A mantle source formed after the lunar magma ocean crystallisation for the 3000 Ma-old lunar basalts

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Using in situ Pb-Pb systematics by SIMS, we determined crystallisation ages and initial Pb isotope ratios of the meteorites North West Africa (NWA) 4734, LaPaz Icefield (LAP) 02224, LAP 02205, NWA 4734, Northeast Africa (NEA) 003 and a newly found meteorite, NWA 14178. Our investigation shows that these samples all belong to a unique chemical and age group, clearly distinct from any other magmatic episode and chemical group known from the Moon. The Pb isotope ratios suggest these basalts originated from a KREEP-free source. Monte Carlo simulations based on a three-stage model suggest a mantle source formed from a depleted mantle at 4260 Ma – that is, after the solidification of the LMO. This mantle source may have formed as a result of deep, crust-breaking impact. Earth and environmental sciences/Planetary science/Geochemistry Earth and environmental sciences/Planetary science/Meteoritics Earth and environmental sciences/Planetary science/Inner planets Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Sequential crystallisation of the Lunar Magma Ocean (LMO) is the current overarching model explaining the formation of basaltic magma sources in the lunar mantle (Warren & Wasson, 1979 ; Warren, 1985 ). This model is satisfactory to explain the occurrence of the three main chemical groups of lunar basalts: the dominant group of low- and very low titanium content (LTi Sensus Lato) basalts would originate from the first, olivine-rich cumulates; the less abundant high-titanium content (HTi) basalts would derive from ilmenite-rich cumulates formed towards the end of the crystallisation of the LMO and finally, the last dregs of liquid, particularly enriched in incompatible elements would crystallise to form the source of the Potassium (K), Rare Earth Elements (REE) and Phosphorus (P)-enriched or KREEP basalts (Warren & Wasson, 1979 ; Neal & Taylor, 1992 ; Giguere et al., 2000 ; Joy et al., 2008 ; Elardo et al., 2011 ; Elkins-Tanton et al., 2011 ). As a consequence, the LTi basalts are expected to be depleted in incompatible elements and have unradiogenic isotope ratios. On the other hand, the KREEP basalts are the most REE-enriched type and have radiogenic initial Sr-Nd-isotope ratios (e.g. Neal and Taylor, 1992 ; Shearer et al., 2006 ; Elardo et al., 2014 ; Borg et al., 2019 ; Snape et al., 2019 ; Tian et al., 2021 ). The LTi basalts are, however, far from homogenous in terms of chemical characteristics (e.g. Neal and Taylor, 1992 ), displaying a wide range of REE enrichment and Sr-Nd-Pb isotope ratios (e.g. Neal and Taylor, 1992 ; Joy and Arai, 2013 ; Elardo et al., 2014 ; Snape et al., 2019 ). These features are usually interpreted as consistent with the identification of a variable contribution from a KREEP component to the chemical characteristics of many lunar basalts (e.g. Jolliff et al., 2003 ; Korotev et al., 2011 ), added either to their sources or assimilated during their assent (e.g. Neal & Taylor, 1992 ; Snyder et al., 1994 ; Sprung et al., 2013 , Hallis et al., 2014 ; Merle et al., 2024 ). This is further supported by the identification of a systematic decrease of the initial 207 Pb/ 206 Pb and 204 Pb/ 206 Pb ratios observed within the LTi basalts dated between 3400 Ma and approximately 3100 Ma that has been interpreted as an increasing contribution of a KREEP-like component in the younger basalts (Snape et al., 2019 ; Merle et al., 2020 ). This evolutionary model for LTi basalts is, however, complicated by a group of basalts erupted around 3000 Ma. This group of basalts includes meteorites NWA 4734, LAP 02205 and LAP 02224 (Rankenburg et al., 2007 ; Borg et al., 2009; Wang et al., 2012 ; Elardo et al., 2014 ). All of these basaltic rocks seem to show rather similar textural, petrological and geochemical characteristics (e.g. Day et al., 2006 ; Connolly et al., 2008 ; Fernandes et al., 2009 ; Wang et al., 2012 ; Elardo et al., 2014 ). The chemical characteristics, in particular the enrichment in incompatible trace elements in these basalts, seem to indicate a derivation from an enriched source. However, the origin of this enrichment is not clear as it was first attributed to the involvement of a KREEP component (Wang et al., 2012 ). However, the higher Ti/Sm, lower (La/Yb) n as well as the lower 87 Rb/ 86 Sr and higher 147 Sm/ 143 Nd source ratios compared to those in KREEP basalts, seem to preclude the involvement of a KREEP-like component (Elardo et al., 2014 ). This might be supported by the only initial Pb isotope ratios determined in NWA 4734, which, unlike the majority of LTi basalts, does not fit a mixing model between a KREEP-like component and low-µ mantle source (Merle et al., 2024 ). However, this latter observation may not be robust as the Pb isotope ratios determined in NWA 4734 might be underestimated (Merle et al., 2024 ). Therefore, the origin of the chemical characteristics of NWA 4734 and LAP samples is not well understood. The lack of agreement concerning the ages of the LAP samples further complicates the interpretation of the chemical data in terms of defining a single chemical group formed at 3000 Ma. These samples have been dated using 40 Ar/ 39 Ar, Rb-Sr, Sm-Nd and U-Pb techniques yielding dates between 3150 and 2889 Ma (Nyquist et al., 2005 ; Anand et al. 2006 ; Rankenburg et al., 2007 ; Fernandes et al., 2009 ; Zhang et al., 2010 ; Wang et al., 2012 ). This age range partly overlaps the age of (1) the Northeast Africa (NEA) 003 meteorite which has been dated through a four point Sm-Nd isochron at 3089 Ma with a precision exceeding 2% (Haloda et al., 2009 ) and (2) the NWA 773 clan (~ 3089 − 3017 Ma, Borg et al., 2009; Shaulis et al., 2017 ; Merle et al., 2020 ) which has the strongest KREEP affinity among the other LTI basalts (Jolliff et al., 2003 ; Merle et al., 2020 ) at the extremity of the Pb isotope trend displayed by the LTi basalts between 3400 Ma and 3100 Ma (Merle et al., 2020 ). The goal of this investigation is to (1) determine whether NWA 4734, the LAP meteorites and NEA 003 belong to a single chemical group formed by basalts erupted at 3000 Ma and (2) decipher the origin of the chemical characteristics of these samples, in particular the involvement of a KREEP-like component. To achieve this, we have determined precise Pb-Pb ages and initial Pb isotopic composition for LAP 02205, LAP 02224 and NEA 003 using SIMS (Secondary Ion Mass Spectrometry). We have also re-investigated the sample NWA 4734 to better constrain its initial Pb isotopic composition. Finally, we have determined major and trace element contents (see supporting information in supplementary material), age and initial Pb isotopic ratios of a newly-recovered meteorite, NWA 14178, which also belongs to this chemical group. Results Images of the investigated samples, full U-Pb dataset and summary of initial Pb isotope ratios are provided in supplementary material (Figs. A1 and A2 and Tables A2 and A3). In NWA 14178, plagioclase, potassium feldspar, phosphate, sulphides and silica-rich phases were identified from the SEM images (Fig. A1 in supplementary material) and fifty-five in-situ analyses of Pb isotope ratios were made (Fig. 1 a). After filtering for removing data suspected to be contaminated by terrestrial Pb, forty-two were used to construct a Pb-Pb isochron which yielded an age of 2963 ± 40 Ma (95% confidence, MSWD = 1.3, P = 0.085; Fig. 1 b). The feldspar analysis at the extremity of the isochron had the highest 207 Pb/ 206 Pb ratio of the dataset used to construct the isochron (analysis Kfeld88: 204 Pb/ 206 Pb = 0.00216 ± 0.00117; 207 Pb/ 206 Pb = 0.948 ± 0.019, 2σ; Fig. 1 b). This isochron, however, excludes the highest 207 Pb/ 206 Pb of the entire dataset, suggesting the latter does not represent the true Pb initial isotopic composition. We therefore applied the approach outlined by Snape et al. ( 2016 ), where the best estimate of the initial Pb isotopic composition is determined by the intersection between the isochron and the regression formed by the composition of modern terrestrial Pb represented by the composition of Earth’s average crust (Stacey & Kramers, 1975 ) and the data with the highest measured 207 Pb/ 206 Pb ratio of the dataset (Fig. 1 a). By applying this method, we obtained 204 Pb/ 206 Pb = 0.00244 ± 0.00013 (2σ) and 207 Pb/ 206 Pb = 0.968 ± 0.020 (2σ). In the basaltic clast identified in NEA 003 (Fig A2 in supplementary material), 74 analyses were made in potassium feldspars, phosphates and sulphides (Fig. 1 c). An isochron was obtained from fourteen data (Fig. 1 d). The isochron yielded an age of 2995 ± 17 Ma (95% confidence, MSWD = 1.6, P = 0.083). One sulphide at the unradiogenic end of the isochron yielded the highest 207 Pb/ 206 Pb ratio of the entire set and is considered as representing the best estimate of the initial Pb isotope composition: 204 Pb/ 206 Pb = 0.00293 ± 0.00085 (2σ) and 207 Pb/ 206 Pb = 0.9300 ± 0.016 (2σ). 