Abstract The Nansha ultra-crust layer-block is confined by ultra-crustal boundary faults of distinctive features, bordering the Kangtai-Shuangzi-Xiongnan extensional faulted zone on the north, the Baxian-Baram-Yoca-Cu...Abstract The Nansha ultra-crust layer-block is confined by ultra-crustal boundary faults of distinctive features, bordering the Kangtai-Shuangzi-Xiongnan extensional faulted zone on the north, the Baxian-Baram-Yoca-Cuyo nappe faulted zone on the south, the Wan'an-Natuna strike-slip tensional faulted zone on the west and the Mondoro-Panay strike-slip compressive faulted zone on the east. These faults take the top of the Nansha asthenosphere as their common detachmental surface. The Cenozoic dynamic process of the ultra-crust layer-block can be divided into four stages: K2-E21, during which the northern boundary faults extended, this ultra-crust layer-block was separated from the South China-Indosinian continental margin, the Palaeo-South China Sea subducted southwards and the Sibu accretion wedge was formed; E22-E31, during which the Southwest sub-sea basin extended and orogeny was active due to the collision of the Sibu accretion wedge; E32-N11, during which the central sub-sea basin extended, the Miri accretion wedge was formed and “A-type” subduction of the southern margin of the north Balawan occurred; N12-the present, during which large-scale thrusting and napping of the boundary faults in the south and mountain-building have taken place and the South China Sea stopped its extension.展开更多
By processing S-wave data from the Fanshi-Huai’an-Taipusiqi DSS profile,which is a three-component,wide-angle reflection/refraction profile,and in the light of the results from P-wave interpretation,two-dimensional(2...By processing S-wave data from the Fanshi-Huai’an-Taipusiqi DSS profile,which is a three-component,wide-angle reflection/refraction profile,and in the light of the results from P-wave interpretation,two-dimensional(2-D)structures of the crust and upper mantle are presented,including S-wave velocity Vs and the physical parameter of medium-Poisson’s ratio a.Taking other geological and geophysical information into account,and with reference to the results from petrophysical experiments at home and abroad,we carried out interpretation and inference with respect to deep crustal structure,tectonics,and lithologic characters.It has been concluded that in the upper and middle crust,a values are mostly not greater than 0.25,and rocks,which generally assume brittle,are mainly composed of granite; the rocks in the lower layer of the upper crust between Yangyuan-Huai’an containing inorganic CO2 itself releases carbon; for the rocks in the lower crust and crust-mantle transitional zone,which are comparatively展开更多
The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of ...The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.展开更多
By use of S wave information from three component records of wide angle reflection/refraction Beijing Fengzhen DSS profile (340.0 km) and its adjacent area, several main S wave phases (wave groups) of the crust a...By use of S wave information from three component records of wide angle reflection/refraction Beijing Fengzhen DSS profile (340.0 km) and its adjacent area, several main S wave phases (wave groups) of the crust and the top of upper mantle have been picked up and identified with digital processing technique. With reference to the results from P wave interpretation, 2 D structures, including S wave velocity vS and Poisson ratio μ , are calculated. After a comprehensive study with information from near vertical reflection, geology and other geophysical explorations, the deep structural configuration of this region is presented and relevant inferences are drawn from the above result: crustal thickness along the profile tends to increase westwards, from 35.0 km at Shunyi to 42.0 km at Fengzhen; there exist three low velocity bodies in the lower crust east of Yanqing, in the middle crust below Yanqing Zhuolu and in the upper crust west of Tianzhen, respectively; from east to west, there is also a crust mantle transitional zone about 5.0～9.0 km thick; in most parts of the region, μ value is 0.25 in the upper and middle crust, 0.27 in the lower crust and 0.28 on top of the upper mantle, indicating that the upper and middle crust is characterized by brittleness, and the lower crust and top of upper mantle is characterized by ductility; between Yanqing Zhuolu, the low μ values of the upper crust suggest that cracks (or pores) grow in the rock masses which present a dry (or gas filled) state, while the high μ values in the middle crust may reflect a fluid filled (or partially fusion) state of the rock masses. On the basis of the characteristics of phases and lateral variation features of μ values, several deep seated faults in this region are ascertained. Most earthquakes occurred near these faults where μ values vary significantly, and concentrate in the brittle rock masses with low μ values.展开更多
On the basis of S wave information from Tai′an Xinzhou DSS profile and with reference to the results from P wave interpretation, the 2 D structures , including S wave velocity V s, ratio γ between V...On the basis of S wave information from Tai′an Xinzhou DSS profile and with reference to the results from P wave interpretation, the 2 D structures , including S wave velocity V s, ratio γ between V p and V s; and Poisson′s ratio σ , are calculated; the structural configuration of the profile is presented and the relevant inferences are drawn from the above results. Upwarping mantle districts (V s≈4.30 km/s)and sloping mantle districts (V s≈4.50 km/s) of the profile with velocity difference about 4% at the top of upper mantle are divided according to the differences of V s , γ and σ in different media and structures, also with reference to the information of their neighbouring regions; the existence of Niujiaqiao Dongwang high angle ultra crustal fault zone is reaffirmed; the properties of low and high velocity blocks(zones) including the crust mantle transitionalzone and the boudary indicators of North China rift valley are discussed. A comprehensive study is conducted on the relation of the interpretation results with earthquakes. It is concluded that the mantle upwarps, thermal material upwells through the high angle fault, the primary hypocenter was located at the crust mantle juncture 30.0～33.0 km deep, and additional stress excited the M S=6.8 and M S=7.2 earthquakes at specific locations around 9.0 km below Niujiaqiao Dongwang, the earthquakes took place around the high angle ultra crustal fault and centered in the brittle media and rock strata with low γ and low σ values.展开更多
文摘Abstract The Nansha ultra-crust layer-block is confined by ultra-crustal boundary faults of distinctive features, bordering the Kangtai-Shuangzi-Xiongnan extensional faulted zone on the north, the Baxian-Baram-Yoca-Cuyo nappe faulted zone on the south, the Wan'an-Natuna strike-slip tensional faulted zone on the west and the Mondoro-Panay strike-slip compressive faulted zone on the east. These faults take the top of the Nansha asthenosphere as their common detachmental surface. The Cenozoic dynamic process of the ultra-crust layer-block can be divided into four stages: K2-E21, during which the northern boundary faults extended, this ultra-crust layer-block was separated from the South China-Indosinian continental margin, the Palaeo-South China Sea subducted southwards and the Sibu accretion wedge was formed; E22-E31, during which the Southwest sub-sea basin extended and orogeny was active due to the collision of the Sibu accretion wedge; E32-N11, during which the central sub-sea basin extended, the Miri accretion wedge was formed and “A-type” subduction of the southern margin of the north Balawan occurred; N12-the present, during which large-scale thrusting and napping of the boundary faults in the south and mountain-building have taken place and the South China Sea stopped its extension.
