UNCORRECTED PROOF 1 2 Crustal age domains in the Kibaran belt of SW-Uganda: 3 Combined zircon geochronology and Sm–Nd isotopic investigation 4 Robert Buchwaldt a,b,c, * , Theofilos Toulkeridis d,b , Wolfgang Todt c , Elias K. Ucakuwun e 5 a Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130-4899, USA 6 b Institut fu ¨ r Geowissenschaften, Johannes Gutenberg-Universita ¨ t, Becherweg 21, D-55099 Mainz, Germany 7 c Max-Planck Institut fu ¨ r Chemie, Postfach 3060, 55020 Mainz, Germany 8 d Center of Geology, Volcanology and Geodynamics, Universidad San Francisco de Quito, Campus Cumbaya ´, 9 Via Interoceanica y Jardines del Este, A.P. 17-12-841, Quito, Ecuador 10 e School of Environmental Studies, Moi University, P.O. Box 3900, Eldoret, Kenya 11 Received 8 November 2006; received in revised form 25 October 2007; accepted 1 November 2007 12 13 Abstract 14 Combination of geochemistry, Nd mean crustal residence ages and single zircon ages reveal distinct provinces not recognized previ- 15 ously within the Kibaran belt of SW-Uganda. Geochemical analyses (HFSE and REE) of four granitoids, namely the Ntungamo, Chit- 16 we, Rwentobo and Kamwezi from the Karagwe Tinfield have been interpreted to be mainly composed of melt components from 17 subduction modified parts of the continental lithospheric mantle. In addition we can demonstrate, from these distinctive batholiths crys- 18 tallization ages that lead to the result of three age groups, one at around 1566 Ma, the second at 1444 Ma to and the third clusters 19 between 1329 Ma and 1363 Ma. The e Nd(t) values from the now precisely dated intrusions of the Kibaran belt indicate subsequently 20 two distinctive groups. The older granites have e Nd(t) values of 20.1 to 23.1 and Nd mean crustal residence ages, based on a depleted 21 mantle model, from 3.52 Ga to 3.84 Ga while the younger granite batholiths show lower e Nd(t) values of 10.1 to 14.0 and Nd mean 22 crustal residence ages from 2.86 Ga to 3.06 Ga, respectively. The distinct geochemical, geochronological and isotopic characteristics and 23 the unrelated geological evolution reconstructed from these data strongly implies that the two now adjacent Precambrian complexes were 24 geologically unrelated crustal packages prior to high grade metamorphism and, as such, represent ‘‘suspect terranes” which were most 25 probably brought together during a middle Proterozoic collision event. 26 Ó 2007 Elsevier Ltd. All rights reserved. 27 Keywords: Uganda; Kibaran; Granites; Zircon; Suspect terranes 28 29 1. Introduction 30 The study of ancient granitic plutons provides an impor- 31 tant insight into geodynamic orogenic processes that com- 32 monly cannot be observed in modern active orogenic belts 33 because most of these expose only the upper brittle part the 34 continental crust (e.g. Ring et al., 1999). In such old eroded 35 belts Nd isotopes together with single zircon geochronol- 36 ogy supply particularly valuable information on crustal 37 genesis, evolution and terrane amalgamation, and can be 38 used to distinguish between old, reworked and juvenile 39 crust (e.g. Mezger et al., 1993; Mo ¨ller et al., 1998). 40 The middle Proterozoic Kibaran orogeny affected large 41 areas of central and southern Africa. Although the Kiba- 42 ran orogeny was initially defined in the Kibaran Mountains 43 of Congo, it has now been recognized that several linear 44 and mostly parallel belts of Kibaran age exist in the eastern 45 part of Africa and occupy a critical place within the com- 46 plex network of Proterozoic mobile belts that surround 47 and separate the Archean cratonic nuclei of southern and 48 central Africa. 1464-343X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2007.11.001 * Corresponding author. Address: Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130-4899, USA. Tel.: +314 935 8069; fax: +314 935 7361. E-mail address: buchwaldt@levee.wustl.edu (R. Buchwaldt). www.elsevier.com/locate/jafrearsci Available online at www.sciencedirect.com Journal of African Earth Sciences xxx (2007) xxxxxx AES 1365 No. of Pages 17, Model 5+ 27 November 2007; Disk Used ARTICLE IN PRESS Please cite this article in press as: Buchwaldt, R. et al., Crustal age domains in the Kibaran belt of SW-Uganda: ..., J. Afr. Earth Sci. (2007), doi:10.1016/j.jafrearsci.2007.11.001