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David R. Hilton - One of the best experts on this subject based on the ideXlab platform.

  • Spatial distribution of Helium Isotopes in Icelandic geothermal fluids and volcanic materials with implications for location, upwelling and evolution of the Icelandic mantle plume
    Chemical Geology, 2018
    Co-Authors: Sunna Harðardóttir, Sæmundur A. Halldórsson, David R. Hilton
    Abstract:

    Abstract The distribution of Helium Isotope ratios (3He/4He) in Icelandic geothermal fluids, volcanic glasses and phyric lavas is investigated. Along with presenting a new Helium Isotope dataset using phyric lavas largely from off-rift regions, we compiled published data and constructed a database of all available Helium Isotope data from Iceland. The new dataset reveals an exceptionally high 3He/4He ratio from a phyric lava in NW-Iceland (47.5 RA, where RA is the 3He/4He ratio of air), which is among the highest values measured in any mantle-derived magma to date. Modifications of primary (i.e., mantle-derived) Helium Isotope ratios, due to additions of air-derived Helium and He from radiogenic ingrowth, were evaluated and the database was filtered accordingly. The geographical information system ArcGIS (ESRI) was used to perform spatial analysis on the filtered database and the interpolation method, Natural Neighbor, was used to calculate representative Helium Isotope ratios for all parts of Iceland, including off-rift regions. The results show that Helium Isotope ratios for the whole of Iceland vary from 5.1 to 47.5 RA. However, this study allows for a fine-scale distinction to be made between individual rift segments and off-rift regions. The results clearly reveal that each rift zone has its own distinctive mean Isotope signature: 12–17 RA in the Western Rift Zone, 8–11 RA in the Northern Rift Zone and 18–21 RA in the Eastern Rift Zone. Our isoscape map places new constraints on a previously inferred high-Helium plateau region in central Iceland (Breddam et al., 2000). The plateau continues southward along the propagating Eastern Rift Zone and through to the South Iceland Seismic Zone and the Mid-Iceland belt. Its location coincides with many geological features, e.g., eruption rates, location of abandoned rift segments, seismic velocity and gravity anomalies. Such high Helium Isotope ratios have been associated with undegassed and primordial mantle sources that have been isolated in the lower mantle over Earth's history. Thus, high-Helium domains throughout Iceland are interpreted to mark the loci of present and past plume conduits which help explain the considerable spatial variation in the sampling of a primordial mantle He component beneath the Iceland hotspot.

  • Helium Isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux
    Geophysical Research Letters, 2011
    Co-Authors: David R. Hilton, Sæmundur A. Halldórsson, Tobias P. Fischer, Peter H. Barry, J. M. De Moor, Carlos Ramírez, F. Mangasini, Paolo Scarsi
    Abstract:

    [1] 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.

  • Helium Isotope variations between Réunion Island and the Central Indian Ridge (17°–21°S): New evidence for ridge–hot spot interaction
    Journal of Geophysical Research : Solid Earth, 2011
    Co-Authors: Evelyn Fûri, Christophe Hemond, David R. Hilton, Bramley J Murton, Jérôme Dyment, James Day
    Abstract:

    We report new Helium abundance and Isotope results for submarine basaltic glasses from the Central Indian Ridge (CIR) between the Marie Celeste (16.7°S) and Egeria fracture zones (FZ) (20.6°S); the adjacent Gasitao, Three Magi, and Rodrigues ridges; and for olivine separates from lavas and cumulate xenoliths from the Mascarene Islands (Réunion, Mauritius, and Rodrigues). Helium Isotope ratios in basaltic glasses range from 7.1 to 12.2 RA (where RA = air 3He/4He) and lie between values of Mid-Ocean Ridge Basalt (MORB) (8 ± 1 RA) and samples from Réunion Island (11.5 to 14.1 RA). The highest 3He/4He values (up to 12.2 RA) are found in glasses recovered off axis from the Three Magi and Gasitao ridges. Along the CIR axis, MORB-like 3He/4He ratios are found near the Egeria FZ, and there is a marked increase to values of ~11 RA between ~19° and 20°S. The lowest 3He/4He values (

