The 3-D geometry of the seismicity in Hindu Kush-Pamir--western China region has been defined by seismic records for 1975-1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,0...The 3-D geometry of the seismicity in Hindu Kush-Pamir--western China region has been defined by seismic records for 1975-1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most Ms≥ 5.0 hypocenters in the area are confined to a major intracontinental seismic shear zone （MSSZ）. The MSSZ, which dips southwards in Pamir has a north- dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India-Asia collisional zone. We demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45-65 km, 95-120 km, and 180-220 km, suggesting different structural relationships where each occurs. Results from focal mechanism solutions in all three seismological concentrations show orientations of the principal maximum stress to be nearly horizontal in an NNW-SSE direction. The south-dipping Pamir subduction slab is wedge-shaped with a wide upper top and a narrow deeper bottom; the slab has a gentle angle of dip in the upper part and steeper dips in the lower part below an elbow depth of ca. 80--120 km. Most of the deformation related to the earthquakes occurs within the hanging wall of the subducting Pamir slab. Published geologic data and repeated GPS measurements in the Pamir document a broad supra-subduc- tion, upper crustal zone of evolving antithetic （i.e. north-dipping） back-thrusts that contribute to northsouth crustal shortening and are responsible for exhumation of some ultrahigh-pressure rocks formed during earlier Tethyan plate convergence. An alternating occurrence in activity of Pamir and Chaman seismic zones indicates that there is interaction between strike-slip movement of the Chaman transform fault system and deep-subduction of the 展开更多
Basic features Bangonghu—Dingqing Suture is the medial and western segment of the Bangonghu—Nujiang Suture which many researchers called as ,and it is often regarded as the Qiangtang Massif boundary line in the nort...Basic features Bangonghu—Dingqing Suture is the medial and western segment of the Bangonghu—Nujiang Suture which many researchers called as ,and it is often regarded as the Qiangtang Massif boundary line in the northern side and the Lasa (Gangdisi) Massif in the souther. The era of the ophiolites spreading along the Bangonghu\|Dingqing suture include every period of the whole Jurassic, and the spreading of the ophiolites has distinct segmentation. From west to east there are Ritu segment,Gaize segment,Dongqiao segment and Dingqing segment.Between the Gaize segment and Dongqiao one ,that is ,between the E89°and E86°40′,no ophiolites are discovered in the surface.Aeromagnetic data shows that the magnetic field of this segment is quite gentle,there are no difference from its adjacent northern and southern sides. When its east adjacent segment extends into this segment, the high areomagnetic anomaly belt corresponding to of the Dongqiao ophiolite disappear abruptly. Apparently,it is impossible for the ophiolites to develop in such a deep crust of the same segment.展开更多
基金supported by the Major State Basic Research Development Program grants 2008DFA20700 and 2008CB425703
文摘The 3-D geometry of the seismicity in Hindu Kush-Pamir--western China region has been defined by seismic records for 1975-1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most Ms≥ 5.0 hypocenters in the area are confined to a major intracontinental seismic shear zone （MSSZ）. The MSSZ, which dips southwards in Pamir has a north- dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India-Asia collisional zone. We demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45-65 km, 95-120 km, and 180-220 km, suggesting different structural relationships where each occurs. Results from focal mechanism solutions in all three seismological concentrations show orientations of the principal maximum stress to be nearly horizontal in an NNW-SSE direction. The south-dipping Pamir subduction slab is wedge-shaped with a wide upper top and a narrow deeper bottom; the slab has a gentle angle of dip in the upper part and steeper dips in the lower part below an elbow depth of ca. 80--120 km. Most of the deformation related to the earthquakes occurs within the hanging wall of the subducting Pamir slab. Published geologic data and repeated GPS measurements in the Pamir document a broad supra-subduc- tion, upper crustal zone of evolving antithetic （i.e. north-dipping） back-thrusts that contribute to northsouth crustal shortening and are responsible for exhumation of some ultrahigh-pressure rocks formed during earlier Tethyan plate convergence. An alternating occurrence in activity of Pamir and Chaman seismic zones indicates that there is interaction between strike-slip movement of the Chaman transform fault system and deep-subduction of the
文摘Basic features Bangonghu—Dingqing Suture is the medial and western segment of the Bangonghu—Nujiang Suture which many researchers called as ,and it is often regarded as the Qiangtang Massif boundary line in the northern side and the Lasa (Gangdisi) Massif in the souther. The era of the ophiolites spreading along the Bangonghu\|Dingqing suture include every period of the whole Jurassic, and the spreading of the ophiolites has distinct segmentation. From west to east there are Ritu segment,Gaize segment,Dongqiao segment and Dingqing segment.Between the Gaize segment and Dongqiao one ,that is ,between the E89°and E86°40′,no ophiolites are discovered in the surface.Aeromagnetic data shows that the magnetic field of this segment is quite gentle,there are no difference from its adjacent northern and southern sides. When its east adjacent segment extends into this segment, the high areomagnetic anomaly belt corresponding to of the Dongqiao ophiolite disappear abruptly. Apparently,it is impossible for the ophiolites to develop in such a deep crust of the same segment.
