High ammonium contents in the 3800 Ma Isua supracrustal rocks, central West Greenland

doi:10.1016/0016-7037(96)00083-X

Geochimica et Cosmochimica Acta

Volume 60, Issue 12, June 1996, Pages 2173-2178

https://doi.org/10.1016/0016-7037(96)00083-X Get rights and content

Abstract

Ammonium contents of whole-rock and biotite samples from the metasedimentary sequence of the 3800 Ma Isua supracrustal belt, central Greenland, have been determined and compared with the ammonium contents of volcanic, sedimentary, metamorphic, and granitic rocks from the Late Archaean-Early Proterozoic.

A sample of the Amitsoq gneiss has an NH₄⁺ content (whole-rock: 9 ppm, biotite: 29 ppm) that is similar to many younger igneous rocks.

Ammonium contents of the supracrustal rocks vary with chemistry and mineralogy of the rock and most likely were inherited from the original sediments. A series of carbonate-bearing and basic plagioclase-bearing biotite-rich schists from sequence A have varying NH₄⁺ contents (whole-rock: 6–24 ppm) that increase with an increasing chemical /clastic component and decreasing volcanogenic component. Biotites in these rocks, together with biotites in mica schists of the same sequence, have high NH₄⁺ contents which vary over a small range of 54–95 ppm, suggesting that the NH₄⁺ in these rocks was contained mostly in authigenic clays of the original sediments. All these data imply that clay minerals were the major sink of NH₄⁺ or other nitrogen compounds on the Earth's surface at 3800 Ma.

Two samples of graphite-bearing garnet-staurolite-mica schist from sequence B have remarkably high NH₄⁺ contents (whole-rock: 68 and 86 ppm, biotite: 234 and 253 ppm), which are as high as, or even higher than, those of common Late Archaean-Early Proterozoic argillites. It appears almost certain that the original, thick, clay-rich bottom sediments contained a large amount of NH₄⁺ or other nitrogen compounds. The most likely major source of nitrogen in these NH₄⁺-enriched, graphite-bearing mica schists might be organic nitrogen.

