The gravity field and tectonic features in the southeast of the Anza Basin, Kenya
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摘要: 肯尼亚Anza盆地东南部地处东非裂谷系，发育了巨厚的中—新生界沉积盖层。然而，该区域勘探程度较低，制约了对其构造体系的认识及油气勘探潜力的评价。文章基于研究区的重力异常数据，针对其构造特征的认识进行了数据处理及解释。研究结果表明，受中非剪切带右旋剪切应力的影响，研究区发育规模较大的北西向基底断裂和规模较小的北东向盖层断裂，且北东向断裂切断北西向断裂；基底深度差异大，总体呈"两凹夹一隆"的特征，凹陷区沉积了巨厚的中—新生界盖层；受北西向拉张断裂和沿构造软弱带发育的北东向断裂的控制，研究区划分为东部凹陷、中部凸起、南部隆起和西部凹陷4个构造单元，呈现"东西分带、南北分块"的构造格局。Abstract: The southeast of the Anza Basin in Kenya, located in the East African Rift System, has developed a very thick Mesozoic and Cenozoic sedimentary cover. However, the low level of exploration in this area restricts us from understanding its structural system and evaluating its oil-gas exploration potential. In this study, we processed and interpreted the gravity anomaly data obtained from the study area based on our understanding of its structural characteristics, and the conclusions drawn from the results are as follows. Under the influence of dextral shear stress of the central Africa shear zone, large-scale NW-oriented basement faults and small-scale NE-oriented caprock faults developed in the study area with the latter cutting off the former. The basement depth of the study area varies greatly and is characterized by "one uplift between two depressions". The very thick Mesozoic and Cenozoic cover layer was deposited in depressions. Controlled by the NW-tensional fault as well as the NE-fault developed along the structural weak zone, the study area is divided into four tectonic units: the eastern depression, the central uplift, the southern uplift and the western depression, showing the structural pattern of the "east-west zone and north-south block".
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Key words:
- Anza Basin /
- gravity anomaly /
- fault structure /
- basement structure
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图 1 研究区区域地质概况(据Dindi, 1994修改)
Figure 1. Regional geological survey of the Anza Basin (modified after Dindi, 1994)
图 2 研究区布格重力异常图(1 mGal=1.0×10-5 m/s2)
Figure 2. Contour plane map showing the Buoguer gravity anomaly in the study area (1 mGal=1.0×10-5 m/s2)
图 3 研究区剩余重力异常图(1 mGal=1.0×10-5 m/s2)
Figure 3. Contour plane map showing the residual gravity anomaly in the study area (1 mGal=1.0×10-5 m/s2)
图 4 研究区布格重力异常处理结果与断裂划分
a—垂向二阶导数; b—水平总梯度; c—TAHG; d—NVDR_THDR
Figure 4. Processing results of gravity data and fault structure distribution in the study area
(a) Vertical second derivative; (b) Horizontal total gradient; (c) TAHG; (d) NVDR_THDR
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