Material Circulation, Arc Rifting and Back‐Arc Spreading Promoted by Deep Mantle Upwelling in Izu‐Bonin‐Mariana

Abstract

Arc rifting and back‐arc spreading reflect complex interactions between deep Earth processes and surface tectonics, playing a fundamental role in understanding oceanic crust formation, material circulation, and Earth's habitability. However, the driving forces of arc rifting and back‐arc spreading remain controversial, particularly due to the lack of seismological evidence. In this study, we investigate the three‐dimensional P‐wave velocity structure down to 700 km depth beneath the Izu‐Bonin‐Mariana subduction zone. Our results reveal distinct low‐velocity (low‐V) anomalies beneath the Izu‐Bonin and central Mariana regions. Beneath Izu‐Bonin, the low‐V anomaly tilts upward from the bottom of the upper mantle to shallower depths away from the Izu‐Bonin arc. In contrast, beneath central Mariana, low‐V anomalies extend subvertically from the mantle transition zone to the Mariana Trough. These low‐V anomalies likely represent Deep mantle upwelling (DMU) and material circulation triggered by devolatilization and oceanic crust melting of the deeply subducted Pacific slab. Integrating our results with previous findings, we propose that the distinct morphologies of DMU are responsible for the different stages of arc rifting and back‐arc spreading that occurred in the Izu‐Bonin and Mariana subduction zones, and possibly play a critical role in facilitating these processes.