Early Archaean subduction and intracrustal processes: experimental evidence from the East Pilbara Terrane, Australia

Domain: biology
Published: 2026-04-04
Editorial outcome: major_revision

Abstract
The growth and recycling of continental crust has resulted in the modification of Earth’s mantle, hydrosphere, atmosphere and biosphere. Before the formation of the oldest stable continents, the Earth’s surface was composed of 25-45 km thick basaltic crust. From 4.3-3.5 billion years ago (Ga), this basaltic crust began to differentiate, generating the first stable silicic continental crust. The tectonic processes responsible for the formation of 4.3-3.5 Ga continental crust remain controversial. Suggested explanations include deep subduction and/or crustal drip/delamination processes and a variety of relatively shallow intracrustal mechanisms . Here, we conduct high-pressure-temperature experiments on a 3.52 Ga early Earth basaltic source rock from the Pilbara Craton, Australia to show that magmas with early continental granitic compositions can form from contemporaneous shallow intracrustal and deep subduction-like tectonic environments. These results suggest that a primitive type of plate tectonics may have operated on the early Earth.

Introduction
The oldest continental crust grew and stabilised in the Eoarchaean-Palaeoarchaean (4.0-3.5 Ga)1 and although recent 142Nd isotopic data suggest that the Nuvvuagittuq gneiss belt in Canada could be as old as 4.3 Ga2, near-chondritic zircon εHIf isotope values in Eoarchaean rocks and the rarity of inherited or detrital zircons with ages >3.9 Ga suggests that the volume of stable continental crust in the Hadean and early Eoarchaean was relatively small3-5. Plate tectonics explains continental crust formation on the present-day Earth, but the tectonic processes operating on the early Earth are poorly understood6-10. The controversy around early tectonic processes means that we do not know: (1) how the planet’s crust began to differentiate; (2) how early surface environments were chemically modified during continental growth (e.g., magmatic volatile release into the atmosphere) and (3) how early continental growth influenced the development of life on our planet (e.g., the volcanic release of reduced gas species and subaerial weathering to liberate nutrient-sensitive elements and metals (e.g., P, Fe, Cu, Zn) for protein and enzyme synthesis). Furthermore, measurements of the Martian and Venusian surfaces show that, while relatively thick basaltic crust predominates, silicic rocks are also found11-15. For example, the discovery of granodiorite by the Curiosity rover in Gale Crater, Mars13 and silicic(?) domes on Venus from Magellan orbital data16. Therefore, investigating how the oldest continental crust developed on Earth may be critical for understanding the formation of early silicic crust on other rocky extra-terrestrial bodies.

The earliest continental material is composed, predominantly, of compositionally heterogeneous tonalite, trondhjemite and granodiorite (TTG) rocks that are derived from the partial melting of hydrated metamorphosed basaltic (metabasic) rocks17,18 followed by secondary magmatic differentiation10,19. Proposed tectonic settings on the early Earth range from relatively high-pressure plate-tectonic-like subduction and/or crustal drip/delamination (plutonic squishy lid)20-23 processes (deep settings >1.4 GPa, >45 km)23 to a variety of relatively low-pressure intracrustal processes such as crustal resurfacing24 ; crustal overturn25 and sagduction26 (shallow settings <1.4 GPa, <45 km). Thus, to investigate the broad tectonic process(es) operating on the early Earth we need to experimentally investigate the temperature, pressure and composition (P-T-X) of the putative source regions that gave rise to early TTG-like continental magmas.

The East Pilbara Terrane of the Pilbara Craton, Western Australia is an ideal location to source such a TTG-like metabasic source composition for experimentation because (1) it is regarded as a classic early Earth terrane and is commonly used to investigate early tectonic settings9,25,27-30; (2) it hosts extensive Palaeoarchaean granitic (sensu lato) and metabasic rock units7,31,32 and (3) the geology of the area has been used to argue for crust formation through both early plate tectonics8,33 and intracrustal processes7,25,34. The East Pilbara Terrane is composed of ten composite 35-120 km diameter granitic-gneiss complexes, each made-up of several generations of plutons, that are surrounded by greenstone rocks (Fig. 1)9,27,33. The older plutonic rocks belong to a TTG suite and younger intrusives are dominantly K-rich granites9,33. The Callina Supersuite represents 3.48-3.46 Ga TTG sections that are mostly found in the Shaw, Carlindi and Muccan complexes and in lower volumes in the Mount Edgar, Corunna Downs, Yule and Warrawagine domes27,33 (Fig. 1). Slightly younger TTG of the 3.45-3.42 Ga Tambina Supersuite are also present and, like the Callina TTG, they are cross cut by younger granitic intrusions33. The East Pilbara Terrane also contains greenstones of the Pilbara Supergroup that comprise four 3.53-3.0 Ga sedimentary and volcanic-dominated groups. The oldest is the 3.53-3.43 Ga Warrawoona Group, with the ~3.52 Ga metabasaltic Coonterunah Subgroup at the base9,27,35. The East Pilbara Terrane TTG are thought to be derived from the partial melting of this Palaeoarchaean basaltic crust9,36 and we test this hypothesis by undertaking partial melt experiments on a metabasic starting composition from the ~3.52 Ga basal section of the Warrawoona Group (Fig. 1).

Results
Previous experimental studies exploring the generation of primitive continental material by Hastie et al. (2016; 2023) and Law and Hastie (2025) investigate Mesozoic and modern oceanic plateau source regions as analogues of the early Earth’s mafic crustal surface. Historically, high pressure-temperature experiments also investigate the generation of silicic plutonic and volcanic rocks (adakites) using modern to Neoarchean source regions (e.g., N- and E-MORB37,38) or synthetic materials39,40. Adam et al. (2012) performed experiments on a boninite composition from the Nuvvuagittuq complex of Quebec, Canada. In contrast, geochemical models suggest that Archean TTG-like rocks form by partial melting incompatible element rich basaltic compositions, and the present study is a major and trace element experimental investigation of such a composition that is present in Hadean-Palaeoarchaean terranes41,42. Our high pressure-temperature experiments use a natural Palaeoarchaean (~3.52 Ga) metabasalt representative sample from the Coonterunah Subgroup that is inferred to be a potential crustal source for East Pilbara Terrane TTG7,31 and it is geochemically different to previous starting compositions (see Table S1 and Figure S1, Supplementary Information). The sample is 179789 from Smithies et al.31 that is a ‘type example’ of the Coonterunah Subgroup, has been used in geochemical and thermodynamic models7 and has also been analysed for full major and trace elements and Nd-Hf radiogenic isotopes5. The sample is relatively unaltered for a Palaeoarchaean metabasalt with K2O and Na2O contents that are representative of the Coonterunah volcanic suite, relict basaltic texture and a loss of ignition of 2.2 wt.%7. The Coonterunah metabasalts commonly have large negative Nb-Ta anomalies7, but some, like 179789, do not. However, sample 179789 has a high TiO2 content (~2 wt.%), that makes it ideal for investigating the potential growth of residua rutile that may be responsible for the formation of negative Nb-Ta anomalies in any Coonterunah-derived TTG magmas. Hawkesworth and Kemp29 demonstrate that Ce/Y and La/Yb ratios can be used to estimate crustal depths and they suggest that the East Pilbara Terrane originally had a crustal thickness of ≤30 km. In addition, the deepest crustal levels estimated for basaltic crust in the Palaeoarchaean are 40-45 km (up to 1.4 GPa)43,44. As such, we test an intracrustal origin for the East Pilbara Terrane TTG at a maximum pressure of 1.4 GPa (~45 km) and then further experiments at 1.6-2.2 GPa (~55-75 km) to simulate deeper (i.e., subduction/dripduction/delamination) environments. Hawkesworth and Kemp29 use Fe3+/ΣFe values from Archaean Pilbara volcanic rocks to suggest water contents of 1.9 wt.% in the source and the oxygen fugacity of modern to Hadean mantle and crust is considered to range from the quartz-fayalite-magnetite (QFM) to the nickel-nickel oxide (NNO) buffer45-47. Therefore, prior to experimentation, our starting Coonterunah metabasalt composition was equilibrated in a NNO environment in an atmosphere-controlled furnace at 1300°C. On removal from the furnace the glass was ground to a fine powder and ~2.0 wt.% water was added.

The experiments generate partial melt in equilibrium with residues of clinopyroxene (cpx), orthopyroxene (opx), plagioclase and titanomagnetite apart from experiments ≥2.0 GPa that have garnet, cpx, titanomagnetite and rutile-bearing residues (Fig. 2a). Amphibole is stable at temperatures of ~950-1020ºC. Garnet is stabilised ≥1.4 GPa, but at 1.4 GPa requires temperatures ≥1015ºC. The stability of garnet at 1.4 GPa and at high temperatures is confirmed in a reversal experiment. Garnet is ubiquitous at 1.8 GPa so reversal experiment EPTgw12 (Source Data, Supplementary Information) involved running starting composition 179789 at 1.8 GPa, 990ºC with 2.1 wt.% water for 24 hours. After 24 hours the EPTgw12 experiment was quenched, the capsule recovered, and the same capsule was run again for 24 hours at 1.4 GPa and 1000 ºC. After quenching the second-stage of the experiment, scanning electron microscope images clearly show that the large garnets that grew at 1.8 GPa are still present at 1.4 GPa, providing evidence of garnet stability at 1.4 GPa and at high temperatures. In contrast, garnet did not grow at 1.2 GPa and 1020ºC (experimental run EPTgw20, see Source Data). Rutile was stabilised as a sub-micron-size accessory phase from 2.0-2.2 GPa (Fig. 2a). The rutile crystals are commonly too small to analyse, but a few are relatively thick (Fig. 2a) and can be analysed cleanly to give a pure TiO2 composition. Rutile is not observed below 2.0 GPa, confirming previous experimental studies that demonstrate rutile is solely a high-pressure phase48-50 and should not be predicted as an accessory phase in lower pressure thermodynamic models using natural metabasic TiO2 starting concentrations and early Earth-like redox states and volatile contents.

Partial melt compositions from our experiments are plotted on the normative An-Ab-Or ternary classification diagram51 to show that nearly all of our experiment-derived liquids have granite and granodiorite compositions (Fig. 2b). Partial melts at 1.4 GPa have 62.7-69.8 wt.% SiO2, 0.4-0.7 wt.% TiO2, 14.8-18.5 wt.% Al2O3, 1.7-5.0 wt.% FeO, 0.9-2.3 wt.% MgO, 2.8-4.1 wt.% Na2O and 3.2-5.0 wt.% K2O, normalised to 100% on an anhydrous basis. Deeper partial melts (≥2.0 GPa), where residual rutile is stabilised, have 65.6-71.2 wt.% SiO2, 0.4-2.0 wt.% TiO2 (higher due to TiO2 saturation), 15.1-18.2 wt.% Al2O3, 1.7-3.4 wt.% FeO, 0.4-1.8 wt.% MgO, 3.5-4.5 wt.% Na2O and 2.2-5.5 wt.% K2O. Experiments with relatively low degrees of partial melting generate granite compositions whereas higher degree partial melts have granodiorite compositions and some just plot into the tonalite field (Fig. 2c). The tonalites and granodiorites that have been formed with >24 % partial melting have 59.8-67.6 wt.% SiO2, 0.4-1.1 wt.% TiO2, 16.5-18.9 wt.% Al2O3, 2.8-6.2 wt.% FeO, 1.3-2.5 wt.% MgO, 2.9-4.5 wt.% Na2O and 2.2-3.4 wt.% K2O. Some of the Coonterunah metabasalts have lower K contents than our starting composition7,31 and these source rocks would potentially enable more tonalitic compositions at similar high partial melt fractions.

Trace element concentrations of the experimental partial melts are plotted on primitive mantle normalised (pmn) multielement diagrams in Figures 3a-b. Liquids formed at 1.4 GPa and in a lower temperature 1.6 GPa experiment (EPTgw10) have relatively flat patterns with only a slight enrichment of the incompatible elements relative to the middle and heavy rare earth elements (M-HREE) (Fig. 3a). Residual plagioclase and titanomagnetite (± amphibole) are responsible for the negative Sr and Ti anomalies respectively. A higher temperature run at 1.6 GPa stabilised garnet in the residue to generate liquids with low HREE contents. All of the 1.4 and 1.6 GPa partial melts have trace element patterns unlike those for East Pilbara Terrane tonalites and trondhjemites (TT) and granites and granodiorites (GG) (Fig. 3a). Significantly, the intracrustal-like 1.4 GPa liquids do not have a substantial primitive mantle-normalised negative Nb anomaly (La/Nbpmn = 1.33-1.65) or low M-HREE concentrations. Importantly, partial melts formed at 1.8 and 2.0 GPa have similar trace element concentrations to the higher temperature 1.6 GPa analysis with residual garnet generating low M-HREE compositions like those of Palaeoarchaean TTG (Fig. 3b). The lack of residual plagioclase ≥2.0 GPa prevents a pronounced negative Sr anomaly from forming. Conversely, experiments from 2.0-2.2 GPa have no residual plagioclase, but have residual rutile and garnet to generate trace element patterns more similar to East Pilbara granitic rocks, especially the beginning of the development of a strong negative Nb anomaly (2.2 GPa: La/Nbpmn = 1.96-2.53) (Fig. 3b).

Methods
High pressure-temperature experiments. Experimental runs were carried out on a ½ inch (1.27 cm) end-loaded piston cylinder press at the Experimental Geoscience Laboratories, School of GeoSciences, University of Edinburgh, U.K using talc-Pyrex®-graphite assemblies (Fig. S1, Supplementary Information). Capsules were centred in assemblies using alumina spacers, within 1mm of the thermocouple junction. Experiments were performed using the hot-piston-out technique in which runs were pressurised to 110% of the reported final pressure, heated, and pressure allowed to bleed off to the desired run pressure over 2-5 mins. Pressure was monitored and maintained during runs within 0.25 kbar of the reported pressure, and a 15% correction to nominal pressure applied to compensate for pressure loss due to internal friction, previously calibrated for the assembly based on the quartz-coesite transition, kyanite-sillimanite transition, jadeite-albite-quartz reaction and the melting point of diopside. Temperature was measured with a Pt-Pt13%Rh thermocouple. No correction for the effects of pressure on thermocouple EMF was applied. Temperature gradients across the sample are small over the temperature range used here, in the order of 10°C, and temperature during runs did not deviate more than 5°C from the reported values. Experiments were quenched by shutting off power to the heating circuits, and fell to below 300°C after 5 seconds, and to below 100°C after 12 seconds.

The starting material was finely-powdered glass of sample 179789 from Smithies et al.31. Sample powder of 179789 was produced using an agate ball mill from hand-picked rock chips rinsed in de-ionised water. The powder was glassed in an atmosphere-controlled Deltech vertical tube gas mixing furnace. A Pt crucible was pre-contaminated with 179789 material at 1300°C in order to saturate the crucible with Fe. The initial 179789 material was removed from the crucible and ~1 gram of new powder was added. This new powder was fused in the furnace at 1300°C for 30 minutes in a stream of CO-H2 gas. In line Bronkhorst Ltd mass flow controllers were used to accurately control and monitor gas flow. Deines (1970) tables were used to determine gas proportions required to anneal the sample at an oxygen fugacity close to that of the Ni-NiO (NNO) buffer, calibrated at run conditions using a zirconium dioxide oxygen sensor. The procedure aimed to limit the time available for Fe loss to the capsule and volatile element (e.g., K) loss to the furnace atmosphere. The synthesised 179789 glass was removed from the crucible and was crushed and finely powdered. Sample 179789 is a rare metabasalt and to ensure material was not potentially lost due to unforeseen circumstances, the material was glassed in three batches: EPT2019, EPT2021 and EPT2024. The glass powders were imaged on a scanning electron microscope to ensure that the material had fully glassed. Glass fragments were analysed (25-30 spot analyses) for major elements on a Cameca SX100 electron microprobe at the UoE. Synthetic 179789 glass major element compositions are near identical to the original 179789 powder and showed no Fe, Na or K loss (Table S1, Supplementary Information). It should also be noted that the new Pilbara starting material is compositionally distinct from oceanic plateau starting materials from Hastie et al.23,56 (1187-8 and 1187-10) that were originally analysed by Fitton and Godard57. EPT2019, 2021 and 2024 trace element compositions were analysed on a NERC ion microprobe at the UoE. Like the major element analyses, synthetic 179789 glass trace element concentrations are near identical to the original 179789 powder (Fig. S2, Supplementary Information).

