Tephrochronology of the southernmost Andean Southern Volcanic Zone, Chile

Abstract

Correlations among and identification of the source volcanoes for over 60 Late Glacial and Holocene tephras preserved in eight lacustrine sediment cores taken from small lakes near Coyhaique, Chile (46 degrees S), were made based on the stratigraphic position of the tephra in the cores, lithostratigraphic data (tephra layer thickness and grain size), and tephra petrochemistry (glass color and morphology, phenocryst phases, and bulk-tephra trace element contents determined by ICP-MS). The cores preserve a record of explosive eruptions, since similar to 17,800 calibrated years before present (cal years BP), of the volcanoes of the southernmost Andean Southern Volcanic Zone (SSVZ). The suggested source volcanoes for 55 of these tephras include Hudson (32 events), Mentolat (10 events), and either Maca or Cay or some of the many minor monogenetic eruptive centers (MECs; 13 events) in the area. Only four of these eruptions had been previously identified in tephra outcrops in the region, indicating the value of lake cores for identifying smaller eruptions in tephrochronologic studies. The tephra records preserved in these lake cores, combined with those in marine cores, which extend these records back to 20,000 cal years BP, prior to the Last Glacial Maximum, suggest that no significant temporal change in the frequency of explosive eruptions was associated with deglaciation. Over this time period, Hudson volcano, one of the largest and longest lived volcanoes in the Southern Andes, has had >55 eruptions (four of them were very large) and has produced >45 km(3) of pyroclastic material, making it also one of the most active volcanoes in the SVZ in terms of both frequency and volume of explosive eruptions.