The Congo Basin: Subsurface structure interpreted using potential field data and constrained by seismic data

Abstract

The Congo Basin (CB) occupies a large part of the Congo Craton, which formed from the amalgamation of different cratonic blocks of Archean age. It records the history of deposition of up to 1 Gyr of sediments, one of the longest geological records on Earth above a crystalline basement. It is considered as a typical intracratonic basin, with its slow and long-lived subsidence history and the largely unknown formation mechanisms. In this study, we analyze the gravity field in the central area of the CB, applying two different methodologies to investigate the depth of the crystalline rock basement and crustal structures. The crustal contribution to the gravity observations is determined in one case by a data driven approach, while in the other using an isostatic compensation model that includes the effect of the rigidity of the lithosphere. Both methods are constrained by density measurements from rock samples/boreholes and interpretations of the reflection seismic profiles, crossing the CB. The results obtained are quite consistent with the aeromagnetic anomalies, showing structural highs and lows, NW-SE trending, matching the axial magnetic zone. The maximum basement depth is between 10 and 18 km, depending on the gravity method and assumptions used. Furthermore, we could identify several small basins that from the interpolation of seismic profiles are not clearly resolved, such as Busira (7–9 km deep), Lokoro (10.5–12 km deep), and Salonga basins (10–11.5 km deep), in the northwestern, southeastern, and central sector of the CB, respectively. The analysis of the gravity anomalies mainly related to the crystalline crust supposes the presence of high-density bodies located in the southern part of the CB that we interpreted as related to the extensional phases that initiated the subsidence of the basin.