The role of magmatically driven lithospheric thickening on arc front migration

Abstract

Volcanic activity at convergent plate margins is localized along lineaments of active volcanoes that focus rising magma generated within the mantle below. In many arcs worldwide, particularly continental arcs, the volcanic front migrates away from the interface of subduction (the trench) over millions of years, reflecting coevolving surface forcing, tectonics, crustal magma transport, and mantle flow. Here we show that extraction of melt from arc mantle and subsequent magmatic thickening of overlying crust and lithosphere can drive volcanic front migration. These processes are consistent with geochemical trends, such as increasing La/Yb, which show that increasing depths of differentiation correlate with arc front migration in continental arcs. Such thickening truncates the underlying mantle flow field, squeezing hot mantle wedge and the melting focus away from the trench while progressively decreasing the volume of melt generated. However, if magmatic thickening is balanced by tectonic extension in the upper plate, a steady crustal thickness is achieved that results in a more stationary arc front with long-lived mantle melting. This appears to be the case for some island arcs. Thus, in combination with tectonic modulation of crustal thickness, magmatic thickening provides a self consistent model for volcanic arc front migration and the composition of arc magmas.

The rise and fall of continental arcs: Interplays between magmatism, uplift, weathering, and climate

“…One could envision magmatism weakening the lower crust by heating it up, thereby decreasing the resistance to tectonic forces. In addition, thickening of the upper plate decreases the "headspace" for decompression melting, and thus, magmatic thickening may itself be a self-limiting process (Karlstrom et al, 2014). Finally, we have not considered gravitational collapse in our models (Bird, 1991;Jadamec et al, 2007;Molnar and Lyon-Caen, 1988).…”

“…What leads to long-lived magmatic flare-ups in continental arcs is unclear, but possibilities include changes in plate motion, lithospheric thinning by delamination/convective removal, and underthrusting of continental lithosphere in the back-arc region (Ducea and Barton, 2007). The eventual decline and termination of magmatism could be caused by thickening of the arc crust (e.g., by magmatism), which limits the extent of decompression melting in the asthenosphere (Chin et al, 2015;Karlstrom et al, 2014). For the purposes of this paper, we take the observed flareup as given.…”

Continental crust formation at arcs, the arclogite “delamination” cycle, and one origin for fertile melting anomalies in the mantle

“…2b). Given a continuous background magmatic flux imparted by subduction-induced decompression melting in the mantle wedge [53], the garnet pyroxenite layer thickens gradually with time [4,18,54]. Due to the high densities of the garnet pyroxenite cumulates compared to typical peridotitic mantle ( Fig.…”

Cretaceous Intraplate Contraction in Southern Patagonia: A Far‐Field Response to Changing Subduction Dynamics?

“…In a pioneering work, Molnar et al () proposed a direct relation between increased convergence velocities and arc broadening. However, most recent numerical modeling analyses indicate that there is no clear correlation between the location of the melting region in arcs and convergence rates (Grove et al, , ), or conversely to Molnar et al's () proposal, there is a trenchward arc broadening with increasing convergence (Karlstrom et al, , Figure 10a). The latter is exactly the opposite evolution followed by the late Early‐Late Cretaceous arc in the study area which expanded toward the continental interior.…”