Chondritic osmium isotope composition of early Earth mantle
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Keywords: Re-Os isotopes, Pt-Os isotopes, highly siderophile elements, geochronology, North Atlantic Craton, ultramafic intrusion
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Abstract
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 Figure 1 (a) Location of the Ujaragssuit Intrusion. (b) Detailed map of the Ujaragssuit Intrusion, showing locations of analysed chromitite and granitoids samples, including granitoid zircon U-Pb ages. ‘Altered Uj.’ refers to the most altered portions of the Ujaragssuit Intrusion, including corundum-bearing amphibolites and reaction zones. (c) High resolution aerial photograph of the Ujaragssuit Intrusion. (d) Outline of the Ujaragssuit Intrusion, showing major lenses connected by thin ‘necks’. |  Figure 2 Geochronological data for the Ujaragssuit Intrusion. All plots show the 2970 Ma minimum age derived from cross-cutting leucogranites (blue dashed line) and the oldest high precision chromitite Re-depletion age, including systematic uncertainties (3246 ± 120 Ma; black dashed line and grey field). (a) Pt-depletion ages calculated from 186Os analyses from this study and Coggon et al. (2013). (b) Re-depletion ages calculated from high precision analyses of massive chromitites from this study and Coggon et al. (2013). (c) Re-depletion ages calculated from other 187Os/188Os literature data (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2015). (d) Lu-Hf model ages calculated from metamorphic zircons within the Ujaragssuit chromitites (Sawada et al., 2023). Model ages are calculated relative to chondritic uniform reservoir (CHUR; Bouvier et al., 2008), depleted mantle formed from CHUR at 3800 Ma (Fisher and Vervoort, 2018), and an end-member case where depleted mantle formed at 4567 Ma. |  Figure 3 ‘Concordia’ plot of Re- and Pt-depletion ages calculated for different Re-Pt-Os mantle evolution models. The Ujaragssuit 187Os-186Os data are consistent with a concordant ∼3250 Ma Re-Pt depletion event from primitive mantle (PM) of Brandon et al. (2006) with Re-Os evolution of O-chondrite (Walker et al., 2002). Uncertainties in mantle models from Day et al. (2017) are not shown for clarity. DM, depleted mantle. |  Figure 4 Nucleosynthetic osmium isotope composition of Ujaragssuit chromitites in epsilon units, relative to the DROsS reference material. 186Os is reported relative to primitive mantle of Brandon et al. (2006) at 3250 Ma. Uncertainty envelope shows average propagated analytical uncertainty on an individual analysis. Note different scale for 184Os. |
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Introduction
The Itsaq Gneiss Complex, North Atlantic Craton (NAC), Greenland, is among the largest and best preserved tracts of Eoarchaean crust on Earth (Nutman et al., 1996
Nutman, A.P., McGregor, V.R., Friend, C.R.L., Bennett, V.C., Kinny, P.D. (1996) The Itsaq Gneiss Complex of southern West Greenland; the world’s most extensive record of early crustal evolution (3900-3600 Ma). Precambrian Research 78, 1–39. https://doi.org/10.1016/0301-9268(95)00066-6
). The Isua Supracrustal Belt and area immediately to the south has been of particular interest due to less intense Neoarchaean metamorphism (Friend and Nutman, 2019Friend, C.R.L., Nutman, A.P. (2019) Tectono-stratigraphic terranes in Archaean gneiss complexes as evidence for plate tectonics: The Nuuk region, southern West Greenland. Gondwana Research 72, 213–237. https://doi.org/10.1016/j.gr.2019.03.004
), the preservation of supracrustal sequences, and an abundance of mantle-derived lavas and ultramafic bodies. This has made the area an attractive target for studies of long lived (Bennett et al., 1993Bennett, V.C., Nutman, A.P., McCulloch, M.T. (1993) Nd isotopic evidence for transient, highly depleted mantle reservoirs in the early history of the Earth. Earth and Planetary Science Letters 119, 299–317. https://doi.org/10.1016/0012-821X(93)90140-5
, 2002Bennett, V.C., Nutman, A.P., Esat, T.M. (2002) Constraints on mantle evolution from 187Os/188Os isotopic compositions of Archean ultramafic rocks from southern West Greenland (3.8 Ga) and Western Australia (3.46 Ga). Geochimica et Cosmochimica Acta 66, 2615–2630. https://doi.org/10.1016/S0016-7037(02)00862-1
; Coggon et al., 2013Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
; Waterton et al., 2022Waterton, P., Guotana, J.M., Nishio, I., Morishita, T., Tani, K., Woodland, S., Legros, H., Pearson, D.G., Szilas, K. (2022) No mantle residues in the Isua Supracrustal Belt. Earth and Planetary Science Letters 579, 117348. https://doi.org/10.1016/j.epsl.2021.117348
), short lived (Bennett et al., 2007Bennett, V.C., Brandon, A.D., Nutman, A.P. (2007) Coupled 142Nd-143Nd Isotopic Evidence for Hadean Mantle Dynamics. Science 318, 1907–1910. https://doi.org/10.1126/science.1145928
; Willbold et al., 2011Willbold, M., Elliott, T., Moorbath, S. (2011) The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment. Nature 477, 195–198. https://doi.org/10.1038/nature10399
), stable (Creech et al., 2017Creech, J.B., Baker, J.A., Handler, M.R., Lorand, J.-P., Storey, M., Wainwright, A.N., Luguet, A., Moynier, F., Bizzarro, M. (2017) Late accretion history of the terrestrial planets inferred from platinum stable isotopes. Geochemical Perspectives Letters 3, 94–104. https://doi.org/10.7185/geochemlet.1710
; Xu et al., 2023Xu, Y., Szilas, K., Zhang, L., Zhu, J.-M., Wu, G., Zhang, J., Qin, B., Sun, Y., Pearson, D.G., Liu, J. (2023) Ni isotopes provide a glimpse of Earth’s pre-late-veneer mantle. Science Advances 9, eadj2170. https://doi.org/10.1126/sciadv.adj2170
) and nucleosynthetic (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.Among the ultramafic bodies in this region, the stratiform chromitite-bearing Ujaragssuit Nunât layered body (hereafter the Ujaragssuit Intrusion) was recognised as the oldest chromitite on Earth (Chadwick and Crewe, 1986
Chadwick, B., Crewe, M.A. (1986) Chromite in the early Archean Akilia association (ca. 3,800 M.Y.), Ivisartoq region, inner Godthabsfjord, southern West Greenland. Economic Geology 81, 184–191. https://doi.org/10.2113/gsecongeo.81.1.184
), with a minimum age of >3.8 Ga indicated by its host orthogneisses (Nutman et al., 1996Nutman, A.P., McGregor, V.R., Friend, C.R.L., Bennett, V.C., Kinny, P.D. (1996) The Itsaq Gneiss Complex of southern West Greenland; the world’s most extensive record of early crustal evolution (3900-3600 Ma). Precambrian Research 78, 1–39. https://doi.org/10.1016/0301-9268(95)00066-6
). High concentrations of highly siderophile elements (HSEs) in the chromitites make them ideal for study using Re-Pt-Os (Bennett et al., 2002Bennett, V.C., Nutman, A.P., Esat, T.M. (2002) Constraints on mantle evolution from 187Os/188Os isotopic compositions of Archean ultramafic rocks from southern West Greenland (3.8 Ga) and Western Australia (3.46 Ga). Geochimica et Cosmochimica Acta 66, 2615–2630. https://doi.org/10.1016/S0016-7037(02)00862-1
; Rollinson et al., 2002Rollinson, H., Appel, P.W.U., Frei, R. (2002) A Metamorphosed, Early Archaean Chromitite from West Greenland: Implications for the Genesis of Archaean Anorthositic Chromitites. Journal of Petrology 43, 2143–2170. https://doi.org/10.1093/petrology/43.11.2143
; Coggon et al., 2013Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
, 2015Coggon, J.A., Luguet, A., Fonseca, R.O.C., Lorand, J.-P., Heuser, A., Appel, P.W.U. (2015) Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation. Geochimica et Cosmochimica Acta 167, 205–240. https://doi.org/10.1016/j.gca.2015.07.025
) and Ru isotopes (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
). These studies identified that the Ujaragssuit Intrusion records evidence of Hadean mantle depletion (Coggon et al., 2013Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
) and was derived from mantle deficient in chondrite relative to modern mantle (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
). In this study, we set out to verify the age of the Ujaragssuit Intrusion and to identify the Os isotope composition of the Ujaragssuit source.top
Results
Field observations and U-Pb zircon dating. Detailed field mapping of the Ujaragssuit Intrusion was supplemented with aerial drone photography to produce a high resolution map (Fig. 1). The Ujaragssuit Intrusion is a boudinaged peridotite-dominated body, comprising major lenses connected by thin necks, reminiscent of pinch and swell structures in sheared mid-crustal domains. This, along with gneissic foliation that wraps the intrusion, suggests that the ultramafic rocks acted as a competent body around which the gneisses deformed (Gardner et al., 2015
Gardner, R.L., Piazolo, S., Daczko, N.R. (2015) Pinch and swell structures: evidence for strain localisation by brittle–viscous behaviour in the middle crust. Solid Earth 6, 1045–1061. https://doi.org/10.5194/se-6-1045-2015
). We found no evidence of large scale faulting within or around the intrusion. Chromitites are abundant in the northern portion of the intrusion, corresponding to its base (Rollinson et al., 2002Rollinson, H., Appel, P.W.U., Frei, R. (2002) A Metamorphosed, Early Archaean Chromitite from West Greenland: Implications for the Genesis of Archaean Anorthositic Chromitites. Journal of Petrology 43, 2143–2170. https://doi.org/10.1093/petrology/43.11.2143
). The majority are stratiform chromitites with 1–20 cm thick layers. Six massive chromitite pods are also observed, ranging from ∼0.5 × 1 m to ∼3 × 7 m (Table S-1). Although all the chromitites have experienced alteration and metasomatism during high grade metamorphism, we divide these into ‘fresh’ and ‘altered’ chromitites based on field characteristics (Supplementary Information).Figure 1 (a) Location of the Ujaragssuit Intrusion. (b) Detailed map of the Ujaragssuit Intrusion, showing locations of analysed chromitite and granitoids samples, including granitoid zircon U-Pb ages. ‘Altered Uj.’ refers to the most altered portions of the Ujaragssuit Intrusion, including corundum-bearing amphibolites and reaction zones. (c) High resolution aerial photograph of the Ujaragssuit Intrusion. (d) Outline of the Ujaragssuit Intrusion, showing major lenses connected by thin ‘necks’.
