Correlation between back-arc spreading center and volcanic arc location

Abstract:

The location of volcanic arcs can be approximated by a melt focusing mechanism that depends primarily on the thermal structure of the overriding plate, independent of the region where melt is generated (Ha et al., submitted to G-cubed, 2020). In that model, melt rises through the mantle wedge, collects in a decompaction channel that nearly follows an isotherm at the base of overriding plate, and travels along that channel to its apex, where it accumulates and traverses the plate to form arc volcanoes. Seen at global scale, the thermal structure of the overriding plate and therefore the expected arc location depends mainly on slab geometry, convergence rate, and the depth at which the slab interface starts to be coupled with the overlying mantle wedge. Mantle flow from back-arc spreading centers can change the thermal balance in the mantle wedge and overriding plate, thereby affecting the location of arc. A spreading related temperature structure should dip away from the spreading center. The resulting tilt in isotherms in the overriding plate may move the expected arc location towards the back-arc spreading center. To search for evidence for this effect, we analyze the locations of arc and back-arc spreading center at the Mariana, Scotia, Vanuatu, and Tonga subduction zone. The distance between trench, arc, and back-arc are measured for each volcano or prominent seamount in a direction parallel to plate convergence. The distance from trench to back-arc appears positively correlated with the distance from trench to arc for each subduction zone (Figure 1a). While the distance from arc to back-arc spreading center globally shows a positive correlation with the trench to back-arc distance for all the investigated subduction zones (Figure 1b). Thus, the distance between the trench and arc changes for each subduction zone and remains around 250 km, reflecting the importance of slab geometry. The influence of the spreading center is from the trench, the lesser its effect on the mantle wedge. As a result, the arc forms closer to the trench where the mantle flow driven by the slab is more dominant. To consider the effect of different subduction geometries and geologic settings, more systematic 2-D modeling is required with the observational data in this study.