珠江口盆地白云凹陷反转构造发育特征

Development Characteristics of Inverted Structures in Baiyun Sag in Pearl River Mouth Basin

为揭示珠江口盆地白云凹陷反转构造的反转强度及反转形成时期,利用反转构造定量分析方法,即生长指数、位移—距离曲线及反转率对白云凹陷反转构造进行了定量分析。结果表明,白云凹陷存在2期反转：早期反转活动始于渐新世早期（34.0×10^6-32.0×10^6a）,主反转期为渐新世晚期（32.0×10^6-23.8×10^6a）,反转程度较强;晚期反转活动始于中新世中期的早期（15.5×10^6-13.8×10^6a）,主反转期为中期的末期（13.8×10^6-12.5×10^6a）,反转程度轻微。早期反转构造应力有2个：一个是白云凹陷强烈沉降引起的重力势,另一个是南海扩张所产生的左行压扭应力,重力势是主控因素;晚期构造应力主要受东沙运动的影响,推测反转应力来自盆地东部,与菲律宾板块挤压有关。晚期反转构造圈闭为更有利的油气成藏区。

To reveal the intensity and timing of inverted structures in Baiyun sag in Pearl River Mouth basin, the quantitative analysis meth-od for inverted structure, including growth index, displacement-distance curve and reversal rate, is applied to quantitative analysis of Bai-yun sag＇s inverted structures. The results show that the tectonic inversion happed twice in Baiyun sag. The early inversion began in the Ear-ly Oligocene（34.0×10^6-32.0×10^6a）, mainly developed in the Late Oligocene（32.0×10^6-23.8×10^6a）, with strong inversion degree; the lateinversion began in early Middle Miocene（15.5×10^6-13.8×10^6a）, mainly developed in late Middle Miocene（13.8×10^6-12.5×10^6a）, withmild inversion degree. The early inverted tectonic stress contains the gravitational potential created by the intensive subsiding of Baiyunsag and the sinistral compressive-torsional stress produced by South China Sea spreading, of which the gravitational potential is the maincontrolling factor. The late tectonic stress is mainly affected by the Dongsha movement, so the inversion stress may come from the easternpart of Pearl River Mouth basin, possibly related with squeezed effect of Philippine plate. The late inverted structural trap could be themore favorable area for hydrocarbon accumulation.