Inferring the Paleo‐Location of Proto‐Arc Magmas During Subduction Infancy in the Izu‐Bonin‐Mariana

Abstract

AbstractSubduction zones are one of the principal drivers of the modern‐day plate tectonics, but the processes that develop as incipient subduction zones mature are yet to be understood. Finding modern analogs for different stages of subduction infancy remains an outstanding challenge to answer questions on how and when an oceanic subduction zone reaches a quasi‐steady state to become long‐lived. Here, we compare the southern Mariana intra‐oceanic arc, in which near‐trench spreading and infant arc magmatism developed ∼3–4 Myr ago, with the Izu‐Bonin‐Mariana (IBM) proto‐arc magmas that formed during subduction infancy ∼52 Myr ago. Building upon this comparison, we propose that the Southern Mariana may be considered as a modern analog to subduction infancy. The similarities between the Southern Mariana arc magmas and the IBM Eocene proto‐arc magmas suggest that the IBM proto‐arc crust might have formed within 80–90 km from the paleo‐trench (slab at < 90 km paleo‐depth), while the Eocene infant arc was likely located at ∼100 km from the paleo‐trench (∼100–125 km slab paleo‐depth). We use our constraints further to propose a new conceptual model of subduction evolution for IBM. In this model, development of the subduction channel during arc infancy facilitated downward slab penetration and intensified corner flow in the sub‐arc asthenosphere of the mantle wedge. As such, cooling and serpentinization of the fore‐arc mantle might be considered as the principal drivers of subduction maturation and stabilization over the IBM lifetime.