The eastern Xinjiang Basin is desperately short of water. Most rivers in the basin originate in the high eastern Tianshan, which has abundant precipitation and numerous alpine glaciers. Fieldwork conducted on three re...The eastern Xinjiang Basin is desperately short of water. Most rivers in the basin originate in the high eastern Tianshan, which has abundant precipitation and numerous alpine glaciers. Fieldwork conducted on three reference glaciers around Mt. Bogda in 1981 and 2009 suggests that they all strongly melt in summer, a process that has tended to accelerate in recent decades. Based on topographic maps from 1962 and 1972 and 2005/2006 satellite imagery, we investigated 203 glaciers near Mt. Bogda and 75 glaciers near Mt. Harlik. The results show that the surface area of the Mt. Bogda glaciers decreased by 21.6% (0.49% a?1) from 1962 to 2006. This was accompanied by a 181 m decrease in length and a 28% drop in ice volume. In the Mt. Harlik region, areal extent was reduced by 10.5% (0.32% a?1), length by 166 m, and volume by 14% between 1972 and 2005. South-facing glaciers lost more of their area than those that are north facing, yielding an areal loss of 25.3% and 16.9% for southern and northern slopes of Mt. Bogda, respectively, and 12.3% and 6.6% for the comparable slopes of Mt. Harlik. Glaciers smaller than 0.5 km2 in area experienced the strongest retreat, whereas glaciers larger than 2 km2 in area experienced gentle recession but may be the main contributors in the future to river runoff. Glacial ablation in eastern Xinjiang tends to be strong, and the water resources in this region are deteriorating. Also, a heavy reduction in the capacity of the local karez system, as well as a significant change in river runoff, can be related to glacial retreat. Combined, this will adversely affect the downstream city of Urumqi and the Turfan Basin.展开更多
The granitioids in question are located in the geosynclinal fold belt of the Northern Tianshan Mountains.The magmas are intruded into a Carboniferous marine volcanic-sedimentary rock series. forming a contempo-raneous...The granitioids in question are located in the geosynclinal fold belt of the Northern Tianshan Mountains.The magmas are intruded into a Carboniferous marine volcanic-sedimentary rock series. forming a contempo-raneous. intermediate-basic to acid. composite intrusion. With a whole-rock Rb-Sr isochron age of 315.7 Ma. itis considered to be of middle Heicynian age. The granitoids have a SiO_2 content of 48-78%, a calc-alkali indexof 60 and silica-alkali indices ρ=2.2-2.4 and σ=1.5-2. From basic to acid compositions, the total REE con-tent increases from 38 to 143 ppm. δEu ranges from 0.47 to 0.86 and the Eu anomalies are negative. Thenormalized curves of REE of various rock types are very similar. These coupled with the characteristics of traceelement geochemistry show that the intrusion is an island arc-continental margin, calc-alkaline one. Theδ^(18)O values range from 5.8 to 8.9‰ and the ^(87)Sr/^(86)Sr initial ratio is 0.705. The materials of the intrusion arecomposed of a mixture of the magmas at the top of the upper mantle and in the lower crust, This indicates thatthe rocks might be consanguineous. differentiated and evolved products and possess the characteristics of Ⅰtype granites.展开更多
The timing of the emplacement of the Weiya pluton remains controversial due to the absence of systematic and precise dating. This paper reports zircon SHRIMP U-Pb dating of different lithologic phases in the Weiya plu...The timing of the emplacement of the Weiya pluton remains controversial due to the absence of systematic and precise dating. This paper reports zircon SHRIMP U-Pb dating of different lithologic phases in the Weiya pluton, and discusses the genesis and tectonic environment. The ages of gabbro, quartz syenite, diorite porphyrite and fine-grained granite are 236±6 Ma, 246±6 Ma, 233±8 Ma and 237±8 Ma, respectively. All these phases were formed in early-middle Indosinian （Triassic） in a post-orogenic environment. In addition to underplating, intraplating of mantle-derived magmas is also a substantial mechanism for magma generation and vertical accretion of the continental crust. Granitoid rocks are important products of vertical continental accretion as underplating evolves gradually to intraplating. The existence of post-orogenic Indosinian granites shows that the middle Tianshan orogenic belt underwent an important tectonic conversion from the Paleo-Asian ocean subduction-collision system to the Paleo-Tethys ocean regime.展开更多
