Sub-Lithospheric Small-Scale Convection Tomographically Imaged Beneath the Pacific Plate

Small-scale convection beneath the oceanic plates has been invoked to explain off-axis nonplume volcanism, departure from simple seafloor depth-age relationships, and intraplate gravity lineations. We deployed 30 broadband ocean bottom seismometer stations on similar to 40 Ma Pacific seafloor in a region notable for gravity anomalies, measured by satellite altimetry, elongated parallel to plate motion. P-wave teleseismic tomography reveals alternating upper mantle velocity anomalies on the order of +/- 2%, aligned with the gravity lineations. These features, which correspond to similar to 300 degrees-500 degrees K lateral temperature contrast, and possible hydrous or carbonatitic partial melt, are-surprisingly-strongest between 150 and 260 km depth, indicating rapid vertical motions through a low-viscosity asthenospheric channel. Coherence and admittance analysis of gravity and topography using new multibeam bathymetry soundings substantiates the presence of mantle density variations, and forward modeling predicts gravity anomalies that qualitatively match observed lineations. This study provides observational support for small-scale convective rolls beneath the oceanic plates.

Automated summary

This study provides observational support for small-scale convective rolls beneath the oceanic plates. The study found alternating upper mantle velocity anomalies aligned with gravity lineations beneath the seafloor. These anomalies, likely caused by temperature variations and possible partial melting, are strongest in deeper regions, indicating rapid vertical motions through a low-viscosity asthenospheric channel.