Terrestrial heat flow in the Malawi Rifted Zone, East Africa: Implications for tectono-thermal inheritance in continental rift basins

Abstract

Rift basins show the widest range of heat flow values compared to passive continental margins and intracratonic sag basins. Elevated heat flow is often used to infer asthenospheric upwelling or subsurface magmatic activity for magma-assisted rifts. Despite the lack of surface volcanism for magma-poor rifts, it is possible that magmatic bodies will be present at lower and mid crustal levels but yet to breach the surface, thus necessitating consideration of heat flow from tectono-thermal inheritance in addition to more recent magmatism. We use aeromagnetic data to investigate the terrestrial heat flow distribution in the Malawi Rifted Zone (MRZ) in East Africa defined as the Neogene Malawi Rift and surrounding Permo-Triassic Karoo rift basins. We use the two-dimensional power-density spectrum technique to estimate the Curie point depth (CPD), geothermal gradient, and heat flow beneath the MRZ. Our results reveal predominance of shallow CPDs (18–20 km), high geothermal gradients (29–32 °C/km) and elevated heat flow (70–82 mW m−2) within the Karoo rift basins. Along the Malawi Rift, geothermal gradient (25–27 °C/km) and heat flow (60–66 mW m−2) are generally lower except pronounced high heat flow (70–82 mW m−2) at the Rungwe Volcanic Province (RVP) in the north, and at the central rift-segment where the rift overprints Karoo rift basins. The surrounding cratonic blocks show deeper CPDs (24–27 km), lower geothermal gradients (22–24 °C/km) and lower heat flow (53–63 mW m−2). We interpret that the elevated heat flow in the Karoo rift basins are related to residual heat flow from the Permo-Triassic rifting-phase, replenished by later Jurassic-Cretaceous diking events. Apart from the thermal anomaly beneath the RVP, which is due to Neogene magmatism, other important targets for geothermal explorations in the MRZ are the residual thermal anomalies in the Karoo rift basins. We infer that in areas of active magma-poor rifting, pronounced heat flow may not only occur in regions of asthenospheric upwelling, but may concentrate in the ancient magmatic rift segments. Our findings have implications for crustal stretching, tectono-thermal inheritance, and geothermal energy potentials in East Africa and other segments of magma-poor rifting.

Department(s)

Geography, Geology, and Planning

Document Type

Article

DOI

https://doi.org/10.1016/j.jvolgeores.2019.07.023

Keywords

Aeromagnetic data, Curie point depth, Geothermal exploration, Heat flow, Malawi Rifted Zone, Tectono-thermal inheritance

Publication Date

12-1-2019

Journal Title

Journal of Volcanology and Geothermal Research

Link to Full Text

Share

COinS