Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, ...Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding-overlapping structures. Based on their genesis, soft-sediment deformation structures can be classified as three types： seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic-induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding- overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the AItyn strike-slip fault was active during the middle Jurassic.展开更多
The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombu...The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombus-shaped Altyn Mountain has long been thought to have an intimate relation with the Altyn Tagh Fault; however, its formation mechanism remains unclear and debatable. In this paper, we focus on the EW-trending uplifts in the Altyn Mountain, and investigated three Cenozoic sedimentary sections in the vicinity of the EW-trending uplifts located along the southern side of the central segment of the Altyn Tagh Fault. Magnetostratigraphy and pollen analysis were used to constrain ages of the sediments. Clast composition of conglomerate and paleocurrents obtained from clast imbrications were applied to determine the provenance. We also established a geological section parallel to the Altyn Tagh Fault on sedimentary facies across the northwestern Qaidam Basin. The results indicate that these en-echelon EW-trending uplifts formed as early as ca. 36 Ma and were preferred to be under the control of basal shear of the Altyn Tagh Fault in the middle-lower crust, symbolizing the early uplift of the Altyn Mountain during the Cenozoic. Left-slip along the Altyn Tagh Fault occurring during the Miocene and afterwards displaced and altered these uplifts, shaping the Altyn Mountain to its present fabric.展开更多
基金The National Natural Science Fund(No:41172093)the research fund(No:2003042500820060425509)for the doctoral program of higher education from Ministry of Education for their financial support
文摘Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding-overlapping structures. Based on their genesis, soft-sediment deformation structures can be classified as three types： seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic-induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding- overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the AItyn strike-slip fault was active during the middle Jurassic.
基金supported by Chinese National Key Scientific and Technological Projects (Grant Nos. 2011ZX05009-001 and2011ZX05003-002)
文摘The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombus-shaped Altyn Mountain has long been thought to have an intimate relation with the Altyn Tagh Fault; however, its formation mechanism remains unclear and debatable. In this paper, we focus on the EW-trending uplifts in the Altyn Mountain, and investigated three Cenozoic sedimentary sections in the vicinity of the EW-trending uplifts located along the southern side of the central segment of the Altyn Tagh Fault. Magnetostratigraphy and pollen analysis were used to constrain ages of the sediments. Clast composition of conglomerate and paleocurrents obtained from clast imbrications were applied to determine the provenance. We also established a geological section parallel to the Altyn Tagh Fault on sedimentary facies across the northwestern Qaidam Basin. The results indicate that these en-echelon EW-trending uplifts formed as early as ca. 36 Ma and were preferred to be under the control of basal shear of the Altyn Tagh Fault in the middle-lower crust, symbolizing the early uplift of the Altyn Mountain during the Cenozoic. Left-slip along the Altyn Tagh Fault occurring during the Miocene and afterwards displaced and altered these uplifts, shaping the Altyn Mountain to its present fabric.
