Eruptive chronology of the Acoculco caldera complex - A resurgent caldera in the eastern Trans-Mexican Volcanic Belt (Mexico)

摘要

The Acoculco caldera complex (ACC) is located in the eastern part of the Trans-Mexican Volcanic Belt in the northern part of the State of Puebla. The complex sits at the intersection of two regional fault systems with NESW and NW-SE orientations. The ACC was built atop Cretaceous limestones, the Zacatan basaltic plateau of unknown age, early Miocene domes (similar to 12.7-10.98 Ma), and Pliocene lava domes (similar to 3.9-3 Ma). Detailed field mapping and stratigraphy studies complemented by Ar-40/Ar-39 and C-14 dating allowed the division of the ACC volcanic succession into 30 volcanic units. Based on the new results and previous studies, the ACC eruptive chronology was grouped in four eruptive phases: syn-caldera, early post-caldera, late post-caldera, and extracaldera. Inception of the ACC volcanism began around 2.7 Ma with the dispersion of an andesitic ignimbrite followed by the collapse of the magma chamber roof as attested by the presence of a lithic breccia in isolated parts of the caldera rim. The collapse produced a 18 x 16 km caldera depression which was partly filled by the ignimbrite (total volume of similar to 127 km(3)) followed by the establishment of an intracaldera lake of unknown total extension. Early post-caldera collapse activity (2.6-2.1 Ma) was restricted within the caldera producing 27 km(3) of lava flows and domes dominantly of basaltic trachyandesite to basaltic composition. Late post-caldera collapse activity (2.0- < 0.016 Ma) migrated dominantly to the caldera rim and periphery emplacing 90 km(3) of magma as rhyolitic domes, lava flows, scoria cones, and two younger ignimbrites. The 1.2 Ma Encimadas ignimbrite (26 km(3)) was vented through the eastern margin of the caldera and dispersed to the northeast, and the 0.6-0.8 Ma Tecoloquillo ignimbrite and dome (11 km(3)) erupted from the southwestern margin of the caldera. The most recent eruption of this phase was vented close to the southeastern caldera rim producing the Cuatzitzingo (< 16,710 +/- 50 years BP) scoria cone. Extra-caldera activity (2.4-0.19 Ma) of the Apan-Tezontepec volcanic field produced scoria cones and lava flows of basaltic trachyandesite to basaltic andesite composition that are interbedded with the products of the caldera complex.Aeromagnetic data further constrains the edge of the caldera rim and is consistent with the presence of at least four intrusive bodies at depths of > 1 km hosted in the Cretaceous limestones. These bodies might represent a series of horizontal mafic intrusions located at different depths that provide the energy that maintains the Acoculco geothermal system active.