Comparative 142Nd and 182W study of MORBs and the 4.5 Gyr evolution of the upper mantle
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Keywords: 142Nd, 182W, MORB, Pacific-Antarctic Ridge, DMM, OIB
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Abstract
Figures and Tables
 Figure 1 (a) μ182W and (b) μ142Nd for PAR MORBs of this study. Vertical thin grey lines with shaded areas show average standards (μ182W = 0 and μ142Nd = 0) with external reproducibility (2 s.d.). Vertical thick black lines show the mean for all MORBs analysed here (μ182W = −1.9 ± 3.5; μ142Nd = −1.6 ± 5.0). Smaller symbols in (b) are duplicate analyses with the average value and 2 s.d. in darker shade. MORB μ182W of East Pacific Rise and Central Indian Ridge are, respectively, from Rizo et al. (2016) and Mundl et al. (2017). The μ142Nd for other MORBs are from Boyet and Carlson (2006), Caro et al. (2006), Jackson and Carlson (2012), and Hyung and Jacobsen (2020), and mantle peridotite data from Cipriani et al. (2011). |  Figure 2 Compilation and computed probability density of (a, b) μ142Nd and (c, d) μ182W for MORB, OIB and mantle peridotites. Upper mantle (a) includes MORB and mantle peridotite samples. Left side plots (a and c) present histograms of all data; grey bands show the analytical reproducibility on the standards obtained during this study; thick bars on box plots present the median, and the triangle notches show the weighted mean values. Right side plots (b, d) show compositions generated by Monte Carlo bootstrap simulations (10,000 runs). Vertical lines and grey areas in b and d show the mean and 2 s.d. envelope of the Nd and W standards derived from the simulations. Database and references provided in the Supplementary Information Data Table S-4. |  Figure 3 μ182W vs. (a) normalised La/Gd ratio, and radiogenic (b) Pb, (c) Nd and (d) Sr isotope compositions, for the PAR MORB analysed here. Blue circles are N-MORB and square is T-MORB sample PAC2DR27-1. Tungsten isotope data from this study. Trace element concentrations and radiogenic isotope compositions from Hamelin et al. (2011). |  Table 1 μ182W and μ142Nd of MORBs from the Pacific-Antarctic Ridge. Detailed isotope compositions can be found in the Supplementary Information (Data Tables S-2 and S-3). |
| Figure 1 | Figure 2 | Figure 3 | Table 1 |
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Introduction
The Earth’s mantle underwent significant chemical evolution during its early history. The short lived isotope systems 182Hf-182W (t1/2 = 8.9 Myr) and 146Sm-142Nd (t1/2 = 103 Myr) applied to the study of terrestrial rocks have provided valuable insights into understanding the nature of these changes, because they are especially capable of tracing the most ancient chemical fractionation processes. Notably, ancient mantle-derived rocks from various Archean cratons exhibit variations in 142Nd abundances (e.g., Carlson et al., 2019
Carlson, R.W., Garçon, M., O’Neil, J., Reimink, J., Rizo, H. (2019) The nature of Earth’s first crust. Chemical Geology 530, 119321. https://doi.org/10.1016/j.chemgeo.2019.119321
), implying silicate differentiation within the first ∼500 million years of Earth’s history. The recent detection of 182W abundance variations in mantle-derived rocks of different ages have initiated debates regarding the main processes controlling 182W variability, including early silicate differentiation as seen by the 146Sm-142Nd system (e.g., Touboul et al., 2012Touboul, M., Puchtel, I.S., Walker, R.J. (2012) 182W evidence for long-term preservation of early mantle differentiation products. Science 335, 1065–1069. https://doi.org/10.1126/science.1216351
), core-mantle chemical interactions (e.g., Rizo et al., 2019Rizo, H., Andrault, D., Bennett, N.R., Humayun, M., Brandon, A., Vlastelic, I., Moine, B., Poirier, A., Bouhifd, M.A., Murphy, D.T. (2019) 182W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspectives Letters 11, 6–11. https://doi.org/10.7185/geochemlet.1917
), differences in the mass of late accreted extra-terrestrial material into the mantle (e.g., 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
) and the recycling of ancient crust or sediments into the mantle (e.g., Tusch et al., 2021Tusch, J., Münker, C., Hasenstab, E., Jansen, M., Marien, C.S., Kurzweil, F., van Kranendonk, M.J., Smithies, H., Maier, W., Garbe-Schönberg, D. (2021) Convective isolation of hadean mantle reservoirs through archean time. Proceedings of the National Academy of Sciences of the United States of America 118, e2012626118. https://doi.org/10.1073/pnas.2012626118
).Variations in 142Nd and 182W abundances, denoted as μ142Nd and μ182W, reflect part-per-million deviations from laboratory standards set at μ = 0. These standards are assumed to represent the compositions of the modern mantle, or the depleted mid-ocean ridge mantle (DMM) reservoir. However, few mantle peridotites (n = 4), or melts directly derived from the depleted upper mantle such as MORB (n = 9), have been analysed for μ142Nd (e.g., Boyet and Carlson, 2006
Boyet, M., Carlson, R.W. (2006) A new geochemical model for the Earth’s mantle inferred from 146Sm–142Nd systematics. Earth and Planetary Science Letters 250, 254–268. https://doi.org/10.1016/j.epsl.2006.07.046
; Caro et al., 2006Caro, G., Bourdon, B., Birck, J.L., Moorbath, S. (2006) High-precision 142Nd/144Nd measurements in terrestrial rocks: constraints on the early differentiation of the Earth’s mantle. Geochimica et Cosmochimica Acta 70, 164–191. https://doi.org/10.1016/j.gca.2005.08.015.
; Cipriani et al., 2011Cipriani, A., Bonatti, E., Carlson, R.W. (2011) Nonchondritic 142Nd in suboceanic mantle peridotites. Geochemistry, Geophysics, Geosystems 12, Q03006. https://doi.org/10.1029/2010GC003415
; Jackson and Carlson 2012Jackson, M.G., Carlson, R.W. (2012) Homogeneous superchondritic 142Nd/144Nd in the mid-ocean ridge basalt and ocean island basalt mantle. Geochemistry, Geophysics, Geosystems 13, Q06011. https://doi.org/10.1029/2012GC004114
; Hyung and Jacobsen, 2020Hyung, E., Jacobsen, S.B. (2020) The 142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings of the National Academy of Sciences 117, 14738–14744. https://doi.org/10.1073/pnas.2006950117
). The W isotopic composition of the DMM has never been properly determined, given that only two MORB samples have been studied to date (Rizo et al., 2016Rizo, H., Walker, R.J., Carlson, R.W., Horan, M.F., Mukhopadhyay, S., Manthos, V., Francis, D., Jackson, M.G. (2016) Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809–812. https://doi.org/10.1126/science.aad8563
; Mundl et al., 2017Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
). Therefore, μ142Nd and μ182W of the upper mantle are presently inadequately constrained, yet are crucial for understanding the composition and chemical evolution of the silicate Earth.This study presents new μ142Nd data for fourteen MORB samples from the Pacific-Antarctic Ridge (PAR), therefore, tripling the current MORB dataset. We also report W concentrations for 18 samples, and μ182W measurements for seven of these PAR samples. The studied MORB samples were collected between 53° S and 42° S (Fig. S-1), a fast-spreading ridge section with no nearby hotspots. All fresh MORB samples were collected on-axis, and have previously been thoroughly characterised for their petrology, geochemistry and isotopic compositions (e.g., Sr, Nd, Pb, Hf, He, D, S, and Mo), showing the lack of plume influence (Hamelin et al., 2011
Hamelin, C., Dosso, L., Hanan, B.B., Moreira, M., Kositsky, A.P., Thomas, M.Y. (2011) Geochemical portray of the Pacific Ridge: New isotopic data and statistical techniques. Earth and Planetary Science Letters 302, 154–162. https://doi.org/10.1016/j.epsl.2010.12.007
; see Supplementary Information for sample descriptions). The MORB μ142Nd and μ182W are used to provide the first robust estimate for the DMM supplying the Pacific-Antarctic Ridge.top
The μ182W and μ142Nd of the Upper Mantle Sources Supplying the PAR Basalts
As mantle-derived melts devoid from continental crustal contamination, MORBs allow to constrain the μ142Nd and μ182W of the upper mantle. The low W abundance of MORB samples, however, makes them susceptible to disturbances related to element mobility or secondary hydrothermal alteration overprinting. This concern does not apply to the less mobile Nd, for which concentration in basalts is higher. Therefore, evaluating whether the W hosted in these rocks is of igneous origin is imperative.
