Mollo Silvio, Moschini Piergiorgio, Galli Gianfranco, Tuccimei Paola, Lucchetti Carlo, Iezzi Gianluca, Scarlato Piergiorgio
Dipartimento di Scienze della Terra, Sapienza - Università di Roma, P.le Aldo Moro 5, 00185 Roma, Italy.
Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Roma, Italy.
R Soc Open Sci. 2021 Feb 10;8(2):201539. doi: 10.1098/rsos.201539.
Radon (Rn) and thoron (Rn) are two isotopes belonging to the noble gas radon () 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 Rn-Rn emissions. Additionally, CO 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 Rn signal caused by dehydration of a zeolitized tuff exposed to variable CO fluxes. Results indicate that, at low CO 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 Rn signal. By contrast, at high CO fluxes, Rn emissions dramatically decrease because of the strong dilution capacity of CO that overprints the advective effect of carrier fluids. We conclude that the sign and magnitude of radon () changes observed in volcanic settings depend on the flux rate of carrier fluids and the rival effects between advective transport and radionuclide dilution.
氡（Rn）和钍射气（Rn）是属于惰性气体氡（）的两种同位素，常用于活火山的地球化学监测。在火山下条件下运行的温度梯度可能会导致造岩矿物及其相关的Rn-Rn排放发生化学和结构变化。此外，CO通量也可能极大地促进放射性核素通过火山下岩石的微裂缝和孔隙的传输。鉴于这些复杂的现象，我们通过实验量化了暴露于可变CO通量下的沸石化凝灰岩脱水引起的Rn信号变化。结果表明，在低CO通量下，吸附在大孔和微孔玻璃表面的水分子和羟基通过分子间质子转移机制被物理去除，导致Rn信号增加。相比之下，在高CO通量下，由于CO的强稀释能力掩盖了载流体的平流效应，Rn排放显著减少。我们得出结论，在火山环境中观察到的氡（）变化的符号和幅度取决于载流体的通量率以及平流传输和放射性核素稀释之间的竞争效应。
