Andreea Apetrei

Arnaud Molin

Cindy Colson

H Mittre

Matthieu Decamp

Nadia Coudray

Marie-Laure Kottler

Nicolas Gruchy

Nicolas Richard

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Identification by whole genome sequencing of a 140Kb inversion in GNAS locus involving NPELP1 and Xlas gene in a family presenting an autosomal dominant pseudohypoparathyroidism type 1b

Patients & Methods :

In this study we investigated a family with two affected individuals, the proband and his sister, both presenting a typical phenotype of PHP1b (Table 1).

A Sanger sequencing of the GNAS locus and a methylation-specific multiplex ligationdependent probe amplification (MS-MLPA) analysis were realized for the 2 affected siblings (II.1 and II.3) and their parents (I.1 and I.2). A whole genome sequencing (WGS) analysis was performed for the proband (I.1) : the library preparation (350pb fragments with paired-end 2x150pb) used the NEBNext DNA Library Prep Kit, the sequencing was performed using an Illumina platform, the sequences were aligned at the reference human genome GRCh38 and the data was processed using the GATK pipeline. The inversion was confirmed by a Sanger analysis of the break-points and by a PCR analysis of the genomic DNA using primers designed to amplify across both breakpoints of the mutant allele. A quantitative real-time polymerase chain reaction (qPCR) was realized for the index case and his parents.

Results :

There was no gain, deletion or mutation in the GNAS locus.

The epigenetic analysis by MS-MLPA showed a complete LOM at A/B-DMR, a partial LOM at Xlas-DMR and normal methylation for AS-DMR and NESP-DMR for the two patients.

There was no LOM for their parents (Table 2).

The WGS analysis revealed a paracentric inversion of 140 Kb with the breakpoint localized at 5': intron NPELP1 and 3': exon Xlas (Figure 1).

A PCR analysis of the genomic DNA using primers designed to amplify across both breakpoints for the wild-type and mutant allele was realized (Figure 2A). Amplicons were obtained for the index case, his sister and his mother, while no PCR product was generated for DNA from the father (Figure 2B). The qPCR analysis showed a 50% augmentation for the father and no significant difference for the mother in the WT allele DNA quantification compared to the index case (Figure 2C). The breakpoints were confirmed by Sanger analysis for both patients and their mother (Figure 3).

Background :

The GNAS complex locus encodes the alpha-subunit of the stimulatory G protein (Gsα) and additional imprinted transcripts. Pseudohypoparathyroidism type 1b (PHP1b) is characterized by renal resistance to PTH (and, sometimes, a mild resistance to TSH), which occurs typically in the absence of any features of Albright's hereditary osteodystrophy. PHP1b is caused by epigenetic modifications at one or several differentially methylated regions (DMR) within GNAS locus that reduce transcription of Gsα from the maternal allele, resulting in diminished GSα expression in the tissues in which the paternal Gsα allele is normally silenced. The most frequent genetic cause for the autosomal dominant PHP1b (AD-PHP1b) is the maternally inherited STX16 deletion, which leads to isolated loss-of-methylation (LOM) at exon A/B alone. Other rare molecular mechanisms are described, especially copy numbers abnormalities encompassing one or several DMRs (NEPS55, NESPAS, XLas).

References :

1 Grigelioniene et al, JBMR, 2017, PMID : 28084650

Contact: apetrei-a@chu-caen.fr ; richard-n@chu-caen.fr

Identification by whole genome sequencing of a 140Kb inversion in GNAS locus involving NPELP1 and Xlas gene in a family presenting an autosomal dominant pseudohypoparathyroidism type 1b

Apetrei A 1 , Molin A 1 , Colson C 1 , Mittre H 1 , Decamp M 1 , Coudray N 1 , Kottler ML 1 , Gruchy N 1 , Richard N 1

Discussion :

We detected a novel genetic rearrangement in a family with AD-PHP1B, an inversion 20q13.3 which includes the region between NPELP1 and XLas.

DNA methylation analysis showed a complete LOM for the DMRs situated outside the inversion for the two patients and a significant increase of methylation (~20%) for the DMRs situated in the inversed region for their mother (Figure 4).

To our knowledge, only one large inversion has been described in AD-PHP1b which included the entire A/B DMR and GNAS gene 1 . The cause of this methylation profile remains unkown, but these results are raising the question of a new imprinted locus in the inversed region. Further studies are necessary in order to verify this hypothesis. The WGS is useful in a diagnosis purpose in the cases in which the recurrent genetic etiologies are not found.

Figure 1 :

 1 Figure 1 : Use of the Integrative Genome Viewer to show WGS data of the centromeric and telomeric breakpoints of the inversion. The blue and the green bars are indicative of nucleotide sequences that match only partially with these regions of chromosome 20.

Figure 3 :

 3 Figure 3 : Nucleotide sequence analysis of the mutant allele across the centromeric and the telomeric breakpoints using genomic DNA of patient II.1. Upper panel: centromeric breakpoint : identical nucleotide sequence up to the breakpoint followed by nucleotide sequence from the WT (black) or the mutant allele (red). Bellow are the representative nucleotide sequences of the mutant allele. Lower panel: telomeric breakpoint : nucleotide sequence from the WT (black) or mutant allele (red) followed by identical nucleotide sequence after the breakpoint. Bellow are the representative nucleotide sequences of the mutant allele.

Figure 2 :

 2 Figure 2 : A. Schematic representation of PCR primers and their approximate locations in the wild-type and mutant alleles comprising the GNAS locus. B. Presence of the inversion detected on II.1, II.3 and I.2's DNAs using PCR across both breakpoints for the wild-type and mutant allele. C. qPCR results: DNA quantification for the WT centromeric region compared to the index case (used as a control).

