Horizontally forced initiation of the Izu-Bonin-Mariana subduction zone

The sparsity of a direct record for the moment of subduction zone initiation has led to various models describing the infancy and evolution of modern oceanic subduction systems. Recently, with increases in available samples and geochemical data for subduction zone initiation-to-mature-arc lavas, better constraints on subduction evolution are possible. Here, by systemically modeling the time-space pattern and geochemical characters of forearc magmas with forward numerical modeling, we attempt to search for a best-fit geodynamic scenario where Izu-Bonin-Mariana-type subduction tends to develop. Our modeling and geochemical constraints have identified a necessary and possibly transitory pre-subduction zone initiation trenchward contraction consistent with observed Izu-Bonin-Mariana forearc magma geochemistry. Our results also reveal a typical maturation process for Izu-Bonin-Mariana-type oceanic subductions, controlled by the pace of the upper plate's rifting and solidification. A three-stage process of contraction, rifting and final maturation best explains subduction zone initiation in Izu-Bonin-Mariana-type systems, according to numerical and geochemical modelling informed by existing geochemical and petrological data.