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Geochemical and Sr-Nd isotopic data on the Birimian of the Kedougou-Kenieba Inlier (Eastern Senegal): Implications on the Palaeoproterozoic evolution of the West African Craton

Geoscience Center, Georg-August-University, Goldschmidtstr. 3, 37077 Goettingen, Germany Present address: Nu Instruments Limited., Unit 74, Clywedog Rd South, Wrexham Industrial Estate, Wrexham LL13 9XS, United Kingdom, email: sabine{at}nu-ins.com

Mamadou Gueye

Institut des Sciences de la Terre, Université Cheikh Anta Diop, Dakar, Senegal, e-mail: mgueye{at}refer.sn

Ralf Klischies, Stefan Schwarz, Klaus Wemmer and Siegfried Siegesmund

Geoscience Center, Georg-August-University, Goldschmidtstr. 3, 37077 Goettingen, Germany, e-mail: ralkli1234{at}web.de; sschwar2{at}gwdg.de; kwemmer{at}gwdg.de; ssieges{at}gwdg.de

Birimian (Paleoproterozoic) granitoids and associated volcanic and sedimentary rocks from the Kedougou-Kenieba-Inlier (KKI) of Eastern Senegal have been analyzed for their major, trace, REE concentrations and their Sr-Nd isotopic compositions. The calc-alkaline I-type granitoids were previously divided into several structural groups. The new geochemical data, however, do not give evidence for this subdivision into pre-, syn- and post-deformational intrusions. The results demonstrate the juvenile character of the granitic igneous rock suite and its isotopic similarities to the adjacent volcanic Mako and sedimentary Dialé-Daléma Supergroups. The Birimian rocks show uniform juvenile features such as low initial Sr isotopic composition (~0.700 to ~0.704), positive _Nd(t) values (2.1 to 4.3) and restricted Nd model ages (~2.0 to ~2.3 Ga). They preclude the contamination of the juvenile Birimian crust of the KKI by notable amounts of reworked Archean crustal material. Comparison with existing data helps to clarify the complex evolution of Birimian Supergroups of the WAC. It can be concluded that the Birimian rocks are the product of a large-scale crustal growth process with large amounts of juvenile crust formed from the depleted mantle in a geodynamic environment compared to modern volcanic arcs. These bimodal volcanic arcs were later accreted to the WAC.

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				E. Dioh, D. Beziat, M. Gregoire, and P. Debat Origin of rare earth element variations in clinopyroxene from plutonic and associated volcanic rocks from the Foulde basin, Northern Kedougou inlier, Senegal, West Africa European Journal of Mineralogy, October 1, 2009; 21(5): 1029 - 1043. [Abstract] [Full Text] [PDF]

				M. Gueye, S. Siegesmund, K. Wemmer, S. Pawlig, M. Drobe, N. Nolte, and P. Layer New evidences for an early Birimian evolution in the West African Craton: An example from the Kedougou-Kenieba inlier, southeast Senegal South African Journal of Geology, December 1, 2007; 110(4): 511 - 534. [Abstract] [Full Text] [PDF]