文摘By processing S-wave data from the Fanshi-Huai’an-Taipusiqi DSS profile,which is a three-component,wide-angle reflection/refraction profile,and in the light of the results from P-wave interpretation,two-dimensional(2-D)structures of the crust and upper mantle are presented,including S-wave velocity Vs and the physical parameter of medium-Poisson’s ratio a.Taking other geological and geophysical information into account,and with reference to the results from petrophysical experiments at home and abroad,we carried out interpretation and inference with respect to deep crustal structure,tectonics,and lithologic characters.It has been concluded that in the upper and middle crust,a values are mostly not greater than 0.25,and rocks,which generally assume brittle,are mainly composed of granite; the rocks in the lower layer of the upper crust between Yangyuan-Huai’an containing inorganic CO2 itself releases carbon; for the rocks in the lower crust and crust-mantle transitional zone,which are comparatively
基金The National Natural Science Foundation of China under contract Nos 41176053,41076029,91028002 and 41176046Dayang 115 under contract No.DYXM-115-02-3-01
文摘The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.
文摘By use of S wave information from three component records of wide angle reflection/refraction Beijing Fengzhen DSS profile (340.0 km) and its adjacent area, several main S wave phases (wave groups) of the crust and the top of upper mantle have been picked up and identified with digital processing technique. With reference to the results from P wave interpretation, 2 D structures, including S wave velocity vS and Poisson ratio μ , are calculated. After a comprehensive study with information from near vertical reflection, geology and other geophysical explorations, the deep structural configuration of this region is presented and relevant inferences are drawn from the above result: crustal thickness along the profile tends to increase westwards, from 35.0 km at Shunyi to 42.0 km at Fengzhen; there exist three low velocity bodies in the lower crust east of Yanqing, in the middle crust below Yanqing Zhuolu and in the upper crust west of Tianzhen, respectively; from east to west, there is also a crust mantle transitional zone about 5.0～9.0 km thick; in most parts of the region, μ value is 0.25 in the upper and middle crust, 0.27 in the lower crust and 0.28 on top of the upper mantle, indicating that the upper and middle crust is characterized by brittleness, and the lower crust and top of upper mantle is characterized by ductility; between Yanqing Zhuolu, the low μ values of the upper crust suggest that cracks (or pores) grow in the rock masses which present a dry (or gas filled) state, while the high μ values in the middle crust may reflect a fluid filled (or partially fusion) state of the rock masses. On the basis of the characteristics of phases and lateral variation features of μ values, several deep seated faults in this region are ascertained. Most earthquakes occurred near these faults where μ values vary significantly, and concentrate in the brittle rock masses with low μ values.
文摘On the basis of S wave information from Tai′an Xinzhou DSS profile and with reference to the results from P wave interpretation, the 2 D structures , including S wave velocity V s, ratio γ between V p and V s; and Poisson′s ratio σ , are calculated; the structural configuration of the profile is presented and the relevant inferences are drawn from the above results. Upwarping mantle districts (V s≈4.30 km/s)and sloping mantle districts (V s≈4.50 km/s) of the profile with velocity difference about 4% at the top of upper mantle are divided according to the differences of V s , γ and σ in different media and structures, also with reference to the information of their neighbouring regions; the existence of Niujiaqiao Dongwang high angle ultra crustal fault zone is reaffirmed; the properties of low and high velocity blocks(zones) including the crust mantle transitionalzone and the boudary indicators of North China rift valley are discussed. A comprehensive study is conducted on the relation of the interpretation results with earthquakes. It is concluded that the mantle upwarps, thermal material upwells through the high angle fault, the primary hypocenter was located at the crust mantle juncture 30.0～33.0 km deep, and additional stress excited the M S=6.8 and M S=7.2 earthquakes at specific locations around 9.0 km below Niujiaqiao Dongwang, the earthquakes took place around the high angle ultra crustal fault and centered in the brittle media and rock strata with low γ and low σ values.
