柳江盆地西部吴庄背斜巨型角砾区的揭层逆冲滑脱及伸展垮塌

Break-Out Thrust Slip and Extension Collapse of Wuzhuang Anticlinal Giant Breccia Area in Western Liujiang Basin

摘要: 本文针对柳江盆地吴庄背斜教学路线中巨型角砾的成因模式问题，研究认为本区巨型角砾发展的早期存在顺层逆冲滑脱的逆冲推覆构造造成了局部“(切层)坡坪式构造”，“(切层)坡坪式构造”形成的菱形块体经过滚动磨圆形成了巨型角砾及其周围的含基质“包裹层”。吴庄背斜西部区域活动分为逆冲推覆和伸展滑塌两个主要期次，并细分为逆冲推覆、顺层伸展滑塌、切层伸展成盆三个具体的阶段。这两个期次都形成“狮爪滚绣球”的巨型角砾活动模式，造成巨型角砾的滚动及磨圆。认为柳江盆地在响山岩体的侵入过程中挤压作用造成顺层逆冲推覆构造，后经过盆地伸展垮塌导致了吴庄背斜西部的伸展、沉陷、顺层滑脱，以及(切层)断陷成盆。(切层)断陷成盆形成西倾断阶控制的断陷向斜，名为“大绪口–车厂向斜”，“大绪口–车厂向斜”在成因上可能和房山岩体西缘向斜有相似之处。

Abstract: This paper focuses on the genesis model of the giant brecta in the Wuzhuang anticline teaching route of the Liujiang Basin. It is studied that in the early stage of the development of the giant brecta in this area, there was a thrust and overburden structure of along-layer thrust and slippage, which caused a local “(cut layer) slope flat structure”. The rhombic blocks formed by the “(cut layer) slope flat structure” are rolled and rounded into giant breccia and the surrounding matrib-containing “enveloping layers”. The activities in the western area of the Wuzhuang Anticline are mainly divided into two phases: retrograde overthrust and extension and collapse, and are further subdivided into three specific stages: retrograde overthrust, extension and collapse along the layer, and cross-layer extension and basin formation. Both of these sessions formed a “lion’s claw rolling hydrangea” giant horn activity pattern, causing the giant horns to roll and be rounded. It is believed that during the intrusion of the Xiangshan rock mass, the compression effect in the Liujiang Basin caused the thrust and overburden structure of the upper layer. Later, through the basin’s extension and collapse, the western part of the Wuzhuang Anticline was extended, subsided, and the upper layer slipped off, as well as the (cut layer) faulted and sank into a basin. The basin formed by the fault depression of the cut layer has created a fault depression syncline controlled by the westward inclined fault step, which is called the “Daxukou-Chechang syncline”. The “Daxukou-Chechang syncline” may have similarities in genesis with the syncline on the west margin of the Fangshan rock mass.