RECENT CONFLAGRATION OF EXPLOSIVE VOLCANISM IN THE CENTRAL VOLCANIC ZONE OF THE ANDES – THE CERRO BLANCO VOLCANIC COMPLEX, CATAMARCA, ARGENTINA

Located at ~26°37’S 67°45’W in the Catamarca Province of Argentina, the late Pleistocene – Holocene Cerro-Blanco Volcanic Complex (CBVC), is one of the most productive young rhyolitic centers in the Central Volcano Zone (CVZ) of the Andes. We are in the midst of a major study to unravel the processes, magmatic fluxes, and timescales that lead to such productive silicic magmatic foci, and we will present a progress report here. This study is built on decades of previous work (see Baez et al. 2020 Bulletin of Volcanology and de Silva et al., 2022 Geosphere and refs therein) that has revealed that the CBVC is an ~15 km diameter, nested caldera cluster resulting from at least two caldera cycles: the older, produced the VEI 6 late Pleistocene Campo de la Piedra Pómez Ignimbrite (CPPI @ 54.6 ± 0.6 kyr); the younger ~4.2 kyr eruption was the VEI 5 to 6 Cerro Blanco ignimbrite (CBI) and associated domes and pyroclastic deposits. Evidence for a third, older, explosive eruption, the Barranca Blanca, ca. 100 ka, is now emerging. The CBVC also hosts an important geothermal field that is in a deflationary cycle since 1995, making the CBVC the only actively deforming caldera in the CVZ.

The CBVC juvenile compositions define a high-K, calc-alkaline bimodal suite of rhyolite and trachyandesite compositions, with the rhyolites being among the most evolved compositions erupted in the Central Andes as a whole. Isotopically, the CBVC rhyolites define a tight group within the southern Puna arc-related small ignimbrites that are distinct from the older Neogene flare-up ignimbrites of Cerro Galan and other centers. The rhyolites have been interpreted to originate through assimilation of local basement by regional basaltic andesite parents, followed by extensive fractional crystallization that may have built a composite pluton beneath the CBVC.

This youthful conflagration is an anomaly for the steady state CVZ arc. Whereas a few modern arc composite volcanoes do have records of cyclic explosive volcanism, multiple eruptions of VEI 5 to 6 are unknown. This conflagration of explosive activity may implicate a role for a localized, elevated magmatic flux. Given its youth, spectacular preservation, and current active state, the CBVC has the potential to reveal critical information about the lead-up to catastrophic eruptions of a scale that have occurred in historic times and are therefore of immediate social relevance.