79 data points were acquired from the sample LAP 02224 (Fig. 2 a) among which 49 form a robust isochron after removing the data showing terrestrial Pb contamination (Fig. 2 b). The isochron yielded an age of 2977 ± 13 Ma (95% confidence, MSWD = 1.3, P = 0.11). One sulphide analysis displays the highest 207 Pb/ 206 Pb ratios of the entire dataset (Fig. 1 b) and is considered as the best estimate for the initial Pb isotope composition: 204 Pb/ 206 Pb = 0.00244 ± 0.00076 (2σ) and 207 Pb/ 206 Pb = 1.008 ± 0.015 (2σ). 75 analyses were made in sample LAP 02205 (Fig. 2 c). After filtering for terrestrial contamination, the 63 remaining data form an isochron yielding an age of 2993 ± 9 Ma (95% confidence, MSWD = 0.95, P = 0.59; Fig. 2 d). One analysis made in a potassium feldspar and located at the end of the isochron, displays the highest 207 Pb/ 206 Pb ratios of the whole dataset (Fig. 2 d) and is considered as possible proxy for the initial Pb isotope composition: 204 Pb/ 206 Pb ratios = 0.00245 ± 0.00056 (2σ); 207 Pb/ 206 Pb = 0.955 ± 0.024 (2σ). 72 analyses were made in sample NWA 4734. Combining these new data with the 20 data published by Merle et al. ( 2020 ), and filtering the new dataset for terrestrial contamination (Fig. 2 e), 73 remaining data form an isochron yielding an age of 2979 ± 12 Ma (95% confidence, MSWD = 0.89, P = 072, Fig. 2 f). One analysis of potassium feldspar yielded the highest 207 Pb/ 206 Pb ratio of the entire dataset ( 204 Pb/ 206 Pb = 0.00267 ± 0.00027; 207 Pb/ 206 Pb = 1.005 ± 0.013). As this analysis plots on the isochron, we consider it as the best estimate of the isotopic ratio of the initial Pb for this sample. These ratios are higher than those previously obtained by Merle et al. ( 2020 ) but similar within uncertainties to the other isotope ratios of initial Pb obtained from the other samples investigated in the present study. Discussion Our new ages for the five investigated samples are all similar within uncertainties and yield an average age of 2986 ± 6 Ma (2σ). The new ages overlap with those previously obtained by other methods (Rankenburg et al., 2007 ; Haloda et al., 2009 ; Wang et al., 2012 ; Merle et al., 2020 ). The new ages for LAP 02205 and NEA 003 are slightly younger than those previously determined by the Pb-Pb and Sm-Nd methods (Rankenburg et al., 2007 ; Haloda et al., 2009 ; Wang et al., 2012 ) but are more precise (Fig. 3 a). Potential analytical and methodological issues have been documented for previously published dates for LAP 02205 and NEA 003 (Merle et al., 2020 ) that could explain the differences between new and previously published dates. The apparent age overlap between the 2990 Ma-old meteorites and the NWA 773 clan can be attributed to the NEA 003 and LAP 02205 dates with potential methodological and analytical issues already mentioned and for sample NWA 773 (Borg et al., 2009) which was obtained from a three-point isochron then cannot not be considered as robust (Ludwig, 2009 ). Once these data have been removed, the dates from NWA 773 clan and 2990 Ma-old meteorites form two distinct age peaks in a probability density plot (Fig. 3 b). We note that the age of the NWA 4734 clan is also distinct from a younger volcanic event at 2950 ± 6 Ma and formed by the two other samples, NWA 032 and NWA 14137 (Borg et al., 2009; Xu et al., 2024 ). This further confirms that NWA 4734, LAP 02205 and LAP 02224 originated from the same volcanic event as previously suggested (Borg et al., 2009; Wang et al., 2012 ; Elardo et al., 2014 ). The major and trace element contents, including REE patterns of NWA 14178 are similar to those of NWA 4734, LAP 02205 and LAP 02224 and distinct from the other lunar basalts by being significantly more enriched (Fig. 4 and Fig. A4 in supplementary material), which requires an incompatible-element enriched source. The REE pattern of the NEA003 clast investigated by Haloda et al. ( 2009 ) is significantly different from those of the other samples but the REE composition of NWA 4734 can be modelled by fractional crystallisation of a mafic melt assuming a cumulate with the composition of NEA 003 (supported by its coarse-grained, cumulative texture; see supplementary material). This also supports the hypothesis that the five investigated samples form a single chemical group, the NWA 4734 clan. The 207 Pb/ 206 Pb and 204 Pb/ 206 Pb initial ratios of all five investigated samples overlap within uncertainties and are higher than those determined previously in NWA 4734 (Fig A5 in supplementary material). A weighted average can be calculated using the five determined 204 Pb/ 206 Pb ratios (0.00249 ± 0.00011, Fig. A5 in supplementary material) but no reliable average can be calculated from the 207 Pb/ 206 Pb ratios (Fig. A5). This suggests that all the investigated samples may have the same Pb isotopic composition but some 207 Pb/ 206 Pb ratios are underestimated, possibly due to the presence of trace U. Sample LAP 02224 displays data with 207 Pb/ 206 Pb ratios measured in potassium feldspars and sulphides that are among the highest of the data set (Table A2). The uncalibrated 238 UO/ 208 Pb ratio was analysed in this sample to give a qualitative estimate of the amount of U present in the minerals. This ratio is decreasing as the 207 Pb/ 206 Pb is increasing (Fig A6). Therefore, Pb present in minerals with the lowest 238 UO/ 208 Pb and the highest 207 Pb/ 206 Pb cannot be supported by in situ decay of U and represents the best estimate for the isotope composition of initial Pb. Three K-feldspar data from sample LAP 02224 form a regression (Fig. A7) with an intersect with the X-axis ( 207 Pb/ 206 Pb) at 1.004 ± 0.024 (2σ). This intercept is interpreted as representing the highest possible 207 Pb/ 206 Pb value from a K-feldspar with no U content then the best estimate for the initial Pb isotope composition. The SEM images of the analysed K-feldspars made after the SIMS analytical session show that the outlier data was made close to cracks (Fig. A8). This could explain why this data does not fit the regression formed by the other K-feldspars. Sulphides form a less robust two-point regression with an intersect with the X-axis (1.017 ± 0.015, 2σ; Fig. A7) that is similar to those of the K-feldspar regression and the weighted average value of the highest 207 Pb/ 206 Pb values determined in NEA 003, LAP 02224 and NWA4734 (1.002 ± 0.008, 2σ). Therefore, we consider the following values as the best estimate of the initial Pb isotope composition for the samples belonging to the NWA 4734 clan: 204 Pb/ 206 Pb = 0.00249 ± 0.00011 (2σ) and 207 Pb/ 206 Pb = 1.002 ± 0.008 (2σ). The initial Sr-Nd-Pb isotope ratios of the samples from the NWA 4734 clan are clearly distinct from those of the other lunar basalts, in particular, the low-Ti basalts (Fig. 5 ). The differences, in particular, in terms of 207 Pb/ 206 Pb ratios between the NWA 4734 clan and the other chemical groups, including the slightly older NWA 773 clan, are too large to be explained by the addition of radiogenic Pb produced by in-situ decay of U and derivation from a single source. The Sr-Nd-Pb isotopic characteristics of the majority of the low-Ti and high-Ti basalts have been explained by a binary mixing through time of material from an enriched KREEP-like reservoir and a more depleted source with a low µ ( 238 U/ 204 Pb) ratio (Fig. 5 ; Merle et al., 2024 ). However, the newly determined initial Pb isotope ratios in the investigated samples do not fit this binary mixing as the average Pb isotope composition of these samples do not plot on the mixing line at 3000 Ma between the KREEP reservoir and the low-µ source (Fig. 5 a). The previously published Sr-Nd isotope