Early formation of primitive achondrites in an outer region of the protoplanetary disc
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Keywords: primitive achondrites, carbonaceous reservoir, outer solar system, planetary formation, redox, Pb-Pb chronology
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 Figure 1 Oxygen isotope compositions of Tafassites. (a) Tafassites define a mass-dependent fractionation line (slope ∼0.51), distinctive from the mass-independent CR mixing line (slope ∼0.71). (b) Tafassites show a homogeneous and unique Δ17O anomaly (−1.67 ± 0.14 ‰, 2 s.d.) distinct from acapulcoite-lodranite (Aca&Lod), winonaite (Win) and CR chondrite meteorites (Schrader et al., 2011). Data are compiled in Table S-4, and carbonaceous chondrite anhydrous mixing (CCAM) and terrestrial fractionation lines (TFL) are shown for reference. |  Figure 2 Comparative chronology from CAI formation (U corrected Pb–Pb average age of 4567.73 ± 0.81 Ma; Sanborn et al., 2019) of selected meteorite groups (data points) and modelled timing of accretion of their parent bodies (boxes) in the carbonaceous (C, blue) and non-carbonaceous (NC, red) reservoirs. Parent body accretion ages are from this study for Tafassites, and taken from Kruijer et al. (2020) and Neumann et al. (2018) for other relevant groups. The Tafassite Hf–W, Mn–Cr (Breton et al., 2015; Göpel et al., 2015) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011) and NWA 6704 (Amelin et al., 2019; Sanborn et al., 2019) grouplets. Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017) and Pb–Pb (Amelin et al., 2002; Bollard et al, 2017), and Hf–W average age obtained in CR chondrites (Budde et al., 2018) after CAIs. Symbols: circle = Al–Mg; full diamond = Hf–W; triangle = Mn–Cr; square = phosphate Pb–Pb; full square = Pb–Pb. |  Figure 3 Thermal evolution model of the Tafassite parent body. (a) Fit quality χn as a function of the planetesimal accretion time t0 and radius R. Tafassite parent body is best fitted to have an accretion time t0 = 1.1+0.3−0.4 Myr and radius R >50 km. (b) Modelled thermal history curves based on Tafassasset Hf–W and Mn–Cr ages, and Tafassasset and T6–T7 Tafassite Pb–Pb Ca phosphate chronological records. The thermal history is shown for an object with R = 120 km and t0 = 1.1 Myr marked in (a) with a red dot, and is representative for bodies with an acceptable fit quality of χn ≤ 4. The fit depths for NWA 12455, Tafassasset, NWA 7317 and NWA 11561 are ∼4.1 km, ∼3.3 km, ∼3.1 km and ∼2.6 km, respectively. |
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Introduction
Mass-independent nucleosynthetic anomalies in meteorites have revealed a fundamental isotopic dichotomy between s-process-rich (slow neutron capture) non-carbonaceous meteorites (NC) and s-process-depleted carbonaceous meteorites (C), accreted within the inner and outer parts of the protoplanetary disc, respectively (Warren, 2011
Warren, P.H. (2011) Stable-isotopic anomalies and the accretionary assemblage of the Earth and Mars: A subordinate role for carbonaceous chondrites. Earth and Planetary Science Letters 311, 93–100. https://doi.org/10.1016/j.epsl.2011.08.047
; Burkhardt et al., 2019Burkhardt, C., Dauphas, N., Hans, U., Bourdon, B., Kleine, T. (2019) Elemental and isotopic variability in solar system materials by mixing and processing of primordial disk reservoirs. Geochimica et Cosmochimica Acta 261, 145–170. https://doi.org/10.1016/j.gca.2019.07.003
; Kruijer et al., 2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
). Presolar stardust grains, as carriers of nucleosynthetic signatures, are thought to have been heterogeneously distributed very early into protoplanetary disc. The two NC and C reservoirs evolved as spatially separate and isotopically distinct entities, potentially as a result of the early formation of Jupiter (Kruijer et al., 2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
) or a pressure maximum in the disc (Brasser and Mojzsis, 2020Brasser, R, Mojzsis, S. (2020) The partitioning of the inner and outer Solar System by a structured protoplanetary disk. Nature Astronomy 4, 492–499. https://doi.org/10.1038/s41550-019-0978-6
). Later inward migration of Jupiter could have scattered NC and C planetesimals, leading to the eventual formation of the asteroid belt (Kruijer et al., 2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
).So far, all NC parent bodies appear to have accreted relatively early (<0.5 to ∼2 Myr after calcium aluminium-rich inclusions; CAIs), while still abundant short-lived 26Al (half-life of ∼0.7 Myr) was the dominant heat source to drive planetesimal differentiation. In contrast, carbonaceous chondrites are proposed to have accreted later (∼2 to >∼4 Myr after CAIs) based on chondrule formation ages and common aqueous alteration processes instead of thermal metamorphism (Budde et al., 2018
Budde, G., Kruijer, T.S., Kleine, T. (2018) Hf–W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26Al in the solar nebula. Geochimica et Cosmochimica Acta 222, 284–304. https://doi.org/10.1016/j.gca.2017.10.014
; Kruijer et al., 2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
). Molybdenum nucleosynthetic isotopic anomalies have related a number of magmatic iron meteorite groups to carbonaceous meteorites (Budde et al., 2019Budde, G., Burkhardt, C., Kleine, T. (2019) Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth. Nature Astronomy 3, 736–741. https://doi.org/10.1038/s41550-019-0779-y
; Burkhardt et al., 2019Burkhardt, C., Dauphas, N., Hans, U., Bourdon, B., Kleine, T. (2019) Elemental and isotopic variability in solar system materials by mixing and processing of primordial disk reservoirs. Geochimica et Cosmochimica Acta 261, 145–170. https://doi.org/10.1016/j.gca.2019.07.003
). Their Hf–W compositions constrain their accretion ages to ∼1–2 Myr after CAIs, therefore representing the earliest evidence of planetary formation in the C region, but slightly later than their NC counterparts (Kruijer et al., 2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
). Only three stony meteorite grouplets have so far been argued to be C-related based on O, Cr and Ti nucleosynthetic anomalies. These include Tafassasset (Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
) and several related meteorites referred to as highly equilibrated CR chondrites (Sanborn et al., 2019Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
), NWA 011-related ungrouped basaltic achondrites (Yamaguchi et al., 2002Yamaguchi, A., Clayton, R.N., Mayeda, T.K., Ebihara, M., Oura, Y., Miura, Y.N., Haramura, H., Misawa, K., Kojima, H., Nagao, K. (2002) A new source of basaltic meteorites inferred from Northwest Africa 011. Science 296, 334–336. https://doi.org/10.1126/science.1069408
