Kohistan Sequence has been considered as island arc formed during the subduction of oceanic lithosphere at the leading edge of northward moving Indian continent.. Sedimentary sequences indicate that formation of the i...Kohistan Sequence has been considered as island arc formed during the subduction of oceanic lithosphere at the leading edge of northward moving Indian continent.. Sedimentary sequences indicate that formation of the intra\|oceanic Kohistan arc began in early Cretaceous time. The isotopic data demonstrate the involvement of enriched, DUPAL type mantle, suggesting that Kohistan arc was formed at or south of the present equator (Khan et al., 1997). The Intra oceanic phase of Kohistan lasted until sometime between 102 and 85 Ma, when Kohistan collided with Asia. From this time until collision with India about 50 Ma ago, Kohistan existed as Andean\|type margin. This paleomagnetic study is from the volcanic and plutonic rocks exposed in Gupis\|Shamran area (west of Gilgit) in northern part of the Kohistan arc. According to geochronological data these rocks were formed 61～55Ma ago (Treloar et al., 1989), when Kohistan was existing as Andean\|type margin. Seven to nine samples were collected from nine sites of Shamran volcanics (58±1)Ma and from five sites of Pingal, Gupis, and Yasin plutons (Ar\|Ar hornblende ages ranges from 61～52Ma). On the basis of one Rb\|Sr age of (59±2)Ma from these plutons, the above\|mentioned Ar/Ar ages may be regarded as reasonable intrusion ages of these plutons (Searle, 1991).展开更多
In order to establish deformation history for the Cenozoic development of the Tibetan Plateau, we conducted geologic mapping along a 120km traverse between Nangqian and Yushu in the northeastern Qiangtang terrane. Thi...In order to establish deformation history for the Cenozoic development of the Tibetan Plateau, we conducted geologic mapping along a 120km traverse between Nangqian and Yushu in the northeastern Qiangtang terrane. This work reveals a complex interaction among Tertiary thrusting, strike\|slip faulting, sedimentation, and igneous activity. Two phases of deformation are recognized. The older northeast—southwest shortening, expressed by thrusting and folding, is followed by left\|slip faulting along northwest\|trending faults. Tertiary thrusts, predominantly southwest\|dipping, are distributed throughout the traverse, and typically juxtapose Mesozoic strata over Paleogene strata. The latter were deposited in several separated basins during folding and thrusting, as indicated by well\|developed growth strata. A preliminary construction of balanced cross\|sections suggests a minimum estimate of 45km of crustal shortening along the traverse. Numerous hypabyssal intrusions were mapped in the southern part of the traverse near Nangqian. They were emplaced into the Paleogene sediments and are dated between 36 and 33Ma by 40 Ar/ 39 Ar and U\|Pb methods. Paleogene sediments are also interbedded with volcanics in both the southern and northern parts of the study area. In the northernmost part of the traverse, a volcanic unit overlies a Tertiary thrust. This unit itself is broadly folded. This relationship suggests that Tertiary igneous activity was coeval with contractional deformation in the region, implying strongly the causal relationship between the two processes. The youngest event in the area is the development of northwest\|trending left\|slip faults. They cut Tertiary thrusts, folds, and about 35Ma igneous intrusions. In contrast to widely distributed Tertiary folds and thrusts, strike\|slip faulting is restricted only to the southern portion of our mapped area near Nangqian. The strike\|slip faults apparently control the distribution of modern drainage systems, suggesting that they may have been active recently. As the younger strike\|slip faults are subparallel to the older folds and thrusts, we have not been able to determine the magnitude of left\|slip on these faults. We interpret the termination of contractional deformation and the subsequent replacement by strike\|slip faulting as a result of both clockwise rotation of the region and westward propagation of strike\|slip deformation in eastern Tibet.展开更多
