High 3He gas emissions of Irpinian Apennine: mantle relations and genetic hypothesis

A gas geochemical prospection has been carried out in a tectonically active area located in the Southern Apenninic Belt (Italy) with the purpose to investigate the origin of local gaseous emissions. On the basis of helium isotopic ratios, a high contribution of deep-marked fluids has been recognised. Local field evidences of gases flow rate do not seem consistent with only a mantle provenance of the fluids. It seems likely that the gases source has to be located at shallower depth than the crust-mantle transition

Light-noble-gas isotopic ratios in gases from Mt. Etna (Southern Italy): Implications for mantle contamination and volcanic activity

Helium isotopic ratios in gases from Mt. Etna are in the range of 6–7 Ra (Ra = atmospheric 3He /4He ratio 1.431026), below the MORB’s typical range, and fall in the same range of those measured in xenoliths from the Northern part of Europe, where a crustal contamination of the sub-continental mantle has been recognized. Taking into account the light-noble-gas isotopic signature of gas samples coming from the Etnean area, it seems that in this area the crustal contamination played a minor role. Instead, processes that enriched the original MORB-type mantle in incompatible elements, have to be considered. The 3He /4He ratios are, thus, lowered because of 4He produced by radioactive decay of U and Th. On the other hand, helium isotopic ratios have shown wide temporal variations sometimes reaching values as high as 7.6 Ra, out of the typical Etnean range. As these unusually high ratios have been measured during phases of unrest of the volcanic activity at Mt. Etna, this apparent discrepancy in the helium isotopic ratios is considered, as the effect of fractionation processes occurred during magma uprising

Helium and Carbon isotopic characterization of the dissolved gases in Mt. Etna groundwater (Italy).

We report the chemistry and He and C isotopic composition of dissolved gases in groundwaters of Mt. Etna for 17 sampling sites (wells, springs, artificial drainage) for the period February 2006-January 2007. A conceptual model on degassing and gas-water interaction processes, including the 2006 eruptive period of Mt. Etna is proposed. For all sites, CO2 is the most abundant dissolved gas phase, reaching concentrations up to 700 cc/l(w). Helium varies from 3,83x10-5 to 1.24x10-3 cc/l. The 13CCO2 (recalculated from 13CTDC) varies from -13.4 to -2.3 ‰ vs. V-PDB; the lower values result from mixing with organic carbon, while the higher values are identical to the C isotopic composition for Mediterranean volcanism. The 3He/4He ratios (R/RA with RA the 3He/4He ratio for air of 1.39x10-6) for dissolved gases in Etna groundwater ranges from 1.3 to 6.4 RA, depending on mixing proportions between air (1RA) and the Etnaean magmatic end-member (3He/4He = 7.1 RA). The groundwater at one site shows a clear trend towards mixing with a different magmatic end-member (3He/4He = 5.3 RA, western periphery), probably the result of the contribution of a more degassed magma. This is confirmed by the fact that this site does not show any temporal variations, as the others do during the 2006 eruption. The values for log(Ct/3He) are generally above 11, and can be as high as >13, clearly higher than log(Ct/3He) values for magmatic systems (~9.6). This is not surprising for dissolved gases, as CO2 is ~30 times more soluble in water than He wish is outgassed more easily.PublishedCluj-Napoca, Romania2.4. TTC - Laboratori di geochimica dei fluidiope

Helium and Carbon isotopic characterization of the dissolved gases in Mt. Etna groundwater (Italy).

We report the chemistry and He and C isotopic composition of dissolved gases in groundwaters of Mt. Etna for 17 sampling sites (wells, springs, artificial drainage) for the period February 2006-January 2007. A conceptual model on degassing and gas-water interaction processes, including the 2006 eruptive period of Mt. Etna is proposed. For all sites, CO2 is the most abundant dissolved gas phase, reaching concentrations up to 700 cc/l(w). Helium varies from 3,83x10-5 to 1.24x10-3 cc/l. The 13CCO2 (recalculated from 13CTDC) varies from -13.4 to -2.3 ‰ vs. V-PDB; the lower values result from mixing with organic carbon, while the higher values are identical to the C isotopic composition for Mediterranean volcanism. The 3He/4He ratios (R/RA with RA the 3He/4He ratio for air of 1.39x10-6) for dissolved gases in Etna groundwater ranges from 1.3 to 6.4 RA, depending on mixing proportions between air (1RA) and the Etnaean magmatic end-member (3He/4He = 7.1 RA). The groundwater at one site shows a clear trend towards mixing with a different magmatic end-member (3He/4He = 5.3 RA, western periphery), probably the result of the contribution of a more degassed magma. This is confirmed by the fact that this site does not show any temporal variations, as the others do during the 2006 eruption. The values for log(Ct/3He) are generally above 11, and can be as high as >13, clearly higher than log(Ct/3He) values for magmatic systems (~9.6). This is not surprising for dissolved gases, as CO2 is ~30 times more soluble in water than He wish is outgassed more easily

Helium isotopes in mafic phenocrysts along the Italian volcanism and inferences on the crust-mantle interaction

