An improved age framework for late Quaternary silicic eruptions in northern Central America

Abstract

Five new stepwise-heating 40 Ar/ 39 Ar ages and one new high-sensitivity 14 C date of ash-fall and ash-flow deposits from late Quaternary silicic volcanoes in northern Central America document the eruption rates and frequencies of five major rhyodacite and rhyolite calderas (Atitlán, Amatitlán, Ayarza, Coatepeque, and Ilopango) located north of the basalt, andesite, and dacite stratovolcanoes of the Central American volcanic front. These deposits form extensive timestratigraphic horizons that intercalate regionally, and knowledge of dates and stratigraphy provides a valuable framework for age determinations of more localized volcanic and nonvolcanic events. The new data, especially when integrated with previous stratigraphic and dating work, show that all five calderas erupted several times in the past 200 ka and, despite a lack of historic activity, should be considered as active centers that could produce highly explosive eruptions again. Because of their locations near the highly vulnerable economic hearts of Guatemala and El Salvador, the risks of eruptions from these calderas should be carefully considered along with risks of major earthquakes and volcanic front volcanoes, which are much more frequent but inflict less severe and extensive damage. This Fig. 1 Location map showing late Quaternary calderas of northern Central America investigation also includes some examples of dating efforts that failed to produce reasonable results.

Structural evolution of the El Salvador Fault Zone: an evolving fault system within a volcanic arc.

“…For example, the last eruption of Ilopango Caldera, TBJ, launched a total volume of 18 km³ of dense rock equivalent (Hart, 1981(Hart, , 1983. The shallow structure of the ESFZ is developed on these young deposits, which overlay more rigid formations (Balsamo formation; Rose et al, 1999). are poorly represented in the ESFZ, indicating that the fault has not reached this level of maturity.…”

“…The regional landscape and drainage system in this area is repeatedly reset by ignimbrite eruptions from the nearby Ilopango caldera. In particular, the Tierra Blanca 3 eruption and associated ignimbrite body of 40 ka (Rose et al, 1999) filled the landscape and brought it to an almost planar surface, which was subsequently incised by the fluvial system. In the Desague area (Fig.10), the ESFZ is made up of three parallel strands, two of them show a 200 ± 20 m right-lateral offset (calculated with LaDiCaoz) affecting several fluvial channels.…”

An 85-ka record of climate change in lowland Central America

“…The recognition and correlation of ash layers is assisted by the widespread distribution of the tephra in the entire Central American region up to the Gulf of Mexico in the north and offshore Equador in the south (Kutterolf et al, 2007(Kutterolf et al, , 2008 Rose et al, 1999), and Los Chocoyos Tephra (LCY; 8470.5 ka; dated by oxygen isotope stratigraphy). The position of the ACT ash introduces a large change in sedimentation rate and has been discarded until the Ar/ Ar age can be verified (Rose et al, 1999).…”

“…The recognition and correlation of ash layers is assisted by the widespread distribution of the tephra in the entire Central American region up to the Gulf of Mexico in the north and offshore Equador in the south (Kutterolf et al, 2007(Kutterolf et al, , 2008 Rose et al, 1999), and Los Chocoyos Tephra (LCY; 8470.5 ka; dated by oxygen isotope stratigraphy). The position of the ACT ash introduces a large change in sedimentation rate and has been discarded until the Ar/ Ar age can be verified (Rose et al, 1999). The age of the base of the PI-6 section is constrained by a tephra from the Los Chocoyos eruption of the Atitlá n Caldera in the Guatemalan highlands, which is dated to 84 ka by its occurrence in Marine Isotope Stage 5a in offshore marine sediment cores (Ledbetter, 1984).…”

Characterisation of the Quaternary eruption record: analysis of the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database

“…C from 2.5-70 ka, calculated in 2,500 year bins. The peak at 56 ka is the Congo (CGT) eruption from Coatepeque Caldera (El Salvador), constrained using high sensitivity 14 C analysis; see Rose et al (1999) for details. For (a) and (b) bin sizes were selected to be larger than typical uncertainties in the age determinations.…”