Zircon LA-ICP-MS U-Pb dating yields a poorly constrained crystallisation age of ∼3.8 Ga for orthogneisses adjacent to the intrusion (Fig. 1; zircon U-Pb methods, data and age interpretations are provided in Supplementary Information and Table S-2). Two orthogneiss samples collected ∼4.5 km west of the intrusion yield more precise igneous ages of 3849 ± 6 Ma and 3842 ± 7 Ma. Though slightly older than previous orthogneiss ages near Ujaragssuit (Nutman et al., 1996
Nutman, A.P., McGregor, V.R., Friend, C.R.L., Bennett, V.C., Kinny, P.D. (1996) The Itsaq Gneiss Complex of southern West Greenland; the world’s most extensive record of early crustal evolution (3900-3600 Ma). Precambrian Research 78, 1–39. https://doi.org/10.1016/0301-9268(95)00066-6
), our data confirms that the intrusion’s host orthogneisses are >3.8 Ga. However, we could not find any exposed contacts between the orthogneisses and ultramafic rocks, so this does not provide a minimum age constraint on the Ujaragssuit Intrusion. Instead, the entire intrusion is ‘sheathed’ and cross-cut by anastomosing sheets of leucogranite. Three of these leucogranites yield much younger crystallisation ages of 2966 ± 6 Ma, 2976 ± 6 Ma, and 2966 ± 8 Ma, consistent with previously determined ages of ∼2.97–2.95 Ga (Sawada et al., 2023Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). These coincide with a population of metamorphic zircon present in all three orthogneiss samples at ∼2.97 Ga, as well as growth of metamorphic zircon within the Ujaragssuit chromitites themselves (Sawada et al., 2023Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). These ages reflect regional metamorphism in this part of the Itsaq Gneiss Complex (Friend and Nutman, 2019Friend, C.R.L., Nutman, A.P. (2019) Tectono-stratigraphic terranes in Archaean gneiss complexes as evidence for plate tectonics: The Nuuk region, southern West Greenland. Gondwana Research 72, 213–237. https://doi.org/10.1016/j.gr.2019.03.004
), driving formation of the leucogranites via intracrustal melting. We also identify ∼3.00–2.99 Ga metamorphic zircon ages in the orthogneisses, which could suggest that the ∼2.97 Ga regional metamorphic event was more protracted than previously recognised. A second event caused further growth of metamorphic zircon at 2693 ± 10 Ma in one of the leucogranites.To summarise, the only robust age constraint on the Ujaragssuit Intrusion is that it is >2.97 Ga, the age of both cross-cutting leucogranites and metamorphic zircon within Ujaragssuit chromitites (Sawada et al., 2023
Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). The average crystallisation age of the leucogranites and of ∼2.97 Ga metamorphic zircon yields a minimum age of 2970 ± 8 Ma for the Ujaragssuit Intrusion.Highly siderophile element abundances and Re-Os isotopic data. All HSE and Re-Pt-Os isotope methods, data and calculations are given in Supplementary Information and Tables S-3 and S-4. Radiogenic Os isotope results are presented as Re- and Pt- model ages assuming chondritic evolution (Walker et al., 2002
Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
) or primitive mantle models (Meisel et al., 2001Meisel, T., Walker, R.J., Irving, A.J., Lorand, J.-P. (2001) Osmium isotopic composition of mantle xenoliths: a global perspective. Geochimica et Cosmochimica Acta 65, 1311–1323. https://doi.org/10.1016/S0016-7037(00)00566-4
; Brandon et al., 2006Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
) based on chondrite; we address this assumption in the Discussion. The analysed massive chromitite samples have high Os contents (96–200 ppb), low Pt (0.72–4.5 ppb) and low Re (one altered sample has 82 ppt Re, the remaining analyses are below the 6.9 pg limit of detection). Their high Os concentrations reflect high modal chromite contents (Bennett et al., 2002Bennett, V.C., Nutman, A.P., Esat, T.M. (2002) Constraints on mantle evolution from 187Os/188Os isotopic compositions of Archean ultramafic rocks from southern West Greenland (3.8 Ga) and Western Australia (3.46 Ga). Geochimica et Cosmochimica Acta 66, 2615–2630. https://doi.org/10.1016/S0016-7037(02)00862-1
; Coggon et al., 2015Coggon, J.A., Luguet, A., Fonseca, R.O.C., Lorand, J.-P., Heuser, A., Appel, P.W.U. (2015) Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation. Geochimica et Cosmochimica Acta 167, 205–240. https://doi.org/10.1016/j.gca.2015.07.025
) and, combined with low 187Re/188Os (<4.1 × 10−3) and 190Pt/188Os (7.1 × 10−6 to 4.4 × 10−5), make Re- (TRD) and Pt-depletion (TDA) model ages resistant to modification through crustal assimilation or metamorphic alteration.High precision unspiked Os analyses of four fresh chromitite samples (Fig. 2) yield a tight range of weighted mean TRD ages (relative to O-chondrite; Walker et al., 2002
Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
), ranging from 3226.6 ± 1.6 Ma (n = 4; 95 % confidence limits) to 3244.2 ± 1.2 Ma (n = 5). Although the observed scatter in each is greater than the ∼0.5 Myr (2s) scatter expected from analytical uncertainties, repeated analyses of the same sample (n ≥ 4) never varied by more than 2.8 Myr. Conventional spiked analyses of the same samples yielded TRD ages from 3232 ± 9 Ma to 3248 ± 9 Ma (2s; one analysis per sample) overlapping the high precision ages.Figure 2 Geochronological data for the Ujaragssuit Intrusion. All plots show the 2970 Ma minimum age derived from cross-cutting leucogranites (blue dashed line) and the oldest high precision chromitite Re-depletion age, including systematic uncertainties (3246 ± 120 Ma; black dashed line and grey field). (a) Pt-depletion ages calculated from 186Os analyses from this study and Coggon et al. (2013)
Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
. (b) Re-depletion ages calculated from high precision analyses of massive chromitites from this study and Coggon et al. (2013)Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
. (c) Re-depletion ages calculated from other 187Os/188Os literature data (Bennett et al., 2002Bennett, V.C., Nutman, A.P., Esat, T.M. (2002) Constraints on mantle evolution from 187Os/188Os isotopic compositions of Archean ultramafic rocks from southern West Greenland (3.8 Ga) and Western Australia (3.46 Ga). Geochimica et Cosmochimica Acta 66, 2615–2630. https://doi.org/10.1016/S0016-7037(02)00862-1
; Rollinson et al., 2002Rollinson, H., Appel, P.W.U., Frei, R. (2002) A Metamorphosed, Early Archaean Chromitite from West Greenland: Implications for the Genesis of Archaean Anorthositic Chromitites. Journal of Petrology 43, 2143–2170. https://doi.org/10.1093/petrology/43.11.2143
; Coggon et al., 2015Coggon, J.A., Luguet, A., Fonseca, R.O.C., Lorand, J.-P., Heuser, A., Appel, P.W.U. (2015) Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation. Geochimica et Cosmochimica Acta 167, 205–240. https://doi.org/10.1016/j.gca.2015.07.025
). (d) Lu-Hf model ages calculated from metamorphic zircons within the Ujaragssuit chromitites (Sawada et al., 2023Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). Model ages are calculated relative to chondritic uniform reservoir (CHUR; Bouvier et al., 2008Bouvier, A., Vervoort, J.D., Patchett, P.J. (2008) The Lu–Hf and Sm–Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48–57. https://doi.org/10.1016/j.epsl.2008.06.010
), depleted mantle formed from CHUR at 3800 Ma (Fisher and Vervoort, 2018Fisher, C.M., Vervoort, J.D. (2018) Using the magmatic record to constrain the growth of continental crust—The Eoarchean zircon Hf record of Greenland. Earth and Planetary Science Letters 488, 79–91. https://doi.org/10.1016/j.epsl.2018.01.031
), and an end-member case where depleted mantle formed at 4567 Ma.Two altered chromitites have younger and more highly variable model ages in repeated analyses of the same sample, with weighted average ages of 3046 ± 123 Ma (95 % confidence; TMA age; the only sample with detectable Re) and 3181 ± 8 Ma (one spiked and two high precision analyses per sample). Taken together, our chromitite data show excellent agreement with previous high precision Re-Os analyses (Coggon et al., 2013
Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
), which show maximum TRD ages of 3246.4 ± 1.0 Ma (n = 4) and increasing scatter in samples that record younger TRD (3209 ± 50 Ma; n = 4).These ‘young’ TRD ages relative to the age of the host orthogneisses and Pt-Os model ages have previously been explained by metamorphic resetting of the Re-Os system (Coggon et al., 2015
Coggon, J.A., Luguet, A., Fonseca, R.O.C., Lorand, J.-P., Heuser, A., Appel, P.W.U. (2015) Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation. Geochimica et Cosmochimica Acta 167, 205–240. https://doi.org/10.1016/j.gca.2015.07.025
). However, this is difficult to reconcile with consistent TRD ages in fresh chromitites from across the intrusion with variable but high Os concentrations. As igneous chromite has high Os and low Re/Os (Puchtel et al., 2004Puchtel, I.S., Humayun, M., Campbell, A.J., Sproule, R.A., Lesher, C.M. (2004) Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada. Geochimica et Cosmochimica Acta 68, 1361–1383. https://doi.org/10.1016/j.gca.2003.09.013
) and the chromitites presently retain these HSE signatures, this would require that large quantities of Re or radiogenic Os were added to the chromitites during metamorphism, in proportion to the Os abundance in each chromitite. If Re was added, it would need to be removed after a long period of 187Os ingrowth to produce the present day low Re/Os. Though some resetting of the Re-Os system is clearly possible given the younger TRD ages in altered chromitites, this is associated with a significant increase in the scatter of these ages, both within and between samples. Instead, we interpret the Re-Os data to indicate an age of ∼3246 ± 120 Ma for the Ujaragssuit Intrusion (oldest age from our data and Coggon et al., 2013Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
, including systematic mantle model uncertainties; Supplementary Information).Pt-Os isotopic data. The TDA (relative to primitive mantle; Brandon et al., 2006
Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
) from all fresh chromitite samples form a single age population with a weighted mean age of 3382 ± 360 Ma (Fig. 2; n = 17; MSWD = 0.65; p = 0.84). Correcting for 190Pt decay since chromitite formation has no significant effect, yielding a Pt-Os model age of 3398 ± 360 Ma. Though some altered chromitite analyses were indistinguishable from this weighted mean, we exclude these due to evidence of Os mobilisation in these samples from the Re-Os system. Use of alternative mantle models (Day et al., 2017Day, J.M.D., Walker, R.J., Warren, J.M. (2017) 186Os–187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys. Geochimica et Cosmochimica Acta 200, 232–254. https://doi.org/10.1016/j.gca.2016.12.013
) yields younger ages.All of these ages appear young compared to previously reported TDA from Ujaragssuit, ranging up to 4.1 Ga (Coggon et al., 2013
Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
). However, the uncertainties reported for both individual analyses and age groups in Coggon et al. (2013)Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
are far smaller than the ∼35 ppm precision they report for the the Durham Romil Osmium Standard (DROsS) (Luguet et al., 2008Luguet, A., Nowell, G.M., Pearson, D.G. (2008) 184Os/188Os and 186Os/188Os measurements by Negative Thermal Ionisation Mass Spectrometry (N-TIMS): Effects of interfering element and mass fractionation corrections on data accuracy and precision. Chemical Geology 248, 342–362. https://doi.org/10.1016/j.chemgeo.2007.10.013
; equivalent to a ∼1.5 Ga uncertainty in each TDA). We therefore re-process these data by propagating the minimum analytical uncertainty indicated by DROsS and find: 1) the TDA are also consistent with a single age population, with no statistically distinct older group; 2) the weighted average TDA of 3558 ± 482 Ma (MSWD = 0.50; p = 0.94) overlaps our data within uncertainty. We combine all data from our fresh chromitite samples and Coggon et al. (2013)Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
to estimate the initial 186Os/188Os of the Ujaragssuit Intrusion, which we believe to be the most precise estimate of this ratio for a single terrestrial locality. This yields 186Os/188Os = 0.1198301 ± 0.0000008 (2 s.e.; n = 32; MSWD = 0.58; p = 0.97; normalised to UMd of Brandon et al., 2006Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
; Supplementary Information), corresponding to a TDA of 3437 ± 288 Ma, or 3437 ± 587 Ma including the ∼12 ppm uncertainty in the solar system initial (Brandon et al., 2006Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
).Although this barely permits a 4.0 Ga age for Ujaragssuit, the mean age is much closer to the age of the intrusion estimated from Re-Os model ages, constituting a concordant Re-Pt-Os depletion age (Fig. 3). Furthermore, the ∼3.25 Ga Re-Os model age overlaps with Hf model ages of metamorphic zircon in the chromitites, which requires special pleading if the Ujaragssuit Intrusion is indeed >3.8 Ga (Sawada et al., 2023
Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). The simplest explanation is therefore that the Ujaragssuit Intrusion formed at ∼3.25 Ga and there is no evidence for Hadean mantle depletion. Given the lack of observed faults, the Ujaragssuit Intrusion likely has an intrusive rather than tectonic relationship with its host orthogneisses. Finally, we note that this ∼3.25 Ga age may have been ‘hiding in plain sight’, with numerous older publications reporting identical 187Os/188Os to our data (Fig. 2).Figure 3 ‘Concordia’ plot of Re- and Pt-depletion ages calculated for different Re-Pt-Os mantle evolution models. The Ujaragssuit 187Os-186Os data are consistent with a concordant ∼3250 Ma Re-Pt depletion event from primitive mantle (PM) of Brandon et al. (2006)
Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
with Re-Os evolution of O-chondrite (Walker et al., 2002Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
). Uncertainties in mantle models from Day et al. (2017)Day, J.M.D., Walker, R.J., Warren, J.M. (2017) 186Os–187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys. Geochimica et Cosmochimica Acta 200, 232–254. https://doi.org/10.1016/j.gca.2016.12.013
are not shown for clarity. DM, depleted mantle.top
Discussion
This study highlights the importance of careful field study and direct dating of ultramafic enclaves in Archaean cratons. While some ultramafic enclaves may be older than their host orthogneisses, others may represent much younger intrusions. In the case of Ujaragssuit, the age determined by direct dating is >550 Myr younger than if the ultramafic rocks are interpreted as an enclave intruded by the orthogneiss protoliths (Nutman et al., 1996
Nutman, A.P., McGregor, V.R., Friend, C.R.L., Bennett, V.C., Kinny, P.D. (1996) The Itsaq Gneiss Complex of southern West Greenland; the world’s most extensive record of early crustal evolution (3900-3600 Ma). Precambrian Research 78, 1–39. https://doi.org/10.1016/0301-9268(95)00066-6
).The precise initial 187Os-186Os systematics allow us to discriminate between potential Pt-Os mantle evolution models (Fig. 3) for the Ujaragssuit mantle source, which is depleted in chondritic components compared to modern mantle (Fischer-Gödde et al., 2020
Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
). A mantle source that evolved with primitive mantle Pt-Os (Brandon et al., 2006Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
) and chondritic Re-Os (Walker et al., 2002Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