Approximately 0.035-0.05 grams of starting material, and ~2 wt.% 18.2MΩm deionised water were loaded in welded Au75Pd25 capsules and run for 24 hours. The run has to be long enough to grow crystal phases of sufficient size for imaging and analyses; however, the longer the experimental run the higher the chance of hydrogen escape from the capsule that will alter the oxygen fugacity. It has long been recognised previously that 24 hours is a good time to grow large enough phases and to avoid damaging hydrogen loss. The experiments are designed to simulate partial melting of wet basaltic lid and hydrous subduction-derived material and thus require an oxygen fugacity (fO2) close to nickel-nickel oxide (NNO) mineralogical equilibrium. However, experiments cannot be buffered using an NNO assemblage due to Ni reaction with the Pd-bearing capsule material. Nevertheless, although not explicitly buffered, the talc-Pyrex® experimental assembly used in this study imparts conditions within the sample volume close to the NNO oxygen buffer, consistent with Fe XANES measurements of silicate glass in other quenched run products (Stokes et al.58). Furthermore, as synthetic glass starting materials were pre-annealed at fO2 close to the NNO buffer and only minimal changes in fO2 are expected during our partial melting experiments. Many previous fluid-absent experiments in the literature do not approach equilibrium, but the use of our synthetic glasses enables us to do so. Equilibrium conditions in our experiments are shown by (1) all mineral phases being homogeneous and un-zoned and (2) similar phase proportions and compositions being derived from previous experiments run for 24 and 48 hours at the same pressures and temperatures (Hastie et al.23,56). Experimental run EPTgw20 confirms that garnet does not grow at 1.2 GPa and 1020ºC (Fig S3, Supplementary Information).

Major element analyses. Experimental charges were encased in epoxy resin, ground down and polished for imaging and major and trace element analysis. Samples were carbon-coated and imaged on a Zeiss Field Emission Gun Environmental SEM at the UoE. Major element and high concentration trace element analyses of run products were determined at the UoE using a five spectrometer Cameca SX100 electron microprobe instrument with 15kV acceleration voltage. Mineral products were measured using a fully focussed beam and two conditions of 4 nA (major elements) and 100 nA (minor and trace elements). For glass analyses, a defocused beam of 2 nA and 5 μm was used for major elements to avoid Na loss and to target the relatively small melt pools, and 80 nA at 5 μm was used for minor and trace elements.

