Abstract:

Yangxin Depression was a typical half-graben in the Eogene. Three tectonic zones inthe depression, including steep-slope, depreessed and senile slope zones, resulted fromsinistral tenso-shear stress.In the Neogene, the faults that controlled the depressionchanged from extensional normal faults into compressive dextral strike-slip fsults,the depression then depressed in its entirety,and hence it is characterized by fault-subSidence inits lower-part but depression in its upper part. Three-stase magmatite developed in the depression: andisite basalt in the 4th member of the Shahejie Formation; quartz-tholeiiticbdsalt and olivine tholeiitic basalts in the 3rd member of the Shahejie Formation and alkalic ultrabasic rock in the Guantao Formation.The tectonic evolution preocess of Yangxin Depression could be divided into following four stages:extenso-fracturing of mantle uplifting, proto-rifting,riftins-subsiding anddepressing. The most favourable stage for hydrocarbon formation and accumulation wasrifting-subsiding stage.