The mountain watersheds of Kaidu River and Urumqi River, which separately originate from the south and north-side of the Tianshan Mountains in Xinjiang, are selected as the study area. The characteristics and trends o...The mountain watersheds of Kaidu River and Urumqi River, which separately originate from the south and north-side of the Tianshan Mountains in Xinjiang, are selected as the study area. The characteristics and trends on variation of temperature, precipitation and runoff, and the correlativity between temperature, precipitation, and runoffwere analyzed based on the past 40 years of observational data from the correlative hydrological and weather stations in the study areas. Various weather scene combinations are assumed and the response models of runoff to climate change are established in order to evaluate the sensitivity of runoff to climate change in the study areas based on the foregoing analysis, Results show that all variations of temperature, precipitation, and runoff overall present an oscillating and increasing trend since the 1960s and this increase are quite evident after 1990. There is a markedly positive correlation between mountain runoff, temperature, and precipitation while there are obvious regional differences of responding degree to precipitation and temperature between mountain runoff of Ummqi River and Kaidu River Basins Also, mountain runoff of Urumqi River Basin is more sensitive to precipitation change than that of Kaidu River Basin, and mountain runoff of Kaidu River Basin is more sensitive to temperature change than that of Ummqi River Basin.展开更多
The existence and subduction of the eastern Mianl黣 oceanic basin in the south Qinling belt are keys to understand the Qinling orogen. Based on geological mapping, several volcanic slices have been identified in Tumen...The existence and subduction of the eastern Mianl黣 oceanic basin in the south Qinling belt are keys to understand the Qinling orogen. Based on geological mapping, several volcanic slices have been identified in Tumen, Zhoujiawan, Xiaofu and Yuantan areas, which distribute in the northern margin of the Dahong Mountains (DHM), and thrust into the Sanli-gang-Sanyang fault. These slices consist mainly of diabases, basaltic-andesitic lavas, pyroclastic rocks and a minor tuff. The geochemistry of the basalts, andesites,and diabases is characterized by depleting in Nb and Ta, enriching in Th and LILE (e.g.K, Rb, Ba), and undifferentiating in HFSE. These geochemical characteristics suggest that the original magma of these rocks was derived from a mantle wedge above a subduction zone, and formed in an island-arc setting in Carboniferous-early Triassic. Comparing with the ophiolites and island-arc volcanic rocks in Mianxian-Leyang area to the west, it is reasonable to consider that there had been an oceanic basin connecting with the Mianle ancient ocean to the westward, distributing along the south edge of the Tongbai-Dabie block. In view of the ophiolite in Huashan area and these island-arc volcanic rocks along the north of the Dahong Mountains, it is suggested that there had been a plate tectonic evolutionary history with oceanic basin rifting and subduction in this region.展开更多
Located in the southern Qinling Mountains of central China, the Guanjiagou Formation has been a con-troversial issue with regard to its depositional age and tec-tonic implications. Being comprised of an approximately ...Located in the southern Qinling Mountains of central China, the Guanjiagou Formation has been a con-troversial issue with regard to its depositional age and tec-tonic implications. Being comprised of an approximately 2050 m thick succession of texturally and compositionally immature, presumed marine turbiditic sandstones and con-glomerate, the Guanjiagou Formation consists of an overall prograding- and coarsening-upward megasequence. Al-though bounded by faults on both its northern and southern margins, it is weakly metamorphosed and deformed. To the north is the Devonian Sanhekou Group and to the south is the Neoproterozoic Hengdan Group. The lower portion of the sequence contains granitic and volcanic clasts (Guanjiagou conglomerate). The feldspars from these clasts were dated using the 40Ar/39Ar method. Two cooling ages of 219.690.49 and 216.460.59 Ma, for K-feldspar from a granitic clast and plagioclase from a volcanic clast, respectively, were obtained. These ages are identical to the time of regional igneous ac-tivities (ca. 240—220 Ma) and are interpreted as the prod-ucts of magmatism associated with collision in the Qinling orogenic belt in the Early Mesozoic, suggesting that the Guanjiagou Formation was deposited in the Norian of the Late Triassic, ca. 220 Ma. Therefore, 40Ar/39Ar and sedimen-tary analyses suggest that the Guanjiagou Formation con-tains sediments that may have filled in a remnant ocean ba-sin, which might be part of the Anyemaqen-Mianle ocean, or Tethys on the southern side of Central Orogenic Belt in China during the Late Paleozoic to Early Mesozoic.展开更多
