High-3He/4He, depleted mantle and low-δ18O, recycled oceanic lithosphere in the source of central Iceland magmatism

Macpherson, Colin G.; Hilton, David R.; Day, James M.D.; Lowry, David

doi:10.1016/j.epsl.2005.02.037

Cited by 85 publications

(91 citation statements)

References 62 publications

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“…These Os isotope systematics for the Iceland picrites are consistent with additional geochemical evidence for ancient recycled slab components in the mantle sources for Iceland magmas (Hemond et al, l993;Hanan and Schilling, l997;Taylor et al, l997;Stecher et al, l999;Hanan et al, 2000;Chauvel and Hemond, 2000;Kempton et al, 2000;Thirlwall et al, 2004;Macpherson et al, 2005;Thirlwall et al, 2006). Ancient melt enrichment processes and/or additions of recycled crust to the mantle source generate radiogenic 187 Os/ 188 Os observed at other mantle plume localities.…”

Section: Mantle Sources For Ossupporting

confidence: 53%

“…Published data for Iceland lavas within the neovolcanic zones have 3 He/ 4 He ranging from 8.0 to 21 R A (Breddam et al, 2000;Macpherson et al, 2005, and references therein), with one glass sample having a value as high as 26 R A (Kurz et al,l985) . A single sample containing both clinopyroxene and olivine shows values of 20.2±10 and 34.3±8 R A (2σ, Macpherson et al, 2005), but given the low He concentrations and large analytical uncertainties, the significance of the high 3 He/ 4 He in this sample is unclear.…”

Section: Resultsmentioning

confidence: 99%

“…These noble gas characteristics likely require a deep mantle source that is distinct from the convecting upper mantle source for MORB (Kurz et al, l982;l985;Graham et al, l998;Harrison et al, l999;Hilton et al, l999;Breddam et al, 2000;Dixon et al, 2000;Moreira and Sarda, 2000;Moreira et al, 2001;Stuart et al, 2003;Graham, 2005;Ballentine et al, 2005;Macpherson et al, 2005). In addition, there is evidence in some Icelandic lavas, from both noble gases and lithophile elements, for varying contributions from the upper mantle MORB source as well as from several ancient crustal and/or mafic components within the mantle (Hemond et al, l993;Hanan and Schilling, l997;Fitton et al, l997;Taylor et al, l997;Stecher et al, l999;Hanan et al, 2000;Breddam et al, 2000;Chauvel and Hemond, 2000;Kempton et al, 2000;Thirlwall et al, 2004;Macpherson et al, 2005;Thirlwall et al, 2006;Kokfelt et al, 2006). These relationships are consistent with melting and mixing that accompanies the physical setting of the present-day Iceland plume beneath the spreading Mid-Atlantic Ridge system.…”

Section: Introductionmentioning

confidence: 99%

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186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites

Brandon

Graham

Waight³

et al. 2007

Geochimica et Cosmochimica Acta

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Picrites from the neovolcanic zones in Iceland display a range in 187 Os/ 188 Os from 0.1297 to 0.1381 (γ Os = 0.0 to 6.5) and uniform 186 Os/ 188 Os of 0.1198375±32 (2σ). The value for 186 Os/ 188 Os is within uncertainty of the present-day value for the primitive upper mantle of 0.1198398±16. These Os isotope systematics are best explained by ancient recycled crust or melt enrichment in the mantle source region. If so, then the coupled enrichments displayed in 186 Os/ 188 Os and 187 Os/ 188 Os from lavas of other plume systems must result from an independent process, the most viable candidate at present remains core-mantle interaction. While some plumes with high 3 He/ 4 He, such as Hawaii, appear to have been subjected to detectable addition of Os (and possibly He) from the outer core, others such as Iceland do not.A positive correlation between 187 Os/ 188 Os and 3 He/ 4 He from 9.6 to 19 R A in Iceland picrites is best modeled as mixtures of 500 Ma or older ancient recycled crust mixed with primitive mantle, creating a hybrid source region that subsequently mixes with the convecting MORB mantle during ascent and melting. This multistage mechanism to explain these isotope systematics is consistent with ancient recycled crust juxtaposed with more primitive, relatively He-rich mantle, in convective isolation from the upper mantle, most likely in the lowermost mantle. This is inconsistent with models that propose random mixing between heterogeneities in the convecting upper mantle as a mechanism to explain the observed isotopic variation in oceanic lavas or models that produce a high 3 He/ 4 He signature in melt depleted and strongly

