中国第四纪冰川作用极大地推动了高亚洲乃至全球冰川形成机制的探讨。青藏高原以及喜马拉雅山地冰川作用的时限和规模研究得到了广泛关注,为西风带与西南季风带对晚第四纪冰川作用差异性问题的解决提供了有利条件。然而,对于中亚西风环流与东亚季风环流影响下的冰川演化差异性关系不甚明确,两大气候系统控制下的山地第四纪冰川的冰进时序、冰期历史和冰川规模显示出不同特点,其差异性主要体现在:西部山地的冰期启动时间早,冰川规模随时间而逐渐缩小,冰川历史较为完整,绝对年代证据显示冰川作用的启动时间是450 ka 左右的中梁赣冰期(MIS12);东部山地的冰期历史较短,仅保留末次冰期(~75 ka)的冰川遗迹,冰川作用的阶段性明显;冰川演化时间与空间的差异性表明,影响冰川发育的因素不仅仅是区域气候,构造因素也起着相当重要的作用。 相似文献
The Sichuan–Yunnan–Guizhou (SYG) metallogenic province of southwest China is one of the most important Zn–Pb ore zones in China, with ~ 200 Mt Zn–Pb ores at mean grades of 10 wt.% Zn and 5 wt.% Pb. The source and mechanism of the regional Zn–Pb mineralization remain controversial despite many investigations that have been conducted. The Wusihe Zn–Pb deposit is a representative large-scale Zn–Pb deposit in the northern SYG, which mainly occurs in the Dengying Formation and yields Zn–Pb resources of ~ 3.7 Mt. In this paper, Zn and S isotopes, and Fe and Cd contents of sphalerite from the Wusihe deposit were investigated in an attempt to constrain the controls on Zn and S isotopic variations, the potential sources of ore-forming components, and the possible mineralization mechanisms. Both the δ66Zn and δ34S values in sphalerite from the Wusihe deposit increase systematically from the bottom to the top of the strata-bound orebodies. Such spatial evolution in δ66Zn and δ34S values of sphalerite can be attributed to isotopic Rayleigh fractionation during sphalerite precipitation with temperature variations. The strong correlations between the Zn–S isotopic compositions and Fe–Cd concentrations in sphalerite suggest that their variations were dominated by a similar mechanism. However, the Rayleigh fractionation mechanism cannot explain the spatial variations of Fe and Cd concentrations of sphalerite in this deposit. It is noted that the bottom and top sphalerites from the strata-bound orebodies document contrasting Zn and S isotopic compositions which correspond to the Zn and S isotopic characteristics of basement rocks and host rocks, respectively. Therefore, the mixing of two-source fluids with distinct Zn–S isotopic signatures was responsible for the spatial variations of Zn–S isotopic compositions of sphalerite from the Wusihe deposit. The fluids from basement rocks are characterized by relatively lighter Zn (~ 0.2 ‰) and S (~ 5 ‰) isotopic compositions while the fluids from host rocks are marked by relatively heavier Zn (~ 0.6 ‰) and S (~ 15 ‰) isotopic compositions.
Because of its landscape heterogeneity, Koshi Basin (KB) is home to one of the world’s most abundant, diverse group of species. Habitat change evaluations for key protected species are very important for biodiversity protection in this region. Based on current and future world climate and land cover data, MaxEnt model was used to simulate potential habitat changes for key protected species. The results shows that the overall accuracy of the model is high (AUC > 0.9), suggesting that the MaxEnt-derived distributions are a close approximation of real-world distribution probabilities. The valley around Chentang Town and Dram Town in China, and Lamabagar and the northern part of Landtang National Park in Nepal are the most important regions for the protection of the habitat in KB. The habitat area of Grus nigricollis, Panax pseudoginseng, and Presbytis entellus is expected to decrease in future climate and land cover scenarios. More focus should be placed on protecting forests and wetlands since these are the main habitats for these species. 相似文献
The Huize Zn-Pb- (Ag-Ge) district is a typical representative of the well-known medium-to large-sized carbonate-hosted Zn-Pb- (Ag-Ge) deposits, occurring in the Sichuan-Yunnan-Guizhou Pb-Zn Ore-forming Zone. Generally, fluid inclusions within calcite, one of the major gangue minerals, are dominated by two kinds of small (1-10 um) inclusions including pure-liquid and liquid. The inclusions exist in concentrated groups along the crystal planes of the calcite. The ore-forming fluids containing Pb and Zn, which belong to the Na+-K+-Ca2+-Cl--F--SO42- type, are characterized by temperatures of 164-221℃, medium salinity in 5-10.8 wt% NaCl, and medium pressure at 410×105 to 661×105 Pa. The contents of Na+-K+ and C1--F-, and ratios of Na+/K+-Cl-/F- in fluid inclusions present good linearity. The ratios of Na+/K+ (4.66-6.71) and Cl-/F- (18.21-31.04) in the fluid inclusions of calcite are relatively high, while those of Na+/K+ (0.29-5.69) and Cl-/F- (5.00-26.0) in the inclusions of sphalerite and pyrite are rela 相似文献
