中扬子地块宜昌斜坡白垩系陆内挤压盆地的断-坳结构

Rift-Sag Structure of Cretaceous Intracontinental Compressional Basin in Yichang Slope of Middle Yangtze Block

宜昌斜坡残留的白垩系盆地是认识中扬子地块白垩纪构造演化的一个窗口.基于对白垩系露头的构造-沉积特征的观察,并结合二维地震剖面的构造-地层解释,厘定了宜昌斜坡白垩系盆地的构造属性和沉积充填特征,构建了白垩系陆内挤压盆地的挤压断-坳结构.宜昌斜坡白垩系盆地是由天阳坪逆冲断裂带控制的陆内挤压盆地.下白垩统盆地为同造山期的挤压断陷,充填有扇三角洲-湖泊沉积体系;上白垩统盆地为后造山期的挤压坳陷,充填了冲积扇-辫状河-风成-浅水含膏湖泊沉积体系.宜昌斜坡和湘鄂西弧形带的上白垩统盆地属于陆内挤压盆地的挤压坳陷,揭示中扬子地块由挤压向伸展构造体制转换的起始时间是新生代.

The residual Cretaceous basin of the Yichang slope is a window to understand the Cretaceous tectonic evolution of the Middle Yangtze block. Based on the observation of tectonic-sedimentary features of the Cretaceous outcrops and combined with the tectonic-stratigraphic interpretation of two-dimensional seismic profiles, the tectonic properties and sedimentary filling of the Cretaceous basin of Yichang slope are identified, and the compressional rift-sag structure of the Cretaceous intracontinental compressional basin is established. The Cretaceous basin of Yichang slope was an intracontinental compressional basin controlled by Tianyangping thrust fault zone. The Lower Cretaceous basin was a compressional rift that had developed during synorogenic period, which was filled with fan delta-lacustrine sedimentary systems,and the Upper Cretaceous basin was a compressional sag that had developed during post-orogenic period and was filled with alluvial fan-braided river-aeolian-shallow lacustrine sedimentary systems. The Upper Cretaceous basin of the Yichang slope and western Hunan-Hubei arcuate fold-thrust belts belong to the compressional sag of the intracontinental compressional basin, which reveals that the initial time of the transition from compressional to extensional tectonic regime in the Middle Yangtze block should be at the Cenozoic.