), and NWA 6704-related ungrouped pyroxenitic achondrites (Hibiya et al., 2019Hibiya, Y., Archer, G.J., Tanaka, R., Sanborn, M.E., Sato, Y., Iizuka, T., Ozawa, K., Walker, R.J., Yamaguchi, A., Yin, Q.Z., Nakamura, T., Irving, A.J. (2019) The origin of the unique achondrite Northwest Africa 6704: Constraints from petrology, chemistry and Re–Os, O and Ti isotope systematics. Geochimica et Cosmochimica Acta 245, 597–627. https://doi.org/10.1016/j.gca.2018.04.031
; Sanborn et al., 2019Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
; Table S-6 and references therein). The parent body formation and evolution history for these meteorite grouplets is however not known with respect to CR chondrites.Tafassasset is an unusual primitive achondrite. It contains predominantly FeO-rich olivine (Fa29), pyroxene (Fs26) and intermediate plagioclase in coexistence with abundant Fe-Ni metal. Tafassasset was initially suggested to be an equilibrated CR achondrite based on its oxygen isotopic composition. Tafassasset was later re-classified as an ungrouped primitive achondrite based on distinct oxygen fugacity and bulk elemental composition, incompatible with a partially molten CR precursor (Gardner-Vandy et al., 2012
Gardner-Vandy, K.G., Lauretta, D.S., Greenwood, R.C., McCoy, T.J., Killgore, M., Franchi, I.A. (2012) The Tafassasset primitive achondrite: Insights into initial stages of planetary differentiation. Geochimica et Cosmochimica Acta 85, 142–159. https://doi.org/10.1016/j.gca.2012.01.014
; Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
). The high FeO contents in silicates in coexistence with abundant Fe-Ni metal (bulk Fe content 23–40 wt. %) distinguishes Tafassasset from any known groups of primitive achondrites (Figs. S-2 to S-4).top
Samples and Methods
Based on their reported mineralogical and oxygen isotopic compositions, here we demonstrate that a group of 13 Tafassasset-related meteorites can be established, for which we recommend the name ‘Tafassites’. The members with corresponding thermal metamorphic types are NWA 7317, NWA 6921 and NWA 2994 as type 6 chondrites (T6); Tafassasset, NWA 11561, NWA 5131, NWA 12869 and NWA 11112 as type 7 primitive achondrites (T7); and NWA 12455, NWA 6901, NWA 3250, NWA 8548 and NWA 3100 as primitive achondrites with melt depletion (T7 depleted or T7 dep.) (Tables S-1, S-2). Together, these meteorites constitute the first and so far unique group of carbonaceous primitive achondrites.
The petrology, geochronology and thermal evolution of four Tafassites (NWA 7317 T6, Tafassasset T7, NWA 11561 T7, and NWA 12455 T7 dep.) were characterised in detail by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy elemental mapping and electron microprobe analysis. We further analysed the Pb isotopic compositions of merrillites (Fig. S-7) to obtain their 207Pb–206Pb ages. Our Pb–Pb phosphate ages along with published Mn–Cr and Hf–W ages on Tafassasset (Breton et al., 2015
Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
; Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
) were fitted using a 1 D thermal model to constrain the thermal history of the Tafassite parent body. Further Tafassite classification criteria and comparison against primitive achondrites, CR chondrites, NWA 011 and NWA 6704 grouplets, including ours and published data, and our analytical and numerical model designs are detailed in the Supplementary Information.top
Petrology of Tafassites
Tafassites are equilibrated meteorites composed of abundant Fe-rich olivine (Ol, Fa27–38, Fe/Mn atomic ratios ranging from 60 to 94, 40–80 vol. %; Fig. S-2), orthopyroxene (Opx, Fs23–31, Fe/Mn 38–67, 10–40 vol. % for two pyroxenes), minor clinopyroxene (Cpx; Fig. S-6), and intermediate plagioclase (Plg, An28–56Ab43–68Or1–5, <1 to >10 vol. %, variable abundance and composition reflecting partial melting and melt extraction), together with abundant Fe-Ni metal, troilite (Tro), Al-rich chromite (Chr, ∼Mg0.2Fe0.8Al0.4Cr1.5Ti0.1O4.0, 7–23 vol. % for all opaques) and trace merrillite (Mer; Fig. S-7, Tables S-1 to S-3).
Tafassites show further prograde textural equilibration from:
- Subsolidus heated poikiloblastic type 6 chondrites (abbreviated as T6, e.g., NWA 7317 T6, metamorphosed at T <1313 K with exsolved metal-sulfide nodules and rare relict chondrules; Figs. S-1, S-8);
- Supersolidus heated poikilitic type 7 primitive achondrites (T7, e.g., Tafassasset T7, NWA 11561 T7, partially molten at T >1353 K with interstitial and heterogeneous plagioclase and inverted pigeonite exsolution of mm-sized pyroxene oikocrysts; Figs. S-1, S-6, S-9, S-10);
- Supersolidus heated protogranular type 7 primitive achondrites with variable degrees of opaque and silicate melt depletion (T7 dep., e.g., NWA 12455 T7 depleted, with curved grain boundaries, thin opaque veins; Figs. S-1, S-11).
Gardner-Vandy, K.G., Lauretta, D.S., Greenwood, R.C., McCoy, T.J., Killgore, M., Franchi, I.A. (2012) The Tafassasset primitive achondrite: Insights into initial stages of planetary differentiation. Geochimica et Cosmochimica Acta 85, 142–159. https://doi.org/10.1016/j.gca.2012.01.014
; Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
).top
Mass-dependent and Mass-independent O Isotopic Compositions
Despite commonly argued similarities, a re-evaluation of published O isotopic data (Table S-4) reveals clear compositional differences between Tafassites, CR chondrites, and NWA 011 and NWA 6704 grouplets (Schrader et al., 2011
Schrader, D.L., Franchi, I.A., Connolly, H.C., Greenwood, R.C., Lauretta, D.S., Gibson, J.M. (2011) The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition. Geochimica et Cosmochimica Acta 75, 308–325. https://doi.org/10.1016/j.gca.2010.09.028
; Gardner-Vandy et al., 2012Gardner-Vandy, K.G., Lauretta, D.S., Greenwood, R.C., McCoy, T.J., Killgore, M., Franchi, I.A. (2012) The Tafassasset primitive achondrite: Insights into initial stages of planetary differentiation. Geochimica et Cosmochimica Acta 85, 142–159. https://doi.org/10.1016/j.gca.2012.01.014
; Hibiya et al., 2019Hibiya, Y., Archer, G.J., Tanaka, R., Sanborn, M.E., Sato, Y., Iizuka, T., Ozawa, K., Walker, R.J., Yamaguchi, A., Yin, Q.Z., Nakamura, T., Irving, A.J. (2019) The origin of the unique achondrite Northwest Africa 6704: Constraints from petrology, chemistry and Re–Os, O and Ti isotope systematics. Geochimica et Cosmochimica Acta 245, 597–627. https://doi.org/10.1016/j.gca.2018.04.031
