The compositional variability of eudialyte-group minerals

J. Schilling, F. Y. Wu, C. McCammon, T. Wenzel, M. A.W. Marks, K. Pfaff, D. E. Jacob, G. Markl*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Citations (Scopus)

Abstract

Eudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic systems. Results are presented here of a combined EPMA, Mössbauer spectroscopy and LA-ICP-MS study and EGM which crystallized in various fractionation stages from different parental melts and mineral assemblages in silica over- and undersaturated systems are compared. Compositional variability is closely related to texture, allowing for reconstruction of locally acting magmatic to hydrothermal processes. Early-magmatic EGM are invariably dominated by Fe whereas hydrothermal EGM can be virtually Fe-free and form pure Mn end-members. Hence the Mn/Fe ratio is the most suitable fractionation indicator, although crystal chemistry effects and co-crystallizing phases play a secondary role in the incorporation of Fe and Mn into EGM. Mössbauer spectroscopy of EGM from three selected occurrences indicates the Fe3+/ΣFe ratio to be governed by the hydration state of EGM rather than by the oxygen fugacity of the coexisting melt. Negative Eu anomalies are restricted to EGM that crystallized from alkali basaltic parental melts while EGM from nephelinitic parental melts invariably lack negative Eu anomalies. Even after extensive differentiation intervals, EGM reflect properties of their respective parental melts and the fractionation of plagioclase and other minerals such as Fe-Ti oxides, amphibole and sulphides.

Original languageEnglish
Pages (from-to)87-115
Number of pages29
JournalMineralogical Magazine
Volume75
Issue number1
DOIs
Publication statusPublished - Feb 2011
Externally publishedYes

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