Rare-earth element and oxygen isotope studies of altered Variscan granites: The western Harz (Germany) and southern Sardinia (Italy)

G. Morteani, P. Möller, J. Hoefs

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18 Scopus citations

Abstract

Studies on whole-rock samples and mineral separates from granitoids of the Harz Mountains, Germany, and southern Sardinia, Italy, have revealed postmagmatic changes of rare-earth element (REE) concentrations and isotopic composition of oxygen. The REE distribution patterns of the altered rocks do not deviate significantly from the unaltered samples, but the REE patterns of the feldspars and biotites show characteristic changes. Some of the feldspars lost their typical positive Eu anomalies, whereas some of the biotites gained negative Ce anomalies. In the altered samples the quartz-feldspar oxygen isotopic fractionation is either too low or even reversed relative to primary magmatic pairs. The observed effects are discussed as the interactions of the cooling granitoids with either surface or magmatic waters. It is concluded that a high-temperature water-rock interaction with essentially magmatic waters best explains the observed phenomena.

Original languageEnglish
Pages (from-to)53-68
Number of pages16
JournalChemical Geology
Volume54
Issue number1-2
DOIs
StatePublished - 30 Jan 1986

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