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U–Pb zircon geochronology of unusual eclogite-facies rocks from Syros and Tinos (Cyclades, Greece)

Published online by Cambridge University Press:  01 March 1999

MICHAEL BRÖCKER  and
MICHAEL ENDERS
MICHAEL BRÖCKER
Affiliation:
Zentrallaboratorium für Geochronologie, Institut für Mineralogie, Corrensstrasse 24, D-48149 Münster, Germany
MICHAEL ENDERS
Affiliation:
Institut für Mineralogie, Corrensstrasse 24, D-48149 Münster, Germany
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Abstract

Low-temperature eclogite-facies rocks from Syros and Tinos (Cyclades, Greece) include meta-igneous blocks of unclear origin (meta-olistostrome or tectonic mélange) with very high trace element concentrations (e.g. Zr up to 4850 ppm; Y up to 475 ppm). The unusual geochemistry is considered to be the result of metasomatic alteration in a subduction-zone environment. Locally, metasomatic exchange with an ultramafic matrix further enhanced compositional anomalies. A concordant U–Pb zircon age of 78±1 Ma recorded for an omphacitite from Syros is interpreted as the time of pre-Eocene high-pressure metamorphism in the Cyclades. Zircon dates of 61 and 63 Ma for a jadeitite from Tinos possibly indicate an additional discrete event (deformation?). These results are a first geochronological indication that high-pressure metamorphism in the Cyclades commenced significantly earlier than indicated by previous white mica chronology which provided ages between c. 50 and 40 Ma.

Type
Research Article
Information
Geological Magazine , Volume 136 , Issue 2 , March 1999 , pp. 111 - 118
Copyright
© 1999 Cambridge University Press

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