Decoupled CO2 flux and thermal output in a recent rhyolitic laccolith: Insights into post-emplacement hydrothermal dynamics

Shallow magmatic intrusions strongly affect fluid circulation in magmatic-hydrothermal systems. This influence may persist long after emplacement, but its spatial expression in heat and volatile fluxes remains poorly quantified. Here, we consider the recent shallow (<200 m depth) laccolith of Puyehue−Cordón Caulle Volcanic Complex, emplaced during the 2011−2012 rhyolitic eruption, assessing its role in controlling the heat transfer and CO2 degassing pathways. Combined soil CO2 flux, ground temperature, and Multi-GAS measurements reveal a decoupling between thermal and degassing signals across the laccolith. Inner zones show high temperatures (up to 100 °C) but low diffuse CO2 gas flux, and steam-rich fumaroles, whereas distal areas display lower temperatures, high diffuse CO2 degassing and CO2-rich fumaroles, the latter linked to deeper magmatic inputs. These patterns indicate that the laccolith acts primarily as a heat source while contributing minimally to CO2 outgassing. We infer that the laccolith primarily sustains shallow hydrothermal activity, while a persistent inflow of magmatic gases from depth occurs along its margins. Our results offer new insights on how shallow intrusions can modulate degassing, reorganize permeability, and decouple heat and volatile transport during post-emplacement evolution, with important implications for interpreting real-time volcanic gas and thermal monitoring data.