转换型Muglad盆地的走滑特征

Sliding feature of the transforming Muglad basin

非洲中部的Muglad盆地 (简称M盆地 )位于中非断裂系中段东端南侧 ,是一个内陆转换型盆地。盆地北部 (走滑 )断陷带以剪切走滑特征为主 ,北部NGL坳陷和南部KK坳陷以拉分走滑特征为主 ,南、北两部明显左行错位 ,两者之间存在与中非走滑断裂系基本平行的近东西向调节转换构造带。早白垩世中非大断裂的右行走滑运动使早白垩世M盆地主体部位诸断陷边界主断层以西倾为主 ,断陷均呈东断西超 ,下白垩统东厚西薄 ;晚白垩世中非大断裂左行走滑 ,M盆地被改造 ,形成了北北西走向东倾断裂系统 ,具有北“箕”南“堑”的特征。M盆地的走滑性质使其白垩系沉积速率大 ,生油条件好 ,沉降中心从早至晚自北而南转移 ,决定了南部KK坳陷的达富尔群泥岩纯净 ,封盖性能好 ,石油地质条件优越 ,大油田均发现于KK坳陷。但火成岩欠发育 ,地热梯度较低。图 6参 9(王孝陵摘 )

Muglad basin, in the middle of Africa, is a continental transforming basin lying in the south of the eastern middle part of the Central African fracture system. Rift belt of the northern edge of the basin mainly has a shear-sliding feature while both NGL depression in north part of the basin and KK depression in south part of the basin mainly have a strike-sliding feature. The south and north parts of the basin misplaced obviously in the left and between the two parts occurs an east-west striking regulator transforming structure belt nearly parallel to the sliding fracture of Central Africa. The right sliding movement of the huge Central African fracture in early Cretaceous resulted in west dipping faults in depression boundaries of the main body of Muglad basin with all the depression faulting in the east and overlying in the west, late Cretaceous thickening in the east and thining in the west. The huge Central African fracture slipping to the left in late Cretaceous reformed Muglad basin and an east dipping fracture system appeared with a NNW strike and halfgraben in the north and graben in the south. The Cretaceous sedimentation rate is high with good oil generating condition because of the slipping of Muglad basin. Subsiding center transferring from north to south created clean mudstone of Darfur group of KK depression in south part of the basin. But Muglad basin has a low geothermal gradient with a low development degree for igneous rock.