  • Helium Isotope variations between reunion island and the central indian ridge 17 21 s new evidence for ridge hot spot interaction
    Journal of Geophysical Research, 2011
    Co-Authors: Christophe Hemond, David R. Hilton, Bramley J Murton, Evelyn Fûri, Jérôme Dyment, James M D Day
    Abstract:

    We report new Helium abundance and Isotope results for submarine basaltic glasses from the Central Indian Ridge (CIR) between the Marie Celeste (16.7°S) and Egeria fracture zones (FZ) (20.6°S); the adjacent Gasitao, Three Magi, and Rodrigues ridges; and for olivine separates from lavas and cumulate xenoliths from the Mascarene Islands (Reunion, Mauritius, and Rodrigues). Helium Isotope ratios in basaltic glasses range from 7.1 to 12.2 R A (where R A = air 3He/4He) and lie between values of Mid‐Ocean Ridge Basalt (MORB) (8 ± 1 R A) and samples from Reunion Island (11.5 to 14.1 R A). The highest 3He/4He values (up to 12.2 R A) are found in glasses recovered off axis from the Three Magi and Gasitao ridges. Along the CIR axis, MORB‐like 3He/4He ratios are found near the Egeria FZ, and there is a marked increase to values of ∼11 R A between ∼19° and 20°S. The lowest 3He/4He values (<8 R A) are found immediately south of the Marie Celeste FZ, where incompatible trace element ratios (e.g., La/Sm) are highest. These low 3He/4He ratios can be explained by closed system radiogenic 4 He ingrowth in either (1) a " fossil " Reunion hot spot mantle component, embedded into the subridge mantle when the CIR migrated over the hot spot at ∼34 Ma or (2) trace element enriched MORB mantle. In contrast, the high 3He/4He ratios observed on the CIR axis adjacent to the Gasitao Ridge, and along the off‐axis volcanic ridges, are consistent with flow of hot spot mantle material from Reunion (∼1100 km to the west) toward the CIR.

  • Helium Isotope variations in mineral separates from costa rica and nicaragua assessing crustal contributions timescale variations and diffusion related mechanisms
    Chemical Geology, 2006
    Co-Authors: David R. Hilton, A M Shaw, T P Fischer, James A Walker, G A M De Leeuw
    Abstract:

    Abstract We report new He abundance and Isotope measurements of phenocryst phases in volcanic tephra and lavas from the Nicaragua-Costa Rica section of the Central American arc, where significant variations in crustal thickness have been inferred. Helium Isotope values range from 4.6 R A to 7.5 R A , with no evidence for crustal thickness influencing measured 3 He/ 4 He ratios. A comparison of He abundances and Isotopes measured in mafic phenocrysts from tephra vs. lavas from two separate eruptions at Cerro Negro show that both sampling media preserve phenocrysts with high 3 He/ 4 He values. 3 He/ 4 He ratios measured in phenocryst phases show good agreement with He Isotope values of geothermal fluids from the same volcanoes. However, we note that the pyroxenes tend to have lower 3 He/ 4 He ratios (4.6–7.0 R A ) than the olivines ( 3 He/ 4 He = 6.1–7.5 R A ) over a range of concentration values and are consistently lower in cogenetic phenocryst pairs at all locations sampled. In order to assess how this difference arises, we explore two alternative mechanisms: (1) diffusion-related isotopic fractionation, and (2) late-stage radiogenic 4 He additions, preferentially influencing pyroxene grains. In the first case, we reject diffusion-related fractionation of He Isotopes since lower 3 He/ 4 He ratios are not accompanied by a decrease in He concentration values. The second scenario is evaluated on the basis of Mg numbers in cogenetic phenocryst pairs and by petrological modeling of the crystallization sequence. Mg numbers and modeling results at low pressure conditions (= 1 kbar) suggest that olivine crystallization preceded pyroxene crystallization. However, since lavas do not show evidence for extensive crustal contamination, we suggest that the best explanation for the lower 3 He/ 4 He ratios in pyroxenes is related to the closure temperatures of the phenocryst phases. Given its lower closure temperatures and higher He diffusion rates, we suggest that pyroxenes would be more susceptible to late-stage He exchange with a low 3 He/ 4 He source during ascent, presumably the surrounding crust.

John E. Lupton - One of the best experts on this subject based on the ideXlab platform.

