The gravity field and tectonic features in the southeast of the Anza Basin, Kenya
-
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".
-
Key words:
- Anza Basin /
- gravity anomaly /
- fault structure /
- basement structure
-
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)
-
BENOIT M H, NYBLADE A A, PASYANOS M E, 2006. Crustal thinning between the Ethiopian and East African plateaus from modeling Rayleigh wave dispersion[J]. Geophysical Research Letters, 33(13): L13301. doi: 10.1029/2006GL025687 BOONE S C, KOHN B P, GLEADOW A J W, et al., 2018. Tectono-thermal evolution of a long-lived segment of the East African Rift System: thermochronological insights from the North Lokichar Basin, Turkana, Kenya[J]. Tectonophysics, 744: 23-46. doi: 10.1016/j.tecto.2018.06.010 BOSWORTH W, MORLEY C K, 1994. Structural and stratigraphic evolution of the Anza rift, Kenya[J]. Tectonophysics, 236(1-4): 93-115. doi: 10.1016/0040-1951(94)90171-6 BRUNE S, CORTI G, RANALLI G, 2017. Controls of inherited lithospheric heterogeneity on rift linkage: Numerical and analog models of interaction between the Kenyan and Ethiopian rifts across the Turkana depression[J]. Tectonics, 36(9): 1767-1786. doi: 10.1002/2017TC004739 CHEN Q, YUAN B Q, DONG Y P, et al., 2013. The new methods to study fault structure by gravity data and applications to TANA sag in Kenya[J]. Journal of Northwest University (Natural Science Edition), 43(4): 599-605. (in Chinese with English abstract) http://en.cnki.com.cn/Article_en/CJFDTOTAL-XBDZ201304027.htm COOPER G R J, COWAN D R, 2006. Enhancing potential field data using filters based on the local phase[J]. Computers & Geosciences, 32(10): 1585-1591. http://pdfs.semanticscholar.org/daa2/1459a92c12c40eb395e20bf972ec64500fc9.pdf CORTI G, 2009. Continental rift evolution: from rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa[J]. Earth-Science Reviews, 96(1-2): 1-53. doi: 10.1016/j.earscirev.2009.06.005 DINDI E W, 1994. Crustal structure of the Anza graben from gravity and magnetic investigations[J]. Tectonophysics, 236(1-4): 359-371. doi: 10.1016/0040-1951(94)90184-8 EBINGER C J, YEMANE T, HARDING D J, et al., 2000. Rift deflection, migration, and propagation: Linkage of the Ethiopian and Eastern rifts, Africa[J]. GSA Bulletin, 112(2): 163-176. doi: 10.1130/0016-7606(2000)112<163:RDMAPL>2.0.CO;2 FERREIRA F J F, DE SOUZA J, DE B. E S. BONGIOLO A, et al., 2013. Enhancement of the total horizontal gradient of magnetic anomalies using the tilt angle[J]. Geophysics, 78(3): J33-J41. doi: 10.1190/geo2011-0441.1 FOSTER D A, GLEADOW A J W, 1996. Structural framework and denudation history of the flanks of the Kenya and Anza Rifts, East Africa[J]. Tectonics, 15(2): 258-271. doi: 10.1029/95TC02744 GREENE L C, RICHARDS D R, JOHNSON R A, 1991. Crustal structure and tectonic evolution of the Anza rift, northern Kenya[J]. Tectonophysics, 197(2-4): 203-211. doi: 10.1016/0040-1951(91)90041-P GUIRAUD R, BOSWORTH W, 