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Introduction

The emergence of complex biogeochemical cycles on Earth is largely owed to the development of plate tectonics, yet it is also tectonics that has almost entirely destroyed Earth’s geochemical record of its origins. For example, the zircon age record implies that nearly half of Earth’s total crust was produced more than 2.5 Gyr ago (Korenaga, 2018

Korenaga, J. (2018) Estimating the formation age distribution of continental crust by unmixing zircon ages. Earth and Planetary Science Letters 482, 388–395. https://doi.org/10.1016/j.epsl.2017.11.039

), yet only ∼5 % of Earth’s modern surface is older than this age (Goodwin, 1996

Goodwin, A.M. (1996) Principles of Precambrian Geology. Academic Press, London.

). This means that our knowledge of Earth’s formational geological processes is fundamentally limited. There has been profitable research aimed at understanding Earth’s development through intensive study of these remnants of ancient geological material (Wilde et al., 2001

Wilde, S.A., Valley, J.W., Peck, W.H., Graham, C.M. (2001) Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature 409, 175–178. https://doi.org/10.1038/35051550

; Bennett et al., 2007

Bennett, V.C., Brandon, A.D., Nutman, A.P. (2007) Coupled ¹⁴²Nd-¹⁴³Nd Isotopic Evidence for Hadean Mantle Dynamics. Science 318, 1907–1910. https://doi.org/10.1126/science.1145928

; Reimink et al., 2014

Reimink, J.R., Chacko, T., Stern, R.A., Heaman, L.M. (2014) Earth’s earliest evolved crust generated in an Iceland-like setting. Nature Geoscience 7, 529–533. https://doi.org/10.1038/ngeo2170

); however, it is unknown whether these results present a complete perspective on Earth’s evolution.

Earth’s volcanic hotspots may represent a complementary view on early Earth processes that can partially remedy this preservation issue. It has long been recognised that the geochemical fingerprints of volcanic hotspots are among the most diverse of any terrestrial rock group. Some geochemical components of different volcanic hotspots have well constrained origins and may be more than 2.5 Gyr old, and therefore potential records of Earth’s geological conditions before the emergence of complex life. The origins of one potential reservoir, variably termed the ‘focus zone’ (FOZO, used preferentially here; cf. Hart et al., 1992

Hart, S.R., Hauri, E.H., Oschmann, L.A., Whitehead, J.A. (1992) Mantle Plumes and Entrainment: Isotopic Evidence. Science 256, 517–520. https://doi.org/10.1126/science.256.5056.517

), ‘common component’ (C), or ‘prevalent mantle’ (PREMA), have evaded conclusive agreement, but FOZO-like reservoirs have some remarkable geochemical characteristics. First, they have a geochemical signature that reflects less magmatic processing than the bulk upper mantle, but more magmatic processing than a theoretical chondritic primitive mantle—thus, FOZO reservoirs are said to be ‘moderately depleted’. Second, nearly all volcanic hotspots appear to tap some form of FOZO, while other geochemical components are unique to one or more hotspots; thus, it has been hypothesised that FOZO reservoirs are widespread in the deep mantle sources of volcanic hotspots. Finally, only hotspot lavas (collectively termed ocean island basalts: OIBs) with geochemical affinity for FOZO reservoirs are known to possess elevated ³He/⁴He ratios (Class and Goldstein, 2005

Class, C., Goldstein, S.L. (2005) Evolution of helium isotopes in the Earth’s mantle. Nature 436, 1107–1112. https://doi.org/10.1038/nature03930

; Jackson et al., 2007

Jackson, M., Kurz, M., Hart, S., Workman, R. (2007) New Samoan lavas from Ofu Island reveal a hemispherically heterogeneous high ³He/⁴He mantle. Earth and Planetary Science Letters 264, 360–374. https://doi.org/10.1016/j.epsl.2007.09.023

) (Fig. 1) compared to young mid-ocean ridge basalts (MORBs). Such elevated ³He/⁴He ratios are a primary signature of ancient geological material (Class and Goldstein, 2005

Class, C., Goldstein, S.L. (2005) Evolution of helium isotopes in the Earth’s mantle. Nature 436, 1107–1112. https://doi.org/10.1038/nature03930

). Thus, it is possible that these FOZO reservoirs are older than any other geochemical component of hotspot volcanism.

