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

摘要

Gas from mud volcanoes, dry mofettes, springs, and wells were sampled in a region of active\udtectonics and high seismicity in the southern Apennines (Italy), where there is a long history of disastrous\udearthquakes, with the latest (Ms = 6.9) occurring in 1980. The fluids consist of a mixture of mantle-derived and\udcrust-derived volatiles, with a low atmosphere-derived contribution, as identified by the He isotope signature\udand He/Ne ratio measurements. One year of monthly monitoring of the He concentrations and He isotopes\udrevealed no seasonal modifications or variations induced by low seismicity. There are extraordinary high\udoutputs of 4He produced in the crust in the area (up to 2.5 × 1028 atoms yr 1). These outputs cannot be\udsolely due to the whole-rock production rate and a long-lasting diffusion degassing through the crust of\udthe produced 4He. This study explored the relation between the volume of fractured rock and the related\udrelease of He. The results support that crustal degassing can be controlled by tectonic events resulting in\udearthquakes. The high seismicity in this sector of the Apennines provides the conditions necessary for a\udmassive release of He that has accumulated in the rock over a long time period. We identified that the\udassessed high crustal 4He output can be attributed to an intense fracturing of a calculable volume of rock,\udwhich gives new constraints on the volume of rock involved in high-magnitude earthquakes in the region.