Carrier and dilution effects of CO2 on thoron emissions from a zeolitized tuff exposed to subvolcanic temperatures. Issue 2 (10th February 2021)

• Record Type: Journal Article
• Authors: Mollo, Silvio; Moschini, Piergiorgio; Galli, Gianfranco; Tuccimei, Paola; Lucchetti, Carlo; Iezzi, Gianluca; Scarlato, Piergiorgio
• Is Part Of: Royal Society open science. Volume 8:Issue 2(2021)
• Publication Date: 2021-02-10
• Subjects: radon and thoron -- zeolitized tuff -- mineral dehydration -- dilution by CO2 degassing; Science -- Periodicals; 500
• DOI: 10.1098/rsos.201539
• Languages: English
• ISSNs: 2054-5703

Abstract

Abstract : Radon ( 222 Rn) and thoron ( 220 Rn) are two isotopes belonging to the noble gas radon ( sensu lato ) that is frequently employed for the geochemical surveillance of active volcanoes. Temperature gradients operating at subvolcanic conditions may induce chemical and structural modifications in rock-forming minerals and their related 222 Rn– 220 Rn emissions. Additionally, CO2 fluxes may also contribute enormously to the transport of radionuclides through the microcracks and pores of subvolcanic rocks. In view of these articulated phenomena, we have experimentally quantified the changes of 220 Rn signal caused by dehydration of a zeolitized tuff exposed to variable CO2 fluxes. Results indicate that, at low CO2 fluxes, water molecules and hydroxyl groups adsorbed on the glassy surface of macro- and micropores are physically removed by an intermolecular proton transfer mechanism, leading to an increase of the 220 Rn signal. By contrast, at high CO2 fluxes, 220 Rn emissions dramatically decrease because of the strong dilution capacity of CO2 that overprints the advective effect of carrier fluids. We conclude that the sign and magnitude of radon ( sensu lato ) changes observed in volcanic settings depend on the flux rate of carrier fluids and the rival effects between advective transport and radionuclide dilution.