Amphibole “sponge” in arc crust?

(28 August 2007)

New research published in Geology by Jon Davidson and others explains geochemical trends in arc volcanics. Carefully-filtered geochemical data from a number of arc volcanoes show a surprising global trend, consistent with a role for the mineral amphibole in the evolution of most suites. Why is this important? Most of the rocks don't actually contain amphibole so it must be a process which occurs at depth and is overprinted - at least petrographically - by processes occurring in shallow magma chambers. Amphibole is important because; 1. It contains water, and therefore may filter out a significant fraction of the water originally present in the magma 2. Recycling of amphibole cumulates is a way to introduce water, along with other amphibole-compatible trace elements, back into the mantle, and 3. As geotherms rise in the crust where amphibole cumulates are stored, the assemblage will eventually melt to produce silicic water-rich magmas which may both provide shallow-level ore-forming fluids, and give rise to large-volume explosive volcanic eruptions. The full reference is: Jon Davidson, Simon Turner, Heather Handley, Colin Macpherson and Anthony Dosseto (2007) Amphibole “sponge” in arc crust? Geology, v.35 p. 787–790.