Figure 4 :

 4 Figure 4 : Methylation percentage obtained by MS-MLPA for 5 DMRs. Gray vertical bar indicate the 95% confidence interval in 12 control subjects. The chromosomal position of the start of each CpG site whose methylation level was assessed by MS-MLPA is written underneath.

Table 1 :

 1 Laboratory analysis of a family with AD-PHP1b. Pedigree of the investigated family, consistent with the mode of inheritance of PHP1b. Birth parameters, age at diagnosis and laboratory findings at presentation are provided.

1 Normandy University, UNICAEN, University Hospital of Caen, Department of Genetics, Reference Center of Rare iseases of Calcium and Phosphorus Metabolism, EA 7450 BioTARGen, Caen, France

Table 2 :

 2 MS-MLPA results as mean values of the percentages of all studied DMRSs.


Inês Pereira
email: ines.pereira@uca.fr

Craig D Storey
email: craig.storey@port.ac.uk

James R Darling
email: james.darling@port.ac.uk

Hugo Moreira
email: hugo.moreira@umontpellier.fr

Robin A Strachan
email: rob.strachan@port.ac.uk

Peter A Cawood
email: peter.cawood@monash.edu

Detrital rutile tracks the first appearance of subduction zone low T/P paired metamorphism in the Palaeoproterozoic

Keywords: metamorphic proxy, low T/P metamorphism, paired metamorphism, detrital rutile, plate tectonics, Palaeoproterozoic

Earth is unique in the Solar System as the only planet characterised by an active plate tectonic regime. However, there is still no consensus on whether this was fully operational in the Archaean or if it did not develop until the Proterozoic. The metamorphic record offers valuable insight into this debate, since paired, high and low T/P metamorphic conditions are a hallmark of modern plate tectonics. However, much of the metamorphic rock record has either been eroded or overprinted by subsequent tectonothermal events. To address this issue, we examine the detrital rock record and evaluate the potential of rutile, a mineral that forms during subduction and deep-crustal metamorphic processes, as a proxy to track the existence of low T/P and paired metamorphism. At temperatures of 550 ºC, rutile is mostly stable at pressures higher than ca. 13 kbar. We use this relationship and the Zr-in-rutile thermometer to determine peak metamorphic temperatures of detrital rutile grains to track the temporal distribution of low T/P metamorphism. We have compiled a dataset of detrital metamorphic rutile from Archaean to Permian age to trace the occurrence of low and high T/P metamorphism through time. The earliest evidence of low T/P from detrital rutile is at about 2.1 Ga. This agrees with the earliest evidence of eclogite facies conditions from the rock record and it also implies that these conditions must have been more prevalent than the present rock record seems to indicate. Together, our study confirms that subduction zone low T/P metamorphism has been fully operating since at least the late Palaeoproterozoic.

INTRODUCTION

The cyclic formation of supercontinents by modern plate tectonics is of critical importance to the secular evolution of the Earth System. It impacts, for example, the oxygenation of the atmosphere [START_REF] Campbell | The mountains that triggered the Late Neoproterozoic increase in oxygen: The Second Great Oxidation Event[END_REF], nutrient addition to the oceans [START_REF] Reinhard | Evolution of the global phosphorus cycle[END_REF][START_REF] Zerkle | Biogeodynamics: Bridging the gap between surface and deep Earth processes[END_REF], and the geological record itself [START_REF] Dhuime | Continental growth seen through the sedimentary record[END_REF][START_REF] Li | Geochemical and Nd isotopic variations in sediments of the South China Sea: A response to Cenozoic tectonism in SE Asia[END_REF].

Earth experienced major changes between 3 and 2 Ga [START_REF] Cawood | Geological archive of the onset of plate tectonics[END_REF][START_REF] Condie | A planet in transition: The onset of plate tectonics on Earth between 3 and 2 Ga?[END_REF][START_REF] Brown | Plate Tectonics and the Archean Earth[END_REF], including variations in the composition of the continental crust (Laurent et al., 2014a), and a change in the rate of continental growth [START_REF] Dhuime | A Change in the Geodynamics of Continental Growth 3 Billion Years Ago[END_REF]. Several of these changes have been linked to the onset of subduction as a response to the secular cooling of the mantle. However, subduction may have been localized and unstable on the early Earth and therefore may not in itself provide evidence for modern plate tectonics, which requires sustained subduction [START_REF] Brown | Plate Tectonics and the Archean Earth[END_REF][START_REF] Cawood | Geological archive of the onset of plate tectonics[END_REF]. It is therefore necessary to investigate the geological record for evidence of the major hallmarks of modern plate tectonics, namely the existence of self-sustained, interlinked subduction systems [START_REF] Lenardic | The diversity of tectonic modes and thoughts about transitions between them[END_REF].

The metamorphic rock record provides strong evidence for sustained subduction for at least the last 700 million years [START_REF] Brown | Plate Tectonics and the Archean Earth[END_REF][START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF][START_REF] Stern | Evidence from ophiolites, blueschists, and ultrahigh-pressure metamorphic that the modern episode tectonics began in Neoproterozoic time[END_REF] with the prevalence of low-temperature eclogite and blueschist facies, and paired metamorphism. This record of cold-subduction is widespread in the Phanerozoic [START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF], but the apparent absence of evidence for low geothermal gradients (T/P) in the greater part of the Proterozoic and during the Archaean [START_REF] Brown | Plate Tectonics and the Archean Earth[END_REF][START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF] has been argued as indicating that a different tectonic regime prevailed prior to the Neoproterozoic [START_REF] Kusky | Plate tectonics in relation to mantle temperatures and properties[END_REF][START_REF] Stern | Evidence from ophiolites, blueschists, and ultrahigh-pressure metamorphic that the modern episode tectonics began in Neoproterozoic time[END_REF]. Exceptionally, late Palaeoproterozoic, partially retrogressed eclogite units have been reported (e.g. [START_REF] François | The earliest evidence for modern-style plate tectonics recorded by HP LT metamorphism in the Paleoproterozoic of the Democratic Republic of the Congo[END_REF][START_REF] Ganne | Modern-style plate subduction preserved in the Palaeoproterozoic West African craton[END_REF][START_REF] Province | Garnet and zircon geochronology of the Paleoproterozoic Kuru-Vaara[END_REF][START_REF] Weller | Record of modern-style plate tectonics in the Palaeoproterozoic Trans-Hudson orogen[END_REF], providing a growing body of evidence for cold-subduction and strong plates that allowed the exhumation of these units.