Laser ablation–inductively coupled plasma–mass spectrometry（LA–ICP–MS） was used to determine the trace element concentrations of magnetite from the Heifengshan, Shuangfengshan, and Shaquanzi Fe（–Cu） deposits ...Laser ablation–inductively coupled plasma–mass spectrometry（LA–ICP–MS） was used to determine the trace element concentrations of magnetite from the Heifengshan, Shuangfengshan, and Shaquanzi Fe（–Cu） deposits in the Eastern Tianshan Orogenic Belt. The magnetite from these deposits typically contains detectable Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn and Ga. The trace element contents in magnetite generally vary less than one order of magnitude. The subtle variations of trace element concentrations within a magnetite grain and between the magnetite grains in the same sample probably indicate local inhomogeneity of ore–forming fluids. The variations of Co in magnetite between samples are probably due to the mineral proportion of magnetite and pyrite. Factor analysis has discriminated three types of magnetite： Ni–Mn–V–Ti（Factor 1）, Mg–Al–Zn（Factor 2）, and Ga– Co（Factor 3） magnetite. Magnetite from the Heifengshan and Shuangfengshan Fe deposits has similar normalized trace element spider patterns and cannot be discriminated according to these factors. However, magnetite from the Shaquanzi Fe–Cu deposit has affinity to Factor 2 with lower Mg and Al but higher Zn concentrations, indicating that the ore–forming fluids responsible for the Fe–Cu deposit are different from those for Fe deposits. Chemical composition of magnetite indicates that magnetite from these Fe（–Cu） deposits was formed by hydrothermal processes rather than magmatic differentiation. The formation of these Fe（–Cu） deposits may be related to felsic magmatism.展开更多
基金supported by the National Basic Research Program of China (2010CB951003)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-EW-311)the National Natural Science Foundation of China (1141001040, 91025012 and 41171057)
文摘The eastern Xinjiang Basin is desperately short of water. Most rivers in the basin originate in the high eastern Tianshan, which has abundant precipitation and numerous alpine glaciers. Fieldwork conducted on three reference glaciers around Mt. Bogda in 1981 and 2009 suggests that they all strongly melt in summer, a process that has tended to accelerate in recent decades. Based on topographic maps from 1962 and 1972 and 2005/2006 satellite imagery, we investigated 203 glaciers near Mt. Bogda and 75 glaciers near Mt. Harlik. The results show that the surface area of the Mt. Bogda glaciers decreased by 21.6% (0.49% a?1) from 1962 to 2006. This was accompanied by a 181 m decrease in length and a 28% drop in ice volume. In the Mt. Harlik region, areal extent was reduced by 10.5% (0.32% a?1), length by 166 m, and volume by 14% between 1972 and 2005. South-facing glaciers lost more of their area than those that are north facing, yielding an areal loss of 25.3% and 16.9% for southern and northern slopes of Mt. Bogda, respectively, and 12.3% and 6.6% for the comparable slopes of Mt. Harlik. Glaciers smaller than 0.5 km2 in area experienced the strongest retreat, whereas glaciers larger than 2 km2 in area experienced gentle recession but may be the main contributors in the future to river runoff. Glacial ablation in eastern Xinjiang tends to be strong, and the water resources in this region are deteriorating. Also, a heavy reduction in the capacity of the local karez system, as well as a significant change in river runoff, can be related to glacial retreat. Combined, this will adversely affect the downstream city of Urumqi and the Turfan Basin.