  • A comprehensive global oceanic dataset of Helium Isotope and tritium measurements
    Earth System Science Data, 2019
    Co-Authors: William J. Jenkins, Scott Doney, Michaela Fendrock, Toshitaka Gamo, Philippe Jean-baptiste, Birgit Klein, John E. Lupton, Rana A. Fine, Robert M. Key, Robert Newton
    Abstract:

    Abstract. Tritium and Helium Isotope data provide key information on ocean circulation, ventilation, and mixing, as well as the rates of biogeochemical processes and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and Helium Isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years. The dataset's DOI is https://doi.org/10.25921/c1sn-9631, and the data are available at https://www.nodc.noaa.gov/ocads/data/0176626.xml (last access: 15 March 2019) or alternately http://odv.awi.de/data/ocean/jenkins-tritium-Helium-data-compilation/ (last access: 13 March 2019) and includes approximately 60 000 valid tritium measurements, 63 000 valid Helium Isotope determinations, 57 000 dissolved Helium concentrations, and 34 000 dissolved neon concentrations. Some quality control has been applied in that questionable data have been flagged and clearly compromised data excluded entirely. Appropriate metadata have been included, including geographic location, date, and sample depth. When available, we include water temperature, salinity, and dissolved oxygen. Data quality flags and data originator information (including methodology) are also included. This paper provides an introduction to the dataset along with some discussion of its broader qualities and graphics.

  • A comprehensive global oceanic dataset of Helium Isotope and tritium measurements
    2018
    Co-Authors: William J. Jenkins, Scott Doney, Michaela Fendrock, Rana Fine, Toshitaka Gamo, Philippe Jean-baptiste, Robert Key, Birgit Klein, John E. Lupton, Monika Rhein
    Abstract:

    Abstract. Tritium and Helium Isotope data provide key information on ocean circulation, ventilation, and mixing, as well as the rates of biogeochemical processes, and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and Helium Isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years. The dataset has a DOI:10.25921/c1sn-9631 and is available at https://www.nodc.noaa.gov/ocads/data/0176626.xml, and includes approximately 60,000 valid tritium measurements, 63,000 valid Helium Isotope determinations, 57,000 dissolved Helium concentrations, and 34,000 dissolved neon concentrations. Some quality control has been applied in that questionable data have been flagged and clearly compromised data excluded entirely. Appropriate metadata has been included, including geographic location, date, and sample depth When available, we include water temperature, salinity, and dissolved oxygen. Data quality flags and data originator information (including methodology) are also included. This paper provides an introduction to the dataset along with some discussion of its broader qualities and graphics.

  • Helium Isotope variations and mantle plume spreading ridge interactions along the galapagos spreading center
    Graham David W. Hanan Barry B. Lupton John E. Hoernle Kaj Werner Reinhard Christie David M. and Sinton John M. (2014) Helium Isotope Variations and ma, 2014
    Co-Authors: David W Graham, John E. Lupton, David M. Christie, Barry B Hanan, Kaj Hoernle, Reinhard Werner, John M Sinton
    Abstract:

    Along the Galapagos Spreading Center (GSC), 3He/4He varies from 8.5–5.9 RA. High 3He/4He ratios, resembling those in the western and southern Galapagos islands, are absent. This lack of high 3He/4He contrasts markedly with other localities of plume–ridge interaction, such as Iceland, Easter, and Amsterdam/St. Paul. The most striking feature is a 3He/4He gradient, decreasing westward from 8.4–7.0 RA between 89 and 93°W, where the GSC is shallowest and shows “axial high” morphology. The intra-segment 3He/4He variability within this region indicates that magma crosses the mantle/crust boundary at multiple points beneath individual ridge segments, and lateral mixing within the crust and upper mantle is limited. Some of the 3He/4He variability may also reflect transfer of discrete heterogeneity from beneath the northern sector of the Galapagos plateau. One possible explanation for the absence of high 3He/4He along the GSC is that Helium is a relatively ineffective downstream tracer of mantle material from the core of the Galapagos plume, due to its preferential extraction beneath the archipelago compared to other incompatible, lithophile tracers. A second explanation is that the heterogeneous Galapagos plume is sheared in the upper mantle by motion of the Nazca Plate relative to the migrating GSC. In this case, plume core material having high 3He/4He (from beneath Fernandina and Isabela) would be dispersed mostly away from the ridge, while plume edge material having low 3He/4He plus enriched Sr and Pb Isotope signatures (from beneath the northern periphery of the archipelago) is smeared into the sub-ridge mantle.

