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A simple mechanism for mid-crustal shear zones to record surface-derived fluid signatures

Tom Raimondo, Chris Clark, Martin Hand, John Cliff and Robert Anczkiewicz
A simple mechanism for mid-crustal shear zones to record surface-derived fluid signatures
Geology (Boulder) (April 2013) 41 (6): 711-714


Ion microprobe analyses of garnet porphyroblasts from three separate splays of the mid-crustal Walter-Outalpa shear zone, Curnamona Province, South Australia, indicate homogeneous delta (super 18) O values of <3 ppm. Integrated Lu-Hf geochronology and electron microprobe compositional mapping demonstrate that closed-system growth of these isotopically light garnets initiated as early as 531 Ma, prior to peak metamorphism and deformation during the Delamerian Orogeny (514-490 Ma). We attribute this to the prograde burial and dehydration of altered fault panels under thick sedimentary sequences during pre-orogenic basin formation. Contrary to established fluid transport models, surficial fluid signatures were not imposed at depth by large fluxes of downward-penetrating fluids, but rather by the exposure and meteoric alteration of fault rocks that were subsequently buried and reactivated as ductile shear zones. The existence of low delta (super 18) O values in deeply exhumed shear zones may therefore be indicative of fault structures that have a prior history of surface exposure, weathering, burial and re-exposure.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 41
Serial Issue: 6
Title: A simple mechanism for mid-crustal shear zones to record surface-derived fluid signatures
Affiliation: University of South Australia, School of Natural and Built Environments, Adelaide, South Aust., Australia
Pages: 711-714
Published: 20130404
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 20
Accession Number: 2013-041367
Categories: Structural geologyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2013194
Illustration Description: illus. incl. geol. sketch map
S38°00'00" - S26°00'00", E129°00'00" - E141°00'00"
Secondary Affiliation: Curtin University, AUS, AustraliaUniversity of Adelaide, AUS, AustraliaUniversity of Western Australia, AUS, AustraliaPoliash Academy of Sciences, POL, Poland
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: 201326
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