). Figure 1a shows that Tafassites plot tightly on a mass-dependent fractionation line (slope ∼0.51) while CR chondrites fall on a mass-independent mixing line (slope ∼0.71). The homogeneous Δ17O anomaly in Tafassites (−1.67 ± 0.14 ‰, 2 s.d.; Fig. 1, Table S-4) barely overlaps with highly heterogeneous CR2 (<−1.5 to >−2.5‰; Schrader et al., 2011Schrader, D.L., Franchi, I.A., Connolly, H.C., Greenwood, R.C., Lauretta, D.S., Gibson, J.M. (2011) The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition. Geochimica et Cosmochimica Acta 75, 308–325. https://doi.org/10.1016/j.gca.2010.09.028
). These O isotopic compositions strongly suggest that Tafassites originated from a common and fairly equilibrated parent body, previously unrecognised and different from the CR chondrite parent body (PB). In this case, the oxygen isotope similarity to CR chondrites, likely reflects similar accreting materials in lieu of a common parent body. Tafassites also have Δ17O values that are distinct from other known groups of primitive achondrites.Figure 1 Oxygen isotope compositions of Tafassites. (a) Tafassites define a mass-dependent fractionation line (slope ∼0.51), distinctive from the mass-independent CR mixing line (slope ∼0.71). (b) Tafassites show a homogeneous and unique Δ17O anomaly (−1.67 ± 0.14 ‰, 2 s.d.) distinct from acapulcoite-lodranite (Aca&Lod), winonaite (Win) and CR chondrite meteorites (Schrader et al., 2011
Schrader, D.L., Franchi, I.A., Connolly, H.C., Greenwood, R.C., Lauretta, D.S., Gibson, J.M. (2011) The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition. Geochimica et Cosmochimica Acta 75, 308–325. https://doi.org/10.1016/j.gca.2010.09.028
). Data are compiled in Table S-4, and carbonaceous chondrite anhydrous mixing (CCAM) and terrestrial fractionation lines (TFL) are shown for reference.NWA 011 and NWA 6704 grouplet meteorites have also been linked with Tafassasset and CR chondrites based on oxygen isotope signatures. NWA 011 grouplet has Δ17O values ranging from −1.43 to −1.86 ‰ overlapping with Tafassites (Yamaguchi et al., 2002
Yamaguchi, A., Clayton, R.N., Mayeda, T.K., Ebihara, M., Oura, Y., Miura, Y.N., Haramura, H., Misawa, K., Kojima, H., Nagao, K. (2002) A new source of basaltic meteorites inferred from Northwest Africa 011. Science 296, 334–336. https://doi.org/10.1126/science.1069408
; Fig. 1b). However, the higher FeO abundance in silicates (Fig. S-2), distinct Fe/Mn ratio in orthopyroxene (Fig. S-3) and calcic plagioclase composition (∼An85) are difficult to reconcile petrogenetically with Tafassites. NWA 6704 grouplet comprises a unique Fe-rich and pyroxenitic lithology with its own oxygen mass-dependent fractionation line different from Tafassites and CR with Δ17O = −1.06 ± 0.06 ‰ (Fig. 1b and Table S-14).top
Thermal History of the Tafassite Parent Body
Merrillite Pb–Pb chronology (Fig. S-12 and Table S-5) provides retrograde metamorphic ages (Tc ∼720 K; Cherniak et al., 1991
Cherniak, D.J., Lanford, W.A., Ryerson, F.J. (1991) Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques. Geochimica et Cosmochimica Acta 55, 1663–1673. https://doi.org/10.1016/0016-7037(91)90137-T
) of 4559.5 ± 5.8 Ma (n = 10, all uncertainties reported as ± 2 s.e.) for NWA 7317 T6; 4560.4 ± 5.7 Ma (n = 21) for NWA 11561 T7; 4557.8 ± 3.4 Ma (n = 16) for NWA 12455 T7 depleted and slightly younger 4548.0 ± 15.9 Ma (n = 7) for Tafassasset T7 (Fig. 2). These ages are consistently younger than Hf–W (2.9 ± 0.9 Myr after CAI, Tc ∼1200 K) and Mn–Cr ages (4.9 ± 0.3 Myr after CAI, Tc ∼950 ± 100 K) (Breton et al., 2015Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
; Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
) reported for Tafassasset, suggesting rapid cooling to <720 K at a rate of ∼100 K/Myr within 9.0 ± 5.0 Myr after CAIs. Thermal numerical modelling indicates that the Tafassite parent body (TPB) accreted within 1.1+0.3−0.4 Myr after CAI into a >50 km radius planetesimal (Fig. 3), before experiencing severe but rapid thermal annealing. Our Pb–Pb ages and thermal history model result in identical accretion age estimation (1.1+0.3−0.4 vs. <1 Myr) compared to Breton et al.Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
(2015Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
), but predict larger PB size (>50 km vs. <25 km) and shallow burial depth (all ≲4 km). Though sharing a thermal history similar to primitive achondrites, the early accretion of TPB is completely unreconcilable with late CR chondrite PB formation based on Al–Mg chondrule ages therefore placing a minimum age for its accretion (> 4.0+0.5−0.3 Myr; Schrader et al., 2017Schrader, D.L., Nagashima, K., Krot, A.N., Ogliore, R.C., Yin, Q.Z., Amelin, Y., Stirling, C.H., Kaltenbach, A. (2017) Distribution of 26Al in the CR chondrite chondrule-forming region of the protoplanetary disk. Geochimica et Cosmochimica Acta 201, 275–302. https://doi.org/10.1016/j.gca.2016.06.023
). Our results support the formation of a partially differentiated TPB with highly equilibrated T6 chondrites and partially molten T7 primitive achondrites at a shallow depth. The TPB may also be fully differentiated within its interior.Figure 2 Comparative chronology from CAI formation (U corrected Pb–Pb average age of 4567.73 ± 0.81 Ma; Sanborn et al., 2019
Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
) of selected meteorite groups (data points) and modelled timing of accretion of their parent bodies (boxes) in the carbonaceous (C, blue) and non-carbonaceous (NC, red) reservoirs. Parent body accretion ages are from this study for Tafassites, and taken from Kruijer et al.Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
(2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
) and Neumann et al.Neumann, W., Kruijer, T. S., Breuer, D., Kleine, T. (2018) Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf‐W Chronometry of Iron Meteorites, Journal of Geophysical Research: Planets 123, 421–444. https://doi.org/10.1002/2017JE005411
(2018Neumann, W., Kruijer, T. S., Breuer, D., Kleine, T. (2018) Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf‐W Chronometry of Iron Meteorites, Journal of Geophysical Research: Planets 123, 421–444. https://doi.org/10.1002/2017JE005411
) for other relevant groups. The Tafassite Hf–W, Mn–Cr (Breton et al., 2015Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
; Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011Bouvier, A., Spivak-Birndorf, L.J., Brennecka, G.A., Wadhwa, M. (2011) New constraints on early Solar System chronology from Al–Mg and U–Pb isotope systematics in the unique basaltic achondrite Northwest Africa 2976. Geochimica et Cosmochimica Acta 75, 5310–5323. https://doi.org/10.1016/j.gca.2011.06.033
