Considerable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum（LGM） in the Larsemann Hills.In this study we use the in situ produced cosmogenic nuclide ^（10...Considerable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum（LGM） in the Larsemann Hills.In this study we use the in situ produced cosmogenic nuclide ^（10）Be（half life 1.51 Ma） to provide minimum exposure ages for six bedrock samples and one erratic boulder in order to determine the last period of deglaciation in the Larsemann Hills and on the neighboring Bolingen Islands.Three bedrock samples taken from Friendship Mountain（the highest peak on the Mirror Peninsula,Larsemann Hills;～2 km from the ice sheet） have minimum exposure ages ranging from 40.0 to 44.7 ka.The erratic boulder from Peak 106（just at the edge of the ice sheet） has a younger minimum exposure age of only 8.8 ka.The minimum exposure ages for two bedrock samples from Blundell Peak（the highest peak on Stornes Peninsula,Larsemann Hills;～2 km from the ice sheet） are about 17 and 18 ka.On the Bolingen Islands（southwest to the Larsemann Hills;～10 km from the ice sheet）,the minimum exposure age for one bedrock sample is similar to that at Friendship Mountain（i.e.,44 ka）.Our results indicate that the bedrock exposure in the Larsemann Hills and on the neighboring Bolingen Islands commenced obviously before the global LGM（i.e.,20-22 ka）,and the bedrock erosion rates at the Antarctic coast areas may be obviously higher than in the interior land.展开更多
The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional ...The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional tectonic polarity.No large shear zone in north-south direction has been identified between ophiolite bodies and flysch layers on both side and a conformable contact relationship can be observed locally between them.A great mass of tectonic mélange has been substantiated as submarine olistolith bodies.The Mesozoic sedimentary facies and its evolution in both north and south of the ophiolite zone are corresponding in time.The ophiolite zone has often been divided into parallel branches,separated by narrow flysch slats.There is also a similarity of the Paleozoic and the basement of the High Himalaya,Lhasa and Qiangtang Terranes,and they are distinctly different from those of the Indian continent.The geologic information does not warrant a postulate that the Himalaya and Tibet were once separated by a great ocean;it is therefore consistent with an alternative tectonic model by back-arc basin collapse with its juvenile narrow oceanic crust.The real plate tectonic suture,the Neotethys might be covered under the Miocene Siwalik molasse in the southern slope of the High Himalaya range.Based on the new model,the Neotethyan ocean floor was subducted beneath the Asia since the Late Triassic.The outer continental margin of Eurasia was split from the Lhasa Terrane so that a back-arc basin came into existence.Hemi-pelagic and deep sea sediments were deposited before the Late Cretaceous flysch sedimentation,with the linear juvenile oceanic crust when back-arc volcanism occurred in the Gandese region.The Yarlung Zangbo back-arc basin was eventually eliminated when the High Himalayas were sutured onto Eurasia.The ocean floor lightly underthrusted to north and south sides,sediments of the basin were deformed as fold-thrusting.The Neotethys was eliminated during the Tertiary when India collided with Himalaya arc from the Oligocene.The crust of southern Tibet suffered penetrative shortening,the ophiolite zone became exposed during regional uplifting,and the South Tibet Detachment System,doming in southern Tibet and rifting in a north-south direction since the Middle Miocene Epoch.展开更多
基金supported by the National Science Fund of China(No.40506003 and 40631004)the Chinese Polar Science Strategy Research Fund(No.20070219).
文摘Considerable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum（LGM） in the Larsemann Hills.In this study we use the in situ produced cosmogenic nuclide ^（10）Be（half life 1.51 Ma） to provide minimum exposure ages for six bedrock samples and one erratic boulder in order to determine the last period of deglaciation in the Larsemann Hills and on the neighboring Bolingen Islands.Three bedrock samples taken from Friendship Mountain（the highest peak on the Mirror Peninsula,Larsemann Hills;～2 km from the ice sheet） have minimum exposure ages ranging from 40.0 to 44.7 ka.The erratic boulder from Peak 106（just at the edge of the ice sheet） has a younger minimum exposure age of only 8.8 ka.The minimum exposure ages for two bedrock samples from Blundell Peak（the highest peak on Stornes Peninsula,Larsemann Hills;～2 km from the ice sheet） are about 17 and 18 ka.On the Bolingen Islands（southwest to the Larsemann Hills;～10 km from the ice sheet）,the minimum exposure age for one bedrock sample is similar to that at Friendship Mountain（i.e.,44 ka）.Our results indicate that the bedrock exposure in the Larsemann Hills and on the neighboring Bolingen Islands commenced obviously before the global LGM（i.e.,20-22 ka）,and the bedrock erosion rates at the Antarctic coast areas may be obviously higher than in the interior land.
基金supported by Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No.KZCX3-SW-143)National Natural Science Foundation of China (Grant No.40631004)
文摘The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional tectonic polarity.No large shear zone in north-south direction has been identified between ophiolite bodies and flysch layers on both side and a conformable contact relationship can be observed locally between them.A great mass of tectonic mélange has been substantiated as submarine olistolith bodies.The Mesozoic sedimentary facies and its evolution in both north and south of the ophiolite zone are corresponding in time.The ophiolite zone has often been divided into parallel branches,separated by narrow flysch slats.There is also a similarity of the Paleozoic and the basement of the High Himalaya,Lhasa and Qiangtang Terranes,and they are distinctly different from those of the Indian continent.The geologic information does not warrant a postulate that the Himalaya and Tibet were once separated by a great ocean;it is therefore consistent with an alternative tectonic model by back-arc basin collapse with its juvenile narrow oceanic crust.The real plate tectonic suture,the Neotethys might be covered under the Miocene Siwalik molasse in the southern slope of the High Himalaya range.Based on the new model,the Neotethyan ocean floor was subducted beneath the Asia since the Late Triassic.The outer continental margin of Eurasia was split from the Lhasa Terrane so that a back-arc basin came into existence.Hemi-pelagic and deep sea sediments were deposited before the Late Cretaceous flysch sedimentation,with the linear juvenile oceanic crust when back-arc volcanism occurred in the Gandese region.The Yarlung Zangbo back-arc basin was eventually eliminated when the High Himalayas were sutured onto Eurasia.The ocean floor lightly underthrusted to north and south sides,sediments of the basin were deformed as fold-thrusting.The Neotethys was eliminated during the Tertiary when India collided with Himalaya arc from the Oligocene.The crust of southern Tibet suffered penetrative shortening,the ophiolite zone became exposed during regional uplifting,and the South Tibet Detachment System,doming in southern Tibet and rifting in a north-south direction since the Middle Miocene Epoch.
