To reveal the Jurassic tectonothermal event occurring to the Nyainrong microcontinent which is gripped among the Bangong-Nujiang suture zone,^40Ar/^39Ar dating was carried out on the basement orthogneiss and Jurassic ...To reveal the Jurassic tectonothermal event occurring to the Nyainrong microcontinent which is gripped among the Bangong-Nujiang suture zone,^40Ar/^39Ar dating was carried out on the basement orthogneiss and Jurassic granitc gneiss in the microcontinent. In the heating stage, four sam- pies exhibited a flat plateau age, with the value Tp concentrated in the range of 166-176 Ma; isochron age Ti was concentrated in the range of 165-175 Ma, and their corresponding ages were the consistent within allowable range. The ages should be representative of the era of the final deformation of the Amdo gneiss and cooling emplacement of the magmatic rock in the Jurassic. The geochronological studies have shown that the final deformation of microcontinent crystalline basement and the cooling of the Mesozoic large-scale tectonothermal events occurred in late Middle Jurassic. In Middle Jurassic, Nyainrong microcontinent experienced strong tectonic movement. Combining with the geochronologi- cal with isotope geochemistry for the microcontinent, the cause of the tectonothermal event should be attributed to the collision between the Nyainrong microcontinent and South Qiangtang Block following the northward subduction of Bangong-Nujiang oceanic crust.展开更多
Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into m...Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into mantle source characteristics and geodynamic setting of Permian ophiolitic fragments. U-Pb isotopic dating using SHRIMP II method reveals that the metamafic rocks were formed at 274.7± 3.9 and 279.8± 3.6 Ma. The metamafic rocks mostly show N-MORB-typed rare earth element patterns and are enrichment in large-ion lithophile elements, indicating that they are probably derived from partial melting of a depleted mantle in a back-arc basin. Our new data, together with recent studied results on Paleozoic ophiolitic fragments suggest the Paleo-Tethys Ocean in Central Qiangtang opened at Cambrian and widened between Ordovician and Devonian. Northward subduction started in the Late Devonian–Early Carboniferous and a back-arc basin developed during Permian.展开更多
This paper reports new zircon U-Pb ages,and Hf isotope and whole-rock major and trace element data for Cambrian plagiogranites from the Tuobeiling ophiolite in central Qiangtang,Tibetan Plateau.Zircon SIMS and LAICP-M...This paper reports new zircon U-Pb ages,and Hf isotope and whole-rock major and trace element data for Cambrian plagiogranites from the Tuobeiling ophiolite in central Qiangtang,Tibetan Plateau.Zircon SIMS and LAICP-MS U-Pb dating of the plagiogranites yield weighted mean ages of 504.8±4.2 and 491.6±1.5 Ma,respectively.The zircons from plagiogranites exhibit positive eHf(t)values(ranging from 11.46 to 15.16),indicating that the plagiogranites are derived from depleted mantle.These plagiogranites are characterized by high SiO2and Na2O,low K2O,low REE contents,and flat REE distribution patterns.These rocks have geochemical compositions typical of oceanic plagiogranite and,considered along with their petrography and field relationships,are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust.The formation age of such type of plagiogranite is slightly younger than that of the associated section of oceanic crust.Thus the new results from these plagiogranites suggest that the Longmu Co–Shuanghu–Lancangjiang ocean had probably opened before the Middle Cambrian.展开更多
基金supported by the National Natural Science Foundation of China(Nos.41272240 and 41072166)China Geological Survey(Nos.1212011121248 and 1212011221093)
文摘To reveal the Jurassic tectonothermal event occurring to the Nyainrong microcontinent which is gripped among the Bangong-Nujiang suture zone,^40Ar/^39Ar dating was carried out on the basement orthogneiss and Jurassic granitc gneiss in the microcontinent. In the heating stage, four sam- pies exhibited a flat plateau age, with the value Tp concentrated in the range of 166-176 Ma; isochron age Ti was concentrated in the range of 165-175 Ma, and their corresponding ages were the consistent within allowable range. The ages should be representative of the era of the final deformation of the Amdo gneiss and cooling emplacement of the magmatic rock in the Jurassic. The geochronological studies have shown that the final deformation of microcontinent crystalline basement and the cooling of the Mesozoic large-scale tectonothermal events occurred in late Middle Jurassic. In Middle Jurassic, Nyainrong microcontinent experienced strong tectonic movement. Combining with the geochronologi- cal with isotope geochemistry for the microcontinent, the cause of the tectonothermal event should be attributed to the collision between the Nyainrong microcontinent and South Qiangtang Block following the northward subduction of Bangong-Nujiang oceanic crust.
基金supported by the Postdoctoral Science Foundation of China (No. 2014M561023)the National Natural Science Foundation of China (Nos. 40872146, 41072166, 41503022)the Project of China Geological Survey (Nos. 1212011086061, 1212011221093, 1212011087009)
文摘Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into mantle source characteristics and geodynamic setting of Permian ophiolitic fragments. U-Pb isotopic dating using SHRIMP II method reveals that the metamafic rocks were formed at 274.7± 3.9 and 279.8± 3.6 Ma. The metamafic rocks mostly show N-MORB-typed rare earth element patterns and are enrichment in large-ion lithophile elements, indicating that they are probably derived from partial melting of a depleted mantle in a back-arc basin. Our new data, together with recent studied results on Paleozoic ophiolitic fragments suggest the Paleo-Tethys Ocean in Central Qiangtang opened at Cambrian and widened between Ordovician and Devonian. Northward subduction started in the Late Devonian–Early Carboniferous and a back-arc basin developed during Permian.
基金supported by the National Natural Science Foundation of China(41072166 and 41272240)
文摘This paper reports new zircon U-Pb ages,and Hf isotope and whole-rock major and trace element data for Cambrian plagiogranites from the Tuobeiling ophiolite in central Qiangtang,Tibetan Plateau.Zircon SIMS and LAICP-MS U-Pb dating of the plagiogranites yield weighted mean ages of 504.8±4.2 and 491.6±1.5 Ma,respectively.The zircons from plagiogranites exhibit positive eHf(t)values(ranging from 11.46 to 15.16),indicating that the plagiogranites are derived from depleted mantle.These plagiogranites are characterized by high SiO2and Na2O,low K2O,low REE contents,and flat REE distribution patterns.These rocks have geochemical compositions typical of oceanic plagiogranite and,considered along with their petrography and field relationships,are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust.The formation age of such type of plagiogranite is slightly younger than that of the associated section of oceanic crust.Thus the new results from these plagiogranites suggest that the Longmu Co–Shuanghu–Lancangjiang ocean had probably opened before the Middle Cambrian.