) yields a concordant age for coupled Re-Pt depletion occurring at ∼3.25 Ga, consistent with Lu-Hf constraints (Sawada et al., 2023Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). By contrast, use of either the primitive or depleted mantle models of Day et al. (2017)Day, J.M.D., Walker, R.J., Warren, J.M. (2017) 186Os–187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys. Geochimica et Cosmochimica Acta 200, 232–254. https://doi.org/10.1016/j.gca.2016.12.013
yields TDA and TRD that are inconsistent. Unfortunately, the large uncertainty on 186Os/188Os compared to its temporal variation means we cannot further distinguish between different Re-Os evolution models for the Ujaragssuit source; providing the Pt-Os evolution follows primitive mantle (Brandon et al., 2006Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
), then Re-Os evolution using any chondrite (Walker et al., 2002Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
) or primitive upper mantle (PUM; Meisel et al., 2001Meisel, T., Walker, R.J., Irving, A.J., Lorand, J.-P. (2001) Osmium isotopic composition of mantle xenoliths: a global perspective. Geochimica et Cosmochimica Acta 65, 1311–1323. https://doi.org/10.1016/S0016-7037(00)00566-4
) model yields concordant Re-Pt depletion ages within uncertainty. Given the presence of nucleosynthetic Ru anomalies at Ujaragssuit with no known cosmochemical analogue (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
), we cannot conclusively rule out a mantle source with exotic Re-Pt-Os isotope systematics. However, any such source would need to reach the Ujaragssuit initial 187Os/188Os and 186Os/188Os at ∼3.2 Ga, within uncertainty of chondritic evolution (Fig. 3), to be consistent with zircon Lu-Hf model ages (Sawada et al., 2023Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). Furthermore, this source requires a nucleosynthetic Os composition indistinguishable from bulk chondrite (see below). The most likely explanation is that the Ujaragssuit source evolved with chondritic Re-Pt-Os isotope systematics until formation of the intrusion at ∼3.25 Ga.We were unable to resolve nucleosynthetic Os anomalies beyond analytical uncertainty (Fig. 4); the slight anomaly in average ɛ184Os appears to be an analytical artefact (Supplementary Information). This lack of resolvable Os isotopic anomalies reflects an absence of bulk Os isotopic anomalies in most major meteorite groups, including chondrites (Goderis et al., 2017
Goderis, S., Brandon, A.D., Mayer, B., Humayun, M. (2017) Osmium isotopic homogeneity in the CK carbonaceous chondrites. Geochimica et Cosmochimica Acta 216, 8–27. https://doi.org/10.1016/j.gca.2017.05.011
). Despite internal variations in Os composition within individual meteorites (Brandon et al., 2005Brandon, A.D., Humayun, M., Puchtel, I.S., Leya, I., Zolensky, M. (2005) Osmium Isotope Evidence for an s-Process Carrier in Primitive Chondrites. Science 309, 1233–1236. https://doi.org/10.1126/science.1115053
), Os was homogeneous at the planetesimal scale in the presolar nebula (Goderis et al., 2017Goderis, S., Brandon, A.D., Mayer, B., Humayun, M. (2017) Osmium isotopic homogeneity in the CK carbonaceous chondrites. Geochimica et Cosmochimica Acta 216, 8–27. https://doi.org/10.1016/j.gca.2017.05.011
). Therefore, even though the Ujaragssuit mantle source was relatively depleted in late-accreted chondritic material (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
), this had no net effect on its Os isotopic composition.Figure 4 Nucleosynthetic osmium isotope composition of Ujaragssuit chromitites in epsilon units, relative to the DROsS reference material. 186Os is reported relative to primitive mantle of Brandon et al. (2006)
Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
at 3250 Ma. Uncertainty envelope shows average propagated analytical uncertainty on an individual analysis. Note different scale for 184Os.Our new ∼3.25 Ga age for the Ujaragssuit Intrusion sheds new light on previously identified isotopic anomalies, which indicate the mantle sources of NAC igneous rocks were depleted in chondritic components relative to bulk Earth (Willbold et al., 2011
Willbold, M., Elliott, T., Moorbath, S. (2011) The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment. Nature 477, 195–198. https://doi.org/10.1038/nature10399
; Creech et al., 2017Creech, J.B., Baker, J.A., Handler, M.R., Lorand, J.-P., Storey, M., Wainwright, A.N., Luguet, A., Moynier, F., Bizzarro, M. (2017) Late accretion history of the terrestrial planets inferred from platinum stable isotopes. Geochemical Perspectives Letters 3, 94–104. https://doi.org/10.7185/geochemlet.1710
; Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
; Xu et al., 2023Xu, Y., Szilas, K., Zhang, L., Zhu, J.-M., Wu, G., Zhang, J., Qin, B., Sun, Y., Pearson, D.G., Liu, J. (2023) Ni isotopes provide a glimpse of Earth’s pre-late-veneer mantle. Science Advances 9, eadj2170. https://doi.org/10.1126/sciadv.adj2170
). In particular, a ∼3.25 Ga age for the Ujaragssuit Intrusion means that nucleosynthetic Ru isotope anomalies (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
) are now known from NAC ultramafic intrusions formed in four major periods: at ∼3.8 Ga in the Narssaq and South of Isua ultramafic bodies, at ∼3.7 Ga in the Isua Supracrustal Belt, at ∼3.25 Ga in the Ujaragssuit Intrusion, and at >3.0 Ga in the Fiskefjord peridotites. These anomalies occur across three different tectonostratigraphic terranes (Friend and Nutman, 2019Friend, C.R.L., Nutman, A.P. (2019) Tectono-stratigraphic terranes in Archaean gneiss complexes as evidence for plate tectonics: The Nuuk region, southern West Greenland. Gondwana Research 72, 213–237. https://doi.org/10.1016/j.gr.2019.03.004
), do not diminish over time and have not been identified in other cratons (Fischer-Gödde et al., 2020Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
), even where mantle depleted in late-accreted materials has been proposed (Maier et al., 2009Maier, W.D., Barnes, S.J., Campbell, I.H., Fiorentini, M.L., Peltonen, P., Barnes, S.-J., Smithies, R.H. (2009) Progressive mixing of meteoritic veneer into the early Earth’s deep mantle. Nature 460, 620–623. https://doi.org/10.1038/nature08205
). Repeated tapping of this potentially unique chondrite-depleted mantle source across various NAC terranes over a period of 600 Myr is difficult to reconcile with a model in which the different terranes identified in the NAC were initially widely dispersed (Friend and Nutman, 2019Friend, C.R.L., Nutman, A.P. (2019) Tectono-stratigraphic terranes in Archaean gneiss complexes as evidence for plate tectonics: The Nuuk region, southern West Greenland. Gondwana Research 72, 213–237. https://doi.org/10.1016/j.gr.2019.03.004
). Instead, it appears to favour autochthonous formation of the various components of the NAC above a mantle source that was relatively isolated and poorly mixed with respect to the rest of the mantle. This most likely supports formation of the NAC within a non-uniformitarian tectonic regime (e.g., Debaille et al., 2013Debaille, V., O’Neill, C., Brandon, A.D., Haenecour, P., Yin, Q.-Z., Mattielli, N., Treiman, A.H. (2013) Stagnant-lid tectonics in early Earth revealed by 142Nd variations in late Archean rocks. Earth and Planetary Science Letters 373, 83–92. https://doi.org/10.1016/j.epsl.2013.04.016
; Webb et al., 2020Webb, A.A.G., Müller, T., Zuo, J., Haproff, P.J., Ramírez-Salazar, A. (2020) A non-plate tectonic model for the Eoarchean Isua supracrustal belt. Lithosphere 12, 166–179. https://doi.org/10.1130/L1130.1
), in which the crust was relatively immobile with respect to the underlying mantle sources that drove the formation of crustal ultramafic intrusions.top
Acknowledgements
This study was supported by the Carlsberg Foundation through grant CF18-0090 to Kristoffer Szilas. We thank Richard Walker and an anonymous reviewer for constructive reviews, and Helen Williams for editorial handling.
