Tectonic and magmatic controls on the evolution of post-collapse volcanism. Insights from the Acoculco Caldera Complex, Puebla, México

Abstract

The Acoculco Caldera Complex (ACC; 2.7–0.06 Ma) is located in the eastern part of the Trans Mexican Volcanic Belt, México. The ACC produced three major explosive eruptions: the Acoculco andesitic ignimbrite (AI; 2.7 Ma; Syn-caldera), Piedras Encimadas rhyolitic ignimbrite (1.3 Ma; Late post-caldera), and the Tecoloquillo rhyolitic ignimbrite (TI; 0.8 Ma; Late post-caldera). Faulting has been active since the Pliocene to the present; the regional stress regime developed a NW-SE normal fault system (graben-horst structures) where the ACC was built on the Rosario-Acoculco horst.We investigated the depth of the Acoculco and Tecoloquillo magmatic chambers with H2O-CO2 content in glass inclusions, magmatic processes (magma mixing), and origin of magmas with major oxides-trace-element geochemistry and mineral chemistry. Magma chambers for TI and AI magmas are isolated from each other and located approximately 6–10 km depth. We related the local stress field to the magmatic processes that modified the AI (syn-caldera) and TI (post-caldera) magmas of the ACC. The extensional regime promoted the ascent of calc-alkaline magma and stopped by a local compressive stress regime (transfer zones; Acoculco fault), generating an entrapment zone (1.5–2.5 kbar). The new ascent of calc-alkaline magmas from a deep reservoir provoked magma mixing that triggered the AI eruption and the collapse of the magma chamber roof. The collapse event destroyed the feeding conduits and created new ascent paths that favored the formation of a new plumbing system. The ascent of melt used the pre-existing structures, probably deep graben-horst NE-SW faults, allowing peralkaline magma ascent that stopped in the entrapment zone. The new alkaline and calc-alkaline magma injection caused magma mixing that catalyzed the TI explosive eruption through NE-SW trending structures forming the TI plumbing system.