The significance of garnet in the Permo-Carboniferous volcanic rocks of the Pyrenees

摘要: Garnet occurs within rhyolitic to dacitic lavas, ignimbrites and volcaniclastic sediments of the Pyrenean calc-alkaline Permo-Carboniferous volcanic rocks. On basis texture major trace element composition, garnet is interpreted as having a phenocrystal opposed xenocrystal or restite origin. The silicic volcanics are strongly peraluminous, consistent with derivation partial melt from sedimentary source. They were erupted contemporaneously Hercynian thermal anomaly, which produced regional granulite facies metamorphism anatectic granites. ‘Late granodiorites’ also intruded at about this time. Geochemical data suggest that petrogenesis rocks differed granodiorites. REE garnet/matrix partition coefficients for garnets welded ignimbrite similar those reported other in rhyolites. abundances imply crystallized HREE depleted considered reflect effects restite. Experimental constraints pressures >4–5kb, implying rhyolites originated > 14–17km depth rapidly these depths order survive. These figures place on regime prevailing late stages orogeny.