This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the prima...This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician- Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0~ clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid- Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent- continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate- Himalaya folded structural belt- Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo- Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.展开更多
This paper reports Precambrian rock magnetic fabrics in the Nyalam area of southern Tibet. The analytical results of magnetic fabrics show that the values of H are high （〉 10% in general）, so the ductile deformatio...This paper reports Precambrian rock magnetic fabrics in the Nyalam area of southern Tibet. The analytical results of magnetic fabrics show that the values of H are high （〉 10% in general）, so the ductile deformations of the Precambrian rock are strong. The orientation of the maximum principal stress inferred from the minimum magnetic susceptibility is nearly S-N, NE-SW and NW-SE. The Flinn diagram of the magnetic fabrics show that the strain pattern is oblate and constrictional type. Magnetic foliation of great majority of rock samples is well developed and the magnetic lineation is poor and the magnetic susceptibility ellipsoid is flattened. The magnetic lineation of the minority rock samples is well developed and the magnetic foliation is poor and the magnetic susceptibility ellipsoid is prolate. According to the geological field and the magnetic fabrics, there are 3 times tectonic stress field in SN directed extruding, NW-SE directed extruding, NW-SE directed extension. It shows that the Nyalam area has undergone process the orientation of SN, NW-SE nappe structure and NW-SE directed extension structure. The change of tectonic stress is reflected by the field characteristics of the Precambrian rock magnetic fabrics that is the direct responding result of the arc-continental, continent-continental collision between the India and Asian continents in the late part of the Late Cretaceous to Late Eocene and subsequently shifted to intra-continental convergent, the plateau uplifting and extension structure stage since the Late Eocene.展开更多
The studied area lies in the eastern sector of the Tethys.Since the Early Paleozoic,the Nujiang-Lancang-Jinsha Rivers(southwest Sanjiang)area has experienced the geological evolutionary phase of the Paleo-Tethys,Meso-...The studied area lies in the eastern sector of the Tethys.Since the Early Paleozoic,the Nujiang-Lancang-Jinsha Rivers(southwest Sanjiang)area has experienced the geological evolutionary phase of the Paleo-Tethys,Meso-Tethys and Neo-Tethys.The multiple tectonic-magmatic activities have been occurred in the region,which have provided very favorable conditions.According to the regional geological characteristics,Geotectonic position is the area which can be divided into the following tectonic units:Kekexili-Yajiang passive continental margin,Garze-Litang plate junction,Dege-Zhongdian plate,Jinshajiang-Ailaoshan plate junction,Changdu-Simao plate,Lanchangjiang plate junction,Zuogong-Baoshan plate,Nujiang plate junction,Bomi-Tengchong plate and nine mineralization zones(Kekexili-Yajiang mineralization zone,Garze-Litang mineralization zone,Dege-Zhongdian mineralization zone,Jinshajiang-Ailaoshan mineralization zone,Changdu-Simao mineralization zone,Lanchangjiang mineralization zone,Zuogong-Baoshan mineralization zone,Nujiang mineralization zone and Bomi-Tengchong mineralization zone).The authors discussed that the geotectonic evolution specializes are relative to the main mineralization in this region.These studies show the geotectonic evolution and mineralization in the Nujiang-Lancang-Jinsha Rivers area have gone through eight stages for the Cambrian.Because the tectonic-magmatic mineralization activities have occurred the rich minerals resources and ore deposit types have been forming in this region.Ore deposits may be divided into seven types:massive sulfide type,stratabound type,turbidite type,postmag-matic hydrothermal type,skarn type,porphyry type and ductile shear zone type gold deposit.Deep geological effect of southwest Sanjiang area for deposit and its mineralization and ore prospecting and metallogenic prediction research work,is expected to find new orebody and ore deposit.The study of geotonics and metallogenesis in the Nujiang-Lancang-Jinsha Rivers area has a new idea and important foundation for prospecting for the ore deposits in Sanjiang(Nujiang-Lancang-Jinsha Rivers area)region.展开更多
In this paper, we report an integrated study of trace element, U-Pb age and Hf isotopic composition of zircons from alkali feldspar granites, granodiorites and diorite enclaves in a recently discovered ring complex at...In this paper, we report an integrated study of trace element, U-Pb age and Hf isotopic composition of zircons from alkali feldspar granites, granodiorites and diorite enclaves in a recently discovered ring complex at Lianghe in western Yunnan, Chi na. The granitoids showed identical U-Pb ages of 127, 115 and 122 Ma, from felsic to mafic, but had different zircon trace el ements and Hf isotopic compositions. Trace element content decreased with a gradual increase in εHf(t) values of ?9.1 to ?5.4, ?4.5 to 0, and 3.6 to 6.2, respectively. Results indicate that changes in zircon trace elements generally correlate with changes in Hf isotope signatures within single samples and among various granitoids. These relationships reflect the mixing of felsic and mafic magmas. Evidence indicates that depleted mantle-derived mafic magma underplating caused ancient crustal melting, and then formed large-scale granites in Lianghe during the Early Cretaceous. These granodiorites were formed mainly by the mix ing of mafic magma and granitic magma.展开更多
基金supported by China Geological Survey(Grant No. H45C004002)the Project of the National Natural Science Foudation of China (Grant No.40272012)
文摘This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician- Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0~ clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid- Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent- continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate- Himalaya folded structural belt- Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo- Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.
