The origin of high helium concentrations in the gas fields of southwestern Tanzania

Mtili, K.M.; Byrne, David; Tyne, Rebecca; Kazimoto, Emmanuel Owden; Kimani, C.N.; Kasanzu, Charles H.; Hillegonds, D. J.; Ballentine, C. J.; Barry, Peter H.

doi:10.1016/j.chemgeo.2021.120542

Cited by 22 publications

(4 citation statements)

References 129 publications

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“…Once all water was displaced by sample gas, the stainless steel clamps were closed in the same way as described above. This technique is particularly useful in low flow gas seeps, where prohibitively long flushing times would be required (e.g., Kimani et al, 2021;Mtili et al, 2021). Water samples require minimal flushing and can often be collected in a matter of minutes.…”

Section: Sample Collectionmentioning

confidence: 99%

The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin

et al. 2022

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Subduction zones represent the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively cycled between Earth reservoirs by plate tectonics. Helium is a sensitive tracer of volatile sources and can be used to deconvolute mantle and crustal sources in arcs; however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems. Here, we report helium isotope and abundance data for 42 deeply-sourced fluid and gas samples from the Central Volcanic Zone (CVZ) and Southern Volcanic Zone (SVZ) of the Andean Convergent Margin (ACM). Data are used to assess the influence of subduction parameters (e.g., crustal thickness, subduction inputs, and convergence rate) on the composition of volatiles in surface volcanic fluid and gas emissions. He isotopes from the CVZ backarc range from 0.1 to 2.6 RA (n = 23), with the highest values in the Puna and the lowest in the Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected He isotopes from the SVZ range from 0.7 to 5.0 RA (n = 19). Taken together, these data reveal a clear southeastward increase in 3He/4He, with the highest values (in the SVZ) falling below the nominal range associated with pure upper mantle helium (8 ± 1 RA), approaching the mean He isotope value for arc gases of (5.4 ± 1.9 RA). Notably, the lowest values are found in the CVZ, suggesting more significant crustal inputs (i.e., assimilation of 4He) to the helium budget. The crustal thickness in the CVZ (up to 70 km) is significantly larger than in the SVZ, where it is just ∼40 km. We suggest that crustal thickness exerts a primary control on the extent of fluid-crust interaction, as helium and other volatiles rise through the upper plate in the ACM. We also report carbon isotopes from (n = 11) sites in the CVZ, where δ13C varies between −15.3‰ and −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] and CO2/3He values that vary by over two orders of magnitude (6.9 × 108–1.7 × 1011). In the SVZ, carbon isotope ratios are also reported from (n = 13) sites and vary between −17.2‰ and −4.1‰. CO2/3He values vary by over four orders of magnitude (4.7 × 107–1.7 × 1012). Low δ13C and CO2/3He values are consistent with CO2 removal (e.g., calcite precipitation and gas dissolution) in shallow hydrothermal systems. Carbon isotope fractionation modeling suggests that calcite precipitation occurs at temperatures coincident with the upper temperature limit for life (122°C), suggesting that biology may play a role in C-He systematics of arc-related volcanic fluid and gas emissions.

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Section: Sample Collectionmentioning

confidence: 99%

The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin

et al. 2022

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“…The importance of dominant structural mechanisms such as basement faults and intrusions in the transport of He from a deep crustal source to reservoir has been speculated before (Danabalan et al, 2022;Halford et al, 2022;Karolyte et al, 2022), together with circumstantial evidence of basement fault control (Boles et al, 2015;Buttitta et al, 2020;Craddock et al, 2017;Mtili et al, 2021;Tardani et al, 2016). Using a spatial analysis of He occurrence with faults and intrusions from high-resolution geophysics, we show that a non-random process indeed controls the relationship between He and faults and intrusions and that there is a strong relationship between He and faults/intrusions that can be quantified and utilized.…”

Section: Discussionmentioning

confidence: 98%

“…Previous work observed little variance in 4 He/N 2 in the Four Corners gas fields to argue for fault controlled advective free‐gas He migration from the crystalline basement to trapping structures (Halford et al., 2022). While high‐He gas has been postulated to be correlated with structural features, such as faults and intrusions (Boles et al., 2015; Buttitta et al., 2020; Craddock et al., 2017; Danabalan et al., 2022; Halford et al., 2022; Karolytė et al., 2022; Mtili et al., 2021; Tardani et al., 2016) the data, until now, to quantifiably test this concept for high‐He gas field formation, has not been available. Using newly acquired high‐resolution geophysical data (Figure 1) combined with geochemical data sets within the Four Corners area, we test the hypothesis that faults and intrusions are spatially correlated with high He, which may be translated to regions outside the Four Corners area.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic Determination of the Role of Faults and Intrusions in Helium‐Rich Gas Fields Formation

