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Radiogenic helium degassing and rock fracturing: A case study of the southern Apennines active tectonic region
Author(s) -
Caracausi Antonio,
Paternoster Michele
Publication year - 2015
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb011462
Subject(s) - radiogenic nuclide , induced seismicity , geology , crust , tectonics , mantle (geology) , seismology , volcano , period (music) , geochemistry , physics , acoustics
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 −1 ). 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.