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Evidence from Mössbauer spectroscopy for intense localization of metamorphic fluid flow during the formation of spaced cleavage
Author(s) -
Boulter C.A.,
McConchie D.M.,
Clarke E.M.
Publication year - 1989
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/j.1365-3121.1989.tb00387.x
Subject(s) - cleavage (geology) , metamorphism , mössbauer spectroscopy , metamorphic rock , geology , quartz , spectroscopy , mineralogy , diagenesis , oxidizing agent , fluid inclusions , crystallography , geochemistry , chemistry , paleontology , physics , quantum mechanics , fracture (geology) , organic chemistry
Arenites in the low‐grade metasedimentary rocks of the Stirling‐Barren Group, Western Australia, contain discrete spaced cleavages. These in part are pure white mica, but up to 30% of the cleavage zones consists of fine‐grained quartz resulting from crystal plastic deformation. A modified Gresens analysis shows that the cleavage domains formed by a 50% volume loss associated primarily with SiO 2 and MgO concentration decreases of 58% and 37%, respectively, and a 12% decrease in Fe 2 O 3 . Mössbauer spectroscopy shows that the Fe 2+ : Fe 3+ ratio from lithon to cleavage changed from 50:SO to 15:85. This substantial difference cannot be accounted for by loss of iron. The data are best explained by the focusing of a highly oxidizing fluid through the cleavage domains where volumetric fluid rock ratios around 150 to 1 are indicated. In this example advectic processes appear to be important in low‐grade regional metamorphism.