Tephrochronology of the southernmost Andean Southern Volcanic Zone, Chile

Correlations among and identification of source volcanoes for different Late-Glacial and Holocene tephra, preserved in eight lacustrine sediment cores taken from small lakes near Coyhaique (46°S), were made based on the stratigraphic position of tephra in the cores 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 >60 explosive eruptions, since ~17,800 cal yrs BP, of volcanoes of the southernmost Andean Southern Volcanic Zone (SSVZ). Suggested source volcanoes for 55 of these tephra include Hudson (32 events), Mentolat (10 events), and either Macá, Cay or some of the many minor monogenetic eruptive centers (MEC; 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. The tephra record preserved in these lake cores suggests that episodic explosive eruptions in this sector of the Andean arc have been regular from LateGlacial to historic times. Tephra records in marine cores extends this conclusion back to 20,000 cal yrs BP, prior to the Last Glacial Maximum, and suggest that no significant temporal change in frequency of eruptions was associated with deglaciation.