南海北缘东部揭阳凹陷的东沙运动:对油气成藏的影响

东沙运动为新近纪中晚期以来发生于南海北缘的一次构造运动,影响范围主要为东沙隆起及其周缘,对油气的晚期成藏具有重要作用。揭阳凹陷位于东沙隆起东侧,东沙运动的响应明显,且具有一定特殊性。基于区域地质背景和三维地震资料,对东沙运动在揭阳凹陷的响应、起因及油气地质意义进行了论述。东沙运动在揭阳凹陷的响应主要包括走滑断层和地层角度不整合,并以发育NE-SW走向的右行强走滑断裂及近E-W走向的左行雁列式断层最为明显,与东沙隆起西侧和北侧凹陷中发育的以近E-W和NWW-SEE走向为主的右行张扭性雁列式断层有较大区别。分析认为中生代俯冲带使基底构造格架存在差异,且揭阳凹陷更靠近力源,造成研究区发育强走滑断裂,而东沙隆起以北只发育张扭性质的雁列式断层。负花状构造和地层角度不整合说明东沙运动为拉张性质的构造运动,且5.33Ma为主构造期。受东沙运动影响,揭阳凹陷北部缓坡带具有较大的油气勘探潜力。

The Dongsha Movement in the Jieyang Sag at the Northern South China Sea Margin: Control on Hydrocarbon Traps

The Dongsha Movement is a key tectonic movement at the north South China Sea margin since the middle and late Neogene,which mainly influenced the Dongsha Rise and its adjacent areas and controlled the late-phase hydrocarbon accumulation.The Jieyang Sag located to the east of the Dongsha Rise shows obvious and unique response to the Dongsha Movement.Based on the regional geological setting and 3D seismic data,the response of the Dongsha Movement and its significance on hydrocarbon accumulation in the Jieyang Sag are discussed.The response of the Dongsha Movement in the Jieyang Sag is mainly exhibited as strike-slip faults and stratigraphic unconformity,particularly the strong NE-SW-trending sinistral strike-slip faults and the near EW-trending dextral en echelon faults.On the contrast,the faults developed in the sags to the north and the west of the Dongsha Rise are sinistral echelon,mainly near EW-and NWW-SEE-trending.It is likely that the different basement-involved structural frameworks were related to the Mesozoic subduction,the strong strike-slip faults and the extensional and twisted energetic faults were developed to the south and north of the subduction zone respectively.The responses of the Dongsha Movement in the Jieyang Sag,such as negative flower-like structure and stratigraphic unconformity,indicate that the Dongsha Movement is an trans-extensional tectonic movement,of which main tectonic period is T30(5.33 Ma).Affected by the Dongsha Movement,the northern gentle slope in the Jieyang Sag is a favorable area for hydrocarbon accumulation.