Date of this Version
INTEGRATED GEOPHYSICAL ANALYSIS OVER BATHYMETRISTS SEAMOUNTS AND THE SIERRA LEONE RISE, An Undergraduate Thesis, University of Nebraska-Lincoln By Alexa Fernández, BS (2021)
The Bathymetrists Seamounts (BSM) are located northeast of the Sierra Leone Rise in the Atlantic Ocean. The northern seamounts have a southwest to northeast trend which is contrary to the current eastward motion of the African tectonic plate where they reside. The geological history and crustal structures of these features are poorly understood. The goal of this study is to integrate multiple geophysical data to better understand the crustal architecture and tectonic history of the BSM.
The seismic refraction study from Jones et al. (2015) was used as the baseline for isostatic modeling. This dataset suggested the presence of magmatic underplating beneath the Sierra Leone Rise but failed to reveal crustal features beneath the Bathymetrists Seamounts. Isostatic modeling was developed to find possible constraints on the crustal architecture beneath the BSM. This was achieved by balancing pressures underneath the SLR and BSM crustal blocks, as well as the other locations studied by Jones et al. (2015). The isostatic model suggested a thick crust with magmatic underplating beneath the BSM, triggering a new hypothesis about the BSM and SLR crustal blocks being formed at the same time.
The two-dimensional model was developed by integrating seismic, gravity, and magnetic data to study the crustal architecture beneath the research area further. The model confirmed the presence of magmatic underplating beneath the BSM as it was essential to satisfy the gravity field. Magnetic data were modeled in accordance with polarity reversals based on published ages of the African oceanic crust. The crust that the Bathymetrists Seamounts reside on was formed during the Cretaceous Magnetic Quiet Zone (121-84 Ma) - a period of normal magnetic polarity, so no reversals were expected. However, a developed two-dimensional model requires multiple reversals over the BSM block to match the observed magnetic data, suggesting that the seamounts are younger than the crust they reside on.
The integration of different geophysical datasets increases the confidence in derived crustal architectures of the Bathymetrists Seamounts and Sierra Leone Rise. The results suggest the presence of a left-lateral fault between these blocks trending in the same direction as seamounts. The hypothesized fault was active at the time when the seamounts were formed and resulted in ~ 100 km offset between SLR and BSM crustal blocks. Further investigations are required to confirm the presence of this fault.
Faculty Mentor: Irina Filina, PhD, Geophysics