珠江口盆地靖海凹陷火成岩发育特征及其地质意义

Igneous rocks in Jinghai Sag,Pearl River Mouth Basin and their geological significance

利用三维地震对靖海凹陷的火成岩体进行了识别,火山岩沉积后上覆地层会直接超覆在火山岩体上,而侵入岩体形成的地层上拱和超覆现象发生在上覆地层之内的不整合面上。研究区岩浆活动时间可分为4期:自老到新依次为晚白垩世内部Tm18不整合形成期,晚中新世T35不整合形成期(10.5Ma),上新世末T20不整合形成期(2.6Ma)和第四纪,且以第四纪火山活动最为强烈。火山口和侵入体主要沿北东向朝南大断裂分布,具小规模中心式分散分布特点,其分布趋势与古地温梯度朝南部洋壳区方向增大似乎没有关系。从绝大多数火山活动发生在第四纪且局部分布来看,它们对油气藏主要起有限的改造和破坏作用。

Igneous rocks in the Jinghai sag are identified through3 D seismic interpretation by the contact relationship between the rocks and the overlying deposits.Four magmatic stages are recognized in the study area,separated by three unconformity reflections,i.e the late Cretaceous Tm18,the late Miocene T35（10.5 Ma）,the late Pliocene T20（2.6 Ma）and the overlying Quaternary.Among them the Quaternary eruption is the strongest.Volcanic and intrusive bodies are mainly distributed along the NE trending Chaoshannan fault,in a form of scatter small scale central volcanoes.The distribution trend of the volcanoes seems irrelevant to the increase in paleogeothermal gradient toward the oceanic crust in the south.Limited impact is expected to the oil gas accumulations in the sag.