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501396 
Journal Article 
Jadeite-gneiss from the eclogite zone, Tauern Window, Eastern Alps, Austria: Metamorphic, geochemical and zircon record of a sedimentary protolith 
Miller, C; Konzett, J; Tiepolo, M; Armstrong, RA; Thoni, M 
2007 
1 
Lithos
ISSN: 0024-4937 
ELSEVIER 
AMSTERDAM 
93 
1-2 
68-88 
English 
WOS:000243631500004 
In the Eclogite Zone of the Tauern Window, a layer of strongly retrogressed leucocratic jadeite-bearing gneiss is intercalated between mafic kyanite-eclogites. The jadeite-gneiss consists of garnet + quartz + paragonite phengite zoisite + zircon + rutile + apatite+pyrite. Kyanite, jadeite or ompbacite are exclusively present as inclusions in gamet. Retrogressive hydration during exhumation led to a breakdown of matrix jadeite to form pseudomorphs of calcic amphibole + albite. Peak metamorphic conditions derived from the primary gneiss assemblage are 2.0-2.4 GPa at approximately 640 degrees C. Major, trace element and isotopic compositions of the jadeite-gneiss are consistent with a siliciclastic sedimentary protolith. Zircon morphology and zonation patterns reveal a complex history. The presence of fracture-truncated zircons suggests a detrital origin, whereas most internal structures and Th/U ratios are characteristic of zircons from magmatic rocks. In situ LA-ICP-MS and SHRIMP U-Pb geochronology and zircon geochemisty provide evidence of at least three magmatic events in the provenance area. These were dated at 466 +/- 2 Ma, 437 +/- 2 Ma and 288 9 Ma. Older ages ranging from 503 to 691 Ma are preserved in the cores of some zircon grains, suggesting derivation from peri-Gondwanan sources. Surprisingly, no firm evidence of the Tertiary high-pressure metamorphic event and subsequent retrograde overprint was seen in any of the studied zircons. However, some zircons show resorbed surfaces suggesting corrosion by a superficial fluid phase undersaturated in zirconium and one extensively altered porous zircon yielded highly discordant Pb-206/U-238 ages in the range 325-109 Ma documenting partial recrystallization by dissolution-reprecipitation of a highly reactive grain. (c) 2006 Elsevier B.V. All rights reserved. 
Tauern Window; Eastern Alps; high-pressure metasediment; U-Pb dating; zircon; high-pressure metamorphism; nappe central alps; u-pb ages; western; alps; trace-element; adula-nappe; sm-nd; geodynamic evolution; pre-variscan; geochronology 
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