1997. Senonian basin inversion and rejuvenation of rifting in Africa and Arabia: synthesis and implications to plate-scale tectonics[J]. Tectonophysics, 282(1-4): 39-82. doi: 10.1016/S0040-1951(97)00212-6 HACKMAN B D, CHARSLEY T J, KEY R M, et al., 1990. The development of the East African Rift System in north-central Kenya[J]. Tectonophysics, 184(2): 189-211. doi: 10.1016/0040-1951(90)90053-B LIU G H, CHEN Q H, 2014. Structure and sedimentary-filling evolution of Anza Basin of East Africa[J]. Journal of Xi'an University of Science and Technology, 34(3): 326-330. (in Chinese with English abstract) http://en.cnki.com.cn/Article_en/CJFDTotal-XKXB201403014.htm MA J, WANG W Y, JI X L, 2019. Tectonic characteristics of Cesar basin and its adjacent areas according to gravity field[J]. Geological Science and Technology Information, 38(1): 285-294. (in Chinese with English abstract) http://en.cnki.com.cn/Article_en/CJFDTotal-DZKQ201901033.htm MILLER H G, SINGH V, 1994. Potential field tilt-a new concept for location of potential field sources[J]. Journal of Applied Geophysics, 32(2-3): 213-217. doi: 10.1016/0926-9851(94)90022-1 MORLEY C K, BOSWORTH W, DAY R A, et al., 1999. Geology and geophysics of the Anza Graben[M]//MORLEY C K. Geoscience of Rift Systems-Evolution of East Africa. America: AAPG Studies in Geology: 67-90. MORLEY C K, WESCOTT W A, STONE D M, et al., 1992. Tectonic evolution of the northern Kenyan Rift[J]. Journal of the Geological Society, 149(3): 333-348. doi: 10.1144/gsjgs.149.3.0333 SHERIFF R E, 1973. Encyclopedic dictionary of exploration geophysics[M]. Tulsa: Society of Exploration Geophysicists: 266. SWAIN C J, 1979. Gravity and Seismic Measurements in Kenya[D]. Leicester: University of Leicester. VERDUZCO B, FAIRHEAD J D, GREEN C M, et al., 2004. New insights into magnetic derivatives for structural mapping[J]. The Leading Edge, 23(2): 116-119. doi: 10.1190/1.1651454 VETEL W, LE GALL B, WALSH J J, 2005. Geometry and growth of an inner rift fault pattern: the Kino Sogo Fault Belt, Turkana Rift (North Kenya)[J]. Journal of Structural Geology, 27(12): 2204-2222. doi: 10.1016/j.jsg.2005.07.003 VETEL W, LE GALL B, 2006. Dynamics of prolonged continental extension in magmatic rifts: the Turkana Rift case study (North Kenya)[J]. Geological Society, London, Special Publications, 259(1): 209-233. doi: 10.1144/GSL.SP.2006.259.01.17 WANG W Y, PAN Y, QIU Z Y, 2009. A new edge recognition technology based on the normalized vertical derivative of the total horizontal derivative for potential field data[J]. Applied Geophysics, 6(3): 226-233. doi: 10.1007/s11770-009-0026-x WANG W Y, QIU Z Y, YANG Y, et al., 2010. Some advances in the edge recognition of the potential field[J]. Progress in Geophysics, 25(1): 196-210. (in Chinese with English abstract) http://en.cnki.com.cn/Article_en/CJFDTOTAL-DQWJ201001029.htm WANG X, LI T L, 2004. Locating the boundaries of magnetic or gravity sources with Tdr and Tdr_Thdr