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Evidences for brittle deformation events in eclogite-facies conditions: the case of the Mt. Emilius kilppe (Western Alps)

Abstract : Eclogitic rocks are crucial in tectonics as they provide key constraints on both the evolution (P-T-t paths) and the deformation modes sustained by the rocks in subduction zones. We herein focus on eclogitized flattened mafic bodies remnants exposed within granulites from the continental basement slice of the Mt. Emilius klippe (Western Alps, Italy). These eclogites exhibit highly deformed (up to mylonitic) garnetite and clinopyroxenite levels found as clasts within meter-thick eclogitic shear zone formed close to the metamorphic peak conditions under lawsonite bearing eclogite facies conditions. The garnet-rich levels tend to behave in a brittle fashion while deformation within clinopyroxene-rich levels is mostly accommodated by creep, as evidenced by the presence of elongated grains, subgrains boundaries and intense grain size reduction. Especially, crystallographic preferred orientation (CPO) measurements in garnet indicate a quasi-random distribution. In most of the clinopyroxene levels nevertheless, the CPO is relatively strong, with multiples of uniform distribution varying from 4 to 5.5 (value of 1 is random texture). This CPO is characterized by a strong alignment of poles of the planes (001) parallel to the lineation and poles of the planes (100) and directions of the planes [010] distributed along girdles cross-cutting the foliation plane. Based on a petrological study, from the outcrop to the microscopic scale, we propose a tectono-metamorphic history of the Mt. Emilius eclogites. This history related to the alpine eclogitic event, allow to link the metamorphic P-T path and the deformation processes in association with the chemical evolutions that could lead to the formation of the Mt. Emilius brecciated eclogites in the Arbole region. This model is consistent with the alternating ductile and brittle events that developed in the same metamorphic facies, at P~2.0-2.5 GPa and T~500-550C, closely associated to metamorphic fluid circulations. Thus, our study attests that the material along the subduction interface, at HP-LT conditions, can locally be brittle where deformation is classically envisioned as ductile.
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https://hal-insu.archives-ouvertes.fr/insu-01388170
Contributor : Isabelle Dubigeon <>
Submitted on : Wednesday, October 26, 2016 - 3:48:38 PM
Last modification on : Friday, April 5, 2019 - 8:17:50 PM

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  • HAL Id : insu-01388170, version 1

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Solenn Hertgen, Philippe Yamato, Luis Morales, Samuel Angiboust. Evidences for brittle deformation events in eclogite-facies conditions: the case of the Mt. Emilius kilppe (Western Alps). 25 ème Réunion des sciences de la Terre (RST 2016), Société Géologique de France, Oct 2016, Caen, France. pp.160. ⟨insu-01388170⟩

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