Laji Shan is located in the eastern part of Qinghai Province,sandwiched between Xining and Hualong Basins.It is about 250km long and 10～20km wide from Riyueshan in the west to Minheguanting in the east.Laji Shan belo...Laji Shan is located in the eastern part of Qinghai Province,sandwiched between Xining and Hualong Basins.It is about 250km long and 10～20km wide from Riyueshan in the west to Minheguanting in the east.Laji Shan belongs to the Caledonian orogenic belt.Its basement consists of the rocks of Palaeo\|Protero zoic Hualong Group (Pt 1 hl ) and Neo\|Proterozoic Huangzhong Group (Pt\-3 h ).There are ptygmatic folds,closely linear type folds,strongly structural d ifferentiation and schistosity developed,suggesting that the basement underwent deep seated ductile deformation.The main part of Laji Shan is composed of Early\|Palaeozoic marine facies volcanic rocks and clastic sedimentary rocks,and suffered greenschist facies metamorphism and brittle\|ductile deformation.Others are composed of Ea rly\|Palaeozoic basic and ultrabasic rocks,intermediate\|acidic intruded rocks a nd dike rocks.Devonian molasse formation in Laji Shan is in uncomfortable contac t with underlying strata.Jurassic and Cretaceous systems are intermont basin dep osits,corresponding to a cover.展开更多
he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward disp...he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward displacement of the Tibet plateau relative to the Tarim. The Altyn Tagh fault zone is a typical transpressional fault zone, characterized by blocks rotation and crustal shortening and vertical extrusion of blocks within the Altyn Tagh strike\|slip system. Differences of three\|dimensional deformation and configuration of the active structures are recognized at different segment of the Altyn Tagh fault zone.1\ Structural configuration of the Altyn Tagh fault zone\;In the Altyn Tagh strike\|slip fault zone, the assemblage pattern of the (active) faults is in the form of parallel plumes, especially in the eastern and the western segments of the Altyn Tagh fault zone. These plumes structures in the eastern segment are assembled by string\|like left lateral strike\|slip fault and broom\|like thrusting faults, and in the western segment by arc\|like left lateral strike\|slip faults along with thrusting faults and normal faults. In the middle segment of the Altyn Tagh fault zone, the structures are characterized by the string\|like left lateral strike\|slip faults in the center and reverse thrusting faults on the two sides.展开更多
The Qilian Shan forms the northeastern margin of the Qinghai\|Xizang (Tibet) Plateau, and is a region of marked relief (reaching elevations in excess of 5000m), reflecting the significant crustal shortening and uplift...The Qilian Shan forms the northeastern margin of the Qinghai\|Xizang (Tibet) Plateau, and is a region of marked relief (reaching elevations in excess of 5000m), reflecting the significant crustal shortening and uplift which has occurred during the Late Cenozoic. Its foreland margins define the Hexi Corridor, which constitutes a series of small sedimentary basins, accommodating thick sequences of Late Cenozoic alluvial sediments. The overall alluvial depositional pattern follows that expected in a foreland basin, where the thickness of the alluvial accumulations relates to thrust emplacement. The Late Cenozoic alluvial associations exhibit striking differences in style: (1) Miocene \| isolated, sheet channels with relatively fine\|textured sediments, set in thick floodplain sequences; (2) Pliocene \| large, strongly crossbedded, multistoreyed channel arrangements, containing coarse to pebbly\|sand with minor conglomerates, set in significant floodplain accumulations, and with sediment coarsening and increasing channel density in the later Pliocene; (3) Quaternary \| thick, monotonous sheet and channel coarse gravel sequences. While some uncertainty remains as to the absolute ages of the sediments (age estimates based on biostratigraphy, paleomagnetics and luminescence techniques), it is clear that the change to strong gravel deposition was a feature of the late Pliocene\|early Pleistocene. Accompanying changes in alluvial style were a reorganization in drainage, with more axial flow directions (Miocene\|Pliocene) becoming progressively more transverse (late Pliocene\|Pleistocene). The alluvial evidence suggests that the onset of significant uplift in the Qilian Shan occurred prior to the Gauss\|Matuyama transition. Additional evidence for such a claim is provided by: (1) paleosols associated with the alluvial sequences; and (2) details of the structural geology. The conclusion reached is that strong tectonic deformation occurred over a relatively restricted time interval during the late Pliocene\|early Pleistocene, possibly persisting into the middle Pleistocene, but with only limited def ormation during the Late Quaternary.展开更多
As a consequence of the collision of India with Asia, the Qilian Shan, rising 4000～5000m above the Gobi, marks the northeastern boundary of the Tibet—Qinghai Plateau. The Qilian Shan developed as a WNW—ESE fold\|an...As a consequence of the collision of India with Asia, the Qilian Shan, rising 4000～5000m above the Gobi, marks the northeastern boundary of the Tibet—Qinghai Plateau. The Qilian Shan developed as a WNW—ESE fold\|and\|thrust belt with most of the movement directed towards the NEN—NE. Its foreland margin, the Jiuxi Basin, accommodates thick sequences of Late Cenozoic alluvial sediments derived from the Qilian Shan. Thin\|skinned fold\|and\|thrust deformation in the Jiuxi basin flanking the Qilian Shan, feature Mesozoic and Cenozoic sedimentary rocks that have been detached from the underlying basal decollement and folded into a series of NW—WNW trending anticlines and synclines. Towards the south deformation in the Jiuxi basin is accommodated by a west\|north\|west fold train (Qingcaowan, Laojunmiao, and Shiyougou folds) developed during the Quaternary. These form a distinct topographic feature separating the Qilian Shan from the central Jiuxi Basin. The doubly plunging Laojunmiao anticline is 10km long and 5km wide. It is asymmetric in shape, having a steep to overturned northern limb, and a backlimb dips to the south at 20～30°. The Laojunmiao anticline is composed of two distinct stratigraphic sequences which are defined by a syntectonic unconformity.展开更多
文摘Laji Shan is located in the eastern part of Qinghai Province,sandwiched between Xining and Hualong Basins.It is about 250km long and 10～20km wide from Riyueshan in the west to Minheguanting in the east.Laji Shan belongs to the Caledonian orogenic belt.Its basement consists of the rocks of Palaeo\|Protero zoic Hualong Group (Pt 1 hl ) and Neo\|Proterozoic Huangzhong Group (Pt\-3 h ).There are ptygmatic folds,closely linear type folds,strongly structural d ifferentiation and schistosity developed,suggesting that the basement underwent deep seated ductile deformation.The main part of Laji Shan is composed of Early\|Palaeozoic marine facies volcanic rocks and clastic sedimentary rocks,and suffered greenschist facies metamorphism and brittle\|ductile deformation.Others are composed of Ea rly\|Palaeozoic basic and ultrabasic rocks,intermediate\|acidic intruded rocks a nd dike rocks.Devonian molasse formation in Laji Shan is in uncomfortable contac t with underlying strata.Jurassic and Cretaceous systems are intermont basin dep osits,corresponding to a cover.
