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Petrography and mineral chemistry of mantle xenoliths in a carbonate-rich melilititic tuff from Mt. Vulture volcano, southern Italy

Jones, AP; Kostoula, T; Stoppa, F; Woolley, AR; (2000) Petrography and mineral chemistry of mantle xenoliths in a carbonate-rich melilititic tuff from Mt. Vulture volcano, southern Italy. MINERALOGICAL MAGAZINE , 64 (4) 593 - 613.

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Abstract

We present petrographic and mineralogical data for 21 mantle xenoliths (12 Iherzolites, 8 wehrlites and 1 composite) selected from a suite of more than 70 samples collected from the Monticchio Formation, Mr. Vulture volcano, southern Italy. The xenoliths an rounded, coarse- to porphyroelastic-textured, and very fresh, with the following equilibrated mineral assemblages; olivine (Fo(90-92)), orthopyroxene (similar to En(89), Wo(2.0)), clinopyroxene (Mg-90-(92), 3-6% Al2O3, 1-1.5% Cr2O3), and chrome-spinel (14-20% MgO, similar to 30-40% Cr2O3). Many xenoliths contain partial melt glasses and accessory sulphide (pentlandite). Some contain primary mica (phlogopite with similar to 4% FeO, 1.8% Cr2O3, 1.4-2.8% TiO2) with slightly zoned rims (Fe-, Ti-, Al-enriched). One contains relies of garnet (pyrope; Mg-84). Secondary veins in several xenoliths contain carbonate with significant Sr levels (similar to 0.5-1.0% SrO), occasional apatite and scarce melanite, all typical of carbonatites and presumably related to the host magma (melilitite/carbonatite). Although amphibole is a common megacryst in the same volcanic units, no primary amphibole was found in the xenoliths themselves. Calculated pressures and temperatures using a range of geothermometers/barometers give values of 14-22 kbar and 1050-1150 degrees C. In particular, the En-Sp and Di-Sp thermo/barometers (Mercier, 1980) show a good positive correlation between P and T. The Monticchio xenoliths lie on the high-T side of an 'oceanic' geotherm. The xenolith geotherm is hotter than general heat flow values in this region at the current day (50 mWm(-2)) but it compares well with the high-pressure end of a typical alkaline continental rift.

Type:Article
Title:Petrography and mineral chemistry of mantle xenoliths in a carbonate-rich melilititic tuff from Mt. Vulture volcano, southern Italy
Location:UNIV COLL LONDON, LONDON, ENGLAND
Keywords:Italy, carbonatite, lherzolite, wehrlite, peridotite, mantle xenoliths, melilitite, ULTRAMAFIC XENOLITHS, PETROLOGY, TANZANIA, PYROXENE, RECRYSTALLIZATION, PETROGENESIS, LHERZOLITE, TEXTURES, GLASSES, OLIVINE
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences

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