Trace element analyses. Trace element analyses on the glasses were determined on a secondary ion mass spectrometer (SIMS) at the UoE. SIMS analysis was performed on a Cameca IMS-7f ion microprobe. Analyses were made using a 16O- primary beam of 15 keV impact energy. A 1nA beam was focussed to a 5-8 micron spot and 4.5 keV positive secondary ions were measured. Molecular ion overlaps were significantly reduced by use of energy filtering (ion energies between 55 and 95 eV measured). Corrections were made for overlap of the light rare earth elements (REE) on the heavy REE and HoO on Ta. Concentrations were determined using a combination of STHS-1, GSD-1G and SRM610 glass standards.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "General comments\nThis is a great and timely study addressing the origin of Paleoarchean continental crust in East Pilbara, northwestern\nAustralia. The study addresses first order, fundamental questions in Earth science related to the origin and tectonic setting of\nearly continental crust. The authors use major and trace element geochemical data to constrain the formation depth of\ngranitic melts that were generated by well-constrained experiments. The authors provide a good introduction to the study\ntopic. Objectives are clear. Arguments presented in the manuscript agree with the data reported in the manuscript and the\ndata in the literature. The results of the study show that most of the assumptions made on the geology of East Pilbara by\nmany previous studies are not supported by robust experimental data. So, these assumptions need to be revised. The topic\nof the manuscript is of great interest to the readers of Nature Communications. I strongly recommend the publication of\nthe study as it is. It will be a well-cited paper. After the publication of this paper, geologists will look at the origin of Archean\ncontinental crust in East Pilbara from a totally new perspective.\nThe East Pilbara Archean terrain represents one of the key regions that is used to test Archean tectonic models. Both plate\ntectonic and non-plate tectonic models are proposed to explain the rock record in East Pilbara. Because of its dome and\nbasin structure, the East Pilbara has been at the center of geological debate on the origin of Archean continental crust for\nmany decades.\nThe authors conducted high pressure-temperature experiments on 3.52 Ga old mafic rock samples from the Coonterunah\nSubgroup to test the models proposed for the origin of the granitic rocks in the East Pilbara terrain. Experiments are\ndescribed in detail. The experiments were conducted under various pressure (1.4 to 2.2 GPa) and temperature (955-1015\n°C) conditions to simulate the depths of melt generation. Experiments at high pressure conditions produced melts whose\nmajor and trace element compositions match those of the granodiorites and tonalites in East Pilbara.\nSpecific comments\nLine 1: I recommend replacement of “early Archaean” with “Paleoarchean”. This is up to the authors.\nLines 35-37: I am not aware of any field data providing evidence for “drips/delamination”.\nLine 44: Add “crust” after “continental”.\nReferences need to be edited.", "reviewer_2": "This study by Hastie et al. conducts high-pressure-temperature petrological experiments on a well-known lithology within the\nArchean igneous geochemistry community in an attempt to understand the tectonic processes giving rise to Earth’s first\ncontinents. While the dataset could be used to generate partition coefficients and inform future phase-equilibrium modelling,\nI cannot recommend it for publication in Nature Communications; the manuscript does not meet the journal’s threshold for\nconceptual advance and breadth of interest. The novelty is narrow because it substantially overlaps with Hastie et al. (2023),\nLaw et al. (2024) and Law and Hastie (2025), without a clear additional and substantial advance. Several core inferences\nrest on evidence that is currently insufficient or internally inconsistent, and the broader geodynamic claims extend beyond\nwhat the new data can support. Therefore, this contribution appears incremental for this venue and would be better suited to\na specialist journal after substantial further development.\nMajor comments:\nThe cornerstone of the ≥2.0 GPa requirement is the appearance of rutile. In the draft, rutile is “sub-micron,” identified via\nacicular habit and a TiO spike on EDS, and explicitly stated to be too small to analyze. No Raman, micro-XRD, or TEM\n2\nconfirmation is provided, and no modal estimates are reported. Given that the Nb argument hinges on rutile, this evidence is\nnot adequate. The authors state in lines 124-126 the presence of titanomagnetite in the residues of all experiments; thus,\nilmenite and titanomagnetite exsolution cannot be excluded, given the inadequate evidence. I request that the authors\nprovide definitive phase identification, otherwise, the pressure threshold for Nb depletion is not demonstrated.\nThe claim that garnet is unstable at 1.2 GPa and 1015 °C is unsupported; no 1.2 GPa experiment is reported in the SI.\nPerhaps the 1.8 GPa experiment should be re-run at 1.2 GPa, as it was at 1.4 GPa? Given that the 24-hour duration of the\nruns seems a little short, this might help clarify this issue. This is particularly notable because the phase equilibrium models\nof Johnson et al. (2017) predict garnet being stable down to a pressure of 0.8 GPa for the same general lithology (CF2, albeit\nan average of more samples).\nI find the choice of samples lacking negative Nb-Ta anomalies difficult to reconcile if the authors’ goal was to perform\nexperiments on a lithology representative of the broader CF2 suite. The manuscript acknowledges compositional diversity\nwithin the Coonterunah metabasalts, including pre-existing Nb troughs. As demonstrated in Johnson et al. (2017), average\nCoucal Basalt has a negative Nb-Ta anomaly, so this calls into question whether the experiments are actually applicable to\nthe stratigraphic unit. The Nb-Ta trough already existing in the average composition of the unit would suggest that, as a\nwhole, rutile isn’t necessary to generate a negative Nb anomaly. Without at least a second protolith run, generalization\nremains speculative.\nThe reduction of the Shaw (1970) relationship to (C= C X) by folding F, P and D into a single constant X requires similar\nl 0\nmodal mineralogy and partitioning across different Coonterunah protoliths. That assumption is strong, and it is not validated.\nThe modelling is then used to argue that a Nb-depleted source can reproduce a Nb trough at 1.4–1.6 GPa, which undercuts\nthe headline claim that TTG-like Nb requires ≥2.0 GPa. I suggest the authors either experimentally test the model with at\nleast one run on the Nb-depleted sample (e.g., 179865) at 1.4–1.6 GPa, or significantly soften the inference. As written, the\nlogic is circular.\nThe authors argue that the granitic and granodioritic compositions of the experimentally-derived partial melts can be\nreconciled with natural observations because Paleoarchean tonalites and trondhjemites in the Pilbara “represent only a very\nsmall volume of the granitic complexes, whereas granites and granodiorites are the dominant silicic plutonic rock-type.” This\nappears to be a misunderstanding. The granitic complexes of the EPT contain multiple supersuites, and the later ones,\nparticularly from Emu Pool onwards, contain increasingly more granites and granodiorites. The granites in the younger\nPaleoarchean supersuites have been demonstrated to be the result of partial derivation from re-melting of older TTG\nsupersuites (e.g., Gardiner et al., 2017; Champion and Smithies, 2019; Hickman, 2021). The same goes for the granites in\nthe Mesoarchean supersuites of the EPT. On the other hand, the Callina and Tambina supersuites, which are subordinate in\narea to the younger supersuites, are only 31% and 7% comprised of granite and granodiorite, respectively (using the\ncompilation of Vandenburg et al., 2023, which incorporates all currently available analyses from the Pilbara). On the other\nhand, tonalites and trondhjemites comprise 30 and 31% of the Callina and Tambina supersuite samples (see attached\nFigure 1). While there might be some sampling bias here, owing to the sparsity of outcrop and the inability to sample\nsignificant portions of some of the domes due to heritage sites, the areal extents of granitoid lithologies in the two\nsupersuites, as mapped by the Geological Survey of Western Australia, are consistent with granites being highly\nsubordinate to tonalites and granodiorites (see attached Figure 2). While there are some examples of granites in these\nsupersuites (e.g., the Homeward Bound Granite in the Callina Supersuite), these low-degree melts are relatively rare.\nThe authors imply that a wet environment would be best explained in a convergent margin. However, all that can really be\nshown here is that the fluid-present or fluxed melting of metabasalts indeed likely contributes to their production (e.g.,\nHernández-Uribe, 2024; Pourteau et al., 2020), but subduction is not a prerequisite for this style of intracrustal melting in the\nArchean (Hartnady et al, 2022), or in the Phanerozoic, for that matter (e.g., Weinberg and Hasalová, 2015). Numerous recent\nworks have demonstrated that the dehydration of mafic-ultramafic lithologies in the crust can release sufficient water to\nproduce TTGs (e.g., Hartnady et al., 2022; Hernández-Uribe, 2024; Pourteau et al., 2020; Tamblyn et al., 2023). Studies that\ninfer a subduction-related petrogenetic origin for TTGs based on evidence for fluid-fluxed melting (e.g., Ge et al., 2023) only\ndemonstrate that this melting process occurred within the crust. I’m not saying that TTGs can’t be produced in subduction\nzones, more that they aren’t diagnostic of the presence or absence of them.\nThe crustal thickness estimates that the Authors invoke as evidence for subduction-like processes are based on La/Yb,\nwhich is only one geochemical parameter. How would this compare to another parameter, such as Eu/Eu* in zircon, or even\nbetter, a method that integrates multiple elemental and isotopic proxies (e.g., Luffi and Ducea, 2022)?\nTTGs are, by definition, melts of pre-existing basaltic crust that have not interacted with mantle peridotite (e.g., Smithies et\nal., 2000; Moyen, 2020). Tonalites and trondhjemites formed directly by subduction-related processes would have to be\nderived from the slab, inevitably reacting with mantle wedge peridotite during ascent, thereby becoming high-Si adakites\n(and producing reciprocal residues that subsequently melt to produce sanukitoids) before they can be emplaced in the crust\n(Martin et al., 2009; Rapp et al., 2010; Smit et al., 2024; Smithies, 2000). I think the authors need to provide a mechanism\nwith which TTGs generated from the slab would be able to ascend to the crust without contamination from the mantle if they\nwant to pursue that interpretation. The authors do not engage with recent work illustrating that many processes obfuscate the\ntraditional interpretation/division of TTGs into LP-HP-MP categories, such as interstitial melt loss (Laurent et al., 2020),\nMgO content of the starting protolith (Johnson et al., 2017), mineral segregation (Kendrick and Yakymchuk, 2020; Kendrick et al.,\n2022), degree of melting and fractional crystallization (Smit et al., 2024), and melt hybridization (Hernández-Montenegro et\nal., 2021).\nThe planetary angle and broad geodynamic statements are not anchored by new data in this study and are read as\noverreach. Plate tectonics is a very specific regime (see e.g., Cawood et al., 2022; Nebel et al., 2024). Neither\ndrips/delamination nor subduction-like processes imply a global network of discrete plates separated by convergent,\ndivergent, and transform boundaries with movements relative to one another governed by slab pull and minor amounts of\nridge push. Such features can also occur in other types of non-plate tectonic regimes, such as sluggish lid (Lenardic, 2018),\nsquishy lid (Lourenço et al., 2020) or lid-and-plate regime (Capitanio et al., 2019). I suggest keeping the focus on what the\nexperiments demonstrate and moving speculative implications to a restrained paragraph.\nThe authors state on line 120 the equilibration of the compositions at a NNO environment, but in the methods state\n\"However, experiments cannot be buffered using an NNO assemblage\". This seems misleading to me and should be\nclarified in the main text, as non-specialists might think the experiments are being run at NNO.\nLine-by-line suggestions:\nLine 66: unlike all the other modes listed here, sagduction is entirely internal.\nLine 72: I think a more detailed map figure might be warranted here; in its current state, it doesn’t provide much context other\nthan the location of the CF2 site.\nLine 79: Following up on my comment on line 66, I’d argue that a study like Vandenburg et al. (2023) deals more with the\ntectonic evolution of the craton than Francois et al. (2014) and would be a more appropriate reference here.\nLines 89-90: Almost all the supersuites in the EPT are intruded by the Split Rock Supersuite, so this information isn’t\ngermane here.\nLine 93: Smithies et al. (2005- Whundo) isn’t really an appropriate reference here. Perhaps you’re thinking of “It started with a plume…” by Smithies et al. (2005)?\nLine 94: Not entirely; see Hickman (2023) for a recent overview of evidence for Eoarchean crust.\nLines 101-103: I don’t see how alteration would be an issue; if anything, studies such as André et al. (2019, 2022) and\nMurphy et al. (2024) suggest that alteration is an important aspect of TTG sources.\nLine 112: Chowdhury et al. (2021) estimated a crustal thickness of ~50 km at 3.35 Ga for the Singhbhum Craton. See also\nFigure 6 in Chowdhury et al. (2025).\nFig. 3: Specify the MORB normalization dataset; it is ambiguous as to which study the normalizing factors are from.\nLikewise, N-MORB is a surprising choice of normalizing factor for Archean rocks, as N-MORB did not exist during the\nArchean (Barnes et al., 2021). I think normalizing to primitive mantle would be a better choice.\nFig. 3: The shaded areas denoted “East Pilbara TT” and “East Pilbara GG”; are they the full range of trace element data for\ncompiled granitoids? They’re so broad that they are not discriminating and don’t really impart much meaningful information.\nPerhaps a better idea would be to plot the mean, median, or geometric means bounded by something like the 25th and 75th\npercentile values?\nFig. 3: Trace element ratio-wise, melts from 179989 don’t seem to be very representative of Pilbara granitoids.\nLines 189-190: The authors state “All of the 1.4 and 1.6 GPa partial melts have trace element patterns unlike those for East\nPilbara tonalites and trondhjemites (TT) and East Pilbara granites and granodiorites (GG) (Fig. 3a).” Yet, the way that the\nfigure is presented currently suggests that the partial melts actually do have trace element patterns similar to EPT granitoids.\nLine 203: I believe this is a misinterpretation once again of Hickman (2004), where the line about granitoids being\n“dominantly monzogranite and granodiorite” is in reference to the granitoids of the Pilbara Craton as a whole, rather than the\nEPT, let alone the Callina and Tambina Supersuites. As I have discussed above, the authors’ assertion that granites and\ngranodiorites are “volumetrically dominant in the East Pilbara plutonic centres” is not germane to the central comparison,\ngiven that this volumetric dominance is the consequence of later magmatism incorporating an increasing amount of\nreworked components, rather than due to conditions during the generation of TTGs of the Callina and Tambina Supersuites.\nLines 256-258: The majority of the evidence does not support this inference (Hickman et al., 2021, 2023), at least not until\nca. 3.25 Ga, ca 200 Myr after emplacement of the Callina and Tambina Supersuites.\nLines 273-276: One wouldn’t expect the eclogitic residue to be observed in outcrop. The TTGs were emplaced into the\nmiddle crust (e.g., Wiemer et al., 2018; Champion and Smithies, 2019), and there are no sections of lower crust exposed in\nthe Pilbara. Given the extreme density contrast between purported eclogites and felsic melts, I don’t see how a scenario\nwhere TTGs carried eclogite fragments during migration from the lower to the middle crust would be physically possible (i.e.,\nStokes’ Law). I also cannot recall, to the best of my knowledge, an example of such a phenomenon occurring in\nPhanerozoic/modern localities associated with crustal delamination.", "reviewer_3": "This study performed direct partial melting experiments on a 3.5 Ga metabasic source-rock from the Pilbara Craton to test\nthe conditions for the formation of earliest felsic continental crust, which support a high-pressure (>45 km) origin as garnet\nstability field only at pressures ≥1.4 GPa. The results are promising and supportive of the conclusion, and can be accepted\nconditionally if my concerns listed below are thoroughly addressed.\nIn general, this study seems quite consistent (and similar) to another published study of the first author (Hastie et al., Nature\nGeoscience, 16, 816-821), which used a different starting material from a basaltic rock that of the southwestern Pacific\nOntong Java Plateau; but for an unclear reason, this publication is not cited in this submission. I would suggest that the\nauthors clearly emphasize the breakthrough of this submission compared to the previous one, if the starting compositions,\nthe logic and design of experiments are quite similar.\nAnother concern is comparing the experimental results with the conflicting data from thermodynamic modeling (Johnson et\nal., 2017, Nature 543, 239-242), which used almost the same starting composition and target TTG for testing their results. A\nreasonable discussion may solve or release the puzzle of readers.\nMy third concern is that, accepting that a pressure of >1.4 GPa (>45 km) is needed for the formation of TTG rocks, how to\nconclude solely that a subduction-like tectonic environment has been the only possibility, i.e., how to exclude crustal\ndrips/delamination model which is similarly consistent with such a high pressure (as the authors put in the abstract)."}, "author_response": "Response to reviewers for manuscript NCOMMS-25-59996-T\nReviewer #1 (Remarks to the Author):\nGeneral comments\nThis is a great and timely study addressing the origin of Paleoarchean continental crust in East\nPilbara, northwestern Australia. The study addresses first order, fundamental questions in Earth\nscience related to the origin and tectonic setting of early continental crust. The authors use major\nand trace element geochemical data to constrain the formation depth of granitic melts that were\ngenerated by well-constrained experiments. The authors provide a good introduction to the study\ntopic. Objectives are clear. Arguments presented in the manuscript agree with the data reported in\nthe manuscript and the data in the literature. The results of the study show that most of the\nassumptions made on the geology of East Pilbara by many previous studies are not supported by\nrobust experimental data. So, these assumptions need to be revised. The topic of the manuscript is\nof great interest to the readers of Nature Communications. I strongly recommend the publication of\nthe study as it is. It will be a well-cited paper. After the publication of this paper, geologists will look\nat the origin of Archean continental crust in East Pilbara from a totally new perspective. The East\nPilbara Archean terrain represents one of the key regions that is used to test Archean tectonic\nmodels. Both plate tectonic and non-plate tectonic models are proposed to explain the rock record\nin East Pilbara. Because of its dome and basin structure, the East Pilbara has been at the center of\ngeological debate on the origin of Archean continental crust for many decades.\nWe thank the reviewer for the highly supportive comments.\nSpecific comments\nLine 1: I recommend replacement of “early Archaean” with “Paleoarchean”. This is up to the\nauthors.\nWording replaced.\nLines 35-37: I am not aware of any field data providing evidence for “drips/delamination”.\nRe-worded.\nLine 44: Add “crust” after “continental”.\n‘crust’ added\nReferences need to be edited.\nDone\nReviewer #2 (Remarks to the Author):\nThis study by Hastie et al. conducts high-pressure-temperature petrological experiments on a well-\nknown lithology within the Archean igneous geochemistry community in an attempt to understand\nthe tectonic processes giving rise to Earth’s first continents. While the dataset could be used to\ngenerate partition coefficients and inform future phase-equilibrium modelling, I cannot recommend\nit for publication in Nature Communications; the manuscript does not meet the journal’s threshold\nfor conceptual advance and breadth of interest. The novelty is narrow because it substantially\noverlaps with Hastie et al. (2023), Law et al. (2024) and Law and Hastie (2025), without a clear\nadditional and substantial advance.\nWe are afraid that there is some confusion over the previous studies by Hastie and Law. The latter\ninvestigate modern oceanic plateau source regions as analogues of the early Earth’s mafic crustal\nsurface. The study here is, to our knowledge, the first and only major and trace element\nexperimental study of an ancient metabasic source region from Pilbara that does not have modern\noceanic plateau compositions. The two starting compositions (the ones from Hastie et al. – 1187-8\nand 1187-10) and this new study (EPT) are completely and utterly different with regards to both\nmajor and trace element concentrations:\nSample SiO TiO Al O FeO(t) MnO MgO CaO Na O K O P O\n2 2 2 3 2 2 2 5\nEPT2019 48.069 2.17 14.855 13.75 0.24 7.72 9.68 2.42 0.96 0.14\nEPT2021 47.822 2.14 14.639 14.44 0.24 7.66 9.59 2.38 0.94 0.14\nEPT2024 48.10 2.07 15.58 13.84 0.25 7.59 9.17 2.32 0.95 0.13\n1187-8 49.22 0.75 14.87 9.76 0.17 9.89 12.39 1.64 0.09 0.06\n1187-10 49.89 0.73 14.53 9.85 0.16 10.20 12.77 1.73 0.10 0.06\nOf the ten major elements, 8 are completely different in the new starting mix (highlighted green)\nand the trace element concentrations are an order of magnitude different. We take full\nresponsibility for this confusion and now modify the text to make it clear that the previous studies\nare not related at all (Lines 97-105). However, Pilbara is at the height of controversy regarding the\nevolution of the early continental crust so the results of this study will be of great interest to the\nscientific community and will be highly sort after.