Timing of uplift of the Tibetan Plateau is a fundamental work to understand global climatic change and mountain\|building mechanism. Because most of the evidence comes from the Himalaya\|South Tibet, the northern marg...Timing of uplift of the Tibetan Plateau is a fundamental work to understand global climatic change and mountain\|building mechanism. Because most of the evidence comes from the Himalaya\|South Tibet, the northern margin of the Plateau may hold the key to unravel a whole view of the Plateau uplift history, in which basin sediments are the most important part because they have continuously recorded the history of pure surface uplift in related mountains. In the whole foredeep bordered by the North Marginal Thrust (Kunlun—Altun—Qilian—Longmen Trusts) along the northern and eastern Tibetan Plateau, thick Cenozoic stratigraphy is widely distributed and records the whole history of the Plateau uplift process. It can be lithologically divided in three large units from top to bottom: light colored sediments, boulder conglomerate and red bed. The red bed is mostly fine sediments of lacustrine and/or fluviolacustrine origins and the boulder conglomerate has been long thought as evidence of rapid uplift of the Tibetan Plateau. The light colored sediments are mostly eolian and/or fluviolacustrine deposits or desert\|gobi sediments. Thus, to date the boulder conglomerate holds the key to unravel the Plateau uplift. We chose the Linxia Basin in the northeastern Tibetan Plateau and Jiuquan Basin in the northern Qilian Mountains as two pilot controlling sites to reconstruct the history of uplift process of the Tibetan Plate au and its accompanied climatic change and to see if a coupling process would ex ist between the uplift of the Plateau and Asian monsoon system.展开更多
The Yunmengshan metamorphic core complex in the middle part of the Yanshan Fold and Thrust Belt records crust extension processes of the eastern North China Craton during its peak destruction.Development of the metamo...The Yunmengshan metamorphic core complex in the middle part of the Yanshan Fold and Thrust Belt records crust extension processes of the eastern North China Craton during its peak destruction.Development of the metamorphic core complex was controlled by the generally NNE-striking Dashuiyu Shear Zone.The shear zone dips SE and becomes shallower NE-wards,leading to exposures of a ductile shear zone in the southern and middle parts and brittle faults in the northern part.Exposure structures,microstructures,and quartz C-axis fabrics indicate that the ductile shear zone belongs to an extensional shear zone with a top-to-the-SE shear sense.Deformation temperatures of 300–520°C suggest a midcrustal origin for the ductile shear zone.A ductile deformation belt in the footwall of the shear zone is only as wide as 1–3 km,indicating no widespread mid-crustal ductile flow in the region during the deformation.Zircon U–Pb dating of dykes and plutons as well as hornblende and biotite40Ar/39Ar dating demonstrate that the metamorphic core complex originated at 135 Ma and experienced intense shearing of the Dashuiyu Shear Zone,development of the supradetachment basins,and synkinematic intrusion during 135–125 Ma.The metamorphic core complex was subjected to rapid exhumation during 125–114 Ma when the Dashuiyu Shear Zone suffered continuous activity and passive doming.The shear zone and its hanging wall were cut or replaced by a series of brittle faults when they wereuplifted to a brittle regime,showing that exhumation took place in continuous extensional activities.The metamorphic core complex turned into slow exhumation in an extensional regime in the following latest Early Cretaceous.The evolution history suggests that the Yunmengshan metamorphic core complex was developed by the rolling-hinge model,a common formation mechanism for intraplate metamorphic core complexes in the North China Craton,under the continuous NW–SE extension during the Early Cretaceous(135–100 Ma).展开更多
文摘Timing of uplift of the Tibetan Plateau is a fundamental work to understand global climatic change and mountain\|building mechanism. Because most of the evidence comes from the Himalaya\|South Tibet, the northern margin of the Plateau may hold the key to unravel a whole view of the Plateau uplift history, in which basin sediments are the most important part because they have continuously recorded the history of pure surface uplift in related mountains. In the whole foredeep bordered by the North Marginal Thrust (Kunlun—Altun—Qilian—Longmen Trusts) along the northern and eastern Tibetan Plateau, thick Cenozoic stratigraphy is widely distributed and records the whole history of the Plateau uplift process. It can be lithologically divided in three large units from top to bottom: light colored sediments, boulder conglomerate and red bed. The red bed is mostly fine sediments of lacustrine and/or fluviolacustrine origins and the boulder conglomerate has been long thought as evidence of rapid uplift of the Tibetan Plateau. The light colored sediments are mostly eolian and/or fluviolacustrine deposits or desert\|gobi sediments. Thus, to date the boulder conglomerate holds the key to unravel the Plateau uplift. We chose the Linxia Basin in the northeastern Tibetan Plateau and Jiuquan Basin in the northern Qilian Mountains as two pilot controlling sites to reconstruct the history of uplift process of the Tibetan Plate au and its accompanied climatic change and to see if a coupling process would ex ist between the uplift of the Plateau and Asian monsoon system.
基金supported by the National Natural Science Foundation of China (91214301)
文摘The Yunmengshan metamorphic core complex in the middle part of the Yanshan Fold and Thrust Belt records crust extension processes of the eastern North China Craton during its peak destruction.Development of the metamorphic core complex was controlled by the generally NNE-striking Dashuiyu Shear Zone.The shear zone dips SE and becomes shallower NE-wards,leading to exposures of a ductile shear zone in the southern and middle parts and brittle faults in the northern part.Exposure structures,microstructures,and quartz C-axis fabrics indicate that the ductile shear zone belongs to an extensional shear zone with a top-to-the-SE shear sense.Deformation temperatures of 300–520°C suggest a midcrustal origin for the ductile shear zone.A ductile deformation belt in the footwall of the shear zone is only as wide as 1–3 km,indicating no widespread mid-crustal ductile flow in the region during the deformation.Zircon U–Pb dating of dykes and plutons as well as hornblende and biotite40Ar/39Ar dating demonstrate that the metamorphic core complex originated at 135 Ma and experienced intense shearing of the Dashuiyu Shear Zone,development of the supradetachment basins,and synkinematic intrusion during 135–125 Ma.The metamorphic core complex was subjected to rapid exhumation during 125–114 Ma when the Dashuiyu Shear Zone suffered continuous activity and passive doming.The shear zone and its hanging wall were cut or replaced by a series of brittle faults when they wereuplifted to a brittle regime,showing that exhumation took place in continuous extensional activities.The metamorphic core complex turned into slow exhumation in an extensional regime in the following latest Early Cretaceous.The evolution history suggests that the Yunmengshan metamorphic core complex was developed by the rolling-hinge model,a common formation mechanism for intraplate metamorphic core complexes in the North China Craton,under the continuous NW–SE extension during the Early Cretaceous(135–100 Ma).
