eastern China. The structure and composition features of some regions in eastern China indicate that extension has played an important role in the continental crust evolution of eastern China.
基金supported by the National Science Foundation of China (Nos. U1839210, 41874097, 41474072, and 41874108)
文摘The Tian Shan is a vast range that spans several countries in Asia.Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics.In this study,we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region.A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P-to S-wave velocities(Vp/Vs)for 91 broadband seismic stations in the central and western Tian Shan.Our results revealed significant lateral variations in crustal thickness and Vp/Vs.A—45-km-thick crust and an intermediate-high Vp/Vs(-1.74-1.84)were found in the Kazakh Shield and Tarim Basin,which we interpreted to indicate a mafic crystalline basement and lower crust.The central Tian Shan varied greatly in crustal thickness(40-64 km)and Vp/Vs ratio(1.65-2.00).which may be due to crustal shortening,mafic underplating,and crustal melting.In contrast,we observed a relatively thin crust(42-50 km)with an intermediate Vp/Vs ratio(-1.78)in the western Tian Shan.The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric.
基金Supported by the National Natural Science Foundation of China(Nos.91858213,41776057,41761134051)part of the PhD work of O J AKINRINADE and the National Key Research and Development Program of China(Nos.2023 YFF 0803400,2023 YFF 0803404)。
文摘Based on Moho and Curie depth,heat flow,and upper mantle S-wave velocity anomaly,we infer the thermo-chemical structure of the lithospheres in Africa and surrounding oceans.The Moho depth is derived from gravity anomaly using the Parker-Oldenburg method,with constraints from seismic Moho.Crustal stratification defined by Curie-Moho depth difference shows that thermal and strong compositional processes may have shaped the lithospheric architecture of the African continental plate.Moho and Curie depths indicate the southern and eastern African cratons have thermochemical structures different from the West African Craton.Large Curie-Moho depth difference in southern and eastern Africa aligns with the low velocity anomaly originated from the core-mantle boundary.Mantle upwelling from the African low-velocity anomaly presumably induced partial melting at great depth,and the release of mineral-rich fluid and large amounts of volatile components facilitates a regional metasomatism,and results in a depleted,predominantly felsic,low-density paramagnetic crust.Mantle xenolith in kimberlites and volcanic rocks supports metasomatism by melts transmitted through narrow conduits as an intermittent or continuous upward flux of mineral-rich fluid.Alignment of the Curie-Moho depth difference at the intra-plate volcanic province correlates with weak lithospheric strength along the corridor connecting the intra-plate volcanic province with the Ethiopian plateau,suggesting a pathway for thermochemical asthenospheric flow.Crustal stratification and compositional-driven density layering support crustal buoyancy and uplift in the Hoggar,and southern and eastern Africa.A magnetized uppermost mantle is prevalent in the entire oceanic region,except at large igneous provinces(LIPs),volcanic seamounts,and oceanic plateaus,which have partial paramagnetic crusts.Our results support thermochemical upwelling related to the low velocity anomaly beneath the African plate.
基金supported by the National Natural Science Foundation of China(Grant Nos.41630320,92062108)the China Geological Survey Project(Grant No.DD20190012)open fund from the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resource,Institute of Geology,Chinese Academy of Geological Sciences(Grant No.J1901-16)。
文摘Crustal thickness and composition are closely related to geology and tectonic evolution of the region.Studying the differences in the crustal thickness and composition of the South China Block(SCB)is important to gain a comprehensive understanding of multi-phase amalgamation,breakup,reworking,and regional geodynamic processes.In this study,teleseismic data from 135 high-density portable broadband stations from Sino Probe were processed using Common Conversion Point(CCP)stacking and H-κstacking methods.The Moho depth and P-wave and S-wave velocity ratio(V_(p)/V_(s))were studied.Our results revealed several insights about the tectonic processes in the SCB.First,the crustal structure and V_(p)/V_(s)ratios of the Cathaysia Block,Jiangnan Orogenic Belt,and Yangtze Block were significantly different.The average depth of the Moho in the Cathaysia Block was approximately 31 km,and the V_(p)/V_(s)ratios increased from the inland area(1.66)to the coastal area(1.78),indicating the oceanward increase of mafic proportion in the lower crust,which is related to the influence of the Paleo-Pacific Plate westward subduction.Second,the crustal thickness of Jiangnan Orogenic Belt deepens from east ca.31 to the west ca.42 km and the V_(p)/V_(s)ratios varied from 1.75 to 1.64,illustrating a relatively felsic crust,which could have been related to the Mesozoic upper crustal thickening under compression followed by the lower crust removal under the extensional background.Third,the average crustal thickness of the Yangtze Block was 42 km,and the V_(p)/V_(s)ratios ranged from 1.64 to 1.84,presenting a positive correlation between the Moho depth and the V_(p)/V_(s)ratio,which is explained by the relatively thick mafic lower crust.Based on the variations in the crustal structure and V_(p)/V_(s)ratios of the profile,we inferred that the central part of the Jiangnan Orogenic Belt was bounded by the Jiangshan-Shaoxing-Hengyang in the east and the Jiujiang-Shitai-Jishou in the west.The small-scale Moho depth undulations at the intersection of the Cathaysia Block and the Jiangnan Orogenic Belt could be related to the Mesozoic compression-extension geodynamic transformation.