Tungsten concentrations in the studied PAR MORBs (n = 18) vary from 6.8 ng g−1 to 220 ng g−1 (Data Table S-1) and are strongly coupled to other immobile and highly incompatible trace elements, such as Th and Nb (Fig. S-2a, b). Narrow ranges for W/Th = 0.1–0.15 (Fig. S-2d), W/Ba = 0.0019–0.0027, W/Ta = 0.08–0.16, and W/U = 0.23–0.43 (not shown) indicate that the W contained in the MORB samples is derived from their mantle sources and free from secondary hydrothermal W overprinting (e.g., König et al., 2011
König, S., Münker, C., Hohl, S., Paulick, H., Barth, A.R., Lagos, M., Pfänder, J., Büchl, A. (2011) The Earth’s tungsten budget during mantle melting and crust formation. Geochimica et Cosmochimica Acta 75, 2119–2136. https://doi.org/10.1016/j.gca.2011.01.031
). Therefore, the W isotopic analyses of these samples accurately establish the μ182W of their mantle sources.The μ182W of the PAR MORBs range from −3.9 ± 4.1 (2 s.e.) to 1.0 ± 2.9 (2 s.e.) with a mean of −1.9 ± 3.5 (2 s.d.; n = 7) (Table 1 and Fig. 1a; Method and detailed isotope data in the Supplementary Information). These results are undistinguishable within errors from the μ182W values of −0.8 ± 4.5 (2 s.e.) and 3.5 ± 4.0 (2 s.e.) in MORBs, respectively, from the East Pacific Rise (Rizo et al., 2016
Rizo, H., Walker, R.J., Carlson, R.W., Horan, M.F., Mukhopadhyay, S., Manthos, V., Francis, D., Jackson, M.G. (2016) Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809–812. https://doi.org/10.1126/science.aad8563
) and the Central Indian Ridge (Mundl et al., 2017Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
). The narrow W isotopic variability observed across three mid-ocean ridge segments from a sparse worldwide coverage suggests that there is little μ182W variation outside the analytical uncertainties within the DMM, on a regional and global scale.Figure 1 (a) μ182W and (b) μ142Nd for PAR MORBs of this study. Vertical thin grey lines with shaded areas show average standards (μ182W = 0 and μ142Nd = 0) with external reproducibility (2 s.d.). Vertical thick black lines show the mean for all MORBs analysed here (μ182W = −1.9 ± 3.5; μ142Nd = −1.6 ± 5.0). Smaller symbols in (b) are duplicate analyses with the average value and 2 s.d. in darker shade. MORB μ182W of East Pacific Rise and Central Indian Ridge are, respectively, from Rizo et al. (2016)
Rizo, H., Walker, R.J., Carlson, R.W., Horan, M.F., Mukhopadhyay, S., Manthos, V., Francis, D., Jackson, M.G. (2016) Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809–812. https://doi.org/10.1126/science.aad8563
and Mundl et al. (2017)Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
. The μ142Nd for other MORBs are from Boyet and Carlson (2006)Boyet, M., Carlson, R.W. (2006) A new geochemical model for the Earth’s mantle inferred from 146Sm–142Nd systematics. Earth and Planetary Science Letters 250, 254–268. https://doi.org/10.1016/j.epsl.2006.07.046
, Caro et al. (2006)Caro, G., Bourdon, B., Birck, J.L., Moorbath, S. (2006) High-precision 142Nd/144Nd measurements in terrestrial rocks: constraints on the early differentiation of the Earth’s mantle. Geochimica et Cosmochimica Acta 70, 164–191. https://doi.org/10.1016/j.gca.2005.08.015.
, Jackson and Carlson (2012)Jackson, M.G., Carlson, R.W. (2012) Homogeneous superchondritic 142Nd/144Nd in the mid-ocean ridge basalt and ocean island basalt mantle. Geochemistry, Geophysics, Geosystems 13, Q06011. https://doi.org/10.1029/2012GC004114
, and Hyung and Jacobsen (2020)Hyung, E., Jacobsen, S.B. (2020) The 142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings of the National Academy of Sciences 117, 14738–14744. https://doi.org/10.1073/pnas.2006950117
, and mantle peridotite data from Cipriani et al. (2011)Cipriani, A., Bonatti, E., Carlson, R.W. (2011) Nonchondritic 142Nd in suboceanic mantle peridotites. Geochemistry, Geophysics, Geosystems 12, Q03006. https://doi.org/10.1029/2010GC003415
.Table 1 μ182W and μ142Nd of MORBs from the Pacific-Antarctic Ridge. Detailed isotope compositions can be found in the Supplementary Information (Data Tables S-2 and S-3).
| Sample | μ182W | ± 2 s.e. | μ142Nd | ± 2 s.e. |
| PAC2DR01-1 | −1.7 | 3.2 | −7.3 | 2.4 |
| PAC2DR01-1 duplicate 1 | −3.6 | 3.6 | ||
| PAC2DR01-1 duplicate 2 | −4.0 | 3.3 | ||
| PAC2DR01-1 average | −5.0 | 2.4 | ||
| PAC2DR02-1 | 1.0 | 2.9 | 0.2 | 2.5 |
| PAC2DR04-2 | −1.8 | 2.4 | ||
| PAC2DR05-2g | −3.0 | 4.8 | 1.4 | 2.4 |
| PAC2DR06-6 | −1.1 | 3.5 | 0.5 | 1.6 |
| PAC2DR08-1 | −3.7 | 5.8 | −2.8 | 2.2 |
| PAC2DR20-1 | −0.8 | 3.4 | −1.0 | 2.4 |
| PAC2DR22-1 | −5.7 | 2.3 | ||
| PAC2DR27-1 | −3.9 | 4.1 | −1.7 | 2.4 |
| PAC2DR30-1 | −0.04 | 3.2 | ||
| PAC2DR31-3 | 2.8 | 2.4 | ||
| PAC2DR32-1 | −5.3 | 2.3 | ||
| PAC2DR33-1 | −1.8 | 2.4 | ||
| PAC2DR36-1 | −1.6 | 2.4 | ||
| Mean ± 2 s.d. | − 1.9 | 3.5 | − 1.6 | 5.0 |
The PAR MORB μ142Nd range from −5.7 ± 2.3 (2 s.e.) to 2.8 ± 2.4 (2 s.e.), with a mean of −1.6 ± 5.0 (2 s.d.; n = 14) (Fig. 1b). Eleven out of 14 samples show μ142Nd within the uncertainty of the JNdi-1, and three samples exhibit lower μ142Nd between −5.7 ± 2.3 (2 s.e.) and −5.0 ± 2.4 (2 s.e.). Most μ142Nd of PAR MORB are within errors of basalts collected from five other ridges (Fig. 1b), showing little μ142Nd variability outside the analytical precision of measurements, regionally or globally, consistent with the μ182W.
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Hadean Differentiation Between DMM and OIB Sources?