However, due to the rather fragmentary and scarce repository of rocks recording these conditions, the assertion that modern plate tectonics has been fully operating since then has proven contentious. The period between the Palaeoproterozoic and the early Neoproterozoic may be characterized by an intermediate plate tectonic cycle between early Earth and modern-like endmembers [START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF].

The identification of certain metamorphic conditions relies on the preservation of indicator minerals; for example, the presence of lawsonite or glaucophane is indicative of HP conditions. However, these hydrous mineral phases are prone to dehydration reactions during retrogression from HP conditions [START_REF] Skelton | Preservation of high-P rocks coupled to rock composition and the absence of metamorphic fluids[END_REF][START_REF] Tsujimori | Very-lowtemperature record of the subduction process: A review of worldwide lawsonite eclogites[END_REF] and therefore pristine blueschist and low-T eclogite are rare even in the modern rock record [START_REF] Lombardo | Two contrasting eclogite types in the Himalayas: Implications for the Himalayan orogeny[END_REF][START_REF] Whitney | Why is lawsonite eclogite so rare? Metamorphism and preservation of lawsonite eclogite, Sivrihisar, Turkey[END_REF]. In this study, we aim to provide a new way of probing the metamorphic record and assessing preservation bias, particularly of low T/P metamorphism, by using detrital rutile.

Rutile most commonly occurs after Ti-bearing precursors in intermediate to high pressure metamorphic rocks, particularly the latter [START_REF] Angiboust | Ilmenite breakdown and rutile-titanite stability in metagranitoids: Natural observations and experimental results[END_REF][START_REF] Liou | Mineral parageneses in the Piampaludo eclogitic body, Gruppo di Voltri, western Ligurian Alps[END_REF][START_REF] Zack | Petrology and Geochronology of Rutile[END_REF]. It is also found within upper amphibolite and granulite facies terrains, and associated with either magmatic or lower temperature and pressure settings due to fluid precipitating processes [START_REF] Carruzzo | Texture, composition, and origin of rutile in the South Mountain Batholith[END_REF][START_REF] Gonçalves | Twenty million years of post-orogenic fluid production and hydrothermal mineralization across the external Araçuaí orogen and adjacent São Francisco craton, SE Brazil[END_REF][START_REF] Kotková | Anatexis during high-pressure crustal metamorphism: Evidence from garnet-whole-rock REE relationships and zircon-rutile Ti-Zr thermometry in leucogranulites from the Bohemian Massif[END_REF]. More rarely, rutile has been described as replacing ilmenite at intermediate grades (480-550 ºC) in metapelites [START_REF] Luvizotto | Rutile occurrence and trace behavior in medium-grade metasedimentary rocks: Example from the Erzgebirge, Germany[END_REF]. Alongside its higher stability at high pressures, Zr concentrations in rutile are temperature-dependent [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF][START_REF] Tomkins | The pressure dependence of the zirconium-inrutile thermometer[END_REF]Zack et al., 2004a). Together, this makes rutile an ideal candidate to be used as a proxy of low T/P metamorphism. Although rutile can re-equilibrate during retrogression from higher metamorphic conditions, it is more robust than other minerals such as lawsonite and glaucophane that due to their hydrated nature are prone to re-equilibrate more readily. Rutile is also ubiquitous in detrital rocks, and thus it commonly survives weathering and transport. By investigating the sedimentary archive using detrital rutile we expect to be able to develop a more complete picture of the metamorphic record through time, compared with that derived from currently exposed metamorphic terrains (Brown and Johnson, 2019). This approach will allow: 1) tackling the individual metamorphic evolution of Precambrian terranes whose current crustal exposure is from deeper orogenic roots and thus bias the known metamorphic record towards higher-grade conditions, and 2) investigating long term metamorphic secular evolution, and its tectonic drivers, at a global scale.

SAMPLES, APPROACH AND METHODS

We have investigated published Zr-in-rutile geothermometry data from metamorphic rocks (appendix 1) to evaluate the potential of rutile as a proxy for low T/P metamorphism and some of the limitations associated with this approach. We also looked at detrital rutile datasets reporting U-Pb ages and a complete range of trace element data that are required for source discrimination and geothermometry, that include Cr, Zr, Nb, Sn, Hf, Ta and W.

This results in the first combined data compilation of detrital rutile, using data from six published datasets [START_REF] Agangi | Compositional modification and trace element decoupling in rutile: Insight from the Capricorn Orogen, Western Australia[END_REF][START_REF] Flowerdew | Assessing mineral fertility and bias in sedimentary provenance studies: examples from the Barents Shelf[END_REF][START_REF] Rösel | Interpretation and significance of combined trace element and U Pb isotopic data of detrital rutile: a case study from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany[END_REF][START_REF] Rösel | LA-ICP-MS U-Pb dating of detrital rutile and zircon from the Reynolds Range: A window into the Palaeoproterozoic tectonosedimentary evolution of the North Australian Craton[END_REF] , from different regions and depositional ages, culminating in a dataset of detrital rutile ages ranging from the Permian to the Archean (appendix 2). To complement this dataset, we collected new trace element data from 161 U-Pb concordant detrital rutile grains, from samples collected in NW Scotland. These correspond to a stratigraphic succession of Neoproterozoic to Cambrian in age: the Torridon Group and the Ardvreck Group, Eriboll Formation. Six samples were prepared from these units (3 from the Torridon Grp. and 3 from the Eriboll Fm.) and rutile grains were handpicked after common mineral separation procedures (see [START_REF] Pereira | Two billion years of evolution enclosed in hydrothermal rutile: Recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes[END_REF]. Sample locations and U-Pb data for these rutile grains are presented and discussed in [START_REF] Pereira | Detrital rutile ages can the tectonic setting of sedimentary basins[END_REF]. U-Pb concordant rutile grains were then subjected to trace element analysis using LA-ICPMS.

