Geochemical modeling of low melt-fraction anatexis in a peraluminous system: The Pena Negra complex (central Spain)

Journal Article · Mon Jul 01 00:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90029-5· OSTI ID:5694589

Bea, F ^[1]

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1. Univ. of Salamanca (Spain)

A study was made of the chemical fractionation associated with four cases of anatectic segregation of low melt-fraction cordieritic granites from migmatized meta-greywackes. The aims of the study were to (1) reveal the fractionation patterns of major and trace elements, (2) compare the major element chemistry of leucogranites and the quantitative behavior of source minerals during anatexis - inferred by mass-balance adjustment - with available experimental data for peraluminous systems, and (3) discuss the behavior of trace elements in crustal melting by comparing the chemically determined composition of leucogranites with the results of three fractionation models. Two of these assume a perfect diffusive behavior of trace elements within residual solids, but they use a different set of distribution coefficients. The third assumes a perfect nondiffusive behavior. In relation to their source rocks, the leucogranites are strongly depleted in Li, Transition Elements, and Light Rare Earth Elements, but enriched in K{sub 2}O, SiO{sub 2}, and Ba. Mass balance analysis using the Anatexis Mixing Model shows that the chemistry of cordierite leucogranites is compatible with its having originated by closed-system, water-undersaturated anatexis on previously migmatized meta-greywackes, leaving a residue enriched in cordierite plus biotite and exhausted in K-feldspar. Biotite melts congruently unless important amounts of sillimanite were also present in the source. Compared with experimental metals obtained from sources with the same chemical composition but with a different femic mineralogy (biotite + sillimanite, instead of cordierite + biotite), the Pena Negra leucogranites are richer in K{sub 2}O and MgO with a lower Fe/(Fe + Mg) ratio. The differences in magnesium are believed to result from the changes in the mineral assemblage of the source rocks.

• OSTI ID: 5694589
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 55:7; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GRANITES
GEOCHEMISTRY
MINERALOGY
PETROGENESIS
GRAYWACKE
METAMORPHISM
ALUMINIUM OXIDES
ALUMINIUM SILICATES
BIOTITE
CHEMICAL COMPOSITION
FRACTIONATION
GEOLOGIC HISTORY
GEOLOGIC MODELS
MAGMATISM
PETROLOGY
SPAIN
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMISTRY
DEVELOPING COUNTRIES
EUROPE
GEOLOGY
IGNEOUS ROCKS
MICA
MINERALS
OXIDES
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
580000* - Geosciences