methods[J]. Progress in Geophysics, 19(3): 625-630. (in Chinese with English abstract) http://en.cnki.com.cn/Article_en/CJFDTOTAL-DQWJ200403022.htm WEN Z X, TONG X G, ZHANG G Y, et al., 2012. Petroleum geology features and exploration potential of basin group in East African Rift system[J]. China Petroleum Exploration, 17(4): 60-65. (in Chinese with English abstract) http://en.cnki.com.cn/Article_en/CJFDTOTAL-KTSY201204011.htm WINN R D JR, STEINMETZ J C, KEREKGYARTO W L, 1993. Stratigraphy and rifting history of the Mesozoic-Cenozoic Anza rift, Kenya[J]. AAPG Bulletin, 77(11): 1989-2005. doi: 10.1306/bdff8f9c-1718-11d7-8645000102c1865d Xi'an Shiyou University, 2007. The research of integrated interpretation of gravity, aeromagnetics and seismic data of block 9 and 10A of ANZA basin in Kenya_Atlas contents[R]. (in Chinese) XU W Q, YUAN B Q, LIU B L, et al., 2020. Multiple gravity and magnetic potential field edge detection methods and their application to the boundary of fault structures in northern South Yellow Sea[J]. Geophysical and Geochemical Exploration, 44(4): 962-974. (in Chinese with English abstract) YANG J S, ZHU X M, 2008. Lower Cretaceous sequence stratigraphy of Fula depression, Muglad basin, Sudan[J]. Acta Sedimentologica Sinica, 26(6): 994-1004. (in Chinese with English abstract) YUAN B Q, XIE W S, LIU G H, et al., 2012. Gravity field and tectonic features of Block L2 in the Lamu basin, Kenya[J]. Geophysical Prospecting, 60(1): 161-178. doi: 10.1111/j.1365-2478.2011.00961.x ZHOU D, WANG W Y, WANG J L, et al., 2006. Mesozoic subduction-accretion zone in northeastern south China sea inferred from geophysical interpretations[J]. Science in China Series D: Earth Sciences, 49(5): 471-482. doi: 10.1007/s11430-006-0471-9 陈青, 袁炳强, 董云鹏, 等, 2013. 断裂识别新方法及其在肯尼亚Tana凹陷中的应用[J]. 西北大学学报(自然科学版), 43(4): 599-605. https://www.cnki.com.cn/Article/CJFDTOTAL-XBDZ201304027.htm 刘桂和, 陈全红, 2014. 东非Anza盆地结构及沉积充填演化[J]. 西安科技大学学报, 34(3): 326-330. doi: 10.3969/j.issn.1672-9315.2014.03.014 马杰, 王万银, 纪晓琳, 2019. 利用重力场研究塞萨尔盆地及邻区构造特征[J]. 地质科技情报, 38(1): 285-294. https://www.cnki.com.cn/Article/CJFDTOTAL-DZKQ201901033.htm 王万银, 邱之云, 杨永, 等, 2010. 位场边缘识别方法研究进展[J]. 地球物理学进展, 25(1): 196-210. https://www.cnki.com.cn/Article/CJFDTOTAL-DQWJ201001029.htm 王想, 李桐林, 2004. Tilt梯度及其水平导数提取重磁源边界位置[J]. 地球物理学进展, 19(3): 625-630. doi: 10.3969/j.issn.1004-2903.2004.03.022 温志新, 童晓光, 张光亚, 等, 2012. 东非裂谷系盆地群石油地质特征及勘探潜力[J]. 中国石油勘探, 17(4): 60-65. https://www.cnki.com.cn/Article/CJFDTOTAL-KTSY201204011.htm 西安石油大学, 2007. 肯尼亚ANZA盆地9、10A区块重磁震联合解释研究报告[R]. 许文强, 袁炳强, 刘必良, 等, 2020. 多种重磁位场边缘识别方法及在南黄海北部断裂构造识别中的应用研究[J]. 物探与化探, 44(4): 962-974. https://www.cnki.com.cn/Article/CJFDTOTAL-WTYH202004035.htm 杨俊生, 朱筱敏, 2008. 苏丹Muglad盆地Fula坳陷白垩系Abu Gabra组层序地层及沉积体系[J]. 沉积学报, 26(6): 994-1004. https://www.cnki.com.cn/Article/CJFDTOTAL-CJXB200806014.htm 周蒂, 王万银, 庞雄, 等, 2006. 地球物理资料所揭示的南海东北部中生代俯冲增生带[J]. 中国科学D辑: 地球科学, 36(3): 209-218. https://www.cnki.com.cn/Article/CJFDTOTAL-JDXK200603000.htm