A history of violence: magma incubation, timing and tephra distribution of the Los Chocoyos supereruption (Atitlan Caldera, Guatemala)

The climactic Los Chocoyos (LCY) eruption from Atitlan caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U-Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 +/- 2 ka. Additionally, the youngest zircon crystallization U-238-Th-230 rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlan caldera, W-Fall (130 (+16)/(-14) ka) and I-Fall eruptions (56 (+8.2)/(-7.7) ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for >80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of similar to 1220 +/- 150 km(3) is obtained (volcanic explosivity index VEI > 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.

Automated summary

A study utilizing zircon (U-Th)/He geochronology determined the eruption age of the climactic Los Chocoyos (LCY) eruption from Atitlan caldera to be 75 thousand years, while also constraining the eruption ages of two other tephra units. Analysis indicated that there was over 80 thousand years of silicic magma storage before the LCY eruption, with magma accumulation peaking within approximately 35 thousand years before the eruption, suggesting the development of a vertically zoned magma chamber.