A reinterpretation of the Archaean stratigraphy south of Nkandla, southern Kaapvaal Craton, South Africa: Geophysical and stratigraphic constraints on a sheared granitoid-greenstone remnant

Abstract

Abstract A new lithostratigraphic framework based upon a review of historic data, field mapping and remote sensing, including aerial photography, high-resolution airborne aeromagnetic and radiometric data, is proposed for the Archaean geology along the southeastern margin of the Kaapvaal Craton, South Africa. A synthesis of new and existing data reveals that previously accepted lithostratigraphic schemes require complete revision, with reinterpretations identifying multiple major shear zones and previously unidentified granitoid successions along the margin of the craton. In this new lithostratigraphic framework, lithologies of the Southern Syncline previously correlated with the Nsuze Group of the Pongola Supergroup, are redefined as greenstone lithologies associated with the Ilangwe Greenstone Belt. The geology of the Nkandla region can be subdivided into five distinct geophysical domains including: (i) an extension of the Ilangwe Greenstone Belt, (Domain 1) which is subdivided into; a lower volcanic succession, the Thathe Formation, comprising pillow and amygdaloidal volcanics; the adjoining Sabiza Formation, comprising pillow volcanics exposed in the southeast of the study area; the volcano-sedimentary Mtshwili Formation, which overlies the Thathe and Sabiza formations, consisting of quartz (sericite) schist, phyllite, metavolcanics and iron formation; the Nomangci Formation, which occurs as a region of highly deformed quartz-kyanite-sericite schists, and the Simbagwezi Formation, which comprises maroon to green phyllites and schists in the north of the study area. (ii) granitoids of the Impisi Granitoid Suite (Domain 2) which border the greenstone succession to the north, intruding the Nomangci and Simbagwezi formations. (iii) a southern complex of sheared granitoids termed the Umgabhi Granitoid Suite (Domain 3), which intrudes the Thathe, Sabiza and Mtshwili formations. (iv) The two remaining domains, comprise the Mesoproterozoic Mfongosi and Ntingwe Groups (Domain 4) and Mesoarchaean volcano-sedimentary sequences of the Pongola Supergroup (Domain 5).