MORB and abyssal peridotite samples are the best proxies for the μ142Nd of the DMM. Although the μ142Nd ≤ −5 values of some MORB and mantle peridotite samples are not resolvable from the μ142Nd of standards (Fig. 1b), they suggest the presence of Hadean mantle heterogeneities in the DMM, given that 142Nd variability can only be produced by Sm/Nd fractionation occurring before the extinction of 146Sm (i.e. before ∼4 Ga). Recent studies propose that Earth’s building blocks may have been characterised by μ142Nd of ∼−7.5 (e.g., Frossard et al., 2022
Frossard, P., Israel, C., Bouvier, A., Boyet, M. (2022) Earth’s composition was modified by collisional erosion. Science 377, 1529–1532. https://doi.org/10.1126/science.abq7351
; Johnston et al., 2022Johnston, S., Brandon, A., McLeod, C., Rankenburg, K., Becker, H., Copeland, P. (2022) Nd isotope variation between the Earth–Moon system and enstatite chondrites. Nature 611, 501–506. https://doi.org/10.1038/s41586-022-05265-0
), and a 147Sm/144Nd ratio of ∼0.201 — approximately 2.5 % higher than the chondritic reference value of 0.1960 (to evolve from initial μ142Nd ∼−7.5 to 0 today). Consequently, the low μ142Nd values (≤−5) detected in certain MORB and mantle peridotite samples might be relics of these primordial components in the DMM. Preservation of primordial heterogeneities in the DMM is, however, difficult to explain. Not only must they survive the mixing of Earth’s magma ocean stage, but must also evolve with a near-chondritic Sm/Nd ratio during the Hadean to preserve their μ142Nd (≤−5) measured today. This early, near-chondritic Sm/Nd ratio contrasts with the later, superchondritic Sm/Nd ratio required to explain the ɛ143Nd > +8 of all analysed PAR MORB samples, even including those exhibiting low μ142Nd.Intriguingly, the weighted mean μ142Nd of all available data for MORB and mantle peridotites (μ142Nd = −1.6 ± 0.9; n = 27), and OIB (μ142Nd = +2.0 ± 0.6; n = 66) (Fig. 2a) reveals slight differences, suggesting distinct mantle sources and evolutionary histories. Despite the small 142Nd difference of ∼3.6 ppm falling within the range of current analytical precision, a student’s t-test comparing the datasets indicates a 99.99 % probability of significant difference (p-value of 9.45 x 10−5). While t-tests are valid statistical methods for distinguishing datasets, they do not consider uncertainties associated with individual data points. To obtain the most accurate μ142Nd estimates for the DMM and the OIB sources, Monte Carlo bootstrap simulations were conducted, accounting for uncertainties associated with each individual μ142Nd data point. Figure 2b shows the resulting probability density plots, implying statistically distinguishable μ142Nd values for the DMM and the OIB sources.
Figure 2 Compilation and computed probability density of (a, b) μ142Nd and (c, d) μ182W for MORB, OIB and mantle peridotites. Upper mantle (a) includes MORB and mantle peridotite samples. Left side plots (a and c) present histograms of all data; grey bands show the analytical reproducibility on the standards obtained during this study; thick bars on box plots present the median, and the triangle notches show the weighted mean values. Right side plots (b, d) show compositions generated by Monte Carlo bootstrap simulations (10,000 runs). Vertical lines and grey areas in b and d show the mean and 2 s.d. envelope of the Nd and W standards derived from the simulations. Database and references provided in the Supplementary Information Data Table S-4.
The lower average μ142Nd value of the DMM compared to the OIB sources indicates differentiation before ∼4 Ga. This early differentiation is consistent with the distinct 129Xe/130Xe ratios observed in MORB and OIB, also implying mantle differentiation around 4.45 Ga (Mukhopadhyay, 2012
Mukhopadhyay, S. (2012) Early differentiation and volatile accretion recorded in deep-mantle neon and xenon. Nature 486, 101–104. https://doi.org/10.1038/nature11141
). Notably, a low Sm/Nd fractionation factor of ∼0.02 at 4.45 Ga (defined as 147Sm/144Nd[newly formed reservoir]/147Sm/144Nd[parent reservoir] −1) can explain the observed ∼3.6 ppm μ142Nd difference between DMM and OIB sources. This scenario, however, requires the DMM to have evolved with a lower Sm/Nd ratio compared to the OIB sources, implying that the DMM was originally less depleted in incompatible elements compared to OIB sources. This contradicts the evidence that the DMM is more depleted, based on its present day ɛ143Nd of nearly +9 of MORB (Gale et al., 2013Gale, A., Dalton, C.A., Langmuir, C.H., Su, Y., Schilling, J.G. (2013) The mean composition of ocean ridge basalts. Geochemistry, Geophysics, Geosystems 14, 489–518. https://doi.org/10.1029/2012GC004334
). Oceanic crust sequestration and preferential slab subduction to the lower mantle have been proposed as a plausible model to deplete the lower mantle to a greater extent than the upper mantle (Tucker et al., 2020Tucker, J.M., van Keken, P.E., Jones, R.E., Ballentine, C.J. (2020) A role for subducted oceanic crust in generating the depleted mid-ocean ridge basalt mantle. Geochemistry, Geophysics, Geosystems 21, e2020GC009148. https://doi.org/10.1029/2020GC009148
). The seemingly opposite time-averaged Sm/Nd required to explain MORB μ142Nd and ɛ143Nd requires Sm/Nd fractionation that could result from extraction of continental crust occurring after extinction of 146Sm (after 4 Ga).top
Modern Mantle μ182W Heterogeneities – Established Early or Acquired Through Time?
A significant observation derived from our results is that the average μ182W of the modern DMM (−1.9) is approximately 10 to 20 ppm lower than the average Hadean-Archean mantle (e.g., Rizo et al., 2019
Rizo, H., Andrault, D., Bennett, N.R., Humayun, M., Brandon, A., Vlastelic, I., Moine, B., Poirier, A., Bouhifd, M.A., Murphy, D.T. (2019) 182W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspectives Letters 11, 6–11. https://doi.org/10.7185/geochemlet.1917
). This difference in μ182W suggests the incorporation of a negative μ182W component to the DMM, in order to decrease the μ182W of the Archean mantle to the present day composition. Component candidates with negative μ182W include: 1) an early-formed enriched crust or mantle domain, 2) late accretionary chondritic material, and 3) mantle plume material.Negative μ182W in the earliest oceanic crust, or differentiated mantle domain formed after Earth’s magma ocean solidification, can result from Hf/W fractionation during the lifetime of 182Hf (i.e. first ∼50 Ma of Solar System history). The remixing of this negative μ182W material into the mantle could lead to the observed decrease in μ182W from the Archean to the modern mantle. If characterised by negative μ182W, such material would also exhibit negative μ142Nd. However, combined negative μ182W and μ142Nd have currently only been observed in ∼3.6 Ga komatiites (Puchtel et al., 2016
Puchtel, I.S., Blichert-Toft, J., Touboul, M., Horan, M.F., Walker, R.J. (2016) The coupled 182W-142Nd record of early terrestrial mantle differentiation. Geochemistry, Geophysics, Geosystems 17, 2168–2193. https://doi.org/10.1002/2016GC006324
). Although early mantle differentiation models capable of explaining decoupled 182W and 142Nd have been proposed (e.g., Tusch et al., 2022Tusch, J., Hoffmann, J.E., Hasenstab, E., Fischer-Gödde, M., Marien, C.S., Wilson, A.H., Münker, C. (2022) Long-term preservation of Hadean protocrust in Earth’s mantle. Proceedings of the National Academy of Sciences 119, e2120241119. https://doi.org/10.1073/pnas.2120241119