\nMajor comments:\nThe cornerstone of the ≥2.0 GPa requirement is the appearance of rutile. In the draft, rutile is “sub-\nmicron,” identified via acicular habit and a TiO spike on EDS, and explicitly stated to be too small to\n2\nanalyze. No Raman, micro-XRD, or TEM confirmation is provided, and no modal estimates are\nreported. Given that the Nb argument hinges on rutile, this evidence is not adequate. The authors\nstate in lines 124-126 the presence of titanomagnetite in the residues of all experiments; thus,\nilmenite and titanomagnetite exsolution cannot be excluded, given the inadequate evidence. I\nrequest that the authors provide definitive phase identification, otherwise, the pressure threshold\nfor Nb depletion is not demonstrated.\nMost of the rutiles are sub-micron, but after days of mapping out the samples by eye several\nrelatively large rutiles have been found and they display their characteristic twins and with a beam\nof 15 kV we have obtained clean spectra of pure TiO2. We can thus confirm the presence of rutile.\nWe now say this in lines 146-150.\nThe claim that garnet is unstable at 1.2 GPa and 1015 °C is unsupported; no 1.2 GPa experiment is\nreported in the SI. Perhaps the 1.8 GPa experiment should be re-run at 1.2 GPa, as it was at 1.4 GPa?\nWe ran a confirmation experiment (EPTgw20) at 1.2 and 1020 degrees and grew no garnet. The\nexperiment generated melt in equilibrium with an amphibole, cpx and plag-rich residue. We now\nhighlight this confirmation experiment in line 140 of the main text and show images of the\nexperiment with no garnet growth in the supplementary material (see lines 143-144 and 396-403\nand new figure S2). The melt analyses and mass balance for this new sample is also added to the\nsupplementary data table and the sample is plotted in Figure 2.\nGiven that the 24-hour duration of the runs seems a little short, this might help clarify this issue. This\nis particularly notable because the phase equilibrium models of Johnson et al. (2017) predict garnet\nbeing stable down to a pressure of 0.8 GPa for the same general lithology (CF2, albeit an average of\nmore samples).\n24 hours is not short. There is always a trade off with experimental runs. The run has to be long\nenough to grow crystal phases of sufficient size that are in equilibrium; however, the longer the\nexperimental run the more chance of hydrogen escape from the capsule that will alter the oxygen\nfugacity. It has long been recognised that 24 hours is a good time to grow large enough phases and\nto avoid damaging hydrogen loss. We now make this point in lines 377-382.\nI find the choice of samples lacking negative Nb-Ta anomalies difficult to reconcile if the authors’\ngoal was to perform experiments on a lithology representative of the broader CF2 suite.\nWe use ‘type example’ 179879, which is representative of the Coonterunah group (CF2 suite). From\nSmithies et al. (2009) our sample (red dot) plots with the other Coonterunah samples (blue dots):\nSmithies et al. (2009) use sample 179879 as a ‘type example’ of CF2 (see Smithies Table 1 below).\nWe now say our sample is representative in lines 102 and 105.\nThe manuscript acknowledges compositional diversity within the Coonterunah metabasalts,\nincluding pre-existing Nb troughs. As demonstrated in Johnson et al. (2017), average Coucal Basalt\nhas a negative Nb-Ta anomaly, so this calls into question whether the experiments are actually\napplicable to the stratigraphic unit.\nYes, the experiments use a sample from the Coucal Basalts so they are applicable to the Coucal\nBasalts – it is the type example from Smithies et al. (2009). Some of the Coucal basalts have strong\nnegative Nb anomalies and some don’t. Our whole point is to stabilise rutile and generate a negative\nNb-Ta anomaly. So, we use a sample that has high TiO (rutile is pure TiO ) so we can maximise the\n2 2\nchance of saturating rutile and demonstrate the growth of a Nb-Ta anomaly. We say this concisely\nin lines 111-115 and we are afraid that we don’t know how to make this point any clearer to the\nreader.\nThe Nb-Ta trough already existing in the average composition of the unit would suggest that, as a\nwhole, rutile isn’t necessary to generate a negative Nb anomaly.\nWe agree partly with the reviewer here. Rutile isn’t necessary in samples with pre-existing Nb-Ta\nanomalies to generate granitoid melts with Nb-Ta anomalies. We say this as our point (2) on line\n273 and we are not sure how to make this clearer. Basically, rutile is not stabilised at pressures <2.0\nGPa. So, granitoid melts matching Pilbara plutonic rocks can be formed by either (1) direct partial\nmelting of a subducting slab or foundering crust composed of Coonterunah-like basalts at ≥2.0 GPa\nto stabilise garnet and rutile in the residue and/or (2) generation of Coonterunah basaltic magmas\nwith negative Nb anomalies that ascended and formed the Pilbara crust which subsequently re-\nmelted ≤1.4 GPa to generate Pilbara granitoids.\nThe reduction of the Shaw (1970) relationship to (C= C X) by folding F, P and D into a single constant\nl 0\nX requires similar modal mineralogy and partitioning across different Coonterunah protoliths. That\nassumption is strong, and it is not validated.\nThe sample we use is representative of the group as a whole (see previous bivariate plots and\nSmithies Table). Therefore, the samples will have similar modal mineral assemblages and the\npartition coefficients will always be near-identical because the trace elements will adhere to Henry’s\nlaw behaviour. We make this point in a modified line 234.\nThe modelling is then used to argue that a Nb-depleted source can reproduce a Nb trough at 1.4–1.6\nGPa, which undercuts the headline claim that TTG-like Nb requires ≥2.0 GPa. I suggest the authors\neither experimentally test the model with at least one run on the Nb-depleted sample (e.g., 179865)\nat 1.4–1.6 GPa, or significantly soften the inference. As written, the logic is circular.\nThis is not circular, it is modelling using standard geochemical mass balance. We also do not\n‘undercut’ a headline as we say specifically that Pilbara plutonic rocks can be formed by either (1)\ndirect partial melting of a subducting slab or foundering crust composed of Coonterunah-like basalts\nat ≥2.0 GPa to stabilise garnet and rutile in the residue and/or (2) generation of Coonterunah\nbasaltic magmas with negative Nb anomalies that ascended and formed the Pilbara crust which\nsubsequently re-melted ≤1.4 GPa to generate Pilbara granitoids.\nThe authors argue that the granitic and granodioritic compositions of the experimentally-derived\npartial melts can be reconciled with natural observations because Paleoarchean tonalites and\ntrondhjemites in the Pilbara “represent only a very small volume of the granitic complexes, whereas\ngranites and granodiorites are the dominant silicic plutonic rock-type.” This appears to be a\nmisunderstanding. The granitic complexes of the EPT contain multiple supersuites, and the later\nones, particularly from Emu Pool onwards, contain increasingly more granites and granodiorites. The\ngranites in the younger Paleoarchean supersuites have been demonstrated to be the result of partial\nderivation from re-melting of older TTG supersuites (e.g., Gardiner et al., 2017; Champion and\nSmithies, 2019; Hickman, 2021). The same goes for the granites in the Mesoarchean supersuites of\nthe EPT. On the other hand, the Callina and Tambina supersuites, which are subordinate in\narea to the younger supersuites, are only 31% and 7% comprised of granite and granodiorite,\nrespectively (using the compilation of Vandenburg et al., 2023, which incorporates all currently available\nanalyses from the Pilbara). On the other hand, tonalites and trondhjemites comprise 30 and 31% of\nthe Callina and Tambina supersuite samples (see attached Figure 1). While there might be some\nsampling bias here, owing to the sparsity of outcrop and the inability to sample significant portions\nof some of the domes due to heritage sites, the areal extents of granitoid lithologies in the two\nsupersuites, as mapped by the Geological Survey of Western Australia, are consistent with granites\nbeing highly subordinate to tonalites and granodiorites (see attached Figure 2). While there are\nsome examples of granites in these supersuites (e.g., the Homeward Bound Granite in the Callina\nSupersuite), these low-degree melts are relatively rare.\nThere are plenty of granite and granodiorites in the EPT. However, one needs to estimate\nproportions based on available geochemical data. The fact is that these more potassic compositions\nare a significant component, and they need to be explained. Some of the oldest rocks at 3.53 Ga are\ngranodiorite. There is the North Pole monzogranite at 3.45 Ga., Plus all of the rhyolitic compositions\nin the eruptive sequences in the greenstone belts, from 3.53 (Coucal), 3.47 (Duffer) to 3.45-3.43 Ga\n(Panorama Fm). We are also afraid that the ‘younger granodiorites forming by remelting the\ntonalites’ is not supported by isotope data, at least to 3.2 Ga, and probably younger. Please see\nKemp 2023 EPSL.\nThe authors imply that a wet environment would be best explained in a convergent margin.\nHowever, all that can really be shown here is that the fluid-present or fluxed melting of metabasalts\nindeed likely contributes to their production (e.g., Hernández-Uribe, 2024; Pourteau et al., 2020),\nbut subduction is not a prerequisite for this style of intracrustal melting in the Archean (Hartnady et\nal, 2022), or in the Phanerozoic, for that matter (e.g., Weinberg and Hasalová, 2015). Numerous\nrecent works have demonstrated that the dehydration of mafic-ultramafic lithologies in the crust\ncan release sufficient water to produce TTGs (e.g., Hartnady et al., 2022; Hernández-Uribe, 2024;\nPourteau et al., 2020; Tamblyn et al., 2023). Studies that infer a subduction-related petrogenetic\norigin for TTGs based on evidence for fluid-fluxed melting (e.g., Ge et al., 2023) only demonstrate\nthat this melting process occurred within the crust. I’m not saying that TTGs can’t be produced in\nsubduction zones, more that they aren’t diagnostic of the presence or absence of them.\nWe thank the reviewer for this comment and we agree with the statement. All we say in the\nmanuscript is that, yes, the source has to be hydrous, but it also has to be, ultimately, deep to\nstabilise rutile and garnet. We do say that subduction and/or crustal drip and/or delamination\ntectonic environments (Lines 121, 280-282 and 289-290) are most applicable to either generate\ndirect melts or the rocks for intraplate partial melting.\nThe crustal thickness estimates that the Authors invoke as evidence for subduction-like processes\nare based on La/Yb, which is only one geochemical parameter. How would this compare to another\nparameter, such as Eu/Eu* in zircon, or even better, a method that integrates multiple elemental\nand isotopic proxies (e.g., Luffi and Ducea, 2022)?\nWe use the modern combined method of Ce/Y and La/Yb to estimate a crustal thickness of 25 km\n(this is from a well renowned high-impact study that focuses specifically on Pilbara). The Luffi and\nDucea method (which is a general technique) also shows a thickness of 25-30 km.\nTTGs are, by definition, melts of pre-existing basaltic crust that have not interacted with mantle\nperidotite (e.g., Smithies et al., 2000; Moyen, 2020).\nThis is incorrect. TTG are a suite of Na-rich granitoid rocks classified by the IUGS using the\nstreckeisen diagram and also using the Barker An-Ab-Or plot. TTG have no petrogenetic mechanism\nas part of their definition.\nTonalites and trondhjemites formed directly by subduction-related processes would have to be\nderived from the slab, inevitably reacting with mantle wedge peridotite during ascent, thereby\nbecoming high-Si adakites (and producing reciprocal residues that subsequently melt to produce\nsanukitoids) before they can be emplaced in the crust (Martin et al., 2009; Rapp et al., 2010; Smit et\nal., 2024; Smithies, 2000). I think the authors need to provide a mechanism with which TTGs\ngenerated from the slab would be able to ascend to the crust without contamination from the\nmantle if they want to pursue that interpretation.\nPotential Pilbara TTG melts, derived from a slab, can easily ascend without incorporating mantle\nmaterial (developing a ‘mantle-signature’) if (a) part of the slab is subducting at a flat angle, previous\nslab melts ‘armour’ ascending melt pathways into the lower crust to prevent/limit slab melt\nhybridisation and/or (c) ascending TTG magmas undergo fractional crystallisation to lower MgO,\nNi and Cr contents. We add this section to lines 300-304.\nThe authors do not engage with recent work illustrating that many processes obfuscate the\ntraditional interpretation/division of TTGs into LP-HP-MP categories, such as interstitial melt loss\n(Laurent et al., 2020), MgO content of the starting protolith (Johnson et al., 2017), mineral\nsegregation (Kendrick and Yakymchuk, 2020; Kendrick et al., 2022), degree of melting and fractional\ncrystallization (Smit et al., 2024), and melt hybridization (Hernández-Montenegro et al., 2021).\nWe are afraid this is not a review paper and it is beyond the scope of our study to discuss the\nobscure and unclear (as the reviewer states) interpretations of the rest of the community. We focus\non studying the type example of the potential source of Pilbara TTG and then present the data.\nThe planetary angle and broad geodynamic statements are not anchored by new data in this study\nand are read as overreach. Plate tectonics is a very specific regime (see e.g., Cawood et al., 2022;\nNebel et al., 2024). Neither drips/delamination nor subduction-like processes imply a global network\nof discrete plates separated by convergent, divergent, and transform boundaries with movements\nrelative to one another governed by slab pull and minor amounts of ridge push. Such features can\nalso occur in other types of non-plate tectonic regimes, such as sluggish lid (Lenardic, 2018), squishy\nlid (Lourenço et al., 2020) or lid-and-plate regime (Capitanio et al., 2019). I suggest keeping the focus\non what the experiments demonstrate and moving speculative implications to a restrained\nparagraph.\nWe respectively disagree with this statement. If mafic crust is subducting or dripping (current drip\nmodels look very much like subduction zones) then new material has to be constructed somewhere.\nThe surface of the Earth is not shrinking. So, if material is going down then it has to be growing\nsomewhere else. This means there must have been constructive plate boundaries and these would\nalso involve transform systems etc. Such a scenario sounds very similar to a proto-type of plate\ntectonics. We modify lines 293-295 to say this.\nThe authors state on line 120 the equilibration of the compositions at a NNO environment, but in the\nmethods state \"However, experiments cannot be buffered using an NNO assemblage\". This seems\nmisleading to me and should be clarified in the main text, as non-specialists might think the\nexperiments are being run at NNO.\nLine now modified.\nLine-by-line suggestions:\nLine 72: I think a more detailed map figure might be warranted here; in its current state, it doesn’t\nprovide much context other than the location of the CF2 site.\nApologies, can we ask what details the reviewer wishes to see?\nLine 79: Following up on my comment on line 66, I’d argue that a study like Vandenburg et al. (2023)\ndeals more with the tectonic evolution of the craton than Francois et al. (2014) and would be a more\nappropriate reference here.\nReference changed.\nLines 89-90: Almost all the supersuites in the EPT are intruded by the Split Rock Supersuite, so this\ninformation isn’t germane here.\nApologies, we don’t know what the reviewer is suggesting here.\nLine 93: Smithies et al. (2005- Whundo) isn’t really an appropriate reference here. Perhaps you’re\nthinking of “It started with a plume…” by Smithies et al. (2005)?\nWe thank the reviewer for this. Reference changed.\nLine 112: Chowdhury et al. (2021) estimated a crustal thickness of ~50 km at 3.35 Ga for the\nSinghbhum Craton. See also Figure 6 in Chowdhury et al. (2025).\nThank you for the information. This supports our 1.4 GPa cut-off nicely.\nFig. 3: Specify the MORB normalization dataset; it is ambiguous as to which study the normalizing\nfactors are from. Likewise, N-MORB is a surprising choice of normalizing factor for Archean rocks, as\nN-MORB did not exist during the Archean (Barnes et al., 2021). I think normalizing to primitive\nmantle would be a better choice. Fig. 3: The shaded areas denoted “East Pilbara TT” and “East\nPilbara GG”; are they the full range of trace element data for compiled granitoids? They’re so broad\nthat they are not discriminating and don’t really impart much meaningful information. Perhaps a\nbetter idea would be to plot the mean, median, or geometric means bounded by something like the\n25th and 75th percentile values?\nFigure 3 is converted to using a primitive mantle normalisation dataset from McDonough and Sun\n(1995). Also, if normalised values are discussed in the text, these have been converted into primitive\nmantle normalised values as well. Finally, mean values plotted.\nFig. 3: Trace element ratio-wise, melts from 179989 don’t seem to be very representative of Pilbara\ngranitoids.\nWe assume the reviewer means 179789. Our sample is representative (see previous comments).\nLines 189-190: The authors state “All of the 1.4 and 1.6 GPa partial melts have trace element\npatterns unlike those for East Pilbara tonalites and trondhjemites (TT) and East Pilbara granites and\ngranodiorites (GG) (Fig. 3a).” Yet, the way that the figure is presented currently suggests that the\npartial melts actually do have trace element patterns similar to EPT granitoids.\nThe modified figure 3a now shows that the trace element patterns do match.\nLine 203: I believe this is a misinterpretation once again of Hickman (2004), where the line about\ngranitoids being “dominantly monzogranite and granodiorite” is in reference to the granitoids of the\nPilbara Craton as a whole, rather than the EPT, let alone the Callina and Tambina Supersuites. As I\nhave discussed above, the authors’ assertion that granites and granodiorites are “volumetrically\ndominant in the East Pilbara plutonic centres” is not germane to the central comparison, given that\nthis volumetric dominance is the consequence of later magmatism incorporating an increasing\namount of reworked components, rather than due to conditions during the generation of TTGs of\nthe Callina and Tambina Supersuites.\nWe are studying the granitoid compositions derived from partial melting of the CF2 basalts, which\ncould represent the source region for all the granitoids in the Pilbara Craton. As such, we discuss\neverything.\nLines 256-258: The majority of the evidence does not support this inference (Hickman et al., 2021,\n2023), at least not until ca. 3.25 Ga, ca 200 Myr after emplacement of the Callina and Tambina\nSupersuites.\nWe are not taking sides here. This section is just to highlight the controversy surrounding the\ndifferent models proposed to explain the formation of Pilbara. We have to present both sides of the\nargument.\nLines 273-276: One wouldn’t expect the eclogitic residue to be observed in outcrop. The TTGs were\nemplaced into the middle crust (e.g., Wiemer et al., 2018; Champion and Smithies, 2019), and there\nare no sections of lower crust exposed in the Pilbara. Given the extreme density contrast between\npurported eclogites and felsic melts, I don’t see how a scenario where TTGs carried eclogite\nfragments during migration from the lower to the middle crust would be physically possible (i.e.,\nStokes’ Law). I also cannot recall, to the best of my knowledge, an example of such a phenomenon\noccurring in Phanerozoic/modern localities associated with crustal delamination.\nThis is a good point by the reviewer. We modify this section. Please see lines 285-286.\nReviewer #3 (Remarks to the Author):\nThe results are promising and supportive of the conclusion, and can be accepted conditionally if my\nconcerns listed below are thoroughly addressed.\nIn general, this study seems quite consistent (and similar) to another published study of the first\nauthor (Hastie et al., Nature Geoscience, 16, 816-821), which used a different starting material from\na basaltic rock that of the southwestern Pacific Ontong Java Plateau; but for an unclear reason, this\npublication is not cited in this submission. I would suggest that the authors clearly emphasize the\nbreakthrough of this submission compared to the previous one, if the starting compositions,\nthe logic and design of experiments are quite similar.