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Evaluating the biosignature potential of nitrogen concentrations in graphite and associated K-silicates
2023, Chemical Geology
Citation Excerpt :
In these graphitic metapelites from Isua, samples with >2 wt% K contain >20 μg/g of nitrogen, suggesting that a significant fraction of the total nitrogen content is hosted in potassic silicate minerals (Stüeken et al., 2021). This phenomenon is well known from other metasedimentary successions in the rock record where TN and K are strongly correlated (reviewed by Busigny and Bebout, 2013), and it is consistent with independent measurements of nitrogen in biotite separates, which contain several tens to hundreds of μg/g (Fig. 7a) (Honma, 1996; Pinti et al., 2001; Papineau et al., 2005). During diagenetic alteration of biomass within sediments, ammonium is released into pore waters, where it can reach concentrations of several millimole per litre (Rosenfeld, 1979; Boudreau and Canfield, 1988).
The oldest remnants of life on Earth from various localities in the Isua supracrustal belt in Greenland date back to >3.7 billion years ago (Ga). They are in the form of graphite, whose biogenicity is controversial. Previous studies used the presence and isotopic composition of nitrogen in graphite from along the Isua belt to argue both for and against biogenicity. To determine if the nitrogen chemistry of graphite can indeed serve as a biosignature, we investigated a hydrothermal graphite deposit from south-east Greenland (1.87–1.82 Ga). We found indications that molar C/N ratios of hydrothermal graphite may be similar to those of biogenic graphite from the Archean rock record, meaning that the nitrogen content of graphite is itself perhaps not diagnostic of ancient life, requiring caution in future studies. However, the hydrothermal graphite deposit also revealed unusually low N concentrations in associated silicates, despite a wide range of K concentrations up to 5 wt%. Using a thermodynamic model of nitrogen speciation in the presence of graphite, paired with previously published partition coefficients for ammonium in K-silicates, we show that abiotic process can explain these low N-concentrations of around 1 μg/g in potassic silicates. Higher concentrations of >10 μg/g, such as those found in graphitic metapelites from the Isua supcracrustal belt, would, however, require an unusually ammonium-rich fluid. Such an ammonium-rich fluid is most easily derived from the breakdown of biomass within sediments prior to graphitization. We therefore conclude that potassic silicates associated with graphite can serve as an indirect biosignature. Our approach supports previous inferences of life on Earth back to at least 3.7 Ga.
Reflectance spectroscopy of ammonium-bearing phyllosilicates
2019, Icarus
Citation Excerpt :
Phyllosilicates of magmatic or metamorphic origin, such as biotite and serpentine, do not show spectral variations due to the presence of ammonium. The presence in nature of micas with ammonium does not exclude that these can be enriched with ammonium under conditions of temperature and pressure higher than those used in this experiment (Vedder, 1965; Itihara and Honma, 1979; Honma, 1996; Busigny et al., 2003; Papineau et al., 2005). When comparing the spectra obtained on the studied ammoniated phyllosilicates to the VIR spectra, the presence of the 3.06 µm band is in good agreement with Ceres’ surface average spectrum, although the presence of water inside the clays tends to mask the NH4+ absorption bands in the 3 µm region.
The identification of NH₄-bearing phyllosilicates on Ceres poses the question on the NH₄-carrier phase(s) and in this study we describe the laboratory production and IR spectroscopic measurements of a suite of ten NH₄-phyllosilicates, starting from the corresponding NH₄-free minerals. For each mineral, we prepared three types of powder samples: raw (R), ammoniated (A), and leached (L). All samples have been spectrally characterized by means of visible/infrared spectroscopy in the INAF-IAPS laboratories with the FieldSpec Pro in the 0.35–2.5 µm range, and with the FT-IR, using a Vertex 80 spectrometer operating in the range of 2–14 µm. The samples were also measured with the SPectral IMager, an imaging spectrometer operating in the spectral range 0.2–5.1 µm, which is a replica of the VIR spectrometer on-board Dawn spacecraft. Reflectance spectra of the ammoniated clays show bands near 1.56 µm, 2.05 µm, 2.12 µm, 3.06 µm, 3.25 µm, 3.55 µm, 4.2 µm, 5.7 µm and 7.0 µm that are related to the presence of nitrogen complexes. Treatment of phyllosilicates with ammonia shows that different minerals behave in different ways: NH₄⁺ ions are easily accepted by the smectites, while other non-expandable structures do not accept these ions. The obtained results can be used to better constrain the NH₄-bearing species present on Ceres and, possibly, other bodies of the solar system.
The nitrogen budget of Earth
