Abstract
A compilation of new and existing gravity data, as well as geophysical and geological data, is used to assess the cumulative effects of multiple rifting episodes on crustal and upper mantle density structures beneath the Uganda-Kenya-Ethiopia-Sudan border region. This compilation includes new gravity and geological data collected in 1990 in south-western Ethiopia. Variations in the trends and amplitudes of Bouguer gravity anomalies reveal three overlapping rift systems: Mesozoic, Paleogene and Miocene-Recent. Each of these rift systems is a number of 40–100 km long sedimentary basins, and each system is approximately 1000 km long. The Bouguer anomaly patterns indicate that the Ethiopian and East African plateaux and corresponding gravity anomalies are discrete tectonic features. Models of structural and gravity profiles of two basins (Omo and Chew Bahir basins) suggest that pre-Oligocene (Cretaceous?) strata underlie 3 km or more of Neogene-Recent strata within the northern Kenya rift, and that more than 2 km of Neogene-Recent strata underlie parts of the southern Main Ethiopian rift. The superposition of perhaps three rifting episodes in the Lake Turkana (Omo) region has led to 90% crustal thinning (β ≈ 2).
Similar content being viewed by others
References
Achauer U (1992) A study of the Kenya rift using delay-time tomography analysis and gravity modelling. In: Ebinger C, Gupta H, Nyambok I (ed) Seismology and Related Sciences in Africa. Tectonophysics 209: 197–207
Asfaw B, Beyene Y, Semaw S, Suwa G, White T, Wolde Gabriel G (1991) Fejej: a new paleoanthropological research area in Ethiopia J Hum Evol 20: 117–122
Asfaw LM (1990) Implication of shear deformation and earthquake distribution in the East African rift between 4° N and 6° N. J Afr Earth Sci 10: 745–751
Bechtel TD, Forsyth DW, Swain CJ (1987) Mechanisms of isostatic compensation around the East African rift, Kenya, Geophys J R Astron Soc 79: 987–1022
Berckhemer H, Baier B, Bartelson H, Behle A, Burkhardt H, Gebrande H, Makris J, Menzel H, Miller H, Vees R (1975) Deep seismic soundings in the Afar region and on the highland of Ethiopia. In: Pilger A, Rösler A (eds) Afar Between Continental and Oceanic Rifting. Schweizerbart, Stuttgart, pp 89–197
Binks, R, Fairhead JD (1992) A plate tectonic framework for evolution of the Cretaceous rift basins in West and Central Africa. In: Ziegler PA (ed) Geodynamics of Rifting. Tectonophysics 213: 141–151
Bosworth W (1992) Mesozoic and Tertiary rifting in East Africa. Tectonophysics 209: 115–137
Bosworth W Morley CK. Structural and stratigraphic evolution of the Anza rift, Kenya. In: Prodehl C, Keller G, Khan MA (eds) Crustal and Upper Mantle Structure of the Kenya rift. Tectonophysics, 236, in press
Bosworth W, Strecker MR, Blisniuk PM (1992) Integration of the East African paleostress and present-day stress data: implications for continental stress field dynamics. J Geophys Res 97: 11851–11865
Braun J, Beaumont C (1989) A physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins. Geology 17: 760–764
Browne S, Fairhead JD, Mohammed II (1985) Gravity study of the White Nile rift, Sudan, and its regional setting. Tectonophysics 113: 123–137
Cerling TE, Powers DW (1977) Paleorifting between the Gregory and Ethiopian rifts. Geology 5: 441–444
Coffin M, Rabinowitz P (1988) Evolution of the conjugate East African-Madagascan margins and the western Somali basin. Spec Pap Geol Soc Am No 226: 78 pp
Davidson A (Compiler) (1983) The Omo River Project, reconnaissance geology and geochemistry of parts of Illubabor, Kefa, Gemu Gofa, and Sidamo. Ministry of Mines and Energy, Ethiopian Inst Geol Surv Bull 2: 1–89
Davidson A, Rex DC (1980) Age of volcanism and rifting in southern Ethiopia. Nature 283: 657–658
Dunkelman T, Rosendahl BR, Karson JA (1989) Structure and stratigraphy of the Turkana rift from seismic reflection data. J. Afr Earth Sci 8: 489–510
Ebinger C, Bechtel T, Forsyth D, Bowin C (1989) Effective elastic thickness beneath the East African and Ethiopian plateaux and dynamic compensation of the uplifts. J Geophys Res 94: 2993–2901
Ebinger C, Rex D, Yemane T, Kelley S (1993a) Volcanism and extension between the Main Ethiopian and Gregory rifts. In: Thorweihe U, Schandelmeier H (eds) Geoscientific Research in NE Africa. Rotterdam: Balkema, pp 301–304
Ebinger, C, Yemane T, Wolde Gabriel G, Aronson J, Walter R (1993b) Late Eocene-Recent volcanism and faulting in the southern Main Ethiopian rift system. J Geol Soc London 150: 99–108