BSE images were used to target the same domains as sampled during the U-Pb isotopic analysis. Rutile grains included in this study are mostly homogeneous, with no apparent BSE (trace element composition) zonation, and yield U-Pb ages ranging from 1.0 to 2.9 Ga.

The total dataset comprises 840 analyses (appendix 4).

Trace element microanalysis by Laser ablation coupled inductively plasma Mass Spectrometry (LA-ICPMS) A sample-standard bracketing method was used to correct for instrumental drift using BCR-2 as the reference material (using reported concentrations from [START_REF] Jochum | Chemical Characterisation of the USGS Reference Glasses and BIR-1G Using EPMA , ID-TIMS , ID-ICP-MS and LA-ICP-MS. Geostand[END_REF]).

R10 (GEOREM database), BHVO (using reported concentrations from [START_REF] Jochum | Chemical Characterisation of the USGS Reference Glasses and BIR-1G Using EPMA , ID-TIMS , ID-ICP-MS and LA-ICP-MS. Geostand[END_REF])

and NIST610 and 612 (reported concentrations from [START_REF] Jochum | Determination of reference values for NIST SRM 610-617 glasses following ISO guidelines[END_REF]) were used as secondary standards, analysed between unknowns and primary standards in the samplestandard bracketing method. NIST610 and R10 were analysed using a 40 µm laser beam diameter. In contrast, for the BHVO reference material, a laser beam of 80 µm diameter was used to directly access the attenuation mode of the ANALYTIK JENA ICP-MS, important for stable measurement of 49 Ti. TiO2 was used as an internal standard to normalise the intensity of all unknowns, using reference reported values for glasses, and using Ti of 58.8 wt% for all rutile grains). Data were processed using the software package IOLITE 3.31. For Zr, we obtained 5% accuracy relative to published values for all glass standards, within 5% from published values for R10 (GEOREM database) and a 0.06 ppm detection limit. The full instrumental and analytical setup and standard data can be found in appendix 3.

ZR-IN-RUTILE GEOTHERMOMETRY APPLIED TO DETRITAL GRAINS

Application of the Zr-in-rutile thermometer

The Zr-in-rutile thermometer has been calibrated based on natural samples by Zack et al. (2004). Several other researchers have subsequently refined the calibration, including [START_REF] Tomkins | The pressure dependence of the zirconium-inrutile thermometer[END_REF] who demonstrated a minor pressure dependency, more significant in the alpha-quartz field. These calibrations have been recently revisited by [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF] who used new natural data, refined previous natural datasets, and combined them with published experimental data into a new equation that we use in this study. In Figure 1, a comparison between temperature estimates obtained by Zr-in-rutile and mineral equilibria using conventional thermobarometry from 14 published studies (appendix 1) is presented. In most circumstances, thermobarometry based on element exchange between mineral pairs yields a larger uncertainty than single grain thermometers (Fig. 1). Uncertainties in applying this calibration are around 10-15 ºC, which is often the variation achieved taking into account the uncertainty in the assumed pressure (Fig. 1). On the other side, the standard deviation of Zr concentrations between grains within the same sample propagates into a larger uncertainty that often exceeds that obtained from mineral equilibria (Fig. 1).

The linear correlation between both methods is consistent, yielding a ratio not far from 1 (Fig. 1A). This correlation is improved if the temperature estimate used for the correlation taken from mineral equilibria is adjusted to its uncertainty (R 2 = 0.72; Fig 1B). For instance, often peak conditions are given as a range, and the true value is enclosed in the interval. Instead of the average, we compare the T estimate determined from Zr-in-rutile and check whether the temperature is enclosed by the interval. If so, the value is taken as the true average T for the correlation. Where this difference is larger than the interval, the uncertainty from the average T estimate from mineral equilibria is either summed or subtracted to obtain the best correlation scenario. In doing so, it becomes clear that for most samples, average Zr concentrations and their uncertainties have a robust fit with the thermobarometric estimate of their rocks, with a tendency line that is essentially 1:1 (Fig. 1).

Regardless of the calibration equation, rutile has to be in equilibrium with zircon and quartz, so that t-ZrO2 and -quartz activities are 1. As [START_REF] Triebold | A recipe for the use of rutile in sedimentary provenance analysis[END_REF][START_REF] Triebold | Deducing source rock lithology from detrital rutile geochemistry: An example from the Erzgebirge[END_REF] demonstrate, by applying a discrimination diagram based on Cr and Nb [START_REF] Meinhold | Rutile chemistry and thermometry as provenance indicator: An example from Chios Island, Greece[END_REF]Zack et al., 2004b), rutile grains that have metafelsic affinity can be presumed to have formed in such conditions. Therefore, a filter was applied to enable distinction between probable protolith sources, and thus to infer silica activity in the system. By applying the log(Cr/Nb) following [START_REF] Meinhold | Rutile chemistry and thermometry as provenance indicator: An example from Chios Island, Greece[END_REF], grains with log(Cr/Nb) < 0 and Nb > 800 ppm were considered as metafelsic and thus yield a -quartz = 1, whereas grains with log(Cr/Nb) > 0 or Nb < 800 ppm were considered metamafic and the -quartz activity is unknown. While at amphibolite facies conditions this discrimination can sometimes fail (metamafic being classified as metafelsic), we stress that metamafic rocks can have a -quartz = 1. Felsic rocks commonly yield zircon and therefore we assume that grains classified as metafelsic-derived yield at-ZrO2 = 1. Therefore, by applying this filter, we have a high level of confidence in the Zr-in-rutile thermometry outputs. The statistically comprehensive dataset compiled from the literature (supplementary file B) shows that only about 10 % of the cases (n total = 764) are false positives (i.e. a metamafic-derived grain being discriminated as metafelsic), and rarely a felsic protolith is discriminated as mafic. It is important to note that from the dataset used to estimate this uncertainty, regardless of protolith composition, quartz was always present (a -quartz = 1).

