Time lag for arc volcanism following subduction initiation: A two-phase flow numerical modeling

Subduction initiation is a fundamental geodynamic process in plate tectonics, yet its mechanisms remain poorly understood due to the scarcity of geological records. Proposed geological records of subduction initiation, including metamorphic soles, fore-arc basalts and fore-arc sediments, are typically associated with spontaneous subduction initiation in hot environments involving mantle upwelling. In contrast, evidence for the more common cold subduction initiation at continental margins is sparse or even absent. Arc volcanic rocks are widely regarded as direct evidence of subduction zones, particularly for identifying ancient subduction zones in orogens. However, the temporal relationship between subduction initiation and the onset of arc volcanism remains poorly constrained. Although arc volcanism is generally considered to develop within ∼10 million years (Myr) of initiation, our analysis of subduction events over the past 15 Myr reveals a highly variable time lag ranging from 2 to 10 Myr. In this study, we investigate the factors controlling this time lag in forced subduction initiation at continental margins, using a newly developed two-phase flow numerical model that incorporates melt transport and melt extraction processes. Our results show that rapid partial melting at shallow depths, primarily driven by high convergence rates, leads to a shorter time lag between subduction initiation and arc volcanism, which is consistent with observations from recent subduction events. These findings suggest that arc volcanic rocks, when considered together with slab age and convergence rate, provide a useful constraint on the timing of subduction initiation in ancient subduction systems.