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The Proterozoic Choma-Kalomo Block, SE Zambia: Exotic terrane or a reworked segment of the Zimbabwe Craton?

Authors
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Glynn,  S.
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Master,  Sharad
External Organizations;

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Wiedenbeck,  Michael
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Davis,  Donald W.
External Organizations;

Kramers,  Jan D.
External Organizations;

Belyanin,  George A.
External Organizations;

Frei,  Dirk
External Organizations;

Oberthür,  Thomas
External Organizations;

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Citation

Glynn, S., Master, S., Wiedenbeck, M., Davis, D. W., Kramers, J. D., Belyanin, G. A., Frei, D., Oberthür, T. (2017): The Proterozoic Choma-Kalomo Block, SE Zambia: Exotic terrane or a reworked segment of the Zimbabwe Craton? - Precambrian Research, 298, 421-438.
https://doi.org/10.1016/j.precamres.2017.06.020


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_2632949
Abstract
The Choma-Kalomo Block in south-eastern Zambia was hitherto considered as solely Mesoproterozoic in age based on granitoids which were previously dated at 1.37 and 1.18 Ga respectively. The Choma-Kalomo Block was therefore thought to constitute an exotic terrane with respect to the neighbouring Palaeoproterozoic Magondi Belt and Archaean Zimbabwe Craton. This study of the Choma-Kalomo Block presents new U-Pb SIMS age data for zircons collected from previously undated metasedimentary rocks, revealing an abundant Palaeoproterozoic component (2040–1861 Ma). Palaeoproterozoic (2040 ± 5 Ma) xenocrystic zircons in a Mesoproterozoic (1370 ± 3 Ma) leuconorite point to reworking of older crustal material, and suggest that the Choma-Kalomo Block is not a juvenile Mesoproterozoic terrane. Our U-Pb age data on columbite-tantalite fragments from tin-bearing pegmatites in both the Choma-Kalomo Block and the Dete-Kamativi Inlier (which is part of the Magondi Belt) indicates that Sn-(Ta-Nb-W-Li-Be) mineralisation within the two terranes occurred c. 1030 to 920 Ma. New 40Ar-39Ar dating, confirms previous data, and indicates that a thermal event affected the region between 1020 and 980 Ma. The similarities between the Choma-Kalomo Block and the Dete-Kamativi Inlier imply that these two terranes have a common history, at least as far back as the Palaeoproterozoic, but were certainly juxtaposed by the late Mesoproterozoic era. A large difference in lithospheric thickness between the Choma-Kalomo Block and the adjacent Zimbabwe Craton could explain the different rheological behaviour of the Choma-Kalomo and Dete-Kamativi areas, with the former being strongly deformed during the Neoproterozoic (Pan-African) orogeny. Our data indicate that the Choma-Kalomo Block is not an exotic terrane, rather it may represent a reworked portion of the Zimbabwe Craton, however what is unclear is whether the subcontinental lithosphere has been thinned, or the Choma-Kalomo Block represents a terrane with an originally thinner lithosphere.