Zr concentration scatter and its significance

Zr-in-rutile has become a popular tool to retrieve peak temperatures from metamorphic rocks. Several issues have been systematically found from applying this thermometer (Cruz-Uribe et al., 2018; [START_REF] Kooijman | Trace element systematics in granulite facies rutile: Implications for Zr geothermometry and provenance studies[END_REF][START_REF] Pape | A systematic evaluation of the Zr-in-rutile thermometer in ultra-high temperature (UHT) rocks[END_REF], such as high Zr concentration deviations in grains from the high temperature domain (> 800 ºC; Fig. 2). Natural scatter present in most metamorphic rocks, and from the subset we have used (appendix 1), is not commonly observed in eclogite (Fig. 2) or blueschist-facies rocks [START_REF] Gao | U-Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen[END_REF][START_REF] Hart | Mineral inclusions in rutile: A novel recorder of HP-UHP metamorphism[END_REF], and when present, it is usually envisaged as recording multiple stages during prograde growth [START_REF] Spear | Zr-in-rutile thermometry in blueschists from Sifnos, Greece[END_REF]. This imparts some uncertainty when applying this tool to detrital rutile, as one single estimate can represent either the prograde history or natural scatter by other competing processes (e.g., diffusion, local equilibrium, recrystallisation).

While scattering of Zr concentration in rutile is commonly present in rocks at higher metamorphic grade, the scatter is significantly more limited at a lower grade, regardless of protolith composition (Fig. 2). The significant data scatter in high grade rocks (granulite, migmatite) amounts to commonly less than or around 100 ºC (including rutile as inclusions in other minerals and matrices), but at lower temperatures it implies an overall standard deviation of ± 50-60 ºC or even less. Importantly, minimum values/outliers of the highergrade rutile grains are never lower than 600 ºC (Fig. 2), suggesting that re-equilibration does not seem to take place below those temperatures.

Temperature estimates, uncertainties, and assumptions

In the approach taken here, we have no independent pressure proxies that can assist in further distinguishing metamorphic grade/geothermal gradient (e.g., blueschist vs low-T eclogite, amphibolite vs eclogite, high-T eclogite vs granulite). However, a few important assumptions (e.g., constraints on rutile phase stability, Zr diffusion behaviour), support the identification of rutile grains equilibrated at low T/P (Fig. 3). Because at lower temperatures, rutile is not commonly stable at lower than 10 to 12 kbar (Fig. 3; for all types of rock compositions), this implies that all rutile yielding temperatures lower than 550 ºC (intersection of minimum low T/P with the rutile-out boundary; yellow star in Fig. 3) will be a proxy for blueschist facies conditions (and low T/P in general).

One of the challenges of utilising Zr concentrations to retrieve peak-T also resides in the thermal histories of the source terranes. Because trace element contents can reset under certain conditions, the potential impact of Zr diffusion during cooling or overprinting during a more recent high temperature event (brown dashed lines, Fig. 3) has been considered in agreement with similar reviews from the literature (e.g., [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF][START_REF] Tomkins | The pressure dependence of the zirconium-inrutile thermometer[END_REF]. For a wide range of cooling rates (0.6 to 75 ºC/Ma), rutile (ca. 200 µm) grains can start to re-equilibrate at mid-to upper-amphibolite facies during retrogression (Fig. 3). If the source terranes endured polymetamorphism, it would require about 50 Ma at midamphibolite/eclogite facies conditions to re-equilibrate the Zr in rutile, or less than 1 Ma at granulite facies conditions (Fig. 3). Zirconium re-equilibration at lower temperatures would require unrealistic cooling rates or thermal-overprinting durations, which again reinforces the suitability of the 550 ºC filter as: a) a conservative approach that will only include low-T, low T/P rutile grains, and b) correspond to a real peak-T estimate under low dT/dP conditions, that has not been affected by either diffusion or recrystallisation processes under any realistic geological conditions.

As introduced earlier, only in rare circumstances rutile will form at lower than 10-13 kbar for T < 550 ºC (e.g. [START_REF] Luvizotto | Rutile occurrence and trace behavior in medium-grade metasedimentary rocks: Example from the Erzgebirge, Germany[END_REF]. Most frequently these are associated with more uncommon protoliths (MgO-rich or CaO-rich metapelites), to fluid-precipitates, and texturally prone not to survive well weathering (due to small size and aggregate-like texture; [START_REF] Luvizotto | Rutile occurrence and trace behavior in medium-grade metasedimentary rocks: Example from the Erzgebirge, Germany[END_REF]. Therefore, any bias resulting from this filter (P of 13 kbar & < 100ppm Zr = 550 ºC) strongly resides when pressures were higher and not lower than our assumption for rutile stability. This implies that we exclude potential low T/P rutile grains derived from higher temperature eclogite facies rocks. Also, this results in a mix in the field -T eclogite and blueschist derived grains (grey field, Fig. 3). But by doing so, we increase the interval of confidence in this assessment, as we do not include false positives (such as grains formed at higher T/P conditions). If we were to use a different filter (pink star, Fig. 3), we could inevitably include more eclogite facies-derived grains (low T/P), but we would introduce uncertainty from potential HP amphibolite facies-derived grains

