Abstract
Amphibole crystallization from hydrous high-magnesium andesite (Shiveluch volcano, Kamchatka) melt has been studied experimentally at pressures 2, 3, 5 kbar. Slightly subliquidus temperatures have been selected for amphibole crystallization. Amphiboles with close to the equilibrium composition have been obtained at low undercoolings in short 4 hours experiments. We select octahedral aluminium content and sum of high charged cations (Ti 4+ , Fe 3+ ) all evaluated with the 13eCNK method as master parameters reflecting pressure of amphibole formation. Asymptotic maximum of Al VI content at the sum Ti+Fe 3+ =0 as a function of pressure was calculated following negative linear correlation trend for each run of the original and published experimental data sets. The derived novel Al VI in amphibole barometer is calibrated in the pressure range of 2-12 kbar for andesitic and basaltic magmas. Reliability and validity of the new geobarometer were tested on the amphibolized ultramafic xenoliths from the Shiveluch Volcano (Kamchatka) and Dish Hill (California). In both cases our estimates appear to be equal within the uncertainty of the method to the predictions done by two-pyroxene geo-thermo-barometer (Putirka, 2008).
Highlights
Amphibole crystallization from hydrous high-magnesium andesite (Shiveluch volcano, Kamchatka) melt has been studied experimentally at pressures 2, 3, 5 kbar
Reliability and validity of the new geobarometer were tested on the amphibolized ultramafic xenoliths from the Shiveluch Volcano (Kamchatka) and Dish Hill (California)
Amphibole is common phase crystallizing from hydrous magmas
Summary
Amphibole crystallization from hydrous high-magnesium andesite (Shiveluch volcano, Kamchatka) melt has been studied experimentally at pressures 2, 3, 5 kbar. Reliability and validity of the new geobarometer were tested on the amphibolized ultramafic xenoliths from the Shiveluch Volcano (Kamchatka) and Dish Hill (California) In both cases our estimates appear to be equal within the uncertainty of the method to the predictions done by two-pyroxene geo-thermo-barometer (Putirka, 2008). Amphibole is a mineral typical for calk-alkaline magmas stable at water content above ca 2 wt.% in the pressure range 1.5-12 kbar or from the crustal to near Moho (crust-mantle boundary) depths This phase composition reflects PT and fO2 of the parental melt and is used to calibrate solo amphibole (Schmidt, 1992; Anderson & Smith 1995) and amphibole-plagioclase (Blundy & Holland, 1990) geo thermo-barometers. In this study we employ this correlation to derive novel AlVI in amphibole geo-barometer while using new data of the experiments with hydrous andesitic melt at pressures 2, 3, 5 kbar. A new geo-barometer was applied to estimate equilibration pressure of mafic xenoliths from the Shiveluch volcano (Kamchatka) and Dish Hill (California)
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