--> Baseline Study of the Volta Basin, Ghana: Geophysical Constraints

2018 AAPG International Conference and Exhibition

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Baseline Study of the Volta Basin, Ghana: Geophysical Constraints

Abstract

The poorly studied ca. 600 Ma Volta Basin of Ghana hosts an inferred 6 km sedimentary sequence that includes a Triad sequence of the much larger Taoudeni Basin, which unconformably overlies the West African Craton (WAC). Scarce outcrop exposure, the undefined extent of the ca 2.0 – 2.2 Ga Birimian basement, the unknown provenance of sediments, and possible mineral and hydrocarbon potential has motivated this baseline study. Both foreland and passive margin tectonic regimes have been proposed for the formation of the Volta Basin. These regimes will lead to distinct basement and basin architecture which can be mapped using magnetic, gravity, radiometric, seismic, and electromagnetic methods. Detailed geological mapping of units with strong geophysical signatures provides constraints on the geophysical interpretations within the basin. We have identified the Birimian supergroup extending at least 170 km from the west beneath the Volta basin based on our aeromagnetic interpretation. These surrounding Birimian lithologies hint at possible gold resources deposited into the basin as does the presence of paleochannels sourcing distant regions. The knickpoints in the paleochannels, which were imaged from aeromagnetic data, record changes in basin tilt and sediment flow rate. Our near surface interpretation of radiometric and Landsat data has identified the source of recent sediments. This has allowed us to develop a detailed map of the temporal evolution of recent sedimentation. In our current tectonic interpretation, the Volta basin developed as a foreland basin at 600 Ma which was modified by the obduction of the Dahomeyan orogenic belt at ca. 550 Ma. We see no evidence for the Birimian supergroup in the aeromagnetic data further east than 170 km. We are interpreting the prominent gravity high further east of this 170 km Birimian extension as a mafic intrusion possibly recording an ancient extensional event. Our preliminary studies imply possible deposition of Birimian sediments from the west which translates into the western edges of the basin being more prospective for gold placer resources.