High flux rates of ignimbrite and stratocone growth at Atitlan Caldera, Guatemala
Abstract
To understand the factors that govern the development of different volcanic edifices, recent studies have quantified eruptive volume, repose interval and crustal thickness among other parameters. Atitlan Caldera, Guatemala provides a compelling locality to contrast the age, volume and repose of several ignimbrite eruptions over the past 160 kyr including the 300 km3 Los Chocoyos ignimbrite, as well as, prolific mafic volcanism from three intracaldera stratocones. Since the caldera-forming eruption 84 kyr, 117 km3 of basaltic andesitic to dacitic lavas have been erupted from stratocones San Pedro, Toliman and Atitlan, resulting in a combined eruption rate of 1.46km3/kyr. These eruption rates are considered minimum values as preliminary 40Ar/39Ar age data suggest the cones are much younger than 84 kyr. Inclusion of the Los Chocoyos eruption increases eruption rates to 4.77 km3/kyr. Average eruption rates of the Atitlan system are an order of magnitude greater than most frontal arc complexes that are commonly characterized by cone growth due to large punctuated silicic eruptions. Although a minor proportion (<5%) of lavas erupted from San Pedro and Toliman are dacitic, the vast majority of stratocone growth occurred due to small lava flows of basaltic andesite and andesite or pyroclastic eruptions. Geochemically the lavas from stratocones San Pedro, Toliman and Atitlan are similar to four stratocones that formed prior to the Los Chocoyos and may have erupted another several hundred km3 of lava. In addition to the large volumes of mafic lava generated, three large ignimbrite eruptions that are geochemically similar to each other have occurred spaced 10s kyr apart. A large geochemical gap exists that suggests the ignimbrite is not related to the stratocone lavas by fractional crystallization. Finally, lavas must traverse ~45 km of continental crust at a very high flux rate to build large stratocones in the Atitlan system over a relatively short geologic time interval. At Atitlan Caldera, recent volcanism is not marked by large punctuated ignimbrite eruptions, but rather by continual profuse outpouring of both rhyolitic and basaltic products.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V13C2365C
- Keywords:
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- 1036 GEOCHEMISTRY / Magma chamber processes;
- 1040 GEOCHEMISTRY / Radiogenic isotope geochemistry;
- 1065 GEOCHEMISTRY / Major and trace element geochemistry