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Eclogite breccias in a subducted ophiolite; a record of intermediate-depth earthquakes?

Samuel Angiboust, P. Agard, P. Yamato and H. Raimbourg
Eclogite breccias in a subducted ophiolite; a record of intermediate-depth earthquakes?
Geology (Boulder) (June 2012) 40 (8): 707-710


Understanding processes acting along the subduction interface is crucial to assess lithospheric-scale coupling between tectonic plates and mechanisms causing intermediate-depth seismicity. Despite a wealth of geophysical studies aimed at better characterizing the subduction interface, we still lack critical data constraining processes responsible for seismicity within oceanic subduction zones. We herein report the finding of eclogite breccias, formed at approximately 80 km depth during subduction, in an almost intact 10-km-scale fragment of exhumed oceanic lithosphere (Monviso ophiolite, Western Alps). These eclogite breccias correspond to meter-sized blocks made of 1-10 cm fragments of eclogite mylonite cemented by interclast omphacite, lawsonite, and garnet, and were later embedded in serpentinite in a 30-150-m-wide eclogite facies shear zone. At the mineral scale, omphacite crack-seal veins and garnet zoning patterns also show evidence for polyphased fracturing-healing events. Our observations suggest that a possible seismic brecciation occurred in the middle part of the oceanic crust, accompanied by the input of externally derived fluids. We also conclude that these eclogite breccias likely mark the locus of an ancient fault zone associated with intraslab, intermediate-depth earthquakes at approximately 80 km depth.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 40
Serial Issue: 8
Title: Eclogite breccias in a subducted ophiolite; a record of intermediate-depth earthquakes?
Affiliation: Universite Pierre et Marie Curie, Institut des Sciences de la Terre de Paris, Paris, France
Pages: 707-710
Published: 20120608
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 27
Accession Number: 2012-065507
Categories: Structural geologyIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2012197; accessed on July 2, 2012
Illustration Description: illus. incl. sketch map
Source Medium: WWW
N44°30'00" - N45°00'00", E06°30'00" - E07°30'00"
Secondary Affiliation: Universite de Rennes I, FRA, FranceUniversite d'Orleans, FRA, France
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: 201234
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