During the past ten years, various types of HP-UHP metamorphic rocks have been discovered in the South Altyn Tagh, the North Qaidam and the North Qinling （秦岭） in the West and Middle Central China orogen. The UHP r...During the past ten years, various types of HP-UHP metamorphic rocks have been discovered in the South Altyn Tagh, the North Qaidam and the North Qinling （秦岭） in the West and Middle Central China orogen. The UHP rocks, as lentoid bodies in regional gneisses, include eclogite （garnet-bearing pyroxenite）, garnet peridotite and various pelitic or felsic gneisses. There are many records of minerals and microstructures of exsolution indicate the UHP metamorphism, such as coesite （or its pseudomorph）, diamond, exsolution of clinopyroxene/amphibole/＋rutile or rutile＋quartz＋apatite in garnet, exsolution of quartz in omphacite and exsolution of kyanite＋spinel in precursor stishovite.The discovery of microstructure evidence for the presence of precursor stishovite in typical Alrich gneiss from the South Altyn Tagh reveals continental subduction and exhumation to and from a depth of more than 350 km. It is the petrological record of the deepest subduction and exhumation of continental rock in the world. The in situ zircon U-Pb dating using LA-ICP- MS or SHRIMP methods shows that the metamorphic ages of the HP-UHP rocks in the South Altyn Tagh, the North Qaidam and the North Qinling are 475-509, 420--457, and 485-514 Ma, respectively. The metamorphic ages of HP-UHP rocks in the North Qaidam are 20-80 Ma younger than those in the South Altyn Tagh and the North Qinling, and the metamorphic ages do not systematically increase or decrease from the South Altyn Tagh through the North Qaidam to the North Qinling. The absence of time transgressive variety of the metamorphism in the three regions does not support the hypothesis that the HP-UHP rocks in these re. gions form the same HP-UHP metamorphic zone. And the HP-UHP rocks in these regions can not be simply correlated to the collision between the North China plate and the South China plate. At present, the study of the HP-UHP rocks in the West and Middle Central China orogen faces several key issues or challenges, such as： （1） the continental subduction to the mantle depth of stishovite stability field （〉9 GPa） is occasional or universal; （2） the mechanism of exhumation for the continental rocks subducted to the depth of stishovite stability field （〉300 km）; （3） the tectonic setting and geodynamical mechanism of producing the HP-UHP metamorphic zones in the South Altyn Tagh, the North Qaidam and the North Qinling. Further studies aiming at these problems will make important progress not only in metamorphlsm of the HP-UHP rocks in the West and Middle Central China orogen, but also in continen. tal deep subduction and exhumation in solid earth science. It will also contribute to the establishment of the theory of continental deep subduction.展开更多
基金supported by the funding of the Key Laboratory of Eco-hydrology Open FundChinese Academy of Sciences and Knowledge Innovation Program of the Chinese Academy of Sciences, No.KZCX2-YW-328
文摘The mountain watersheds of Kaidu River and Urumqi River, which separately originate from the south and north-side of the Tianshan Mountains in Xinjiang, are selected as the study area. The characteristics and trends on variation of temperature, precipitation and runoff, and the correlativity between temperature, precipitation, and runoffwere analyzed based on the past 40 years of observational data from the correlative hydrological and weather stations in the study areas. Various weather scene combinations are assumed and the response models of runoff to climate change are established in order to evaluate the sensitivity of runoff to climate change in the study areas based on the foregoing analysis, Results show that all variations of temperature, precipitation, and runoff overall present an oscillating and increasing trend since the 1960s and this increase are quite evident after 1990. There is a markedly positive correlation between mountain runoff, temperature, and precipitation while there are obvious regional differences of responding degree to precipitation and temperature between mountain runoff of Ummqi River and Kaidu River Basins Also, mountain runoff of Urumqi River Basin is more sensitive to precipitation change than that of Kaidu River Basin, and mountain runoff of Kaidu River Basin is more sensitive to temperature change than that of Ummqi River Basin.
基金This work was supported by the National Natu-ral Science Foundation of China (Grant Nos. 49732080, 40003003,40234041).
文摘The existence and subduction of the eastern Mianl黣 oceanic basin in the south Qinling belt are keys to understand the Qinling orogen. Based on geological mapping, several volcanic slices have been identified in Tumen, Zhoujiawan, Xiaofu and Yuantan areas, which distribute in the northern margin of the Dahong Mountains (DHM), and thrust into the Sanli-gang-Sanyang fault. These slices consist mainly of diabases, basaltic-andesitic lavas, pyroclastic rocks and a minor tuff. The geochemistry of the basalts, andesites,and diabases is characterized by depleting in Nb and Ta, enriching in Th and LILE (e.g.K, Rb, Ba), and undifferentiating in HFSE. These geochemical characteristics suggest that the original magma of these rocks was derived from a mantle wedge above a subduction zone, and formed in an island-arc setting in Carboniferous-early Triassic. Comparing with the ophiolites and island-arc volcanic rocks in Mianxian-Leyang area to the west, it is reasonable to consider that there had been an oceanic basin connecting with the Mianle ancient ocean to the westward, distributing along the south edge of the Tongbai-Dabie block. In view of the ophiolite in Huashan area and these island-arc volcanic rocks along the north of the Dahong Mountains, it is suggested that there had been a plate tectonic evolutionary history with oceanic basin rifting and subduction in this region.
