Geophysical and geological investigation of the spatial and subsurface extent of the Segwagwa and Masoke igneous ring complexes in southeast Botswana: Geotectonic implications

Abstract

The Segwagwa-Masoke Igneous Ring Complex (SMIRC) occurs within the Kanye Basin and is part of a suite of elliptical igneous complexes in SE Botswana. We used map analyses and three-dimensional (3D) joint inversion modelling of airborne magnetic and ground gravity data to examine the internal structure and configuration of the SMIRC. Our results show the SMIRC as nested ring-within-ring structures characterized by high magnetic intensity and high gravity anomalies. The Segwagwa and Masoke Complexes are both elliptical in shape and cover surface areas of 127 km2 and 26 km2, respectively. Additionally, our results reveal two new intrusions, termed here Selokolela A and B, which form part of the SMIRC, bringing the total number of individual intrusions in the SMIRC to four. The 3D models suggest that the Segwagwa and Masoke Complexes are vertically oriented and steep-sided, extending to 12 km and ∼5 km depths, respectively. Two-dimensional (2D) forward modelling of the gravity and magnetic data confirms that the Segwagwa Complex is steep-sided and has a depth extent of 13 km. We interpret the ring-shaped magnetic anomalies to represent magma crystallization along concentric fracture zones that developed in association with the collapse of calderas.