文摘he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward displacement of the Tibet plateau relative to the Tarim. The Altyn Tagh fault zone is a typical transpressional fault zone, characterized by blocks rotation and crustal shortening and vertical extrusion of blocks within the Altyn Tagh strike\|slip system. Differences of three\|dimensional deformation and configuration of the active structures are recognized at different segment of the Altyn Tagh fault zone.1\ Structural configuration of the Altyn Tagh fault zone\;In the Altyn Tagh strike\|slip fault zone, the assemblage pattern of the (active) faults is in the form of parallel plumes, especially in the eastern and the western segments of the Altyn Tagh fault zone. These plumes structures in the eastern segment are assembled by string\|like left lateral strike\|slip fault and broom\|like thrusting faults, and in the western segment by arc\|like left lateral strike\|slip faults along with thrusting faults and normal faults. In the middle segment of the Altyn Tagh fault zone, the structures are characterized by the string\|like left lateral strike\|slip faults in the center and reverse thrusting faults on the two sides.
文摘The Qilian Shan forms the northeastern margin of the Qinghai\|Xizang (Tibet) Plateau, and is a region of marked relief (reaching elevations in excess of 5000m), reflecting the significant crustal shortening and uplift which has occurred during the Late Cenozoic. Its foreland margins define the Hexi Corridor, which constitutes a series of small sedimentary basins, accommodating thick sequences of Late Cenozoic alluvial sediments. The overall alluvial depositional pattern follows that expected in a foreland basin, where the thickness of the alluvial accumulations relates to thrust emplacement. The Late Cenozoic alluvial associations exhibit striking differences in style: (1) Miocene \| isolated, sheet channels with relatively fine\|textured sediments, set in thick floodplain sequences; (2) Pliocene \| large, strongly crossbedded, multistoreyed channel arrangements, containing coarse to pebbly\|sand with minor conglomerates, set in significant floodplain accumulations, and with sediment coarsening and increasing channel density in the later Pliocene; (3) Quaternary \| thick, monotonous sheet and channel coarse gravel sequences. While some uncertainty remains as to the absolute ages of the sediments (age estimates based on biostratigraphy, paleomagnetics and luminescence techniques), it is clear that the change to strong gravel deposition was a feature of the late Pliocene\|early Pleistocene. Accompanying changes in alluvial style were a reorganization in drainage, with more axial flow directions (Miocene\|Pliocene) becoming progressively more transverse (late Pliocene\|Pleistocene). The alluvial evidence suggests that the onset of significant uplift in the Qilian Shan occurred prior to the Gauss\|Matuyama transition. Additional evidence for such a claim is provided by: (1) paleosols associated with the alluvial sequences; and (2) details of the structural geology. The conclusion reached is that strong tectonic deformation occurred over a relatively restricted time interval during the late Pliocene\|early Pleistocene, possibly persisting into the middle Pleistocene, but with only limited def ormation during the Late Quaternary.
文摘As a consequence of the collision of India with Asia, the Qilian Shan, rising 4000～5000m above the Gobi, marks the northeastern boundary of the Tibet—Qinghai Plateau. The Qilian Shan developed as a WNW—ESE fold\|and\|thrust belt with most of the movement directed towards the NEN—NE. Its foreland margin, the Jiuxi Basin, accommodates thick sequences of Late Cenozoic alluvial sediments derived from the Qilian Shan. Thin\|skinned fold\|and\|thrust deformation in the Jiuxi basin flanking the Qilian Shan, feature Mesozoic and Cenozoic sedimentary rocks that have been detached from the underlying basal decollement and folded into a series of NW—WNW trending anticlines and synclines. Towards the south deformation in the Jiuxi basin is accommodated by a west\|north\|west fold train (Qingcaowan, Laojunmiao, and Shiyougou folds) developed during the Quaternary. These form a distinct topographic feature separating the Qilian Shan from the central Jiuxi Basin. The doubly plunging Laojunmiao anticline is 10km long and 5km wide. It is asymmetric in shape, having a steep to overturned northern limb, and a backlimb dips to the south at 20～30°. The Laojunmiao anticline is composed of two distinct stratigraphic sequences which are defined by a syntectonic unconformity.