) and NWA 6704 (Amelin et al., 2019Amelin, Y., Koefoed, P., Iizuka, T., Fernandes, V.A., Huyskens, M.H., Yin, Q.Z., Irving, A.J. (2019) U–Pb, Rb–Sr and Ar–Ar systematics of the ungrouped achondrites Northwest Africa 6704 and Northwest Africa 6693. Geochimica et Cosmochimica Acta 245, 628–642. https://doi.org/10.1016/j.gca.2018.09.021
; Sanborn et al., 2019Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
) grouplets. Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017Schrader, D.L., Nagashima, K., Krot, A.N., Ogliore, R.C., Yin, Q.Z., Amelin, Y., Stirling, C.H., Kaltenbach, A. (2017) Distribution of 26Al in the CR chondrite chondrule-forming region of the protoplanetary disk. Geochimica et Cosmochimica Acta 201, 275–302. https://doi.org/10.1016/j.gca.2016.06.023
) and Pb–Pb (Amelin et al., 2002Amelin, Y., Krot, A.N., Hutcheon, I.D., Ulyanov, A.A. (2002) Lead isotopic ages of chondrules and calcium-aluminum–rich inclusions. Science 297, 1678–1683. https://doi.org/10.1126/science.1073950
; Bollard et al, 2017Bollard, J., Connelly, J.N., Whitehouse, M.J., Pringle, E.A., Bonal, L., Jørgensen, J.K., Nordlund, Å., Moynier, F., Bizzarro, M. (2017) Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules. Science Advances 3, https://doi.org/10.1126/sciadv.1700407
), and Hf–W average age obtained in CR chondrites (Budde et al., 2018Budde, G., Kruijer, T.S., Kleine, T. (2018) Hf–W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26Al in the solar nebula. Geochimica et Cosmochimica Acta 222, 284–304. https://doi.org/10.1016/j.gca.2017.10.014
) after CAIs. Symbols: circle = Al–Mg; full diamond = Hf–W; triangle = Mn–Cr; square = phosphate Pb–Pb; full square = Pb–Pb.Figure 3 Thermal evolution model of the Tafassite parent body. (a) Fit quality χn as a function of the planetesimal accretion time t0 and radius R. Tafassite parent body is best fitted to have an accretion time t0 = 1.1+0.3−0.4 Myr and radius R >50 km. (b) Modelled thermal history curves based on Tafassasset Hf–W and Mn–Cr ages, and Tafassasset and T6–T7 Tafassite Pb–Pb Ca phosphate chronological records. The thermal history is shown for an object with R = 120 km and t0 = 1.1 Myr marked in (a) with a red dot, and is representative for bodies with an acceptable fit quality of χn ≤ 4. The fit depths for NWA 12455, Tafassasset, NWA 7317 and NWA 11561 are ∼4.1 km, ∼3.3 km, ∼3.1 km and ∼2.6 km, respectively.
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Isotopic Anomalies
Tafassasset belongs to the carbonaceous reservoir (Fig. S-13) based on reported mass-independent isotopic anomalies for several elements (Table S-6) i.e. ɛ50Ti = 2.07 ± 0.14, ɛ54Cr = 1.44 ± 0.08 (Sanborn et al., 2019
Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
), ɛ94Mo = 1.54 ± 0.40 (Burkhardt et al., 2011Burkhardt, C., Kleine, T., Oberli, F., Pack, A., Bourdon, B., Wieler, R. (2011) Molybdenum isotope anomalies in meteorites: Constraints on solar nebula evolution and origin of the Earth. Earth and Planetary Science Letters 312, 390–400. https://doi.org/10.1016/j.epsl.2011.10.010
) and ɛ100Rumetal = −1.15 ± 0.04 (Fischer-Gödde et al., 2015Fischer-Gödde, M., Burkhardt, C., Kruijer, T.S., Kleine, T. (2015) Ru isotope heterogeneity in the solar protoplanetary disk. Geochimica et Cosmochimica Acta 168, 151–171. https://doi.org/10.1016/j.gca.2015.07.032
). Other Tafassites also show similar compositions with ɛ54Cr (1.31 to 1.50) and ɛ50Ti (1.91 to 2.90), distinct from any known groups of primitive achondrites (all NC-like; Kruijer et al., 2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
) but similar to carbonaceous (in particular CR) chondrites. Tafassites show rather homogeneous ɛ54Cr and Δ17O but somewhat more heterogeneous ɛ50Ti anomalies presumably due to limited number of measurements and/or slower diffusion rate of Ti4+ over Cr3+ and O2−, also consistent with their partially differentiated nature.Based on chemical and isotopic signatures, we rule out a common parent body hypothesis for all CR chondrite and achondrite-related meteorites, and Tafassites that constitute a unique group of carbonaceous primitive achondrites. The parent body of Tafassites accreted early, ∼1.1 Myr after CAIs, in an outer region of the disc, close to where the parent body of CR chondrites will form, at least ∼ 3 Myr later. Similarly, the NWA 011 and NWA 6704 achondrite grouplets form two groups of carbonaceous achondrites for which the time of accretion is currently not as well constrained, but suggested to be within 1.5 Myr after CAIs (Sanborn et al., 2019
Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
). Their respective parent bodies likely accreted in close regions of the outer protoplanetary disc (Figs. 1, S-2, S-4, S-13).top
The Protoplanetary Disc Farther Out is Just as Diverse
We show Tafassites as the first known group of carbonaceous primitive achondrites, which expands the diversity of meteorite parent bodies, providing essential clues about planetesimal formation and protoplanetary disc evolution beyond the snow line. We identified at least four parent bodies for Tafassites, NWA 011 grouplet, NWA 6704 grouplet, and CR chondrites. The PB accretion age of Tafassites (1.1+0.3−0.4 Myr, likely comparable to NWA 011 and NWA 6704 grouplets) is similar to C magmatic irons and pallasites (0.9+0.4−0.2 Myr; Kruijer et al., 2020
Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
) and provides evidence for early accretion of rocky planetesimals beyond the snow line and with coeval planetesimal formation between the inner and outer disc (Fig. 2). The divergent PB accretion ages and O, 54Cr and 50Ti isotopic anomalies for Tafassites and CR chondrites (1.1+0.3−0.4 vs. > 4.0+0.5−0.3 Myr; Schrader et al., 2017Schrader, D.L., Nagashima, K., Krot, A.N., Ogliore, R.C., Yin, Q.Z., Amelin, Y., Stirling, C.H., Kaltenbach, A. (2017) Distribution of 26Al in the CR chondrite chondrule-forming region of the protoplanetary disk. Geochimica et Cosmochimica Acta 201, 275–302. https://doi.org/10.1016/j.gca.2016.06.023
) indicate a prolonged and multi-epoch of planetesimal formation in the Tafassite-feeding zone (related to the metal-rich carbonaceous chondrites CR, CH and CB) associated with limited radial mixing of building materials throughout planetesimal formation period.top
Author Contributions
AB and NM designed the study, and characterised the samples. WN and MT carried out the thermal modelling. NM, WS, TL carried out the SIMS analyses, assisted by AB and MT. AN and NM carried out the thermodynamic calculations. HK discussed the implications of the findings to our current understanding of planetesimal formation. All co-authors contributed to writing the manuscript and discussion. NM and WN contributed equally to the data included in this manuscript.
