Destructive episodes and morphological rejuvenation during the lifecycles of tectonically active seamounts: Insights from the Gorringe Bank in the NE Atlantic

Abstract

Seamounts are spectacular bathymetric features common within volcanic and tectonically active continental margins. During their lifecycles, they evolve through stages of construction and destruction. The latter are marked by variable magnitude flank collapses that often interrupt the evolution of seamounts and constitute a major source of hazard. The Southwest Iberian Margin is a tectonically complex region with moderate to high seismicity where numerous seamounts occur. On such a setting, earthquake-triggered collapses on seamount flanks are common, leading to the deposition of Mass-Transport Deposits (MTDs) on the surrounding abyssal plains. Using a wealth of 2D seismic reflection profiles, we investigate the lifecycle of the tectonic Gorringe Bank (GB), the largest submarine seamount offshore European margins, based on the magnitude and recurrence patterns of MTDs along the active thrust flank. Eight MTDs with relevant expression on the seismic data were analysed, four of estimated Miocene age and four on a Pliocene-Quaternary interval. Miocene MTDs are overall larger and correlate with the main uplift stages of the GB structure. Their distribution and relative timing suggest that failure-triggering earthquakes were common along the whole length of the GB. Pliocene to Quaternary MTDs tend to cluster along the northern half of the GB flank and are generally smaller. Overall, the size and magnitude of the mass-waste events is directly relatable to the magnitude of the uplift stages. Given the lack of indicators of large MTDs on the modern GB morphology, we propose that the lifecycle of tectonic seamounts is marked by morphological rejuvenation driven by thrust fault activity in between major collapse events or cycles. Tectonic-driven rejuvenation is thus key to hinder or obliterate evidence of past high-magnitude destructive events on tectonic seamount morphology.