Amphibole-bearing Cumulate Inclusions, Grand Canyon, Arizona and their bearing on Silica-Undersaturated Hydrous Magmas in the Upper Mantle

Abstract

Rare inclusions in Holocene basanite within the western Grand Canyon are comprised of poikilitic titaniferous amphibole together with variable proportions of relatively Fe-rich clinopyroxene, orthopyroxene, olivine, Cr-poor spinel, and pyropic garnet, magnesian ilmenite, and titaniferous phlogopite. No feldspar has been found in the 219 inclusions investigated. Available experimental data suggest crystallization at approximately 20 kb (∼65 km depth) in a region where the crust is 30–40 km thick.