Editor: Helen Williams
top
References
Bennett, V.C., Nutman, A.P., McCulloch, M.T. (1993) Nd isotopic evidence for transient, highly depleted mantle reservoirs in the early history of the Earth. Earth and Planetary Science Letters 119, 299–317. https://doi.org/10.1016/0012-821X(93)90140-5
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
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Bennett, V.C., Nutman, A.P., Esat, T.M. (2002) Constraints on mantle evolution from 187Os/188Os isotopic compositions of Archean ultramafic rocks from southern West Greenland (3.8 Ga) and Western Australia (3.46 Ga). Geochimica et Cosmochimica Acta 66, 2615–2630. https://doi.org/10.1016/S0016-7037(02)00862-1
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
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High concentrations of highly siderophile elements (HSEs) in the chromitites make them ideal for study using Re-Pt-Os (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2013, 2015) and Ru isotopes (Fischer-Gödde et al., 2020).
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Their high Os concentrations reflect high modal chromite contents (Bennett et al., 2002; Coggon et al., 2015) and, combined with low 187Re/188Os (<4.1 × 10−3) and 190Pt/188Os (7.1 × 10−6 to 4.4 × 10−5), make Re- (TRD) and Pt-depletion (TDA) model ages resistant to modification through crustal assimilation or metamorphic alteration.
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(c) Re-depletion ages calculated from other 187Os/188Os literature data (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2015).
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Bennett, V.C., Brandon, A.D., Nutman, A.P. (2007) Coupled 142Nd-143Nd Isotopic Evidence for Hadean Mantle Dynamics. Science 318, 1907–1910. https://doi.org/10.1126/science.1145928
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
View in article
Bouvier, A., Vervoort, J.D., Patchett, P.J. (2008) The Lu–Hf and Sm–Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48–57. https://doi.org/10.1016/j.epsl.2008.06.010
Show in context Model ages are calculated relative to chondritic uniform reservoir (CHUR; Bouvier et al., 2008), depleted mantle formed from CHUR at 3800 Ma (Fisher and Vervoort, 2018), and an end-member case where depleted mantle formed at 4567 Ma.
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Brandon, A.D., Humayun, M., Puchtel, I.S., Leya, I., Zolensky, M. (2005) Osmium Isotope Evidence for an s-Process Carrier in Primitive Chondrites. Science 309, 1233–1236. https://doi.org/10.1126/science.1115053
Show in context Despite internal variations in Os composition within individual meteorites (Brandon et al., 2005), Os was homogeneous at the planetesimal scale in the presolar nebula (Goderis et al., 2017).
View in article
Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
Show in context Radiogenic Os isotope results are presented as Re- and Pt- model ages assuming chondritic evolution (Walker et al., 2002) or primitive mantle models (Meisel et al., 2001; Brandon et al., 2006) based on chondrite; we address this assumption in the Discussion.
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The TDA (relative to primitive mantle; Brandon et al., 2006) from all fresh chromitite samples form a single age population with a weighted mean age of 3382 ± 360 Ma (Fig. 2; n = 17; MSWD = 0.65; p = 0.84).
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This yields 186Os/188Os = 0.1198301 ± 0.0000008 (2 s.e.; n = 32; MSWD = 0.58; p = 0.97; normalised to UMd of Brandon et al., 2006; Supplementary Information), corresponding to a TDA of 3437 ± 288 Ma, or 3437 ± 587 Ma including the ∼12 ppm uncertainty in the solar system initial (Brandon et al., 2006).
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The Ujaragssuit 187Os-186Os data are consistent with a concordant ∼3250 Ma Re-Pt depletion event from primitive mantle (PM) of Brandon et al. (2006) with Re-Os evolution of O-chondrite (Walker et al., 2002).
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A mantle source that evolved with primitive mantle Pt-Os (Brandon et al., 2006) and chondritic Re-Os (Walker et al., 2002) yields a concordant age for coupled Re-Pt depletion occurring at ∼3.25 Ga, consistent with Lu-Hf constraints (Sawada et al., 2023).
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By contrast, use of either the primitive or depleted mantle models of Day et al. (2017) yields TDA and TRD that are inconsistent. Unfortunately, the large uncertainty on 186Os/188Os compared to its temporal variation means we cannot further distinguish between different Re-Os evolution models for the Ujaragssuit source; providing the Pt-Os evolution follows primitive mantle (Brandon et al., 2006), then Re-Os evolution using any chondrite (Walker et al., 2002) or primitive upper mantle (PUM; Meisel et al., 2001) model yields concordant Re-Pt depletion ages within uncertainty.
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186Os is reported relative to primitive mantle of Brandon et al. (2006) at 3250 Ma. Uncertainty envelope shows average propagated analytical uncertainty on an individual analysis.
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Chadwick, B., Crewe, M.A. (1986) Chromite in the early Archean Akilia association (ca. 3,800 M.Y.), Ivisartoq region, inner Godthabsfjord, southern West Greenland. Economic Geology 81, 184–191. https://doi.org/10.2113/gsecongeo.81.1.184
Show in context Among the ultramafic bodies in this region, the stratiform chromitite-bearing Ujaragssuit Nunât layered body (hereafter the Ujaragssuit Intrusion) was recognised as the oldest chromitite on Earth (Chadwick and Crewe, 1986), with a minimum age of >3.8 Ga indicated by its host orthogneisses (Nutman et al., 1996).
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Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
View in article
High concentrations of highly siderophile elements (HSEs) in the chromitites make them ideal for study using Re-Pt-Os (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2013, 2015) and Ru isotopes (Fischer-Gödde et al., 2020).
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These studies identified that the Ujaragssuit Intrusion records evidence of Hadean mantle depletion (Coggon et al., 2013) and was derived from mantle deficient in chondrite relative to modern mantle (Fischer-Gödde et al., 2020).
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(a) Pt-depletion ages calculated from 186Os analyses from this study and Coggon et al. (2013).
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(b) Re-depletion ages calculated from high precision analyses of massive chromitites from this study and Coggon et al. (2013).
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Taken together, our chromitite data show excellent agreement with previous high precision Re-Os analyses (Coggon et al., 2013), which show maximum TRD ages of 3246.4 ± 1.0 Ma (n = 4) and increasing scatter in samples that record younger TRD (3209 ± 50 Ma; n = 4).
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Instead, we interpret the Re-Os data to indicate an age of ∼3246 ± 120 Ma for the Ujaragssuit Intrusion (oldest age from our data and Coggon et al., 2013, including systematic mantle model uncertainties; Supplementary Information).
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All of these ages appear young compared to previously reported TDA from Ujaragssuit, ranging up to 4.1 Ga (Coggon et al., 2013).
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However, the uncertainties reported for both individual analyses and age groups in Coggon et al. (2013) are far smaller than the ∼35 ppm precision they report for the the Durham Romil Osmium Standard (DROsS) (Luguet et al., 2008; equivalent to a ∼1.5 Ga uncertainty in each TDA).
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We combine all data from our fresh chromitite samples and Coggon et al. (2013) to estimate the initial 186Os/188Os of the Ujaragssuit Intrusion, which we believe to be the most precise estimate of this ratio for a single terrestrial locality.
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Coggon, J.A., Luguet, A., Fonseca, R.O.C., Lorand, J.-P., Heuser, A., Appel, P.W.U. (2015) Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation. Geochimica et Cosmochimica Acta 167, 205–240. https://doi.org/10.1016/j.gca.2015.07.025
Show in context High concentrations of highly siderophile elements (HSEs) in the chromitites make them ideal for study using Re-Pt-Os (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2013, 2015) and Ru isotopes (Fischer-Gödde et al., 2020).
