Formation and fill of continental rift basins: An integrated study based on the Bornu Basin, Onshore NE Nigeria

Abstract

Intra-plate magmatism and tectonic inversion in most frontier basins are poorly documented. The relationship of these plate interior geodynamics to the plate boundary interactions is also only partially understood due to restricted access to the limited available datasets from such basins. In the West to Central African Rift System (WCARS) for example, there are no well documented studies on the magmatism and the development of the inversion-related structures. Therefore, it is not yet clear how these events are linked to the regional plate boundary interactions and also how they could impact the development of the basins petroleum systems. Here, I investigate the relationships between the plate boundary interactions and plate interior magmatism as well as inversion geodynamics by focusing on the tectono-stratigraphic evolution of the Bornu Basin, NE Nigeria. The Bornu Basin is one of several continental rifts located in the WCARS. More specifically, I use 2D and 3D time-migrated seismic reflection, borehole, field and geochemical data to map out the geometry of the emplaced igneous bodies, analyse the magma emplacement mechanics and establish the timing of the events. I also determine how plate margin processes impact normal fault growth, inversion, stratigraphic patterns, igneous activity and petroleum systems development within interior basins. I demonstrate that these key tectonic events in the Bornu Basin were to a certain degree time equivalent to the periods of major plate boundary interactions as preserved in the changes in the azimuth of the major oceanic fracture zones. For example, the timing of rift initiation in Bornu Basin during the early Albian correlates with the initiation of separation of the South American and African plates and this to some degree correlates with early change in azimuth observed in Kane Oceanic Fracture Zone (KFZ). The timing of the early Santonian tectonic inversion in the basin correlates with the period of collision of the African and the Eurasian plates. This event resulted in a compressional stress regime across the affected continental blocks. The timing apparently correlates with early change in azimuth observed in the Kane Oceanic Fracture Zone (KFZ) in the Santonian. However, of the three main phases of igneous activity established in the Bornu Basin, Early Cretaceous, Late Cretaceous and Cenozoic, only the latter two can be described to correlate with the timing of the major azimuth changes observed in the Kane, Fifteen Twenty and St. Paul Oceanic fracture zones. This may caution a general claim of the direct link of the changes in the azimuth and intra-plate geodynamics. My study highlights that the geodynamics of plate boundary interactions during continental break up may not only be expressed by changes in the azimuth of oceanic fracture zones, but may also be recorded in the surrounding, intra-plate continental rift basins. Furthermore, it shows how the understanding of the timing of normal fault inversion and igneous activity can help to minimize exploration risks associated with trap charging, reservoir quality and source rock hydrocarbon potential.