), these still require an initial ∼4.35 Ga source with low μ182W and low μ142Nd, which existence has yet to be proven. Furthermore, although some negative μ182W has been detected in Paleoarchean rocks and diamictites from South Africa (Puchtel et al., 2016Puchtel, I.S., Blichert-Toft, J., Touboul, M., Horan, M.F., Walker, R.J. (2016) The coupled 182W-142Nd record of early terrestrial mantle differentiation. Geochemistry, Geophysics, Geosystems 17, 2168–2193. https://doi.org/10.1002/2016GC006324
; Mundl et al., 2018Mundl, A., Walker, R.J., Reimink, J.R., Rudnick, R.L., Gaschnig, R.M. (2018) Tungsten-182 in the upper continental crust: Evidence from glacial diamictites. Chemical Geology 494, 144–152. https://doi.org/10.1016/j.chemgeo.2018.07.036
; Tusch et al., 2022Tusch, J., Hoffmann, J.E., Hasenstab, E., Fischer-Gödde, M., Marien, C.S., Wilson, A.H., Münker, C. (2022) Long-term preservation of Hadean protocrust in Earth’s mantle. Proceedings of the National Academy of Sciences 119, e2120241119. https://doi.org/10.1073/pnas.2120241119
), more than 95 % of ancient rocks currently analysed instead have positive μ182W between +10 and +20 (e.g., Rizo et al., 2019Rizo, H., Andrault, D., Bennett, N.R., Humayun, M., Brandon, A., Vlastelic, I., Moine, B., Poirier, A., Bouhifd, M.A., Murphy, D.T. (2019) 182W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspectives Letters 11, 6–11. https://doi.org/10.7185/geochemlet.1917
). The scarce evidence for negative μ182W in ancient rocks, and the rather constant positive μ182W in throughout the Archean, suggests that if abundant negative-μ182W material existed, either early crustal subduction was deep enough to escape subsequent sampling, or most of that negative μ182W crust has now been recycled into the mantle.Alternatively, the late accretion of materials with chondritic bulk compositions after core formation is a hypothesis proposed to account for the abundance of highly siderophile elements (HSE) in the upper mantle. This accretion could also explain the decrease of μ182W of the DMM (e.g., 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
), given the μ182W of ∼−200 of chondrites (e.g., Kleine and Walker, 2017Kleine, T., Walker, R.J. (2017) Tungsten isotopes in planets. Annual Review of Earth and Planetary Sciences 45, 389–417. https://doi.org/10.1146/annurev-earth-063016-020037
), and would be unrelated to μ142Nd. The common absence of correlations between μ182W and HSE abundances (e.g., Rizo et al., 2019Rizo, H., Andrault, D., Bennett, N.R., Humayun, M., Brandon, A., Vlastelic, I., Moine, B., Poirier, A., Bouhifd, M.A., Murphy, D.T. (2019) 182W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspectives Letters 11, 6–11. https://doi.org/10.7185/geochemlet.1917
), however, suggests that late accretion is not the predominant process explaining the decrease of μ182W in the mantle. Furthermore, late accretion cannot explain μ182W-He correlations found in some OIB (e.g., Mundl et al., 2017Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
), since noble gas characteristics are most likely not preserved after impacts.The model that would best explain the μ182W observations, supported by a wide range of evidence such as seismology, multiple radiogenic isotope systems, and trace element geochemistry, is some mass transfer from mantle plumes into the upper mantle. Negative μ182W in modern rocks is currently exclusively associated with plume-derived magmas, showing μ182W values as low as −22.7 (Mundl et al., 2017
Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
). Ocean island basalts, the lavas derived from mantle plumes, also display a range of Sr, Nd and Pb isotope compositions (e.g., Zindler and Hart, 1986Zindler, A., Hart, S. (1986) Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493–571. https://doi.org/10.1146/annurev.ea.14.050186.002425
), believed to result from the incorporation of recycled components (sediments, crust) into the plume sources over time (e.g., Hofmann and White, 1982Hofmann, A.W., White, W.M. (1982) Mantle plumes from ancient oceanic crust. Earth and Planetary Science Letters 57, 421–436. https://doi.org/10.1016/0012-821X(82)90161-3
). Although the μ182W variability of the PAR MORB is only within 5 ppm, μ182W values appear to be correlated with (La/Gd)N and Sr, Pb, and Nd isotopic compositions (Fig. 3a–d). For example, sample PAC2DR27-1, characterised as a Transitional-MORB (T-MORB), presents the lowest measured μ182W and is the most trace element enriched basalt, with the most radiogenic 206Pb/204Pb and 87Sr/86Sr ratios, and the lowest 143Nd/144Nd (Fig. 3a–d, and Fig. S-2). The correlations between μ182W vs. (La/Gd)N and Sr, Pb, and Nd isotopic compositions could be evidence of the progressive incorporation of mantle plume material into the upper mantle. Although the μ182W variability observed in the PAR MORB is small, mantle melting averages the isotope heterogeneity present in the mantle sources (e.g., Stracke, 2021Stracke, A. (2021) A process-oriented approach to mantle geochemistry. Chemical Geology 579, 120350. https://doi.org/10.1016/j.chemgeo.2021.120350
), and thus the μ182W variability shown in Figures 3a–d likely represent a minimum estimate for the total range of μ182W variability of their mantle sources.Figure 3 μ182W vs. (a) normalised La/Gd ratio, and radiogenic (b) Pb, (c) Nd and (d) Sr isotope compositions, for the PAR MORB analysed here. Blue circles are N-MORB and square is T-MORB sample PAC2DR27-1. Tungsten isotope data from this study. Trace element concentrations and radiogenic isotope compositions from Hamelin et al. (2011)
Hamelin, C., Dosso, L., Hanan, B.B., Moreira, M., Kositsky, A.P., Thomas, M.Y. (2011) Geochemical portray of the Pacific Ridge: New isotopic data and statistical techniques. Earth and Planetary Science Letters 302, 154–162. https://doi.org/10.1016/j.epsl.2010.12.007
.top
Different Causes for 142W and 142Nd Variability, but Shared Process for Their Decrease
The ultimate source of negative μ182W in plume-derived magmas, and the 10–20 ppm μ182W decrease from the Archean to the modern mantle, has recently been the subject of active research. For example, chemical interaction between the core and the base of the mantle has been proposed to explain the negative μ182W of plume-derived magmas (e.g., Rizo et al., 2019
Rizo, H., Andrault, D., Bennett, N.R., Humayun, M., Brandon, A., Vlastelic, I., Moine, B., Poirier, A., Bouhifd, M.A., Murphy, D.T. (2019) 182W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspectives Letters 11, 6–11. https://doi.org/10.7185/geochemlet.1917
), given that the core is characterised by μ182W of ∼−200 and W concentration of ∼0.5 ppm (e.g., Kleine and Walker, 2017Kleine, T., Walker, R.J. (2017) Tungsten isotopes in planets. Annual Review of Earth and Planetary Sciences 45, 389–417. https://doi.org/10.1146/annurev-earth-063016-020037
). While the decrease in μ182W was found to require unrealistically high time-integrated plume flux or unrealistically low μ182W in the plumes (Peters et al., 2021Peters, B.J., Mundl-Petermeier, A., Carlson, R.W., Walker, R.J., Day, J.M.D. (2021) Combined Lithophile-Siderophile Isotopic Constraints on Hadean Processes Preserved in Ocean Island Basalt Sources. Geochemistry, Geophysics, Geosystems 22, 1–20. https://doi.org/10.1029/2020GC009479
), recent studies propose viable models for the μ182W decline taking into account W diffusion from the core into the mantle and the residence time of W at the core-mantle boundary (Kaare-Rasmussen et al., 2023Kaare-Rasmussen, J., Peters, D., Rizo, H., Carlson, R.W., Nielsen, S.G., Horton, F. (2023) Tungsten isotopes in Baffin Island lavas: Evidence of Iceland plume evolution. Geochemical Perspectives Letters 28, 7–12. https://doi.org/10.7185/geochemlet.2337