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Section: Mantle Sources For Ossupporting

confidence: 53%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites

Brandon

Graham

Waight³

et al. 2007

Geochimica et Cosmochimica Acta

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“…He is more soluble in basaltic magma than Ar (S He /S Ar ~ 9.5; Jambon et al, 1986) (Fig. 6a), suggesting that crustal contamination had a negligible effect on He (Hilton et al, 1993;Hilton et al, 1995;Macpherson et al, 1998;Macpherson et al, 2005). Therefore, in the Kolbeinsey and Tjörnes glasses, 4 He/ 40 Ar * should reflect only the effects of degassing.…”

Section: Evolution Of Vesicle Gasmentioning

confidence: 99%

Sources, degassing, and contamination of CO2, H2O, He, Ne, and Ar in basaltic glasses from Kolbeinsey Ridge, North Atlantic

Macpherson

Hilton

Mertz

et al. 2005

Geochimica et Cosmochimica Acta

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“…1b. Although a magmatic origin (from a MORB-mantle plume mixture) is implicated for both CO 2 and noble gases, based on isotopic data (Barry et al, 2014;Ilyinskaya et al, 2015;Kurz et al, 1985;Macpherson et al, 2005;Polak et al, 1976;Poreda et al, 1980Poreda et al, , 1986Poreda et al, , 1992, these gas samples show clear signs of hydrothermal derivation of the emitted fluids, including (Fig. 1b): (i) very high H 2 O/CO 2 ratios (often N 100 and up to 630), (ii) very low total sulfur contents (S TOT b 0.3% vol; CO 2 /S TOT 1.9-61,450), and (iii) dominance of H 2 S over SO 2 (typically below detection).…”

Section: The Natural Gas Datasetmentioning

confidence: 99%

Reaction path models of magmatic gas scrubbing

et al. 2016

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Gas-water-rock reactions taking place within volcano-hosted hydrothermal systems scrub reactive, water-soluble species (sulfur, halogens) from the magmatic gas phase, and as such play a major control on the composition of surface gas manifestations. A number of quantitative models of magmatic gas scrubbing have been proposed in the past, but no systematic comparison of model results with observations from natural systems has been carried out, to date. Here, we present the results of novel numerical simulations, in which we initialized models of hydrothermal gaswater-rock at conditions relevant to Icelandic volcanism. We focus on Iceland as an example of a "wet" volcanic region where scrubbing is widespread. Our simulations were performed (using the EQ3/6 software package) at shallow (temperature b 106°C; low-T model runs) and deep hydrothermal reservoir (200-250°C; high-T model runs) conditions. During the simulations, a high-temperature magmatic gas phase was added stepwise to an initial meteoric water, in the presence of a dissolving aquifer rock. At each step, the chemical compositions of coexisting aqueous solution and gas phase were returned by the model. The model-derived aqueous solutions have compositions that describe the maturation path of hydrothermal fluids, from immature, acidic Mg-rich waters, toward Na-Cl-rich mature hydrothermal brines. The modeled compositions are in fair agreement with measured compositions of natural thermal waters and reservoir fluids from Iceland. We additionally show that the composition of the modelgenerated gases is strongly temperature-dependent, and ranges from CO 2(g) -dominated (for temperatures ≤80°C) to H 2 O (g) -dominated (and more H 2 S (g) rich) for temperatures N 100°C. We find that this range of model gas compositions reproduces well the (H 2 O-CO 2 -S TOT ) compositional range of reservoir waters and surface gas emissions in Iceland. From this validation of the model in an extreme end-member environment of high scrubbing, we conclude that EQ3/6-based reaction path simulations offer a realistic representation of gas-water-rock interaction processes occurring underneath active magmatic-hydrothermal systems.

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High-3He/4He, depleted mantle and low-δ18O, recycled oceanic lithosphere in the source of central Iceland magmatism

Cited by 85 publications

References 62 publications

186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites

186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites

Sources, degassing, and contamination of CO2, H2O, He, Ne, and Ar in basaltic glasses from Kolbeinsey Ridge, North Atlantic

Reaction path models of magmatic gas scrubbing

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