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Authors: | Sunye Puchol, Ivan* Aguirre-Diaz, Gerardo J.* Dávila Harris, Pablo* Miggins, Daniel P.* Pedrazzi, Dario* Costa, Antonio* Ortega-Obregón, Carlos* Lacan, Pierre* Hernández, Walter* Gutierrez, Eduardo* |
Title: | The Ilopango caldera complex, El Salvador: Origin and early ignimbrite-forming eruptions of a graben/pull-apart caldera structure | Journal: | Journal of Volcanology and Geothermal Research | Series/Report no.: | /371 (2019) | Issue Date: | 2019 | DOI: | 10.1016/j.jvolgeores.2018.12.004 | Keywords: | Central America Volcanic Arc Tecton Fault |
Subject Classification: | 04.08. Volcanology | Abstract: | The 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, pro- viding 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 N 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 N11 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 ex- plosive eruption that formed the Apopa Ignimbrite at ~1.34 Ma BP, with N9 km3 DRE volume. The latter ignim- brite 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. |
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