).The μ142Nd difference between the DMM and OIB sources (Fig. 2) shows that these reservoirs could have separated ∼4.45 Gyr ago, consistent with the I-Xe interpretation (Mukhopadhyay, 2012
Mukhopadhyay, S. (2012) Early differentiation and volatile accretion recorded in deep-mantle neon and xenon. Nature 486, 101–104. https://doi.org/10.1038/nature11141
). The coupled low μ182W and low μ142Nd in some ∼3.6 Ga komatiites could represent remanent fingerprints of this differentiation (Puchtel et al., 2016Puchtel, I.S., Blichert-Toft, J., Touboul, M., Horan, M.F., Walker, R.J. (2016) The coupled 182W-142Nd record of early terrestrial mantle differentiation. Geochemistry, Geophysics, Geosystems 17, 2168–2193. https://doi.org/10.1002/2016GC006324
). Most 182W and 142Nd comparative studies, however, imply different causes for the isotope variability in mantle-derived magmas. Nevertheless, shared underlying processes could have driven the decrease in magnitude of 182W and 142Nd variations. Given the available data, the period of μ182W decrease between 3 and 2.4 Ga (Tusch et al., 2021Tusch, J., Münker, C., Hasenstab, E., Jansen, M., Marien, C.S., Kurzweil, F., van Kranendonk, M.J., Smithies, H., Maier, W., Garbe-Schönberg, D. (2021) Convective isolation of hadean mantle reservoirs through archean time. Proceedings of the National Academy of Sciences of the United States of America 118, e2012626118. https://doi.org/10.1073/pnas.2012626118
; Nakanishi et al., 2023Nakanishi, N., Puchtel, I.S., Walker, R.J., Nabelek, P.I. (2023) Dissipation of Tungsten-182 Anomalies in the Archean Upper Mantle: Evidence from the Black Hills, South Dakota, USA. Chemical Geology 617, 121255. https://doi.org/10.1016/j.chemgeo.2022.121255
) seems to coincide with the timing of the homogenisation of μ142Nd heterogeneities due to mantle mixing (e.g., Carlson et al., 2019Carlson, R.W., Garçon, M., O’Neil, J., Reimink, J., Rizo, H. (2019) The nature of Earth’s first crust. Chemical Geology 530, 119321. https://doi.org/10.1016/j.chemgeo.2019.119321
). The onset of deep cold slab subduction in the early Earth (Klein et al., 2017Klein, B.Z., Jagoutz, O., Behn, M.D. (2017) Archean crustal compositions promote full mantle convection. Earth and Planetary Science Letters 474, 516–526. https://doi.org/10.1016/j.epsl.2017.07.003
) might have generated upwellings from the core-mantle boundary, carrying negative μ182W, which gets remixed into the convective mantle. The number of combined 182W and 142Nd isotope studies in the same rock samples is limited. However, conducting similar additional investigations in Proterozoic rocks is crucial for enhancing our understanding of the timescales of mantle stirring and the geodynamic processes that have shaped Earth’s modern mantle composition.top
Acknowledgements
We acknowledge the generous support from the Carnegie Institution for Science Tuve Fellow Visiting Scientists program to H.R. and to J.O., allowing the writing of this manuscript. We thank Mike Walter, Peter van Keken and James W. Dottin III for helpful discussions, as well as the comments from Bradley Peters and an anonymous reviewer, which contributed to enhancing this manuscript. We are grateful to Pierre-Luc Lacroix for generating the code for the Monte Carlo bootstrap simulations. We thank the technical support provided by Shuangquan Zhang, Nimal DeSilva and Smita Mohanty at the IGGRC of Carleton University and the University of Ottawa Geochemistry Laboratory. This research was funded by the Natural Sciences and Engineering Research Council of Canada Discovery grant to H.R. (RGPIN-477144-2015) to J.O. (RGPIN 435589-2013), and the Ontario Early Researcher Award to H.R.
Editor: Helen Williams
top
References
Boyet, M., Carlson, R.W. (2006) A new geochemical model for the Earth’s mantle inferred from 146Sm–142Nd systematics. Earth and Planetary Science Letters 250, 254–268. https://doi.org/10.1016/j.epsl.2006.07.046
Show in context However, few mantle peridotites (n = 4), or melts directly derived from the depleted upper mantle such as MORB (n = 9), have been analysed for μ142Nd (e.g., Boyet and Carlson, 2006; Caro et al., 2006; Cipriani et al., 2011; Jackson and Carlson 2012; Hyung and Jacobsen, 2020).
View in article
The μ142Nd for other MORBs are from Boyet and Carlson (2006), Caro et al. (2006), Jackson and Carlson (2012), and Hyung and Jacobsen (2020), and mantle peridotite data from Cipriani et al. (2011).
View in article
Carlson, R.W., Garçon, M., O’Neil, J., Reimink, J., Rizo, H. (2019) The nature of Earth’s first crust. Chemical Geology 530, 119321. https://doi.org/10.1016/j.chemgeo.2019.119321
Show in context The Earth’s mantle underwent significant chemical evolution during its early history. The short lived isotope systems 182Hf-182W (t1/2 = 8.9 Myr) and 146Sm-142Nd (t1/2 = 103 Myr) applied to the study of terrestrial rocks have provided valuable insights into understanding the nature of these changes, because they are especially capable of tracing the most ancient chemical fractionation processes. Notably, ancient mantle-derived rocks from various Archean cratons exhibit variations in 142Nd abundances (e.g., Carlson et al., 2019), implying silicate differentiation within the first ∼500 million years of Earth’s history.
View in article
Nevertheless, shared underlying processes could have driven the decrease in magnitude of 182W and 142Nd variations. Given the available data, the period of μ182W decrease between 3 and 2.4 Ga (Tusch et al., 2021; Nakanishi et al., 2023) seems to coincide with the timing of the homogenisation of μ142Nd heterogeneities due to mantle mixing (e.g., Carlson et al., 2019).
View in article
Caro, G., Bourdon, B., Birck, J.L., Moorbath, S. (2006) High-precision 142Nd/144Nd measurements in terrestrial rocks: constraints on the early differentiation of the Earth’s mantle. Geochimica et Cosmochimica Acta 70, 164–191. https://doi.org/10.1016/j.gca.2005.08.015
Show in context However, few mantle peridotites (n = 4), or melts directly derived from the depleted upper mantle such as MORB (n = 9), have been analysed for μ142Nd (e.g., Boyet and Carlson, 2006; Caro et al., 2006; Cipriani et al., 2011; Jackson and Carlson 2012; Hyung and Jacobsen, 2020).
View in article
The μ142Nd for other MORBs are from Boyet and Carlson (2006), Caro et al. (2006), Jackson and Carlson (2012), and Hyung and Jacobsen (2020), and mantle peridotite data from Cipriani et al. (2011).
View in article
Cipriani, A., Bonatti, E., Carlson, R.W. (2011) Nonchondritic 142Nd in suboceanic mantle peridotites. Geochemistry, Geophysics, Geosystems 12, Q03006. https://doi.org/10.1029/2010GC003415
Show in context However, few mantle peridotites (n = 4), or melts directly derived from the depleted upper mantle such as MORB (n = 9), have been analysed for μ142Nd (e.g., Boyet and Carlson, 2006; Caro et al., 2006; Cipriani et al., 2011; Jackson and Carlson 2012; Hyung and Jacobsen, 2020).
View in article
The μ142Nd for other MORBs are from Boyet and Carlson (2006), Caro et al. (2006), Jackson and Carlson (2012), and Hyung and Jacobsen (2020), and mantle peridotite data from Cipriani et al. (2011).
View in article
Frossard, P., Israel, C., Bouvier, A., Boyet, M. (2022) Earth’s composition was modified by collisional erosion. Science 377, 1529–1532. https://doi.org/10.1126/science.abq7351
Show in context Recent studies propose that Earth’s building blocks may have been characterised by μ142Nd of ∼−7.5 (e.g., Frossard et al., 2022; Johnston et al., 2022), and a 147Sm/144Nd ratio of ∼0.201 — approximately 2.5 % higher than the chondritic reference value of 0.1960 (to evolve from initial μ142Nd ∼−7.5 to 0 today).
