An Early Paleozoic ophiolitic mélange has recently been documented in the W.Gangma Co area,north-central Tibetan Plateau.It is composed of serpentinite,isotropic and cumulate gabbros,basalt and plagiogranite.Whole-
The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we car...The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ？ 4 Ma for the cores and 508 ？ 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ？ 3 Ma for a coarse-grained felsic orthogneiss and 507 ？ 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged （i.e., Late Mesoproterozoic/Early Neoproterozoic） metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.展开更多
The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system ...The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system in the north and a latest PaleozoicMesozoic collisional orogenic system in the south, it may serve as an ideal place to study the tectonic evolution between the North and South China Blocks. The available literature data in the past 20 years indicate that the tectonic processes of the Tongbai-Hong'an orogen involved four stages during the Phanerozoic:(1) Early Paleozoic(490–420 Ma) oceanic subduction, arc magmatism and arc-continent collision created a new Andean-type active continental margin on the North China Block;(2) Late Paleozoic(340–310 Ma) oceanic subduction and accretion generated separated paired metamorphic belts: a medium P/T Wuguan-Guishan complex belt in the south of the Shandan-Songpa fault and a high P/T Xiongdian eclogite belt in the northern edge of the Mesozoic HP metamorphic terrane;(3) Latest Paleozoic-Early Mesozoic(255–200 Ma) continental subduction and collision formed the Tongbai HP terrane in the west and the Hong'an HP/UHP terrane in the east as a consequence of deep subduction towards the east and syn-subduction detachment/exhumation of the down-going slab;(4) Late Mesozoic(140–120 Ma) extension, voluminous magma intrusion and tectonic extrusion led to the final exhumation of the Tongbai-Hong'an-Dabie HP/UHP terrane and the wedge-shaped architecture of the terrane narrowing towards the west. However, many open questions still remain about the details of each evolutionary stage and earlier history of the orogen. Besides an extensive study directly on the Tongbai-Hong'an orogen in the future, integrated investigation on the "soft-collisional" Qinling orogen in the west and the "hard-collisional" Dabie-Sulu orogen in the east is required to establish a general tectonic model for the whole Qinling-TongbaiHong'an-Dabie-Sulu orogenic belt.展开更多
High-pressure(HP)metamorphic terrane in the Tongbai orogen comprises two HP slices(I and II)and a tectonic mélange zone in the northeast and a blueschist-greenschist zone in the southwest.HP slice I is represente...High-pressure(HP)metamorphic terrane in the Tongbai orogen comprises two HP slices(I and II)and a tectonic mélange zone in the northeast and a blueschist-greenschist zone in the southwest.HP slice I is represented by the northern and southern eclogite zones on the two sides of the Tongbaishan antiform.HP slice II is represented by retrograded eclogite-bearing metamorphic enclaves in Cretaceous gneissic granites in the Tongbai Complex.U-Pb,Lu-Hf,Rb-Sr and40Ar/39Ar multichronometric data indicate that the peak metamorphism of HP slice I took place at^255 Ma,whereas the metamorphic ages of HP slice II are as young as232–220 Ma.By contrast,the tectonic mélange zone near the suture was metamorphosed at^256 Ma.Such a diachroneity of different slices across the direction of the orogen in the Hong’an-Dabie-Sulu HP/UHP terrane is ubiquitous,and it can be interpreted by a syn-subduction detachment/exhumation model.Furthermore,the metamorphic age of HP slice I in the Tongbai orogen is older than that of the equivalent HP slice in the Hong’an orogen by^15 Ma,suggesting that the diachroneity may have also existed along the direction of the orogen.A seesaw-type subduction/exhumation model is proposed to explain this age disparity and the subduction of the South China Block becomimg shallower towards the west.展开更多
文摘An Early Paleozoic ophiolitic mélange has recently been documented in the W.Gangma Co area,north-central Tibetan Plateau.It is composed of serpentinite,isotropic and cumulate gabbros,basalt and plagiogranite.Whole-
基金financial support from the National Natural Science Foundation of China (Grant no.41530209)the Central Public-Interest Scientific Institution Basal Research Fund (Grant no.JYYWF201819)
文摘The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ？ 4 Ma for the cores and 508 ？ 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ？ 3 Ma for a coarse-grained felsic orthogneiss and 507 ？ 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged （i.e., Late Mesoproterozoic/Early Neoproterozoic） metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.
基金supported by the National Basic Research Program of China(Grant Nos.2015CB856104,2009CB825006)the National Natural Science Foundation of China(Grant Nos.41472064,40672047)the Geological Investigation Project of China Geological Survey(Grant No.1212010711812)
文摘The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system in the north and a latest PaleozoicMesozoic collisional orogenic system in the south, it may serve as an ideal place to study the tectonic evolution between the North and South China Blocks. The available literature data in the past 20 years indicate that the tectonic processes of the Tongbai-Hong'an orogen involved four stages during the Phanerozoic:(1) Early Paleozoic(490–420 Ma) oceanic subduction, arc magmatism and arc-continent collision created a new Andean-type active continental margin on the North China Block;(2) Late Paleozoic(340–310 Ma) oceanic subduction and accretion generated separated paired metamorphic belts: a medium P/T Wuguan-Guishan complex belt in the south of the Shandan-Songpa fault and a high P/T Xiongdian eclogite belt in the northern edge of the Mesozoic HP metamorphic terrane;(3) Latest Paleozoic-Early Mesozoic(255–200 Ma) continental subduction and collision formed the Tongbai HP terrane in the west and the Hong'an HP/UHP terrane in the east as a consequence of deep subduction towards the east and syn-subduction detachment/exhumation of the down-going slab;(4) Late Mesozoic(140–120 Ma) extension, voluminous magma intrusion and tectonic extrusion led to the final exhumation of the Tongbai-Hong'an-Dabie HP/UHP terrane and the wedge-shaped architecture of the terrane narrowing towards the west. However, many open questions still remain about the details of each evolutionary stage and earlier history of the orogen. Besides an extensive study directly on the Tongbai-Hong'an orogen in the future, integrated investigation on the "soft-collisional" Qinling orogen in the west and the "hard-collisional" Dabie-Sulu orogen in the east is required to establish a general tectonic model for the whole Qinling-TongbaiHong'an-Dabie-Sulu orogenic belt.
基金supportedby the National Basic Research Program of China(2009CB825006)
文摘High-pressure(HP)metamorphic terrane in the Tongbai orogen comprises two HP slices(I and II)and a tectonic mélange zone in the northeast and a blueschist-greenschist zone in the southwest.HP slice I is represented by the northern and southern eclogite zones on the two sides of the Tongbaishan antiform.HP slice II is represented by retrograded eclogite-bearing metamorphic enclaves in Cretaceous gneissic granites in the Tongbai Complex.U-Pb,Lu-Hf,Rb-Sr and40Ar/39Ar multichronometric data indicate that the peak metamorphism of HP slice I took place at^255 Ma,whereas the metamorphic ages of HP slice II are as young as232–220 Ma.By contrast,the tectonic mélange zone near the suture was metamorphosed at^256 Ma.Such a diachroneity of different slices across the direction of the orogen in the Hong’an-Dabie-Sulu HP/UHP terrane is ubiquitous,and it can be interpreted by a syn-subduction detachment/exhumation model.Furthermore,the metamorphic age of HP slice I in the Tongbai orogen is older than that of the equivalent HP slice in the Hong’an orogen by^15 Ma,suggesting that the diachroneity may have also existed along the direction of the orogen.A seesaw-type subduction/exhumation model is proposed to explain this age disparity and the subduction of the South China Block becomimg shallower towards the west.
