Evolution and maturation of the nascent Mariana arc

Abstract

Long-standing debate remains regarding the processes by which nascent island arcs evolve into thicker-crust, mature volcanic edifices, long before being accreted into continental crust. How mature island arcs maintain their location for millions of years is still unclear. Arc location is currently believed to be controlled by slab dehydration or by the thermal state of the sub-arc mantle. However, most studies have focused on modern island arcs that have developed mature and stable volcanic edifices. Using published geochemical datasets, here we show that the southern Mariana arc is an incipient island arc that evolves into stable, thicker-crust stratovolcanoes to the north. Because it shares similar geochemical features with the early arc that formed during subduction infancy, it can place new important constraints onto the processes that occurred during island arc infancy. Examination of the Mariana arc along a S-N transect suggests that the growth of the serpentinized fore-arc mantle has the potential to modulate the depth of arc magma generation, which allows, in return, stabilization of the volcanic edifices during arc maturation. Arc stabilization further enables the deeply-sourced, slab fluids to infiltrate the sub-arc mantle wedge, which results in magmas with a typical arc fingerprint to the north. Melt focusing along magmatic conduits further promotes magma differentiation, magma-crust assimilation, and subsequent crustal thickening. We further propose that transient magmatic activity may also occur during island arc infancy in the Izu-Bonin-Mariana convergent margin, until serpentinization of the fore-arc mantle develops and stabilizes.