Chemistry, mineralogy and petrology of an eclogite from the type locality (Saualpe, Austria)

Abstract

An eclogite and five of its coexisting minerals (omphacite, garnet, carinthine, kyanite and zoisite) from the probable type locality of eclogites (Kupplerbrunn, Saualpe, Austria) described by Haüy (1822) have been analysed. Optical and X-ray data for these minerals are also given. Comparison of the Kupplerbrunn rock with those of other eclogites from the Saualpe region indicates they all have roughly similar compositions. When plotted on an A-C-F diagram the majority of these analyses fall in the region of kyanite-bearing eclogites suggested by Tilley (1936) although the Kupplerbrunn rock is the only sample containing kyanite; the others containing zoisite. The garnet and omphacite compositions of the Kupplerbrunn rock differ markedly from those of other Saualpe eclogites, possibly due to different metamorphic conditions of their formation. Carinthine analyses are all very similar for eclogites from Saualpe. On the basis of geological, analytical and limited experimental evidence, it is postulated that the Kupplerbrunn eclogite was derived from an original gabbroic rock low in water content such that amphibole and zoisite formed from plagioclase, pyroxene and water; omphacite, garnet and kyanite formed from plagioclase and pyroxene, once all the water was used up in the form of amphibole and zoisite. These reactions are believed to have taken place at 5–8 kb pressure at around 600° C; a value close to that suggested by Lodemann (1966) from field data.