  • changes in the atmospheric Helium Isotope ratio over the past 40 years
    Geophysical Research Letters, 2013
    Co-Authors: John E. Lupton, L J Evans
    Abstract:

    [1] We have compared the Helium Isotope ratio in five samples of Pacific marine air spanning the 40 year period between 1973 and 2013 against a secondary gas standard. In a separate experiment we directly compared the 3He/4He ratio in air samples collected in 1973 and 2013 at the same location in La Jolla, California, eliminating any geographical bias. Both experiments are consistent with zero time rate of change for atmospheric 3He/4He. Our best estimate for the rate of change of the 3He/4He ratio in Pacific marine air is −0.0014 ± 0.0045%/yr (2σ), indicating that air Helium is still a valid standard for terrestrial Helium Isotope measurements.

  • Changes in the atmospheric Helium Isotope ratio over the past 40 years
    Geophysical Research Letters, 2013
    Co-Authors: John E. Lupton, L J Evans
    Abstract:

    To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article is copyrighted by the American Geophysical Union. It can be found at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1944-8007.We have compared the Helium Isotope ratio in five\ud samples of Pacific marine air spanning the 40 year period\ud between 1973 and 2013 against a secondary gas standard. In\ud a separate experiment we directly compared the ³He/⁴He\ud ratio in air samples collected in 1973 and 2013 at the same\ud location in La Jolla, California, eliminating any geographical\ud bias. Both experiments are consistent with zero time rate of\ud change for atmospheric ³He/⁴He. Our best estimate for the\ud rate of change of the ³He/⁴He ratio in Pacific marine air is\ud -0.0014 ± 0.0045%/yr (2σ), indicating that air Helium is still\ud a valid standard for terrestrial Helium Isotope measurements

Monika Rhein - One of the best experts on this subject based on the ideXlab platform.

  • A comprehensive global oceanic dataset of Helium Isotope and tritium measurements
    2018
    Co-Authors: William J. Jenkins, Scott Doney, Michaela Fendrock, Rana Fine, Toshitaka Gamo, Philippe Jean-baptiste, Robert Key, Birgit Klein, John E. Lupton, Monika Rhein
    Abstract:

    Abstract. Tritium and Helium Isotope data provide key information on ocean circulation, ventilation, and mixing, as well as the rates of biogeochemical processes, and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and Helium Isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years. The dataset has a DOI:10.25921/c1sn-9631 and is available at https://www.nodc.noaa.gov/ocads/data/0176626.xml, and includes approximately 60,000 valid tritium measurements, 63,000 valid Helium Isotope determinations, 57,000 dissolved Helium concentrations, and 34,000 dissolved neon concentrations. Some quality control has been applied in that questionable data have been flagged and clearly compromised data excluded entirely. Appropriate metadata has been included, including geographic location, date, and sample depth When available, we include water temperature, salinity, and dissolved oxygen. Data quality flags and data originator information (including methodology) are also included. This paper provides an introduction to the dataset along with some discussion of its broader qualities and graphics.

  • coastal upwelling off peru and mauritania inferred from Helium Isotope disequilibrium
    Biogeosciences, 2015
    Co-Authors: R. Steinfeldt, Marcus Dengler, T. Fischer, Jurgen Sultenfus, Monika Rhein
    Abstract:

    Abstract. Upwelling is an important process, bringing gases and nutrients into the ocean mixed layer. The upwelling velocities, however, are too small to be measured directly. Here we use the surface disequilibrium of the 3He / 4He ratio measured in two coastal upwelling regions off Peru in the Pacific ocean and off Mauritania in the Atlantic ocean to calculate the regional distribution of vertical velocities. To also account for the fluxes by diapycnal mixing, microstructure-based observations of the vertical diffusivity have been performed on all four cruises analysed in this study. The upwelling velocities in the coastal regions vary between 1.1 ± 0.3 × 10−5 and 2.8 ± 1.5 × 10−5 m s−1 for all cruises. Vertical velocities are also inferred from the divergence of the wind-driven Ekman transport. In the coastal regimes, both methods agree within the error range. Further offshore, the Helium-derived vertical velocity still reaches 1 × 10−5 m s−1, whereas the wind-driven upwelling from Ekman suction is smaller by up to 1 order of magnitude. One reason for this difference is ascribed to eddy-induced upwelling. Both advective and diffusive nutrient fluxes into the mixed layer are calculated based on the Helium-derived vertical velocities and the vertical diffusivities. The advective part of these fluxes makes up at about 50 % of the total. The nutrient flux into the mixed layer in the coastal upwelling regimes is equivalent to a net community production (NCP) of 1.3 ± 0.3 g C m2 d−1 off Peru and 1.6–2.1 ± 0.5 g C m2 d−1 off Mauritania.