The recent advances of 3D seismic technique applied in geological study of sedimentary basin analysis were reviewed.The achievements in the study of the sedimentology,structural analysis, fluid-rock interaction and ig...The recent advances of 3D seismic technique applied in geological study of sedimentary basin analysis were reviewed.The achievements in the study of the sedimentology,structural analysis, fluid-rock interaction and igneous geology were summarized.Because 3D seismic resolution and interpretation technology are enhanced surprisingly。展开更多
文摘Kohistan Sequence has been considered as island arc formed during the subduction of oceanic lithosphere at the leading edge of northward moving Indian continent.. Sedimentary sequences indicate that formation of the intra\|oceanic Kohistan arc began in early Cretaceous time. The isotopic data demonstrate the involvement of enriched, DUPAL type mantle, suggesting that Kohistan arc was formed at or south of the present equator (Khan et al., 1997). The Intra oceanic phase of Kohistan lasted until sometime between 102 and 85 Ma, when Kohistan collided with Asia. From this time until collision with India about 50 Ma ago, Kohistan existed as Andean\|type margin. This paleomagnetic study is from the volcanic and plutonic rocks exposed in Gupis\|Shamran area (west of Gilgit) in northern part of the Kohistan arc. According to geochronological data these rocks were formed 61～55Ma ago (Treloar et al., 1989), when Kohistan was existing as Andean\|type margin. Seven to nine samples were collected from nine sites of Shamran volcanics (58±1)Ma and from five sites of Pingal, Gupis, and Yasin plutons (Ar\|Ar hornblende ages ranges from 61～52Ma). On the basis of one Rb\|Sr age of (59±2)Ma from these plutons, the above\|mentioned Ar/Ar ages may be regarded as reasonable intrusion ages of these plutons (Searle, 1991).
文摘In order to establish deformation history for the Cenozoic development of the Tibetan Plateau, we conducted geologic mapping along a 120km traverse between Nangqian and Yushu in the northeastern Qiangtang terrane. This work reveals a complex interaction among Tertiary thrusting, strike\|slip faulting, sedimentation, and igneous activity. Two phases of deformation are recognized. The older northeast—southwest shortening, expressed by thrusting and folding, is followed by left\|slip faulting along northwest\|trending faults. Tertiary thrusts, predominantly southwest\|dipping, are distributed throughout the traverse, and typically juxtapose Mesozoic strata over Paleogene strata. The latter were deposited in several separated basins during folding and thrusting, as indicated by well\|developed growth strata. A preliminary construction of balanced cross\|sections suggests a minimum estimate of 45km of crustal shortening along the traverse. Numerous hypabyssal intrusions were mapped in the southern part of the traverse near Nangqian. They were emplaced into the Paleogene sediments and are dated between 36 and 33Ma by 40 Ar/ 39 Ar and U\|Pb methods. Paleogene sediments are also interbedded with volcanics in both the southern and northern parts of the study area. In the northernmost part of the traverse, a volcanic unit overlies a Tertiary thrust. This unit itself is broadly folded. This relationship suggests that Tertiary igneous activity was coeval with contractional deformation in the region, implying strongly the causal relationship between the two processes. The youngest event in the area is the development of northwest\|trending left\|slip faults. They cut Tertiary thrusts, folds, and about 35Ma igneous intrusions. In contrast to widely distributed Tertiary folds and thrusts, strike\|slip faulting is restricted only to the southern portion of our mapped area near Nangqian. The strike\|slip faults apparently control the distribution of modern drainage systems, suggesting that they may have been active recently. As the younger strike\|slip faults are subparallel to the older folds and thrusts, we have not been able to determine the magnitude of left\|slip on these faults. We interpret the termination of contractional deformation and the subsequent replacement by strike\|slip faulting as a result of both clockwise rotation of the region and westward propagation of strike\|slip deformation in eastern Tibet.
文摘The recent advances of 3D seismic technique applied in geological study of sedimentary basin analysis were reviewed.The achievements in the study of the sedimentology,structural analysis, fluid-rock interaction and igneous geology were summarized.Because 3D seismic resolution and interpretation technology are enhanced surprisingly。