(intermediate T/P).
A pressure of 13 kbar was applied to all grains in the dataset, and uncertainties on this selected pressure (2 kbar) are propagated in quadrature. We consider Zr measurement uncertainty, the calibration uncertainty, and the weighted mean average of the standard deviation of temperature calculated based on all rutile grains from single metamorphic rocks to calculate the final uncertainty (see below). Together, these should account for both Zr-inrutile variability in natural rocks, and for the analytical uncertainties. A minimum 10-15 ºC uncertainty in the calibration is reported from [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF], while in the literature there is a discussion of the effects on -quartz activity in the temperature estimate that can amount to about 50-100 ºC (that does not affect the metafelsic-derived grains). On average, the propagated natural variance uncertainty amounts to around 3%. We use this value (natural variance) to propagate uncertainties on each single-grain analysis as follows:

By applying a 13 kbar pressure to the entire dataset, in order to better estimate the low temperature end, we bias most of the higher Zr concentrations in rutile towards the following the isopleths from eclogite facies conditions to 13 kbar). For example, a rutile grain that originally formed at 25 kbar containing 600 ppm Zr (750 ºC), when recalculated at 13 kbar yields a 670 ºC estimate and will plot in the intermediate T/P field (Fig. 3). The opposite occurs with low-P granulite rutile grains (< 10 kbar, formed under high T/P) when recalculated to 13 kbar. Yet, this P variance is restricted to ca. 5 kbar, and thus it might only account for a small T variation (sometimes enclosed within all the propagated uncertainties; < 30 ºC; Fig. 3). Therefore, we do not discuss in any particular detail the variance seen in the high-grade metamorphic realm, as this variance reflects several competing factors, but it does indicate the presence of highgrade rutile and thus of high T/P.

ASSESSING THE METAMORPHIC RECORD BY UTILISING DETRITAL RUTILE

4.1. Detrital rutile grains nature: discriminating sources

As mentioned in section 1, rutile can grow after metamorphic reactions, in a wide range of bulk rock compositions, or associated to magmatic and fluid precipitating processes. To retrieve peak-T estimates from the Zr-in-rutile geothermometer, rutile grains were screened to assess the process by which they were formed. High field strength elements (HFSE), Sn and W can be used to distinguish some of these different rutile growth processes [START_REF] Agangi | Antimony in rutile as a pathfinder for orogenic gold deposits[END_REF][START_REF] Pereira | Two billion years of evolution enclosed in hydrothermal rutile: Recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes[END_REF]. Some key features of magmatic-related rutile include very high W, Sn, Sb and Nb concentrations (e.g. Meinhold et al., 2010;[START_REF] Agangi | Antimony in rutile as a pathfinder for orogenic gold deposits[END_REF] or very high Nb/Ta ratios. Rutile is also known to form in ore mineralisation settings yielding very high Sb/V, Sn, Sb and W. Authigenic rutile and/or rutile related to low-T fluids yields low Nb/Ta ratios, as Ta becomes more compatible with rutile in the presence of aqueous fluids, combined with low Zr/Hf ratios [START_REF] Pereira | Two billion years of evolution enclosed in hydrothermal rutile: Recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes[END_REF]. Because published analyses of detrital rutile usually lack full trace element composition reporting, only a small fraction of the available U-Pb detrital rutile data could be included in this work.

While trace-element based discrimination diagrams are often sensitive to variations in protolith composition, in [START_REF] Agangi | Antimony in rutile as a pathfinder for orogenic gold deposits[END_REF] data come from 8 samples, from 3 different areas (nrut = 245) and are combined with extensive published data, making it a rather comprehensive study. In [START_REF] Pereira | Two billion years of evolution enclosed in hydrothermal rutile: Recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes[END_REF], the fluid-related field is based on 3 samples from a single unit (nrut = 50), presented together with data from another study reporting authigenic rutile and combined with published metamorphic rutile data (ntot = 453). These boundaries might be broader than depicted in Figure 4, and future studies might better refine these. Still, by combining these different discriminating diagrams, we preclude, as most as possible, inclusion of low-T and -P rutile, as well as magmatic-related rutile grains.

Rutile grains from NW Scotland show no significant zonation or alteration, and they mostly lack inclusions. No inclusions of sulphides or extreme porosity were observed, such as commonly reported in rutile from ore deposit settings (Scott and Radford, 2007;Scott et al., 2011;[START_REF] Agangi | Antimony in rutile as a pathfinder for orogenic gold deposits[END_REF][START_REF] Pereira | Two billion years of evolution enclosed in hydrothermal rutile: Recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes[END_REF]appendix 4). Published studies also reported similar textures and included only chemically homogeneous grains. Trace elementbased discrimination diagrams were applied to our dataset (Fig. 4). The majority of rutile grains yield Nb/Ta and Zr/Hf values commonly found in metamorphic settings, although a few grains yield very low or high Nb/Ta values (Fig. 4A). Most rutile grains yield Sn and W concentrations below 1000 ppm (Fig. 4B,C) and Sb values under 20 ppm (Fig. 4D). Some published data show Sn/Sb-W values compatible with magmatic-related or Au-mineralised sources. Generally, rutile grains included in this study have low Sb/V (Fig. 4C) suggesting that even when Sn-W are more elevated (Fig. 4B), the rutile grains are of a metamorphic origin (Fig. 4).

We excluded grains that plot in the fluid-related or magmatic fields, which reduced the dataset from 840 to 735 (appendix 2). Therefore, the resulting dataset includes only grains that grew from metamorphic reactions, and thus can be used to infer metamorphic conditions.