systematics obtained for these samples also do not plot on the 3000 Ma mixing line (Fig. 5 b) confirming that these samples do not fit the mixing model. Initial Pb isotope ratios of NWA 14137 are close to those of the NWA 4734 clan but the younger age of these samples and lack of REE data preclude assignment of this sample to the NWA 4734 group. The initial Pb isotope composition of this sample plots close to the mixing line at 2900 Ma between KREEP and low-µ mantle components (Merle et al., 2024 ) suggesting that the model can be appropriate for this sample so long the initial Pb isotope composition is correct. Therefore, the NWA 4734 clan represents a single volcanic event in the history and characterised by unique chemistry. The chemical characteristics of the NWA 4734 clan have been interpreted as either (1) addition of enriched (KREEP) material through assimilation by ascending magmas (Wang et al., 2012 ) or (2) melting of an enriched source formed at the end of the LMO crystallisation (Elardo et al., 2014 ). By not fitting into the KREEP-low µ mixing model, the Sr-Nd-Pb isotopic characteristics of the NWA 4734 clan support the interpretation ruling out a contribution of urKREEP to the chemical characteristics of NWA 4734 clan (Elardo et al., 2014 ). The misfit of the mixing model implies that the source of the NWA4734 clan must have been different and isolated from the KREEP mantle component. The Procellarum KREEP terrane (PKT) from which all the Apollo samples were collected, is strongly associated with the KREEP chemical characteristics (Jolliff et al., 2000 ) and LMO crystallisation sequence model (e.g. Elkins-Tanton, 2011). As the enriched chemical signature in the NWA 4734 clan is likely not related to the presence of a KREEP component, this suggests that (1) these 2990 Ma basalts might have originated from a volcanic unit geographically away from PKT and, (2) the presence of enriched domains in the lunar mantle distinct from PKT. To constrain the nature of the source of the lunar basalts, theoretical curves describing the evolution of Pb isotopic composition proved to be a useful tool (Snape et al., 2016 , 2019 ; Merle et al., 2024 ). Our present approach relied on Monte Carlo simulations to circumvent the limitation of several unconstrained parameters needed for the calculations (see supplementary material) and derived from the model used by Merle et al. ( 2024 ). This model does not rely on assumptions about the age of the Moon or formation of lunar mantle sources at the same time (Merle et al., 2024 ). The aim of the modelling was to determine a µ value and age of formation for the source of the NWA 4734 basalts (see details in supplementary material). We have tested two-stages (basalt source directly derived from the LMO) then three-stages models (basalt source derived from a mantle component which was differentiated from LMO). Only the latter model yielded results when the basalt source was differentiated from a low-µ type mantle source. We calculated a µ value of 1115 ± 58 and a source formation at 4261 Ma ± 20 Ma. Using these parameters, we have constructed a theoretical evolution curve matching the composition of the NWA 4734 clan basalts in the 204 Pb/ 206 Pb vs 207 Pb/ 206 Pb plot (Fig. 5 a). The calculated µ value is compatible with an enriched source which differentiated around 4260 Ma that is shortly after the final solidification of LMO estimated at 4336 Ma ± 32 Ma (Borg et al., 2019 ; 2020 ). Possible processes able to promote mantle differentiation (i.e. melting event) after its solidification include mantle overturn, convection, tidal heating, radioactive decay and possibly deep-basin forming impacts. The four first processes would require at least several tens to hundreds Myrs to trigger melting-induced mantle differentiation making these processes unsuitable to explain the formation of the source of the 3000-Ma old basalts. Alternatively, the period between 4200 Ma and 4000 Ma corresponds to a main phase of bombardment (Bottke and Norman, 2017) with possibly large crust-breaking impacts. Such large impacts would potentially reach the mantle and process it through melting and possibly degassing when exposed to vacuum. A mantle chemically processed by a deep impact is consistent with (1) the highly siderophile and platinum group element contents measured in the LAP samples higher than those in other lunar basalts (Anand et al., 2006 ; Day et al., 2007 ) as well as (2) REE and U-enriched mantle source by triggering large degassing of volatiles elements. Conclusions The five lunar basaltic meteorites investigated here form a single chemical group of lunar basalts, the NWA 4734 clan, which erupted at approximately 2990 Ma. The characteristics of these basalts, in particular their initial Pb composition, are incompatible with a contribution from a KREEP component as previously suggested. The mantle source of the NWA 4734 clan seems to have originated outside PKT, confirming the presence of enriched domains in the lunar mantle outside this area. Our new modelling suggests that this source was differentiated from a low-µ (depleted) mantle after the solidification of the LMO. 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Bizzarro, M. (2020). Pb-Pb ages and initial Pb isotopic composition of lunar meteorites: NWA 773 clan, NWA 4734, and Dhofar 287. Meteoritics and Planetary Science, 55 , 1808–1832. Merle, R. E., Nemchin A. A., Whitehouse M. J., Kenny G. G., Snape J. F. (2024). Pb isotope signature of a low-µ ( 238 U/ 204 Pb) lunar mantle component. Journal of Petrology , 65, egae062. Neal, C. R., Taylor, L. A. (1992). Petrogenesis of mare basalts: A record of lunar volcanism. Geochimica et Cosmochimica Acta , 56, 2177–2211. Nyquist, L. E., Shih, C.-Y., Reese, Y., Bogard, D. D. (2005). Age of lunar meteorite LAP 02205 and implications for impact-sampling of planetary surfaces. Lunar Planetary Science conference XXXVI, Abstract #1374. Rankenburg, K., Brandon, A. D., Norman, M. D. (2007). A Rb-Sr and Sm-Nd isotope geochronology and trace element study of lunar meteorite LaPaz Icefield 02205. Geochimica et Cosmochimica Acta , 71, 2120–2135. Shearer, C. K., Hess, P. C., Wieczorek, M. A., Pritchard, M. E., Parmentier, E. M., Borg, L. E., Longhi, J., Elkins-Tanton, L. T., Neal, C. R., Antonenko, I., Canup, R. M., Halliday, A. N., Grove, T. L., Hager, B. H., Lee, D.-C. C., Wiechert, U. (2006). Thermal and Magmatic Evolution of the Moon. Reviews in Mineralogy and Geochemistry , 60, 365–518. Sio, C. K., Borg, L. E., Cassata, W. S. (2020). The timing of lunar solidification and mantle overturn recorded in ferroan anorthosite 62237. Earth and Planetary Science Letters , 538, 116219. Shaulis, B. J., Righter, M., Lapen, T. J., Jolliff, B. L., Irving, A. J. (2017). 3.1 Ga crystallization age for magnesian and ferroan gabbro lithologies in the Northwest Africa 773 clan of lunar meteorites. Geochimica et Cosmochimica Acta 213: 435-456. Snape, J. F., Nemchin, A. A., Bellucci, J. J., Whitehouse, M. J., Tartèse, R., Barnes, J. J., Anand M., Crawford I. A., Joy K. H. (2016). Lunar basalt chronology, mantle differentiation and implications for determining the age of the Moon. Earth and Planetary Sciences Letters , 451, 149–158. Snape, J. F., Nemchin, A. A., Whitehouse, M. J., Merle, R. E., Hopkinson, T., Anand, M. (2019). The timing of basaltic volcanism at the Apollo landing sites. Geochimica et Cosmochimica Acta , 266, 29–53. Snyder, G. A., Lee, D.-C., Taylor, L. A., Halliday, A. N., Jerde, E. A. (1994). Evolution of the upper mantle of the Earth’s Moon: Neodymium and strontium isotopic constraints from high-Ti mare basalts. Geochimica et Cosmochimica Acta , 58, 4795–4808. Sprung, P., Kleine, T., Scherer, E. E. (2013). Isotopic evidence for chondritic Lu/Hf and Sm/Nd of the Moon. Earth and Planetary Science Letters , 380 , 77–87. Stacey, J. S., Kramers, J. D. (1975). Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters , 26, 207–221. Tian, H.-C., Wang, H., Chen, Y., Yang, W., Zhou, Q., Zhang, C., Lin, H.-L., Huang, C., Wu, S.-T., Jia, L.-H., Xu, L., Zhang, D., Li, X.-G., Chang, R., Yang, Y.-H., Xie, L.-W., Zhang, D.-P., Zhang, G.-L., Yang, S.-H., Wu, F.