非洲中部Muglad盆地Fula凹陷断裂特征分析

Fault characteristics of Fula sag,Muglad Basin in central Africa

Muglad盆地是非洲中部的一个中-新生代裂谷盆地,Fula凹陷是其北部的一个富油气凹陷。凹陷的圈闭类型包括断背斜、断鼻、断垒和断块等,均与断裂有关。本文通过地震资料解释,对凹陷内断裂的几何特征和发育期次进行分析,识别出Fula凹陷的主要构造样式,并制作了骨干剖面的构造平衡剖面,恢复了研究区自白垩纪以来的构造演化过程。研究结果表明:Fula凹陷可划分为4个构造层,分别为基底、第一裂陷、第二裂陷和第三裂陷构造层。自下而上,各构造层断裂走向逐渐由NNW转变为NWW。其中,基底构造层发育主干断层,控制Fula凹陷的构造格局;第一裂陷构造层发育大量的次级断层;第二、三裂陷构造层断裂密度变小,断距减小。研究区发育三级断裂,平面上多呈斜列式、平行、“帚状”或“辫状”组合,而剖面上多呈多米诺式、斜列式、铲式扇等组合。其中多数一、二级断裂在Abu Gabra期形成。由各断陷期的伸展速率可知,自白垩纪以来,Fula凹陷的断裂活动强度逐渐减弱。

The Muglad Basin is a Mesozoic-Cenozoic rift basin in central Africa.The Fula sag is a hydrocarbon-rich depression in the north of Muglad Basin.All of its traps are fault-related,such as faulted anticline,fault nose,fault horst,fault block.Based on the seismic data interpretation,we analyzed the geometric characteristics and developmental stages of faults,identified the main structural styles developed in the study area.At the same time,the tectonic evolution process of Fula sag since the Cretaceous was restored by compiling tectonic evolution sections.The results show that Fula sag can be divided into four tectonic layers,which are basement tectonic layer,first-rift tectonic layer,second-rift tectonic layer and third-rift tectonic layer.The strikes of faults from bottom to top at Fula sag regularly change,from NNW to NWW.The basement tectonic layer develops main faults,forming the tectonic framework in Fula sag;the first-rift tectonic layer develops many secondary faults;the second-rift tectonic layer and the third-rift tectonic layer become smaller in fault density and the fault displacement.The faults in the study area are En Echelon,parallel,“brush-like”or“braided”in plane,while domino,En Echelon,shovel fan in profile.There are three levels of faults,in which most of the first and second faults were formed in the Abu Gabra period.According to the extension rate of each faulted period,the faults’active intensity in Fula sag has gradually bean weakened since the Cretaceous.