Experimental data for a proposed empirical igneous geobarometer: Aluminum in hornblende at 10 kbar pressure

Abstract

Knowledge of the depth of solidification of talc-alkalic plutons is critical to understanding and unraveling the complex spatial, temporal, and chemical evolution of orogenic belts. An empirical geobarometer has recently been proposed based on the total Al content (AlT) of near-solidus calcic hornblendes in tonalite and granodiorite intrusive rocks in the pressure range < 1 to 8 kbar. Pressures were estimated from mineral assemblages in associated metamorphic country rocks. We report experimental data on newly crystallized near-solidus amphiboles in partly melted, vapor-absent garnet tonalite at 10 kbar that provide some experimental support for the proposed geobarometer consistent with the extrapolated empirical result, and confirm its limited applicability to specific, multimineral assemblages.