New insights into the stratigraphy and 230Th/U geochronology of the post-caldera explosive volcanism of La Primavera caldera, Mexico

Abstract

La Primavera caldera is a Quaternary rhyolitic volcanic field located in the western part of the Trans-Mexican-Volcanic-Belt (TMVB). The caldera forming eruption of La Primavera occurred ~95 ka with the emplacement of the Tala ignimbrite. Here, we present a new stratigraphy and evolution of the post-caldera activity based on intense fieldwork, correlation of deposits, and ten 230Th/U geochronology dates in zircons. The collapse produced an 11-km wide caldera followed by the formation of an intra-caldera lake. After the caldera collapse, several rhyolitic domes were extruded, inside and outside the caldera ring-fault until 26.8 ka. The first post-caldera pyroclastic event took place 86.4 ka with the eruption that emplaced the Giant Pumice (GP) followed by the occurrence of at least fourteen pyroclastic units (UA to UN). The intra-caldera explosive activity came from the central resurgent Nejahuete composite dome with the deposition of the GP and A to D units between 86.4 and 71.5 ka. The extra-caldera explosive activity came from the San Miguel, Planillas and Tajo volcanic centers with the deposition of the E to N units inside the caldera and south of the caldera ring fault between 71.5 and 26.8 ka. Three eruptions were originated at San Miguel volcanic center between 71.5 and 60.3 ka (units E, G and H) and six eruptions dated between 68.9 and 44.7 ka were originated at Planillas volcanic center (units F, I, J, K, L and M). The last eruption of the caldera occurred between 44.7 and 26.8 ka at the Tajo volcanic center (UN). The eruptions appear as pyroclastic successions interbedded with lake deposits (units GP and A-B) and as subaerial deposits separated by paleosols or lahar deposits (units C-M). The revised stratigraphy indicates that the caldera resurgence occurred right after the caldera collapse 93.8 ka and continued until 75.8 ka. This new pyroclastic stratigraphy provides key information on the post-caldera evolution of La Primavera.