Significance of Europium anomalies in silicate melts and crystal-melt equilibria: a re-evaluation

Autor: G. K. Muecke, P. Möller
Rok vydání: 1984
Předmět:
Zdroj: Contributions to Mineralogy and Petrology. 87:242-250
ISSN: 1432-0967
0010-7999
DOI: 10.1007/bf00373057
Popis: Although europium speciation in silicate melts partly reflects prevailing oxygen fugacities, melt composition and structure play the major role in determining Eu2+/ Eu3+ ratios and europium partitioning into mineral phases. Experimental evidence by different investigators on the magnitude of the compositional effect on Eu2+/Eu3+ provides consistent results only if account is taken of the oxygen buffer system employed in the experiments. The medium-dependent reduction of europium can be understood in terms of the preferential stabilization of Eu2+ by a strong aluminosilicate complex in the melt phase, and to a much lesser degree by metasilicate complexes. The stability of these complexes increases as the field strength of the associated cation species decreases. Hence Eu2+-aluminosilicate complexes are preferentially stabilized relative to trivalent lanthanides in melts of appropriate composition and their presence minimizes the enthalpy of the melt. The influence of these complexes is particularly pronounced in melts with a high feldspathic component and a strongly polymerized structure. Their petrogenetic influence is best documented through the behaviour of europium relative to the other lanthanides during “anhydrous” anatexis in high-grade metamorphic terrains and in the anomalous europium partition coefficients of phenocryst phases which formed during the crystallization of highly silicic magmas.
Databáze: OpenAIRE
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