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We comprehensively compile and review N content in geologic materials to calculate a new N budget for Earth. Using analyses of rocks and minerals in conjunction with N–Ar geochemistry demonstrates that the Bulk Silicate Earth (BSE) contains ~ 7 ± 4 times present atmospheric N (4 × 10¹⁸ kg N, or PAN), with 27 ± 16 × 10¹⁸ kg N. Comparison to chondritic composition, after subtracting N sequestered into the core, yields a consistent result, with BSE N between 17 ± 13 × 10¹⁸ kg to 31 ± 24 × 10¹⁸ kg N. Embedded in the chondritic comparison we calculate a N mass in Earth's core (180 ± 110 to 30 ± 180 × 10¹⁸ kg) as well as present discussion of the Moon as a proxy for the early mantle.
Significantly, our study indicates that the majority of the planetary budget of N is in the solid Earth. We suggest that the N estimate here precludes the need for a “missing N” reservoir. Nitrogen–Ar systematics in mantle rocks and primary melts identify the presence of two mantle reservoirs: MORB-source like (MSL) and high-N. High-N mantle is composed of young, N-rich material subducted from the surface and identified in OIB and some xenoliths. In contrast, MSL appears to be made of old material, though a component of subducted material is evident in this reservoir as well.
Taking into account N mass and isotopic character of the atmosphere and BSE, we calculate a δ¹⁵N value of ~ 2%. This value should be used when discussing bulk Earth N isotope evolution. Additionally, our work indicates that all surface N could pass through the mantle over Earth history, and in fact the mantle may act as a long-term sink for N. Since N acts as a tracer of exchange between the atmosphere, oceans, and mantle over time, clarifying its distribution in the Earth is critical for evolutionary models concerned with Earth system evolution. We suggest that N be viewed in the same light as carbon: it has a fast, biologically mediated cycle which connects it to a slow, tectonically-controlled geologic cycle.
Ammonium loss and nitrogen isotopic fractionation in biotite as a function of metamorphic grade in metapelites from western Maine, USA
2010, Geochimica et Cosmochimica Acta
Ammonium fixed in micas of metamorphic rocks is a sensitive indicator both of organic–inorganic interactions during diagenesis as well as of the devolatilization history and fluid/rock interaction during metamorphism. In this study, a collection of geochemically well-characterized biotite separates from a series of graphite-bearing Paleozoic greenschist- to upper amphibolite-facies metapelites, western Maine, USA, were analyzed for ammonium nitrogen ( ${NH}_{4}^{+} -N$ ) contents and isotopic composition (δ¹⁵N_NH4) using the HF-digestion distillation technique followed by the EA-IRMS technique. Biotite separates, sampled from 9 individual metamorphic zones, contain 3000 to 100 ppm ${NH}_{4}^{+} -N$ with a wide range in δ¹⁵N from +1.6‰ to +9.1‰. Average ${NH}_{4}^{+} -N$ contents in biotite show a distinct decrease from about 2750 ppm for the lowest metamorphic grade (∼500 °C) down to 218 ppm for the highest metamorphic grade (∼685 °C). Decreasing abundances in ${NH}_{4}^{+}$ are inversely correlated in a linear fashion with increasing K⁺ in biotite as a function of metamorphic grade and are interpreted as a devolatilization effect. Despite expected increasing δ¹⁵N_NH4 values in biotite with nitrogen loss, a significant decrease from the Garnet Zones to the Staurolite Zones was found, followed by an increase to the Sillimanite Zones. This pattern for δ¹⁵N_NH4 values in biotite inversely correlates with Mg/(Mg + Fe) ratios in biotite and is discussed in the framework of isotopic fractionation due to different exchange processes between ${NH}_{4}^{+} - {NH}_{3}$ or ${NH}_{4}^{+} - N_{2}$ , reflecting devolatilization history and redox conditions during metamorphism.
The behavior of nitrogen and nitrogen isotopes during metamorphism and mineralization: Evidence from the Otago and Alpine Schists, New Zealand
2005, Earth and Planetary Science Letters
Metamorphism is a major mechanism for the re-distribution of fluids and mass in the Earth's crust, with these processes most prominently highlighted by the occurrence of major gold resources within these terranes. However, although orogenic gold deposits have contributed over 20% of the global gold production, their origins remain controversial. The nitrogen concentration and isotopic composition of rocks and minerals are potentially powerful tracers of crustal metamorphism and mineralization, but there have been few detailed applications of this approach to date. Although nitrogen isotopes have recently been used to elucidate the source of fluids in some Neoarchean orogenic gold deposits and Proterozoic to Paleozoic mountain belts, due to their age and geological complexity of these terranes, major uncertainties as to the behavior of nitrogen remain. The Otago and Alpine Schists in the South Island of New Zealand comprise a large, comparatively young (< 190 Ma), metasedimentary belt with multiple generations of quartz ± carbonate veins, some of which are mineralized with gold. A range of rocks, with little primary compositional variation, is exposed from unmetamorphosed protolith to high-grade amphibolites and as such they present an ideal laboratory to investigate the mobility of nitrogen and potential nitrogen isotopic fractionations during metamorphism and mineralization. Here we present nitrogen concentrations and isotopic analyses of whole rock samples and mica separates from a number of crustal transects through the Otago crust.