Low T/P metamorphic record

Each datapoint displayed on Figure 5 has been calculated using [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF] Zr-in-rutile combined equation and a pressure of 13 kbar, following the discussion in section 3. Despite the natural bias in assuming a given temperature, the uncertainties associated with it (discussed in section 3 and that for high T/P rocks it can amount to an overestimation of 30 ºC) still allow us to draw conclusions regarding the existence of very high, moderately high or low temperature rutile. Rutile temperature data show periods with a wide range, separated by periods of more uniform growth temperatures (Fig. 5) that correspond to events within the supercontinental cycle (e.g. Brown and Johnson, 2019). Periods showing the widest variations in peak metamorphic temperatures occur between 0.3 and 0.55 Ga, 1.0 and 1.2 Ga, and 1.7 and 2.1 Ga, corresponding with periods of supercontinent assembly and collisional orogenesis. A significant number of detrital rutile yield temperatures above 850 ºC, which despite the method used for its determination, are only compatible with rutile formed at granulite facies conditions. These take place during assembly of the Gondwana-Pangea, Nuna and Kenor supercontinents (Fig. 5).

Few rutile grains record peak temperatures lower than 550 ºC (n = 31) or than 580 ºC (n = 62), and the majority of these low T rutile are Phanerozoic in age (Fig. 5). Although the data offers no insight into the geothermal gradient at any particular time, as they overlap with the different T/P fields from [START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF], we can directly link estimated peak temperatures with the geothermal gradient index (Fig. 5). These wide temperature variations are compatible with those described for paired metamorphic belts [START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF], indicating quite different metamorphic grades in rocks of the same age. In the Carboniferous and in the Ediacaran where low and high T/P are known, our dataset shows evidence of low-and high-T rutile (and hence low and high T/P), tying together the metamorphic rock and rutile record, and reinforcing the suitability of this approach in probing earlier periods. From this small detrital rutile dataset, we obtained a few low T rutile grains between 1.0 and 1.2 Ga, and also between 1.7 and 2.2 Ga (Fig. 5). We note that those low T/P rutile grains have the same provenance as some of those derived from higher T/P.

Therefore, this new approach and dataset confirm the existence of low T/P and paired metamorphism during the late Palaeoproterozoic and late Mesoproterozoic, during both Nuna and Rodinia assembly, as well as in the Neoproterozoic to Palaeozoic during Gondwana and then Pangea assemblies. The number of cases recording Rodinia assembly are few in comparison to Gondwana-Pangea or Nuna, and they only record tectonometamorphic processes from the Grenville Province on east Laurentia [START_REF] Pereira | Detrital rutile ages can the tectonic setting of sedimentary basins[END_REF]. U-Pb and Zr resetting of rutile have been reported in other studies [START_REF] Zack | Petrology and Geochronology of Rutile[END_REF] and show that Pb diffuses much faster than Zr. Full resetting of the U-Pb system in rutile in these cases would imply the existence of such conditions prior to the late Palaeoproterozoic. Indeed, a few rutile grains with ages between 2.3 and 2.55 Ga yield temperature estimates between 550 and 580 ºC but not lower. No older, Archaean rutile grains selected in this study yield low-T indicative of a low T/P gradient (Fig. 5), but more data are required to confirm this observation.

Preservation Bias of the Exposed Metamorphic Crust a

In this new compilation of detrital rutile data, we have probed the sedimentary record in the search for low T/P metamorphism by applying the Zr-in-rutile geothermometer to detrital metamorphic rutile . We show that both low and high T/P conditions can be inferred since at least 2.1 Ga. The absence of Archaean rutile grains yielding < 550 ºC is consistent with the absence of low T/P rocks of this age in the Archaean geological record (Brown and Johnson, 2019). Despite the relatively restricted number of low-T eclogite occurrences of Proterozoic age, our relatively small dataset show that these conditions prevailed. Thus, the lack of preserved blueschists and low-T eclogites prior to the Neoproterozoic represents a preservation bias that can be probably linked to retrogression and overprinting of HP-UHP units at suture zones and to the small stability fields of some indicator minerals (e.g. lawsonite). We argue that metamorphic rutile, preserved as detrital grains in the sedimentary record, can track low and high/intermediate T/P conditions through time. Applied to a given basin and using detrital grains of similar age, it can also provide the missing evidence of paired metamorphic conditions over time, which is envisaged as a hallmark of sustained subduction zones in modern plate tectonics. Our data show that both during Rodinia and Nuna assemblies, rutile grains show this dual low and high T/P and thus that modern plate tectonics has been operating since at least the late Palaeoproterozoic, shaping and conditioning the evolution of the continental crust. Furthermore, the absence of low T/P conditions in the late Archaean, both from the detrital rutile and rock records, suggests that contrasting mechanisms were operating during continental assembly at that time. However, some detrital rutile with late Archean, early Palaeoproterozoic age yield growth temperatures between

In quartz-absent rocks, Zr will be preferentially taken by rutile, implying that by applying the Zr-in-rutile thermometer calibrated for a -quartz = 1 we are overestimating the temperature.

Since there is no other line of evidence to assist in a -quartz estimation at the time of rutile growth, we can not ascertain if these temperatures are overestimated, but it leads to an open possibility that low T/P subduction could have taken place at the end of the Archean.

More detrital rutile data yielding those ages are thus required.

CONCLUSIONS

To investigate metamorphic conditions through time, we have looked at detrital rutile preserved in the sedimentary record as a tracer of past metamorphic conditions. Rutile yielding temperatures lower than 550-580 ºC is linked to low T/P conditions, which together with very high temperature detrital rutile and the rock record can be used to infer the presence of paired metamorphic conditions and tectonic processes through time.

While the likely transition between early Earth geodynamics and the onset of subduction seems to have been diachronous as recorded on different cratons [START_REF] Cawood | Geological archive of the onset of plate tectonics[END_REF]Laurent et al., 2014), we suggest that it is the youngest evidence of this transition that serves as evidence of a completed switch to modern plate tectonics, with an interconnected plate boundary system operating worldwide.