  • Upwelling and associated heat flux in the equatorial Atlantic inferred from Helium Isotope disequilibrium
    Journal of Geophysical Research, 2010
    Co-Authors: Monika Rhein, Jürgen Sültenfuß, Sabine Hüttl-kabus, Marcus Dengler, Rebecca Hummels, Bernard Bourlès
    Abstract:

    Upwelling velocities w in the equatorial band are too small to be directly observed. Here, we apply a recently proposed indirect method, using the observed Helium Isotope (3He or 4He) disequilibria in the mixed layer. The Helium data were sampled from three cruises in the eastern tropical Atlantic in September 2005 and June/July 2006. A one-dimensional two-box model was applied, where the Helium air-sea gas exchange is balanced by upwelling from 3He-rich water below the mixed layer and by vertical mixing. The mixing coefficients Kv were estimated from microstructure measurements, and on two of the cruises, Kv exceeded 1 × 10−4 m2/s, making the vertical mixing term of the same order of magnitude as the gas exchange and the upwelling term. In total, Helium disequilibrium was observed on 54 stations. Of the calculated upwelling velocities, 48% were smaller than 1.0 × 10−5 m/s, 19% were between 1.0 and 2.0 × 10−5 m/s, 22% were between 2.0 and 4.0 × 10−5 m/s, and on 11% of upwelling velocities exceeded this limit. The highest upwelling velocities were found in late June 2006. Meridional upwelling distribution indicated an equatorial asymmetry with higher vertical velocities between the equator and 1° to 2° south compared to north of the equator, particularly at 10°W. Associated heat flux into the mixed layer could be as high as 138 W/m2, but this depends strongly on the chosen depths where the upwelled water comes from. By combining upwelling velocities with sea surface temperature and productivity distributions, a mean monthly equatorial upwelling rate of 19 Sv was estimated for June 2006 and a biweekly mean of 24 Sv was estimated for September 2005.

  • Equatorial upwelling rates inferred from Helium Isotope and QuikSCAT wind-stress data
    2009
    Co-Authors: D. Kühnel, Monika Rhein, Jürgen Sültenfuß, Sabine Hüttl-kabus
    Abstract:

    Being hampered by the small velocities on scales of 1 m/day, vertical motion has to be estimated by indirect methods. Klein and Rhein (2004) proposed a novel approach to infer equatorial upwelling velocities by exploiting the Helium Isotope disequilibrium between atmosphere and equatorial oceanic mixed layer. Using this approach, equatorial upwelling rates are calculated from Helium measurements in the pelagic.

  • equatorial upwelling rates inferred from Helium Isotope data a novel approach
    Geophysical Research Letters, 2004
    Co-Authors: Birgit Klein, Monika Rhein
    Abstract:

    [1] Upwelling is one of the key processes to maintain the Tropical Atlantic cold tongue. This feature is of special interest to climate research, since its SST variability is significantly correlated with the West African Monsoon. Direct measurements of the upwelling have been hampered by the small speeds involved. Instead, vertical motion has to be estimated by indirect methods. Here we propose a novel approach to infer equatorial upwelling velocities by exploiting the Helium Isotope disequilibrium between atmosphere and equatorial oceanic mixed layer. The data were collected during WOCE cruises A13 and A14. Although the vertical and horizontal resolution of the Helium data in the upper tropical oceans was too poor to support a detailed study, it was sufficient to show the potential of the method.

Matthijs C Van Soest - One of the best experts on this subject based on the ideXlab platform.

