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Crustal age domains in the Kibaran belt of SW-Uganda: Combined zircon geochronology and Sm-Nd isotopic investigation

Abstract:

Combination of geochemistry, Nd mean crustal residence ages and single zircon ages reveal distinct provinces not recognized previously within the Kibaran belt of SW-Uganda. Geochemical analyses (HFSE and REE) of four granitoids, namely the Ntungamo, Chitwe, Rwentobo and Kamwezi from the Karagwe Tinfield have been interpreted to be mainly composed of melt components from subduction modified parts of the continental lithospheric mantle. In addition we can demonstrate, from these distinctive batholiths crystallization 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 between 1329 Ma and 1363 Ma. The εNd(t) values from the now precisely dated intrusions of the Kibaran belt indicate subsequently two distinctive groups. The older granites have εNd(t) values of -20.1 to -23.1 and Nd mean crustal residence ages, based on a depleted mantle model, from 3.52 Ga to 3.84 Ga while the younger granite batholiths show lower εNd(t) values of -10.1 to -14.0 and Nd mean crustal residence ages from 2.86 Ga to 3.06 Ga, respectively. The distinct geochemical, geochronological and isotopic characteristics and the unrelated geological evolution reconstructed from these data strongly implies that the two now adjacent Precambrian complexes were geologically unrelated crustal packages prior to high grade metamorphism and, as such, represent "suspect terranes" which were most probably brought together during a middle Proterozoic collision event. © 2007 Elsevier Ltd. All rights reserved.