Abstract

DAGA, Romina et al. Textural and compositional heterogeneities in pyroclastic products from 1960 Cordón Caulle eruption (40º30'S, 72º10'W). Rev. Asoc. Geol. Argent. [online]. 2012, vol.69, n.4, pp.496-507. ISSN 0004-4822.

Volcanic ash deposits are excellent stratigraphical and chronological markers as they can be dispersed hundreds of kilometers from its source, but sometimes the correlation with the source can be problematic. While most of the studies support these correlations in whole rock geochemical analyses, juvenile volcanic particles have great heterogeneity in fragment shapes, texture, and groundmass and mineral phases composition. Previous works on volcanic deposits identified in a lacustrine sedimentary sequence of lake Nahuel Huapi allowed the identification of products from the 1960 Cordón Caulle volcanic complex eruption, showing high variability in the juvenile volcanic particles, like white and brown pumice, scoria and glass shards, with variation in the whole rock composition. With this information as a background, this paper presents the first morphological, textural and compositional analyses of different juvenile products in order to identify the origin of morphological and whole rock geochemical variations. The results allowed the association of such differences with variations in crystal content and size, shape and distribution of vesicles. Such variations, in turn, were related to processes of fractionation previous to the 1960 Cordón Caulle eruption, thus providing valuable information to use these layers as chronostratigraphic markers.

Keywords : Volcanic ashes; Texture; Geochemistry; Dating; Lakes.

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