广西钦防海槽迁移与沉积-构造转换面

广西的钦州－防城－带，素以钦防海槽称之，系指加里东期构造运动后，扬子与华夏陆块间的“残留海”。其两侧为古隆所夹持，西为大明山古隆起，东为云开大山古隆起，其间划分为四个构造单元，由东向西依次为：博白坳陷，六万大山隆起，钦州坳陷和十万大山坳陷。现构造形迹的排列，反馈防海槽在早古生代至中生代间深海盆或浅海深水盆地在构造和沉积上有自东向西迁移的特点。晚古生代盆地迁移过程至少有八个沉积－构造转换面可记录盆地的构造演化：第1转换面为早奥陶世与晚寒武世间的沉积界面；第2转换面为早志留世与晚奥陶世间的沉积界面；第3转换面为早泥盆世早期与晚志留世间的海侵上超面；第4转换面为中泥盆世的海侵上超面；第5转换面为中二叠世与晚二叠世间的沉积界面；第6转换面为早三叠世的海侵面；第7转换面为中晚三叠世与早三叠世间的沉积界面；第8转换面为早侏罗世与晚三叠世间的沉积界面。前两个界面为盆山转换面，与华南加里东构造运动过程相耦合，为挤压的构造背景；第3界面为水下间断面，下泥盆统与上志留统为不连续沉积，在构造上应是挤压机制下的破裂不整合，也是加里东期构造运动的响应；第4界为海西期的海侵上超面，与盆地走滑拉张同步；第5界面则反馈于印支期造山的初始阶段，第6界面为中生代盆地迁移转换面；第7界面为印支期造山过程的盆地转换面；第8界面为燕山期造山造盆转换面。其转换面性质的转化，代表钦防海槽可能是个复杂大陆边缘前陆盆地演化史。

The migration of the Qinzhou-Fangcheng trough in Guangxi and associated sedimentary-tectonic transform surfaces

The Qinzhou-Fangcheng trough in Guangxi refers to a residual sea sandwiched between the post-Caledonian Yangtze and Cathaysian landmasses, and bounded by the Damingshan uplift to the west and Yunkaidashan uplift to the east. Four tectonic elements are recognized: Bobai depression, Liuwandashan uplift, Qinzhou depression and Shiwandashan depression. The tectonic alignment shows that the Qinzhou-Fangcheng trough was migrated as a deep-marine basin or a shallower deep- water basin from east to west during the Early Palaeozoic to Mesozoic.
The basin migration during the Late Palaeozoic resulted in the formation of eight sedimentary-tectonic transform surfaces as the depositional boundaries of: (1) Early Ordovician/Late Cambrian, (2) Early Silurian/Late Ordovician, (3) early Early Devonian/Late Silurian, (4) Middle Devonian, (5) Middle/Late Permian, (6) Early Triassic, (7) Early Triassic/Middle-Late Triassic, and (8) Early Jurassic/Late Triassic. The former two represent the basin-range transitional surfaces in response to the compression-dominated Caledonian orogeny in southern China. The third boundary indicates a subaqueous depositional hiatus separated the Lower Devonian from the Upper Silurian strata. The fourth boundary indicates the Hercynian transgressive onlap surface formed during the strike-slip extension of the basin. The fifth boundary was developed during the initial stage of the Indosinian orogeny. The sixth boundary represents the transform surface showing the migration of the Mesozoic basin. The seventh boundary represents the basin-range transitional surface during the Indosinian orogeny. The eighth boundary indicates the Yanshanian mountain- and basin-building transform surface. The variation in the transform surfaces cited above might have recorded a complex history of the Qinzhou-Fangcheng trough as a continental marginal foreland basin.