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Title

The Ilopango caldera complex, El Salvador: Origin and early ignimbrite-forming eruptions of a graben/pull-apart caldera structure

AuthorsSuñe-Puchol, I.; Aguirre-Díaz, Gerardo ; Dávila-Harris, P.; Miggins, D.P.; Pedrazzi, Dario ; Costa, Antonio
KeywordsCentral America Volcanic Arc
Tectono-volcanism
El Salvador Fault Zone
Fissure eruption
Hydromagmatism
Issue DateFeb-2019
PublisherElsevier
CitationJournal of Volcanology and Geothermal Research, 371: 1-19 (2019)
AbstractThe Ilopango caldera is located in the central part of El Salvador, within the right-lateral El Salvador Fault System (ESFZ) and adjacent to the capital city of San Salvador. The caldera has a polygonal shape of 17 × 13 km and hosts an intra-caldera lake. Ilopango caldera had multiple collapse eruptions that formed widespread and voluminous silicic ignimbrites. Volcanic activity of the caldera has been controlled by strike-slip faults of the ESFZ. In this work we present the geological characteristics of the first three ignimbrite-forming eruptions of Ilopango caldera, providing an interpretation of the origin and initial stages of the volcanic evolution of this caldera complex. An initial extensional regime of the ESFZ possibly developed a graben at or near the actual Ilopango caldera, where the graben's master faults worked as fissure vents during the first caldera collapse. The Olocuilta Ignimbrite was emplaced at 1.785 ± 0.01 Ma BP, with a Dense Rock Equivalent (DRE) volume > 50 km3 (probably ~300 km3). The ESFZ stress gradually changed from extensive to transtensive, inducing the second collapse associated with a pull-apart caldera, producing the Colima Ignimbrite at 1.56 ± 0.01 Ma BP, with a DRE volume of >11 km3. The transtensive regime increased along the ESFZ, producing the third collapse in the pull-apart graben caldera apparently affected by the newly formed strike-slip San Vicente Fault. This phase corresponds to the explosive eruption that formed the Apopa Ignimbrite at ~1.34 Ma BP, with >9 km3 DRE volume. The latter ignimbrite marks a change in the eruptive style producing hydromagmatic pyroclastic flows followed by a dense ignimbrite with coignimbrite lithic breccias. These features suggest the involvement of water that could come from a paleoIlopango lake within the caldera depression associated with the second caldera collapse at 1.56 Ma BP. Ilopango is thus a multistage caldera system associated with the largest explosive events registered in El Salvador so far.
Publisher version (URL)https://doi.org/10.1016/j.jvolgeores.2018.12.004
URIhttp://hdl.handle.net/10261/174035
DOI10.1016/j.jvolgeores.2018.12.004
ISSN0377-0273
Appears in Collections:(ICTJA) Artículos
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