\nThis point is the same as point 1 from Reviewer 2. The previous study by Hastie et al. (2023)\ninvestigates a modern oceanic plateau source region (the Ontong Java Plateau: 1187-8 and 1187-10)\nas analogues of the early Earth’s mafic crustal surface. The compositions of the old material (1187-8\nand 1187-10) and the starting mixes here (EPT) are shown below:\nSample SiO TiO Al O FeO(t) MnO MgO CaO Na O K O P O\n2 2 2 3 2 2 2 5\nEPT2019 48.069 2.17 14.855 13.75 0.24 7.72 9.68 2.42 0.96 0.14\nEPT2021 47.822 2.14 14.639 14.44 0.24 7.66 9.59 2.38 0.94 0.14\nEPT2024 48.10 2.07 15.58 13.84 0.25 7.59 9.17 2.32 0.95 0.13\n1187-8 49.22 0.75 14.87 9.76 0.17 9.89 12.39 1.64 0.09 0.06\n1187-10 49.89 0.73 14.53 9.85 0.16 10.20 12.77 1.73 0.10 0.06\nOf the ten major elements, 8 are completely different in the new starting mix (highlighted green)\nand the trace element concentrations are an order of magnitude different. We take full\nresponsibility for this confusion and now modify the text to make it clear that the previous studies\nare not related (Lines 97-101).\nAnother concern is comparing the experimental results with the conflicting data from\nthermodynamic modeling (Johnson et al., 2017, Nature 543, 239-242), which used almost the same\nstarting composition and target TTG for testing their results. A reasonable discussion may solve or\nrelease the puzzle of readers.\nWe are afraid that we are not sure we can do this now. There are problems with the older\nthermodynamic models because equations of state behind these thermodynamic packages had\nalgebraic errors and they cannot predict accessory phase stability, please see:\nGreen, Holland, Powell, Weller, Reil. 2025. Corrigendum to: Melting of Peridotites through to Granites:\na Simple Thermodynamic Model in the System KNCFMASHTOCr, and, a Thermodynamic Model for\nthe Subsolidus Evolution and Melting of Peridotite. Journal of Petrology.\nhttps://doi.org/10.1093/petrology/egae079.\nSpecifically, many of these previous modelling studies rely on the stability of the accessory phase\n‘rutile’ in relatively shallow crustal environments (<45 km depth) in order to form magmas that\nsolidified into the oldest continental crust. However, the thermodynamic models are now heavily\nsuspect with regards to accessory phase stability.\nHowever, our study provides direct experimental evidence for melting the Pilbara source region. Such\nexperiments underpin thermodynamic models. Thus, if the experiments contradict the models, this is\nbecause the models, for some reason or another, are not generating accurate results.\nMy third concern is that, accepting that a pressure of >1.4 GPa (>45 km) is needed for the formation\nof TTG rocks, how to conclude solely that a subduction-like tectonic environment has been the only\npossibility, i.e., how to exclude crustal drips/delamination model which is similarly consistent with\nsuch a high pressure (as the authors put in the abstract).\nWe apologise we meant to emphasise that a drip/delamination model is also viable. We modify what\nwe say now and mention that subduction and/or crustal drip and/or delamination tectonic\nenvironments (Lines 121, 280-282 and 289-290) are most applicable to either generate direct melts\nor the rocks for intraplate partial melting.\nResponse to referee 2 for manuscript NCOMMS-25-59996-T\nFrom the perspective of a geochemist, I still believe it substantially overlaps with Hastie et al. (2023),\nLaw et al. (2024) and Law and Hastie (2025), without a clear additional and substantial advance, beyond\nanything that will be evident to readers other than those from a niche portion of the experimental\npetrology community.\nThis statement by referee 2 is a factual error. Firstly, Law et al. (2024) is a whole rock geochemical study of\nIcelandic rocks and involves no experimentation (https://www.nature.com/articles/s43247-024-01513-5).\nFurther, we demonstrated in our first response that the starting composition and results of this manuscript\nare completely different to the older studies. We clearly showed that our manuscript uses a composition that\nis hugely different to the older studies with regards to both major and trace elements – it would be difficult\nto find two compositions further apart! Referee 2 chose to ignore this completely. However, to repeat\nourselves:\nThis study is, to our knowledge, the first and only major and trace element experimental study of an ancient\nmetabasic source region from Pilbara that has starting compositions similar to ‘island arc basalts (Samples\n179789, EPT2019, EPT2021, EPT2024). The two starting compositions (the ones from Hastie and Law – 1187-\n8 and 1187-10) are completely and utterly different with regards to both major and trace element\nconcentrations:\nSample SiO TiO Al O FeO(t) MnO MgO CaO Na O K O P O\n2 2 2 3 2 2 2 5\nEPT2019 48.069 2.17 14.855 13.75 0.24 7.72 9.68 2.42 0.96 0.14\nEPT2021 47.822 2.14 14.639 14.44 0.24 7.66 9.59 2.38 0.94 0.14\nEPT2024 48.10 2.07 15.58 13.84 0.25 7.59 9.17 2.32 0.95 0.13\n1187-8 49.22 0.75 14.87 9.76 0.17 9.89 12.39 1.64 0.09 0.06\n1187-10 49.89 0.73 14.53 9.85 0.16 10.20 12.77 1.73 0.10 0.06\nOf the ten major elements, 8 are completely different in the new starting mix (highlighted green) and the\ntrace element concentrations are an order of magnitude different. Finally, Pilbara is at the height of\ncontroversy regarding the evolution of the early continental crust so the results of this study will be of great\ninterest to the scientific community and will be highly sought after.\nThis isn’t the first experimental study with major and trace elements measured in tandem (see e.g., Xiong et\nal., 2005). For experimental studies using Archean rocks (which inherently do not have modern oceanic\nplateau-like compositions), this is neither the first one to measure major elements (Rapp et al., 1991 and\nRapp and Watson, 1995 use WR-40, a Neoarchean amphibolite from the Wyoming Craton), nor is it the first\nto measure major and trace elements in tandem (Adam et al., 2012 used Eoarchean Nuvvuagittuq\namphibolites from the Superior Craton as their starting materials). These may be compositionally different\nfrom the Coonterunah metabasalts, but it does void the statement of priority.\nThis whole statement is factually misleading. Specifically:\n1. Xiong et al. 2005 used a MORB starting mix and nothing from an ancient source; thus, further\ndemonstrating that our starting mix is unique. Also, they only measured Ta, Nb, Hf, Zr, La, Sm, Lu, Rb,\nCs, and Sc, but unlike our analyses that are natural and specifically investigating TTG genesis, Xiong\ndoped their experiments with 100 ppm of each element. This is because they were not replicating\nTTG genesis sensu stricto, they were exploring elemental partitioning.\n2. For the Rapp study, referee 2 proves our point. Rapp used a sample that was 2.7-2.6 billion years\nold and has an E-MORB composition. In contrast, our starting composition is nearly a billion years\nolder and has an island arc-like basaltic composition – completely different.\n3. Adam did experiment on a sample from Superior, but it was a geochemically unique boninite\ncomposition that is very distinct to many of the rocks found in ancient Greenstone belts – completely\ndifferent to our composition as well.\nBasically, our study is the first natural (undoped) major and trace element experimental study using an\nancient island arc basalt-like metabasic rock that are ubiquitous in Hadean-Palaeoarchaean terranes. To\nmake this clear we have highlighted the novelty of our approach and results by re-writing lines 100-113. We\nhave also added all previous experiments in Table S1 for comparison.\nOne glaring issue that I don’t believe I caught in the original manuscript is that the experiments in this study\ndo not produce magmas with trondhjemitic compositions, which are typically associated with the high-\npressure subgroup of TTG series magmas inferred to be produced by a plagioclase-free rutile and garnet-\nbearing source (e.g., Hoffmann et al., 2019; Laurent et al., 2024; Moyen and Martin, 2012; Moyen, 2020).\nThis begs the question whether the results of the experiments can genuinely be considered representative\nof high-pressure TTGs, let alone those in the East Pilbara and thus calls into question the authors’ inferences\nbased on these results.\nMost direct partial melts of metabasic sources are tonalites and granodiorites – so our results are perfectly\nsound. In fact, it would be more irregular to get trondhjemites! Trondhjemites are sub-ordinate to thetwo\nformer rock types. So, it is no surprise that the experimental liquids are not trondhjemitic. Trondhjemites are\ndominantly formed by the fractional crystallisation of tonalite and granodiorite magmas (see Barker 1979 for\nan original take on this and a good summary in Drummond et al. 1996).\nAnother related issue involves the discrepancies between the experimental results and data from\nthermodynamic modelling (e.g., Johnson et al., 2017). I’m not satisfied with the authors’ response to\nReviewer 3’s comment on this issue. The issues arising from the Magmatic NCKFMASHTOCr dataset of\nHolland et al. (2018) are unlikely to have a substantial impact on the stability of accessory phases. While the\nauthors cite the corrigendum of this study as evidence for something being faulty with thermodynamic\nmodelling, this dataset is entirely irrelevant to the results of Johnson et al. (2017) or White et al. (2017), as\nthese studies used the metabasite NCKFMASHTO dataset of Green et al. (2016). Furthermore, the issues that\nthe authors misattribute as being the main contributors to the discrepancy with their results have been fixed,\nso it is an easy (30 minutes tops) and worthwhile endeavour for the authors to compare their results with\nthe most up-to-date thermodynamic modelling in MAGEMin or Thermocalc. It is unlikely that the\nthermodynamic datasets, which are constantly updated and informed by the results of numerous\nexperiments, are incorrect, and I am not convinced of this on the basis of one experimental study.\nApologies, but again, this whole statement is factually incorrect. Specifically:\n1. The issues with the thermodynamic software have a huge impact on the stability of accessory phases.\nThe authors of the correction paper state that accessory phase stability has a large uncertainty in the\nmodelling outputs and the models for accessory phases are particularly imprecise. We have taken\nthe liberty of showing this directly in a screen shot of the paper below (see highlighted). The\ncorrection shows that the problems with the accessory phases cannot be ‘fixed’ because their Gibbs\nfree energy contributions are too small at present. Also, coincidentally, in the same highlighted\nsection, the correction highlights modelling discrepancies between older tonalite models and more\nrecent results. So, older tonalite genesis models are to be viewed with extreme suspicion.\n2. Additionally, Referee 2 wishes to believe thermodynamic modelling results over experimental\nevidence – this is odd in itself as experiments are needed to refine these models. So, asking for a\nmodel to prove an experiment is highly irregular and is not supported by basic scientific principles.\nThe authors have removed their original argument towards the end of the main text about eclogite\nentrainment, but now jumps from inferences on TTGs made based on experimental results to\nunsubstantiated claims about the origin of the mafic protoliths employed in this study. This reads equally\nunsatisfactorily, given that this is unsubstantiated, beyond the scope of this study, and disregards substantial\nevidence to the contrary.\nIt now obvious to us that trying to present arguments for both subduction and intracrustal processes is\ncausing some concern. Thus, on advice from the Nat Comm editorial team we have slimmed this section\ndown and removed sentences in lines 178-182, 270-281, 298-305 and 320-322. We advocate a complex\ntectonic environment on the early Earth with both subduction and intracrustal processes (other studies pick\none or the other) – this also makes our study unique. We now highlight this better in the text and we have\neven modified the title to include both models.\nGranitoids:\nTTGs can be IUGS-defined tonalites, trondhjemites and granodiorites. However, the “TTG series”, which I\nassume the authors are employing as the basis of their arguments, has a specific connotation in the Archean\ncommunity (e.g., Moyen and Martin, 2012; Moyen, 2020; Spencer, 2025). Attributing all compositionally\ntrondhjemitic, tonalitic and granodioritic compositions to the TTG series reflects a lack of engagement with\nthe literature and the commonly used criteria that separate the TTG series from other Archean granitoids.\nAsserting that tonalites, trondhjemites and granodiorites are compositionally identical to the TTG series as\ndefined by seminal studies/articles such as Smithies and Champion (2000), Martin et al. (2005), Moyen and\nMartin (2012), Moyen (2020) and Laurent et al. (2024) without actively employing such criteria, perpetuates\na misconception in the broader igneous community that the two are analogous.\nThe authors should perhaps consider the alternative models of Laurent et al. (2021) and Smit et al. (2024) as\nthe processes outlined in this study have a direct impact on Nb contents, which is traditionally a proxy for\nresidual rutile in TTGs.\nApologies, but again, this whole statement is factually incorrect. TTG are strictly defined under IUGS\nguidelines. All serious studies related to TTG use these guidelines. In our manuscript we follow IUGS\ndefinitions.\nGeological observations:\nAs I discussed in my comments on the previous round of reviews, granites and granodiorites are not the\ndominant silicic plutonic rock types for the Callina and Tambina Supersuites. While there are occurrences of\ngranites in these supersuites as pointed out by the authors, and although I agree that some of these > 3.5-\n3.4 Ga granites are likely produced by low-degree melting of amphibolites, in reality, these are volumetrically\nsubordinate. To use the example that the authors provide as evidence, the North Pole Monzogranite is a\nrelatively small intrusion. Likewise, rhyolites are not particularly germane to the argument as many of these\nare not genetically related to TTGs and do not share the same source (e.g., Smithies et al., 2019), with some\nexceptions, including the Coucal “TTG flow” of Smithies et al. (2009).\nIn their rebuttal, the authors state, “one needs to estimate proportions based on available geochemical\ndata.” I did just that in the original round of reviews, providing two figures using two methods to demonstrate\nthat granites and granodiorites are subordinate to tonalites and trondhjemites in the Callina and Tambina\nSupersuites. I have reattached the two figures from the original round of reviews and recommend that the\nauthors reread my original comments, as their response has been unsatisfactory.\nI’m familiar with Kemp et al. (2023), and it is certainly an important study. However, it doesn’t exist in a\nvacuum, especially with respect to Hf isotope data in granitoids and has its shortfalls. For one, Kemp et al.\n(2023) do not consider the work of Gardiner et al. (2017, 2021). Additionally, samples from all terranes are\npresented together in the εHf-Age diagrams rather than the samples from each terrane separately.\nBecause the different terranes of the Pilbara evolved as independent entities, this can lead to some spurious\ninferences when grouped on the same diagrams. I believe this could explain the authors’ incorrect assertion\nthat “younger granodiorites forming by remelting the tonalites’ is not supported by isotope data, at least to\n3.2 Ga” in response to my comment about the presence of reworked components in granitoids from some\nof the 3.32-3.29 Ga Emu Pool Supersuite intrusions and many of the 3.27-3.22 Ga Cleland Supersuite\nintrusions. To demonstrate the presence of this component from 3.3 Ga onwards, I’ve plotted all available\nHf isotope in zircon data for magmatic grains (within ± < 5% discordance) from East Pilbara Terrane granitoids\nversus time in Fig. 3. As can be seen, both sample mean εHf and individual zircon grain εHf begins to decrease\naround 3.3 Ga (coinciding with the Emu Pool Supersuite) and gets especially pronounced and subchondritic\naround 3.27 Ga (coinciding with the Cleland Supersuite). This shift is best reconciled with the presence of a\nreworked component. This isn’t to say that all granitoids from these supersuites contain the component, as\nthere are clearly intrusions with suprachrondritic εHf, but many do.\nOther lines of evidence exist in addition to the changes in granitoid geochemistry towards more potassic\ncompositions (Vandenburg et al., 2023) and the outlined Hf isotope systematics. Gardiner et al. (2021) also\nprovide further evidence for reworked components based on the presence of xenocrysts in the central\nportions of Emu Pool Supersuite intrusions, suggesting inheritance occurred at depth in their sources, rather\nthan due to wall rock entrainment. Furthermore, oxygen isotope data presented by Smithies et al. (2021) and\nJohnson et al. (2022) from granitoids of the Emu Pool and Cleland Supersuites are best reconciled with the\npresence of a reworked component. Altogether, evidence from the literature most parsimoniously suggests\nthat the latter two Paleoarchean granitoid supersuites of the East Pilbara increasingly incorporated a\nreworked component, as opposed to being produced by low-degree melting of an amphibolite source.\nTherefore, the results of this study are not entirely relevant to the <3.3 Ga granitoids of the Pilbara and the\nauthors should be more explicit to state that these results apply mostly to the > 3.3 Ga supersuites.\nI understand that this is not a review paper, but the authors need to take a more holistic approach when\nmaking inferences based on their results and account for the existing literature from the Pilbara. The four\nPaleoarchean granitoid supersuites of the East Pilbara Terrane were emplaced contemporaneously with the\nultramafic-felsic lavas of the Pilbara Supergroup. If subduction-like processes produced the TTGs, then one\nwould expect that the Pilbara Supergroup lavas would bear geochemical signatures consistent with such a\ntectonomagmatic setting, given their close spatio-temporal association. However, there is no evidence for\nsuch an origin for the lavas of the Pilbara Supergroup, and they are better explained by variably crustally\ncontaminated volcanism in a mafic plateau setting above a mantle upwelling (e.g., Brown et al., 2024;\nHasenstab et al., 2021; Maier et al., 2009; Murphy et al., 2021; Nebel et al., 2014; Puchtel et al., 2022;\nSmithies et al., 2005; Tympel et al., 2021). Thus, as concluded by numerous studies using field,\ngeochronological, structural, and geochemical data, geological context of the EPT in the Paleoarchean\nremains most parsimoniously explained by processes not diagnostic of plate tectonics (e.g., Brown et al.,\n2024; Campbell and Davies, 2017; Gardiner et al., 2017; Hasenstab et al., 2021; Hawkesworth and Kemp,\n2021; Hickman, 2021, 2023; Johnson et al., 2017, 2022; Roberts et al., 2022; Smithies et al., 2005a, 2009,\n2021; Van Kranendonk et al., 2015, 2019; Wiemer et al., 2018). While experiments can offer interpretations\nand possible explanations of data, experimental results do not constitute proof of the operation of a given\nprocess.\nWe thank referee 2 for the time they have taken to write up this background. Unfortunately, most of this\nextensive section is not relevant.\n3. We do not say that granites and granodiorites are not the dominant silicic plutonic rock types for the\nCallina and Tambina Supersuites.\n4. Referee 2 says we say that ‘younger granodiorites forming by remelting the tonalites’. I am afraid we\ndo not say this in the manuscript.\n5. The information deals with much younger rocks <3.25 Ga. Our study relates to rocks and processes\n250 million years before this at 3.52 Ga.\n6. Also, we repeat that: it now obvious to us that trying to present arguments for and against both\nsubduction and intracrustal processes is causing some concern. Referee 2 is very supportive of the\nintracrustal model, which is fine. But, referee 2 must realise that the studies involving subduction as\na mechanism give equally robust defences of their evidence. Thus, on advice from the Nat Comm\neditorial team we have slimmed our tectonic sections down and removed sentences in lines 178-182,\n270-281, 298-305 and 320-322. We have even modified the title to include both models.\nGeodynamics:\nThe planetary angle and broad geodynamic statements are not anchored by new data in this study and still\nread as overreach; the authors’ response to my original comment on this matter does not rectify this issue.\nAgain, we repeat that: it now obvious to us that trying to present arguments for and against both\nsubduction and intracrustal processes is causing some concern. Referee 2 is very supportive of the\nintracrustal model, which is fine. But, referee 2 must realise that the studies involving subduction as\na mechanism give equally robust defences of their evidence. Thus, on advice from the Nat Comm\neditorial team we have slimmed our tectonic sections down and removed sentences in lines 178-182,\n270-281, 298-305 and 320-322. We advocate a complex tectonic environment on the early Earth with both\nsubduction and intracrustal processes (other studies pick one or the other) – this also makes our study unique.\nWe now highlight this better in the text and we have even modified the title to include both models.\nAs I said in the original round of reviews, plate tectonics is a very specific type of geodynamic regime. To\nquote Stern and Gerya (2018), plate tectonics is defined as “a theory of global tectonics powered by\nsubduction in which the lithosphere is divided into a mosaic of strong lithospheric plates, which move on and\nsink into weaker ductile asthenosphere. Three types of localized plate boundaries form the interconnected\nglobal network: new oceanic plate material is created by seafloor spreading at mid-ocean ridges, old oceanic\nlithosphere sinks at subduction zones, and two plates slide past each other along transform faults. The\nnegative buoyancy of old dense oceanic lithosphere, which sinks in subduction zones, mostly powers plate\nmovements.”