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| Titel |
Geospeedometry in the inverted metamorphic gradient of the Nestos Thrust Zone in central Rhodope (Northern Greece) |
| VerfasserIn |
Stefania Cioldi, Evangelos Moulas, Jean-Pierre Burg |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102590
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| Publikation (Nr.) |
 EGU/EGU2015-1919.pdf |
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| Zusammenfassung |
| Thrust tectonics and inverted metamorphic gradients are major consequences of large
and likely fast movements of crustal segments in compressional environments.
The purpose of this study is to investigate the tectonic setting and the timescale of
inverted metamorphic zonations related to crustal-scale thrusting. The aim is to
contribute understanding the link between mechanical and thermal evolution of
major thrust zones and to clarify the nature and the origin of orogenic heat. The
Rhodope metamorphic complex (Northern Greece) is interpreted as a part of the
Alpine-Himalaya orogenic belt and represents a collisional system with an association of
both large-scale thrusting and pervasive exhumation tectonics. The Nestos Shear Zone
overprints the suture boundary with a NNE-dipping pile of schists displaying inverted
isograds. The inverted metamorphic zones start from chlorite-muscovite grade at the
bottom and reach kyanite-sillimanite grades with migmatites in the upper structural
levels.
In order to reconstruct the thermo-tectonic evolution of inverted metamorphic zonation,
reliable geochronological data are essential. 40Ar/39Ar geochronology with step-heating
technique on white mica from micaschists provided a temporal resolution with the potential
to characterize shearing. 40Ar/39Ar dating across the Nestos Shear Zone yields Late
Eocene-Early Oligocene (40-30 Ma) cooling (~400-350Ë C) ages, which correspond to local
thermo-deformation episodes linked to late and post-orogenic intrusions. U-Pb Sensitive
High Resolution Ion Microprobe (SHRIMP) zircon geochronology on leucosomes from
migmatitic orthogneisses were considered to estimate the age of peak metamorphic
conditions, contemporaneous with anatexis. U-Pb ages of zircon rims specify regional partial
melting during the Early Cretaceous (160-120 Ma). This is in disagreement with previous
assertions, which argued that the formation of leucosomes in this region is Late Eocene
(42-35 Ma) and implied multiple subductions and multiple metamorphic cycles during
orogeny.
Garnet geospeedometry considers the kinetic response of minerals and allowed estimating
the absolute time-dependent thermal evolution by diffusive element profiles in garnet.
Inverse-fitting numerical model considering Fractionation and Diffusion in GarnEt
(FRIDGE) calculates garnet composition profiles by introducing P-T-t paths and
bulk-rock composition of a specific sample. Preliminary results of Fe-Mg – Ca – Mn
garnet fractionation-diffusion modelling indicate very short timescale (between 2
and 5 Ma) for peak metamorphic conditions in the Rhodope collisional system. |
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