-Y. (2021). Non-KREEP origin for Chang’e-5 basalts in the Procellarum KREEP Terrane. Nature , 600, 59–63. Vermeesch, P. (2012). On the visualisation of detrital age distributions. Chemical Geology, 312-313, 190–194. Wang, Y., Hsu, W., Guan, Y., Li, X., Li, Q., Liu, Y., Tang, G. (2012). Petrogenesis of the Northwest Africa 4734 basaltic lunar meteorite. Geochimica et Cosmochimica Acta , 92, 329–344. Warren, P. H. (1985). The magma ocean concept and lunar evolution. Annual Review of Earth and Planetary Sciences , 13, 201–240. Warren, P. H., Wasson, J. T. (1979). the origin of KREEP. Reviews of Geophysics and Space Physics , 17, 73–88. Xu, J.-Y., Li, Q.-L., Lu, K., Li, X.-H. (2024). Chang’e-5 basalt-like non-KREEP young lunar meteorite. Science Bulletin , 69, 601–605. Zhang, A., Hsu, W., Li, Q., Liu,Y., Jiang, Y., Tang, G. (2010). SIMS Pb/Pb dating of Zr-rich minerals in lunar meteorites Miller Range 05035 and LaPaz Icefield 02224: implications for the petrogenesis of mare basalt. Science China-Earth Sciences, 53, 327–334. Additional Declarations There is NO Competing Interest. Supplementary Files supplementarymaterial.docx supplementary information master file FigA6.pdf supplementary material figure A6 FigA7.pdf supplementary material figure A7 FigA9.pdf supplementary material figure A9 FigA8.pdf supplementary material figure A8 FigA2.pdf supplementary material figure A2 figA4.pdf supplementary material figure A4 figA3.pdf supplementary material figure A3 figA5.pdf supplementary material figure A5 FigA1.pdf supplementary material figure A1 Cite Share Download PDF Status: Published Journal Publication published 22 Jan, 2026 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6530311","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":470867891,"identity":"78031524-0a5b-4096-804e-b5c85c7ed706","order_by":0,"name":"Renaud Merle","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA60lEQVRIiWNgGAWjYNACNhDB3MDwgUQtjA2MM0jWwsxDjGLz9t6Dn3nKGKL5pQ82Prb5ZSPHIJFjwPijArcWmTPnkqV5zjHkzuxLbDbO7UszBmlh5jmDW4sEUIE0bxtD7oYzjG3SuT2HExtAWhjb8GiRf2P8G6Rl/xnG9t+WPf/BWhh//sNnC48ZxBYexjZmhh8HwFoYeBvwaOHJMbOcc04id8YZxmbJ3oZkYzaeZwWHeY7h0cJ+xvjGmzKb3P4e5oMffvyxk+NnT9748EcNbi0wnRAK5GtQHB0gqAEB/pCgdhSMglEwCkYMAAClXUi4KQZr7wAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-9018-6862","institution":"Uppsala University","correspondingAuthor":true,"prefix":"","firstName":"Renaud","middleName":"","lastName":"Merle","suffix":""},{"id":470867892,"identity":"d00397f5-56c3-445b-b2a6-eefac57284b9","order_by":1,"name":"Cecile Deligny","email":"","orcid":"","institution":"Department of Geosciences, Swedish Museum of Natural History","correspondingAuthor":false,"prefix":"","firstName":"Cecile","middleName":"","lastName":"Deligny","suffix":""},{"id":470867893,"identity":"693426e9-b7b9-49de-82b9-1889fe367bad","order_by":2,"name":"Martin Whitehouse","email":"","orcid":"","institution":"Department of Geosciences, Swedish Museum of Natural History","correspondingAuthor":false,"prefix":"","firstName":"Martin","middleName":"","lastName":"Whitehouse","suffix":""},{"id":470867894,"identity":"041eda4c-dbd5-4609-b52f-ca9d98170d67","order_by":3,"name":"Gavin Kenny","email":"","orcid":"","institution":"Swedish Museum of Natural History","correspondingAuthor":false,"prefix":"","firstName":"Gavin","middleName":"","lastName":"Kenny","suffix":""},{"id":470867895,"identity":"8e9194da-95dc-46ab-8339-8fc672ec61ec","order_by":4,"name":"Kirsten Larsen","email":"","orcid":"","institution":"Centre for Star and Planet Formation","correspondingAuthor":false,"prefix":"","firstName":"Kirsten","middleName":"","lastName":"Larsen","suffix":""}],"badges":[],"createdAt":"2025-04-25 15:41:47","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6530311/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6530311/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s43247-025-03002-9","type":"published","date":"2026-01-22T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84795512,"identity":"21c94b02-ab4a-419e-9c12-0b61a059bb4c","added_by":"auto","created_at":"2025-06-17 12:19:26","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":380192,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb \u003cem\u003evs.\u003c/em\u003e \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb plot for NWA 14178 and NEA 003. All data points are represented as error crosses. In panels (a) and (c), black crosses are data used for the isochron and light grey crosses are data rejected for the isochron construction. Also shown, the composition of average modern terrestrial Pb from Stacey and Kramers (1975). The intersect between the isochron and the two-points regression formed by the composition of modern terrestrial Pb and the analysis from NWA 14178 with the highest measured \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratio, yields the best estimate of the composition of the initial Pb composition. In the panels (b) and (d), only data used to construct the isochron are shown. Red crosses: phosphates; blue crosses: K-feldspars; black crosses: sulphides.\u003c/p\u003e","description":"","filename":"fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/11c1f0da570c33f49349a514.jpg"},{"id":84796690,"identity":"896d3d43-e5a3-4dc3-b6b0-543fc7ce888f","added_by":"auto","created_at":"2025-06-17 12:27:26","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":523873,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb \u003cem\u003evs.\u003c/em\u003e \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb plot for LAP 02224, LAP 02205 and NWA 4734. All data points are represented as error crosses. In the panels (a), (c) and (e), black crosses are data used for the isochron and light grey crosses are data rejected for the isochron construction. Also shown, the composition of average modern terrestrial Pb from Stacey and Kramers (1975). In the panels (b), (d) and (f), only data used to construct the isochron are shown. Red crosses: phosphates; blue crosses: K-feldspars; black crosses: sulphides; green crosses: phosphate-K feldspar mixtures and yellow crosses: baddeleyites.\u003c/p\u003e","description":"","filename":"fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/bf639b59c8350a24224ce3e4.jpg"},{"id":84795515,"identity":"4beacdf0-c4ac-42e8-b97f-1bec3d7608f1","added_by":"auto","created_at":"2025-06-17 12:19:26","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":428227,"visible":true,"origin":"","legend":"\u003cp\u003e(a) compilation of the dates from the LAP samples, NEA 003, NWA 4734 and NWA 14178 lunar basalts. Also indicated, the age data for the NWA 773 clan. All the previously published data reported here, have been screened for data quality in Merle et al. (2020). Only data with uncertainties lower or equal to 2% are considered as significant for high-resolution chronology and are represented. Data with potnetial analytical or methodological issues are represented as dash lined boxes. Data from Borg et al. (2009); Wang et al., 2012; Elardo et al. (2014); Merle et al. (2020, this work); Rankenburg et al. (2007); Shaulis et al. (2017); Snape et al. (2016, 2018, 2019); (b) ages distribution plot for the NWA 4734 and NWA 773 clans, based on Probability Density Plot (PDP) and using the Density plotter algorithm (Vermeesh, 2012). The circles at the bottom of the plot indicate the number of samples.\u003c/p\u003e","description":"","filename":"fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/3f469008637102a303bc3702.jpg"},{"id":84796688,"identity":"53e3a3c3-8ab3-4f3e-aeb4-eaa5eddfde92","added_by":"auto","created_at":"2025-06-17 12:27:26","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":343986,"visible":true,"origin":"","legend":"\u003cp\u003eRare Earth Element patterns of NWA14178 compared to other low-Ti basalts. The pattern of the NWA 773 clan and other meteorites dated at 3000 Ma are indicated. Carbonaceous chondrites normalisation values according to Sun and McDonough, 1989. Same references as previous figure for the lunar basalts.\u003c/p\u003e","description":"","filename":"fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/da9849dcff0500ef91b170f2.jpg"},{"id":84795521,"identity":"18af49e0-50fc-412d-b95a-c1fb945380cf","added_by":"auto","created_at":"2025-06-17 12:19:26","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":711161,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Initial Pb isotopic composition of lunar basalts plotted as \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb \u003cem\u003evs.