合肥坳陷构造形成机制分析

合肥坳陷位于华北板块，扬子板块和秦岭褶皱带的结合部位。该坳陷在印支期挤压强烈，形成较２的前陆总断体系，造成古生界推覆叠置；燕山中期挤压运动较弱，先期断裂复活冲断；燕山晚期－喜山期在拉张应力场作用下，中，新生界沿先期逆断裂反转正断，形成箕状断陷。

STRUCTURE FORMATION MECHANISM OF HEFEI DEPRESSION

Hefei depression is located at the junction point of Huabei plate, Yangzi plate and Qinling fold belt, which formed the unique foreland thrust system after undergoing the strong Indosinian compression, and consequently resulting in the napping and superimposing of Palaeozoic strata. DUring the middle Yanshan movement the compression was comparatively weak and the faulting prior to that reactivated the thrusting, and in late Yanshan to Himalayan movement the Meso-Cenozoic made a reverse along the previous reverse fault due to the extensional stress field and formed the half graben-like depression. There are three major hydrocarbon source rocks in the Hefei depression: the Permo-Carboniferous coal measures entered into its gas generating phase 150Ma ago and at present is at its dry gas stagei the coal measures of the Lower Jurassic Fanghushan Formation entered into its peak gas generating stage proximately in middle and late Yanshan movement and currently reaches its wet gas-dry gas generating stage; while the dark mudstones of the Lower Cretaceous Zhuxiang Formation at present is closing to its peak oil generating phase. The main structure belt of the depression was formed in late Yanshan pericxl, which has a good matching to the peak gas generating time of the main source rocks, resulting in a good potential for oil and gas exploration, where the Jurassic and Paleozoic internal structures of Hefei-Liu'an low relief zone and the thrust belts at the front of the Mesozoic and lndosinian nappes in the Daqiao sag should be taken as the exploratory targets.