Resumen

The Lastarria (ca. 5,700 m, 25°10'S) and Bayo (5,380 m, 25°25'S) volcanoes in northern Chile have been historically inactive, although fumaroles are currently present in the former. Interesting 50-300 m long sulphur flows are recognized in both volcanoes. These flows show surface structures and textures similar to "pahoehoe" lavas. They have incorporated Up to 28% of accidental fragments, having up to 30% of vesicles. Retained colors suggest that sulphur flows were emplaced in a low temperature-viscosity molten stage (113-160°C, ca. 10-1 poise), remobilized from secondary sublimated sulphur deposits, although small flows emplaced at high temperature-viscosity (250°C, 102 - 103 poise) have also been observed. For 220 and 350 m long flows emission times of molten sulphur have been estimated in 30 and 50 Minutes, respectively. These times are comparable to the unique S flow observed during emplacement at Siretoko-Iosan Volcano, Japan, in 1939. Theoretical models for volcanism on "lo", the nearest Jupiter's moon, should consider the possibility of including 'contaminant" accidental fragments and vesicles as Lastarria and Bayo S flows present. The unusual S enrichment of the Central Andes compared with the Southern Andes volcanoes, would be due either to a magmatic Source originally enriched and/or by crustal assimilation of Mesozoic sedimentary deposits of sulphur-rich minerals under the northern Chilean volcanoes.