Abstract

Tilocálar Norte lava flow and Tilocálar Sur small-lava shield are two monogenetic volcanoes of intermediate composition located in the Central Andes formed between 460 and 730 ± 50 ka. These volcanoes allow us to constrain the lifespan of the effusive activity and investigate the magmatic processes underlying monogenetic volcanism. This study provides new 40Ar/39Ar and geochemical data to constrain the eruptive history. It also establishes the magmatic processes based on their lifespans or transitions, and understands the volcanic hazards associated with these small-volume magmatic systems. Tilocálar Norte was dated in the present work at 684 ± 143 ka, while Tilocálar Sur from basal west flow was dated at 693 ± 38 ka, defining an eruption interval within 9 ± 2 kyr at 692 ± 37 ka (2σ errors). The initial magma batches of Tilocálar Norte and Tilocálar Sur originate from the same source, derived from magma-crust interaction with the lower crust (suitable for garnet growth) under increasing pressure, and from depleted and/or dehydrated sources with partial melting and delamination of the lower crust. However, these batches were separated en route to the surface. They underwent different degrees of fractionation, with the least fractionated batch reaching the surface first (Tilocálar Sur) and the most fractionated batch last (Tilocálar Norte). Our results provide quantitative constraints on monogenetic volcanism regarding the transition of their emplacement, with implications for risk mitigation in the event of future lava flow eruptions that could pose a threat to nearby infrastructure (villages and mining operations).