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Acknowledgements
We are grateful to Alexander Rother, Dorothea Wiesner and Detlef Krauße at BGI for careful sample preparation and maintenance of the FIB-SEM and EMP instruments, Andreas Audétat for assistance with the LA-ICP-MS measurements, David Chew for the Durango and McClure Mountain apatites, and to Ben Hoefnagels for sample donations. AB thanks support from UBT and BGI. MT and WN acknowledge support by Klaus Tschira Foundation, and support by the Deutsche Forschungsgemeinschaft to WN (project number 434933764). We thank three anonymous reviewers for their careful reading, providing both supportive and critical comments which helped us to improve our manuscript, and Dr. Francis McCubbin for editorial handling.
Editor: Francis McCubbin
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References
Amelin, Y., Krot, A.N., Hutcheon, I.D., Ulyanov, A.A. (2002) Lead isotopic ages of chondrules and calcium-aluminum–rich inclusions. Science 297, 1678–1683. https://doi.org/10.1126/science.1073950
Show in context Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017) and Pb–Pb (Amelin et al., 2002; Bollard et al, 2017), and Hf–W average age obtained in CR chondrites (Budde et al., 2018) after CAIs.
View in article
Amelin, Y., Koefoed, P., Iizuka, T., Fernandes, V.A., Huyskens, M.H., Yin, Q.Z., Irving, A.J. (2019) U–Pb, Rb–Sr and Ar–Ar systematics of the ungrouped achondrites Northwest Africa 6704 and Northwest Africa 6693. Geochimica et Cosmochimica Acta 245, 628–642. https://doi.org/10.1016/j.gca.2018.09.021
Show in context The Tafassite Hf–W, Mn–Cr (Breton et al., 2015; Göpel et al., 2015) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011) and NWA 6704 (Amelin et al., 2019; Sanborn et al., 2019) grouplets.
View in article
Bollard, J., Connelly, J.N., Whitehouse, M.J., Pringle, E.A., Bonal, L., Jørgensen, J.K., Nordlund, Å., Moynier, F., Bizzarro, M. (2017) Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules. Science Advances 3, https://doi.org/10.1126/sciadv.1700407
Show in context Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017) and Pb–Pb (Amelin et al., 2002; Bollard et al, 2017), and Hf–W average age obtained in CR chondrites (Budde et al., 2018) after CAIs.
View in article
Bouvier, A., Spivak-Birndorf, L.J., Brennecka, G.A., Wadhwa, M. (2011) New constraints on early Solar System chronology from Al–Mg and U–Pb isotope systematics in the unique basaltic achondrite Northwest Africa 2976. Geochimica et Cosmochimica Acta 75, 5310–5323. https://doi.org/10.1016/j.gca.2011.06.033
Show in context The Tafassite Hf–W, Mn–Cr (Breton et al., 2015; Göpel et al., 2015) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011) and NWA 6704 (Amelin et al., 2019; Sanborn et al., 2019) grouplets.
View in article
Brasser, R, Mojzsis, S. (2020) The partitioning of the inner and outer Solar System by a structured protoplanetary disk. Nature Astronomy 4, 492–499. https://doi.org/10.1038/s41550-019-0978-6
Show in context The two NC and C reservoirs evolved as spatially separate and isotopically distinct entities, potentially as a result of the early formation of Jupiter (Kruijer et al., 2020) or a pressure maximum in the disc (Brasser and Mojzsis, 2020).
View in article
Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
Show in context Our Pb–Pb phosphate ages along with published Mn–Cr and Hf–W ages on Tafassasset (Breton et al., 2015; Göpel et al., 2015) were fitted using a 1 D thermal model to constrain the thermal history of the Tafassite parent body.
View in article
These ages are consistently younger than Hf–W (2.9 ± 0.9 Myr after CAI, Tc ∼1200 K) and Mn–Cr ages (4.9 ± 0.3 Myr after CAI, Tc ∼950 ± 100 K) (Breton et al., 2015; Göpel et al., 2015) reported for Tafassasset, suggesting rapid cooling to <720 K at a rate of ∼100 K/Myr within 9.0 ± 5.0 Myr after CAIs.
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Our Pb–Pb ages and thermal history model result in identical accretion age estimation (1.1+0.3−0.4 vs. <1 Myr) compared to Breton et al. (2015), but predict larger PB size (>50 km vs. <25 km) and shallow burial depth (all ≲4 km).
View in article
The Tafassite Hf–W, Mn–Cr (Breton et al., 2015; Göpel et al., 2015) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011) and NWA 6704 (Amelin et al., 2019; Sanborn et al., 2019) grouplets.
View in article
Budde, G., Kruijer, T.S., Kleine, T. (2018) Hf–W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26Al in the solar nebula. Geochimica et Cosmochimica Acta 222, 284–304. https://doi.org/10.1016/j.gca.2017.10.014
Show in context In contrast, carbonaceous chondrites are proposed to have accreted later (∼2 to >∼4 Myr after CAIs) based on chondrule formation ages and common aqueous alteration processes instead of thermal metamorphism (Budde et al., 2018; Kruijer et al., 2020).
View in article
Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017) and Pb–Pb (Amelin et al., 2002; Bollard et al, 2017), and Hf–W average age obtained in CR chondrites (Budde et al., 2018) after CAIs.
View in article
Budde, G., Burkhardt, C., Kleine, T. (2019) Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth. Nature Astronomy 3, 736–741. https://doi.org/10.1038/s41550-019-0779-y
Show in context Molybdenum nucleosynthetic isotopic anomalies have related a number of magmatic iron meteorite groups to carbonaceous meteorites (Budde et al., 2019; Burkhardt et al., 2019).
View in article
Burkhardt, C., Kleine, T., Oberli, F., Pack, A., Bourdon, B., Wieler, R. (2011) Molybdenum isotope anomalies in meteorites: Constraints on solar nebula evolution and origin of the Earth. Earth and Planetary Science Letters 312, 390–400. https://doi.org/10.1016/j.epsl.2011.10.010
Show in context Tafassasset belongs to the carbonaceous reservoir (Fig. S-13) based on reported mass-independent isotopic anomalies for several elements (Table S-6) i.e. ɛ50Ti = 2.07 ± 0.14, ɛ54Cr = 1.44 ± 0.08 (Sanborn et al., 2019), ɛ94Mo = 1.54 ± 0.40 (Burkhardt et al., 2011) and ɛ100Rumetal = −1.15 ± 0.04 (Fischer-Gödde et al., 2015).
View in article
Burkhardt, C., Dauphas, N., Hans, U., Bourdon, B., Kleine, T. (2019) Elemental and isotopic variability in solar system materials by mixing and processing of primordial disk reservoirs. Geochimica et Cosmochimica Acta 261, 145–170. https://doi.org/10.1016/j.gca.2019.07.003
Show in context Mass-independent nucleosynthetic anomalies in meteorites have revealed a fundamental isotopic dichotomy between s-process-rich (slow neutron capture) non-carbonaceous meteorites (NC) and s-process-depleted carbonaceous meteorites (C), accreted within the inner and outer parts of the protoplanetary disc, respectively (Warren, 2011; Burkhardt et al., 2019; Kruijer et al., 2020).