Hendrie D, Kusznir N, Morley C, Ebinger C. A quantitative model of rift basin development in the northern Kenya rift: evidence for the Turkana region as an “accommodation zone” during the Palaeogene. Tectonophysics, 236, in press
Ibrahim A (1993) Interpretation of gravity and magnetic data from the Central African rift system, Sudan. PbD Thesis, Univ Leeds, 208 pp
Kebede F, Kulhanek O (1991) Recent seismicity of the East African rift system and its implications. Phys Earth Planet Interiors 68: 259–273
Keller GR, Braile L, Davis P, Meyer R, Mooney W, and 27 others (1992) Kenya Rift International Seismic Project, 1989–1990 Experiment. Eos Trans Am Geophys Union 73: 345–351
Key RM, Watkins RT (1988) Geology of the Sabarei area, Report 111 (Reconnaissance). Nairobi: Ministry of Environment and Natural Resources, 57 pp
Kirby S (1983) Rheology of the lithosphere. Rev Geophys 21: 1458–1487
McKenzie DP (1978) Some remarks on the development of sedimentary basins. Earth Planet Sci Lett 40: 25–32
Maguire PKH, Swain CJ, Masotti R, Khan MA. A crustal and uppermost mantle cross-sectional model of the Kenya rift derived from seismic and gravity data. Tectonophysics, 236, in press
Makris J, Menzel H, Zimmermann J, Gouin P (1975) Gravity field and crustal structure of northern Ethiopia. In: Pilger A, Rösler A (eds) Afar Between Continental and Oceanic Rifting. Schweizerbart, Stuttgart, pp 135–144
Morley CK, Wescott WA, Stone DM, Harper RM, Wigger ST, Karanja FM (1992) Tectonic evolution of the northern Kenya rift. Geol Soc London 149: 333–348
Mukasa RK (1993) Estimates of basin depth beneath the Cenozoic rifts in W. Uganda and E. Zaire. MSc Thesis, Univ Leeds, 101 pp Prodehl C, Jacob B, Dindi E, Stangl R, Thybo H. Crustal structure of the eastern flank of the Kenya rift. In: Prodehl C, Keller G, Khan MA (eds) Crustal and Upper Mantle Structure of the Kenya Rift. Tectonophysics, 236, in press
Reeves CV, Karanja FM, MacLeod IN (1986-1987) Geophysical evidence for a failed Jurassic rift and triple junction in Kenya. Earth Planet Sci Lett 81: 299–311
Reynolds P-O (1993) Plate tectonic aspects of continental rift basin formation in Central and West Sudan. In: Thorweihe U, Schandelmeier H (eds) Geoscientific Research in Northeast Africa. Balkema, Rotterdam pp 207–212
Rosendahl BR, Kilembe E, Kaczmarick K (1993) Comparison of the Tanganyika, Rukwa, and Turkana rift zones from analyses of seismic reflection data. Tectonophysics 213: 235–256
Schandelmeier H, Reynolds P-O, Kuster D (1993) Spatial and temporal relationship between alkaline magnetism and early rifting in north/central Sudan. In: Thorweihe U, Schandelmeier H (eds) Geoscientific Research in Northeast Africa. Balkema, Rotterdam, Balkema, pp 221–225
Schult TJ (1988) Rift basins of interior Sudan: petroleum exploration and discovery. Am Assoc Petrol Geol Bull 72: 1128–1142
Swain CJ, Khan MA (1978) Gravity measurements in Kenya. Geophys J R Astron Soc 53: 427–429
Talwani M, Worzel JL, Landisman M (1959) Rapid gravity computations for two-dimensional bodies with application to the Mendocino submarine fracture zone. J Geophys Res 64: 49–59
Vening Meinesz FA (1950) Les grabens africains: résultats de compression ou de tension dans le croûte? Bull Inst Colon Belge 21: 539–552
Watkins RT Frostick L, Renaut R, Reid I, Tiercelin J-J (eds) (1986) Volcano-tectonic control on sedimentation in the Kochi Fora sedimentary basin, Lake Turkana. In: Frostick L et al. (eds) Sedimentation in the African Rifts. Spec Publ Geol Soc London 25: 85–95
Weissel J, Karner G (1989) Flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension. J Geophys Res 94: 13919–13950
Wolde Gabriel G, Aronson J, Walter RC (1990) Tectonic development of the Main Ethiopian rift. Geol Soc Am Bull 102: 439–458
Wolde Gabriel G, Yemane T, Suwa G, White T, Asfaw B (1991) Age of volcanism and rifting in the Burji-Soyoma area, southern Main Ethiopian rift: Geo- and biochronologic data. J Afr Earth Sci 13: 437–447
Zanettin B, Nicoletti M, Petrucciani C (1978) The evolution of the Chencha escarpment and the Ganjuli graben (Lake Abbaya) in the southern Ethiopian rift. N Jb Geol Palaontol 9: 567–574
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Ebinger, C.J., Ibrahim, A. Multiple episodes of rifting in Central and East Africa: A re-evaluation of gravity data. Geol Rundsch 83, 689–702 (1994). https://doi.org/10.1007/BF00251068
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00251068