Fission track dating was applied to analyze the 20 samples from Nyainrong microcontinent, and we obtained 20 apatite and 15 zircon fission track ages. The results show single population grain ages with a single mean a...Fission track dating was applied to analyze the 20 samples from Nyainrong microcontinent, and we obtained 20 apatite and 15 zircon fission track ages. The results show single population grain ages with a single mean age and associated central ages mainly ranging from 108±7Ma to 35±4Ma.Their mean track lengths are 12.2-13.9 μm with a single peak. Zircon fission track age range from 78±3 Ma to 117±4 Ma. The results represented the two tectonic uplift events in the study area, namely the Cretaceous and Paleogene periods. According to thermal history modeling results, uplifting rates of two tectonic events is 0.31-0.1 mm/a and 0.07-0.04 mm/a respectively. Combined with field condition and study results, it is suggested that the Cretaceous tectonic uplift event was related to the closure ocean basin caused by Qaingtang-Lhasa collision, and the Paleogene tectonic uplift event was related to the south to thrust system caused by Indo-Asian collision.展开更多
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
To better understand the Pan-African-early Paleozoic tectonothermal events of the Nyainrong microcontinent and the constraints on its tectonic evolution,here we report the results of zircon LA-ICP-MS U-Pb dating and g...To better understand the Pan-African-early Paleozoic tectonothermal events of the Nyainrong microcontinent and the constraints on its tectonic evolution,here we report the results of zircon LA-ICP-MS U-Pb dating and geochemical features of Amdo gneiss in the Nyainrong microcontinent.The outcrops of Amdo gneiss is about 30 km south of Amdo County in northern Tibet.The field occurrence,mineral composition,textural characteristics,and whole-rock geochemical features of the four gneiss samples indicate the protolith of the gneisses is intermediate-acid intrusive rock.Gneiss zircon trace element tracing and genetic analysis shows that zircon has typical characteristics of magmatic zircon.The206Pb/238U concordant age of zircon is505–517 Ma,corresponding to the Middle-Late Cambrian,which is the formation age of the protolith.The samples have characteristics of high silicon,alkali-rich,alkalic rate AR=1.73–3.7,the differentiation index DI=70.78–90.28;rock aluminum saturation index ranges from 1.02 to 1.05,FeO/MgO ranges from 2.63 to 4.50,10000×Ga/Al ranges from 2.12 to 2.41,and P2O5and Al2O3content decreased with SiO2increasing.Th and Y contents have a good positive correlation with Rb content;the genetic type of protolith of the gneiss is the differentiation of subalkaline over aluminum I-type granite.Combined with regional data,the tectonic setting of the Amdo gneiss protolith is closely related to the collision orogenic process.The preliminary view is that the Middle-Late Cambrian magmatic events developed on the microcontinent could be the result of Andeantype orogeny along the Gondwana super-continental margin after the end of the Pan-African orogeny.展开更多
基金financially supported by the geological survey project of China Geological Survey(Grant No:1212011120185 and Grant No:1212011120182)
文摘Fission track dating was applied to analyze the 20 samples from Nyainrong microcontinent, and we obtained 20 apatite and 15 zircon fission track ages. The results show single population grain ages with a single mean age and associated central ages mainly ranging from 108±7Ma to 35±4Ma.Their mean track lengths are 12.2-13.9 μm with a single peak. Zircon fission track age range from 78±3 Ma to 117±4 Ma. The results represented the two tectonic uplift events in the study area, namely the Cretaceous and Paleogene periods. According to thermal history modeling results, uplifting rates of two tectonic events is 0.31-0.1 mm/a and 0.07-0.04 mm/a respectively. Combined with field condition and study results, it is suggested that the Cretaceous tectonic uplift event was related to the closure ocean basin caused by Qaingtang-Lhasa collision, and the Paleogene tectonic uplift event was related to the south to thrust system caused by Indo-Asian collision.
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 National Natural Science Foundation of China(Grant Nos.41072166 and 41272240)Program of China Geological Survey(Grant Nos.1212011121248,1212011221093)
文摘To better understand the Pan-African-early Paleozoic tectonothermal events of the Nyainrong microcontinent and the constraints on its tectonic evolution,here we report the results of zircon LA-ICP-MS U-Pb dating and geochemical features of Amdo gneiss in the Nyainrong microcontinent.The outcrops of Amdo gneiss is about 30 km south of Amdo County in northern Tibet.The field occurrence,mineral composition,textural characteristics,and whole-rock geochemical features of the four gneiss samples indicate the protolith of the gneisses is intermediate-acid intrusive rock.Gneiss zircon trace element tracing and genetic analysis shows that zircon has typical characteristics of magmatic zircon.The206Pb/238U concordant age of zircon is505–517 Ma,corresponding to the Middle-Late Cambrian,which is the formation age of the protolith.The samples have characteristics of high silicon,alkali-rich,alkalic rate AR=1.73–3.7,the differentiation index DI=70.78–90.28;rock aluminum saturation index ranges from 1.02 to 1.05,FeO/MgO ranges from 2.63 to 4.50,10000×Ga/Al ranges from 2.12 to 2.41,and P2O5and Al2O3content decreased with SiO2increasing.Th and Y contents have a good positive correlation with Rb content;the genetic type of protolith of the gneiss is the differentiation of subalkaline over aluminum I-type granite.Combined with regional data,the tectonic setting of the Amdo gneiss protolith is closely related to the collision orogenic process.The preliminary view is that the Middle-Late Cambrian magmatic events developed on the microcontinent could be the result of Andeantype orogeny along the Gondwana super-continental margin after the end of the Pan-African orogeny.