. The return of mafic crust to the mantle (either through dripping or subduction) would, of\ncourse, be accompanied by rifting elsewhere to replace the volume of crust returned to the mantle, but it\nneed not comprise a global, interlinked network of ridges, transform faults and subduction zones. As shown\nby multiple numerical modelling studies (e.g., Capitanio et al., 2019, 2020, 2022; Lenardic, 2018; Lourenço et\nal., 2020), this does not necessarily imply plate tectonics. If it did, then Venus would also be considered to\nhave a “proto-type of plate tectonics” (e.g., Byrne et al., 2021; Capitanio et al., 2024; Gillmann et al., 2025),\nthereby voiding part of this pitch aimed at a more general scientific audience.\nTo repeat ourselves again, it now obvious to us that trying to present arguments for and against both\nsubduction and intracrustal processes is causing some concern. Referee 2 is very supportive of the\nintracrustal model, which is fine. But, referee 2 must realise that the studies involving subduction as\na mechanism give equally robust defences of their evidence. Thus, on advice from the Nat Comm\neditorial team we have slimmed our tectonic sections down and removed sentences in lines 178-182,\n270-281, 298-305 and 320-322. However, the models cited are done in two dimensions. It is geodynamically implausible\nto have spreading and subduction localised to small areas of the planet – it just doesn’t make sense at all.\nWe advocate a complex tectonic environment on the early Earth with both subduction and intracrustal\nprocesses (other studies pick one or the other) – this also makes our study unique. We now highlight this\nbetter in the text and we have even modified the title to include both models.\nLine-by-line comments:\nLine 34: What’s meant by “continental” here? Does this refer to the UCC, MCC, LCC or the bulk CC? These all\nmean different things and have different implications.\nLine re-worded.\nLine 42: Absence? They’re certainly rare, but Hadean xenocrystic and detrital zircons have been found in\nmultiple cratons (see e.g., Condie, 2019 for a brief review).\nLine re-worded.\nLine 100: For metabasites without oceanic plateau-like compositions, this isn’t the first experimental study\nwith major and trace elements measured in tandem (see e.g., Xiong et al., 2005). For experimental studies\nusing Archean rocks (which inherently do not have modern oceanic plateau-like compositions), this is neither\nthe first one to measure major elements (Rapp et al., 1991 and Rapp and Watson, 1995 use WR-40, an\nArchean amphibolite from the Wyoming Craton), nor is it the first to measure major and trace elements in\ntandem (Adam et al., 2012 used Nuvvuagittuq amphibolites as their starting materials). These may be\ncompositionally different from the Coonterunah metabasalts, but it does void the statement of priority.\nStatement addressed above.\nLine 110-111: Sample 179789 does, in fact, show evidence for crustal contamination by older silicic crust, as\ndemonstrated in the SI of Johnson et al. (2017), so stating that the Coonterunah metabasalts “show no\nevidence that their parental magmas have been contaminated with older silicic crust” is inaccurate.\nSmithies et al 2009 and the isotope data in Kemp et al 2023 suggests otherwise.\nLines 167-168: See discussion above about granitoids and geological observations\nStatement addressed above.\nFig. 3: Given the above comments, I recommend the authors only plot > 3.32 Ga granitoids from the East\nPilbara as shaded areas on their primitive mantle normalized extended trace element diagrams. Including\nthe younger granitoids will invariably lead to spurious comparisons.\nThis is the case anyhow.\nLines 214-215: Again, see the discussion above about granitoids and geological observations. Each of the\ngranitoid complexes in the East Pilbara is comprised of sets of composite intrusions spanning > 700 Myr of\nEarth’s history and if one looks at a geological map of the area, it is evident that the < 3.32 Ga intrusions are\nmore widespread. I believe this is a misinterpretation once again of Hickman (2004), where the line about\ngranitoids being “dominantly monzogranite and granodiorite” is in reference to the granitoids of the\nPilbara Craton as a whole, rather than the EPT, let alone the Callina and Tambina Supersuites. As I have discussed\nabove, the authors’ assertion that granites and granodiorites are “volumetrically dominant in the East Pilbara\nplutonic centres” is not germane to the central comparison, given that this volumetric dominance is the\nconsequence of later magmatism incorporating an increasing amount of reworked components, rather than\ndue to conditions during the generation of TTGs of the Callina and Tambina Supersuites.\nStatement addressed above.\nLines 284-288: Not all TTGs are derived from eclogites, some are derived from amphibolites, as demonstrated\nby field evidence (e.g., Kendrick et al., 2024; Pourteau et al., 2020). Ascribing the entire source to eclogites is\ninaccurate, especially given that high-pressure group TTGs are not as common as low-pressure group TTGs\nin the Pilbara (e.g., Champion and Smithies, 2019; Vandenburg et al., 2023).\nSection removed to tone down tectonic discussion.\nLine 289: This study does not show that a wet and deep tectonic environment is required to produce the Nb\nanomalies in the F2 Coonterunah basalts. This is granitoid petrology paper, not one on the mantle source of\nCF2. For what it’s worth crustal contamination better explains many of the Nb anomalies in the CF2 basalts\n(e.g., Brown et al., 2024; Johnson et al., 2017). Crustal contamination can be quite cryptic in many cases as\nwell (see e.g., Vite-Sánchez et al., 2024).\nSection removed to tone down tectonic discussion.\nLines 296-298: In my opinion, this is overly speculative, lacks proper substantiation and diverts from the core\nmessage of this study.\nSection removed to tone down tectonic discussion.\nLines 302-303: If subduction is occurring at a flat angle, then doesn’t that contradict the statement in line\n298 about the existence of steep subduction with a mantle wedge?\nLine re-worded.\nLines 304-305: Fractional crystallization does not remove the mantle signature in modern adakites, even on\nthe rhyolitic side of things, so I don’t see how that would be the case in the Archean with TTGs. If there is\nsubduction, it is unlikely for there to be a mantle wedge, not only because of the aforementioned\nconsiderations (see also Smithies, 2000; Martin et al., 2005), but also because all that armouring required to\nprevent mantle signatures in the TTGs would ultimately have to melt, producing sanukitoids and\nmetasomatized mantle-derived mafic lavas, which are conspicuously absent from the East Pilbara Terrane.\nThis statement is false.\nLines 306-311: Wrt the ability of subduction-like processes to emit gases into the atmosphere, the\nemplacement style of the volcanoes is a critical question. The geological evidence is overwhelmingly in favour\nof subaqueous emplacement (e.g., Flament et al., 2008; Hickman, 2023) in most places, such that the\nhydrostatic pressure of the overlying oceanic water column affected the nature of emitted gases (e.g.,\nGaillard et al., 2011). This is consistent with multiple lines of evidence for very low sulfate concentrations in\nthe Archaean ocean. There are many more related pieces of evidence regarding Archaean atmosphere-\nhydrosphere-lithosphere interaction that should be considered if trying to pursue this route (e.g.,\nKamber and Ossa-Ossa, 2025).\nResponse to referee 4 for manuscript NCOMMS-25-59996-T\nWe thank Reviewer 4 for their thorough and insightful review that has improved our manuscript. We now\nrespond to the specific suggestions by review 4 below:\n(1) A clearer definition of the specific time-frame the study is relevant to.\nThe title states ‘Early Archaean’, the abstract mentions 4.3-3.5 Ga and 4.0-3.5 Ga time periods, lines 83—93\nappear to indicate the study is specifically focusing generation of the Callina and Tambina supersuites (~3.5-\n3.4 Ga), and several places in the text mention Eoarchean-Paleoarchean or Hadean-Paleoarchean crustal\nformation. Do the experimental results only pertain to the generation of Paleoarchean TTGs in the East\nPilbara Terrane? If so, this could be stated more explicitly. Note that the Eoarchean record of the East\nPilbara Terrane is sparse so line 77 needs amending (the Paleoarchean might be extensive, but the\nEoarchean is only known from rare enclaves and detrital zircon and apatite grains). It is possible that the\ncomposition and crust-forming processes of the Eoarchean crust of the East Pilbara Terrane differ from the\npreserved Paleoarchean crust (compare Hickman, 2023, Archean Evolution of the Pilbara Craton and\nFortescue Basin and Kharkongor et al. 2025, Geology). This point is also true for other Archean terranes\nwhere any Hadean-Eoarchean record is primarily preserved as detrital or xenocrystic zircon grains. There is\nno consensus on the composition of the original host rocks of Hadean-Eoarchean zircons (a quick survey of\nrecent literature on Hadean zircon trace element chemistry includes estimates ranging from peraluminous\ngranites, andesites, mafic rocks, and TTGs). As written the paper implies that the Paleoarchean TTGs of the\nEPT are representative of all early continental crust (including Eoarchean-Hadean). I think this is a\nreasonable assertion but the debate regarding the composition and origin of Eoarchean-Hadean crust and\nthe possibility that it differed from the more widely preserved Paleo-Mesoarchean crust should be\nacknowledged.\nWe apologise for the confusion with the timings. We have now tidied up the text. 4.0 is changed to 4.3 in\nthe abstract and ‘Eoarchaean’ has been removed from lines 79, 122, 201 and 275 to show that we only\nreference Palaeoarchaean TTG and the Palaeoarchaean in general.\n(2) The discussion of lithospheric recycling on the early Earth could be framed in the context of recent\ngeodynamic modelling studies.\nInferring Early Earth geodynamic settings from geochemical data is highly contested and non-unique. I\nrecognise that the authors have already made a significant effort to tone-down this aspect of the\nmanuscript during earlier reviews. However, the inferences of the geodynamic setting of early Archean\ncrust formation could be strengthened by discussing this aspect of the study in the context of recent\ngeodynamic modelling. The study advocates for deep subduction and ‘proto’ or ‘primitive’ plate tectonics\nto generate Paleoarchean TTGs in the East Pilbara Terrane. ‘Proto plate tectonics’ and ‘ primitive plate\ntectonics’ are nebulous terms and there have been recent efforts to clearly define the difference between\nmodern plate tectonics and the geodynamic environments operating on the early Earth (see Cawood et al.\n2022 for an accessible summary). Numerical and thermomechanical modelling also highlight important\ndifferences in geodynamic settings on a hotter early Earth compared to modern plate tectonics. These\nstudies recognise several possible geodynamic modes on early Earth, for example, stagnant lid, squishy lid,\nmobile lid modes.\nWe have further ‘toned down’ the argument and referenced a few geodynamic models. We add sentence\n274 to highlight support for co-existing tectonic models that we advocate with subduction and intracrustal\nprocesses. Also, we recognise that we shouldn’t use ‘proto’ and ‘primitive’ so we have removed the term\n‘proto’.\nSubduction or lithospheric dripping are cited as possible mechanisms for generating high-pressure TTG\nmelts but the authors lean in favour of subduction and a plate tectonic like regime (e.g., in the title and\nabstract). Both these processes are consistent with ‘squishy’ or ‘mobile’ lid tectonic modes. Many readers\nmay find these definitions more palatable than referring explicitly to plate tectonics. In my opinion, using\nexperimental data to demonstrate a diversity of melt-generating environments on the early Earth is an\nimportant and impactful finding alone. Describing the geodynamic setting of melting might be an issue of\nsemantics, but at least using the more recent definitions outlined above provides a common framework for\ncommunicating the geodynamic setting the authors are envisaging.\nWe have indicated plutonic squishy lid terminology in lines 32, 63, 273. For mobile lids, I think we still\nprefer the terms ‘subduction’ and ‘primitive plate tectonics’.\nMinor points:\nInconsistent naming of the study area. The study area is referred to as ‘Pilbara terrane’ , ‘northern Pilbara\ncraton’ , ‘East Pilbara’. The study focuses on the EAST PILBARA TERRANE, which is a terrane within the\nPilbara Craton. This should be updated throughout the text.\nThe terminology has been updated throughout the text. Apologies for any confusion."}, {"round": 2, "reviewer_comments": {"reviewer_2": "[Editorial Note: Please also see attachments at end of file]\n(Remarks to the Author)\nThis revised manuscript by Hastie et al. conducts high-pressure-temperature petrological experiments on a well-known\nlithology within the Archean igneous geochemistry community to understand the tectonic processes giving rise to Earth’s\nfirst continents. While the revised manuscript is an improvement over the original version dataset could be used to generate\npartition coefficients and inform future phase-equilibrium modelling, I do not believe it is suitable for publication in Nature\nCommunications; the manuscript does not meet the journal’s threshold for conceptual advance and breadth of interest. The\nnovelty is narrow. Despite the authors stating otherwise, this is not the first major and trace element experimental study of\npartial melting of an Archean amphibolite purported to be a potential source lithology for TTGs (see below). From the\nperspective of a geochemist, I still believe it substantially overlaps with Hastie et al. (2023), Law et al. (2024) and Law and\nHastie (2025), without a clear additional and substantial advance, beyond anything that will be evident to readers other than\nthose from a niche portion of the experimental petrology community. Therefore, this contribution appears incremental for this\nvenue and would be better suited to a specialist journal after substantial further development. The responses to my review\ncomments don't adequately address my criticisms. Several core inferences still rest on evidence that is currently insufficient\nor internally inconsistent, and the broader geodynamic claims extend beyond what the new data can support. I hope that my\ncomments and concerns help improve this manuscript.\nAs I mentioned previously, this manuscript doesn’t strike me as particularly novel in using experimental petrology to\ninvestigate the origins of TTGs. For metabasites without oceanic plateau-like compositions, this isn’t the first experimental\nstudy with major and trace elements measured in tandem (see e.g., Xiong et al., 2005). For experimental studies using\nArchean rocks (which inherently do not have modern oceanic plateau-like compositions), this is neither the first one to\nmeasure major elements (Rapp et al., 1991 and Rapp and Watson, 1995 use WR-40, a Neoarchean amphibolite from the\nWyoming Craton), nor is it the first to measure major and trace elements in tandem (Adam et al., 2012 used Eoarchean\nNuvvuagittuq amphibolites from the Superior Craton as their starting materials). These may be compositionally different\nfrom the Coonterunah metabasalts, but it does void the statement of priority.\nOne glaring issue that I don’t believe I caught in the original manuscript is that the experiments in this study do not produce\nmagmas with trondhjemitic compositions, which are typically associated with the high-pressure subgroup of TTG series\nmagmas inferred to be produced by a plagioclase-free rutile and garnet-bearing source (e.g., Hoffmann et al., 2019;\nLaurent et al., 2024; Moyen and Martin, 2012; Moyen, 2020). This begs the question whether the results of the experiments can\ngenuinely be considered representative of high-pressure TTGs, let alone those in the East Pilbara and thus calls into\nquestion the authors’ inferences based on these results.\nAnother related issue involves the discrepancies between the experimental results and data from thermodynamic modelling\n(e.g., Johnson et al., 2017). I’m not satisfied with the authors’ response to Reviewer 3’s comment on this issue. The issues\narising from the Magmatic NCKFMASHTOCr dataset of Holland et al. (2018) are unlikely to have a substantial impact on the\nstability of accessory phases. While the authors cite the corrigendum of this study as evidence for something being faulty\nwith thermodynamic modelling, this dataset is entirely irrelevant to the results of Johnson et al. (2017) or White et al. (2017),\nas these studies used the metabasite NCKFMASHTO dataset of Green et al. (2016). Furthermore, the issues that\nthe authors misattribute as being the main contributors to the discrepancy with their results have been fixed, so it is an easy (30\nminutes tops) and worthwhile endeavour for the authors to compare their results with the most up-to-date thermodynamic\nmodelling in MAGEMin or Thermocalc. It is unlikely that the thermodynamic datasets, which are constantly updated and\ninformed by the results of numerous experiments, are incorrect, and I am not convinced of this on the basis of one\nexperimental study.\nThe authors have removed their original argument towards the end of the main text about eclogite entrainment, but now\njumps from inferences on TTGs made based on experimental results to unsubstantiated claims about the origin of the mafic\nprotoliths employed in this study. This reads equally unsatisfactorily, given that this is unsubstantiated, beyond the scope of\nthis study, and disregards substantial evidence to the contrary. Furthermore, on a related note, multiple points between lines\n284-305 contradict each other with respect to inferences made about subduction based on TTGs.\nI find some of the responses to my original comments to be unsatisfactory, particularly those relating to granitoids,\ngeological observations from the Pilbara Craton, and those regarding geodynamics.\nGranitoids:\nTTGs can be IUGS-defined tonalites, trondhjemites and granodiorites. However, the “TTG series”, which I assume the\nauthors are employing as the basis of their arguments, has a specific connotation in the Archean community (e.g., Moyen\nand Martin, 2012; Moyen, 2020; Spencer, 2025). Attributing all compositionally trondhjemitic, tonalitic and granodioritic\ncompositions to the TTG series reflects a lack of engagement with the literature and the commonly used criteria that\nseparate the TTG series from other Archean granitoids. Asserting that tonalites, trondhjemites and granodiorites are\ncompositionally identical to the TTG series as defined by seminal studies/articles such as Smithies and Champion (2000),\nMartin et al. (2005), Moyen and Martin (2012), Moyen (2020) and Laurent et al. (2024) without actively employing such\ncriteria, perpetuates a misconception in the broader igneous community that the two are analogous.\nThe authors should perhaps consider the alternative models of Laurent et al. (2021) and Smit et al. (2024) as the processes\noutlined in this study have a direct impact on Nb contents, which is traditionally a proxy for residual rutile in TTGs.\nGeological observations:\nAs I discussed in my comments on the previous round of reviews, granites and granodiorites are not the dominant silicic\nplutonic rock types for the Callina and Tambina Supersuites. While there are occurrences of granites in these supersuites as\npointed out by the authors, and although I agree that some of these > 3.5-3.4 Ga granites are likely produced by low-degree\nmelting of amphibolites, in reality, these are volumetrically subordinate. To use the example that the authors provide as\nevidence, the North Pole Monzogranite is a relatively small intrusion. Likewise, rhyolites are not particularly germane to the\nargument as many of these are not genetically related to TTGs and do not share the same source (e.g., Smithies et al., 2019),\nwith some exceptions, including the Coucal “TTG flow” of Smithies et al. (2009).\nIn their rebuttal, the authors state, “one needs to estimate proportions based on available geochemical data.” I did just that in\nthe original round of reviews, providing two figures using two methods to demonstrate that granites and granodiorites are\nsubordinate to tonalites and trondhjemites in the Callina and Tambina Supersuites. I have reattached the two figures from\nthe original round of reviews and recommend that the authors reread my original comments, as their response has been\nunsatisfactory.\nI’m familiar with Kemp et al. (2023), and it is certainly an important study. However, it doesn’t exist in a vacuum, especially\nwith respect to Hf isotope data in granitoids and has its shortfalls. For one, Kemp et al. (2023) do not consider the work of\nGardiner et al. (2017, 2021). Additionally, samples from all terranes are presented together in the εHf-Age diagrams rather\nthan the samples from each terrane separately.\nBecause the different terranes of the Pilbara evolved as independent entities, this can lead to some spurious\ninferences when grouped on the same diagrams. I believe this could explain the authors’ incorrect assertion that “younger\ngranodiorites forming by remelting the tonalites’ is not supported by isotope data, at least to 3.2 Ga” in response to my\ncomment about the presence of reworked components in granitoids from some of the 3.32-3.29 Ga Emu Pool Supersuite\nintrusions and many of the 3.27-3.22 Ga Cleland Supersuite intrusions. To demonstrate the presence of this component from\n3.3 Ga onwards, I’ve plotted all available Hf isotope in zircon data for magmatic grains (within ± < 5% discordance) from East\nPilbara Terrane granitoids versus time in Fig. 3. As can be seen, both sample mean εHf and individual zircon grain εHf begins to\ndecrease around 3.3 Ga (coinciding with the Emu Pool Supersuite) and gets especially pronounced and subchondritic\naround 3.27 Ga (coinciding with the Cleland Supersuite). This shift is best reconciled with the presence of a\nreworked component. This isn’t to say that all granitoids from these supersuites contain the component, as there are clearly\nintrusions with suprachrondritic εHf, but many do.