雅鲁藏布大峡谷格嘎古堰塞湖沉积岩石磁学性质指示的溃决事件

末次冰期时，在雅鲁藏布大峡谷入口处发育了一个古冰川堰塞湖，称为格嘎古堰塞湖.该堰塞湖是认识冰川阻江地貌效应的重要地质证据.古冰川堰塞湖可能会发生多次溃决洪水，通过堰塞湖沉积的分析可以获取堰塞期间的水文事件的信息.本文通过对古堰塞湖沉积39个样品多种磁学参数的详细分析发现，湖相沉积中的砂层低频磁化率（X_lf）为291×10^-8m³/kg，泥质沉积的X_lf仅为42×10^-8m³/kg；而非磁滞剩磁磁化率（X_ARM）和饱和等温剩磁（SIRM）的差别则较小.进一步的X-T、Loop和IRM研究以及X_ARM/X_lf表明，砂层中包含较多的粗颗粒磁铁矿是X_lf较高的主要原因，说明砂层中的磁性矿物没有经过风化破坏，应为近源沉积，并且快速埋藏，指示了溃决事件.本文的结果表明，利用岩石磁学性质以检测古堰塞湖溃决事件是一种可行的新方法.

Sediment rock magnetic properties indicate outburst events for Gega dammed lake at the Tsangpo Gorge in the Tibetan Plateau

A large ice-dammed lake exists at the entrance of Tsangpo gorge in the Tibetan Plateau. Many megafloods occured down the Tasangpo gorge during the last glaciation. The lacustrine sediments are important for understanding these periodic outburst floods. Through detailed rock magnetic studies of 39 lacustrine samples, we found the low frequency magnetic susceptibility (X_lf) is high in fine sand and low in clay, but the value of susceptibility of anhysteretic remanent magnetization (X_ARM) and saturation isothermal remanent magnetization(SIRM) are similar. X-T, Loop and IRM show that coarse-grained magnetite is the main magnetic minerals in fine sand. X_ARM/X_lf also shows that the grain size of magnetite in fine sand is coarser than that in clay. Rock magnetic properties indicate that the fine sand of lacustrine sediment experienced no weathering damage and should be deposited near the source and then quickly buried. Thus, the rock magnetic properties of fine sand of lacustrine may indicate the outburst event, which could be a new method for detecting the event.