青藏高原东南部贡嘎山海螺沟冰川冰下沉积物形成与变形

冰岩界面的冰川动力学是冰川系统的重要组成部分, 海螺沟冰川地处温暖湿润的海洋环境, 冰川运动速度较快, 冰川底部接近压融点, 是研究冰下过程的较理想地点. 在海螺沟冰川大型磨光面上浅显侵蚀坑内发现了碎屑物质. 对碎屑物质理化特征研究表明: 粒度特征、地球化学与石英砂SEM 分析表明沉积在冰岩界面上的物质来自于冰川底部的底碛层, 而不是冰上环境的产物. 偏光显微镜下观察到的冰下沉积物呈现出一系列塑性变形(微旋转、褶皱)和脆性变形(线性结构、支撑结构、断层)微观结构和构造. 两种变形结构的存在是碎屑物质在形成过程中其含水量波动情况的反映. 冰下碎屑物质是冰下融出、滞碛作用的共同产物. 在整个冰下碎屑物质形成与变形过程中, 由于冰下水系季节性变化带来的冰岩界面上冰川融水含量的波动起了决定性作用.

Formation and Deformation of Subglacial Deposits of Hailuogou Glacier in Mt. Gongga,Southeastern Tibetan Plateau

The glacier dynamics at the ice-bed interface form an important element of the glacier system. Hailuogou Glacier is located in a warm and humid environment with maritime characteristics. The bottom of the glacier rich in debris slides intensively and the temperature at the bottom approaches the pressure melting point. Therefore, research on subglacial environment of this glacier makes a significant sense. We have sampled a sequence of subglacial deposits in the shallow eroded depression on the polished surfaces of Hailuogou Glacier. The investigated site provides evidence of sediment deposition and deformation to understand subglacial processes. We used an integrated approach to demonstrate a subglacial deposition and deformation model based on field observation and laboratory analysis. The results of grain-size, geochemical and SEM analyses testify each other that the source materials of the subglacial deposits are derived mainly from the glacier basal layer. Micromorphological work reveals that the subglacial deposits exhibits a range of ductile deformation microstructures (rotation structures, folding structure) and brittle deformation ones (lineation, edge-to-edge crushing and grain stacking, faulting structure). A subglacial deposition model has been established and the model exhibits a complex process including subglacial meltwater deposition, lodging. Sediment deposition and deformation is controlled by fluctuations in basal-water pressure, which determine changes in subglaciall meltwater drainage. Therefore subglacial meltwater at the ice-bed interface plays an important role in glacier dynamics, glacier deformation and sediment deposition processes. The maritime feature of Hailouogou Glacier examines this well.