  • flow of mantle fluids through the ductile lower crust Helium Isotope trends
    Lawrence Berkeley National Laboratory, 2008
    Co-Authors: Mack B Kennedy, Matthijs C Van Soest
    Abstract:

    Flow of Mantle Fluids Through the Duct,le Lower Crust: Helium Isotope Trends I B. Mack Kennedyl andlMatthijs C. van Soest ICenter for Isoto~e Geochemistry Earth Scienoes Division Lawrence Berkeley National Laboratory Berkeley, (:A 94720 2Noble Gas Geochemistry and Geochronology Laboratory School of Earth and Space Exploration Arizona State University Tempe, AZ 85287-1404 Abstract Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3 He /4 He ratios in surface fluids from the northern Basin and Range province, western North America increase systematically from low, crustal values in the east to high, mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of Helium Isotope ratios and active trans-tensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere in regions even where there is no significant magmatism. Superimposed on the regional trend are local, high- He/ He anomalies signifying hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.

  • Flow of mantle fluids through the ductile lower crust: Helium Isotope trends
    Science (New York N.Y.), 2007
    Co-Authors: B. Mack Kennedy, Matthijs C Van Soest
    Abstract:

    Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3He/4He ratios in surface fluids from the northern Basin and Range Province, western North America, increase systematically from low crustal values in the east to high mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of Helium Isotope ratios and active transtensional deformation indicates a deformation-enhanced permeability and that mantle fluids can penetrate the ductile lithosphere, even in regions where there is no substantial magmatism. Superimposed on the regional trend are local, high 3He/4He anomalies indicating hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.

  • A Systematic Regional Trend in Helium Isotopes Across the Northern Basin and Range Province, Western North America
    Lawrence Berkeley National Laboratory, 2006
    Co-Authors: B. Mack Kennedy, Matthijs C Van Soest
    Abstract:

    An extensive study of Helium Isotopes in fluids collected from surface springs, fumaroles and wells across the northern Basin and Range Province reveals a systematic trend of decreasing 3He/4He ratios from west to east. The western margin of the Basin and Range is characterized by mantle-like ratios (6-8 Ra) associated with active or recently active crustal magma systems (e.g., Coso, Long Valley, Steamboat, and the Cascade volcanic complex). Moving towards the east, the ratios decline systematically to a background value of ~;0.1 Ra. The regional trend is consistent with extensive mantle melting concentrated along the western margin and is coincident with an east-to-west increase in the magnitude of northwest strain. The increase in shear strain enhances crustal permeability resulting in high vertical fluid flow rates that preserve the high Helium Isotope ratios at the surface. Superimposed on the regional trend are Helium spikes, local anomalies in the Helium Isotope composition. These spikes reflect either local zones of mantle melting or locally enhanced crustal permeability. In the case of the Dixie Valley hydrothermal system, it appears to be a combination of both.

  • A Helium Isotope perspective on the Dixie Valley, Nevada, hydrothermal system
    Geothermics, 2006
    Co-Authors: B. Mack Kennedy, Matthijs C Van Soest
    Abstract:

    Abstract Fluids from springs, fumaroles, and wells throughout Dixie Valley, NV were analyzed for noble gas abundances and isotopic compositions. The Helium isotopic compositions of fluids produced from the Dixie Valley geothermal field range from 0.70 to 0.76 Ra, are among the highest values in the valley, and indicate that ∼7.5% of the total Helium is derived from the mantle. A lack of recent volcanics or other potential sources requires flow of mantle-derived Helium up along the valley bounding Stillwater Range Front Fault, from which the geothermal fluids are produced. Using a one-dimensional flow model, a lower limit fluid flow rate up through the fault of 7 mm/yr is estimated, corresponding to a mantle 3 He flux of ∼10 4  atoms m −2  s −1 . A comparison between the fluids from Dixie Valley springs, fumaroles, and wells and the fluids produced from the geothermal field reveals a mixing trend between the geothermal fluid and younger, cooler groundwaters. The exceptions are those features that either emanate directly from the Stillwater fault or wells that penetrate and extract fluids from the fault zone, all of which have Helium isotopic compositions that are indistinguishable from the geothermal production fluids. The results of our study indicate that the Stillwater Range Front Fault system must act as a permeable conduit that can sustain high vertical fluid flow rates from deep within the crust and crust-mantle boundary and that high permeability may exist along most of its length. This suggests that the geothermal potential of the Stillwater fault may be significantly greater than the 6–8 km long system presently under production. Since all the numerous springs, wells, and fumaroles in the valley also contain a fluid component that is indistinguishable from the geothermal/Stillwater fault fluid, the potential for an additional deeper and more pervasive geothermal system also exists and should be further evaluated. Furthermore, we suggest that elevated Helium Isotope compositions in regions with little or no recent magmatism are an indicator of the deep crustal permeability that is required to drive and sustain extensional geothermal systems.

