This study examines the relationship between high positive isostatic gravity anomalies(IGA),steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau.IGA data has revealed uplift and ex...This study examines the relationship between high positive isostatic gravity anomalies(IGA),steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau.IGA data has revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains(the LMS).Firstly,The high positive IGA zone corresponds to the LMS orogenic belt.It is shown that abrupt changes in IGA correspond to zones of abrupt change of topography,crustal thickness and rock density along the LMS.Secondly,on the basis of the Airy isostasy theory,simulations and inversions of the positive IGA were conducted using three-dimensional bodies.The results indicated that the LMS lacks a mountain root,and that the top surface of the lower crust has been elevated by 11 km,leading to positive IGA,tectonic load and density load.Thirdly,according to Watts's flexural isostasy model,elastic deflection occurs,suggesting that the limited(i.e.narrow)tectonic and density load driven by lower crustal flow in the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge.Finally,based on the correspondence between zones of extremely high positive IGA and the presence of the Precambrian Pengguan-Baoxing complexes in the LMS,the first appearance of erosion gravels from the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower crustal flow in the LMS took place at 3.6 Ma or slightly earlier.展开更多
Block faults, as the -dominant tectonic framwork of western Shandong, were formed by the linked extensional fault system through two extensional movements during the Meso-Cenozoic. Both of the extensional movements ex...Block faults, as the -dominant tectonic framwork of western Shandong, were formed by the linked extensional fault system through two extensional movements during the Meso-Cenozoic. Both of the extensional movements experienced the same evloutional process: first, the upper crust was pulled apart to form faults; then the Tai-Lu-Yi (Taishan-Lushan-Yishan) fault block occurring in the footwall of the extensional fault was uplifted, which induced the shallow-level detachment movement along the early Precambrian and Palaeozoic unconformity; the ' branching' fault in the upper part of the deep-level detachment layer propagated. As the shallow detachment moved towards the north and the deep one towards the south, the Tai-Lu-Yi fault block acted as the common footwall of both the southern and northern detachment systems. The Tai-Lu-Yi fault block rebounded and uplifted as the overlying material was pulled apart to cause an unloading. Sialic material of the mid-crust below the deep detachment flowed to and accumulated in the free space below the rebounding uplifted body and thickened the body; whereas the mid-crust thinned under the graben systems. The rebounding uplifted body cooled, and then the graben system was occluded, which resulted in the crust-mantle isostatic adjustment and asthenospheric convection. As a result of the two extensional movements, the uplifted central Shandong block with the Tai-Lu-Yi area as the core stands highly above the surrounding plain characterized by graben systems. The present Mount Taishan forms the climax of the uplift.展开更多
Panzhihua-Xichang (Panxi) micro-palaeoland is the oldest terrane on the western margin of the Yangtze Block. Some intermediate-basic granulites are considered to be the crys-talline basement of lower crust in the terr...Panzhihua-Xichang (Panxi) micro-palaeoland is the oldest terrane on the western margin of the Yangtze Block. Some intermediate-basic granulites are considered to be the crys-talline basement of lower crust in the terrane. Granulite-facies metamorphism of the granulites was developed in the period from 1186 Ma to 1128 Ma. The origin of granulites was related to the collision orogenic process occurring when the micro-palaeolands merged to form the Rodinia Supercontinent. Amphibolite-facies retrogressive metamorphism of granulites took place in the period from 877 Ma to 825 Ma. This period was consistent with the breakup time of the Rodinia Supercontinent. 40Ar/39Ar ages and fission track (FT) ages of granulites in the Panxi mi-cro-palaeoland show that the vertical movement history of crustal rocks was a slow uplift process of the rigid terrane in the time from Neoproterozoic to Mesozoic. The subduction of India Plate towards Euroasia Plate resulted in the rapid uplift of the Qinghai-Tibetan Block in Cenozoic. Meanwhile, the Qinghai-Tibetan Block moved towards east. Consequently the Panxi terrane was uplifted rapidly. As a result of the collision orogeny between the Qinghai-Tibetan Block and the Panxi terrane, the granulite-facies crystalline basement in this region was exhumed and exposed to the surface.展开更多
The Tanggula （唐古拉） thrust system and the Tuotuohe （沱沱河） foreland basin, which represent major Cenozoic tectonic units of the central Tibetan plateau, have been recently studied. Field investigation, analyse...The Tanggula （唐古拉） thrust system and the Tuotuohe （沱沱河） foreland basin, which represent major Cenozoic tectonic units of the central Tibetan plateau, have been recently studied. Field investigation, analyses of deformation and construction of two restored balanced structural sections suggest 75-100 km （51%-64%） of N-S shortening in the Tanggula thrust system and 55-114 km （42%-47%） of N-S shortening in the Tuotuohe basin. The shortening ratios indicate that the Tanggula- Tuotuohe area has undergone intensive deformation and crustal shortening during the Early Tertiary, resulting not only in crustal thickening, but also in large scale volcanism and in rapid uplift of the Tanggula Mountains.展开更多
