Phase equilibria in the silica-undersaturated part of the KAlSiO4-Mg2SiO4-Ca2SiO4-SiO2-F system at 1 atm and the larnite-normative trend of melt evolution

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doi: 10.1007/s004100050397
Authors:Veksler, Ilya V.; Fedorchuk, Yana M.; Nielsen, Troels F. D.
Author Affiliations:Primary:
Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow, Russian Federation
Geological Survey of Denmark and Greenland, Denmark
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 131(4), p.347-363. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1998
Note:In English. Includes appendices. 37 refs.; illus., incl. 6 tables
Summary:On the pseudo-ternary forsterite-diopside-KAlSiO3F2 join, forsterite, diopside, F-phlogopite and leucite crystallization field and a fluoride-silicate liquid immiscibility solvus are present on the liquidus surface. Sub-liquidus and sub-solidus phases include akermanite, cuspidine, spinel, fluorite and some other minor fluorine phases. The second system studied is the pseudo-binary akermanite-F-phlogopite join that intersects the forsterite-diopside-KAlSiO3F2 join; akermanite, forsterite, diopside, F-phlogopite, leucite and cuspidine crystallize on this join. Forsterite and leucite are related to F-phlogopite by a reaction with the F-bearing liquid: fo + lc + liquid + phl, the reaction proceeding until forsterite or leucite are completely consumed; reaction T and resulting phase association depend on batch composition. Thus, leucite is not stable in the sub-solidus of the akermanite-F-phlogopite join, but is preserved in part of the forsterite-diopside-KAlSiO3F2 system here forsterite reacts out, or does not crystallize at all. The phlogopite-in reaction has an important effect on the composition of the coexisting liquid; those liquids initially saturated in forsterite evolve to extremely Ca-rich larnite-normative residuals. The data show that larnite-normative melilitolites can crystallize from evolved melilitic melts generated from 'normal' melanephelinite parental magmas with no normative larnite. Evolution towards melilitites requires fractionation of phlogopite-bearing assemblages until volatile pressure. [R.A.H.]
Sections:Experimental mineralogy
Subjects:Akermanite; Assemblages; Chain silicates; Chemical composition; Clinopyroxene; Crystallization; Diopside; Electron probe data; Experimental studies; Forsterite; Fractional crystallization; Framework silicates; Glasses; Igneous rocks; Instruments; Leucite; Magmas; Melilite group; Melts; Mica group; Nesosilicates; Olivine group; Orthosilicates; Phase equilibria; Phlogopite; Pressure; Pyroxene group; Sheet silicates; Silicates; Sorosilicates; Temperature; Topology; Volcanic rocks
Abstract Numbers:98M/3720
Record ID:1999057565
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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