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ISSN 2096-7780 CN 10-1665/P

远安地堑地壳沉积层和基岩层厚度与vP/vS比值及其构造暗示

Thickness and vP/vS of sedimentary and bedrock layers in the crust in the Yuan’an Graben and their tectonic implication

  • 摘要: 远安地堑位于江汉盆地和黄陵地块交界区域,富含页岩气,研究其深部结构对分析盆山相互作用和页岩气沉积层响应具有重要意义。本文采用接收函数多层H-κ叠加方法获得了远安地堑7个流动地震台下方沉积层和基岩层的厚度与vP/vS。结果表明:远安地堑沉积层平均厚度为3.68 km,平均波速比为1.98;基岩层平均厚度为31.51 km,平均波速比为1.70;地壳平均厚度为35.19 km,平均波速比为1.73。观测表明,远安地堑在长期的盆山相互作用下经历过下地壳减薄但地壳整体尚保持典型克拉通结构特征。远安地堑西侧的峡口—远安背斜带沉积层厚度2.55 km,薄于富集页岩气的东侧巡检—溪前向斜带沉积层厚度4.14 km,但西侧沉积层vP/vS为2.17,高于东侧的1.93。研究表明,背斜带在隆升剥蚀过程中破坏了页岩气能长期保存的构造环境,页岩气富集区域沉积层的vP/vS比不一定比周边页岩气匮乏区域高。

     

    Abstract: The Yuan’an Graben, which holds abundant shale gas, is located at the junction of the Jianghan Basin and the Huangling Block. Information about the graben’s deep structure has great significance for analysis of the basin-mountain interaction and the sedimentary response of shale gas. In this study, the thickness and vP/vS of the sedimentary and bedrock layers beneath seven temporary seismic stations in the Yuan’an Graben were obtained using the multi-layer H-κ stacking approach of receiver function. The results show that the average thickness and vP/vS of the sedimentary layer in the Yuan’an Graben are 3.68 km and 1.98, respectively. Those of the bedrock layer are 31.51 km and 1.70, respectively. The average crustal thickness is 35.19 km, and the average vP/vS is 1.73. These observations support the inference that the Yuan’an Graben has experienced thinning of the lower crust under long-term basin-mountain interaction, but the crust as a whole still maintains the characteristics of typical cratonic crust. The thickness of the sedimentary layer in the Xiakou-Yuan’an anticline zone on the west side of the Yuan’an Graben is 2.55 km, which is less than the thickness of 4.14 km of the sedimentary layer in the Xunjian-Xiqian syncline zone on the east side, which is enriching in shale gas. However, the average vP/vS of its sedimentary layer is 2.17, which is higher than 1.93 on the east side. The aforementioned results show that the tectonic environment of long-term preservation of shale gas in the anticline belt may be destroyed during the uplift and denudation process and that the vP/vS of the sedimentary layer with enriching shale gas is not necessarily higher than that in the surrounding area with a shortage of shale gas.

     

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