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The status of the Makrotantalon Unit (Andros, Greece) within the structural framework of the Attic-Cycladic Crystalline Belt

Published online by Cambridge University Press:  19 July 2013

MAGDALENA H. HUYSKENS  and
MICHAEL BRÖCKER
MAGDALENA H. HUYSKENS*
Affiliation:
Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, 48149 Münster, Germany
MICHAEL BRÖCKER
Affiliation:
Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, 48149 Münster, Germany
*
†Author for correspondence: [email protected]
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Abstract

This study focuses on the status of the Makrotantalon Unit (Andros, Greece) within the framework of the Cycladic nappe stack. We document unambiguous evidence that this unit has experienced blueschist-facies metamorphism and identify previously unknown lawsonite ± pumpellyite assemblages in glaucophane-free metasediments. The position of the presumed tectonic contact at the base of this unit is vague, but roughly outlined by serpentinites. Only a single outcrop displays a weak angular unconformity with cohesive cataclasites in the footwall. Rb–Sr geochronology was carried out on 11 samples representing various rock types collected within or close to inferred or visible fault zones. Owing to a lack of initial isotopic equilibration and/or subsequent disturbance of the Rb–Sr isotope systematics, isochron relationships are poorly developed or non-existing. In NW Andros, direct dating of distinct displacement events has not been possible, but a lower age limit of ~ 40 Ma for final thrusting is constrained by the new data. Sporadically preserved Cretaceous ages either indicate regional differences in the P–T–d history or a different duration of metamorphic overprinting, which failed to completely eliminate inherited ages. The detachment on the NE coast records a later stage of the structural evolution and accommodates extension-related deformation. Apparent ages of ~ 29–25 Ma for samples from this location are interpreted to constrain the time of a significant deformation increment. On a regional scale, the Makrotantalon Unit can be correlated with the South Evia Blueschist Belt, but assignment to a specific subunit is as yet unconfirmed.

Keywords

Makrotantalon UnitAndrosCycladesAttic-Cycladic Crystalline BeltGreeceRb–Sr geochronology
Type
Original Articles
Information
Geological Magazine , Volume 151 , Issue 3 , May 2014 , pp. 430 - 446
Copyright
Copyright © Cambridge University Press 2013 

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Footnotes

‡

Present address: Research School of Earth Sciences, The Australian National University, Bldg 142 Mills Road, 0200 Canberra, ACT, Australia

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