Kebede Bisrat, Mammo Tilahun, Misgie Abebe
School of Earth Science, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.
Ministry of Mines and Petroleum, P.O. Box 486, Addis Ababa, Ethiopia.
Heliyon. 2022 May 23;8(5):e09525. doi: 10.1016/j.heliyon.2022.e09525. eCollection 2022 May.
The Southern Main Ethiopian Rift is part of the great East African Rift system situated within the limit of 37-38.5 east and 5.5-7 north. Unlike the Central and Northern Main Ethiopian Rift where numerous geophysical studies have been conducted, the subsurface geology of Southern Main Ethiopian Rift is poorly constrained. Geological field work on Amaro Horst shows the basement outcrops are dominated by High grade gneisses and Intrusive with an average density of 6 gm/cm overlain by Mesozoic sedimentary rocks possibly extend into the studied sub-basins. In addition, field structural measurements and extracted lineaments from digital elevation model show NE-SW, NW-SE and N-S directions in agreement with fault block geometries identified by Invariance Tensor analysis. The Precambrian basement morphology of the area is delineated using constrained Tensor Gravity Inversion by applying Parker-Oldenburg algorisms. The basement morphology depicts the sub-basins; Northern Abaya, Southern Abaya, Chamo and Gelana basins where these areas are characterized by low Bouguer anomaly below -175mGal and lower Invariance Tensor anomaly may show the sediment infill of the sub-basins. The deepest depression exceeds 2500m below sea level in northern Abaya sub-basin where the maximum sediment thickness is more than 3700m. The result agrees with Spectral and Euler source depths solutions that show the limits of the crystalline basement vary between 2500m and 3500m. Amaro Horst, Chencha and Agere Selam are the basement structural high with average sediment thickness of 500m. The basement morphology revealed the N-S orientation of Gelana basin and other sub-basins aligns with NE-SW Tertiary Rifting. This result agrees with the structural analysis as well as previous regional studies on directions of prominent geological structures. These structurally controlled sub-basins having thick sedimentary sections are favorable zones for follow-up hydrocarbon exploration.
埃塞俄比亚大裂谷南部是东非大裂谷系统的一部分，位于东经37 - 38.5度、北纬5.5 - 7度范围内。与埃塞俄比亚大裂谷中部和北部不同，那里已经进行了大量地球物理研究，而埃塞俄比亚大裂谷南部的地下地质情况约束较少。阿马罗地垒的地质野外工作表明，基底露头主要由高级片麻岩和侵入岩组成，平均密度为6克/立方厘米，其上覆盖着中生代沉积岩，这些沉积岩可能延伸到研究的子盆地。此外，野外构造测量以及从数字高程模型中提取的线性构造显示出NE - SW、NW - SE和N - S方向，这与不变张量分析确定的断块几何形状一致。该地区前寒武纪基底形态通过应用帕克 - 奥尔登堡算法进行约束张量重力反演来描绘。基底形态描绘出了子盆地，即北阿巴亚、南阿巴亚、查莫和盖拉纳盆地，这些地区的特征是布格异常低于 - 175毫伽，较低的不变张量异常可能显示了子盆地的沉积物充填情况。北阿巴亚子盆地海平面以下最深凹陷超过2500米处，最大沉积物厚度超过3700米。这一结果与谱分析和欧拉源深度解一致，表明结晶基底的深度在2500米至3500米之间变化。阿马罗地垒、陈查和阿盖雷塞拉姆是基底构造高地，平均沉积物厚度为500米。基底形态显示盖拉纳盆地和其他子盆地的N - S方向与NE - SW第三纪裂谷一致。这一结果与构造分析以及先前关于显著地质构造方向的区域研究一致。这些受构造控制、具有厚沉积层段的子盆地是后续油气勘探的有利区域。