View in article
Gale, A., Dalton, C.A., Langmuir, C.H., Su, Y., Schilling, J.G. (2013) The mean composition of ocean ridge basalts. Geochemistry, Geophysics, Geosystems 14, 489–518. https://doi.org/10.1029/2012GC004334
Show in context This contradicts the evidence that the DMM is more depleted, based on its present day ɛ143Nd of nearly +9 of MORB (Gale et al., 2013).
View in article
Hamelin, C., Dosso, L., Hanan, B.B., Moreira, M., Kositsky, A.P., Thomas, M.Y. (2011) Geochemical portray of the Pacific Ridge: New isotopic data and statistical techniques. Earth and Planetary Science Letters 302, 154–162. https://doi.org/10.1016/j.epsl.2010.12.007
Show in context All fresh MORB samples were collected on-axis, and have previously been thoroughly characterised for their petrology, geochemistry and isotopic compositions (e.g., Sr, Nd, Pb, Hf, He, D, S, and Mo), showing the lack of plume influence (Hamelin et al., 2011; see Supplementary Information for sample descriptions).
View in article
Trace element concentrations and radiogenic isotope compositions from Hamelin et al. (2011).
View in article
Hofmann, A.W., White, W.M. (1982) Mantle plumes from ancient oceanic crust. Earth and Planetary Science Letters 57, 421–436. https://doi.org/10.1016/0012-821X(82)90161-3
Show in context Ocean island basalts, the lavas derived from mantle plumes, also display a range of Sr, Nd and Pb isotope compositions (e.g., Zindler and Hart, 1986), believed to result from the incorporation of recycled components (sediments, crust) into the plume sources over time (e.g., Hofmann and White, 1982).
View in article
Hyung, E., Jacobsen, S.B. (2020) The 142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings of the National Academy of Sciences 117, 14738–14744. https://doi.org/10.1073/pnas.2006950117
Show in context However, few mantle peridotites (n = 4), or melts directly derived from the depleted upper mantle such as MORB (n = 9), have been analysed for μ142Nd (e.g., Boyet and Carlson, 2006; Caro et al., 2006; Cipriani et al., 2011; Jackson and Carlson 2012; Hyung and Jacobsen, 2020).
View in article
The μ142Nd for other MORBs are from Boyet and Carlson (2006), Caro et al. (2006), Jackson and Carlson (2012), and Hyung and Jacobsen (2020), and mantle peridotite data from Cipriani et al. (2011).
View in article
Jackson, M.G., Carlson, R.W. (2012) Homogeneous superchondritic 142Nd/144Nd in the mid-ocean ridge basalt and ocean island basalt mantle. Geochemistry, Geophysics, Geosystems 13, Q06011. https://doi.org/10.1029/2012GC004114
Show in context However, few mantle peridotites (n = 4), or melts directly derived from the depleted upper mantle such as MORB (n = 9), have been analysed for μ142Nd (e.g., Boyet and Carlson, 2006; Caro et al., 2006; Cipriani et al., 2011; Jackson and Carlson 2012; Hyung and Jacobsen, 2020).
View in article
The μ142Nd for other MORBs are from Boyet and Carlson (2006), Caro et al. (2006), Jackson and Carlson (2012), and Hyung and Jacobsen (2020), and mantle peridotite data from Cipriani et al. (2011).
View in article
Johnston, S., Brandon, A., McLeod, C., Rankenburg, K., Becker, H., Copeland, P. (2022) Nd isotope variation between the Earth–Moon system and enstatite chondrites. Nature 611, 501–506. https://doi.org/10.1038/s41586-022-05265-0
Show in context Recent studies propose that Earth’s building blocks may have been characterised by μ142Nd of ∼−7.5 (e.g., Frossard et al., 2022; Johnston et al., 2022), and a 147Sm/144Nd ratio of ∼0.201 — approximately 2.5 % higher than the chondritic reference value of 0.1960 (to evolve from initial μ142Nd ∼−7.5 to 0 today).
View in article
Kaare-Rasmussen, J., Peters, D., Rizo, H., Carlson, R.W., Nielsen, S.G., Horton, F. (2023) Tungsten isotopes in Baffin Island lavas: Evidence of Iceland plume evolution. Geochemical Perspectives Letters 28, 7–12. https://doi.org/10.7185/geochemlet.2337
Show in context While the decrease in μ182W was found to require unrealistically high time-integrated plume flux or unrealistically low μ182W in the plumes (Peters et al., 2021), recent studies propose viable models for the μ182W decline taking into account W diffusion from the core into the mantle and the residence time of W at the core-mantle boundary (Kaare-Rasmussen et al., 2023).
View in article
Klein, B.Z., Jagoutz, O., Behn, M.D. (2017) Archean crustal compositions promote full mantle convection. Earth and Planetary Science Letters 474, 516–526. https://doi.org/10.1016/j.epsl.2017.07.003
Show in context The onset of deep cold slab subduction in the early Earth (Klein et al., 2017) might have generated upwellings from the core-mantle boundary, carrying negative μ182W, which gets remixed into the convective mantle.
View in article
Kleine, T., Walker, R.J. (2017) Tungsten isotopes in planets. Annual Review of Earth and Planetary Sciences 45, 389–417. https://doi.org/10.1146/annurev-earth-063016-020037
Show in context This accretion could also explain the decrease of μ182W of the DMM (e.g., Willbold et al., 2011), given the μ182W of ∼−200 of chondrites (e.g., Kleine and Walker, 2017), and would be unrelated to μ142Nd.
View in article
For example, chemical interaction between the core and the base of the mantle has been proposed to explain the negative μ182W of plume-derived magmas (e.g., Rizo et al., 2019), given that the core is characterised by μ182W of ∼−200 and W concentration of ∼0.5 ppm (e.g., Kleine and Walker, 2017).
View in article
König, S., Münker, C., Hohl, S., Paulick, H., Barth, A.R., Lagos, M., Pfänder, J., Büchl, A. (2011) The Earth’s tungsten budget during mantle melting and crust formation. Geochimica et Cosmochimica Acta 75, 2119–2136. https://doi.org/10.1016/j.gca.2011.01.031
Show in context Narrow ranges for W/Th = 0.1–0.15 (Fig. S-2d), W/Ba = 0.0019–0.0027, W/Ta = 0.08–0.16, and W/U = 0.23–0.43 (not shown) indicate that the W contained in the MORB samples is derived from their mantle sources and free from secondary hydrothermal W overprinting (e.g., König et al., 2011).
View in article
Mukhopadhyay, S. (2012) Early differentiation and volatile accretion recorded in deep-mantle neon and xenon. Nature 486, 101–104. https://doi.org/10.1038/nature11141
Show in context This early differentiation is consistent with the distinct 129Xe/130Xe ratios observed in MORB and OIB, also implying mantle differentiation around 4.45 Ga (Mukhopadhyay, 2012).
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The μ142Nd difference between the DMM and OIB sources (Fig. 2) shows that these reservoirs could have separated ∼4.45 Gyr ago, consistent with the I-Xe interpretation (Mukhopadhyay, 2012).
View in article
Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
Show in context The W isotopic composition of the DMM has never been properly determined, given that only two MORB samples have been studied to date (Rizo et al., 2016; Mundl et al., 2017).
View in article
These results are undistinguishable within errors from the μ182W values of −0.8 ± 4.5 (2 s.e.) and 3.5 ± 4.0 (2 s.e.) in MORBs, respectively, from the East Pacific Rise (Rizo et al., 2016) and the Central Indian Ridge (Mundl et al., 2017).
View in article
Smaller symbols in (b) are duplicate analyses with the average value and 2 s.d. in darker shade. MORB μ182W of East Pacific Rise and Central Indian Ridge are, respectively, from Rizo et al. (2016) and Mundl et al. (2017).
