Oriented quartz + calcic amphibole inclusions in omphacite from the Saualpe and Pohorje Mountain eclogites, Eastern Alps-An assessment of possible formation mechanisms based on IR- and mineral chemical data and water storage in Eastern Alpine eclogites
- Author(s)
- Jürgen Konzett, Eugen Libowitzky, Clivia Hejny, Christine Miller, Alberto Zanetti
- Abstract
The compn. of mineral phases and their modal proportions have been detd. for three representative Eoalpine eclogites from the Saualpe type locality/Eastern Austria (sample SKP31) and the Pohorje Massif/Slovenia (CM31/03 and CM15/01) using electron microprobe, laser ICP-MS, IR spectroscopy and modal anal. to evaluate possible mechanisms for the formation of composite oriented calcic amphibole + quartz inclusions (COIs) in omphacite and to assess the relative importance of hydrous and nominally anhyd. phases as H2O carriers in these eclogites. For omphacites in CM31/03 with a zonal distribution of COIs, a comparison of water and trace element concns. of areas contg. COIs and those free of COIs and a comparison with the trace element concn. of calcic amphibole indicate that COIs have formed through an open-system alteration of clinopyroxene and not through a closed system exsoln. process. In sample SKP31, both textural and mineral chem. evidence suggests that COIs did not form by exsoln. involving a Ca-Eskola component in clinopyroxene but formed by progressive growth under eclogite-facies P-T conditions and prior to the onset of retrogressive symplectite formation analogous to the formation of poikiloblastic quartz-calcic amphibole grains in the matrix. Bulk H2O contents of the eclogites are between ca. 750 and 2150 ppm with 6-25% of the total water contributed by nominally anhyd. minerals (NAMs). Because of high modal amts. of 37-65%, omphacite is the major nominally anhyd. water carrier, contg. 145-580 ppm H2O with significant concn. variations on a thin section scale. Due to their very low H2O concns. of <5-10 ppm (garnet, kyanite) or insignificant modal amts. 3% (rutile) the remaining NAMs contribute less than 1.5% to the bulk eclogite H2O content. Calcic amphibole forming part of COIs may be a major carrier of H2O as evidenced by CM31/03 contg. both COIs and texturally primary calcic amphibole.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Leopold-Franzens-Universität Innsbruck, Università degli studi di Pavia
- Journal
- Lithos
- Volume
- 106
- Pages
- 336-350
- No. of pages
- 15
- ISSN
- 0024-4937
- DOI
- https://doi.org/10.1016/j.lithos.2008.09.002
- Publication date
- 2008
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1030 Physics, Astronomy, 105116 Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/53657216-46ca-4d46-a32d-fc110ba6962b