库车前陆冲断带西部却勒盐推覆体变形特征分析

摘要

库车前陆冲断带西部发育中国最好的地表盐构造,可作为盐构造研究的天然实验室.前人对本区盐构造的研究主要集中于地下,包括地下盐构造样式的识别、地下盐构造分段性研究及盐构造形成机制研究等,而对于地表盐构造的研究相对较少.文章在前人研究的基础上,通过详细的野外填图,并辅以地震解释、遥感解译等方法,对库车前陆冲断带西部却勒盐推覆体变形特征进行分析,认为却勒盐推覆体的发育受控于却勒逆冲断层,库姆格列木群盐岩随逆冲断层出露地表.盐推覆体在东西向上构造差异较大,具有明显的分段性,在推覆体的中、西部,推覆体上盘地层发育齐全,盐岩仅沿推覆体逆冲前缘出露地表,属于典型的露趾增生型盐席;而在推覆体东部的察尔汗盐席处,盐上地层被剥蚀,盐岩出露地表后在重力的驱动下向周缘流动,属于溢流增生型盐席.察尔汗盐席受地表径流和降水作用影响明显,发育大量溶洞和盐山构造,并以“脉动流”的形式向前增生.盐内能干层的变形特征是反映盐岩流动性强弱的指标,盐推覆体东部察尔汗盐席盐内能干层变形样式更复杂,盐岩的流变性更强.缺少厚层顶板的限制和受降水及地表径流的充分影响是察尔汗盐席盐岩流变性较强的原因.%The western Kuqa foreland thrust belt hosts the best surface salt structures in China,and hence can be regarded as a natural laboratory for salt structure research.Previous researches have been mainly focused on the underground salt structures,such as the identification of the underground salt structures,the segmentation of the underground salt structures and the formation mechanism of the salt structures,while the researches on the surface salt structures in this region are relatively less.Based on previous researches,the authors used the methods of field mapping,seismic interpretation and remote sensing images interpretation to analyze the deformation characteristics of the Quele salt nappe in the western Kuqa foreland thrust belt.The development of the Quele salt nappe was controlled by the Quele thrust fault,and the salt rock of Kumugeliemu Group rose to the surface with the thrust fault.The Quele salt nappe is characterized by segmentation,and the deformation characteristics change from west to east.In the western and central part of the Quele salt nappe,the overburden of the salt is intact,and the salt rose to the surface only along the thrust frontier of the nappe.The salt structure pattern of the western and central part of the Quele salt nappe belongs to "open-toed advance salt sheet".Nevertheless,in the eastern part of the Quele salt nappe which is also called Charerhan Namakier,the overburden of the salt was eroded and the salt was driven to flow downward by gravity after the migration of the salt to the surface.The Charerhan Namakier belongs to "extrusive advance salt sheet".The topography of the Charerhan Namakier has been strongly affected by the surface runoff and rainfall,which has caused a lot of karst caves and salt hills to form at the surface of the Charerhan Namakier.Heavy rainfall could affect the advance way of the namakier,making the Namakier advance as "surging flow".The deformation characteristics of the competent interlayers can reflect the rheological strength of the salt.The deformation patterns of the competent layers inside the Charerhan Namakier are more complicated,indicating that the salt in the Charerhan Namakier has experienced stronger rheology,resulting from the lack of limit of the overburden and the full effect from the surface runoff and rainfall.