Helium isotope characteristics of Andean geothermal fluids and lavas

Hilton, David R.; Hammerschmidt, Konrad; Teufel, Stefan; Friedrichsen, Hans

doi:10.1016/0012-821x(93)90244-4

Cited by 175 publications

(105 citation statements)

References 33 publications

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“…Consequently, we dismiss it both as a main contributor to the He inventory at RVP and as a likely endmember composition fortuitously mixing with a high 3 (Figure 3). This observation can be explained by pre-eruptive degassing of magma coupled with contamination by radiogenic He from surrounding wallrock [Hilton et al, 1993]. Crucially, contamination must occur just prior to eruption (presumably at shallow crustal levels) to preserve He disequilibrium conditions [Hilton et al, 1995].…”

Section: Discussionmentioning

confidence: 99%

Helium isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux

Hilton

Halldórsson

Barry

et al. 2011

Geophys. Res. Lett.

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We report helium isotope ratios (3He/4He) of lavas and tephra of the Rungwe Volcanic Province (RVP) in southern Tanzania. Values as high as 15RA (RA = air 3He/4He) far exceed typical upper mantle values, and are the first observation of plume‐like ratios south of the Turkana Depression which separates the topographic highs of the Ethiopia and Kenya domes. The African Superplume ‐ a tilted low‐velocity seismic anomaly extending to the core‐mantle boundary beneath southern Africa – is the likely source of these high 3He/4He ratios. High 3He/4He ratios at RVP together with similarly‐high values along the Main Ethiopian Rift and in Afar provide compelling evidence that the African Superplume is a feature that extends through the 670‐km seismic discontinuity and provides dynamic support – either as a single plume or via multiple upwellings – for the two main topographic features of the East Africa Rift System as well as heat and mass to drive continuing rift‐related magmatism.

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Section: Discussionmentioning

confidence: 99%

Helium isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux

Hilton

Halldórsson

Barry

et al. 2011

Geophys. Res. Lett.

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“…If indeed the N 2 /He ratios are the result of various degrees of degassing, samples from extensively degassed magmas (i.e. MB) should also have (a) lower gas fractions or higher H 2 O contents due to a higher contribution of meteoric water, and (b) lower 3 He/ 4 He ratios due to higher susceptibility to contamination by crustal 4 He (Hilton et al, 1993) than samples from less degassed magmas (i.e. MW, MM).…”

Section: Fractionation Of Volatile Species During Devolatilization Dmentioning

confidence: 99%

Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Elkins

Fischer

Hilton

et al. 2006

Geochimica et Cosmochimica Acta

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114

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We report new chemical and isotopic data from 26 volcanic and geothermal gases, vapor condensates, and thermal water samples, collected along the Nicaraguan volcanic front. The samples were analyzed for chemical abundances and stable isotope compositions, with a focus on nitrogen abundances and isotope ratios. These data are used to evaluate samples for volatile contributions from magma, air, air-saturated water, and the crust. Samples devoid of crustal contamination (based upon He isotope composition) but slightly contaminated by air or air-saturated water are corrected using N 2 /Ar ratios in order to obtain primary magmatic values, composed of contributions from upper mantle and subducted hemipelagic sediment on the down-going plate. Using a mantle endmember with d 15 N = À5& and N 2 /He = 100 and a subducted sediment component with d 15 N = +7& and N 2 /He = 10,500, the average sediment contribution to Nicaraguan volcanic and geothermal gases was determined to be 71%. Most of the gases were dominated by sediment-derived nitrogen, but gas from Volcán Mombacho, the southernmost sampling location, had a mantle signature (46% from subducted sediment, or 54% from the mantle) and an affinity with mantle-dominated gases discharging from Costa Rica localities to the south. High CO 2 /N 2 exc. ratios (N 2 exc. is the N 2 abundance corrected for contributions from air) in the south are similar to those in Costa Rica, and reflect the predominant mantle wedge input, whereas low ratios in the north indicate contribution by altered oceanic crust and/or preferential release of nitrogen over carbon from the subducting slab. Sediment-derived nitrogen fluxes at the Nicaraguan volcanic front, estimated by three methods, are 7.8 · 10 8 mol N/a from 3 He flux, 6.9 · 10 8 mol/a from SO 2 flux, and 2.1 · 10 8 and 1.3 · 10 9 mol/a from CO 2 fluxes calculated from 3 He and SO 2 , respectively. These flux results are higher than previous estimates for Central America, reflecting the high sediment-derived volatile contribution and the high nitrogen content of geothermal and volcanic gases in Nicaragua. The fluxes are also similar to but higher than estimated hemipelagic nitrogen inputs at the trench, suggesting addition of N from altered oceanic basement is needed to satisfy these flux estimates. The similarity of the calculated input of N via the trench to our calculated outputs suggests that little or none of the subducted nitrogen is being recycled into the deeper mantle, and that it is, instead, returned to the surface via arc volcanism.

