Radiogenic helium degassing and rock fracturing: A case study of the southern Apennines active tectonic region

Abstract

Gas from mud volcanoes, dry mofettes, springs, and wells were sampled in a region of active tectonics and high seismicity in the southern Apennines (Italy), where there is a long history of disastrous earthquakes, with the latest (M s = 6.9) occurring in 1980. The fluids consist of a mixture of mantle-derived and crust-derived volatiles, with a low atmosphere-derived contribution, as identified by the He isotope signature and He/Ne ratio measurements. One year of monthly monitoring of the He concentrations and He isotopes revealed no seasonal modifications or variations induced by low seismicity. There are extraordinary high outputs of 4 He produced in the crust in the area (up to 2.5 × 10 28 atoms yr À1 ). These outputs cannot be solely due to the whole-rock production rate and a long-lasting diffusion degassing through the crust of the produced 4 He. This study explored the relation between the volume of fractured rock and the related release of He. The results support that crustal degassing can be controlled by tectonic events resulting in earthquakes. The high seismicity in this sector of the Apennines provides the conditions necessary for a massive release of He that has accumulated in the rock over a long time period. We identified that the assessed high crustal 4 He output can be attributed to an intense fracturing of a calculable volume of rock, which gives new constraints on the volume of rock involved in high-magnitude earthquakes in the region.

Boron Isotopes in the Mount Vulture Groundwaters (Southern Italy): Constraints for the Assessment of Natural and Anthropogenic Contaminant Sources

“…Boron isotopic composition was determined by negative-ion thermal-ionization mass spectrometry (N-TIMS), direct loading procedure at the Isotope Science Laboratory of University of Calgary (ISL-UC), following the methods described by Gaillardet [34]. The external reproducibility of ±1δ (2σ mean corresponding to 2s/n 0 5 , where n = 3 replicate analyses) for the B isotope measurements was [36][37][38]. The HSW group is related to prolonged water circulation in alkali and feldspathoid-rich pyroclastic layers interbedded with clay deposits [33].…”

Geological degassing enhances microbial metabolism in the continental subsurface

“…This process, also termed mantle degassing, is the transition of volatiles from the mantle (supercritical) to the subcritical zone of the upper crust fueled by lower pressure of volatiles near the surface compared to the mantle 20 . Modern Earth has few areas with active mantle degassing, which are usually restricted to terrestrial volcanoes or hydrothermal vents in oceans 21,22,23,24 . At hydrothermal vents, chemolithoautotrophs initiate the microbial trophic network and proliferate at high rates leading to high microbial cell numbers 1 .…”

Mantle Degassing Through Continental Crust Triggered by Active Faults: The Case of the Baja California Peninsula, Mexico

“…Gas chemistry, specifically noble gases and CO 2 and CH 4 isotopes, represent excellent natural tracers to evaluate the origin of volatiles and the relationship between active tectonic and magmatic activity (e.g., Caracausi & Paternoster, 2015;Graham, 2002;Kurz et al, 1982;Moreira & Allègre, 1998;Moreira & Sarda, 2000;Rizzo et al, 2015Rizzo et al, , 2016Sano & Marty, 1995). Helium has two stable isotopes, 3 He and 4 He, whose ratio is useful to distinguish crustal from mantle sources.…”