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Some of these unique geochemical characteristics have recently been linked to short-lived radiogenic isotope systems, which record the effects of early geological processes. Only OIBs with moderately depleted isotopic signatures preserve deficits in ¹⁸²W, which must have been generated in the first 1 % of Earth’s history (≳4.5 Gyr ago), compared to the bulk Earth (Fig. 1c). Similarly, heterogeneous ¹⁴²Nd compositions, which were generated in the first 10 % of Earth’s history (≳4.0 Gyr ago), are primarily observed in OIB samples with moderately depleted isotopic signatures (Horan et al., 2018

Horan, M.F., Carlson, R.W., Walker, R.J., Jackson, M., Garçon, M., Norman, M. (2018) Tracking Hadean processes in modern basalts with 142-Neodymium. Earth and Planetary Science Letters 484, 184–191. https://doi.org/10.1016/j.epsl.2017.12.017

; Peters et al., 2018

Peters, B.J., Carlson, R.W., Day, J.M.D., Horan, M.F. (2018) Hadean silicate differentiation preserved by anomalous (142)Nd/(144)Nd ratios in the Reunion hotspot source. Nature 555, 89–93. https://doi.org/10.1038/nature25754

). However, the high precision ¹⁴²Nd database for global hotspots remains relatively small and, thus, small scale ¹⁴²Nd heterogeneity in modern ocean island basalts may remain undetected. The convergence of global OIBs toward a moderately depleted isotopic signature, as well as the selectivity of this signature for predicting elevated ³He/⁴He ratios and heterogeneous ¹⁴²Nd and ¹⁸²W signatures, have led to the common conclusion that FOZO is a singular, ancient reservoir in Earth’s deep mantle. This interpretation is particularly attractive when attempting to reconcile an ancient FOZO with the presence of two discrete large low shear velocity provinces (LLSVPs) identified in Earth’s lower mantle. Despite this, evidence for the existence of multiple mantle components with elevated ³He/⁴He has been found both within single hotspots (Willhite et al., 2019

Willhite, L.N., Jackson, M.G., Blichert‐Toft, J., Bindeman, I., Kurz, M.D., Halldórsson, S.A., Harðardóttir, S., Gazel, E., Price, A.A., Byerly, B.L. (2019) Hot and Heterogenous High‐³He/⁴He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island. Geochemistry, Geophysics, Geosystems 20, 5939–5967. https://doi.org/10.1029/2019GC008654

) and between global volcanic hotspots (Jackson et al., 2007

Jackson, M., Kurz, M., Hart, S., Workman, R. (2007) New Samoan lavas from Ofu Island reveal a hemispherically heterogeneous high ³He/⁴He mantle. Earth and Planetary Science Letters 264, 360–374. https://doi.org/10.1016/j.epsl.2007.09.023

). Further, many hotspots that are spatially associated with different LLSVPs share common correlations between He and W isotopic compositions, implying that they have a shared ancient heritage that is independent of LLSVPs. Further, the lack of global correlations between ¹⁴²Nd and either short (¹⁸²W) or long lived (⁴He, ⁸⁷Sr, ¹⁴³Nd, ¹⁸⁷Os, ²⁰⁶Pb) isotopic tracers has complicated interpretations of Hadean-aged processes preserved in both geologically young and ancient rocks. Thus, the timing and nature of the evolution of moderately depleted isotopic signatures akin to FOZO, as well as their global extent, remains unclear.

