Geochronology of basement rocks in the Kalahari Desert, Botswana, and implications for regional Proterozoic tectonics

Autor: Roger Key, Brets B Direng, Richard E. Hanson, James L. Crowley, S. J. Singletary, Mark W. Martin, Michael A. Krol, Lepate V Ramokate, Samuel A. Bowring
Rok vydání: 2003
Předmět:
Zdroj: Precambrian Research. 121:47-71
ISSN: 0301-9268
DOI: 10.1016/s0301-9268(02)00201-2
Popis: U–Pb, 40 Ar/ 39 Ar , and Sm–Nd geochronological results from isolated basement exposures and drill-core samples in the Kalahari Desert, Botswana constrain the distribution and temporal evolution of Proterozoic crustal provinces in this part of Africa. There is evidence that a buried, northeast-trending Mesoproterozoic orogen lies outboard of older crustal provinces in eastern Botswana. The subsurface part of this orogen includes a granitic-gneissic terrain in northern Botswana that records plutonism and amphibolite-grade deformation between 1.2 and 1.1 Ga. Limited exposures of bimodal volcanic rocks in the Kalahari Desert are interpreted to represent extensional magmatism superimposed on the buried Mesoproterozoic belt. Previously published geochronological data and new U–Pb zircon crystallization ages presented here indicate that these volcanic rocks and associated subvolcanic intrusions were emplaced at 1.1 Ga, as part of the widespread Umkondo within-plate igneous province. Geophysical data, sparse outcrops, drill-core samples, and reconnaissance 40 Ar/ 39 Ar geochronology show the buried Mesoproterozoic orogen to be separated from the Congo craton by a continuation of the Neoproterozoic–Lower Paleozoic Damara belt exposed in Namibia. Limited outcrops of 2.05 Ga augen gneiss within a largely buried basement massif in northwestern Botswana are inferred to be part of a Paleoproterozoic crustal province developed along the southern margin of the Congo craton. The massif was intruded by granites at 1.02–1.00 Ga, but the extent and tectonic significance of this plutonism are uncertain. Deformed granite in the subsurface extension of the Damara belt has a protolith crystallization age of 0.72 Ga. Complex structural patterns in northwestern Botswana are inferred to reflect heterogeneous Damaran deformation around a promontory extending from the southern margin of the Congo craton.
Databáze: OpenAIRE
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