Based on deep geophysical detections, we have reconstructed the crustal structure from the eastern margin of the Tibetan Plateau to the Jiangnan-Xuefeng orogenic belt. The results suggest that the Yangtze Block was ov...Based on deep geophysical detections, we have reconstructed the crustal structure from the eastern margin of the Tibetan Plateau to the Jiangnan-Xuefeng orogenic belt. The results suggest that the Yangtze Block was overthrusted by crustal materials in its NW direction from the eastern Tibetan Plateau but in its SE direction from the Jiangnan orogen. These overthrusting effects control the crustal structure from the western Sichuan to the western area of the Jiangnan orogen-Xuefeng orogenic belt. The eastward extruded materials from the eastern Tibetan Plateau were blocked by the rigid basement in the Sichuan Basin, where upper-middle crust was overthrusted whereas the lower crust was underthrusted beneath the Sichuan Basin. The underthrusted unit was absorbed by crustal folding, shortening and thickening in the Yangtze Block, forming the Xiongpo and Longquan Mountains tectonic belts and resulting in the NW-directed thrusting of the Pujiang-Chengdu-Deyang fault, and the western hillsiden fault in the Longquan Mountain. These results provide resolution to the controversy where the eastward extrusion material from the Qinghai-Tibet Plateau had gone. Overall, that Yangtze Block was subjected to thrusting of the crustal materials from the orogenic belts over its both sides. This finding has implications for the study of the intracontinental orogenic mechanism in South China, the reconstruction of tectonic evolutionary history and the kinematics processes during the lateral extrusion of the Tibet Plateau.展开更多
The exact determination of isotopic ages of hydrocarbon accumulation,reconstruction and destruction periods using traditional isotopic dating methods is complex because of the small numbers of minerals that correlate ...The exact determination of isotopic ages of hydrocarbon accumulation,reconstruction and destruction periods using traditional isotopic dating methods is complex because of the small numbers of minerals that correlate with hydrocarbons.The quantitative and direct study of hydrocarbon geochronology is therefore an important scientific problem for isotope geochronology and petroleum geology.This study obtains two isotopic ages from a quartz vein sample associated with bitumen in a reverse fault located in the Bankeng paleo-reservoir on the southern margin of the middle Yangtze block (the northern margin of the JiangnanXuefeng uplift) by inclusion 40Ar/39Ar stepwise crushing in a vacuum.Two different and good linear inverse isochrons that correspond to two age plateaus were determined.The two ages correspond to primary inclusions of about 228 Ma and secondary inclusions of about 149 Ma.These inclusion groups represent two distinct kinds of fluids.Quartz veins associated with bitumen in faulted paleo-reservoirs,which have a strict response relationship with tectonization and hydrocarbon accumulation,are the unified products of tectonic processes,hydrocarbon accumulation and reconstruction.Therefore,they can be used to constrain the hydrocarbon accumulation,reconstruction and destruction periods that are controlled by multiphase and complicated tectonic actions.The evolutionary processes of hydrocarbon accumulation can be divided into two periods consisting of a primary oil and gas reservoir formation period in the late Indosinian epoch (about 228 Ma) and a period of oil and gas reservoir reconstruction in the early Yanshan epoch (about 149 Ma).This study quantitatively reconstructs the hydrocarbon accumulation and destruction chronological framework of a giant hydrocarbon accumulation belt along the southern margin of the middle Yangtze block (the northern margin of the Jiangnan-Xuefeng uplift) controlled by multiphase and complicated tectonism.The two ages associated with hydrocarbons here correspond to the special controlling actions of continental tectonics in the Jiangnan-Xuefeng uplift that affected the timeline of reconstruction and destruction in this giant marine hydrocarbon accumulation.This study shows the feasibility and usefulness of dating inclusions with the 40Ar/39Ar technique for hydrocarbon geochronology,especially in the marine hydrocarbon accumulation region of southern China within a geological setting of old strata,high thermal evolution hydrocarbons,and complex,multiphase and multicycle tectonization.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41574093,41774114)SinoProbe-02(Grant No.A1011B)
