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Influence of high strain rate deformation on (super 40) Ar/ (super 39) Ar mica ages from marble mylonites (Syros, Greece)

Anna Rogowitz, Benjamin Huet, David Schneider and Bernhard Grasemann
Influence of high strain rate deformation on (super 40) Ar/ (super 39) Ar mica ages from marble mylonites (Syros, Greece)
Lithosphere (July 2015) 7 (5): 535-540

Abstract

Interpreting isotopic ages as deformation ages when they are acquired from moderate-temperature metamorphic environments can be a challenging task. Syros Island (Cyclades, Greece) is famous for Eocene high-pressure metamorphic rocks reworked by localized Miocene greenschist-facies deformation. In this work, we investigate phengites from coarse-grained marbles, which experienced the high-pressure event, and phengites from fine-grained localized marble shear zones attributed to the low-grade Miocene deformation. Based on structural criteria, both events can be easily discriminated because of their opposing kinematics. Laser-heating (super 40) Ar/ (super 39) Ar analysis on phengite yielded a 40 + or - 1.6 Ma age for the host rock and a 37 + or - 1.3 Ma age for the shear zone. Both ages are statistically indistinguishable, consistent with the regional Eocene event, and not the Miocene deformation event responsible for the formation of the shear zone. Thermodynamic modeling indicates that the observed high-variance mineral assemblage is stable without compositional change along the pressure-temperature path followed by the rocks of Syros. Although the marble within the shear zone was deformed at extremely fast strain rates (10 (super -10) s (super -1) ), we observed no intracrystalline deformation of phengite grains and no resetting in the isotopic system, because strain was mostly accommodated by calcite. Consequently, a high strain rate does not necessarily create deformation ages in rocks with high-variance assemblages, such as marble mylonites.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 7
Serial Issue: 5
Title: Influence of high strain rate deformation on (super 40) Ar/ (super 39) Ar mica ages from marble mylonites (Syros, Greece)
Affiliation: University of Vienna, Department of Geodynamics and Sedimentology, Vienna, Austria
Pages: 535-540
Published: 20150706
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 50
Accession Number: 2015-078928
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N37°25'60" - N37°25'60", E24°55'00" - E24°55'00"
Secondary Affiliation: University of Ottawa, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201534
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