Petrology and geochemistry of the Murta basalts: a subglacial eruption in the Patagonian Andes (46 degrees lat. S.), Chile. Relationship with the subduction of the Chile Ridge

The Holocene Murta basalts represent a small volume monogenetic centre loca ted in the northern Patagonian Andes at the latitude of the Chile Triple Ju nction. These basalts show morphological evidence of subglacial eruption. T hey are locally porphyritic with large plagioclase feldspar, clinopyroxene and olivine megacrysts. The major- and trace-element concentrations, REE: p atterns, and isotopic data, distinguish them clearly from the other Holocen e are basalts or the Palaeocene back-are lavas. Their asthenospheric signat ure is in accordance with a geodynamic context characterised, since the Mio cene, by the subduction of the Chile Ridge below the South American Plate a nd the progressive development of a slab window.