View in article
Furthermore, late accretion cannot explain μ182W-He correlations found in some OIB (e.g., Mundl et al., 2017), since noble gas characteristics are most likely not preserved after impacts.
View in article
The model that would best explain the μ182W observations, supported by a wide range of evidence such as seismology, multiple radiogenic isotope systems, and trace element geochemistry, is some mass transfer from mantle plumes into the upper mantle. Negative μ182W in modern rocks is currently exclusively associated with plume-derived magmas, showing μ182W values as low as −22.7 (Mundl et al., 2017).
View in article
Mundl, A., Walker, R.J., Reimink, J.R., Rudnick, R.L., Gaschnig, R.M. (2018) Tungsten-182 in the upper continental crust: Evidence from glacial diamictites. Chemical Geology 494, 144–152. https://doi.org/10.1016/j.chemgeo.2018.07.036
Show in context Furthermore, although some negative μ182W has been detected in Paleoarchean rocks and diamictites from South Africa (Puchtel et al., 2016; Mundl et al., 2018; Tusch et al., 2022), more than 95 % of ancient rocks currently analysed instead have positive μ182W between +10 and +20 (e.g., Rizo et al., 2019).
View in article
Nakanishi, N., Puchtel, I.S., Walker, R.J., Nabelek, P.I. (2023) Dissipation of Tungsten-182 Anomalies in the Archean Upper Mantle: Evidence from the Black Hills, South Dakota, USA. Chemical Geology 617, 121255. https://doi.org/10.1016/j.chemgeo.2022.121255
Show in context Nevertheless, shared underlying processes could have driven the decrease in magnitude of 182W and 142Nd variations. Given the available data, the period of μ182W decrease between 3 and 2.4 Ga (Tusch et al., 2021; Nakanishi et al., 2023) seems to coincide with the timing of the homogenisation of μ142Nd heterogeneities due to mantle mixing (e.g., Carlson et al., 2019).
View in article
Peters, B.J., Mundl-Petermeier, A., Carlson, R.W., Walker, R.J., Day, J.M.D. (2021) Combined Lithophile-Siderophile Isotopic Constraints on Hadean Processes Preserved in Ocean Island Basalt Sources. Geochemistry, Geophysics, Geosystems 22, 1–20. https://doi.org/10.1029/2020GC009479
Show in context While the decrease in μ182W was found to require unrealistically high time-integrated plume flux or unrealistically low μ182W in the plumes (Peters et al., 2021), recent studies propose viable models for the μ182W decline taking into account W diffusion from the core into the mantle and the residence time of W at the core-mantle boundary (Kaare-Rasmussen et al., 2023).
View in article
Puchtel, I.S., Blichert-Toft, J., Touboul, M., Horan, M.F., Walker, R.J. (2016) The coupled 182W-142Nd record of early terrestrial mantle differentiation. Geochemistry, Geophysics, Geosystems 17, 2168–2193. https://doi.org/10.1002/2016GC006324
Show in context However, combined negative μ182W and μ142Nd have currently only been observed in ∼3.6 Ga komatiites (Puchtel et al., 2016).
View in article
Furthermore, although some negative μ182W has been detected in Paleoarchean rocks and diamictites from South Africa (Puchtel et al., 2016; Mundl et al., 2018; Tusch et al., 2022), more than 95 % of ancient rocks currently analysed instead have positive μ182W between +10 and +20 (e.g., Rizo et al., 2019).
View in article
The coupled low μ182W and low μ142Nd in some ∼3.6 Ga komatiites could represent remanent fingerprints of this differentiation (Puchtel et al., 2016).
View in article
Rizo, H., Walker, R.J., Carlson, R.W., Horan, M.F., Mukhopadhyay, S., Manthos, V., Francis, D., Jackson, M.G. (2016) Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809–812. https://doi.org/10.1126/science.aad8563
Show in context The W isotopic composition of the DMM has never been properly determined, given that only two MORB samples have been studied to date (Rizo et al., 2016; Mundl et al., 2017).
View in article
These results are undistinguishable within errors from the μ182W values of −0.8 ± 4.5 (2 s.e.) and 3.5 ± 4.0 (2 s.e.) in MORBs, respectively, from the East Pacific Rise (Rizo et al., 2016) and the Central Indian Ridge (Mundl et al., 2017).
View in article
Smaller symbols in (b) are duplicate analyses with the average value and 2 s.d. in darker shade. MORB μ182W of East Pacific Rise and Central Indian Ridge are, respectively, from Rizo et al. (2016) and Mundl et al. (2017).
View in article
Rizo, H., Andrault, D., Bennett, N.R., Humayun, M., Brandon, A., Vlastelic, I., Moine, B., Poirier, A., Bouhifd, M.A., Murphy, D.T. (2019) 182W evidence for core-mantle interaction in the source of mantle plumes. Geochemical Perspectives Letters 11, 6–11. https://doi.org/10.7185/geochemlet.1917
Show in context A significant observation derived from our results is that the average μ182W of the modern DMM (−1.9) is approximately 10 to 20 ppm lower than the average Hadean-Archean mantle (e.g., Rizo et al., 2019).
View in article
The recent detection of 182W abundance variations in mantle-derived rocks of different ages have initiated debates regarding the main processes controlling 182W variability, including early silicate differentiation as seen by the 146Sm-142Nd system (e.g., Touboul et al., 2012), core-mantle chemical interactions (e.g., Rizo et al., 2019), differences in the mass of late accreted extra-terrestrial material into the mantle (e.g., Willbold et al., 2011) and the recycling of ancient crust or sediments into the mantle (e.g., Tusch et al., 2021).
View in article
The common absence of correlations between μ182W and HSE abundances (e.g., Rizo et al., 2019), however, suggests that late accretion is not the predominant process explaining the decrease of μ182W in the mantle.
View in article
Furthermore, although some negative μ182W has been detected in Paleoarchean rocks and diamictites from South Africa (Puchtel et al., 2016; Mundl et al., 2018; Tusch et al., 2022), more than 95 % of ancient rocks currently analysed instead have positive μ182W between +10 and +20 (e.g., Rizo et al., 2019).
View in article
For example, chemical interaction between the core and the base of the mantle has been proposed to explain the negative μ182W of plume-derived magmas (e.g., Rizo et al., 2019), given that the core is characterised by μ182W of ∼−200 and W concentration of ∼0.5 ppm (e.g., Kleine and Walker, 2017).
View in article
Stracke, A. (2021) A process-oriented approach to mantle geochemistry. Chemical Geology 579, 120350. https://doi.org/10.1016/j.chemgeo.2021.120350
Show in context Although the μ182W variability observed in the PAR MORB is small, mantle melting averages the isotope heterogeneity present in the mantle sources (e.g., Stracke, 2021), and thus the μ182W variability shown in Figures 3a–d likely represent a minimum estimate for the total range of μ182W variability of their mantle sources.
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Touboul, M., Puchtel, I.S., Walker, R.J. (2012) 182W evidence for long-term preservation of early mantle differentiation products. Science 335, 1065–1069. https://doi.org/10.1126/science.1216351
Show in context The recent detection of 182W abundance variations in mantle-derived rocks of different ages have initiated debates regarding the main processes controlling 182W variability, including early silicate differentiation as seen by the 146Sm-142Nd system (e.g., Touboul et al., 2012), core-mantle chemical interactions (e.g., Rizo et al., 2019), differences in the mass of late accreted extra-terrestrial material into the mantle (e.g., Willbold et al., 2011) and the recycling of ancient crust or sediments into the mantle (e.g., Tusch et al., 2021).
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Tucker, J.M., van Keken, P.E., Jones, R.E., Ballentine, C.J. (2020) A role for subducted oceanic crust in generating the depleted mid-ocean ridge basalt mantle. Geochemistry, Geophysics, Geosystems 21, e2020GC009148. https://doi.org/10.1029/2020GC009148
Show in context Oceanic crust sequestration and preferential slab subduction to the lower mantle have been proposed as a plausible model to deplete the lower mantle to a greater extent than the upper mantle (Tucker et al., 2020).