文摘Based on deep geophysical detections, we have reconstructed the crustal structure from the eastern margin of the Tibetan Plateau to the Jiangnan-Xuefeng orogenic belt. The results suggest that the Yangtze Block was overthrusted by crustal materials in its NW direction from the eastern Tibetan Plateau but in its SE direction from the Jiangnan orogen. These overthrusting effects control the crustal structure from the western Sichuan to the western area of the Jiangnan orogen-Xuefeng orogenic belt. The eastward extruded materials from the eastern Tibetan Plateau were blocked by the rigid basement in the Sichuan Basin, where upper-middle crust was overthrusted whereas the lower crust was underthrusted beneath the Sichuan Basin. The underthrusted unit was absorbed by crustal folding, shortening and thickening in the Yangtze Block, forming the Xiongpo and Longquan Mountains tectonic belts and resulting in the NW-directed thrusting of the Pujiang-Chengdu-Deyang fault, and the western hillsiden fault in the Longquan Mountain. These results provide resolution to the controversy where the eastward extrusion material from the Qinghai-Tibet Plateau had gone. Overall, that Yangtze Block was subjected to thrusting of the crustal materials from the orogenic belts over its both sides. This finding has implications for the study of the intracontinental orogenic mechanism in South China, the reconstruction of tectonic evolutionary history and the kinematics processes during the lateral extrusion of the Tibet Plateau.
基金Basin-range tectonics,composite structural system,hydrocarbon accumu-lation and reconstruction in middle Yangtze block (YPH08002)Research Fund of Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences Wuhan)+2 种基金Ministry of Education (TPR-2009-06)the National Natural Science Foundation of China (40902038)the Natural Science Foundation of Hubei Province (2009CDB217)
文摘The exact determination of isotopic ages of hydrocarbon accumulation,reconstruction and destruction periods using traditional isotopic dating methods is complex because of the small numbers of minerals that correlate with hydrocarbons.The quantitative and direct study of hydrocarbon geochronology is therefore an important scientific problem for isotope geochronology and petroleum geology.This study obtains two isotopic ages from a quartz vein sample associated with bitumen in a reverse fault located in the Bankeng paleo-reservoir on the southern margin of the middle Yangtze block (the northern margin of the JiangnanXuefeng uplift) by inclusion 40Ar/39Ar stepwise crushing in a vacuum.Two different and good linear inverse isochrons that correspond to two age plateaus were determined.The two ages correspond to primary inclusions of about 228 Ma and secondary inclusions of about 149 Ma.These inclusion groups represent two distinct kinds of fluids.Quartz veins associated with bitumen in faulted paleo-reservoirs,which have a strict response relationship with tectonization and hydrocarbon accumulation,are the unified products of tectonic processes,hydrocarbon accumulation and reconstruction.Therefore,they can be used to constrain the hydrocarbon accumulation,reconstruction and destruction periods that are controlled by multiphase and complicated tectonic actions.The evolutionary processes of hydrocarbon accumulation can be divided into two periods consisting of a primary oil and gas reservoir formation period in the late Indosinian epoch (about 228 Ma) and a period of oil and gas reservoir reconstruction in the early Yanshan epoch (about 149 Ma).This study quantitatively reconstructs the hydrocarbon accumulation and destruction chronological framework of a giant hydrocarbon accumulation belt along the southern margin of the middle Yangtze block (the northern margin of the Jiangnan-Xuefeng uplift) controlled by multiphase and complicated tectonism.The two ages associated with hydrocarbons here correspond to the special controlling actions of continental tectonics in the Jiangnan-Xuefeng uplift that affected the timeline of reconstruction and destruction in this giant marine hydrocarbon accumulation.This study shows the feasibility and usefulness of dating inclusions with the 40Ar/39Ar technique for hydrocarbon geochronology,especially in the marine hydrocarbon accumulation region of southern China within a geological setting of old strata,high thermal evolution hydrocarbons,and complex,multiphase and multicycle tectonization.
