First-report on Mesozoic eclogite-facies metamorphism preceding Barrovian overprint from the western Rhodope (Chalkidiki, northern Greece)

The Chalkidiki block in Northern Greece represents the southwesternmost piece of the ultrahigh-pressure Rhodope and has played an important role in the evolution of the North Aegean. The eastern part of the Chalkidiki block is a basement complex (Vertiskos Unit) that is made largely of Palaeozoic gr...

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Bibliographic Details
Published in:Lithos 2015-04, Vol.220-223, p.147-163
Main Authors: Kydonakis, Konstantinos, Moulas, Evangelos, Chatzitheodoridis, Elias, Brun, Jean-Pierre, Kostopoulos, Dimitrios
Format: Article
Language:English
Subjects:
Aegean
Earth Sciences
Eclogite
Garnet–staurolite schists
High-pressure low-temperature metapelites
Isochemical phase diagrams
Sciences of the Universe
Serbo-Macedonian
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Summary:The Chalkidiki block in Northern Greece represents the southwesternmost piece of the ultrahigh-pressure Rhodope and has played an important role in the evolution of the North Aegean. The eastern part of the Chalkidiki block is a basement complex (Vertiskos Unit) that is made largely of Palaeozoic granitoids and clastic sediments that metamorphosed during the Mesozoic. This basement is traditionally considered as part of the Rhodopean hanging-wall, an assignment mainly supported by the absence of high-pressure mineral indicators and the presence of a regional medium-pressure/medium-temperature amphibolite-facies Barrovian metamorphic imprint. Toward the west, the basement is juxtaposed with meta-sedimentary (Circum-Rhodope belt) and arc units (Chortiatis Magmatic Suite) that carry evidence of a Mesozoic high-pressure/low-temperature event. In this study, garnet–staurolite-mica schists from the eastern part of the basement were examined by means of micro-textures, mineral chemistry and isochemical phase-diagram sections in the system NCKFMASHMn(Ti) [Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–MnO–(TiO2)]. The schists represent former Mesozoic sedimentary sequences deposited on the Palaeozoic basement. We document the presence of a relict eclogite-facies mineral assemblage (garnet+chloritoid+phengite+rutile) in an amphibolite-facies matrix composed of garnet+staurolite+phengite±kyanite. Model results suggest the existence of a high-pressure/medium-temperature metamorphic event (1.9GPa/520°C) that preceded regional re-equilibration at medium-pressure/medium-temperature conditions (1.2GPa/620°C). Clearly, the eastern part of the Chalkidiki block (basement complex) retains memory of an as yet unidentified Mesozoic eclogitic metamorphic event that was largely erased by the later Barrovian overprint. In light of our findings, the basement complex of the Chalkidiki block shares a common tectono-metamorphic evolution with both the high-pressure units to the west, and the high-grade Rhodopean gneisses further to the northeast. Our results are consequential for the geodynamic reconstruction of the Rhodope since they require participation of the Chalkidiki block to the well-established Mesozoic subduction system. •We found eclogite-facies assemblage in a Barrovian complex of northern Greece.•The pelitic eclogites were re-equilibrated at amphibolite-facies conditions.•Our results suggest subduction of the Barrovian complex prior to the overprint.
ISSN:0024-4937
1872-6143
DOI:10.1016/j.lithos.2015.02.007