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The μ¹⁴²Nd Signatures of FOZO-Type Lavas From Volcanic Hotspots

We measured the μ¹⁴²Nd compositions (parts per million deviation of the ¹⁴²Nd/¹⁴⁴Nd ratio of a sample from that of the terrestrial standard) of OIBs from the Crozet (³He/⁴He ≤ 14 R_A, n = 17) and Juan Fernandez (³He/⁴He ≤ 17 R_A, n = 13) archipelagos, which display FOZO-like isotopic compositions and elevated ³He/⁴He ratios, and lack geochemical influence from non-FOZO end members. Notably, only hotspots that show clear geochemical influence from geochemical end member reservoirs, such as enriched mantle (EM), depleted mantle (DM), or high μ (high ²³⁸U/²⁰⁴Pb, HIMU), in addition to influence from FOZO, display very high ³He/⁴He (>30 R_A; e.g., Jackson et al., 2017

Jackson, M.G., Konter, J.G., Becker, T.W. (2017) Primordial helium entrained by the hottest mantle plumes. Nature 542, 340–343. https://doi.org/10.1038/nature21023

). Our strategy was instead to focus on hotspot islands that display tightly distributed Sr-¹⁴³Nd-Pb isotopic compositions that lie near the convergence point of global OIB isotopic arrays, without showing geochemical influence from any non-FOZO end member (Fig. 1; cf. Stracke et al., 2005

Stracke, A., Hofmann, A.W., Hart, S.R. (2005) FOZO, HIMU, and the rest of the mantle zoo. Geochemistry, Geophysics, Geosystems 6, Q05007. https://doi.org/10.1029/2004GC000824

, for different definitions of FOZO). We used high precision analytical methods (adapted from Garçon et al., 2018

Garçon, M., Boyet, M., Carlson, R.W., Horan, M.F., Auclair, D., Mock, T.D. (2018) Factors influencing the precision and accuracy of Nd isotope measurements by thermal ionization mass spectrometry. Chemical Geology 476, 493–514. https://doi.org/10.1016/j.chemgeo.2017.12.003

; Wang and Carlson, 2022

Wang, D., Carlson, R.W. (2022) Tandem-column extraction chromatography for Nd separation: minimizing mass-independent isotope fractionation for ultrahigh-precision Nd isotope-ratio analysis. Journal of Analytical Atomic Spectrometry 37, 185–193. https://doi.org/10.1039/D1JA00365H

) designed to resolve very small scale μ¹⁴²Nd heterogeneity, since observed variations in μ¹⁴²Nd values are very small among post-Archean rocks (Horan et al., 2018

Horan, M.F., Carlson, R.W., Walker, R.J., Jackson, M., Garçon, M., Norman, M. (2018) Tracking Hadean processes in modern basalts with 142-Neodymium. Earth and Planetary Science Letters 484, 184–191. https://doi.org/10.1016/j.epsl.2017.12.017

; Hyung and Jacobsen, 2020

Hyung, E., Jacobsen, S.B. (2020) The ¹⁴²Nd/¹⁴⁴Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings National Academy Sciences USA 117, 14738–14744. https://doi.org/10.1073/pnas.2006950117

). We relied on intensive sample replication (more than 80 individual, high precision analyses) to constrain the μ¹⁴²Nd compositions of the two hotspots.

Samples from both studied islands of the Juan Fernandez hotspot samples display homogeneous μ¹⁴²Nd compositions with an average of μ¹⁴²Nd = +1.0 ± 0.9 (all uncertainties represent 95 % c.i., n = 13; Fig. 2, Tables S-1, S-2). Among Crozet hotspot OIBs, samples from Penguin Island similarly display homogeneous compositions (μ¹⁴²Nd = −0.6 ± 0.9, n = 11), whereas samples from Possession Island have somewhat more heterogeneous and negative μ¹⁴²Nd values (μ¹⁴²Nd = −1.4 ± 1.7, n = 6), producing a hotspot average μ¹⁴²Nd of −0.8 ± 0.8 (Fig. 2). The μ¹⁴²Nd compositions of Crozet and Juan Fernandez OIBs are thus resolved at the 95 % confidence level and pass a t-test for the statistical resolution of their sample means (p = 0.006). Importantly, statistical resolution of μ¹⁴²Nd compositions between individual samples or between sample groups requires that these samples or groups recorded distinct Hadean-aged histories even when no samples or sample groups are statistically resolved from the JNdi-1 terrestrial standard (cf. Horan et al., 2018

Horan, M.F., Carlson, R.W., Walker, R.J., Jackson, M., Garçon, M., Norman, M. (2018) Tracking Hadean processes in modern basalts with 142-Neodymium. Earth and Planetary Science Letters 484, 184–191. https://doi.org/10.1016/j.epsl.2017.12.017

). Further, the presence of statistically resolvable μ¹⁴²Nd values in modern rocks implies that their mantle sources previously preserved much greater μ¹⁴²Nd heterogeneity, since this tends to be erased by mantle convection over time (e.g., Hyung and Jacobsen, 2020

Hyung, E., Jacobsen, S.B. (2020) The ¹⁴²Nd/¹⁴⁴Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proceedings National Academy Sciences USA 117, 14738–14744. https://doi.org/10.1073/pnas.2006950117

).