In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plat...In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plateau, adjacent to the Sichuan basin, is characterized by very steep relief with high mountain ranges. The crust beneath this region slows the velocities in the middle and lower crust. We have adopted a relatively dense network to inverse the detailed structure of the crust and upper mantle along the eastern margin of the Tibetan plateau and Sichuan basin, using teleseismic data via receiver function analysis. The results are in-line with the hypothesis that viscous crustal material is flowing beneath the eastern margin of the Tibetan plateau and that this process drives overlying crustal material around the strong and rigid Sichuan basin. When the viscous material hits this obstruction, flows are divided into two or more branches with different directions. The upper part of the upwelling viscous flow produces the pressure to intrude the upper crust, thereby driving uplift of mountain ranges and high peaks. In contrast, the lower part of the downwelling viscous flow produces the pressure to intrude the lower crust and upper mantle to deepen the Moho discontinuity, causing observed crustal thickening.展开更多
A test of deep seismic reflection profiling across the central uplift or metamorphic belt of the Qiangtang （羌塘） terrane, Tibet plateau, provides a first image of the crustal structure. Complex reflection patterns ...A test of deep seismic reflection profiling across the central uplift or metamorphic belt of the Qiangtang （羌塘） terrane, Tibet plateau, provides a first image of the crustal structure. Complex reflection patterns in the upper crust are interpreted as a series of folds and thrusts, and bivergent reflections in the lower crust may represent a convergence between the Indian and the Eurasian plates.展开更多
This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical chara...This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly （Gh） and the crustal density structure reveal that （1） the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault （F4） and Helandonglu fault （F6）, which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; （2） the main active faults correspond to the Gh contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault （F1） or the southeast boundary of Alxa block is in accord with the western change belt of Gh, a belt about 10 km wide that extends to about 30 km; （3） Yinchuan- Pingluo fault （FS） is the seismogenic structure of the Pin- gluo M earthquake, and its focal depth is about 15 km; （4） the Moho depth trend and Bouguer gravity anomaly vari- ation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.展开更多
基金funded by the National Natural Science Foundation of China(Grant Nos.41372114,41502116,41340005,41172162,40972083,40841010)a research project of the National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Grant No.SK-0801)
文摘This study examines the relationship between high positive isostatic gravity anomalies(IGA),steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau.IGA data has revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains(the LMS).Firstly,The high positive IGA zone corresponds to the LMS orogenic belt.It is shown that abrupt changes in IGA correspond to zones of abrupt change of topography,crustal thickness and rock density along the LMS.Secondly,on the basis of the Airy isostasy theory,simulations and inversions of the positive IGA were conducted using three-dimensional bodies.The results indicated that the LMS lacks a mountain root,and that the top surface of the lower crust has been elevated by 11 km,leading to positive IGA,tectonic load and density load.Thirdly,according to Watts's flexural isostasy model,elastic deflection occurs,suggesting that the limited(i.e.narrow)tectonic and density load driven by lower crustal flow in the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge.Finally,based on the correspondence between zones of extremely high positive IGA and the presence of the Precambrian Pengguan-Baoxing complexes in the LMS,the first appearance of erosion gravels from the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower crustal flow in the LMS took place at 3.6 Ma or slightly earlier.
文摘Block faults, as the -dominant tectonic framwork of western Shandong, were formed by the linked extensional fault system through two extensional movements during the Meso-Cenozoic. Both of the extensional movements experienced the same evloutional process: first, the upper crust was pulled apart to form faults; then the Tai-Lu-Yi (Taishan-Lushan-Yishan) fault block occurring in the footwall of the extensional fault was uplifted, which induced the shallow-level detachment movement along the early Precambrian and Palaeozoic unconformity; the ' branching' fault in the upper part of the deep-level detachment layer propagated. As the shallow detachment moved towards the north and the deep one towards the south, the Tai-Lu-Yi fault block acted as the common footwall of both the southern and northern detachment systems. The Tai-Lu-Yi fault block rebounded and uplifted as the overlying material was pulled apart to cause an unloading. Sialic material of the mid-crust below the deep detachment flowed to and accumulated in the free space below the rebounding uplifted body and thickened the body; whereas the mid-crust thinned under the graben systems. The rebounding uplifted body cooled, and then the graben system was occluded, which resulted in the crust-mantle isostatic adjustment and asthenospheric convection. As a result of the two extensional movements, the uplifted central Shandong block with the Tai-Lu-Yi area as the core stands highly above the surrounding plain characterized by graben systems. The present Mount Taishan forms the climax of the uplift.
