渭河盆地结构特征及演化研究

摘要

渭河盆地是位于秦岭造山带和鄂尔多斯盆地之间的断陷盆地.渭河盆地的形成时间以及基底构成目前仍存在着争议.近几年来,对于渭河盆地天然气类型、形成机制、成藏条件、资源潜力以及盆地结构构造等方面的研究取得了很大进展,为解决以上争议提供了迸一步的资料.根据盆地的钻探资料和物化探新成果,发现渭河盆地是由固市凹陷、西安凹陷、泾河鼻隆、宝鸡凸起、骊山凸起、咸阳斜坡带和富平—蒲城斜坡带组成,并具有新生代、中生代—古生代复式盖层和两盆一鼻两凸两斜坡镶嵌复合结构特征;渭河盆地新生代之下的中生代—古生代盖层为:西部宝鸡凸起为古生界地层,中部西安凹陷和成阳斜坡带为中生代地层,东北部富平—蒲城斜坡带基底为奥陶系地层,东南部固市凹陷基底为晚古生代地层;渭河盆地与鄂尔多斯盆地具有相同的基底和相似的盖层;太要断裂(约1800 Ma)形成,为渭河盆地形成奠定了构造基础,奥陶世马家沟末加里东运动及渭北隆起南缘同生逆冲断裂形成,标志着渭河盆地独立演化的开始,主沉降期为中生代—新生代;结合已有研究,给出了渭河盆地的基底模型和渭河盆地的演化模式.%The Weihe basin is the graben basin located between the Qinling orogenic belt and the Ordos basin,and there are some controversies about the formation time and basement constitutions of the Weihe basin.In recent years,natural gas types,formation mechanism,accumulation condition,resources potentiality and basin structure in the Weihe basin have been well studied,which provides considerable evidences to resolve the controversies mentioned above.According to the drilling data and the new results of geophysical and geochemical prospecting in the Weihe basin,we found that the Weihe basin covered by Cenozoic,Mesozoic-Palaeozoic complex cap rocks,and composed of two depressions,one nose structure,two bulges and two slope belts,which respectively are Gucheng depression,Xi'an depression,Jinghe nose structural,Baoji bulge,Lishan bulge,Xianyang slope belt and Fuping-Pucheng slope belt.Baoji bulge in the west,Xi'an depression and Xianyang slope belt in the central section are covered by Paleozoic strata and Mesozoic strata,respectively.The basement of Fuping-Pucheng slope belt in the northeast and Gucheng depression in the northwest are composed of Ordovician strata and Paleozoic strata,respectively.The Weihe basin and the Ordos basin display similar basement and overlying strata.The formation of Taiyao fault (ca.1800 Ma) provides the structural condition,and the formation of syngenetic thrust faults in Weibei uplift during Caledonian movement at the end of the Ordovician marks the beginning of independent evolution of the Weihe basin.After that,Mesozoic and Cenozoic are the main sedimentation period of the basin.Combined with previous studies,basement model and evolution model of the Weihe basin are built in this article.