\u003c/em\u003e \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb. Dash lines between these evolution curves are mixing lines at a given time. Details regarding the construction of the theoretical curves displaying the isotopic evolution of KREEP and low-µ mantle components and mixing parameters are given in Merle et al. (2024). Pb isotope data from Snape et al. (2016, 2019) and Merle et al. (2020, 2024 and this work). The green curve showing the theoretical evolution of the isotopic composition of the source of the NWA 4734 clan (see text for details of construction parameters). (b) Initial \u003csup\u003e143\u003c/sup\u003eNd/\u003csup\u003e144\u003c/sup\u003eNd vs \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr of lunar basalts. Measured ratios were corrected for \u003cem\u003ein situ\u003c/em\u003e decay using ages from Snape et al. (2019) for Apollo rocks and from Merle et al. (2020, 2024) and this work for meteorites. Dash lines between these evolution curves are mixing lines at a given time. Compilation of Nd and Sr data and related references, details of the construction of evolution curves and mixing parameters are given in Merle et al. (2024).\u003c/p\u003e","description":"","filename":"fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/bc5728dd6e1b12e1c59ab258.jpg"},{"id":102284771,"identity":"bf9ea035-c550-4ef6-959c-07c907edd85a","added_by":"auto","created_at":"2026-02-10 08:07:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2848066,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/22398524-2950-4696-bd88-c52a79e885ae.pdf"},{"id":84797079,"identity":"8e17f157-6669-4c40-a078-4a64de663bce","added_by":"auto","created_at":"2025-06-17 12:35:26","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":95443,"visible":true,"origin":"","legend":"supplementary information master 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A5","description":"","filename":"figA5.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/bdee0adde4cd91da96e7cf8f.pdf"},{"id":84795540,"identity":"bf770238-a47d-4047-a7c0-3c513305124e","added_by":"auto","created_at":"2025-06-17 12:19:27","extension":"pdf","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":6095000,"visible":true,"origin":"","legend":"supplementary material figure A1","description":"","filename":"FigA1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6530311/v1/6442969e442d032e50b77cb4.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"A mantle source formed after the lunar magma ocean crystallisation for the 3000 Ma-old lunar basalts","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSequential crystallisation of the Lunar Magma Ocean (LMO) is the current overarching model explaining the formation of basaltic magma sources in the lunar mantle (Warren \u0026amp; Wasson, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Warren, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). This model is satisfactory to explain the occurrence of the three main chemical groups of lunar basalts: the dominant group of low- and very low titanium content (LTi Sensus Lato) basalts would originate from the first, olivine-rich cumulates; the less abundant high-titanium content (HTi) basalts would derive from ilmenite-rich cumulates formed towards the end of the crystallisation of the LMO and finally, the last dregs of liquid, particularly enriched in incompatible elements would crystallise to form the source of the Potassium (K), Rare Earth Elements (REE) and Phosphorus (P)-enriched or KREEP basalts (Warren \u0026amp; Wasson, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Neal \u0026amp; Taylor, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Giguere et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Joy et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Elardo et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Elkins-Tanton et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). As a consequence, the LTi basalts are expected to be depleted in incompatible elements and have unradiogenic isotope ratios. On the other hand, the KREEP basalts are the most REE-enriched type and have radiogenic initial Sr-Nd-isotope ratios (e.g. Neal and Taylor, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Shearer et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Borg et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Snape et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The LTi basalts are, however, far from homogenous in terms of chemical characteristics (e.g. Neal and Taylor, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), displaying a wide range of REE enrichment and Sr-Nd-Pb isotope ratios (e.g. Neal and Taylor, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Joy and Arai, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Snape et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These features are usually interpreted as consistent with the identification of a variable contribution from a KREEP component to the chemical characteristics of many lunar basalts (e.g. Jolliff et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Korotev et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), added either to their sources or assimilated during their assent (e.g. Neal \u0026amp; Taylor, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Snyder et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Sprung et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, Hallis et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This is further supported by the identification of a systematic decrease of the initial \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb and \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios observed within the LTi basalts dated between 3400 Ma and approximately 3100 Ma that has been interpreted as an increasing contribution of a KREEP-like component in the younger basalts (Snape et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis evolutionary model for LTi basalts is, however, complicated by a group of basalts erupted around 3000 Ma. This group of basalts includes meteorites NWA 4734, LAP 02205 and LAP 02224 (Rankenburg et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Borg et al., 2009; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). All of these basaltic rocks seem to show rather similar textural, petrological and geochemical characteristics (e.g. Day et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Connolly et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Fernandes et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The chemical characteristics, in particular the enrichment in incompatible trace elements in these basalts, seem to indicate a derivation from an enriched source. However, the origin of this enrichment is not clear as it was first attributed to the involvement of a KREEP component (Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). However, the higher Ti/Sm, lower (La/Yb)\u003csub\u003en\u003c/sub\u003e as well as the lower \u003csup\u003e87\u003c/sup\u003eRb/\u003csup\u003e86\u003c/sup\u003eSr and higher \u003csup\u003e147\u003c/sup\u003eSm/\u003csup\u003e143\u003c/sup\u003eNd source ratios compared to those in KREEP basalts, seem to preclude the involvement of a KREEP-like component (Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). This might be supported by the only initial Pb isotope ratios determined in NWA 4734, which, unlike the majority of LTi basalts, does not fit a mixing model between a KREEP-like component and low-\u0026micro; mantle source (Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, this latter observation may not be robust as the Pb isotope ratios determined in NWA 4734 might be underestimated (Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Therefore, the origin of the chemical characteristics of NWA 4734 and LAP samples is not well understood.