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Although the Sr-¹⁴³Nd isotopic compositions of Crozet and Juan Fernandez OIBs fall into a global FOZO-type compositional range (Breton et al., 2013

Breton, T., Nauret, F., Pichat, S., Moine, B., Moreira, M., Rose-Koga, E.F., Auclair, D., Bosq, C., Wavrant, L.-M. (2013) Geochemical heterogeneities within the Crozet hotspot. Earth and Planetary Science Letters 376, 126–136. https://doi.org/10.1016/j.epsl.2013.06.020

; Truong et al., 2018

Truong, T.B., Castillo, P.R., Hilton, D.R., Day, J.M.D. (2018) The trace element and Sr-Nd-Pb isotope geochemistry of Juan Fernandez lavas reveal variable contributions from a high-³He/⁴He mantle plume. Chemical Geology 476, 280–291. https://doi.org/10.1016/j.chemgeo.2017.11.024

) (Fig. 1), there are also observable differences between the compositions of the two hotspots (Figs. 2b and 3). In particular, the Sr-¹⁴³Nd isotopic compositions of Penguin and Possession Island OIBs (Crozet) bracket those of both studied islands of Juan Fernandez, meaning that the Sr-^142,143Nd isotopic compositions of the islands could potentially be attributed to discrete, shared compositional domains that are variably mixed into the sources of these islands. We tested this possibility using several binary mixing models (Fig. 3). Model 1 assumes that Penguin and Possession represent unmixed FOZO-like components, and that Juan Fernandez OIBs represent an intermediate mixture of these components. This model can explain the Sr-¹⁴³Nd isotopic compositions of Juan Fernandez OIBs, albeit at comparatively extreme trace element abundances (Table S-3). However, mixing two components (Penguin and Possession) that both possess negative μ¹⁴²Nd values cannot produce an intermediate composition (Juan Fernandez) with a positive μ¹⁴²Nd value. Mixing model 2 instead assumes that Penguin Island represents a discrete FOZO component and that the isotopic compositions of Juan Fernandez and Possession OIB are explained by minor admixing of an EM component (cf. Breton et al., 2013

Breton, T., Nauret, F., Pichat, S., Moine, B., Moreira, M., Rose-Koga, E.F., Auclair, D., Bosq, C., Wavrant, L.-M. (2013) Geochemical heterogeneities within the Crozet hotspot. Earth and Planetary Science Letters 376, 126–136. https://doi.org/10.1016/j.epsl.2013.06.020

). This model can successfully reproduce the Sr-^142,143Nd compositions of Juan Fernandez lavas assuming that the EM end member possesses a μ¹⁴²Nd value of ≳ + 8. However, this assumption cannot simultaneously explain the negative μ¹⁴²Nd compositions of Possession OIBs, which would require the EM end member to have μ¹⁴²Nd ≲ –5. Further, there is no independent evidence that 1) such an EM component exists in Juan Fernandez lavas (Truong et al., 2018

Truong, T.B., Castillo, P.R., Hilton, D.R., Day, J.M.D. (2018) The trace element and Sr-Nd-Pb isotope geochemistry of Juan Fernandez lavas reveal variable contributions from a high-³He/⁴He mantle plume. Chemical Geology 476, 280–291. https://doi.org/10.1016/j.chemgeo.2017.11.024

), and 2) that this EM component would possess a resolvable positive or negative μ¹⁴²Nd value.

