Age and significance of the Marble Hall breccia, Bushveld Complex, South Africa

Abstract

Diorite and associated breccia form scattered outcrops on the Marble Hall Fragment, in the vicinity of the town of Marble Hall, Mpumalanga Province, South Africa. The diorite (2055.6 ± 3.1 Ma) intruded as sub-horizontal sills in highly deformed and metamorphosed supracrustal rocks of the Transvaal Supergroup. The breccia, which ranges from polymictic to monomictic, consists of angular to Sub-rounded fragments of meta-dolomite, chert and adinole, as well as intensely scapolitized Marble Hall diorite and Bushveld B1-type sill rock. Predominantly sodic pargasite constitutes the breccia-fill of the monomictic breccia and represents the fractionated liquid of transitional basalt that crystallized..