No abstract available

Integrated silicon optical sensors based on hollow core waveguide

In this work we show that integrated silicon hollow core AntiResonant Reflecting Optical Waveguide (ARROW) can be used as a basic tool for the realization of optical sensors. ARROW waveguides, with hollow core, permit to confine the light in a low refractive index liquid core, by means of two cladding layers designed to form a high reflectivity Fabry-Perot antiresonant cavity. This arrangement allows to realize microchannels that can simultaneously act as microfluidic networks and optical waveguides with a strong advantage in the integration and with an increased interaction efficiency between the light and the liquid substance that can be very useful in sensing applications (fluorescence, absorption spectroscopy, etc.). Another ARROW waveguides advantage is the ability to tailor the wavelength response of the device. In fact, the waveguide propagation losses strongly depend on the change of the resonant condition inside the interference cladding. In this paper we report three sensing applications of hollow core ARROW waveguide. A long path absorbance cell for colorimetric protein assay, a high sensitivity integrated refractometer and a micro flow cytometer for cell/particles analysis. The proposed devices have been realized in standard silicon technology by using two silicon wafers bonded together

Constraints on mantle source and interactions from He-Sr isotope variation in Italian Plio-Quaternary volcanism

Helium isotope ratios of olivine and pyroxene phenocrysts from Plio-Quaternary volcanic rocks from southern Italy (seven Aeolian Islands, Mt. Vulture, Etna, Ustica, and Pantelleria) range from 2.3 to 7.1 R <sub>a</sub>. Importantly, the phenocryst <sup>3</sup>He/<sup>4</sup>He correlate well with whole rock Sr isotopic composition (0.70309–0.70711), reflecting the mixing of two sources. A significant contribution of He from crustal contamination is recorded only occasionally (e.g., pyroxenes from Vulcano). When merged with data from the Roman Comagmatic Province, a remarkably strong near-linear He-Sr isotope correlation is apparent. The general northward decrease in <sup>3</sup>He/<sup>4</sup>He corresponds to an increase in <sup>87</sup>Sr/<sup>86</sup>Sr (and a decrease in <sup>143</sup>Nd/<sup>144</sup>Nd and <sup>206</sup>206Pb/<sup>204</sup>Pb) that is due to increasing metasomatic enrichment of the mantle wedge via subduction of the Ionian-Adriatic plate. Calculations based on the ingrowth of <sup>4</sup>He in the wedge and on the <sup>4</sup>He content of the subducting crust show that mechanisms of enrichment in radiogenic He are effective only if the wedge is strongly depleted in He relative to best estimates of the depleted mantle. This can be accommodated if the process of metasomatism by the subduction fluids depletes the mantle wedge. The <sup>3</sup>He/<sup>4</sup>He of Pantelleria, Etna, Iblei, Ustica, Alicudi, and Filicudi basalts (7.0 ± 0.6 R a) define the mantle composition least affected by subduction-related metasomatism. Although these volcanoes are from a variety of tectonic regimes (subduction-related, intraplate, rifting), their similarities suggest a common origin of geochemical features. Their characteristics are consistent with a HIMU-type mantle that either is younger than the Cook-Austral island end-member or has a lower <sup>238</sup>U/<sup>204</sup>Pb

Helium isotopes in mafic phenocrysts along the Italian volcanism and inferences on the crust-mantle interaction

No abstract available

Helium-strontium isotope constraints on mantle evolution beneath the Roman Comagmatic Province, Italy

A study of the He isotopic ratios of fluid inclusions in olivine and pyroxene from the Roman Comagmatic Province (RCP), Italy, is presented together with <sup>87</sup>Sr/<sup>86</sup>Sr isotope compositions of the whole rock or pyroxene phenocrysts. A clear covariation in He and Sr isotopes is apparent, with a strong northward increase in radiogenic He and Sr being evident. He and Sr isotopes ratios range from <sup>3</sup>He/<sup>4</sup>He=5.2 <i>R</i><sub>a</sub> and <sup>87</sup>Sr/<sup>86</sup>Sr=0.7056 in south Campania, to <sup>3</sup>He/<sup>4</sup>He=0.44 <i>R</i><sub>a</sub> and <sup>87</sup>Sr/<sup>86</sup>Sr=0.715905 in the northernmost Latium. Helium isotope ratios are significantly lower than MORB values and are among the lowest yet measured in subduction zone volcanism. The <sup>3</sup>He/<sup>4</sup>He of olivine and pyroxene phenocryst-hosted volatiles appear to be little influenced by posteruptive processes and magma-crust interaction. The <sup>3</sup>He/<sup>4</sup>He–<sup>87</sup>Sr/<sup>86</sup>Sr covariation is consistent with binary mixing between an asthenospheric mantle similar to HIMU ocean island basalts, and an enriched (radiogenic) mantle end member generated from subduction of the Ionian/Adriatic plate. The contribution of radiogenic He from metasomatic fluids and postmetasomatism radiogenic ingrowth in the wedge is strongly dependent on the initial He concentration of the mantle. Only when asthenosphere He concentrations are substantially lower than the MORB source mantle, and metasomatism, occurred at the beginning of the subduction (~30 Ma), can ingrowth in the mantle wedge account for the <sup>3</sup>He/<sup>4</sup>He of most radiogenic basalts