\nOther lines of evidence exist in addition to the changes in granitoid geochemistry towards more potassic compositions\n(Vandenburg et al., 2023) and the outlined Hf isotope systematics. Gardiner et al. (2021) also provide further evidence for\nreworked components based on the presence of xenocrysts in the central portions of Emu Pool Supersuite intrusions,\nsuggesting inheritance occurred at depth in their sources, rather than due to wall rock entrainment. Furthermore, oxygen\nisotope data presented by Smithies et al. (2021) and Johnson et al. (2022) from granitoids of the Emu Pool and Cleland\nSupersuites are best reconciled with the presence of a reworked component. Altogether, evidence from the literature most\nparsimoniously suggests that the latter two Paleoarchean granitoid supersuites of the East Pilbara increasingly incorporated\na reworked component, as opposed to being produced by low-degree melting of an amphibolite source. Therefore, the\nresults of this study are not entirely relevant to the <3.3 Ga granitoids of the Pilbara and the authors should be more explicit\nto state that these results apply mostly to the > 3.3 Ga supersuites.\nI understand that this is not a review paper, but the authors need to take a more holistic approach when making inferences\nbased on their results and account for the existing literature from the Pilbara. The four Paleoarchean granitoid supersuites of\nthe East Pilbara Terrane were emplaced contemporaneously with the ultramafic-felsic lavas of the Pilbara Supergroup. If\nsubduction-like processes produced the TTGs, then one would expect that the Pilbara Supergroup lavas would bear\ngeochemical signatures consistent with such a tectonomagmatic setting, given their close spatio-temporal association.\nHowever, there is no evidence for such an origin for the lavas of the Pilbara Supergroup, and they are better explained by\nvariably crustally contaminated volcanism in a mafic plateau setting above a mantle upwelling (e.g., Brown et al., 2024;\nHasenstab et al., 2021; Maier et al., 2009; Murphy et al., 2021; Nebel et al., 2014; Puchtel et al., 2022; Smithies et al., 2005;\nTympel et al., 2021). Thus, as concluded by numerous studies using field, geochronological, structural, and geochemical\ndata, geological context of the EPT in the Paleoarchean remains most parsimoniously explained by processes not\ndiagnostic of plate tectonics (e.g., Brown et al., 2024; Campbell and Davies, 2017; Gardiner et al., 2017; Hawkesworth and\nKemp, 2021; Hickman, 2021, 2023; Johnson et al., 2017, 2022; Roberts et al., 2022; Smithies et al., 2005a, 2009, 2021; Van\nKranendonk et al., 2015, 2019; Wiemer et al., 2018). While experiments can offer interpretations\nand possible explanations of data, experimental results do not constitute proof of the operation of a given process.\nGeodynamics:\nThe planetary angle and broad geodynamic statements are not anchored by new data in this study and still read as overreach;\nthe authors’ response to my original comment on this matter does not rectify this issue.\nAs I said in the original round of reviews, plate tectonics is a very specific type of geodynamic regime. To quote Stern and\nGerya (2018), plate tectonics is defined as “a theory of global tectonics powered by subduction in which the lithosphere is\ndivided into a mosaic of strong lithospheric plates, which move on and sink into weaker ductile asthenosphere. Three types\nof localized plate boundaries form the interconnected global network: new oceanic plate material is created by seafloor\nspreading at mid-ocean ridges, old oceanic lithosphere sinks at subduction zones, and two plates slide past each other\nalong transform faults. The negative buoyancy of old dense oceanic lithosphere, which sinks in subduction zones, mostly\npowers plate movements.”\nThe return of mafic crust to the mantle (either through dripping or subduction) would, of course, be accompanied by rifting\nelsewhere to replace the volume of crust returned to the mantle, but it need not comprise a global, interlinked network of\nridges, transform faults and subduction zones. As shown by multiple numerical modelling studies (e.g., Capitanio et al.,\n2019, 2020, 2022; Lenardic, 2018; Lourenço et al., 2020), this does not necessarily imply plate tectonics. If it did, then\nVenus would also be considered to have a “proto-type of plate tectonics” (e.g., Byrne et al., 2021; Capitanio et al., 2024; Gillmann et\nal., 2025), thereby voiding part of this pitch aimed at a more general scientific audience.\nThe tectonic regime of Earth has evolved along a continuum through its history (see e.g., the review in Cawood et al., 2022),\nso by the authors’ overly broad definition, every possible geodynamic regime with lithospheric recycling would be a “proto-\ntype of plate tectonics.”\nTherefore, I think the wording here needs to change, as the findings of this study do not implicate plate tectonics, even in a\nsubduction-like scenario.\nLine-by-line comments:\nLine 34: What’s meant by “continental” here? Does this refer to the UCC, MCC, LCC or the bulk CC? These all mean\ndifferent things and have different implications.\nLine 42: Absence? They’re certainly rare, but Hadean xenocrystic and detrital zircons have been found in multiple cratons\n(see e.g., Condie, 2019 for a brief review).\nFig. 1: If the authors refer to the Callina and Tambina Supersuites in Lines 85-90, then it would make sense to demarcate the\ndistribution of these supersuites on the map, especially when the Split Rock Supersuite is already on there. Also, I’m\nconfused as to why the Fortescue Group and Kurrana Terrane are included on this map, while the Central Pilbara Tectonic\nZone is not, as the former two are also not part of the East Pilbara Terrane. I’d also recommend symbolizing the sample\nlocality on the map as a dot, perhaps.\nLine 100: For metabasites without oceanic plateau-like compositions, this isn’t the first experimental study with major and\ntrace elements measured in tandem (see e.g., Xiong et al., 2005). For experimental studies using Archean rocks (which\ninherently do not have modern oceanic plateau-like compositions), this is neither the first one to measure major elements\n(Rapp et al., 1991 and Rapp and Watson, 1995 use WR-40, an Archean amphibolite from the Wyoming Craton), nor is it the\nfirst to measure major and trace elements in tandem (Adam et al., 2012 used Nuvvuagittuq amphibolites as their starting\nmaterials). These may be compositionally different from the Coonterunah metabasalts, but it does void the statement of\npriority.\nLine 110-111: Sample 179789 does, in fact, show evidence for crustal contamination by older silicic crust, as demonstrated\nin the SI of Johnson et al. (2017), so stating that the Coonterunah metabasalts “show no evidence that their parental\nmagmas have been contaminated with older silicic crust” is inaccurate.\nLines 167-168: See discussion above about granitoids and geological observations.\nFig. 3: Given the above comments, I recommend the authors only plot > 3.32 Ga granitoids from the East Pilbara as shaded\nareas on their primitive mantle normalized extended trace element diagrams. Including the younger granitoids will invariably\nlead to spurious comparisons.\nLines 214-215: Again, see the discussion above about granitoids and geological observations. Each of the granitoid\ncomplexes in the East Pilbara is comprised of sets of composite intrusions spanning > 700 Myr of Earth’s history and if one\nlooks at a geological map of the area, it is evident that the < 3.32 Ga intrusions are more widespread. I believe this is a\nmisinterpretation once again of Hickman (2004), where the line about granitoids being “dominantly monzogranite and\ngranodiorite” is in reference to the granitoids of the Pilbara Craton as a whole, rather than the EPT, let alone the Callina and\nTambina Supersuites. As I have discussed above, the authors’ assertion that granites and granodiorites are “volumetrically\ndominant in the East Pilbara plutonic centres” is not germane to the central comparison, given that this volumetric\ndominance is the consequence of later magmatism incorporating an increasing amount of reworked components, rather than\ndue to conditions during the generation of TTGs of the Callina and Tambina Supersuites.\nLines 284-288: Not all TTGs are derived from eclogites, some are derived from amphibolites, as demonstrated by field\nevidence (e.g., Kendrick et al., 2024; Pourteau et al., 2020). Ascribing the entire source to eclogites is inaccurate, especially\ngiven that high-pressure group TTGs are not as common as low-pressure group TTGs in the Pilbara (e.g., Champion and\nSmithies, 2019; Vandenburg et al., 2023).\nLine 289: This study does not show that a wet and deep tectonic environment is required to produce the Nb anomalies in the\nF2 Coonterunah basalts. This is granitoid petrology paper, not one on the mantle source of CF2. For what it’s worth crustal\ncontamination better explains many of the Nb anomalies in the CF2 basalts (e.g., Brown et al., 2024; Johnson et al., 2017).\nCrustal contamination can be quite cryptic in many cases as well (see e.g., Vite-Sánchez et al., 2024).\nLines 296-298: In my opinion, this is overly speculative, lacks proper substantiation and diverts from the core message of\nthis study.\nLines 302-303: If subduction is occurring at a flat angle, then doesn’t that contradict the statement in line 298 about the\nexistence of steep subduction with a mantle wedge?\nLines 304-305: Fractional crystallization does not remove the mantle signature in modern adakites, even on the rhyolitic side\nof things, so I don’t see how that would be the case in the Archean with TTGs. If there is subduction, it is unlikely for there to\nbe a mantle wedge, not only because of the aforementioned considerations (see also Smithies, 2000; Martin et al., 2005),\nbut also because all that armouring required to prevent mantle signatures in the TTGs would ultimately have to melt,\nproducing sanukitoids and metasomatized mantle-derived mafic lavas, which are conspicuously absent from the East\nPilbara Terrane.\nLines 306-311: Wrt the ability of subduction-like processes to emit gases into the atmosphere, the emplacement style of the\nvolcanoes is a critical question. The geological evidence is overwhelmingly in favour of subaqueous emplacement (e.g.,\nFlament et al., 2008; Hickman, 2023) in most places, such that the hydrostatic pressure of the overlying oceanic water\ncolumn affected the nature of emitted gases (e.g., Gaillard et al., 2011). This is consistent with multiple lines of evidence for\nvery low sulfate concentrations in the Archaean ocean. There are many more related pieces of evidence regarding\nArchaean atmosphere-hydrosphere-lithosphere interaction that should be considered if trying to pursue this route (e.g.,\nKamber and Ossa-Ossa, 2025).", "reviewer_3": "I found that, in the responese and revise ms, all my concerns have been adequately addressed, which make me to suggest\nacceptance. Congratulations to the authors for a nice work that show the power of experimental study on geodynmics."}, "author_response": "Response to referee 2 for manuscript NCOMMS-25-59996-T\nFrom the perspective of a geochemist, I still believe it substantially overlaps with Hastie et al. (2023), Law et al. (2024) and Law and Hastie (2025), without a clear additional and substantial advance, beyond anything that will be evident to readers other than those from a niche portion of the experimental petrology community.\nThis statement by referee 2 is a factual error. Firstly, Law et al. (2024) is a whole rock geochemical study of\nIcelandic rocks and involves no experimentation (https://www.nature.com/articles/s43247-024-01513-5).\nFurther, we demonstrated in our first response that the starting composition and results of this manuscript\nare completely different to the older studies. We clearly showed that our manuscript uses a composition that\nis hugely different to the older studies with regards to both major and trace elements – it would be difficult\nto find two compositions further apart! Referee 2 chose to ignore this completely. However, to repeat\nourselves:\nThis study is, to our knowledge, the first and only major and trace element experimental study of an ancient\nmetabasic source region from Pilbara that has starting compositions similar to ‘island arc basalts (Samples\n179789, EPT2019, EPT2021, EPT2024). The two starting compositions (the ones from Hastie and Law – 1187-\n8 and 1187-10) are completely and utterly different with regards to both major and trace element\nconcentrations:\nSample SiO TiO Al O FeO(t) MnO MgO CaO Na O K O P O\n2 2 2 3 2 2 2 5\nEPT2019 48.069 2.17 14.855 13.75 0.24 7.72 9.68 2.42 0.96 0.14\nEPT2021 47.822 2.14 14.639 14.44 0.24 7.66 9.59 2.38 0.94 0.14\nEPT2024 48.10 2.07 15.58 13.84 0.25 7.59 9.17 2.32 0.95 0.13\n1187-8 49.22 0.75 14.87 9.76 0.17 9.89 12.39 1.64 0.09 0.06\n1187-10 49.89 0.73 14.53 9.85 0.16 10.20 12.77 1.73 0.10 0.06\nOf the ten major elements, 8 are completely different in the new starting mix (highlighted green) and the\ntrace element concentrations are an order of magnitude different. Finally, Pilbara is at the height of\ncontroversy regarding the evolution of the early continental crust so the results of this study will be of great\ninterest to the scientific community and will be highly sought after.\nThis isn’t the first experimental study with major and trace elements measured in tandem (see e.g., Xiong et\nal., 2005). For experimental studies using Archean rocks (which inherently do not have modern oceanic\nplateau-like compositions), this is neither the first one to measure major elements (Rapp et al., 1991 and\nRapp and Watson, 1995 use WR-40, a Neoarchean amphibolite from the Wyoming Craton), nor is it the first\nto measure major and trace elements in tandem (Adam et al., 2012 used Eoarchean Nuvvuagittuq\namphibolites from the Superior Craton as their starting materials). These may be compositionally different\nfrom the Coonterunah metabasalts, but it does void the statement of priority.\nThis whole statement is factually misleading. Specifically:\n1. Xiong et al. 2005 used a MORB starting mix and nothing from an ancient source; thus, further\ndemonstrating that our starting mix is unique. Also, they only measured Ta, Nb, Hf, Zr, La, Sm, Lu, Rb,\nCs, and Sc, but unlike our analyses that are natural and specifically investigating TTG genesis, Xiong\ndoped their experiments with 100 ppm of each element. This is because they were not replicating\nTTG genesis sensu stricto, they were exploring elemental partitioning.\n2. For the Rapp study, referee 2 proves our point. Rapp used a sample that was 2.7-2.6 billion years\nold and has an E-MORB composition. In contrast, our starting composition is nearly a billion years\nolder and has an island arc-like basaltic composition – completely different.\n3. Adam did experiment on a sample from Superior, but it was a geochemically unique boninite\ncomposition that is very distinct to many of the rocks found in ancient Greenstone belts – completely\ndifferent to our composition as well.\nBasically, our study is the first natural (undoped) major and trace element experimental study using an\nancient island arc basalt-like metabasic rock that are ubiquitous in Hadean-Palaeoarchaean terranes. To\nmake this clear we have highlighted the novelty of our approach and results by re-writing lines 100-113. We\nhave also added all previous experiments in Table S1 for comparison.\nOne glaring issue that I don’t believe I caught in the original manuscript is that the experiments in this study\ndo not produce magmas with trondhjemitic compositions, which are typically associated with the high-\npressure subgroup of TTG series magmas inferred to be produced by a plagioclase-free rutile and garnet-\nbearing source (e.g., Hoffmann et al., 2019; Laurent et al., 2024; Moyen and Martin, 2012; Moyen, 2020).\nThis begs the question whether the results of the experiments can genuinely be considered representative\nof high-pressure TTGs, let alone those in the East Pilbara and thus calls into question the authors’ inferences\nbased on these results.\nMost direct partial melts of metabasic sources are tonalites and granodiorites – so our results are perfectly\nsound. In fact, it would be more irregular to get trondhjemites! Trondhjemites are sub-ordinate to thetwo\nformer rock types. So, it is no surprise that the experimental liquids are not trondhjemitic. Trondhjemites are\ndominantly formed by the fractional crystallisation of tonalite and granodiorite magmas (see Barker 1979 for\nan original take on this and a good summary in Drummond et al. 1996).\nAnother related issue involves the discrepancies between the experimental results and data from\nthermodynamic modelling (e.g., Johnson et al., 2017). I’m not satisfied with the authors’ response to\nReviewer 3’s comment on this issue. The issues arising from the Magmatic NCKFMASHTOCr dataset of\nHolland et al. (2018) are unlikely to have a substantial impact on the stability of accessory phases. While the\nauthors cite the corrigendum of this study as evidence for something being faulty with thermodynamic\nmodelling, this dataset is entirely irrelevant to the results of Johnson et al. (2017) or White et al. (2017), as\nthese studies used the metabasite NCKFMASHTO dataset of Green et al. (2016). Furthermore, the issues that\nthe authors misattribute as being the main contributors to the discrepancy with their results have been fixed,\nso it is an easy (30 minutes tops) and worthwhile endeavour for the authors to compare their results with\nthe most up-to-date thermodynamic modelling in MAGEMin or Thermocalc. It is unlikely that the\nthermodynamic datasets, which are constantly updated and informed by the results of numerous\nexperiments, are incorrect, and I am not convinced of this on the basis of one experimental study.\nApologies, but again, this whole statement is factually incorrect. Specifically:\n1. The issues with the thermodynamic software have a huge impact on the stability of accessory phases.\nThe authors of the correction paper state that accessory phase stability has a large uncertainty in the\nmodelling outputs and the models for accessory phases are particularly imprecise. We have taken\nthe liberty of showing this directly in a screen shot of the paper below (see highlighted). The\ncorrection shows that the problems with the accessory phases cannot be ‘fixed’ because their Gibbs\nfree energy contributions are too small at present. Also, coincidentally, in the same highlighted\nsection, the correction highlights modelling discrepancies between older tonalite models and more\nrecent results. So, older tonalite genesis models are to be viewed with extreme suspicion.\n2. Additionally, Referee 2 wishes to believe thermodynamic modelling results over experimental\nevidence – this is odd in itself as experiments are needed to refine these models. So, asking for a\nmodel to prove an experiment is highly irregular and is not supported by basic scientific principles.\nThe authors have removed their original argument towards the end of the main text about eclogite\nentrainment, but now jumps from inferences on TTGs made based on experimental results to\nunsubstantiated claims about the origin of the mafic protoliths employed in this study. This reads equally\nunsatisfactorily, given that this is unsubstantiated, beyond the scope of this study, and disregards substantial\nevidence to the contrary.\nIt now obvious to us that trying to present arguments for both subduction and intracrustal processes is\ncausing some concern. Thus, on advice from the Nat Comm editorial team we have slimmed this section\ndown and removed sentences in lines 178-182, 270-281, 298-305 and 320-322. We advocate a complex\ntectonic environment on the early Earth with both subduction and intracrustal processes (other studies pick\none or the other) – this also makes our study unique. We now highlight this better in the text and we have\neven modified the title to include both models.\nGranitoids:\nTTGs can be IUGS-defined tonalites, trondhjemites and granodiorites. However, the “TTG series”, which I\nassume the authors are employing as the basis of their arguments, has a specific connotation in the Archean\ncommunity (e.g., Moyen and Martin, 2012; Moyen, 2020; Spencer, 2025). Attributing all compositionally\ntrondhjemitic, tonalitic and granodioritic compositions to the TTG series reflects a lack of engagement with\nthe literature and the commonly used criteria that separate the TTG series from other Archean granitoids.\nAsserting that tonalites, trondhjemites and granodiorites are compositionally identical to the TTG series as\ndefined by seminal studies/articles such as Smithies and Champion (2000), Martin et al. (2005), Moyen and\nMartin (2012), Moyen (2020) and Laurent et al. (2024) without actively employing such criteria, perpetuates\na misconception in the broader igneous community that the two are analogous.\nThe authors should perhaps consider the alternative models of Laurent et al. (2021) and Smit et al. (2024) as\nthe processes outlined in this study have a direct impact on Nb contents, which is traditionally a proxy for\nresidual rutile in TTGs.