Syngenetic inclusions of silicate and carbonate melts were found and examined in olivine and melilite in fine-grained melilitite lavas, bombs, and lapilli tuffs of Pian di Celle volcano in central Italy. The silicate melts conserved in the inclusions are chemically different. The highest temperature (>> 1360°C) melt type, cor- responding to alkaline pyroxenite in composition, was found in inclusions in a fragment of the most magnesian phenocryst of Fo97, which could be a mantle xenocryst. There are good reasons to believe that the composition of these inclusions reflects the composition of either the primitive melts or the conserved relics of the depleted mantle. Fo92–91 and melilite most often contain inclusions of melilitite melts and their derivatives, while Fo91–88 also bears inclusions of trachybasalt–trachytic melts. Their evolutionary trends have different directions: the melilitite trend is directed toward hyperagpaitic melts and is characterized by an enrichment in alkalis and depletion aluminum, while the trachybasaltic melts become enriched in silicon and aluminum in the course of their evolution, i.e., their trend is directed toward miaskitic aluminous residues. The melilitite melt inclusions are higher temperature (> equal1360°C), whereas the trachybasalt inclusions homogenize at 1100–1200°C. The presence of the latter suggests that the magmatic chamber could contain trachybasaltic melts, along with volumetrically predominant kamafugite magma. The inflow of the former was insignificant and did not notably affect the evolutionary trend of the melilititic melts. The trachybasaltic melts could be genetically related to the alkaline basaltoid magma of the Roman comagmatic province. The carbonate inclusions comprise silicate–carbonate and predominantly carbonate varieties, whose presence is obviously related to silicate–carbonate immiscibility of the magma, a phenomenon that seems to have first occurred at significant depths and temperatures above 1300°C. The salt melts evolved from silicate-bearing alkaline to predominantly calcic carbonate liquids with a simultaneous enrichment in Ba, Sr, F, and Cl. Our results and analysis of literature materials led us to conclude that the liquidus crystallization of melilite in natural larnite-normative systems can proceed only at carbonate–silicate immiscibility.

Genesis of melilitite rocks of Pian di Celle Volcano, Umbrian Kamafugite Province, Italy: evidence from melt inclusions in minerals

STOPPA, Francesco;
2003-01-01

Abstract

Syngenetic inclusions of silicate and carbonate melts were found and examined in olivine and melilite in fine-grained melilitite lavas, bombs, and lapilli tuffs of Pian di Celle volcano in central Italy. The silicate melts conserved in the inclusions are chemically different. The highest temperature (>> 1360°C) melt type, cor- responding to alkaline pyroxenite in composition, was found in inclusions in a fragment of the most magnesian phenocryst of Fo97, which could be a mantle xenocryst. There are good reasons to believe that the composition of these inclusions reflects the composition of either the primitive melts or the conserved relics of the depleted mantle. Fo92–91 and melilite most often contain inclusions of melilitite melts and their derivatives, while Fo91–88 also bears inclusions of trachybasalt–trachytic melts. Their evolutionary trends have different directions: the melilitite trend is directed toward hyperagpaitic melts and is characterized by an enrichment in alkalis and depletion aluminum, while the trachybasaltic melts become enriched in silicon and aluminum in the course of their evolution, i.e., their trend is directed toward miaskitic aluminous residues. The melilitite melt inclusions are higher temperature (> equal1360°C), whereas the trachybasalt inclusions homogenize at 1100–1200°C. The presence of the latter suggests that the magmatic chamber could contain trachybasaltic melts, along with volumetrically predominant kamafugite magma. The inflow of the former was insignificant and did not notably affect the evolutionary trend of the melilititic melts. The trachybasaltic melts could be genetically related to the alkaline basaltoid magma of the Roman comagmatic province. The carbonate inclusions comprise silicate–carbonate and predominantly carbonate varieties, whose presence is obviously related to silicate–carbonate immiscibility of the magma, a phenomenon that seems to have first occurred at significant depths and temperatures above 1300°C. The salt melts evolved from silicate-bearing alkaline to predominantly calcic carbonate liquids with a simultaneous enrichment in Ba, Sr, F, and Cl. Our results and analysis of literature materials led us to conclude that the liquidus crystallization of melilite in natural larnite-normative systems can proceed only at carbonate–silicate immiscibility.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11564/110877
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