Evidence for petit-spot volcanism in the Puerto Rico trench

Abstract

Petit-spot volcanism occurs in intraplate settings along the outer rise of subducting plates. Here we present evidence for petit-spot type of volcanism from multibeam bathymetry and backscatter data from the Puerto Rico Trench (PRT). It is the first report of such volcanism in the Atlantic basin. Up to 34 possible petit-spot volcanic cones are mapped in the eastern section of the PRT, with an average diameter of 950 m and a mean height of 92 m. The seamounts are in a region of the PRT that has the longest and highest bending faults, up to 50.6 km long and 1.49 km high. Some of the volcanic cones are associated with fault scarps. The larger bending fault scarps in the region of the volcanic cones suggest the stress state in the eastern PRT is favorable for allowing asthenospheric melt to escape to the surface.

late tectonic theory explains most of the places where volcanos occur on Earth, like the mid-ocean ridges and hot spots like Hawaii. “Petit-spot” volcanos are special because they occur where the tectonic plates are bending and breaking near deep ocean trenches, and pre-existing ambient melt in the mantle escapes through the cracks. Due to this unique process, the petit-spots offer a glimpse into the chemistry and melting dynamics of the ambient mantle beneath tectonic plates that is not over printed by the aforementioned large-scale plate tectonic melting processes. In this paper we present evidence for petit-spot volcanism and associated faulting based on echo sounder mapping of the seafloor offshore Puerto Rico, USA. This is the first evidence for this type of volcano in the Atlantic and will lead to future studies sampling these volcanos to understand mantle convection and chemistry.