文摘The granitioids in question are located in the geosynclinal fold belt of the Northern Tianshan Mountains.The magmas are intruded into a Carboniferous marine volcanic-sedimentary rock series. forming a contempo-raneous. intermediate-basic to acid. composite intrusion. With a whole-rock Rb-Sr isochron age of 315.7 Ma. itis considered to be of middle Heicynian age. The granitoids have a SiO_2 content of 48-78%, a calc-alkali indexof 60 and silica-alkali indices ρ=2.2-2.4 and σ=1.5-2. From basic to acid compositions, the total REE con-tent increases from 38 to 143 ppm. δEu ranges from 0.47 to 0.86 and the Eu anomalies are negative. Thenormalized curves of REE of various rock types are very similar. These coupled with the characteristics of traceelement geochemistry show that the intrusion is an island arc-continental margin, calc-alkaline one. Theδ^(18)O values range from 5.8 to 8.9‰ and the ^(87)Sr/^(86)Sr initial ratio is 0.705. The materials of the intrusion arecomposed of a mixture of the magmas at the top of the upper mantle and in the lower crust, This indicates thatthe rocks might be consanguineous. differentiated and evolved products and possess the characteristics of Ⅰtype granites.
文摘The timing of the emplacement of the Weiya pluton remains controversial due to the absence of systematic and precise dating. This paper reports zircon SHRIMP U-Pb dating of different lithologic phases in the Weiya pluton, and discusses the genesis and tectonic environment. The ages of gabbro, quartz syenite, diorite porphyrite and fine-grained granite are 236±6 Ma, 246±6 Ma, 233±8 Ma and 237±8 Ma, respectively. All these phases were formed in early-middle Indosinian （Triassic） in a post-orogenic environment. In addition to underplating, intraplating of mantle-derived magmas is also a substantial mechanism for magma generation and vertical accretion of the continental crust. Granitoid rocks are important products of vertical continental accretion as underplating evolves gradually to intraplating. The existence of post-orogenic Indosinian granites shows that the middle Tianshan orogenic belt underwent an important tectonic conversion from the Paleo-Asian ocean subduction-collision system to the Paleo-Tethys ocean regime.
基金financially supported by the Chinese 973 project(2012CB416804)the ‘‘CAS Hundred Talents’’ Project from the Chinese Academy of Sciences(KZCX2-YW-BR-09)to Qi Liang
文摘Laser ablation–inductively coupled plasma–mass spectrometry（LA–ICP–MS） was used to determine the trace element concentrations of magnetite from the Heifengshan, Shuangfengshan, and Shaquanzi Fe（–Cu） deposits in the Eastern Tianshan Orogenic Belt. The magnetite from these deposits typically contains detectable Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn and Ga. The trace element contents in magnetite generally vary less than one order of magnitude. The subtle variations of trace element concentrations within a magnetite grain and between the magnetite grains in the same sample probably indicate local inhomogeneity of ore–forming fluids. The variations of Co in magnetite between samples are probably due to the mineral proportion of magnetite and pyrite. Factor analysis has discriminated three types of magnetite： Ni–Mn–V–Ti（Factor 1）, Mg–Al–Zn（Factor 2）, and Ga– Co（Factor 3） magnetite. Magnetite from the Heifengshan and Shuangfengshan Fe deposits has similar normalized trace element spider patterns and cannot be discriminated according to these factors. However, magnetite from the Shaquanzi Fe–Cu deposit has affinity to Factor 2 with lower Mg and Al but higher Zn concentrations, indicating that the ore–forming fluids responsible for the Fe–Cu deposit are different from those for Fe deposits. Chemical composition of magnetite indicates that magnetite from these Fe（–Cu） deposits was formed by hydrothermal processes rather than magmatic differentiation. The formation of these Fe（–Cu） deposits may be related to felsic magmatism.