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Their high Os concentrations reflect high modal chromite contents (Bennett et al., 2002; Coggon et al., 2015) and, combined with low 187Re/188Os (<4.1 × 10−3) and 190Pt/188Os (7.1 × 10−6 to 4.4 × 10−5), make Re- (TRD) and Pt-depletion (TDA) model ages resistant to modification through crustal assimilation or metamorphic alteration.
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(c) Re-depletion ages calculated from other 187Os/188Os literature data (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2015).
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These ‘young’ TRD ages relative to the age of the host orthogneisses and Pt-Os model ages have previously been explained by metamorphic resetting of the Re-Os system (Coggon et al., 2015).
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Creech, J.B., Baker, J.A., Handler, M.R., Lorand, J.-P., Storey, M., Wainwright, A.N., Luguet, A., Moynier, F., Bizzarro, M. (2017) Late accretion history of the terrestrial planets inferred from platinum stable isotopes. Geochemical Perspectives Letters 3, 94–104. https://doi.org/10.7185/geochemlet.1710
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
View in article
Our new ∼3.25 Ga age for the Ujaragssuit Intrusion sheds new light on previously identified isotopic anomalies, which indicate the mantle sources of NAC igneous rocks were depleted in chondritic components relative to bulk Earth (Willbold et al., 2011; Creech et al., 2017; Fischer-Gödde et al., 2020; Xu et al., 2023).
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Day, J.M.D., Walker, R.J., Warren, J.M. (2017) 186Os–187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys. Geochimica et Cosmochimica Acta 200, 232–254. https://doi.org/10.1016/j.gca.2016.12.013
Show in context Use of alternative mantle models (Day et al., 2017) yields younger ages.
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Uncertainties in mantle models from Day et al. (2017) are not shown for clarity. DM, depleted mantle.
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By contrast, use of either the primitive or depleted mantle models of Day et al. (2017) yields TDA and TRD that are inconsistent. Unfortunately, the large uncertainty on 186Os/188Os compared to its temporal variation means we cannot further distinguish between different Re-Os evolution models for the Ujaragssuit source; providing the Pt-Os evolution follows primitive mantle (Brandon et al., 2006), then Re-Os evolution using any chondrite (Walker et al., 2002) or primitive upper mantle (PUM; Meisel et al., 2001) model yields concordant Re-Pt depletion ages within uncertainty.
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Debaille, V., O’Neill, C., Brandon, A.D., Haenecour, P., Yin, Q.-Z., Mattielli, N., Treiman, A.H. (2013) Stagnant-lid tectonics in early Earth revealed by 142Nd variations in late Archean rocks. Earth and Planetary Science Letters 373, 83–92. https://doi.org/10.1016/j.epsl.2013.04.016
Show in context This most likely supports formation of the NAC within a non-uniformitarian tectonic regime (e.g., Debaille et al., 2013; Webb et al., 2020), in which the crust was relatively immobile with respect to the underlying mantle sources that drove the formation of crustal ultramafic intrusions.
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Fischer-Gödde, M., Elfers, B.-M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020) Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks. Nature 579, 240–244. https://doi.org/10.1038/s41586-020-2069-3
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
View in article
High concentrations of highly siderophile elements (HSEs) in the chromitites make them ideal for study using Re-Pt-Os (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2013, 2015) and Ru isotopes (Fischer-Gödde et al., 2020).
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These studies identified that the Ujaragssuit Intrusion records evidence of Hadean mantle depletion (Coggon et al., 2013) and was derived from mantle deficient in chondrite relative to modern mantle (Fischer-Gödde et al., 2020).
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The precise initial 187Os-186Os systematics allow us to discriminate between potential Pt-Os mantle evolution models (Fig. 3) for the Ujaragssuit mantle source, which is depleted in chondritic components compared to modern mantle (Fischer-Gödde et al., 2020).
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Given the presence of nucleosynthetic Ru anomalies at Ujaragssuit with no known cosmochemical analogue (Fischer-Gödde et al., 2020), we cannot conclusively rule out a mantle source with exotic Re-Pt-Os isotope systematics. However, any such source would need to reach the Ujaragssuit initial 187Os/188Os and 186Os/188Os at ∼3.2 Ga, within uncertainty of chondritic evolution (Fig. 3), to be consistent with zircon Lu-Hf model ages (Sawada et al., 2023).
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Therefore, even though the Ujaragssuit mantle source was relatively depleted in late-accreted chondritic material (Fischer-Gödde et al., 2020), this had no net effect on its Os isotopic composition.
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Our new ∼3.25 Ga age for the Ujaragssuit Intrusion sheds new light on previously identified isotopic anomalies, which indicate the mantle sources of NAC igneous rocks were depleted in chondritic components relative to bulk Earth (Willbold et al., 2011; Creech et al., 2017; Fischer-Gödde et al., 2020; Xu et al., 2023).
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In particular, a ∼3.25 Ga age for the Ujaragssuit Intrusion means that nucleosynthetic Ru isotope anomalies (Fischer-Gödde et al., 2020) are now known from NAC ultramafic intrusions formed in four major periods: at ∼3.8 Ga in the Narssaq and South of Isua ultramafic bodies, at ∼3.7 Ga in the Isua Supracrustal Belt, at ∼3.25 Ga in the Ujaragssuit Intrusion, and at >3.0 Ga in the Fiskefjord peridotites.
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These anomalies occur across three different tectonostratigraphic terranes (Friend and Nutman, 2019), do not diminish over time and have not been identified in other cratons (Fischer-Gödde et al., 2020), even where mantle depleted in late-accreted materials has been proposed (Maier et al., 2009).
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Fisher, C.M., Vervoort, J.D. (2018) Using the magmatic record to constrain the growth of continental crust—The Eoarchean zircon Hf record of Greenland. Earth and Planetary Science Letters 488, 79–91. https://doi.org/10.1016/j.epsl.2018.01.031
Show in context Model ages are calculated relative to chondritic uniform reservoir (CHUR; Bouvier et al., 2008), depleted mantle formed from CHUR at 3800 Ma (Fisher and Vervoort, 2018), and an end-member case where depleted mantle formed at 4567 Ma.
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Friend, C.R.L., Nutman, A.P. (2019) Tectono-stratigraphic terranes in Archaean gneiss complexes as evidence for plate tectonics: The Nuuk region, southern West Greenland. Gondwana Research 72, 213–237. https://doi.org/10.1016/j.gr.2019.03.004
Show in context The Isua Supracrustal Belt and area immediately to the south has been of particular interest due to less intense Neoarchaean metamorphism (Friend and Nutman, 2019), the preservation of supracrustal sequences, and an abundance of mantle-derived lavas and ultramafic bodies.
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These ages reflect regional metamorphism in this part of the Itsaq Gneiss Complex (Friend and Nutman, 2019), driving formation of the leucogranites via intracrustal melting.
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Repeated tapping of this potentially unique chondrite-depleted mantle source across various NAC terranes over a period of 600 Myr is difficult to reconcile with a model in which the different terranes identified in the NAC were initially widely dispersed (Friend and Nutman, 2019).
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These anomalies occur across three different tectonostratigraphic terranes (Friend and Nutman, 2019), do not diminish over time and have not been identified in other cratons (Fischer-Gödde et al., 2020), even where mantle depleted in late-accreted materials has been proposed (Maier et al., 2009).
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Gardner, R.L., Piazolo, S., Daczko, N.R. (2015) Pinch and swell structures: evidence for strain localisation by brittle–viscous behaviour in the middle crust. Solid Earth 6, 1045–1061. https://doi.org/10.5194/se-6-1045-2015
Show in context This, along with gneissic foliation that wraps the intrusion, suggests that the ultramafic rocks acted as a competent body around which the gneisses deformed (Gardner et al., 2015).
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Goderis, S., Brandon, A.D., Mayer, B., Humayun, M. (2017) Osmium isotopic homogeneity in the CK carbonaceous chondrites. Geochimica et Cosmochimica Acta 216, 8–27. https://doi.org/10.1016/j.gca.2017.05.011
Show in context This lack of resolvable Os isotopic anomalies reflects an absence of bulk Os isotopic anomalies in most major meteorite groups, including chondrites (Goderis et al., 2017).
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Despite internal variations in Os composition within individual meteorites (Brandon et al., 2005), Os was homogeneous at the planetesimal scale in the presolar nebula (Goderis et al., 2017).