\u003c/p\u003e \u003cp\u003eThe lack of agreement concerning the ages of the LAP samples further complicates the interpretation of the chemical data in terms of defining a single chemical group formed at 3000 Ma. These samples have been dated using \u003csup\u003e40\u003c/sup\u003eAr/\u003csup\u003e39\u003c/sup\u003eAr, Rb-Sr, Sm-Nd and U-Pb techniques yielding dates between 3150 and 2889 Ma (Nyquist et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Anand et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Rankenburg et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Fernandes et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). This age range partly overlaps the age of (1) the Northeast Africa (NEA) 003 meteorite which has been dated through a four point Sm-Nd isochron at 3089 Ma with a precision exceeding 2% (Haloda et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) and (2) the NWA 773 clan (~\u0026thinsp;3089\u0026thinsp;\u0026minus;\u0026thinsp;3017 Ma, Borg et al., 2009; Shaulis et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) which has the strongest KREEP affinity among the other LTI basalts (Jolliff et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) at the extremity of the Pb isotope trend displayed by the LTi basalts between 3400 Ma and 3100 Ma (Merle et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe goal of this investigation is to (1) determine whether NWA 4734, the LAP meteorites and NEA 003 belong to a single chemical group formed by basalts erupted at 3000 Ma and (2) decipher the origin of the chemical characteristics of these samples, in particular the involvement of a KREEP-like component. To achieve this, we have determined precise Pb-Pb ages and initial Pb isotopic composition for LAP 02205, LAP 02224 and NEA 003 using SIMS (Secondary Ion Mass Spectrometry). We have also re-investigated the sample NWA 4734 to better constrain its initial Pb isotopic composition. Finally, we have determined major and trace element contents (see supporting information in supplementary material), age and initial Pb isotopic ratios of a newly-recovered meteorite, NWA 14178, which also belongs to this chemical group.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eImages of the investigated samples, full U-Pb dataset and summary of initial Pb isotope ratios are provided in supplementary material (Figs. A1 and A2 and Tables A2 and A3).\u003c/p\u003e \u003cp\u003eIn NWA 14178, plagioclase, potassium feldspar, phosphate, sulphides and silica-rich phases were identified from the SEM images (Fig. A1 in supplementary material) and fifty-five in-situ analyses of Pb isotope ratios were made (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). After filtering for removing data suspected to be contaminated by terrestrial Pb, forty-two were used to construct a Pb-Pb isochron which yielded an age of 2963\u0026thinsp;\u0026plusmn;\u0026thinsp;40 Ma (95% confidence, MSWD\u0026thinsp;=\u0026thinsp;1.3, P\u0026thinsp;=\u0026thinsp;0.085; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe feldspar analysis at the extremity of the isochron had the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratio of the dataset used to construct the isochron (analysis Kfeld88: \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.00216\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00117; \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.948\u0026thinsp;\u0026plusmn;\u0026thinsp;0.019, 2σ; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). This isochron, however, excludes the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb of the entire dataset, suggesting the latter does not represent the true Pb initial isotopic composition. We therefore applied the approach outlined by Snape et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), where the best estimate of the initial Pb isotopic composition is determined by the intersection between the isochron and the regression formed by the composition of modern terrestrial Pb represented by the composition of Earth\u0026rsquo;s average crust (Stacey \u0026amp; Kramers, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1975\u003c/span\u003e) and the data with the highest measured \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratio of the dataset (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). By applying this method, we obtained \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.00244\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00013 (2σ) and \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.968\u0026thinsp;\u0026plusmn;\u0026thinsp;0.020 (2σ).\u003c/p\u003e \u003cp\u003eIn the basaltic clast identified in NEA 003 (Fig A2 in supplementary material), 74 analyses were made in potassium feldspars, phosphates and sulphides (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). An isochron was obtained from fourteen data (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). The isochron yielded an age of 2995\u0026thinsp;\u0026plusmn;\u0026thinsp;17 Ma (95% confidence, MSWD\u0026thinsp;=\u0026thinsp;1.6, P\u0026thinsp;=\u0026thinsp;0.083). One sulphide at the unradiogenic end of the isochron yielded the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratio of the entire set and is considered as representing the best estimate of the initial Pb isotope composition: \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.00293\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00085 (2σ) and \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.9300\u0026thinsp;\u0026plusmn;\u0026thinsp;0.016 (2σ).\u003c/p\u003e \u003cp\u003e79 data points were acquired from the sample LAP 02224 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) among which 49 form a robust isochron after removing the data showing terrestrial Pb contamination (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The isochron yielded an age of 2977\u0026thinsp;\u0026plusmn;\u0026thinsp;13 Ma (95% confidence, MSWD\u0026thinsp;=\u0026thinsp;1.3, P\u0026thinsp;=\u0026thinsp;0.11). One sulphide analysis displays the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios of the entire dataset (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) and is considered as the best estimate for the initial Pb isotope composition: \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.00244\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00076 (2σ) and \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 1.008\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015 (2σ).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e75 analyses were made in sample LAP 02205 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). After filtering for terrestrial contamination, the 63 remaining data form an isochron yielding an age of 2993\u0026thinsp;\u0026plusmn;\u0026thinsp;9 Ma (95% confidence, MSWD\u0026thinsp;=\u0026thinsp;0.95, P\u0026thinsp;=\u0026thinsp;0.59; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). One analysis made in a potassium feldspar and located at the end of the isochron, displays the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios of the whole dataset (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) and is considered as possible proxy for the initial Pb isotope composition: \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios\u0026thinsp;=\u0026thinsp;0.00245\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00056 (2σ); \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.955\u0026thinsp;\u0026plusmn;\u0026thinsp;0.024 (2σ).\u003c/p\u003e \u003cp\u003e72 analyses were made in sample NWA 4734. Combining these new data with the 20 data published by Merle et al. (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), and filtering the new dataset for terrestrial contamination (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), 73 remaining data form an isochron yielding an age of 2979\u0026thinsp;\u0026plusmn;\u0026thinsp;12 Ma (95% confidence, MSWD\u0026thinsp;=\u0026thinsp;0.89, P\u0026thinsp;=\u0026thinsp;072, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). One analysis of potassium feldspar yielded the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratio of the entire dataset (\u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.00267\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00027; \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 1.005\u0026thinsp;\u0026plusmn;\u0026thinsp;0.013). As this analysis plots on the isochron, we consider it as the best estimate of the isotopic ratio of the initial Pb for this sample. These ratios are higher than those previously obtained by Merle et al. (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) but similar within uncertainties to the other isotope ratios of initial Pb obtained from the other samples investigated in the present study.