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Mixing models 3 and 4 take the alternative perspective that Juan Fernandez OIBs represent a discrete FOZO component, and that Penguin and Possession lavas reflect admixing of a depleted MORB mantle (DMM) or an EM component, respectively. These models can successfully reproduce the Sr-^142,143Nd isotopic compositions of both Penguin and Possession lavas; however, they require that the bulk DMM has μ¹⁴²Nd ≲ −4 and the Possession EM component has μ¹⁴²Nd < −100 (Table S-3). Although there is evidence that global MORBs possess slightly negative μ¹⁴²Nd values (ca. μ¹⁴²Nd = −1 to −2; Peters et al., 2024

Peters, D., Rizo, H., O’Neil, J., Hamelin, C., Shirey, S.B. (2024) Comparative ¹⁴²Nd and ¹⁸²W study of MORBs and the 4.5 Gyr evolution of the upper mantle. Geochemical Perspectives Letters 29, 51–56. https://doi.org/10.7185/geochemlet.2412

), there is no indication that the bulk DMM systematically possesses more negative μ¹⁴²Nd compositions. Similarly, there is no evidence that EM components have μ¹⁴²Nd compositions significantly more extreme than what has been observed in the Archean rock record (ca. −20 to +20). Thus, we infer that the μ¹⁴²Nd compositions of Crozet and Juan Fernandez OIBs cannot be reconciled by binary mixing processes. Instead, they must be explained by the existence of multiple mantle domains with similar, FOZO-like long lived isotopic compositions but heterogeneous μ¹⁴²Nd signatures. This conclusion expands the long held view of FOZO as a diffuse component without the clear, singular end member compositions exhibited by EM and HIMU (Hart et al., 1992

Hart, S.R., Hauri, E.H., Oschmann, L.A., Whitehead, J.A. (1992) Mantle Plumes and Entrainment: Isotopic Evidence. Science 256, 517–520. https://doi.org/10.1126/science.256.5056.517

; Stracke et al., 2005

Stracke, A., Hofmann, A.W., Hart, S.R. (2005) FOZO, HIMU, and the rest of the mantle zoo. Geochemistry, Geophysics, Geosystems 6, Q05007. https://doi.org/10.1029/2004GC000824

).

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The Hadean-Aged Heritage of FOZO

The short half-life of the ¹⁴⁶Sm-¹⁴²Nd system (recently updated to 92 ± 3 Ma; Chiera et al., 2024

Chiera, N.M., Sprung, P., Amelin, Y., Dressler, R., Schumann, D., Talip, Z. (2024) The ¹⁴⁶Sm half-life re-measured: consolidating the chronometer for events in the early Solar System. Science Reports 14, 17436. https://doi.org/10.1038/s41598-024-64104-6

) requires that detectible μ¹⁴²Nd heterogeneity was generated before ca. 4 Ga ago, during the Hadean Eon. This means that the differing μ¹⁴²Nd compositions of Crozet and Juan Fernandez OIBs reflect distinct FOZO domains that experienced different geochemical histories during the first ca. 10 % of Earth’s history. This finding implies that FOZO is not a singular component, but rather reflects different silicate differentiation histories that began in the Hadean Eon and have been partially preserved until the present. This result is particularly striking given the long lived isotopic characteristics of Crozet and Juan Fernandez OIBs. In particular, the ³He/⁴He ratios of lavas from both archipelagos do not extend to the very high values observed in other hotspots (Jackson et al., 2017

Jackson, M.G., Konter, J.G., Becker, T.W. (2017) Primordial helium entrained by the hottest mantle plumes. Nature 542, 340–343. https://doi.org/10.1038/nature21023

). However, the He-Pb isotopic characteristics of Crozet and Juan Fernandez OIBs overlap with the trend toward high ³He/⁴He ratios defined by Galápagos and Samoa OIBs, implying that they have primitive components with comparable origins (cf. Jackson et al., 2007

Jackson, M., Kurz, M., Hart, S., Workman, R. (2007) New Samoan lavas from Ofu Island reveal a hemispherically heterogeneous high ³He/⁴He mantle. Earth and Planetary Science Letters 264, 360–374. https://doi.org/10.1016/j.epsl.2007.09.023

) (Fig. 1b). Further, Juan Fernandez lavas record some of the lowest known ¹⁸²W/¹⁸⁴W ratios among OIBs, well below OIBs from other hotspots with similar or higher ³He/⁴He ratios, such as Samoa (Mundl-Petermeier et al., 2020