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Luguet, A., Nowell, G.M., Pearson, D.G. (2008) 184Os/188Os and 186Os/188Os measurements by Negative Thermal Ionisation Mass Spectrometry (N-TIMS): Effects of interfering element and mass fractionation corrections on data accuracy and precision. Chemical Geology 248, 342–362. https://doi.org/10.1016/j.chemgeo.2007.10.013
Show in context However, the uncertainties reported for both individual analyses and age groups in Coggon et al. (2013) are far smaller than the ∼35 ppm precision they report for the the Durham Romil Osmium Standard (DROsS) (Luguet et al., 2008; equivalent to a ∼1.5 Ga uncertainty in each TDA).
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Maier, W.D., Barnes, S.J., Campbell, I.H., Fiorentini, M.L., Peltonen, P., Barnes, S.-J., Smithies, R.H. (2009) Progressive mixing of meteoritic veneer into the early Earth’s deep mantle. Nature 460, 620–623. https://doi.org/10.1038/nature08205
Show in context These anomalies occur across three different tectonostratigraphic terranes (Friend and Nutman, 2019), do not diminish over time and have not been identified in other cratons (Fischer-Gödde et al., 2020), even where mantle depleted in late-accreted materials has been proposed (Maier et al., 2009).
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Meisel, T., Walker, R.J., Irving, A.J., Lorand, J.-P. (2001) Osmium isotopic composition of mantle xenoliths: a global perspective. Geochimica et Cosmochimica Acta 65, 1311–1323. https://doi.org/10.1016/S0016-7037(00)00566-4
Show in context Radiogenic Os isotope results are presented as Re- and Pt- model ages assuming chondritic evolution (Walker et al., 2002) or primitive mantle models (Meisel et al., 2001; Brandon et al., 2006) based on chondrite; we address this assumption in the Discussion.
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By contrast, use of either the primitive or depleted mantle models of Day et al. (2017) yields TDA and TRD that are inconsistent. Unfortunately, the large uncertainty on 186Os/188Os compared to its temporal variation means we cannot further distinguish between different Re-Os evolution models for the Ujaragssuit source; providing the Pt-Os evolution follows primitive mantle (Brandon et al., 2006), then Re-Os evolution using any chondrite (Walker et al., 2002) or primitive upper mantle (PUM; Meisel et al., 2001) model yields concordant Re-Pt depletion ages within uncertainty.
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Nutman, A.P., McGregor, V.R., Friend, C.R.L., Bennett, V.C., Kinny, P.D. (1996) The Itsaq Gneiss Complex of southern West Greenland; the world’s most extensive record of early crustal evolution (3900-3600 Ma). Precambrian Research 78, 1–39. https://doi.org/10.1016/0301-9268(95)00066-6
Show in context The Itsaq Gneiss Complex, North Atlantic Craton (NAC), Greenland, is among the largest and best preserved tracts of Eoarchaean crust on Earth (Nutman et al., 1996).
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Among the ultramafic bodies in this region, the stratiform chromitite-bearing Ujaragssuit Nunât layered body (hereafter the Ujaragssuit Intrusion) was recognised as the oldest chromitite on Earth (Chadwick and Crewe, 1986), with a minimum age of >3.8 Ga indicated by its host orthogneisses (Nutman et al., 1996).
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Though slightly older than previous orthogneiss ages near Ujaragssuit (Nutman et al., 1996), our data confirms that the intrusion’s host orthogneisses are >3.8 Ga.
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In the case of Ujaragssuit, the age determined by direct dating is >550 Myr younger than if the ultramafic rocks are interpreted as an enclave intruded by the orthogneiss protoliths (Nutman et al., 1996).
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Puchtel, I.S., Humayun, M., Campbell, A.J., Sproule, R.A., Lesher, C.M. (2004) Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada. Geochimica et Cosmochimica Acta 68, 1361–1383. https://doi.org/10.1016/j.gca.2003.09.013
Show in context As igneous chromite has high Os and low Re/Os (Puchtel et al., 2004) and the chromitites presently retain these HSE signatures, this would require that large quantities of Re or radiogenic Os were added to the chromitites during metamorphism, in proportion to the Os abundance in each chromitite.
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Rollinson, H., Appel, P.W.U., Frei, R. (2002) A Metamorphosed, Early Archaean Chromitite from West Greenland: Implications for the Genesis of Archaean Anorthositic Chromitites. Journal of Petrology 43, 2143–2170. https://doi.org/10.1093/petrology/43.11.2143
Show in context High concentrations of highly siderophile elements (HSEs) in the chromitites make them ideal for study using Re-Pt-Os (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2013, 2015) and Ru isotopes (Fischer-Gödde et al., 2020).
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We found no evidence of large scale faulting within or around the intrusion. Chromitites are abundant in the northern portion of the intrusion, corresponding to its base (Rollinson et al., 2002).
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(c) Re-depletion ages calculated from other 187Os/188Os literature data (Bennett et al., 2002; Rollinson et al., 2002; Coggon et al., 2015).
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Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
Show in context Three of these leucogranites yield much younger crystallisation ages of 2966 ± 6 Ma, 2976 ± 6 Ma, and 2966 ± 8 Ma, consistent with previously determined ages of ∼2.97–2.95 Ga (Sawada et al., 2023).
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These coincide with a population of metamorphic zircon present in all three orthogneiss samples at ∼2.97 Ga, as well as growth of metamorphic zircon within the Ujaragssuit chromitites themselves (Sawada et al., 2023).
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To summarise, the only robust age constraint on the Ujaragssuit Intrusion is that it is >2.97 Ga, the age of both cross-cutting leucogranites and metamorphic zircon within Ujaragssuit chromitites (Sawada et al., 2023).
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(d) Lu-Hf model ages calculated from metamorphic zircons within the Ujaragssuit chromitites (Sawada et al., 2023).
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Furthermore, the ∼3.25 Ga Re-Os model age overlaps with Hf model ages of metamorphic zircon in the chromitites, which requires special pleading if the Ujaragssuit Intrusion is indeed >3.8 Ga (Sawada et al., 2023).
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A mantle source that evolved with primitive mantle Pt-Os (Brandon et al., 2006) and chondritic Re-Os (Walker et al., 2002) yields a concordant age for coupled Re-Pt depletion occurring at ∼3.25 Ga, consistent with Lu-Hf constraints (Sawada et al., 2023).
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Given the presence of nucleosynthetic Ru anomalies at Ujaragssuit with no known cosmochemical analogue (Fischer-Gödde et al., 2020), we cannot conclusively rule out a mantle source with exotic Re-Pt-Os isotope systematics. However, any such source would need to reach the Ujaragssuit initial 187Os/188Os and 186Os/188Os at ∼3.2 Ga, within uncertainty of chondritic evolution (Fig. 3), to be consistent with zircon Lu-Hf model ages (Sawada et al., 2023).
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Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
Show in context Radiogenic Os isotope results are presented as Re- and Pt- model ages assuming chondritic evolution (Walker et al., 2002) or primitive mantle models (Meisel et al., 2001; Brandon et al., 2006) based on chondrite; we address this assumption in the Discussion.
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High precision unspiked Os analyses of four fresh chromitite samples (Fig. 2) yield a tight range of weighted mean TRD ages (relative to O-chondrite; Walker et al., 2002), ranging from 3226.6 ± 1.6 Ma (n = 4; 95 % confidence limits) to 3244.2 ± 1.2 Ma (n = 5).
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The Ujaragssuit 187Os-186Os data are consistent with a concordant ∼3250 Ma Re-Pt depletion event from primitive mantle (PM) of Brandon et al. (2006) with Re-Os evolution of O-chondrite (Walker et al., 2002).
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A mantle source that evolved with primitive mantle Pt-Os (Brandon et al., 2006) and chondritic Re-Os (Walker et al., 2002) yields a concordant age for coupled Re-Pt depletion occurring at ∼3.25 Ga, consistent with Lu-Hf constraints (Sawada et al., 2023).
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By contrast, use of either the primitive or depleted mantle models of Day et al. (2017) yields TDA and TRD that are inconsistent. Unfortunately, the large uncertainty on 186Os/188Os compared to its temporal variation means we cannot further distinguish between different Re-Os evolution models for the Ujaragssuit source; providing the Pt-Os evolution follows primitive mantle (Brandon et al., 2006), then Re-Os evolution using any chondrite (Walker et al., 2002) or primitive upper mantle (PUM; Meisel et al., 2001) model yields concordant Re-Pt depletion ages within uncertainty.
