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Igneous garnets have the potential to strongly fractionate rare earth elements (REE). Yet informations on partition coefficients are very scant, and criteria for distinguishing between hydrothermal and magmatic garnets are ambiguous. To fill this gap, we present trace element and isotopic data for two types of Ca-rich garnets from phonolites (Mt. Somma-Vesuvius). Both Ca-garnet populations are different in their style and dynamics of fractionation: one population is progressively strongly depleted in HREE from core to rim, reflecting REE fractionation in the host phonolite via earlier-crystallized garnets. Such examples for extreme changes in HREE in garnets are only known for hydrothermal grandites by REE-bearing fluids. The second garnet population is homogeneous and formed in a closed system. Near-flat patterns between Sm and Lu confirm experimental data indicating lower D(Sm)/ D(Lu) for Ca-rich garnets than for e.g. pyrope-rich garnets. It follows: D Grt/PhMelt for La = 0.5, Sm = 48 and Yb = 110. [ABSTRACT FROM AUTHOR]

Glassy orthopyroxene granodiorite-tonalite (namedpinciniteafter type locality) was described from basaltic lapilli tuffs of the Pliocene maar near Pinciná village in the Slovakian part of the Pannonian Basin. Two pincinite types exhibitaqualitativelysimilar mineral composition (quartz, An20-55 plagioclase, intergranular silicic glass with orthopyroxene and ilmenite, ±K-feldspar), but strongly different redox potential and formationPTconditions. Peraluminous pincinite is reduced (6-7% of total iron as Fe3+ in corundum-normative intergranular dacitic glass) and contains ilmenite with 8-10 mol% Fe2O3 and orthopyroxene dominated by ferrosilite. High-density (up to 0.85 g/cm3) primary CO2 inclusions with minor H2, CH4, H2S, CO and N2 (<2 mol% total) are present in Qtz and Plg. EquilibriumPTconditions inferred from the intergranular Opx-Ilm-Glass assemblage and fluid density correspond to 1,170±50°C, 5.6±0.4 kbar, respectively. Metaluminous pincinite is more oxidised (25-27% of total iron as Fe3+ in diopside-normative intergranular glass of rhyolite-trachyte-dacite composition) and contains Fe2O3-rich ilmenite (17-29 mol%) associated with enstatite. Fluid inclusions are composed of CO2-H2O mixtures with up to 38 mol% H2O. Raman spectroscopy revealed H2S along with dominant CO2 in the carbonic phase. EquilibriumPTparameters for the intergranular Opx-Ilm-Glass assemblage correspond to 740±15°C, 2.8±0.1 kbar, respectively. Reducing gas species (<2 mol% total) in the CO2-inclusions of the peraluminous pincinite resulted from hydrogen diffusion due tofH2 gradient imposed during decrease of redox potential from the logfO2 values near QFM during Qtz + Plg growth, to QFM-2 incidental to the superimposed Opx + Ilm assemblage in the intergranular melt. The decrease in oxygen fugacity was recorded also in the metaluminous pincinite, where logfO2 values changed from ~QFM + 2.6 to QFM + 0.4, but hydrogen diffusion did not occur. Absence of OH-bearing minerals, major and trace element abundances (e.g. SREE 300-320, Nb 55-57, Th 4-31, Zr 240-300 ppm, FeOtot/MgO up to 11), and Sr-O isotope ratios in the pincinites are diagnostic of high-temperature anorogenic magmas originated by dehydration melting of biotite in quartz-feldspathoid crust (87Sr/86Sr>0.705-0.706, d18O>9‰ V-SMOW) around alkali basalt reservoir in depths between 17 and 20 km, and around late stage derivatives of the basalt fractionation, intruding the crust up to depths of 10-11 km. Low water activity in the pincinite parental melt was caused by CO2-flux from the Tertiary basaltic reservoirs and intrusions. The anatexis leads to generation of a melt-depleted granulitic crust beneath the Pannonian Basin, and the pincinites are interpreted as equivalents of igneous charnockites and enderbites quenched at temperatures above solidus and unaffected by sub-solidus re-equilibration and metamorphic overprint. [ABSTRACT FROM AUTHOR]