基金This work was supported by the National Natural Science Foundation of China(Grant No.49972062)by the Ministry of Education(Grant No.104089).
文摘Panzhihua-Xichang (Panxi) micro-palaeoland is the oldest terrane on the western margin of the Yangtze Block. Some intermediate-basic granulites are considered to be the crys-talline basement of lower crust in the terrane. Granulite-facies metamorphism of the granulites was developed in the period from 1186 Ma to 1128 Ma. The origin of granulites was related to the collision orogenic process occurring when the micro-palaeolands merged to form the Rodinia Supercontinent. Amphibolite-facies retrogressive metamorphism of granulites took place in the period from 877 Ma to 825 Ma. This period was consistent with the breakup time of the Rodinia Supercontinent. 40Ar/39Ar ages and fission track (FT) ages of granulites in the Panxi mi-cro-palaeoland show that the vertical movement history of crustal rocks was a slow uplift process of the rigid terrane in the time from Neoproterozoic to Mesozoic. The subduction of India Plate towards Euroasia Plate resulted in the rapid uplift of the Qinghai-Tibetan Block in Cenozoic. Meanwhile, the Qinghai-Tibetan Block moved towards east. Consequently the Panxi terrane was uplifted rapidly. As a result of the collision orogeny between the Qinghai-Tibetan Block and the Panxi terrane, the granulite-facies crystalline basement in this region was exhumed and exposed to the surface.
基金supported by the National Natural Science Foundation of China (No. 40672086)the Ministry of Science and Technology of China (No. 2006CB701400)
文摘The Tanggula （唐古拉） thrust system and the Tuotuohe （沱沱河） foreland basin, which represent major Cenozoic tectonic units of the central Tibetan plateau, have been recently studied. Field investigation, analyses of deformation and construction of two restored balanced structural sections suggest 75-100 km （51%-64%） of N-S shortening in the Tanggula thrust system and 55-114 km （42%-47%） of N-S shortening in the Tuotuohe basin. The shortening ratios indicate that the Tanggula- Tuotuohe area has undergone intensive deformation and crustal shortening during the Early Tertiary, resulting not only in crustal thickening, but also in large scale volcanism and in rapid uplift of the Tanggula Mountains.
基金supported by National Natural Science Foundation of China under grant Nos. 40839909,41074062, and 40674040
文摘In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plateau, adjacent to the Sichuan basin, is characterized by very steep relief with high mountain ranges. The crust beneath this region slows the velocities in the middle and lower crust. We have adopted a relatively dense network to inverse the detailed structure of the crust and upper mantle along the eastern margin of the Tibetan plateau and Sichuan basin, using teleseismic data via receiver function analysis. The results are in-line with the hypothesis that viscous crustal material is flowing beneath the eastern margin of the Tibetan plateau and that this process drives overlying crustal material around the strong and rigid Sichuan basin. When the viscous material hits this obstruction, flows are divided into two or more branches with different directions. The upper part of the upwelling viscous flow produces the pressure to intrude the upper crust, thereby driving uplift of mountain ranges and high peaks. In contrast, the lower part of the downwelling viscous flow produces the pressure to intrude the lower crust and upper mantle to deepen the Moho discontinuity, causing observed crustal thickening.
基金supported by the National Natural Science Foundation of China (Nos. 40830316, 40874045 and 40704016)the Ministry of Science and Technology of China (Nos. SinoProbe-02, 2006DFA21340)+1 种基金the Ministry of Land and Resources of China (Nos. 2004-06, 200811021)the Open Fund of Key Laboratory of Geo-detection of China Uni-versity of Geosciences (Beijing) (No. GDL0603)
文摘A test of deep seismic reflection profiling across the central uplift or metamorphic belt of the Qiangtang （羌塘） terrane, Tibet plateau, provides a first image of the crustal structure. Complex reflection patterns in the upper crust are interpreted as a series of folds and thrusts, and bivergent reflections in the lower crust may represent a convergence between the Indian and the Eurasian plates.
基金supported by the Key Projects of China Seismic Array(201308011)Earthquake Science(201508006)the China Earthquake Administration,Institute of Seismology Foundation(201326126)
文摘This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly （Gh） and the crustal density structure reveal that （1） the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault （F4） and Helandonglu fault （F6）, which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; （2） the main active faults correspond to the Gh contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault （F1） or the southeast boundary of Alxa block is in accord with the western change belt of Gh, a belt about 10 km wide that extends to about 30 km; （3） Yinchuan- Pingluo fault （FS） is the seismogenic structure of the Pin- gluo M earthquake, and its focal depth is about 15 km; （4） the Moho depth trend and Bouguer gravity anomaly vari- ation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.