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Waterton, P., Guotana, J.M., Nishio, I., Morishita, T., Tani, K., Woodland, S., Legros, H., Pearson, D.G., Szilas, K. (2022) No mantle residues in the Isua Supracrustal Belt. Earth and Planetary Science Letters 579, 117348. https://doi.org/10.1016/j.epsl.2021.117348
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
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Webb, A.A.G., Müller, T., Zuo, J., Haproff, P.J., Ramírez-Salazar, A. (2020) A non-plate tectonic model for the Eoarchean Isua supracrustal belt. Lithosphere 12, 166–179. https://doi.org/10.1130/L1130.1
Show in context This most likely supports formation of the NAC within a non-uniformitarian tectonic regime (e.g., Debaille et al., 2013; Webb et al., 2020), in which the crust was relatively immobile with respect to the underlying mantle sources that drove the formation of crustal ultramafic intrusions.
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Willbold, M., Elliott, T., Moorbath, S. (2011) The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment. Nature 477, 195–198. https://doi.org/10.1038/nature10399
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
View in article
Our new ∼3.25 Ga age for the Ujaragssuit Intrusion sheds new light on previously identified isotopic anomalies, which indicate the mantle sources of NAC igneous rocks were depleted in chondritic components relative to bulk Earth (Willbold et al., 2011; Creech et al., 2017; Fischer-Gödde et al., 2020; Xu et al., 2023).
View in article
Xu, Y., Szilas, K., Zhang, L., Zhu, J.-M., Wu, G., Zhang, J., Qin, B., Sun, Y., Pearson, D.G., Liu, J. (2023) Ni isotopes provide a glimpse of Earth’s pre-late-veneer mantle. Science Advances 9, eadj2170. https://doi.org/10.1126/sciadv.adj2170
Show in context This has made the area an attractive target for studies of long lived (Bennett et al., 1993, 2002; Coggon et al., 2013; Waterton et al., 2022), short lived (Bennett et al., 2007; Willbold et al., 2011), stable (Creech et al., 2017; Xu et al., 2023) and nucleosynthetic (Fischer-Gödde et al., 2020) isotope systematics, to identify both ancient mantle differentiation events and primordial heterogeneities from Earth’s accretion.
View in article
Our new ∼3.25 Ga age for the Ujaragssuit Intrusion sheds new light on previously identified isotopic anomalies, which indicate the mantle sources of NAC igneous rocks were depleted in chondritic components relative to bulk Earth (Willbold et al., 2011; Creech et al., 2017; Fischer-Gödde et al., 2020; Xu et al., 2023).
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Supplementary Information
The Supplementary Information includes:
- 1. Samples
- 2. Methods and Data Processing
- 3. Interpretation of Zircon U-Pb Data
- 4. Are ɛ184Os Anomalies Real?
- Tables S-1 to S-4
- Figures S-1 to S-10
- Supplementary Information References
Download the Supplementary Information (PDF)
Download Table S-2 (.xlsx)
Download Table S-3 (.xlsx)
Download Table S-4 (.xlsx)
Figures
Figure 1 (a) Location of the Ujaragssuit Intrusion. (b) Detailed map of the Ujaragssuit Intrusion, showing locations of analysed chromitite and granitoids samples, including granitoid zircon U-Pb ages. ‘Altered Uj.’ refers to the most altered portions of the Ujaragssuit Intrusion, including corundum-bearing amphibolites and reaction zones. (c) High resolution aerial photograph of the Ujaragssuit Intrusion. (d) Outline of the Ujaragssuit Intrusion, showing major lenses connected by thin ‘necks’.
Figure 2 Geochronological data for the Ujaragssuit Intrusion. All plots show the 2970 Ma minimum age derived from cross-cutting leucogranites (blue dashed line) and the oldest high precision chromitite Re-depletion age, including systematic uncertainties (3246 ± 120 Ma; black dashed line and grey field). (a) Pt-depletion ages calculated from 186Os analyses from this study and Coggon et al. (2013)
Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
. (b) Re-depletion ages calculated from high precision analyses of massive chromitites from this study and Coggon et al. (2013)Coggon, J.A., Luguet, A., Nowell, G.M., Appel, P.W.U. (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures. Nature Geoscience 6, 871–874. https://doi.org/10.1038/ngeo1911
. (c) Re-depletion ages calculated from other 187Os/188Os literature data (Bennett et al., 2002Bennett, V.C., Nutman, A.P., Esat, T.M. (2002) Constraints on mantle evolution from 187Os/188Os isotopic compositions of Archean ultramafic rocks from southern West Greenland (3.8 Ga) and Western Australia (3.46 Ga). Geochimica et Cosmochimica Acta 66, 2615–2630. https://doi.org/10.1016/S0016-7037(02)00862-1
; Rollinson et al., 2002Rollinson, H., Appel, P.W.U., Frei, R. (2002) A Metamorphosed, Early Archaean Chromitite from West Greenland: Implications for the Genesis of Archaean Anorthositic Chromitites. Journal of Petrology 43, 2143–2170. https://doi.org/10.1093/petrology/43.11.2143
; Coggon et al., 2015Coggon, J.A., Luguet, A., Fonseca, R.O.C., Lorand, J.-P., Heuser, A., Appel, P.W.U. (2015) Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation. Geochimica et Cosmochimica Acta 167, 205–240. https://doi.org/10.1016/j.gca.2015.07.025
). (d) Lu-Hf model ages calculated from metamorphic zircons within the Ujaragssuit chromitites (Sawada et al., 2023Sawada, H., Morishita, T., Vezinet, A., Stern, R., Tani, K., Nishio, I., Takahashi, K., Pearson, D.G., Szilas, K. (2023) Zircon within chromitite requires revision of the tectonic history of the Eoarchean Itsaq Gneiss complex, Greenland. Geoscience Frontiers 14, 101648. https://doi.org/10.1016/j.gsf.2023.101648
). Model ages are calculated relative to chondritic uniform reservoir (CHUR; Bouvier et al., 2008Bouvier, A., Vervoort, J.D., Patchett, P.J. (2008) The Lu–Hf and Sm–Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48–57. https://doi.org/10.1016/j.epsl.2008.06.010
), depleted mantle formed from CHUR at 3800 Ma (Fisher and Vervoort, 2018Fisher, C.M., Vervoort, J.D. (2018) Using the magmatic record to constrain the growth of continental crust—The Eoarchean zircon Hf record of Greenland. Earth and Planetary Science Letters 488, 79–91. https://doi.org/10.1016/j.epsl.2018.01.031
), and an end-member case where depleted mantle formed at 4567 Ma.
Figure 3 ‘Concordia’ plot of Re- and Pt-depletion ages calculated for different Re-Pt-Os mantle evolution models. The Ujaragssuit 187Os-186Os data are consistent with a concordant ∼3250 Ma Re-Pt depletion event from primitive mantle (PM) of Brandon et al. (2006)
Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
with Re-Os evolution of O-chondrite (Walker et al., 2002Walker, R.J., Horan, M.F., Morgan, J.W., Becker, H., Grossman, J.N., Rubin, A.E. (2002) Comparative 187Re-187Os systematics of chondrites: Implications regarding early solar system processes. Geochimica et Cosmochimica Acta 66, 4187–4201. https://doi.org/10.1016/S0016-7037(02)01003-7
). Uncertainties in mantle models from Day et al. (2017)Day, J.M.D., Walker, R.J., Warren, J.M. (2017) 186Os–187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys. Geochimica et Cosmochimica Acta 200, 232–254. https://doi.org/10.1016/j.gca.2016.12.013
are not shown for clarity. DM, depleted mantle.
Figure 4 Nucleosynthetic osmium isotope composition of Ujaragssuit chromitites in epsilon units, relative to the DROsS reference material. 186Os is reported relative to primitive mantle of Brandon et al. (2006)
Brandon, A.D., Walker, R.J., Puchtel, I.S. (2006) Platinum-osmium isotope evolution of the Earth’s mantle: Constraints from chondrites and Os-rich alloys. Geochimica et Cosmochimica Acta 70, 2093–2103. https://doi.org/10.1016/j.gca.2006.01.005
at 3250 Ma. Uncertainty envelope shows average propagated analytical uncertainty on an individual analysis. Note different scale for 184Os.