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“…As shown in Fig. 7, which includes the hydrothermal systems from SVZ (Hilton et al, 1993;Ray et al, 2009;Dobson et al, 2013), the Rc/Ra values of the EPC gases were lower than those shown by fumarolic fluids from active volcanoes in the SVZ, such as the Tupungatito (Tu) (Benavente et al, 2013), Plachón-Peteroa (PP) (Saltori et al, 2012) and Copahue-Caviahue (CC) (Agusto et al, 2013) volcanoes, the latter depicting an increasing trend toward south. This trend seems to reflect the composition of the local magma reservoirs residing in the crust (magma aging), which in the northern zone have higher contents of crustal-derived components (e. He contamination occurring within magmas residing in the crust to the north.…”

Section: O-h 2 O and δD-h 2 O) Of Gasesmentioning

confidence: 99%

“…2a), is marked by an anomalously high heat flow (up to 220 mW/m 2 ; Hamza and Muñoz, 1996), and hosts thermal springs with relatively high TDS values (up to 20,000 mg/L). A geochemical study focused on the He isotope ratios from geothermal fluids and rocks from a wide region of the Andes (Hilton et al, 1993) reported two relatively low Rc/Ra values for gases from this domain (2.16 and 1.56 for Baños Morales and Termas Cauquenes, respectively). To the best of our knowledge, more detailed information on the geochemical features of these fluid discharges is currently not available.…”

Section: Introductionmentioning

confidence: 99%

Chemical and isotopic features of cold and thermal fluids discharged in the Southern Volcanic Zone between 32.5°S and 36°S: Insights into the physical and chemical processes controlling fluid geochemistry in geothermal systems of Central Chile

et al. 2016

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The Principal Cordillera of Central Chile is characterized by two belts of different ages and lithologies: (i) an eastern Mesozoic belt, consisting of limestone-and gypsum-rich sedimentary rocks at the border between Central Chile and Argentina, where the active volcanic arc occurs; and (ii) a western belt of Cenozoic age containing basaltic to andesitic volcanic and volcanoclastic sequences. This distinctive geological setting controls water chemistry of cold and thermal springs in the region, which are fed by meteoric water that circulates through deep regional structures. In the western sector of Principal Cordillera, water-rock interaction processes produce low TDS, slightly alkaline HCO 3 − dominated waters, although dissolution of underlying Mesozoic evaporitic rocks occasionally causes SO 4 2− and Cl − enrichments. In this area, few Na dolomite, anhydrite, fluorite, albite, K-feldspar and Ca-and Mg-saponites at a broad range of temperatures (up tõ 300°C) In the associated gas phase, equilibria of chemical reactions characterized by slow kinetics (e.g. sabatier reaction) suggested significant contributions from hot and oxidizing magmatic gases. This hypothesis is consistent with the δ 13 C-CO 2 , Rc/Ra, CO 2 / 3 He values of the fumarolic gases. Accordingly, the isotopic signatures of the fumarolic steam is similar to that of fluids discharged from the summit craters of the two active volcanoes in the study area (Tupungatito and Planchón-Peteroa). These results encourage the development of further geochemical and geophysical surveys aimed to provide an exhaustive evaluation of the geothermal potential of these volcanic-hydrothermal systems.

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Helium isotope characteristics of Andean geothermal fluids and lavas

Cited by 175 publications

References 33 publications

Helium isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux

Helium isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux

Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

Chemical and isotopic features of cold and thermal fluids discharged in the Southern Volcanic Zone between 32.5°S and 36°S: Insights into the physical and chemical processes controlling fluid geochemistry in geothermal systems of Central Chile

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