During 2001–2005, Mount Etna was characterized by intense eruptive activity involving the emission ofpetrologically different products from several vents, which involved at least two types of magma withdifferent degrees of evolution. We investigated the ratios and abundances for noble-gas isotopes in fluidinclusions trapped in olivines and pyroxenes in the erupted products. We confirm that olivine has the mostefficient crystalline structure for preserving the pristine composition of entrapped gases, while pyroxene cansuffer diffusive He loss. Both the minerals also experience noble gas air contamination after eruption. Heliumisotopes of the products genetically linked to the two different magmas fall in the isotopic range typical ofthe Etnean volcanism. This result is compatible with the metasomatic process that the Etnean mantle isundergoing by fluids from the Ionian slab during the last ten kyr, as previously inferred by isotope and traceelement geochemistry. Significant differences were also observed among olivines of the same parentalmagma that erupted throughout 2001–2005, with 3He/4He ratios moving from about 7.0 Ra in 2001volcanites, to 6.6 Ra in 2004–2005 products. Changes in He abundances and isotope ratios were attributed tovariations in protracted degassing of the same magma bodies from the 2001 to the 2004–2005 events, withthe latter lacking any contribution of undegassed magma. The decrease in 3He/4He is similar to that foundfrom measurements carried out every fifteen days during the same period in gases discharged at theperiphery of the volcano. To our knowledge this is the first time that such a comparison has been performedso in detail, and provides strong evidence of the real-time feeding of peripheral emissions by magmaticdegassing.
|Numero di pagine||8|
|Rivista||Earth and Planetary Science Letters|
|Stato di pubblicazione||Published - 2008|
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science