Slab structure controls arc magmatism diversity in subduction zones

Abstract Arc magmatism exhibits significant diversity in both geochemical composition and spatial distribution (defined as the depth from a volcano to the subducted slab). The primary mechanisms driving these variations remain poorly understood. We present boron (B) isotope data for mafic lavas from the volcanic front and rear arc in Java, along with geophysical constraints, to decipher how slab structure controls the diversity of arc magmatism. Our data demonstrate that slab tearing, which induces upwelling of the asthenospheric mantle, causes intensive melting of the subducted slab and mantle wedge at shallower depths beneath the forearc. This results in volcanism forming closer to the trench, and a decrease in δ11B values in arc lavas with input of melts from subducted sediments. Elevated surface temperature near slab tearing could also result in more significant water loss in subducted slab. Thus, in a rear-arc environment, the lavas from volcanos above the slab tearing show lower B/Nb ratios than those from the volcano away from the slab tearing. Less water was transferred into the deep mantle, resulting in less melting of the mantle wedge near the slab window in the rear-arc environment. Variations in the composition and location of arc magmatism in Java are primarily controlled by changes in slab structure. This generalization applies to global arc magmatism, with increasing slab depths correlating with greater water flux and more melting of the mantle wedge in colder subduction settings. The results of this study indicate that the diversity of arc magmatism is primarily regulated by the thermal structure of the subducted slab.