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Petrographic insights into recent volcanism in the Carrán -- Los Venados Distributed Volcanic Field, Southern Andes (Chile)

Deborah Cáceres-Baez1 , Patricia Larrea1, Débora Morales-Soto1, Sofía Pinilla1, Laura Becerril2, Sergio Salinas3, Lizette Bertin4, Angelo Castruccio1

  • Affiliations: 1Universidad de Chile, Departamento de Geología, Santiago, Chile; 2Universidad de O'Higgins, Instituto de Ciencias de la Ingeniería, Rancagua, Chile; 3Universidad Nacional Autónoma de México, División SUAyED, CDMX, Ciudad de México, México; 4Servicio Nacional de Geología y Minería, Observatorio Volcanológico de Los Andes del Sur, Chile 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 49

  • Programme No: 1.7.36

  • Theme 1 > Session 7

Abstract

The Carrán-Los Venados Distributed Volcanic Field (CLV), ranked 6th in Chile's active volcano-specific risk, is the largest cluster of minor eruptive centers in the Southern Andes. Formed during the Pleistocene and is still active, the CLV comprises three main units: (1) the basal lavas, forming flows up to 14 km long that fill the Riñinahue and Nilahue valleys; (2) two medium-sized peripheral volcanoes, Los Guindos shield and Media Luna scoria cone, and (3) 72 minor eruptive centers (scoria cones and maars) aligned ENE-WSW, with strombolian and phreatomagmatic eruption styles. This study examines three historical eruptions: the 1907 Riñinahue maar, a phreatomagmatic eruption that formed a pyroclastic ring, with a lava flow filling the crater, and a small pyroclastic cone; the 1955 Carrán maar, a phreatomagmatic eruption with an 8-10 km eruptive column and pyroclastic surges up to 3 km; and the 1979 Mirador strombolian eruption, which produced a scoria cone, fall-out deposits, and two lava flows. These eruptions produced basaltic to basaltic-andesitic rocks (51-55 wt% SiO2, 7-4 wt% MgO) with typical arc signatures and microporphyric textures, characterized by microphenocrysts of plagioclase, olivine, pyroxene, and oxides, showing disequilibrium textures (such as resorption sieve and reaction rims). Textures indicating complex histories are still under study. Detailed mineral chemistry analyses reveal pre-eruptive conditions and, through comparison with the peripheral volcanoes and the basal lavas, suggest a magmatic storage level at ~12 km depth. These findings improve understanding of the CLV's plumbing system and behavior, contributing to enhanced hazard assessment for future eruptions.