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur new ages for the five investigated samples are all similar within uncertainties and yield an average age of 2986\u0026thinsp;\u0026plusmn;\u0026thinsp;6 Ma (2σ). The new ages overlap with those previously obtained by other methods (Rankenburg et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Haloda et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The new ages for LAP 02205 and NEA 003 are slightly younger than those previously determined by the Pb-Pb and Sm-Nd methods (Rankenburg et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Haloda et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) but are more precise (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Potential analytical and methodological issues have been documented for previously published dates for LAP 02205 and NEA 003 (Merle et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) that could explain the differences between new and previously published dates. The apparent age overlap between the 2990 Ma-old meteorites and the NWA 773 clan can be attributed to the NEA 003 and LAP 02205 dates with potential methodological and analytical issues already mentioned and for sample NWA 773 (Borg et al., 2009) which was obtained from a three-point isochron then cannot not be considered as robust (Ludwig, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Once these data have been removed, the dates from NWA 773 clan and 2990 Ma-old meteorites form two distinct age peaks in a probability density plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). We note that the age of the NWA 4734 clan is also distinct from a younger volcanic event at 2950\u0026thinsp;\u0026plusmn;\u0026thinsp;6 Ma and formed by the two other samples, NWA 032 and NWA 14137 (Borg et al., 2009; Xu et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This further confirms that NWA 4734, LAP 02205 and LAP 02224 originated from the same volcanic event as previously suggested (Borg et al., 2009; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe major and trace element contents, including REE patterns of NWA 14178 are similar to those of NWA 4734, LAP 02205 and LAP 02224 and distinct from the other lunar basalts by being significantly more enriched (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Fig. A4 in supplementary material), which requires an incompatible-element enriched source. The REE pattern of the NEA003 clast investigated by Haloda et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) is significantly different from those of the other samples but the REE composition of NWA 4734 can be modelled by fractional crystallisation of a mafic melt assuming a cumulate with the composition of NEA 003 (supported by its coarse-grained, cumulative texture; see supplementary material). This also supports the hypothesis that the five investigated samples form a single chemical group, the NWA 4734 clan.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb and \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb initial ratios of all five investigated samples overlap within uncertainties and are higher than those determined previously in NWA 4734 (Fig A5 in supplementary material). A weighted average can be calculated using the five determined \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios (0.00249\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00011, Fig. A5 in supplementary material) but no reliable average can be calculated from the \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios (Fig. A5). This suggests that all the investigated samples may have the same Pb isotopic composition but some \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios are underestimated, possibly due to the presence of trace U. Sample LAP 02224 displays data with \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios measured in potassium feldspars and sulphides that are among the highest of the data set (Table A2). The uncalibrated \u003csup\u003e238\u003c/sup\u003eUO/\u003csup\u003e208\u003c/sup\u003ePb ratio was analysed in this sample to give a qualitative estimate of the amount of U present in the minerals. This ratio is decreasing as the \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb is increasing (Fig A6). Therefore, Pb present in minerals with the lowest \u003csup\u003e238\u003c/sup\u003eUO/\u003csup\u003e208\u003c/sup\u003ePb and the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb cannot be supported by in situ decay of U and represents the best estimate for the isotope composition of initial Pb. Three K-feldspar data from sample LAP 02224 form a regression (Fig. A7) with an intersect with the X-axis (\u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb) at 1.004\u0026thinsp;\u0026plusmn;\u0026thinsp;0.024 (2σ). This intercept is interpreted as representing the highest possible \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb value from a K-feldspar with no U content then the best estimate for the initial Pb isotope composition. The SEM images of the analysed K-feldspars made after the SIMS analytical session show that the outlier data was made close to cracks (Fig. A8). This could explain why this data does not fit the regression formed by the other K-feldspars. Sulphides form a less robust two-point regression with an intersect with the X-axis (1.017\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015, 2σ; Fig. A7) that is similar to those of the K-feldspar regression and the weighted average value of the highest \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb values determined in NEA 003, LAP 02224 and NWA4734 (1.002\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008, 2σ). Therefore, we consider the following values as the best estimate of the initial Pb isotope composition for the samples belonging to the NWA 4734 clan: \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 0.00249\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00011 (2σ) and \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb = 1.002\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008 (2σ).\u003c/p\u003e \u003cp\u003eThe initial Sr-Nd-Pb isotope ratios of the samples from the NWA 4734 clan are clearly distinct from those of the other lunar basalts, in particular, the low-Ti basalts (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The differences, in particular, in terms of \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ratios between the NWA 4734 clan and the other chemical groups, including the slightly older NWA 773 clan, are too large to be explained by the addition of radiogenic Pb produced by in-situ decay of U and derivation from a single source. The Sr-Nd-Pb isotopic characteristics of the majority of the low-Ti and high-Ti basalts have been explained by a binary mixing through time of material from an enriched KREEP-like reservoir and a more depleted source with a low \u0026micro; (\u003csup\u003e238\u003c/sup\u003eU/\u003csup\u003e204\u003c/sup\u003ePb) ratio (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, the newly determined initial Pb isotope ratios in the investigated samples do not fit this binary mixing as the average Pb isotope composition of these samples do not plot on the mixing line at 3000 Ma between the KREEP reservoir and the low-\u0026micro; source (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The previously published Sr-Nd isotope systematics obtained for these samples also do not plot on the 3000 Ma mixing line (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) confirming that these samples do not fit the mixing model. Initial Pb isotope ratios of NWA 14137 are close to those of the NWA 4734 clan but the younger age of these samples and lack of REE data preclude assignment of this sample to the NWA 4734 group. The initial Pb isotope composition of this sample plots close to the mixing line at 2900 Ma between KREEP and low-\u0026micro; mantle components (Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) suggesting that the model can be appropriate for this sample so long the initial Pb isotope composition is correct. Therefore, the NWA 4734 clan represents a single volcanic event in the history and characterised by unique chemistry.