View in article
Molybdenum nucleosynthetic isotopic anomalies have related a number of magmatic iron meteorite groups to carbonaceous meteorites (Budde et al., 2019; Burkhardt et al., 2019).
View in article
Cherniak, D.J., Lanford, W.A., Ryerson, F.J. (1991) Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques. Geochimica et Cosmochimica Acta 55, 1663–1673. https://doi.org/10.1016/0016-7037(91)90137-T
Show in context Merrillite Pb–Pb chronology (Fig. S-12 and Table S-5) provides retrograde metamorphic ages (Tc ∼720 K; Cherniak et al., 1991) of 4559.5 ± 5.8 Ma (n = 10, all uncertainties reported as ± 2 s.e.) for NWA 7317 T6; 4560.4 ± 5.7 Ma (n = 21) for NWA 11561 T7; 4557.8 ± 3.4 Ma (n = 16) for NWA 12455 T7 depleted and slightly younger 4548.0 ± 15.9 Ma (n = 7) for Tafassasset T7 (Fig. 2).
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Fischer-Gödde, M., Burkhardt, C., Kruijer, T.S., Kleine, T. (2015) Ru isotope heterogeneity in the solar protoplanetary disk. Geochimica et Cosmochimica Acta 168, 151–171. https://doi.org/10.1016/j.gca.2015.07.032
Show in context Tafassasset belongs to the carbonaceous reservoir (Fig. S-13) based on reported mass-independent isotopic anomalies for several elements (Table S-6) i.e. ɛ50Ti = 2.07 ± 0.14, ɛ54Cr = 1.44 ± 0.08 (Sanborn et al., 2019), ɛ94Mo = 1.54 ± 0.40 (Burkhardt et al., 2011) and ɛ100Rumetal = −1.15 ± 0.04 (Fischer-Gödde et al., 2015).
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Gardner-Vandy, K.G., Lauretta, D.S., Greenwood, R.C., McCoy, T.J., Killgore, M., Franchi, I.A. (2012) The Tafassasset primitive achondrite: Insights into initial stages of planetary differentiation. Geochimica et Cosmochimica Acta 85, 142–159. https://doi.org/10.1016/j.gca.2012.01.014
Show in context Tafassasset was later re-classified as an ungrouped primitive achondrite based on distinct oxygen fugacity and bulk elemental composition, incompatible with a partially molten CR precursor (Gardner-Vandy et al., 2012; Göpel et al., 2015).
View in article
Bulk chemical analyses on Tafassasset show from nearly chondritic to depleted trace element patterns, consistent with variable melt extraction (Gardner-Vandy et al., 2012; Göpel et al., 2015).
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Despite commonly argued similarities, a re-evaluation of published O isotopic data (Table S-4) reveals clear compositional differences between Tafassites, CR chondrites, and NWA 011 and NWA 6704 grouplets (Schrader et al., 2011; Gardner-Vandy et al., 2012; Hibiya et al., 2019).
View in article
Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
Show in context These include Tafassasset (Göpel et al., 2015) and several related meteorites referred to as highly equilibrated CR chondrites (Sanborn et al., 2019), NWA 011-related ungrouped basaltic achondrites (Yamaguchi et al., 2002), and NWA 6704-related ungrouped pyroxenitic achondrites (Hibiya et al., 2019; Sanborn et al., 2019; Table S-6 and references therein).
View in article
Tafassasset was later re-classified as an ungrouped primitive achondrite based on distinct oxygen fugacity and bulk elemental composition, incompatible with a partially molten CR precursor (Gardner-Vandy et al., 2012; Göpel et al., 2015).
View in article
Our Pb–Pb phosphate ages along with published Mn–Cr and Hf–W ages on Tafassasset (Breton et al., 2015; Göpel et al., 2015) were fitted using a 1 D thermal model to constrain the thermal history of the Tafassite parent body.
View in article
Bulk chemical analyses on Tafassasset show from nearly chondritic to depleted trace element patterns, consistent with variable melt extraction (Gardner-Vandy et al., 2012; Göpel et al., 2015).
View in article
These ages are consistently younger than Hf–W (2.9 ± 0.9 Myr after CAI, Tc ∼1200 K) and Mn–Cr ages (4.9 ± 0.3 Myr after CAI, Tc ∼950 ± 100 K) (Breton et al., 2015; Göpel et al., 2015) reported for Tafassasset, suggesting rapid cooling to <720 K at a rate of ∼100 K/Myr within 9.0 ± 5.0 Myr after CAIs.
View in article
The Tafassite Hf–W, Mn–Cr (Breton et al., 2015; Göpel et al., 2015) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011) and NWA 6704 (Amelin et al., 2019; Sanborn et al., 2019) grouplets.
View in article
Hibiya, Y., Archer, G.J., Tanaka, R., Sanborn, M.E., Sato, Y., Iizuka, T., Ozawa, K., Walker, R.J., Yamaguchi, A., Yin, Q.Z., Nakamura, T., Irving, A.J. (2019) The origin of the unique achondrite Northwest Africa 6704: Constraints from petrology, chemistry and Re–Os, O and Ti isotope systematics. Geochimica et Cosmochimica Acta 245, 597–627. https://doi.org/10.1016/j.gca.2018.04.031
Show in context These include Tafassasset (Göpel et al., 2015) and several related meteorites referred to as highly equilibrated CR chondrites (Sanborn et al., 2019), NWA 011-related ungrouped basaltic achondrites (Yamaguchi et al., 2002), and NWA 6704-related ungrouped pyroxenitic achondrites (Hibiya et al., 2019; Sanborn et al., 2019; Table S-6 and references therein).
View in article
Despite commonly argued similarities, a re-evaluation of published O isotopic data (Table S-4) reveals clear compositional differences between Tafassites, CR chondrites, and NWA 011 and NWA 6704 grouplets (Schrader et al., 2011; Gardner-Vandy et al., 2012; Hibiya et al., 2019).
View in article
Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
Show in context Mass-independent nucleosynthetic anomalies in meteorites have revealed a fundamental isotopic dichotomy between s-process-rich (slow neutron capture) non-carbonaceous meteorites (NC) and s-process-depleted carbonaceous meteorites (C), accreted within the inner and outer parts of the protoplanetary disc, respectively (Warren, 2011; Burkhardt et al., 2019; Kruijer et al., 2020).
View in article
The two NC and C reservoirs evolved as spatially separate and isotopically distinct entities, potentially as a result of the early formation of Jupiter (Kruijer et al., 2020) or a pressure maximum in the disc (Brasser and Mojzsis, 2020).
View in article
Later inward migration of Jupiter could have scattered NC and C planetesimals, leading to the eventual formation of the asteroid belt (Kruijer et al., 2020).
View in article
In contrast, carbonaceous chondrites are proposed to have accreted later (∼2 to >∼4 Myr after CAIs) based on chondrule formation ages and common aqueous alteration processes instead of thermal metamorphism (Budde et al., 2018; Kruijer et al., 2020).