  • Regional and Local Trends in Helium Isotopes, basin and range province, western North America: Evidence for deep permeable pathways
    Lawrence Berkeley National Laboratory, 2005
    Co-Authors: B. Mack Kennedy, Matthijs C Van Soest
    Abstract:

    Fluids from the western margin of the Basin and Range have Helium Isotope ratios as high as ~;6-7 Ra, indicating a strong mantle melt influence and consistent with recent and current volcanic activity. Moving away from these areas, Helium Isotope ratios decrease rapidly to 'background' values of around 0.6 Ra, and then gradually decrease toward the east to low values of ~;0.1 Ra at the eastern margin of the Basin and Range. Superimposed on this general regional trend are isolated features with elevated Helium Isotope ratios (0.8-2.1 Ra) compared to the local background. Spring geochemistry and local geology indicate that these He-spikes are not related to current or recent magmatic activity, suggesting that the spikes may reflect either localized zones deep mantle melting or deep permeable pathways (faults) with high vertical fluid flow rates. A detailed study of one of the He-spikes (Dixie Valley and the Stillwater Range Front Fault system), indicates that features with high 3He/4He ratios are confined to the range front normal faults characteristic of the extensional regime in the Basin and Range, suggesting that these faults are deep permeable pathways. However, not all range front fault systems transmit fluids with a mantle signature, implying that not all have deep permeable pathways.

Philippe Jean-baptiste - One of the best experts on this subject based on the ideXlab platform.

  • A comprehensive global oceanic dataset of Helium Isotope and tritium measurements
    Earth System Science Data, 2019
    Co-Authors: William J. Jenkins, Scott Doney, Michaela Fendrock, Toshitaka Gamo, Philippe Jean-baptiste, Birgit Klein, John E. Lupton, Rana A. Fine, Robert M. Key, Robert Newton
    Abstract:

    Abstract. Tritium and Helium Isotope data provide key information on ocean circulation, ventilation, and mixing, as well as the rates of biogeochemical processes and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and Helium Isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years. The dataset's DOI is https://doi.org/10.25921/c1sn-9631, and the data are available at https://www.nodc.noaa.gov/ocads/data/0176626.xml (last access: 15 March 2019) or alternately http://odv.awi.de/data/ocean/jenkins-tritium-Helium-data-compilation/ (last access: 13 March 2019) and includes approximately 60 000 valid tritium measurements, 63 000 valid Helium Isotope determinations, 57 000 dissolved Helium concentrations, and 34 000 dissolved neon concentrations. Some quality control has been applied in that questionable data have been flagged and clearly compromised data excluded entirely. Appropriate metadata have been included, including geographic location, date, and sample depth. When available, we include water temperature, salinity, and dissolved oxygen. Data quality flags and data originator information (including methodology) are also included. This paper provides an introduction to the dataset along with some discussion of its broader qualities and graphics.

  • A comprehensive global oceanic dataset of Helium Isotope and tritium measurements
    Earth System Science Data, 2019
    Co-Authors: William Jenkins, Scott Doney, Michaela Fendrock, Rana Fine, Toshitaka Gamo, Philippe Jean-baptiste, Robert Key, Birgit Klein, John Lupton, Robert Newton
    Abstract:

    Tritium and Helium Isotope data provide key information on ocean circulation, ventilation, and mixing , as well as the rates of biogeochemical processes and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and Helium Isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years.

