A non-magmatic origin for compositionally zoned euhedral garnets in silicic Neogene volcanics from SE Spain

Niels Munksgaard

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The Mn-, Mg-, Ca- and Fe-zoning has been studied in 29 garnet crystals from 13 samples of peraluminous dacites and their inclusions in metamorphic rocks. The compositional range and zoning of the garnets from the dacites and those from the inclusions are almost identical. Typically the zoning consists of Mn- and Ca-rich cores and Mg- and Fe-rich rims, which is different from the pattern shown in garnets crystallized directly from a melt. Most zoning in the garnets may be explained by metamorphic growth involving a fractionation process. These findings support an interpretation of the dacite garnets as monocrystal inclusions corresponding with garnet crystals in the metamorphic rock inclusions. The Mg-Fe distribution between garnet and the cordierite and biotite in the metamorphic rock inclusions also supports this interpretation. Previous interpretations that the dacite garnets are of magmatic origin are difficult to accept. (Author's abstract)-E.v.P. Geological Inst., Copenhagen Univ., Oster Voldgade 10, 1350 Copenhagen K, Denmark. 
Original languageEnglish
Article number8
Pages (from-to)73-82
Number of pages10
JournalNeues Jahrbuch fuer Mineralogie (Abhandlungen)
Volume1985
Issue numberH.2
Publication statusPublished - Feb 1985
Externally publishedYes

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Garnets
Neogene
garnet
Zoning
Metamorphic rocks
dacite
zoning
metamorphic rock
crystal
Crystals
cordierite
Fractionation
biotite
fractionation
melt

Cite this

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abstract = "The Mn-, Mg-, Ca- and Fe-zoning has been studied in 29 garnet crystals from 13 samples of peraluminous dacites and their inclusions in metamorphic rocks. The compositional range and zoning of the garnets from the dacites and those from the inclusions are almost identical. Typically the zoning consists of Mn- and Ca-rich cores and Mg- and Fe-rich rims, which is different from the pattern shown in garnets crystallized directly from a melt. Most zoning in the garnets may be explained by metamorphic growth involving a fractionation process. These findings support an interpretation of the dacite garnets as monocrystal inclusions corresponding with garnet crystals in the metamorphic rock inclusions. The Mg-Fe distribution between garnet and the cordierite and biotite in the metamorphic rock inclusions also supports this interpretation. Previous interpretations that the dacite garnets are of magmatic origin are difficult to accept. (Author's abstract)-E.v.P. Geological Inst., Copenhagen Univ., Oster Voldgade 10, 1350 Copenhagen K, Denmark. ",
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A non-magmatic origin for compositionally zoned euhedral garnets in silicic Neogene volcanics from SE Spain. / Munksgaard, Niels.

In: Neues Jahrbuch fuer Mineralogie (Abhandlungen), Vol. 1985, No. H.2, 8, 02.1985, p. 73-82.

Research output: Contribution to journalArticleResearchpeer-review

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AB - The Mn-, Mg-, Ca- and Fe-zoning has been studied in 29 garnet crystals from 13 samples of peraluminous dacites and their inclusions in metamorphic rocks. The compositional range and zoning of the garnets from the dacites and those from the inclusions are almost identical. Typically the zoning consists of Mn- and Ca-rich cores and Mg- and Fe-rich rims, which is different from the pattern shown in garnets crystallized directly from a melt. Most zoning in the garnets may be explained by metamorphic growth involving a fractionation process. These findings support an interpretation of the dacite garnets as monocrystal inclusions corresponding with garnet crystals in the metamorphic rock inclusions. The Mg-Fe distribution between garnet and the cordierite and biotite in the metamorphic rock inclusions also supports this interpretation. Previous interpretations that the dacite garnets are of magmatic origin are difficult to accept. (Author's abstract)-E.v.P. Geological Inst., Copenhagen Univ., Oster Voldgade 10, 1350 Copenhagen K, Denmark. 

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