The Volcanism of the Meseta del Lago Buenos Aires, Patagonia: the Transition from Subduction to Slab Window.

This article focuses on the geochemical and isotopic evolution of volcanic lavas from the Meseta del Lago Buenos Aires (MLBA) in southern Patagonia, examining their transition from a subduction regime to the formation of a slab window caused by the collision of the Chile Ridge with the Andean subduction zone. The study identifies three distinct geochemical endmembers in MLBA basalts: a subduction-influenced component, a transitional component similar to South Atlantic enriched mid-ocean ridge basalts (E-MORB), and an enriched component akin to the EM1 mantle composition associated with the South Atlantic Discovery hotspot. Lavas older than ~1.5 million years show a continuum between subduction-influenced and transitional types, while younger lavas (<1.7 Ma) uniquely exhibit the enriched EM1 signature coinciding with slab window formation. The data suggest that the mantle source beneath southern Patagonia is more consistent with a subduction-modified South Atlantic mantle influenced by Discovery, Shona, and Bouvet hotspots, rather than Pacific sub-slab mantle from the Chile Ridge, and that metasomatized subcontinental lithospheric mantle (SCLM) plays a significant role in the petrogenesis of these lavas.