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe chemical characteristics of the NWA 4734 clan have been interpreted as either (1) addition of enriched (KREEP) material through assimilation by ascending magmas (Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) or (2) melting of an enriched source formed at the end of the LMO crystallisation (Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). By not fitting into the KREEP-low \u0026micro; mixing model, the Sr-Nd-Pb isotopic characteristics of the NWA 4734 clan support the interpretation ruling out a contribution of urKREEP to the chemical characteristics of NWA 4734 clan (Elardo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe misfit of the mixing model implies that the source of the NWA4734 clan must have been different and isolated from the KREEP mantle component. The Procellarum KREEP terrane (PKT) from which all the Apollo samples were collected, is strongly associated with the KREEP chemical characteristics (Jolliff et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) and LMO crystallisation sequence model (e.g. Elkins-Tanton, 2011). As the enriched chemical signature in the NWA 4734 clan is likely not related to the presence of a KREEP component, this suggests that (1) these 2990 Ma basalts might have originated from a volcanic unit geographically away from PKT and, (2) the presence of enriched domains in the lunar mantle distinct from PKT.\u003c/p\u003e \u003cp\u003eTo constrain the nature of the source of the lunar basalts, theoretical curves describing the evolution of Pb isotopic composition proved to be a useful tool (Snape et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Our present approach relied on Monte Carlo simulations to circumvent the limitation of several unconstrained parameters needed for the calculations (see supplementary material) and derived from the model used by Merle et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This model does not rely on assumptions about the age of the Moon or formation of lunar mantle sources at the same time (Merle et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The aim of the modelling was to determine a \u0026micro; value and age of formation for the source of the NWA 4734 basalts (see details in supplementary material). We have tested two-stages (basalt source directly derived from the LMO) then three-stages models (basalt source derived from a mantle component which was differentiated from LMO). Only the latter model yielded results when the basalt source was differentiated from a low-\u0026micro; type mantle source. We calculated a \u0026micro; value of 1115\u0026thinsp;\u0026plusmn;\u0026thinsp;58 and a source formation at 4261 Ma\u0026thinsp;\u0026plusmn;\u0026thinsp;20 Ma. Using these parameters, we have constructed a theoretical evolution curve matching the composition of the NWA 4734 clan basalts in the \u003csup\u003e204\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb vs \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The calculated \u0026micro; value is compatible with an enriched source which differentiated around 4260 Ma that is shortly after the final solidification of LMO estimated at 4336 Ma\u0026thinsp;\u0026plusmn;\u0026thinsp;32 Ma (Borg et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePossible processes able to promote mantle differentiation (i.e. melting event) after its solidification include mantle overturn, convection, tidal heating, radioactive decay and possibly deep-basin forming impacts. The four first processes would require at least several tens to hundreds Myrs to trigger melting-induced mantle differentiation making these processes unsuitable to explain the formation of the source of the 3000-Ma old basalts. Alternatively, the period between 4200 Ma and 4000 Ma corresponds to a main phase of bombardment (Bottke and Norman, 2017) with possibly large crust-breaking impacts. Such large impacts would potentially reach the mantle and process it through melting and possibly degassing when exposed to vacuum. A mantle chemically processed by a deep impact is consistent with (1) the highly siderophile and platinum group element contents measured in the LAP samples higher than those in other lunar basalts (Anand et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Day et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) as well as (2) REE and U-enriched mantle source by triggering large degassing of volatiles elements.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe five lunar basaltic meteorites investigated here form a single chemical group of lunar basalts, the NWA 4734 clan, which erupted at approximately 2990 Ma. The characteristics of these basalts, in particular their initial Pb composition, are incompatible with a contribution from a KREEP component as previously suggested. The mantle source of the NWA 4734 clan seems to have originated outside PKT, confirming the presence of enriched domains in the lunar mantle outside this area. Our new modelling suggests that this source was differentiated from a low-\u0026micro; (depleted) mantle after the solidification of the LMO. The potential processes that led to the formation of this source remain elusive. Impact-related chemical processing of the mantle cannot be excluded.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnand, M., Taylor, L. A., Floss, C., Neal, C. R., Terada, K., Tanikawa, S. (2006). Petrology and geochemistry of LaPaz Icefield 02205: A new unique low-Ti mare-basalt meteorite. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e, 70, 246\u0026ndash;264. \u003c/li\u003e\n\u003cli\u003eAnand, M., Taylor, L. A., Misra, K. C., Demidova, S. I., Nazarov, M. A. (2003). 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SIMS Pb/Pb dating of Zr-rich minerals in lunar meteorites Miller Range 05035 and LaPaz Icefield 02224: implications for the petrogenesis of mare basalt. \u003cem\u003eScience China-Earth Sciences,\u003c/em\u003e 53, 327\u0026ndash;334. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6530311/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6530311/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThere is no satisfactory model explaining the incompatible element-enriched chemical characteristics observed in few approximately 3000 Ma-old, low-titanium (low-Ti) lunar basalts. Using in situ Pb-Pb systematics by SIMS, we determined crystallisation ages and initial Pb isotope ratios of the meteorites North West Africa (NWA) 4734, LaPaz Icefield (LAP) 02224, LAP 02205, NWA 4734, Northeast Africa (NEA) 003 and a newly found meteorite, NWA 14178. Our investigation shows that these samples all belong to a unique chemical and age group, clearly distinct from any other magmatic episode and chemical group known from the Moon. The Pb isotope ratios suggest these basalts originated from a KREEP-free source. Monte Carlo simulations based on a three-stage model suggest a mantle source formed from a depleted mantle at 4260 Ma \u0026ndash; that is, after the solidification of the LMO. This mantle source may have formed as a result of deep, crust-breaking impact.\u003c/p\u003e","manuscriptTitle":"A mantle source formed after the lunar magma ocean crystallisation for the 3000 Ma-old lunar basalts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-17 12:19:21","doi":"10.21203/rs.3.rs-6530311/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0e304aa7-f515-41a6-9c08-48fc0c4d0a91","owner":[],"postedDate":"June 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":50006520,"name":"Earth and environmental sciences/Planetary science/Geochemistry"},{"id":50006521,"name":"Earth and environmental sciences/Planetary science/Meteoritics"},{"id":50006522,"name":"Earth and environmental sciences/Planetary science/Inner planets"}],"tags":[],"updatedAt":"2026-02-10T08:06:54+00:00","versionOfRecord":{"articleIdentity":"rs-6530311","link":"https://doi.org/10.1038/s43247-025-03002-9","journal":{"identity":"communications-earth-and-environment","isVorOnly":false,"title":"Communications Earth \u0026 Environment"},"publishedOn":"2026-01-22 05:00:00","publishedOnDateReadable":"January 22nd, 2026"},"versionCreatedAt":"2025-06-17 12:19:21","video":"","vorDoi":"10.1038/s43247-025-03002-9","vorDoiUrl":"https://doi.org/10.1038/s43247-025-03002-9","workflowStages":[]},"version":"v1","identity":"rs-6530311","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6530311","identity":"rs-6530311","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}