View in article
Their Hf–W compositions constrain their accretion ages to ∼1–2 Myr after CAIs, therefore representing the earliest evidence of planetary formation in the C region, but slightly later than their NC counterparts (Kruijer et al., 2020).
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Parent body accretion ages are from this study for Tafassites, and taken from Kruijer et al. (2020) and Neumann et al. (2018) for other relevant groups.
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Other Tafassites also show similar compositions with ɛ54Cr (1.31 to 1.50) and ɛ50Ti (1.91 to 2.90), distinct from any known groups of primitive achondrites (all NC-like; Kruijer et al., 2020) but similar to carbonaceous (in particular CR) chondrites.
View in article
The PB accretion age of Tafassites (1.1+0.3−0.4 Myr, likely comparable to NWA 011 and NWA 6704 grouplets) is similar to C magmatic irons and pallasites (0.9+0.4−0.2 Myr; Kruijer et al., 2020) and provides evidence for early accretion of rocky planetesimals beyond the snow line and with coeval planetesimal formation between the inner and outer disc (Fig. 2).
View in article
Neumann, W., Kruijer, T. S., Breuer, D., Kleine, T. (2018) Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf‐W Chronometry of Iron Meteorites, Journal of Geophysical Research: Planets 123, 421–444. https://doi.org/10.1002/2017JE005411
Show in context Parent body accretion ages are from this study for Tafassites, and taken from Kruijer et al. (2020) and Neumann et al. (2018) for other relevant groups.
View in article
Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
Show in context These include Tafassasset (Göpel et al., 2015) and several related meteorites referred to as highly equilibrated CR chondrites (Sanborn et al., 2019), NWA 011-related ungrouped basaltic achondrites (Yamaguchi et al., 2002), and NWA 6704-related ungrouped pyroxenitic achondrites (Hibiya et al., 2019; Sanborn et al., 2019; Table S-6 and references therein).
View in article
Comparative chronology from CAI formation (U corrected Pb–Pb average age of 4567.73 ± 0.81 Ma; Sanborn et al., 2019) of selected meteorite groups (data points) and modelled timing of accretion of their parent bodies (boxes) in the carbonaceous (C, blue) and non-carbonaceous (NC, red) reservoirs.
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The Tafassite Hf–W, Mn–Cr (Breton et al., 2015; Göpel et al., 2015) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011) and NWA 6704 (Amelin et al., 2019; Sanborn et al., 2019) grouplets.
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Tafassasset belongs to the carbonaceous reservoir (Fig. S-13) based on reported mass-independent isotopic anomalies for several elements (Table S-6) i.e. ɛ50Ti = 2.07 ± 0.14, ɛ54Cr = 1.44 ± 0.08 (Sanborn et al., 2019), ɛ94Mo = 1.54 ± 0.40 (Burkhardt et al., 2011) and ɛ100Rumetal = −1.15 ± 0.04 (Fischer-Gödde et al., 2015).
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Similarly, the NWA 011 and NWA 6704 achondrite grouplets form two groups of carbonaceous achondrites for which the time of accretion is currently not as well constrained, but suggested to be within 1.5 Myr after CAIs (Sanborn et al., 2019).
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Schrader, D.L., Franchi, I.A., Connolly, H.C., Greenwood, R.C., Lauretta, D.S., Gibson, J.M. (2011) The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition. Geochimica et Cosmochimica Acta 75, 308–325. https://doi.org/10.1016/j.gca.2010.09.028
Show in context Despite commonly argued similarities, a re-evaluation of published O isotopic data (Table S-4) reveals clear compositional differences between Tafassites, CR chondrites, and NWA 011 and NWA 6704 grouplets (Schrader et al., 2011; Gardner-Vandy et al., 2012; Hibiya et al., 2019).
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The homogeneous Δ17O anomaly in Tafassites (−1.67 ± 0.14 ‰, 2 s.d.; Fig. 1, Table S-4) barely overlaps with highly heterogeneous CR2 (<−1.5 to >−2.5‰; Schrader et al., 2011).
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(b) Tafassites show a homogeneous and unique Δ17O anomaly (−1.67 ± 0.14 ‰, 2 s.d.) distinct from acapulcoite-lodranite (Aca&Lod), winonaite (Win) and CR chondrite meteorites (Schrader et al., 2011).
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Schrader, D.L., Nagashima, K., Krot, A.N., Ogliore, R.C., Yin, Q.Z., Amelin, Y., Stirling, C.H., Kaltenbach, A. (2017) Distribution of 26Al in the CR chondrite chondrule-forming region of the protoplanetary disk. Geochimica et Cosmochimica Acta 201, 275–302. https://doi.org/10.1016/j.gca.2016.06.023
Show in context Though sharing a thermal history similar to primitive achondrites, the early accretion of TPB is completely unreconcilable with late CR chondrite PB formation based on Al–Mg chondrule ages therefore placing a minimum age for its accretion (1.1+0.3−0.4 vs. > 4.0+0.5−0.3 Myr; Schrader et al., 2017).
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Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017) and Pb–Pb (Amelin et al., 2002; Bollard et al, 2017), and Hf–W average age obtained in CR chondrites (Budde et al., 2018) after CAIs.
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The divergent PB accretion ages and O, 54Cr and 50Ti isotopic anomalies for Tafassites and CR chondrites (1.1+0.3−0.4 vs. > 4.0+0.5−0.3 Myr; Schrader et al., 2017) indicate a prolonged and multi-epoch of planetesimal formation in the Tafassite-feeding zone (related to the metal-rich carbonaceous chondrites CR, CH and CB) associated with limited radial mixing of building materials throughout planetesimal formation period.
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Warren, P.H. (2011) Stable-isotopic anomalies and the accretionary assemblage of the Earth and Mars: A subordinate role for carbonaceous chondrites. Earth and Planetary Science Letters 311, 93–100. https://doi.org/10.1016/j.epsl.2011.08.047
Show in context Mass-independent nucleosynthetic anomalies in meteorites have revealed a fundamental isotopic dichotomy between s-process-rich (slow neutron capture) non-carbonaceous meteorites (NC) and s-process-depleted carbonaceous meteorites (C), accreted within the inner and outer parts of the protoplanetary disc, respectively (Warren, 2011; Burkhardt et al., 2019; Kruijer et al., 2020).
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Yamaguchi, A., Clayton, R.N., Mayeda, T.K., Ebihara, M., Oura, Y., Miura, Y.N., Haramura, H., Misawa, K., Kojima, H., Nagao, K. (2002) A new source of basaltic meteorites inferred from Northwest Africa 011. Science 296, 334–336. https://doi.org/10.1126/science.1069408
Show in context These include Tafassasset (Göpel et al., 2015) and several related meteorites referred to as highly equilibrated CR chondrites (Sanborn et al., 2019), NWA 011-related ungrouped basaltic achondrites (Yamaguchi et al., 2002), and NWA 6704-related ungrouped pyroxenitic achondrites (Hibiya et al., 2019; Sanborn et al., 2019; Table S-6 and references therein).
