应用音频大地电磁法探测内蒙古巴丹吉林高大沙山结构及成因

Applying Audio-magnetelluric Method to the Study of Megadune Structure and Formation in Badain Jaran Desert,Inner Mongolia

巴丹吉林沙漠拥有世界罕见的高大沙山群。为了解巴丹吉林高大沙山结构与成因,应用音频大地电磁法进行测量,利用非线性共轭梯度法二维反演得到了沙山的横截电性剖面。沙山电性剖面深部呈现明显的低阻,而沙山中部存在一定规模高阻区域。判断巴丹吉林沙漠众多高大沙山群的形成是由其稳定的西北风作用、源源不断的地下水补给机制和特殊的地层环境共同作用的结果。地下水由于蒸腾作用上升遇到古老沙丘的钙质层阻挡,由背风坡底部蒸发出来。水蒸气凝结在顶部滚落的沙子表面,使其抗风蚀能力增强,起到固沙作用;随着时间推移,沙山越来越大,形成高大沙山。

Badain Jaran Desert has a rare group of megadunes in the world;the audio-magnetelluric（AMT） method was used to study the structure of megadunes in Badain Jaran desert.The audio-magnetelluric data was processed by nonlinear conjugate gradients method,and the resistivity sections of megadunes were obtained.There is a apparent low-resistivity zone existing in the deep of the section,and a certain scale high-resistivity zone in the central of the megadunes.It is inferred that the formation of megadunes is related to the stabilized northwest wind,continuous groundwater replenishment and the special environment.The groundwater rises through transpiration and is obstructed by calcareous layers in the ancient sand dunes,then is evaporated from the bottom of the leeward slope;the water vapor is condensed on the surface of sands which roll down from the top of dunes,enhancing the ability to resisting wind erosion of sands,thus the sand dunes get larger and larger as time goes by,turning to megadunes.