The range of δ¹⁵N values for mica and whole rock samples from the schists spans 0.2 to 7.0‰, and the nitrogen concentration from 23 to 3483 ppm. Sample provenance and rock type have minimal influence on the nitrogen concentration and isotopic value, which appears to have been inherited from the original sedimentary kerogen. There is no systematic variation between metamorphic temperature and δ¹⁵N or N concentration in micas, suggesting that there has been little discernible loss of ¹⁵N-depleted fluids from silicates with increasing metamorphic temperature. Comparison of fluid mobile alkali element (K, Rb and Cs), carbon and nitrogen whole rock concentrations, indicates that for the Otago and Alpine Schists, in rocks up to upper greenschist facies significant nitrogen remains hosted in phases other than micas, most likely poorly matured carbonaceous material. Samples from Macraes Flat, a major gold producer, have a similar range of δ¹⁵N values to the host terrane, but show distinctly higher nitrogen concentrations relative to unmineralized samples, due to the incorporation of nitrogen from the mineralizing hydrothermal fluid. This suggests that there is only a subtle metamorphic re-distribution of nitrogen during mineralization, albeit with minimal isotopic fractionation. In the case of nitrogen at least, the isotopic signatures of mineralized rocks support a metamorphic fluid source, and are inconsistent with mantle or meteoric fluid reservoirs. However, due to the high relative abundance of nitrogen in sedimentary rocks compared to other potential reservoirs, unless fluid fluxes are very large and well channeled, nitrogen signatures are not sensitive recorders of fluid inputs from mantle, magmatic or meteoric reservoirs. Conversely, the absence of a “sedimentary”-source nitrogen isotope signature similar to the host rock in an orogenic deposit would be a very strong indicator of an external, exotic source for the mineralizing fluids.
Nitrogen isotopic composition of ammoniated phyllosilicates: Case studies from Precambrian metamorphosed sedimentary rocks
2005, Chemical Geology
Citation Excerpt :
Additional detailed analyses are required to understand this characteristic of the Isua samples. It has been suggested that an igneous or metasedimentary protolith for metamorphosed rocks can be distinguished on the basis of ammonium concentration (especially in biotite; Itihara and Honma, 1979; Honma and Itihara, 1981; Itihara and Suwa, 1985; Duit et al., 1986; Tainosho and Itihara, 1988; Itihara and Tainosho, 1989; Honma, 1996). The elevated [NH4+]biotite values measured in our samples from West Greenland may therefore be viewed as yet another diagnostic for a sedimentary protolith of these rocks.
Ammonium concentrations in phyllosilicates from Archean and Proterozoic schists and carbonates were evaluated by Fourier Transform Infrared microspectrometry (μFTIR). The δ¹⁵N_air values of structural nitrogen in these phases were subsequently measured by laser mass spectrometry. A rapid estimate of the concentration of NH₄⁺ in biotite by μFTIR allows the preselection of the samples to be analyzed for their isotopic composition. Micas from 1.90–2.09 Ga metasediments from Finland and from 1.025–1.500 Ga biotite schists from the Moine Succession in Scotland have high concentrations of structural ammonium (between 176 and 1549 ppm), suggestive of a biological origin for the nitrogen. The heavy nitrogen isotopic signatures (δ¹⁵N=+4.9‰ to +19.7‰) of structural NH₄⁺ in these micas are considered consistent with biological denitrification in operation at the time of sedimentation. Evidence for denitrification in the Mesoproterozoic is in agreement with geological and geochemical data for abundant free oxygen in the atmosphere, facilitating the stability of marine NO₃⁻. Sequences of early Archean (ca. 3.8 Ga) garnet–mica schists from the Isua Supracrustal Belt (ISB) in southern West Greenland contain biotite rich in NH₄⁺ (between 233 and 512 ppm) and nitrogen isotopic signatures (δ¹⁵N=−1.9‰ to +5.9‰), which possibly point to an early evolution of ammonium assimilation and/or nitrogen fixation. This result appears to be consistent with molecular phylogenetic studies in the bacterial and archaeal domains, which suggest that nitrogen fixation and ammonium assimilation were metabolic features of the last common ancestor (LCA) of all organisms.

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ArticleHigh ammonium contents in the 3800 Ma Isua supracrustal rocks, central West Greenland

Abstract

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Precambrian Res.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Precambrian Res.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

The pre-3760 m.y. old supracrustal rocks of the Isua area, central West Greenland, and the associated occurrence of quartz-banded ironstone

Field work on the very early Precambrian rocks of the Isua area, southern West Greenland

Rapp. Grønlands Geol. Unders

Archaean gneiss complex of Greenland

Microfossil-like objects from the Archaean of Greenland: a cautionary note

Nature

Data of geochemistry

USGS Bull.

Article
High ammonium contents in the 3800 Ma Isua supracrustal rocks, central West Greenland