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NWA 011 grouplet has Δ17O values ranging from −1.43 to −1.86 ‰ overlapping with Tafassites (Yamaguchi et al., 2002; Fig. 1b).
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Supplementary Information
The Supplementary Information includes:
Download Tables S-1 to S-8 (.xlsx)
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Figures
Figure 1 Oxygen isotope compositions of Tafassites. (a) Tafassites define a mass-dependent fractionation line (slope ∼0.51), distinctive from the mass-independent CR mixing line (slope ∼0.71). (b) Tafassites show a homogeneous and unique Δ17O anomaly (−1.67 ± 0.14 ‰, 2 s.d.) distinct from acapulcoite-lodranite (Aca&Lod), winonaite (Win) and CR chondrite meteorites (Schrader et al., 2011
Schrader, D.L., Franchi, I.A., Connolly, H.C., Greenwood, R.C., Lauretta, D.S., Gibson, J.M. (2011) The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition. Geochimica et Cosmochimica Acta 75, 308–325. https://doi.org/10.1016/j.gca.2010.09.028
). Data are compiled in Table S-4, and carbonaceous chondrite anhydrous mixing (CCAM) and terrestrial fractionation lines (TFL) are shown for reference.
Figure 2 Comparative chronology from CAI formation (U corrected Pb–Pb average age of 4567.73 ± 0.81 Ma; Sanborn et al., 2019
Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
) of selected meteorite groups (data points) and modelled timing of accretion of their parent bodies (boxes) in the carbonaceous (C, blue) and non-carbonaceous (NC, red) reservoirs. Parent body accretion ages are from this study for Tafassites, and taken from Kruijer et al.Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
(2020Kruijer, T.S., Kleine, T., Borg, L.E. (2020) The great isotopic dichotomy of the early Solar System. Nature Astronomy 4, 32–40. https://doi.org/10.1038/s41550-019-0959-9
) and Neumann et al.Neumann, W., Kruijer, T. S., Breuer, D., Kleine, T. (2018) Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf‐W Chronometry of Iron Meteorites, Journal of Geophysical Research: Planets 123, 421–444. https://doi.org/10.1002/2017JE005411
(2018Neumann, W., Kruijer, T. S., Breuer, D., Kleine, T. (2018) Multistage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf‐W Chronometry of Iron Meteorites, Journal of Geophysical Research: Planets 123, 421–444. https://doi.org/10.1002/2017JE005411
) for other relevant groups. The Tafassite Hf–W, Mn–Cr (Breton et al., 2015Breton, T., Quitté, G., Toplis, M.J., Monnereau, M., Birck, J.L., Göpel, C., Charles, C. (2015) Tafassasset: Evidence of early incipient differentiation on a metal-rich chondritic parent body. Earth and Planetary Science Letters 425, 193–203. https://doi.org/10.1016/j.epsl.2015.06.002
; Göpel et al., 2015Göpel, C., Birck, J.L., Galy, A., Barrat, J.A., Zanda, B. (2015) Mn–Cr systematics in primitive meteorites: Insights from mineral separation and partial dissolution. Geochimica et Cosmochimica Acta 156, 1–24. https://doi.org/10.1016/j.gca.2015.02.008
) and average Pb–Pb phosphate ages of 4558.4 ± 5.0 Myr (2 s.e.) (open square, this study) are comparable to Mn–Cr, Al–Mg and Pb–Pb isochron ages measured for the NWA 011 (Bouvier et al., 2011Bouvier, A., Spivak-Birndorf, L.J., Brennecka, G.A., Wadhwa, M. (2011) New constraints on early Solar System chronology from Al–Mg and U–Pb isotope systematics in the unique basaltic achondrite Northwest Africa 2976. Geochimica et Cosmochimica Acta 75, 5310–5323. https://doi.org/10.1016/j.gca.2011.06.033
) and NWA 6704 (Amelin et al., 2019Amelin, Y., Koefoed, P., Iizuka, T., Fernandes, V.A., Huyskens, M.H., Yin, Q.Z., Irving, A.J. (2019) U–Pb, Rb–Sr and Ar–Ar systematics of the ungrouped achondrites Northwest Africa 6704 and Northwest Africa 6693. Geochimica et Cosmochimica Acta 245, 628–642. https://doi.org/10.1016/j.gca.2018.09.021
; Sanborn et al., 2019Sanborn, M.E., Wimpenny, J., Williams, C.D., Yamakawa, A., Amelin, Y., Irving, A.J., Yin, Q.Z. (2019) Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy. Geochimica et Cosmochimica Acta 245, 577–596. https://doi.org/10.1016/j.gca.2018.10.004
) grouplets. Tafassasset Hf–W age is however older than most CR2 individual chondrule ages obtained by Al–Mg (Schrader et al., 2017Schrader, D.L., Nagashima, K., Krot, A.N., Ogliore, R.C., Yin, Q.Z., Amelin, Y., Stirling, C.H., Kaltenbach, A. (2017) Distribution of 26Al in the CR chondrite chondrule-forming region of the protoplanetary disk. Geochimica et Cosmochimica Acta 201, 275–302. https://doi.org/10.1016/j.gca.2016.06.023
) and Pb–Pb (Amelin et al., 2002Amelin, Y., Krot, A.N., Hutcheon, I.D., Ulyanov, A.A. (2002) Lead isotopic ages of chondrules and calcium-aluminum–rich inclusions. Science 297, 1678–1683. https://doi.org/10.1126/science.1073950
; Bollard et al, 2017Bollard, J., Connelly, J.N., Whitehouse, M.J., Pringle, E.A., Bonal, L., Jørgensen, J.K., Nordlund, Å., Moynier, F., Bizzarro, M. (2017) Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules. Science Advances 3, https://doi.org/10.1126/sciadv.1700407
), and Hf–W average age obtained in CR chondrites (Budde et al., 2018Budde, G., Kruijer, T.S., Kleine, T. (2018) Hf–W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26Al in the solar nebula. Geochimica et Cosmochimica Acta 222, 284–304. https://doi.org/10.1016/j.gca.2017.10.014
) after CAIs. Symbols: circle = Al–Mg; full diamond = Hf–W; triangle = Mn–Cr; square = phosphate Pb–Pb; full square = Pb–Pb.
Figure 3 Thermal evolution model of the Tafassite parent body. (a) Fit quality χn as a function of the planetesimal accretion time t0 and radius R. Tafassite parent body is best fitted to have an accretion time t0 = 1.1+0.3−0.4 Myr and radius R >50 km. (b) Modelled thermal history curves based on Tafassasset Hf–W and Mn–Cr ages, and Tafassasset and T6–T7 Tafassite Pb–Pb Ca phosphate chronological records. The thermal history is shown for an object with R = 120 km and t0 = 1.1 Myr marked in (a) with a red dot, and is representative for bodies with an acceptable fit quality of χn ≤ 4. The fit depths for NWA 12455, Tafassasset, NWA 7317 and NWA 11561 are ∼4.1 km, ∼3.3 km, ∼3.1 km and ∼2.6 km, respectively.