Glacial pumping of a magma-charged lithosphere: A model for glaciovolcanic causality in magmatic arcs

摘要

Glacial loading and unloading can influence the rates and timing of magmatism in tectonic settings where the lithosphere is relatively thin and hot. In continental arcs, where the lithosphere is substantially thicker, nominal loading by surface glaciers is unlikely to affect the production of subduction-related magmas. However, geologic evidence suggests that a causal linkage between volcanism and glaciations in arcs does exist. The last deglaciation of the Garibaldi volcanic belt in southwestern British Columbia, Canada saw a similar to 5-fold volumetric increase in volcanism over the mean Pleistocene (background) rate that coincided with similar to 400 m of rapid postglacial crustal uplift. Here, we use a cylindrical, thin plate bending approximation to calculate the horizontally oriented stresses developed in the crust during glacial loading/unloading (up to +/- 12 MPa). The distribution of compressive and extensional stresses is shown to modulate magma transport and storage by facilitating or suppressing magma ascent by dike propagation. We use Monte Carlo simulations to track the depth of upward migrating magma bodies in the crust over a single glacial cycle (i.e., during crustal depression and rebound). During loading, volcanism is suppressed as magma becomes trapped by compressive deviatoric stress in the upper part of the crust. During unloading, relaxation of this stress acts to release accumulated magma from the upper crust and causes an increase in eruption rate immediately following deglaciation. This model of "glacial pumping" of a magma-charged lithosphere suggests a causal linkage between volcanism and glaciation in volcanic arcs that explains the persistent observation that the volume and timing of volcanism is correlated with the major climate cycles. (C) 2020 Elsevier B.V. All rights reserved.