珠江口盆地白云凹陷新生代构造-热演化模拟

珠江口盆地是我国海洋油气勘探的重点区域,白云凹陷是珠江口盆地内最大新生代凹陷,具有齐全的新生代地层及丰富的钻井地震资料,是构造-热演化模拟研究的理想区域.本文基于多期次非瞬时伸展模型,选取白云凹陷6条地震解释剖面进行新生代构造-热演化模拟,以揭示白云凹陷热演化的时空差异性,为探讨珠江口盆地演化机制及深部动力学过程提供依据.模拟结果表明:白云凹陷经历了两期拉张过程,第一期(47.8~33.9 Ma)拉张自始新世发生,凹陷中心及白云西洼拉张强度高,基底古热流快速上升,最高达到~80 mW·m^-2;第二期(23~13.8 Ma)拉张发生于中新世,此次拉张在白云凹陷南部更强烈,白云凹陷基底主体在13.8 Ma达到最高古热流~100 mW·m^-2,此后基底热流值一直缓慢下降,逐渐接近稳态.白云凹陷拉张强度总体呈现西高东低,中间高、边缘低,北部一期高,南部二期高.第一期拉张主要受裂陷期强烈的裂谷作用控制,而伸展作用重启和高速层引起的“下地壳流”的共同作用可能是造成第二期拉张(裂后异常沉降)的主要动力学机制.

Tectono-thermal modelling of Baiyun Sag,Pearl River Mouth Basin,since Cenozoic

The Pearl River Mouth Basin(PRMB)is a key area for marine oil and gas exploration in China,and the Baiyun Sag is the largest Cenozoic depression in PRMB.With complete Cenozoic strata and abundant drilling and seismic data,Baiyun sag is an ideal region for tectono-thermal modelling.In this paper,based on the multi-phase extensional model,tectono-thermal modelling is performed along six seismic profiles in Baiyun Sag to reveal the temporal and spatial differences of the thermal evolution,which can provide evidence for the evolution mechanism of PRMB and deep geodynamic process.The modelling results show that Baiyun Sag has undergone two phases of extension.The first phase(47.8~33.9 Ma)had started since the Eocene.The center and west part of Baiyun Sag have high tensile degree.The rapid rise of basal heat flow reached 80 mW·m^-2;the second phase(23~13.8 Ma)tension occurred in the Miocene,the tension was stronger in the south and center of Baiyun Sag.The basal heat flow of the center reached the~100 mW·m^-2at 13.8 Ma,and then decreased slowly and reached a steady state gradually.In general view,the stretch factor is large in the west and small in the east,large in the center and small in the margin.In the first phase,the stretch factor is large in the north,but in the second phase,the stretch factor is large in the south.The first phase was controlled by the strong extension during the rifting period.And the reactivation of extension and the“lower crustal flow”caused by the high velocity layer could be the main reason of the second phase(the post-breakup abnormal subsidence).