Tectonic History of Diebold Knoll from Integration of Seismic, Gravity and Magnetic Data

Subducting seamounts are thought to be a major factor affecting subduction zone processes, although details of their impact remain poorly understood. Incorporating seamounts into geodynamic models requires accurate knowledge of their density structure and tectonic history, but determining these parameters is challenging, especially when the seamounts are partially or completely buried by a thick sediment cover on the subducting plate. We focus on an intraplate seamount known as Diebold Knoll, which is evident in bathymetry approximately 60 km west of the Cascadia subduction zone deformation front. The objectives of this research are to determine the settings the Diebold Knoll was formed and to evaluate heterogeneities in the physical properties of oceanic crust resulting from its addition. We present an integrated geophysical analysis combining seismic reflection data, gravity, and magnetic anomalies along two intersecting profiles across the seamount. Our gravity analysis reveals that Diebold Knoll is not isostatically compensated and may have up to 1 km thick root. Our modeling suggests that the top ~ 1 km of the seamount exhibits lower values of density (2.6 g/cm³) and magnetic susceptibility (100 µcgs) relative to the adjacent crust, attributed to syn-formation faulting and post-formation hydration. The negative magnetic anomaly of the seamount and the stratigraphic relationships of the seamount complex and the hosting sedimentary layers, including the presence of a 0.9 Ma horizon, indicate that Diebold Knoll is considerably younger (4.5–0.9 Ma) than the underlying oceanic crust (7-7.5 Ma) and was formed in the intraplate settings.