Mundl-Petermeier, A., Walker, R.J., Fischer, R.A., Lekic, V., Jackson, M.G., Kurz, M.D. (2020) Anomalous ¹⁸²W in high ³He/⁴He ocean island basalts: Fingerprints of Earth’s core? Geochimica et Cosmochimica Acta 271, 194–211. https://doi.org/10.1016/j.gca.2019.12.020

). Identifying hotspots with shared ancient heritage is therefore clearly complicated, and a better view may be obtained by combining multi-dimensional isotopic data to explore isotopic heterogeneity within FOZO-type OIBs. A baseline analysis, utilising the normalisation scheme of Jackson et al. (2020)

Jackson, M.G., Blichert-Toft, J., Halldorsson, S.A., Mundl-Petermeier, A., Bizimis, M., Kurz, M.D., Price, A.A., Harethardottir, S., Willhite, L.N., Breddam, K., Becker, T.W., Fischer, R.A. (2020) Ancient helium and tungsten isotopic signatures preserved in mantle domains least modified by crustal recycling. Proceedings National Academy Sciences USA 117, 30993–31001. https://doi.org/10.1073/pnas.2009663117

(Fig. 1d) for the combined long lived radiogenic (He-Sr-¹⁴³Nd-²⁰⁶Pb) compositions of global OIBs, suggests that there are at least three distinct trends to high ³He/⁴He values. Some hotspots, such as Iceland, appear to transverse multiple trends. This raises the possibility that primitive mantle domains are not discrete and may rather be unique to each hotspot system.

We developed a machine learning model to approach the challenge of visualising and interpreting multi-dimensional isotopic data in this context. We initially compiled He-Sr-¹⁴³Nd-Pb isotopic and trace element data from 33 hotspots using the individual pre-compiled files available on the GEOROC database (DIGIS, Geoscience Centre Göttingen). Due to the requirement of machine learning models for relatively large datasets, the small amount of available ¹⁴²Nd and ¹⁸²W data precluded their direct inclusion in our model. We used the t-distributed stochastic neighbor embedding (TSNE) method to reduce the dimensionality of the data to produce simpler visual representations of the multi-dimensional data (e.g., Fig. S-1). We found that the inclusion of He isotopic or trace element compositions made geological interpretation significantly more complex (Supplementary Information), and so we focused on the interpretation of results for Sr-¹⁴³Nd-Pb isotopic data alone. We used the initial findings for all compiled hotspots to guide the development of a refined K-means cluster analysis for nine hotspots with the greatest data availability, plus Juan Fernandez and Crozet. This resulted in the appearance of clusters with clear association to established mantle end member compositions, such as EM and HIMU (Fig. 4a; e.g., White et al., 2025

White, W.M., Jackson, M.G., Hardardottir, S. (2025) Insights Into Mantle Plume Geochemistry From Machine Learning. Geochemistry, Geophysics, Geosystems 26, e2024GC011870. https://doi.org/10.1029/2024GC011870

). We then used this cluster analysis as an objective criterion to filter out samples that represented significantly depleted or enriched isotopic compositions relative to FOZO, and subsequently repeated the TSNE dimensionality reduction on the filtered data alone. For a full overview of the model development, see the Supplementary Information.

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Among the FOZO-filtered dataset, at least three visually resolved groups are apparent (Fig. 4b). One is comprised of nearly all Hawaii and a majority of Iceland OIBs, which show strong overlap and are distinct from other hotspots. A second group is comprised primarily of the remaining Iceland and Hawaii lavas, along with Galápagos, Pitcairn and most Marquesas lavas, along with all but one sample from Penguin Island (Crozet). The final group is comprised of a few Iceland lavas along with Mascarene (Réunion), Samoa, Juan Fernandez and the remaining Marquesas and Crozet lavas. Although these groups are clearly distinct from one another, they each include OIBs that have differing compositions on binary isotope plots alone (Fig. 1). For example, the Sr-¹⁴³Nd-Pb and He-W isotopic systematics of Galápagos OIBs appear to be unlike those of Pitcairn or Marquesas OIBs; however, in the filtered TSNE analysis (Fig. 4b) these three hotspots mainly occupy the same cluster. Further, the TSNE analysis preserves apparent compositional differences between Penguin and Possession Island OIBs. However, Penguin Island lavas are not associated with either Juan Fernandez or Mascarene lavas, which share their FOZO-like Sr-¹⁴³Nd-Pb and moderately elevated ³He/⁴He compositions. Likewise, the association of Juan Fernandez and Possession OIBs, which have distinct μ¹⁴²Nd compositions, highlights that there must also be multiple independent geological histories preserved within a single TSNE group, since the TSNE reduction was done using only long lived isotopic compositions. One exception to these associations is lavas from Hawaii and Iceland OIBs, which were previously noted to have similar isotopic signatures (e.g., Jackson et al., 2007

