Occurrence of Zoned Uvarovite—Grossular Garnet in a Rodingite from the Vumba Schist Belt, Botswana, Africa: Implications for the Origin of Rodingites

A. Mogessie and D. Rammlmair
Institute of Mineralogy - Crystallography and Petrology Karl - Franzens University Graz, Universitatsplatz 2, A-8010 Graz, Austria
Federal Institute for Geosciences and Natural Resources, Stilleweg 2, D-30655 Hannover, Germany

Abstract: Based on petrographic, mineralogical and geochemical data, two groups of rodingites have been documented from the polymetamorphic Vumba Schist Belt of Botswana. Group I rodingites contain relict chromite grains with zoned uvarovite-grossular + clinopyroxene + epidote/zoisite ± quartz, whereas group II rodingites contain no chromite and uvarovite. Although the presence of chromite with Cr/(Cr + Al + Fe3+) ratio > 90, similar to chromites found in komatiites, suggests a possible komatiitic origin of group I rodingites, the major and trace element chemical data of most analysed basic rocks from this belt indicate that the protoliths of both groups of rodingites are related to basalt/gabbro of komatiitic affinity. The rodingites formed during the M3 phase of metamorphism.

Keywords: rodingite • chromite • uvarovite • grossular • Vumba • Botswana

Mineralogical Magazine; September 1994 v. 58; no. 392; p. 375-386; DOI: 10.1180/minmag.1994.058.392.03
© 1994, The Mineralogical Society
Mineralogical Society (www.minersoc.org)