Local origin of high pressure vein material in eclogite facies rocks of the Zermatt-Saas Zone, Switzerland

Citation
T. Widmer et Ab. Thompson, Local origin of high pressure vein material in eclogite facies rocks of the Zermatt-Saas Zone, Switzerland, AM J SCI, 301(7), 2001, pp. 627-656
Citations number
70
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
AMERICAN JOURNAL OF SCIENCE
ISSN journal
0002-9599 → ACNP
Volume
301
Issue
7
Year of publication
2001
Pages
627 - 656
Database
ISI
SICI code
0002-9599(200109)301:7<627:LOOHPV>2.0.ZU;2-6
Abstract
Prograde dehydration reactions within metabasalts at the blueschist-eclogit e fades transition produce kyanite veins, usually with quartz, sometimes wi th omphacite or chloritoid, of up to several meters length and 20 cm width. Bulk rock analyses show clear depletion haloes for Al2O3 and SiO2 near the veins. Mass balance calculations support the suggestion that the vein mate rial must have been derived from the immediate surroundings. These veins ar e interpreted as local segregation phenomena and not as fluid dehydration c hannels of the eo-Alpine subduction zone. Calculations have been performed for a stagnant vein formation model that considers the rate of the dehydrat ion reactions (k) responsible for providing the H2O for Al and Si transport and the rate of diffusion (D) of these from wall rock to growing vein. The model is satisfied for quite a wide range of values for k/D and upper limi ts on the duration of diffusional vein formation of about I Ma are indicate d.