J. Pablo Canales | Geology Reports

USGS2025

Evidence for petit-spot volcanism in the Puerto Rico Trench

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.

Puerto Rico Trench↗

USGS2025

Slab tearing and segmented subduction termination driven by transform tectonics

Subduction may terminate when a mid-ocean ridge approaches a trench, introducing buoyant lithosphere that resists subduction, leading to slab detachment and plate boundary reconfiguration. Yet, the spatial and temporal dynamics of slab tearing remain enigmatic due to a lack of modern examples. Here, we integrate new seismic images with regional seismicity to investigate an actively fragmenting subduction system at northern Cascadia’s ridge-trench-fault triple junction where subduction termination is imminent. Our analyses reveal a broad shear-zone initiated at ~4 Ma by exploiting ridge-parallel fabrics of nascent oceanic lithosphere and progressively localized into a mature trench-perpendicular transform boundary. This process severed an oceanic microplate and enabled its diminished subduction relative to adjacent subducting lithosphere. Downdip, we image trench-parallel slab tears offset by the transform, suggesting lateral tear propagation was intersected by the transform boundary, facilitating efficient decoupling of the microplate while allowing adjacent subduction to continue. We propose a 4D model where transform boundaries drive laterally diachronous slab fragmentation and subduction termination.

Vancouver, Washington↗