Halford,

Karolytė,

Andreason

et al. 2024

Geochem Geophys Geosyst

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Natural gas fields with economic helium (>0.3 He %) require the radioactive decay of crustal uranium (U) and thorium (Th) to generate He and tectonic/structural regimes favorable to releasing and concentrating He. An unknown is determining the role of faults and structural features in focusing deep‐seated He sources on shallow accumulations. We tested the correlation between high‐He wells (n = 94) and structural features using a new high‐resolution aeromagnetic survey in the Four Corners area, USA. A depth‐to‐basement map with basement lineaments/faults, an intrusion map, and a flattened basement structural high map were created using Werner deconvolution algorithms by combining magnetic, gravity, and topography data with magnetic and gravity depth profiles. We show quantitatively (via analysis of variance) that a non‐random process controls the relationship between He (>0.3%) and both basement faults and intrusions: 88% of high‐He wells occur <1 km of basement faults; and 85% of high‐He wells occur <1 km of intrusions. As He % increases, the distance to the structural features decreases. Strong spatial/statistical correlations of He wells to both basement faults and intrusions suggest that advective transport via faults/intrusions facilitates He migration. The role of gas phase buoyancy and structural trapping is confirmed: 88% of high‐He occurs within basement structural highs, and 91% of the remaining wells are <1 km from intrusions (potential structural high). We present a composite figure to illustrate how a probabilistic approach can be used as a predictive model to improve He exploration success by targeting zones of intersection of basement faults and intrusions within basement structural highs.

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“…Yama Tomonaga and co-workers used this device to monitor the free gas phase in an underground rock laboratory in Switzerland in the context of a large scale radioactive waste management test (Tomonaga et al, 2019). The system has also been applied, for example, at a CO 2 capture facility in Norway (Weber et al, 2021), to analyse noble gases, CO 2 , and N 2 at the East African Rift system in Tanzania within a few hours of sampling (Mtili et al, 2021), and to study geogenic arsenic contamination of groundwaters with noble gases (Lightfoot et al, 2022).…”

Section: Mass Spectrometry In the Fieldmentioning

confidence: 99%

A journey in Noble Gas Cosmochemistry and Geochemistry

Wieler¹

2023

Geochem. Persp.

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I started my journey in science by studying noble gases implanted by the solar wind in dust grains on the surface of the Moon, and with many colleagues I have studied solar wind implanted noble gases in natural and artificial samples throughout my career, the latter exposed primarily by the Genesis space mission. Major questions are what noble gases in the solar wind can tell us about the present and the past Sun, and how they can contribute to understanding the formation and history of the planets and their building blocks, represented, for example, by meteorites. Since my early years as a postdoc, I have also been interested in noble gases (and radioactive nuclides) produced in meteorites and other extraterrestrial samples by interactions with energetic elementary particles from galactic cosmic radiation (and the Sun). These so called “cosmogenic” nuclides allow us to study the transport of meteorites to Earth, and the dynamics of the top surface layers (“regoliths”) on the Moon, asteroids, and comets. Cosmogenic noble gases are also crucial for studying even more exotic topics such as the history of tiny presolar grains that formed in the cooling envelopes of earlier generations of stars towards the end of their lives and were eventually incorporated into the meteoritic matter where they are found today. Cosmogenic noble gases in some tiny phases in meteorites are also likely tracers of our highly active Sun at a very early stage in its history. A few years later, I started my third major research topic in cosmochemistry, the study of primordial noble gases in meteorites and other extraterrestrial samples. These noble gases were incorporated into meteorites or their precursors in the early solar system or even in a presolar environment. I also participated in studies by colleagues of isotopic anomalies of other elements important in cosmochemistry, my expertise being mainly in aspects of the influence of cosmic rays on these elements. Although working in an Earth Science institution, it took quite a while before I started to also study noble gases (and radionuclides) in terrestrial samples. This is described in the second part of this contribution. A major focus was on cosmogenic noble gases and radionuclides produced in samples near the Earth’s surface. Although production rates of cosmogenic nuclides on Earth are several orders of magnitude lower than in space, making their analysis more challenging, they have become an important tool in geomorphology. Because stable noble gas nuclides are particularly well suited to the study of ancient landscapes, much of our work focused on areas with arid climates, such as Antarctica and the Andes in Chile, in collaboration with geoscience colleagues. We also participated in the large multinational CRONUS collaboration, funded by the European Union, a community effort to improve our knowledge of nuclide production rates at the Earth’s surface. In another major collaboration with external colleagues we are involved in noble gas analyses of water samples, ranging from lakes to aquifers to tiny inclusions in stalagmites. This research focuses on studying lake and groundwater dynamics, including contributions of mantle-derived noble gases such as in volcanic lakes. Atmospheric noble gases dissolved in suitable samples are also palaeotemperature indicators, supplementing information from other proxies such as oxygen isotopes.

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The origin of high helium concentrations in the gas fields of southwestern Tanzania

Cited by 22 publications

References 129 publications

The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin

The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin

Probabilistic Determination of the Role of Faults and Intrusions in Helium‐Rich Gas Fields Formation

A journey in Noble Gas Cosmochemistry and Geochemistry

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