Volcanic evolution of the Bathymetrists Seamounts (equatorial Atlantic Ocean) since the Paleocene

The Bathymetrists Seamounts (BSM) are an elongated intra-plate volcanic province in the equatorial Eastern Atlantic Ocean. They are situated north of the Sierra Leone Rise, a smooth, aseismic seafloor elevation, believed to have formed above a hot spot at the Mid Atlantic Ridge. The arrangement of the 40 elongated seamounts, some of which are over 100 km long, is enigmatic. The strike direction of the seamounts is either parallel to the intersecting fracture and transcurrent zones or tilted by about 30° to 60°, which has been interpreted as evidence of Riedel shears. Previous age models are based on the geochemistry of a few dredged (surface) rock samples.

With the first set of ca. 4000 km of high-resolution multichannel seismic reflection data, we provide new insights into the structural and temporal evolution of the BSMs. Subsurface images reveal stacked seamount structures, offering direct evidence for their relative order of formation. Based on the DSDP site 366 findings, we establish a chrono-stratigraphic model for the sediment basins between the seamounts. This allows us to approximate the age of the underlying volcanic flanks and to refine the spatial and temporal evolution of BSM edifices through the Paleocene to Eocene. Furthermore, our data reveal signs of recent hydrothermal and magmatic activity, including intrusions, mud diapirism, and fluid chimneys penetrating the volcanic flanks. These findings highlight the BSMs as a dynamic system with both ancient origins and ongoing activity, offering new perspectives on understudied intra-plate volcanism and its associated processes.