基金Acknowledgements This work was supported by China Geological Survey （Grant No. H45C004002, 1212010784007） and the Project of the National Natural Science Foundation of China （Grant No. 40272012）.
文摘This paper reports Precambrian rock magnetic fabrics in the Nyalam area of southern Tibet. The analytical results of magnetic fabrics show that the values of H are high （〉 10% in general）, so the ductile deformations of the Precambrian rock are strong. The orientation of the maximum principal stress inferred from the minimum magnetic susceptibility is nearly S-N, NE-SW and NW-SE. The Flinn diagram of the magnetic fabrics show that the strain pattern is oblate and constrictional type. Magnetic foliation of great majority of rock samples is well developed and the magnetic lineation is poor and the magnetic susceptibility ellipsoid is flattened. The magnetic lineation of the minority rock samples is well developed and the magnetic foliation is poor and the magnetic susceptibility ellipsoid is prolate. According to the geological field and the magnetic fabrics, there are 3 times tectonic stress field in SN directed extruding, NW-SE directed extruding, NW-SE directed extension. It shows that the Nyalam area has undergone process the orientation of SN, NW-SE nappe structure and NW-SE directed extension structure. The change of tectonic stress is reflected by the field characteristics of the Precambrian rock magnetic fabrics that is the direct responding result of the arc-continental, continent-continental collision between the India and Asian continents in the late part of the Late Cretaceous to Late Eocene and subsequently shifted to intra-continental convergent, the plateau uplifting and extension structure stage since the Late Eocene.
基金This work was supported by China Geological Survey(Grant No.H45C004002,1212010784007,ZKD-94-17)and the Project of the National Natural Science Foundation of China(Grant No.40272012).
文摘The studied area lies in the eastern sector of the Tethys.Since the Early Paleozoic,the Nujiang-Lancang-Jinsha Rivers(southwest Sanjiang)area has experienced the geological evolutionary phase of the Paleo-Tethys,Meso-Tethys and Neo-Tethys.The multiple tectonic-magmatic activities have been occurred in the region,which have provided very favorable conditions.According to the regional geological characteristics,Geotectonic position is the area which can be divided into the following tectonic units:Kekexili-Yajiang passive continental margin,Garze-Litang plate junction,Dege-Zhongdian plate,Jinshajiang-Ailaoshan plate junction,Changdu-Simao plate,Lanchangjiang plate junction,Zuogong-Baoshan plate,Nujiang plate junction,Bomi-Tengchong plate and nine mineralization zones(Kekexili-Yajiang mineralization zone,Garze-Litang mineralization zone,Dege-Zhongdian mineralization zone,Jinshajiang-Ailaoshan mineralization zone,Changdu-Simao mineralization zone,Lanchangjiang mineralization zone,Zuogong-Baoshan mineralization zone,Nujiang mineralization zone and Bomi-Tengchong mineralization zone).The authors discussed that the geotectonic evolution specializes are relative to the main mineralization in this region.These studies show the geotectonic evolution and mineralization in the Nujiang-Lancang-Jinsha Rivers area have gone through eight stages for the Cambrian.Because the tectonic-magmatic mineralization activities have occurred the rich minerals resources and ore deposit types have been forming in this region.Ore deposits may be divided into seven types:massive sulfide type,stratabound type,turbidite type,postmag-matic hydrothermal type,skarn type,porphyry type and ductile shear zone type gold deposit.Deep geological effect of southwest Sanjiang area for deposit and its mineralization and ore prospecting and metallogenic prediction research work,is expected to find new orebody and ore deposit.The study of geotonics and metallogenesis in the Nujiang-Lancang-Jinsha Rivers area has a new idea and important foundation for prospecting for the ore deposits in Sanjiang(Nujiang-Lancang-Jinsha Rivers area)region.
基金supported by China Geological Survey (Grant No. 1212010784007)
文摘In this paper, we report an integrated study of trace element, U-Pb age and Hf isotopic composition of zircons from alkali feldspar granites, granodiorites and diorite enclaves in a recently discovered ring complex at Lianghe in western Yunnan, Chi na. The granitoids showed identical U-Pb ages of 127, 115 and 122 Ma, from felsic to mafic, but had different zircon trace el ements and Hf isotopic compositions. Trace element content decreased with a gradual increase in εHf(t) values of ?9.1 to ?5.4, ?4.5 to 0, and 3.6 to 6.2, respectively. Results indicate that changes in zircon trace elements generally correlate with changes in Hf isotope signatures within single samples and among various granitoids. These relationships reflect the mixing of felsic and mafic magmas. Evidence indicates that depleted mantle-derived mafic magma underplating caused ancient crustal melting, and then formed large-scale granites in Lianghe during the Early Cretaceous. These granodiorites were formed mainly by the mix ing of mafic magma and granitic magma.