Jackson, M., Kurz, M., Hart, S., Workman, R. (2007) New Samoan lavas from Ofu Island reveal a hemispherically heterogeneous high ³He/⁴He mantle. Earth and Planetary Science Letters 264, 360–374. https://doi.org/10.1016/j.epsl.2007.09.023

) and likewise have strongly overlapping TSNE compositions for a variety of multi-dimensional analyses, among them those including He isotopic compositions (Figs. 4, S-2), despite their geographic distance and association with different LLSVP.

Given these results, it is clear that the geological interpretation of machine learning models is not straightforward (cf. Stracke et al., 2022

Stracke, A., Willig, M., Genske, F., Béguelin, P., Todd, E. (2022) Chemical Geodynamics Insights From a Machine Learning Approach. Geochemistry, Geophysics, Geosystems 23, e2022GC010606. https://doi.org/10.1029/2022GC010606

; White et al., 2025

White, W.M., Jackson, M.G., Hardardottir, S. (2025) Insights Into Mantle Plume Geochemistry From Machine Learning. Geochemistry, Geophysics, Geosystems 26, e2024GC011870. https://doi.org/10.1029/2024GC011870

). In particular, given that the model associates OIBs with differing μ¹⁴²Nd compositions, the observed sample grouping must represent a minimum number of discrete FOZO components present in the mantle. Further, the presence of heterogeneous μ¹⁴²Nd values in a single TSNE cluster implies that Hadean-aged heterogeneity could be present throughout global OIBs and more high precision data is required in order to detect it. Our results thus highlight an opportunity for further tests of the geochemical relationship between potential common components of global hotspots. Given the lack of clear association between FOZO compositional clusters and geographic position of LLSVPs, further spatial analysis is required to understand where Hadean-aged components are stored and protected within the mantle. Further, as the ¹⁴²Nd and ¹⁸²W datasets for modern OIBs are expanded (Mundl-Petermeier et al., 2020

Mundl-Petermeier, A., Walker, R.J., Fischer, R.A., Lekic, V., Jackson, M.G., Kurz, M.D. (2020) Anomalous ¹⁸²W in high ³He/⁴He ocean island basalts: Fingerprints of Earth’s core? Geochimica et Cosmochimica Acta 271, 194–211. https://doi.org/10.1016/j.gca.2019.12.020

), the Hadean origins of modern volcanism can be better understood through multi-dimensional analysis and the geological processes responsible for Earth’s development can be scrutinised more closely.

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Acknowledgements

This project was supported by ETH Zürich/Marie Skłodowska-Curie Actions COFUND (18-1 FEL-28 to BJP) and the Swiss National Science Foundation (PZ00P2_186064 to BJP). The authors thank editor Raúl Fonseca for editorial handling and for thoughtful reviews from Catherine Chauvel, Bill White, and Erik Scherer, which helped improve the manuscript.

Editor: Raúl O.C. Fonseca

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Data Availability Statement

All data generated in this study are available in the Supplementary Tables and have also been archived in the EarthChem database at https://doi.org/10.60520/IEDA/113771.

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References

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Supplementary Information

The Supplementary Information includes:

• Supplementary Materials and Methods Information
• Supplementary Information Regarding the Machine Learning Model
• Tables S-1 to S-6
• Figures S-1 to S-7
• Supplementary Information References

Download the Supplementary Information (PDF)

Download Tables S-1 to S-6 (.xlsx)