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Tusch, J., Münker, C., Hasenstab, E., Jansen, M., Marien, C.S., Kurzweil, F., van Kranendonk, M.J., Smithies, H., Maier, W., Garbe-Schönberg, D. (2021) Convective isolation of hadean mantle reservoirs through archean time. Proceedings of the National Academy of Sciences of the United States of America 118, e2012626118. https://doi.org/10.1073/pnas.2012626118
Show in context The recent detection of 182W abundance variations in mantle-derived rocks of different ages have initiated debates regarding the main processes controlling 182W variability, including early silicate differentiation as seen by the 146Sm-142Nd system (e.g., Touboul et al., 2012), core-mantle chemical interactions (e.g., Rizo et al., 2019), differences in the mass of late accreted extra-terrestrial material into the mantle (e.g., Willbold et al., 2011) and the recycling of ancient crust or sediments into the mantle (e.g., Tusch et al., 2021).
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Nevertheless, shared underlying processes could have driven the decrease in magnitude of 182W and 142Nd variations. Given the available data, the period of μ182W decrease between 3 and 2.4 Ga (Tusch et al., 2021; Nakanishi et al., 2023) seems to coincide with the timing of the homogenisation of μ142Nd heterogeneities due to mantle mixing (e.g., Carlson et al., 2019).
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Tusch, J., Hoffmann, J.E., Hasenstab, E., Fischer-Gödde, M., Marien, C.S., Wilson, A.H., Münker, C. (2022) Long-term preservation of Hadean protocrust in Earth’s mantle. Proceedings of the National Academy of Sciences 119, e2120241119. https://doi.org/10.1073/pnas.2120241119
Show in context Although early mantle differentiation models capable of explaining decoupled 182W and 142Nd have been proposed (e.g., Tusch et al., 2022), these still require an initial ∼4.35 Ga source with low μ182W and low μ142Nd, which existence has yet to be proven.
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Furthermore, although some negative μ182W has been detected in Paleoarchean rocks and diamictites from South Africa (Puchtel et al., 2016; Mundl et al., 2018; Tusch et al., 2022), more than 95 % of ancient rocks currently analysed instead have positive μ182W between +10 and +20 (e.g., Rizo et al., 2019).
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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 The recent detection of 182W abundance variations in mantle-derived rocks of different ages have initiated debates regarding the main processes controlling 182W variability, including early silicate differentiation as seen by the 146Sm-142Nd system (e.g., Touboul et al., 2012), core-mantle chemical interactions (e.g., Rizo et al., 2019), differences in the mass of late accreted extra-terrestrial material into the mantle (e.g., Willbold et al., 2011) and the recycling of ancient crust or sediments into the mantle (e.g., Tusch et al., 2021).
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This accretion could also explain the decrease of μ182W of the DMM (e.g., Willbold et al., 2011), given the μ182W of ∼−200 of chondrites (e.g., Kleine and Walker, 2017), and would be unrelated to μ142Nd.
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Zindler, A., Hart, S. (1986) Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493–571. https://doi.org/10.1146/annurev.ea.14.050186.002425
Show in context Ocean island basalts, the lavas derived from mantle plumes, also display a range of Sr, Nd and Pb isotope compositions (e.g., Zindler and Hart, 1986), believed to result from the incorporation of recycled components (sediments, crust) into the plume sources over time (e.g., Hofmann and White, 1982).
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Supplementary Information
- Sample Description
- Methods
- Figures S-1 to S-4
- Data Tables S-1 to S-4
- Supplementary Information References
Download the Supplementary Information (PDF)
Download Data Table S-1 (.xlsx)
Download Data Table S-2 (.xlsx)
Download Data Table S-3 (.xlsx)
Download Data Table S-4 (.xlsx)
Figures
Figure 1 (a) μ182W and (b) μ142Nd for PAR MORBs of this study. Vertical thin grey lines with shaded areas show average standards (μ182W = 0 and μ142Nd = 0) with external reproducibility (2 s.d.). Vertical thick black lines show the mean for all MORBs analysed here (μ182W = −1.9 ± 3.5; μ142Nd = −1.6 ± 5.0). Smaller symbols in (b) are duplicate analyses with the average value and 2 s.d. in darker shade. MORB μ182W of East Pacific Rise and Central Indian Ridge are, respectively, from Rizo et al. (2016)
Rizo, H., Walker, R.J., Carlson, R.W., Horan, M.F., Mukhopadhyay, S., Manthos, V., Francis, D., Jackson, M.G. (2016) Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809–812. https://doi.org/10.1126/science.aad8563
and Mundl et al. (2017)Mundl, A., Touboul, M., Jackson, M.G., Day, J.M.D., Kurz, M.D., Lekic, V., Helz, R.T., Walker, R.J. (2017) Tungsten-182 heterogeneity in modern ocean island basalts. Science 356, 66–69. https://doi.org/10.1126/science.aal4179
. The μ142Nd for other MORBs are from Boyet and Carlson (2006)Boyet, M., Carlson, R.W. (2006) A new geochemical model for the Earth’s mantle inferred from 146Sm–142Nd systematics. Earth and Planetary Science Letters 250, 254–268. https://doi.org/10.1016/j.epsl.2006.07.046
, Caro et al. (2006)Caro, G., Bourdon, B., Birck, J.L., Moorbath, S. (2006) High-precision 142Nd/144Nd measurements in terrestrial rocks: constraints on the early differentiation of the Earth’s mantle. Geochimica et Cosmochimica Acta 70, 164–191. https://doi.org/10.1016/j.gca.2005.08.015.
, Jackson and Carlson (2012)Jackson, M.G., Carlson, R.W. (2012) Homogeneous superchondritic 142Nd/144Nd in the mid-ocean ridge basalt and ocean island basalt mantle. Geochemistry, Geophysics, Geosystems 13, Q06011. https://doi.org/10.1029/2012GC004114
, and Hyung and Jacobsen (2020)Hyung, E., Jacobsen, S.B. (2020) The 142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings of the National Academy of Sciences 117, 14738–14744. https://doi.org/10.1073/pnas.2006950117
, and mantle peridotite data from Cipriani et al. (2011)Cipriani, A., Bonatti, E., Carlson, R.W. (2011) Nonchondritic 142Nd in suboceanic mantle peridotites. Geochemistry, Geophysics, Geosystems 12, Q03006. https://doi.org/10.1029/2010GC003415
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Figure 2 Compilation and computed probability density of (a, b) μ142Nd and (c, d) μ182W for MORB, OIB and mantle peridotites. Upper mantle (a) includes MORB and mantle peridotite samples. Left side plots (a and c) present histograms of all data; grey bands show the analytical reproducibility on the standards obtained during this study; thick bars on box plots present the median, and the triangle notches show the weighted mean values. Right side plots (b, d) show compositions generated by Monte Carlo bootstrap simulations (10,000 runs). Vertical lines and grey areas in b and d show the mean and 2 s.d. envelope of the Nd and W standards derived from the simulations. Database and references provided in the Supplementary Information Data Table S-4.
Figure 3 μ182W vs. (a) normalised La/Gd ratio, and radiogenic (b) Pb, (c) Nd and (d) Sr isotope compositions, for the PAR MORB analysed here. Blue circles are N-MORB and square is T-MORB sample PAC2DR27-1. Tungsten isotope data from this study. Trace element concentrations and radiogenic isotope compositions from Hamelin et al. (2011)
Hamelin, C., Dosso, L., Hanan, B.B., Moreira, M., Kositsky, A.P., Thomas, M.Y. (2011) Geochemical portray of the Pacific Ridge: New isotopic data and statistical techniques. Earth and Planetary Science Letters 302, 154–162. https://doi.org/10.1016/j.epsl.2010.12.007
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