文摘Located in the southern Qinling Mountains of central China, the Guanjiagou Formation has been a con-troversial issue with regard to its depositional age and tec-tonic implications. Being comprised of an approximately 2050 m thick succession of texturally and compositionally immature, presumed marine turbiditic sandstones and con-glomerate, the Guanjiagou Formation consists of an overall prograding- and coarsening-upward megasequence. Al-though bounded by faults on both its northern and southern margins, it is weakly metamorphosed and deformed. To the north is the Devonian Sanhekou Group and to the south is the Neoproterozoic Hengdan Group. The lower portion of the sequence contains granitic and volcanic clasts (Guanjiagou conglomerate). The feldspars from these clasts were dated using the 40Ar/39Ar method. Two cooling ages of 219.690.49 and 216.460.59 Ma, for K-feldspar from a granitic clast and plagioclase from a volcanic clast, respectively, were obtained. These ages are identical to the time of regional igneous ac-tivities (ca. 240—220 Ma) and are interpreted as the prod-ucts of magmatism associated with collision in the Qinling orogenic belt in the Early Mesozoic, suggesting that the Guanjiagou Formation was deposited in the Norian of the Late Triassic, ca. 220 Ma. Therefore, 40Ar/39Ar and sedimen-tary analyses suggest that the Guanjiagou Formation con-tains sediments that may have filled in a remnant ocean ba-sin, which might be part of the Anyemaqen-Mianle ocean, or Tethys on the southern side of Central Orogenic Belt in China during the Late Paleozoic to Early Mesozoic.
基金supported by the National Basic Research Pro-gram of China (No. 2009CB825003)the National Natural Science Foundation of China (Nos. 40972128, 40572111)the Ministry of Science and Technology of China for the State Key Laboratory of Continental Dynamics of Northwest University
文摘During the past ten years, various types of HP-UHP metamorphic rocks have been discovered in the South Altyn Tagh, the North Qaidam and the North Qinling （秦岭） in the West and Middle Central China orogen. The UHP rocks, as lentoid bodies in regional gneisses, include eclogite （garnet-bearing pyroxenite）, garnet peridotite and various pelitic or felsic gneisses. There are many records of minerals and microstructures of exsolution indicate the UHP metamorphism, such as coesite （or its pseudomorph）, diamond, exsolution of clinopyroxene/amphibole/＋rutile or rutile＋quartz＋apatite in garnet, exsolution of quartz in omphacite and exsolution of kyanite＋spinel in precursor stishovite.The discovery of microstructure evidence for the presence of precursor stishovite in typical Alrich gneiss from the South Altyn Tagh reveals continental subduction and exhumation to and from a depth of more than 350 km. It is the petrological record of the deepest subduction and exhumation of continental rock in the world. The in situ zircon U-Pb dating using LA-ICP- MS or SHRIMP methods shows that the metamorphic ages of the HP-UHP rocks in the South Altyn Tagh, the North Qaidam and the North Qinling are 475-509, 420--457, and 485-514 Ma, respectively. The metamorphic ages of HP-UHP rocks in the North Qaidam are 20-80 Ma younger than those in the South Altyn Tagh and the North Qinling, and the metamorphic ages do not systematically increase or decrease from the South Altyn Tagh through the North Qaidam to the North Qinling. The absence of time transgressive variety of the metamorphism in the three regions does not support the hypothesis that the HP-UHP rocks in these re. gions form the same HP-UHP metamorphic zone. And the HP-UHP rocks in these regions can not be simply correlated to the collision between the North China plate and the South China plate. At present, the study of the HP-UHP rocks in the West and Middle Central China orogen faces several key issues or challenges, such as： （1） the continental subduction to the mantle depth of stishovite stability field （〉9 GPa） is occasional or universal; （2） the mechanism of exhumation for the continental rocks subducted to the depth of stishovite stability field （〉300 km）; （3） the tectonic setting and geodynamical mechanism of producing the HP-UHP metamorphic zones in the South Altyn Tagh, the North Qaidam and the North Qinling. Further studies aiming at these problems will make important progress not only in metamorphlsm of the HP-UHP rocks in the West and Middle Central China orogen, but also in continen. tal deep subduction and exhumation in solid earth science. It will also contribute to the establishment of the theory of continental deep subduction.
