PALEOSTRESS ANALYSIS OF KAROO SUPERGROUP OF THE TSHIPISE-PAFURI BASIN, SOUTH AFRICA

Abstract

The Tshipise-Pafuri basin is located in the Limpopo Province, north-eastern South Africa. This paper presents the first paleostress-analysis results from fault-slip data on the sedimentary rocks of Karoo Supergroup of late Palaeozoic to early Mesozoic in Tshipise-Pafuri basin. Stress inversion of 251 fault-slip data was performed using an improved Right-Dihedral method, followed by rotational optimization (WINTENSOR Program, Delvaux, 2012). Fault-slip data including fault planes, striations and sense of movements, were obtained from rock exposures distributed in ten stations in the basin. The orientation of the principal stress axes (σ1, σ2 and σ3) and the ratio of the principal stress differences (R) show a paleostress field marking two main stress regimes. The main strain field in the Tshipise-Pafuri basin is characterised by west to east to east-northeast to west-southwest extension and the second strain field is a minor north to south to west-northwest to east-southeast reactivated extension. It includes two paleostress regimes, one with dominantly dip-slip normal faulting (extensional regime) and a minor normal faulting (extensional regime). The north-eastern margin of the Kaapvaal craton was down-faulted into a graben structure, in which the pre-Karoo Soutpansberg Group was deposited. This faulting, which controlled graben formation, continued during the deposition of the Karoo sediments and was reactivated in post-Karoo times, resulting in a very complex structural setting. The east-west trends of the stress fields in the basin follows the east-west elongated low lying Limpopo Mobile Belt.