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The Rehoboth Province; a buried craton in southern Africa.

Författare och institution:
Valby van Schijndel (Institutionen för geovetenskaper); David H. Cornell (Institutionen för geovetenskaper)
Publicerad i:
23rd Colloquium of African Geology (CAG23), University of Johannesburg, Johannesburg, South Africa, January 10-14, 2011, abstracts, s. 411
Konferensbidrag, övrigt
Sammanfattning (abstract):
We are investigating the origin and history of the Rehoboth Province, which is an enigmatic area due to the extensive Kalahari sand cover. Outcrops are mainly located in Namibia and Botswana along the borders of the magnetically quiet crustal terrane (Fig. 1). Palaeoproterozoic and Mesoprotorozoic stratigraphic successions are found at the northern boundary in the Rehoboth Basement Inlier (RBI), a thrust complex in the Damara front. The relationships between Paleoproterozoic and Mesoproterozoic formations or even within formations are often complicated by thrusting. Using U-Pb zircon geochronology we have now documented the existence of an hitherto unrecognized 3.4-2.4 Ga Archaean crustal component in Palaeoproterozoic metasediments, which was probably exposed as granitoids in the northern Rehoboth Province. This indicates a much longer geological history for the Rehoboth Province than previously known. Published zircon geochronology in the south-eastern corner of the Rehoboth Province has also indicated the presence of ancient crust. Zircon xenocrysts dated in Koras bimodal intrusives and volcanic rocks, north of Upington are in the range 1.7 to 2.1 Ga reflecting Paleoproterozoic basement (Pettersson et al., 2007). Glacial diamictites of the Permian Dwyka Group exposed at Rietfontein west of the Kalahari carry cobbles plucked from the bedrock by the ice sheet which covered the Gondwana supercontinent about 300 Ma ago. Microbeam U-Pb zircon dating of these granitic cobbles indicate the presence of a 2.5 to 2.9 Ga Archean crust beneath the Kalahari, with a lesser ~2050 Ma component (Cornell et al., 2010). Our data shows that there were at least three crustal development events at 3.4-2.4 Ga, 2.1-1.7 and 1.32-1.1 Ga. The volcanic and sedimentary rocks of the Mesoproterozoic Sinclair Supergroup (SS) lie in the Konkiep Subprovince between the Rehoboth Province and Namaqua Province. The basement of the Sinclair Supergroup is not yet constrained. In a preliminary study zircon xenocrysts in ~1.2 Ga migmatites gave an age of ~1.75 Ga, indicating a Palaeoproterozoic protolith and possibly an extension of the Rehoboth Province basement. The timing of accretion of the Rehoboth Province to the Kaapvaal Craton is still unclear and data is slim. Additional 39Ar-40Ar on hornblende and muscovite in the Groblershoop and Olifantshoek areas will increase the dataset and hopefully provide more constraints.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Geovetenskap och miljövetenskap
Rehoboth Province, Rehoboth Basement Inlier, Sinclair Supergroup, U-Pb zircon geochronology
Postens nummer:
Posten skapad:
2011-12-06 11:26

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