Petrologie et geochimie des basaltes de Murta: Une eruption sous-glaciaire dans les Andes patagoniennes (46°lat. S.), Chili. Relation avec la subduction de la ride du Chili

The Holocene Murta basalts represent a small volume monogenetic centre located in the northern Patagonian Andes at the latitude of the Chile Triple Junction. These basalts show morphological evidence of subglacial eruption. They are locally porphyritic with large plagioclase feldspar, clinopyroxene and olivine megacrysts. The major- and trace-element concentrations, REE patterns, and isotopic data, distinguish them clearly from the other Holocene arc basalts or the Palaeocene back-arc lavas. Their asthenospheric signature is in accordance with a geodynamic context characterised, since the Miocene, by the subduction of the Chile Ridge below the South American Plate and the progressive development of a slab window.