\nApologies, but again, this whole statement is factually incorrect. TTG are strictly defined under IUGS\nguidelines. All serious studies related to TTG use these guidelines. In our manuscript we follow IUGS\ndefinitions.\nGeological observations:\nAs I discussed in my comments on the previous round of reviews, granites and granodiorites are not the\ndominant silicic plutonic rock types for the Callina and Tambina Supersuites. While there are occurrences of\ngranites in these supersuites as pointed out by the authors, and although I agree that some of these > 3.5-\n3.4 Ga granites are likely produced by low-degree melting of amphibolites, in reality, these are volumetrically\nsubordinate. To use the example that the authors provide as evidence, the North Pole Monzogranite is a\nrelatively small intrusion. Likewise, rhyolites are not particularly germane to the argument as many of these\nare not genetically related to TTGs and do not share the same source (e.g., Smithies et al., 2019), with some\nexceptions, including the Coucal “TTG flow” of Smithies et al. (2009).\nIn their rebuttal, the authors state, “one needs to estimate proportions based on available geochemical\ndata.” I did just that in the original round of reviews, providing two figures using two methods to demonstrate\nthat granites and granodiorites are subordinate to tonalites and trondhjemites in the Callina and Tambina\nSupersuites. I have reattached the two figures from the original round of reviews and recommend that the\nauthors reread my original comments, as their response has been unsatisfactory.\nI’m familiar with Kemp et al. (2023), and it is certainly an important study. However, it doesn’t exist in a\nvacuum, especially with respect to Hf isotope data in granitoids and has its shortfalls. For one, Kemp et al.\n(2023) do not consider the work of Gardiner et al. (2017, 2021). Additionally, samples from all terranes are\npresented together in the εHf-Age diagrams rather than the samples from each terrane separately.\nBecause the different terranes of the Pilbara evolved as independent entities, this can lead to some spurious\ninferences when grouped on the same diagrams. I believe this could explain the authors’ incorrect assertion\nthat “younger granodiorites forming by remelting the tonalites’ is not supported by isotope data, at least to\n3.2 Ga” in response to my comment about the presence of reworked components in granitoids from some\nof the 3.32-3.29 Ga Emu Pool Supersuite intrusions and many of the 3.27-3.22 Ga Cleland Supersuite\nintrusions. To demonstrate the presence of this component from 3.3 Ga onwards, I’ve plotted all available\nHf isotope in zircon data for magmatic grains (within ± < 5% discordance) from East Pilbara Terrane granitoids\nversus time in Fig. 3. As can be seen, both sample mean εHf and individual zircon grain εHf begins to decrease\naround 3.3 Ga (coinciding with the Emu Pool Supersuite) and gets especially pronounced and subchondritic\naround 3.27 Ga (coinciding with the Cleland Supersuite). This shift is best reconciled with the presence of a\nreworked component. This isn’t to say that all granitoids from these supersuites contain the component, as\nthere are clearly intrusions with suprachrondritic εHf, but many do.\nOther lines of evidence exist in addition to the changes in granitoid geochemistry towards more potassic\ncompositions (Vandenburg et al., 2023) and the outlined Hf isotope systematics. Gardiner et al. (2021) also\nprovide further evidence for reworked components based on the presence of xenocrysts in the central\nportions of Emu Pool Supersuite intrusions, suggesting inheritance occurred at depth in their sources, rather\nthan due to wall rock entrainment. Furthermore, oxygen isotope data presented by Smithies et al. (2021) and\nJohnson et al. (2022) from granitoids of the Emu Pool and Cleland Supersuites are best reconciled with the\npresence of a reworked component. Altogether, evidence from the literature most parsimoniously suggests\nthat the latter two Paleoarchean granitoid supersuites of the East Pilbara increasingly incorporated a\nreworked component, as opposed to being produced by low-degree melting of an amphibolite source.\nTherefore, the results of this study are not entirely relevant to the <3.3 Ga granitoids of the Pilbara and the\nauthors should be more explicit to state that these results apply mostly to the > 3.3 Ga supersuites.\nI understand that this is not a review paper, but the authors need to take a more holistic approach when\nmaking inferences based on their results and account for the existing literature from the Pilbara. The four\nPaleoarchean granitoid supersuites of the East Pilbara Terrane were emplaced contemporaneously with the\nultramafic-felsic lavas of the Pilbara Supergroup. If subduction-like processes produced the TTGs, then one\nwould expect that the Pilbara Supergroup lavas would bear geochemical signatures consistent with such a\ntectonomagmatic setting, given their close spatio-temporal association. However, there is no evidence for\nsuch an origin for the lavas of the Pilbara Supergroup, and they are better explained by variably crustally\ncontaminated volcanism in a mafic plateau setting above a mantle upwelling (e.g., Brown et al., 2024;\nHasenstab et al., 2021; Maier et al., 2009; Murphy et al., 2021; Nebel et al., 2014; Puchtel et al., 2022;\nSmithies et al., 2005; Tympel et al., 2021). Thus, as concluded by numerous studies using field,\ngeochronological, structural, and geochemical data, geological context of the EPT in the Paleoarchean\nremains most parsimoniously explained by processes not diagnostic of plate tectonics (e.g., Brown et al.,\n2024; Campbell and Davies, 2017; Gardiner et al., 2017; Hasenstab et al., 2021; Hawkesworth and Kemp,\n2021; Hickman, 2021, 2023; Johnson et al., 2017, 2022; Roberts et al., 2022; Smithies et al., 2005a, 2009,\n2021; Van Kranendonk et al., 2015, 2019; Wiemer et al., 2018). While experiments can offer interpretations\nand possible explanations of data, experimental results do not constitute proof of the operation of a given\nprocess.\nWe thank referee 2 for the time they have taken to write up this background. Unfortunately, most of this\nextensive section is not relevant.\n3. We do not say that granites and granodiorites are not the dominant silicic plutonic rock types for the\nCallina and Tambina Supersuites.\n4. Referee 2 says we say that ‘younger granodiorites forming by remelting the tonalites’. I am afraid we\ndo not say this in the manuscript.\n5. The information deals with much younger rocks <3.25 Ga. Our study relates to rocks and processes\n250 million years before this at 3.52 Ga.\n6. Also, we repeat that: it now obvious to us that trying to present arguments for and against both\nsubduction and intracrustal processes is causing some concern. Referee 2 is very supportive of the\nintracrustal model, which is fine. But, referee 2 must realise that the studies involving subduction as\na mechanism give equally robust defences of their evidence. Thus, on advice from the Nat Comm\neditorial team we have slimmed our tectonic sections down and removed sentences in lines 178-182,\n270-281, 298-305 and 320-322. We have even modified the title to include both models.\nGeodynamics:\nThe planetary angle and broad geodynamic statements are not anchored by new data in this study and still\nread as overreach; the authors’ response to my original comment on this matter does not rectify this issue.\nAgain, we repeat that: it now obvious to us that trying to present arguments for and against both\nsubduction and intracrustal processes is causing some concern. Referee 2 is very supportive of the\nintracrustal model, which is fine. But, referee 2 must realise that the studies involving subduction as\na mechanism give equally robust defences of their evidence. Thus, on advice from the Nat Comm\neditorial team we have slimmed our tectonic sections down and removed sentences in lines 178-182,\n270-281, 298-305 and 320-322. We advocate a complex tectonic environment on the early Earth with both\nsubduction and intracrustal processes (other studies pick one or the other) – this also makes our study unique.\nWe now highlight this better in the text and we have even modified the title to include both models.\nAs I said in the original round of reviews, plate tectonics is a very specific type of geodynamic regime. To\nquote Stern and Gerya (2018), plate tectonics is defined as “a theory of global tectonics powered by\nsubduction in which the lithosphere is divided into a mosaic of strong lithospheric plates, which move on and\nsink into weaker ductile asthenosphere. Three types of localized plate boundaries form the interconnected\nglobal network: new oceanic plate material is created by seafloor spreading at mid-ocean ridges, old oceanic\nlithosphere sinks at subduction zones, and two plates slide past each other along transform faults. The\nnegative buoyancy of old dense oceanic lithosphere, which sinks in subduction zones, mostly powers plate\nmovements.”. The return of mafic crust to the mantle (either through dripping or subduction) would, of\ncourse, be accompanied by rifting elsewhere to replace the volume of crust returned to the mantle, but it\nneed not comprise a global, interlinked network of ridges, transform faults and subduction zones. As shown\nby multiple numerical modelling studies (e.g., Capitanio et al., 2019, 2020, 2022; Lenardic, 2018; Lourenço et\nal., 2020), this does not necessarily imply plate tectonics. If it did, then Venus would also be considered to\nhave a “proto-type of plate tectonics” (e.g., Byrne et al., 2021; Capitanio et al., 2024; Gillmann et al., 2025),\nthereby voiding part of this pitch aimed at a more general scientific audience.\nTo repeat ourselves again, it now obvious to us that trying to present arguments for and against both\nsubduction and intracrustal processes is causing some concern. Referee 2 is very supportive of the\nintracrustal model, which is fine. But, referee 2 must realise that the studies involving subduction as\na mechanism give equally robust defences of their evidence. Thus, on advice from the Nat Comm\neditorial team we have slimmed our tectonic sections down and removed sentences in lines 178-182,\n270-281, 298-305 and 320-322. However, the models cited are done in two dimensions. It is geodynamically implausible\nto have spreading and subduction localised to small areas of the planet – it just doesn’t make sense at all.\nWe advocate a complex tectonic environment on the early Earth with both subduction and intracrustal\nprocesses (other studies pick one or the other) – this also makes our study unique. We now highlight this\nbetter in the text and we have even modified the title to include both models.\nLine-by-line comments:\nLine 34: What’s meant by “continental” here? Does this refer to the UCC, MCC, LCC or the bulk CC? These all\nmean different things and have different implications.\nLine re-worded.\nLine 42: Absence? They’re certainly rare, but Hadean xenocrystic and detrital zircons have been found in\nmultiple cratons (see e.g., Condie, 2019 for a brief review).\nLine re-worded.\nLine 100: For metabasites without oceanic plateau-like compositions, this isn’t the first experimental study\nwith major and trace elements measured in tandem (see e.g., Xiong et al., 2005). For experimental studies\nusing Archean rocks (which inherently do not have modern oceanic plateau-like compositions), this is neither\nthe first one to measure major elements (Rapp et al., 1991 and Rapp and Watson, 1995 use WR-40, an\nArchean amphibolite from the Wyoming Craton), nor is it the first to measure major and trace elements in\ntandem (Adam et al., 2012 used Nuvvuagittuq amphibolites as their starting materials). These may be\ncompositionally different from the Coonterunah metabasalts, but it does void the statement of priority.\nStatement addressed above.\nLine 110-111: Sample 179789 does, in fact, show evidence for crustal contamination by older silicic crust, as\ndemonstrated in the SI of Johnson et al. (2017), so stating that the Coonterunah metabasalts “show no\nevidence that their parental magmas have been contaminated with older silicic crust” is inaccurate.\nSmithies et al 2009 and the isotope data in Kemp et al 2023 suggests otherwise.\nLines 167-168: See discussion above about granitoids and geological observations\nStatement addressed above.\nFig. 3: Given the above comments, I recommend the authors only plot > 3.32 Ga granitoids from the East\nPilbara as shaded areas on their primitive mantle normalized extended trace element diagrams. Including\nthe younger granitoids will invariably lead to spurious comparisons.\nThis is the case anyhow.\nLines 214-215: Again, see the discussion above about granitoids and geological observations. Each of the\ngranitoid complexes in the East Pilbara is comprised of sets of composite intrusions spanning > 700 Myr of\nEarth’s history and if one looks at a geological map of the area, it is evident that the < 3.32 Ga intrusions are\nmore widespread. I believe this is a misinterpretation once again of Hickman (2004), where the line about\ngranitoids being “dominantly monzogranite and granodiorite” is in reference to the granitoids of the\nPilbara Craton as a whole, rather than the EPT, let alone the Callina and Tambina Supersuites. As I have discussed\nabove, the authors’ assertion that granites and granodiorites are “volumetrically dominant in the East Pilbara\nplutonic centres” is not germane to the central comparison, given that this volumetric dominance is the\nconsequence of later magmatism incorporating an increasing amount of reworked components, rather than\ndue to conditions during the generation of TTGs of the Callina and Tambina Supersuites.\nStatement addressed above.\nLines 284-288: Not all TTGs are derived from eclogites, some are derived from amphibolites, as demonstrated\nby field evidence (e.g., Kendrick et al., 2024; Pourteau et al., 2020). Ascribing the entire source to eclogites is\ninaccurate, especially given that high-pressure group TTGs are not as common as low-pressure group TTGs\nin the Pilbara (e.g., Champion and Smithies, 2019; Vandenburg et al., 2023).\nSection removed to tone down tectonic discussion.\nLine 289: This study does not show that a wet and deep tectonic environment is required to produce the Nb\nanomalies in the F2 Coonterunah basalts. This is granitoid petrology paper, not one on the mantle source of\nCF2. For what it’s worth crustal contamination better explains many of the Nb anomalies in the CF2 basalts\n(e.g., Brown et al., 2024; Johnson et al., 2017). Crustal contamination can be quite cryptic in many cases as\nwell (see e.g., Vite-Sánchez et al., 2024).\nSection removed to tone down tectonic discussion.\nLines 296-298: In my opinion, this is overly speculative, lacks proper substantiation and diverts from the core\nmessage of this study.\nSection removed to tone down tectonic discussion.\nLines 302-303: If subduction is occurring at a flat angle, then doesn’t that contradict the statement in line\n298 about the existence of steep subduction with a mantle wedge?\nLine re-worded.\nLines 304-305: Fractional crystallization does not remove the mantle signature in modern adakites, even on\nthe rhyolitic side of things, so I don’t see how that would be the case in the Archean with TTGs. If there is\nsubduction, it is unlikely for there to be a mantle wedge, not only because of the aforementioned\nconsiderations (see also Smithies, 2000; Martin et al., 2005), but also because all that armouring required to\nprevent mantle signatures in the TTGs would ultimately have to melt, producing sanukitoids and\nmetasomatized mantle-derived mafic lavas, which are conspicuously absent from the East Pilbara Terrane.\nThis statement is false.\nLines 306-311: Wrt the ability of subduction-like processes to emit gases into the atmosphere, the\nemplacement style of the volcanoes is a critical question. The geological evidence is overwhelmingly in favour\nof subaqueous emplacement (e.g., Flament et al., 2008; Hickman, 2023) in most places, such that the\nhydrostatic pressure of the overlying oceanic water column affected the nature of emitted gases (e.g.,\nGaillard et al., 2011). This is consistent with multiple lines of evidence for very low sulfate concentrations in\nthe Archaean ocean. There are many more related pieces of evidence regarding Archaean atmosphere-\nhydrosphere-lithosphere interaction that should be considered if trying to pursue this route (e.g.,\nKamber and Ossa-Ossa, 2025).\nResponse to referee 4 for manuscript NCOMMS-25-59996-T\nWe thank Reviewer 4 for their thorough and insightful review that has improved our manuscript. We now\nrespond to the specific suggestions by review 4 below:\n(1) A clearer definition of the specific time-frame the study is relevant to.\nThe title states ‘Early Archaean’, the abstract mentions 4.3-3.5 Ga and 4.0-3.5 Ga time periods, lines 83—93\nappear to indicate the study is specifically focusing generation of the Callina and Tambina supersuites (~3.5-\n3.4 Ga), and several places in the text mention Eoarchean-Paleoarchean or Hadean-Paleoarchean crustal\nformation. Do the experimental results only pertain to the generation of Paleoarchean TTGs in the East\nPilbara Terrane? If so, this could be stated more explicitly. Note that the Eoarchean record of the East\nPilbara Terrane is sparse so line 77 needs amending (the Paleoarchean might be extensive, but the\nEoarchean is only known from rare enclaves and detrital zircon and apatite grains). It is possible that the\ncomposition and crust-forming processes of the Eoarchean crust of the East Pilbara Terrane differ from the\npreserved Paleoarchean crust (compare Hickman, 2023, Archean Evolution of the Pilbara Craton and\nFortescue Basin and Kharkongor et al. 2025, Geology). This point is also true for other Archean terranes\nwhere any Hadean-Eoarchean record is primarily preserved as detrital or xenocrystic zircon grains. There is\nno consensus on the composition of the original host rocks of Hadean-Eoarchean zircons (a quick survey of\nrecent literature on Hadean zircon trace element chemistry includes estimates ranging from peraluminous\ngranites, andesites, mafic rocks, and TTGs). As written the paper implies that the Paleoarchean TTGs of the\nEPT are representative of all early continental crust (including Eoarchean-Hadean). I think this is a\nreasonable assertion but the debate regarding the composition and origin of Eoarchean-Hadean crust and\nthe possibility that it differed from the more widely preserved Paleo-Mesoarchean crust should be\nacknowledged.\nWe apologise for the confusion with the timings. We have now tidied up the text. 4.0 is changed to 4.3 in\nthe abstract and ‘Eoarchaean’ has been removed from lines 79, 122, 201 and 275 to show that we only\nreference Palaeoarchaean TTG and the Palaeoarchaean in general.\n(2) The discussion of lithospheric recycling on the early Earth could be framed in the context of recent\ngeodynamic modelling studies.\nInferring Early Earth geodynamic settings from geochemical data is highly contested and non-unique. I\nrecognise that the authors have already made a significant effort to tone-down this aspect of the\nmanuscript during earlier reviews. However, the inferences of the geodynamic setting of early Archean\ncrust formation could be strengthened by discussing this aspect of the study in the context of recent\ngeodynamic modelling. The study advocates for deep subduction and ‘proto’ or ‘primitive’ plate tectonics\nto generate Paleoarchean TTGs in the East Pilbara Terrane. ‘Proto plate tectonics’ and ‘ primitive plate\ntectonics’ are nebulous terms and there have been recent efforts to clearly define the difference between\nmodern plate tectonics and the geodynamic environments operating on the early Earth (see Cawood et al.\n2022 for an accessible summary). Numerical and thermomechanical modelling also highlight important\ndifferences in geodynamic settings on a hotter early Earth compared to modern plate tectonics. These\nstudies recognise several possible geodynamic modes on early Earth, for example, stagnant lid, squishy lid,\nmobile lid modes.\nWe have further ‘toned down’ the argument and referenced a few geodynamic models. We add sentence\n274 to highlight support for co-existing tectonic models that we advocate with subduction and intracrustal\nprocesses. Also, we recognise that we shouldn’t use ‘proto’ and ‘primitive’ so we have removed the term\n‘proto’.\nSubduction or lithospheric dripping are cited as possible mechanisms for generating high-pressure TTG\nmelts but the authors lean in favour of subduction and a plate tectonic like regime (e.g., in the title and\nabstract). Both these processes are consistent with ‘squishy’ or ‘mobile’ lid tectonic modes. Many readers\nmay find these definitions more palatable than referring explicitly to plate tectonics. In my opinion, using\nexperimental data to demonstrate a diversity of melt-generating environments on the early Earth is an\nimportant and impactful finding alone. Describing the geodynamic setting of melting might be an issue of\nsemantics, but at least using the more recent definitions outlined above provides a common framework for\ncommunicating the geodynamic setting the authors are envisaging.\nWe have indicated plutonic squishy lid terminology in lines 32, 63, 273. For mobile lids, I think we still\nprefer the terms ‘subduction’ and ‘primitive plate tectonics’.\nMinor points:\nInconsistent naming of the study area. The study area is referred to as ‘Pilbara terrane’ , ‘northern Pilbara\ncraton’ , ‘East Pilbara’. The study focuses on the EAST PILBARA TERRANE, which is a terrane within the\nPilbara Craton. This should be updated throughout the text.\nThe terminology has been updated throughout the text. Apologies for any confusion."}, {"round": 3, "reviewer_comments": {"reviewer_4": "I am satisfied that the authors have addressed my queries."}, "author_response": ""}]

Decision letter