Natural production of tritium in permeable rocks

Andrews, John N.; Kay, Robert L.

doi:10.1038/298361a0

Cited by 107 publications

(53 citation statements)

References 7 publications

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“…Lithospheric mantle contamination could change Nb/Y at a given Zr/Y (see so it is important to use this diagram only for uncontaminated CFB samples. Data sources: Armstrong et al (1984), Lightfoot et al (1997), Storey et al (1997), Melluso et al (2001Melluso et al ( , 2005, Thompson et al (2001), Stuart et al (2003), Kent et al (2004), Starkey et al (2009); data for SWIR MORBs compiled from PetDB (www.earthchem.org/petdb) and data for Prince Edward Islands compiled from GEOROC (www.georoc.mpch-mainz.gwdg.de).…”

Section: Trace Elementsmentioning

confidence: 99%

Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province

Heinonen

Kurz

2015

Earth and Planetary Science Letters

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Keywords:Karoo large igneous province continental flood basalts helium isotopes mantle sourceThe massive outpourings of Karoo and Ferrar continental flood basalts (CFBs) ∼180 Ma ago mark the initial Jurassic rifting stages of the Gondwana supercontinent. The origin and sources of these eruptions have been debated for decades, largely due to difficulties in defining their parental melt and mantle source characteristics. Recent findings of Fe-and Mg-rich dikes (depleted ferropicrite suite) from Vestfjella, western Dronning Maud Land, Antarctica, have shed light on the composition of the deep sub-Gondwanan mantle: these magmas have been connected to upper mantle sources presently sampled by the Southwest Indian Ocean mid-ocean ridge basalts (SWIR MORBs) or to high 3 He/ 4 He plume-entrained non-chondritic primitive mantle sources formed early in Earth's history. In an attempt to determine their He isotopic composition and relative contributions from magmatic, cosmogenic, and radiogenic He sources, we performed in-vacuo stepwise crushing and melting analyses of olivine mineral separates, some of which were abraded to remove the outer layer of the grains. The best estimate for the mantle isotopic composition is given by a sample with the highest amount of He released (>50%) during the first crushing step of an abraded coarse fraction. It has a 3 He/ 4 He of 7.03 ± 0.23 (2σ ) times the atmospheric ratio (R a ), which is indistinguishable from those measured from SWIR MORBs (6.3-7.3 R a ; source 3 He/ 4 He ∼6.4-7.6 R a at 180 Ma) and notably lower than in the most primitive lavas from the North Atlantic Igneous Province (up to 50 R a ), considered to represent the epitome magmas from non-chondritic primitive mantle sources. Previously published trace element and isotopic (Sr, Nd, and Pb) compositions do not suggest a direct genetic link to any modern hotspot of Indian or southern Atlantic Oceans. Although influence of a mantle plume cannot be ruled out, the high magma temperatures and SWIR MORB-like geochemistry of the suite are best explained by supercontinent insulation of a precursory Indian Ocean upper mantle source. Such a model is also supported by the majority of the recent studies on the structure, geochronology, and petrology of the Karoo CFBs.

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Section: Trace Elementsmentioning

confidence: 99%

Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province

Heinonen

Kurz

2015

Earth and Planetary Science Letters

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“…Considering both in situ production and fluxes from deeper regions, Stute et al (1992) expressed the evolution of 4 He concentration in groundwater as follows: A, Akeyo formation; TU, Upper Toki Lignite-bearing formation; TL, Lower Toki Lignite-bearing formation; G, Toki granite a Helium production ratio from rocks: 3 He production rate / 4 He production rate. The 3 He and 4 He production rates were estimated from U and Th concentrations of rocks and from Li concentration of rocks, neutron production rates, and the probability of neutron capture by 6 Li, respectively (Andrews and Kay 1982;Andrews 1985) Fig. 4.…”

Section: Helium and Neon Isotopesmentioning

confidence: 99%

Dissolved helium distribution in deep groundwaters from the Tono area, central Japan: a tool for tracing groundwater flow in fractured granite

Morikawa¹

2004

Limnology

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The helium isotopic composition of groundwater collected from boreholes was measured in the Tono area from up to 840 m underground. The 3 He/ 4 He and 4 He/ 20 Ne ratios ranged from 9.1 ϫ 10 Ϫ8 to 1.48 ϫ 10 Ϫ6 and from 0.22 to 190, respectively, implying that the groundwater accumulates significant amounts of radiogenic 4 He as it flows. In groundwater from sedimentary rocks, the levels of accumulated helium increase with depth, whereas those in the samples from fractured granite vary from borehole to borehole. Considering the hydrogeological and topographical model together, dissolved He concentrations in groundwater indicate the groundwater flow direction. Although the groundwater flow in fractured granite is generally thought to be controlled by the fracture pattern, the overall flow of the Tono area inferred from helium isotopes is also controlled by topography.

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“…Theoretical models for the evolution of 234U/ z38U activity ratios for dissolved U in the Stripa granite have been discussed by Andrews et al (1982). It is probable that the South Crofty waters have similarly envolved through a shallow recoildominated zone of limited extent, where their activity ratios reached a value >~ 2 at a depth around 250 m ( fig.…”

Section: Age Of the Saline Componentmentioning

confidence: 99%

The evolution of saline and thermal groundwaters in the Carnmenellis granite

et al. 1984

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ABSTRACT. The Carnmenellis granite and its aureole contain the only recorded thermal groundwaters (up to 52 ~ in British granites. They occur as springs in tin mines at depths between 200 and 700 m and most are saline (maximum mineralization 19 310 mg 1-1). Mining activity has disturbed the groundwater circulation pattern developed over a geological time-scale and levels of bomb-produced tritium (> 4 TU) indicate that a significant component (up to 65 %) of the most saline waters are of recent origin. All components of all the mine waters are of meteoric origin. Radiogenic 4He contents, 4~ ratios, and uranium series geochemistry suggest that the thermal component has a likely residence time of at least 5 x 104 years and probably of order 10 6 years.The thermal waters have molar Na+/C1 -ratios considerably less than i but they are enriched relative to sea water in all major cations except Mg.

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Natural production of tritium in permeable rocks

Cited by 107 publications

References 7 publications

Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province

Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province

Dissolved helium distribution in deep groundwaters from the Tono area, central Japan: a tool for tracing groundwater flow in fractured granite

The evolution of saline and thermal groundwaters in the Carnmenellis granite

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