楚雄中生代前陆盆地的构造沉降史研究

Mesozoic tectonic subsidence in the Chuxiong foreland basin, Yunnan

关键词:  构造沉降  沉积速率  前陆盆地  中生代

Key words:  tectonic subsidence  sedimentation rate  foreland basin  Mesozoic

摘要:

云南楚雄盆地位于扬子陆块的西南边缘,为一典型的中生代周缘前陆盆地。盆地演化阶段明显,晚三叠世为前陆早期复理石沉积,侏罗纪则为前陆晚期磨拉石沉积。对盆地构造沉降史研究后笔者认为:①晚三叠世复理石沉积盆地构造沉降幅度巨大,沉降与沉积中心位于盆地最西部,紧邻古哀牢山造山带,沉积体呈楔形展布;②侏罗纪磨拉石沉积盆地构造沉降和沉积中心以及前缘隆起向内陆方向迁移明显;③中生代构造快速沉降的沉积体的楔形展布表明盆地具有前陆岩石圈挠曲成因特征;④盆地的高沉积速率受构造和超补偿沉积作用的共同控制。

Abstract:

The Chuxiong Basin in Yunnan on the southwestern margin of the Yangtze landmass is a Mesozoic peripheral foreland basin. Tectonically, three units may be distinguished for the basin:western thrust zone, central depression zone and eastern uplifted zone. In terms of sedimentary facies, sequence stratigraphy and palaeogeographic evolution in combination with tectonic evolution of the Ailaoshan orogenic zone, the basin shows a depositional evolution from the Palaeozoic passive continental margin to the Mesozoic foreland basin. Two phases of the sedimentation have been identified in the Chuxiong foreland basin:the foreland flysch sedimentation during the Late Triassic and the foreland molasse sedimentation during the Jurassic. The following conclusions are generalized on the basis of the tectonic history of the basin. (1) The Late Triassic flysch basin is characterized by high amplitudes of tectonic subsidence. The centres of subsidence and deposition lay in the westernmost part of the basin close to the Ailaoshan orogenic belt. The sedimentary bodies there display the wedge-shaped distribution. (2) The forebulges and centresof subsidence and deposition in the molasse basin migrated landwards during the Jurassic. (3)The Mesozoic rapid tectonic subsidence and wedge-shaped sedimentary bodies indicate the origin of lithospheric flexure in the Chuxiong Basin. (4) The higher sedimentation rates are controlled by both the tectonic and overcompensational sedimentation.