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SHRIMP U–Pb zircon geochronology of gneisses from the Gweta borehole, northeast Botswana: implications for the Palaeoproterozoic Magondi Belt in southern Africa

Published online by Cambridge University Press:  05 July 2001

R. B. M. MAPEO ,
R. A. ARMSTRONG  and
A. B. KAMPUNZU
R. B. M. MAPEO
Affiliation:
Department of Geology, University of Botswana, Private Bag 0022, Gaborone, Botswana
R. A. ARMSTRONG
Affiliation:
Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200 Australia
A. B. KAMPUNZU
Affiliation:
Department of Geology, University of Botswana, Private Bag 0022, Gaborone, Botswana
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Abstract

This paper presents new U–Pb zircon analyses from garnet–sillimanite paragneisses from the Gweta borehole in northeast Botswana. Concordant to near-concordant analyses of zircon from these rocks reveal a billion year history from 3015 ± 21 Ma for the oldest detrital grain measured, to the age of high-grade metamorphism, 2027 ± 8 Ma. The maximum age of sedimentation in the Magondi belt is constrained by the age of the youngest concordant detrital zircon at 2125 ± 6 Ma. This contrasts with the age of sedimentation in the Central Zone of the Limpopo belt which is Archaean. The comparison of our results with U–Pb zircon data from the Magondi belt in Zimbabwe suggests that the granulite-facies metamorphism in this belt extended between c. 2027–1960 Ma. Granulite-facies rocks with U–Pb zircon ages in this interval are also known in the Ubendian belt and lend support to the correlation of these two segments of Palaeoproterozoic belts in southern and central–eastern Africa. The granulite facies metamorphism in the Magondi belt is coeval with the high-grade metamorphism and granitoids documented further south in the Central Zone of the Limpopo Belt.

Type
Research Article
Information
Geological Magazine , Volume 138 , Issue 3 , May 2001 , pp. 299 - 308
Copyright
© 2001 Cambridge University Press

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