  • A comprehensive global oceanic dataset of Helium Isotope and tritium measurements
    2018
    Co-Authors: William J. Jenkins, Scott Doney, Michaela Fendrock, Rana Fine, Toshitaka Gamo, Philippe Jean-baptiste, Robert Key, Birgit Klein, John E. Lupton, Monika Rhein
    Abstract:

    Abstract. Tritium and Helium Isotope data provide key information on ocean circulation, ventilation, and mixing, as well as the rates of biogeochemical processes, and deep-ocean hydrothermal processes. We present here global oceanic datasets of tritium and Helium Isotope measurements made by numerous researchers and laboratories over a period exceeding 60 years. The dataset has a DOI:10.25921/c1sn-9631 and is available at https://www.nodc.noaa.gov/ocads/data/0176626.xml, and includes approximately 60,000 valid tritium measurements, 63,000 valid Helium Isotope determinations, 57,000 dissolved Helium concentrations, and 34,000 dissolved neon concentrations. Some quality control has been applied in that questionable data have been flagged and clearly compromised data excluded entirely. Appropriate metadata has been included, including geographic location, date, and sample depth When available, we include water temperature, salinity, and dissolved oxygen. Data quality flags and data originator information (including methodology) are also included. This paper provides an introduction to the dataset along with some discussion of its broader qualities and graphics.

  • Simulation of the mantle and crustal Helium Isotope signature in the Mediterranean Sea using a high-resolution regional circulation model
    Ocean Science, 2015
    Co-Authors: Mohamed Ayache, Philippe Jean-baptiste, Jean-claude Dutay, E. Fourré
    Abstract:

    Abstract. Helium Isotopes (3He, 4He) are useful tracers for investigating the deep ocean circulation and for evaluating ocean general circulation models, because Helium is a stable and conservative nuclide that does not take part in any chemical or biological process. Helium in the ocean originates from three different sources, namely, (i) gas dissolution in equilibrium with atmospheric Helium, (ii) Helium-3 addition by radioactive decay of tritium (called tritiugenic Helium), and (iii) injection of terrigenic Helium-3 and Helium-4 by the submarine volcanic activity which occurs mainly at plate boundaries, and also addition of (mainly) Helium-4 from the crust and sedimentary cover by α-decay of uranium and thorium contained in various minerals. We present the first simulation of the terrigenic Helium Isotope distribution in the whole Mediterranean Sea using a high-resolution model (NEMO-MED12). For this simulation we build a simple source function for terrigenic Helium Isotopes based on published estimates of terrestrial Helium fluxes. We estimate a hydrothermal flux of 3.5 mol3 He yr−1 and a lower limit for the crustal flux at 1.6 × 10−7 4He mol m−2 yr−1. In addition to providing constraints on Helium Isotope degassing fluxes in the Mediterranean, our simulations provide information on the ventilation of the deep Mediterranean waters which is useful for assessing NEMO-MED12 performance. This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

  • Helium Isotope systematics of volcanic gases and thermal waters of Guadeloupe Island, Lesser Antilles
    Journal of Volcanology and Geothermal Research, 2014
    Co-Authors: Philippe Jean-baptiste, P. Allard, Elise Fourré, Francesco Parello, Alessandro Aiuppa
    Abstract:

    Abstract The island of Guadeloupe is located in the middle of the 850 km long Lesser Antilles island arc. Present-day volcanic and geothermal activity is concentrated in two systems both located in the southwestern part of the island (Basse Terre): the La Soufriere volcanic complex and the Bouillante hydrothermal system, some 20 km to the northwest of the volcano. We report here the largest isotopic data set for Helium Isotopes in hydrothermal gases and waters from both systems, acquired between 1980 and 2012. 3 He/ 4 He ratios in the fumarolic gases of La Soufriere volcano have been quite homogeneous and stable over the last thirty years. The average ratio of 8.2 ± 0.2 R a confirms that the volcano is tapping a MORB-like mantle source. In contrast, the nearby Bouillante geothermal system displays a much lower 3 He/ 4 He ratio (4.5 ± 0.1 R a ). He–C elemental and isotopic relationships show that both systems are actually fed by the same magmatic source, and that their marked difference in 3 He/ 4 He results from the 4 He contamination of the Bouillante deep aquifer by the surrounding wallrock. This conclusion is strengthened by the spatial distribution of 3 He/ 4 He ratios which shows that La Soufriere fumaroles and the Bouillante geothermal system are the two end-members of a spatial trend of decreasing 3 He/ 4 He ratio with distance from La Soufriere summit dome, implying an increasing addition of radiogenic 4 He from the host rocks away from the present-day active volcanic edifice.