The period between the first onset of subduction between 3.2-3.0 Ga [START_REF] Cawood | Geological archive of the onset of plate tectonics[END_REF][START_REF] Dhuime | A Change in the Geodynamics of Continental Growth 3 Billion Years Ago[END_REF] and the last appearance of a TTG to sanukitoid transition culminates at 2.13 Ga [START_REF] Moreira | Petrogenetic processes at tipping point of plate tectonics: Hfsanukitoid transition[END_REF][START_REF] Moreira | Evolution of Siderian juvenile crust to Rhyacian high Ba-Sr magmatism in the Mineiro Belt, southern Francisco Craton[END_REF]. This final transition is marked by the first appearance of low T/P and paired metamorphism, as recorded by detrital rutile, in agreement with a few retro-eclogite occurrences with this age (see Brown et al., 2019 for references, andHolder et al., 2019). This transition is also manifested in the current crustal structure of several Palaeoproterozoic age belts, where recent seismological data is consistent with development of a palaeo-subduction network by ca. 2 Ga [START_REF] Wan | Seismological evidence for the earliest global subduction network at 2 Ga ago[END_REF] and also with the oldest preserved linked linear orogenic belts of Eburnean age [START_REF] Condie | Preservation and recycling of crust during accretionary and collisional phases of Proterozoic orogens: A bumpy road from Nuna to Rodinia[END_REF]. Thus, although the metamorphic rock record is envisaged as supporting a major change in geodynamics at the dawn of the Phanerozoic after a protracted transition [START_REF] Brown | Plate Tectonics and the Archean Earth[END_REF][START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF][START_REF] Stern | Evidence from ophiolites, blueschists, and ultrahigh-pressure metamorphic that the modern episode tectonics began in Neoproterozoic time[END_REF], we contend that the preserved rock record indicates that the onset of modern plate tectonics took place during the late Palaeoproterozoic. By using sedimentary rocks as an archive of the continental crust we have started to contribute towards a more complete overview of the low T/P metamorphic conditions through time and of its forcing mechanisms. Comparison between temperature estimates based on Zr-in-rutile [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF] and on mineral equilibria for 45 samples from 14 published studies (appendix 1). For Zr-in-rutile estimates, average Zr concentrations were used. Uncertainty on the Zr-in-rutile temperatures was calculated using mineral equilibria determined pressure variation and the Zr concentration standard deviation of each sample. A) correlation between both methods using average estimates; B) correlation between both methods adjusting the temperature estimate of mineral equilibria taking into account its variation from classical thermometry.

Figure 2. Boxplot diagram depicting temperature estimates based on single grain Zr-in-rutile [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF] for multiple samples (n=52), totalling 1123 rutile grains (appendix 1). Each Boxplot corresponds to a different sample, and data are coloured according to different metamorphic grade derived from the mineral assemblage. In cold colours, data derived from metamafic rocks, while warm colours from metafelsic rocks.

Figure 3. Temperature-Pressure diagram for Zr concentrations in rutile (isopleths in grey shades; Kohn 2020). In dashed blue, the minimum conditions for P-T path following low geothermal gradients, and in red, maximum for high geothermal gradients (from Palin et al., 2020). Orange lines correspond to the rutile-in reaction boundary in high silica system (granitoid composition similar to average pelite), the darker line corresponding to the most stable conditions at all given protolith compositions, while light orange to rutile occurrence under low CaO (1 wt%) compositions (from [START_REF] Angiboust | Ilmenite breakdown and rutile-titanite stability in metagranitoids: Natural observations and experimental results[END_REF]. The black line corresponds to the boundary of blueschist to eclogite facies conditions (from Palin et al., 2020). Yellow star corresponds to the intersection of low T/P minimum conditions with the rutile-in reaction and Zr isopleth. This defines for a 100 ppm Zr, at 13 kbar, 550 maximum temperature filter. The dashed black triangle highlights the range of conditions that are ignored by applying a temperature filter to the data, which would still be considered low T/P-related conditions. The brown dashed lines correspond to estimates of diffusivity of Zr in rutile (from Cherniak et al., 2007). Each line can be used to interpret the effects of cooling rate or timescales of thermal overprinting-induced diffusion for 200µm grain sizes (which corresponds to the average of observed grain sizes in our samples). Very slow (0.6 /Ma), slow (2.5 /Ma) or fast (75 /Ma) cooling rates of metamorphic terranes can lead to re-equilibration of Zr in rutile to equivalent concentrations of 600 , 650 or 800 , respectively. Thermal overprinting events can lead to Zr diffusion if thermal regimes overprint at higher than 600 for more than 50Ma, than 650 if more than 10 Ma, and to 800 for over 0.5 Ma. Pink star corresponds to conditions at which rutile could still be assigned as from T/P conditions, but with a lower level of confidence, if we also consider analytical/experimental uncertainties. The black field represents impossible high P, low-T conditions on Earth. Figure 4. Discrimination diagrams applied to detrital rutile (data can be found in appendix 2); a. based on Zr/Hf and Nb/Ta from [START_REF] Pereira | Two billion years of evolution enclosed in hydrothermal rutile: Recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes[END_REF] with discriminative fields for low-P fluid-related, metamorphic s.s. and peridotite-related rutile. b., c., and d. based on Sn and W, W an Sb/V, and Sb and W concentrations, respectively, from [START_REF] Agangi | Antimony in rutile as a pathfinder for orogenic gold deposits[END_REF] with discriminative fields for metamorphic sensu stricto, Au-mineralised related rutile and granitoid-related rutile. Symbols include measurement uncertainties as 1-sigma. Detrital rutile data used in this study to estimate temperatures plot within the metamorphic sensu stricto field of both diagrams. Dashed, red lines indicate filters applied for this discrimination.

Figure 5. The metamorphic record retrieved from the detrital archive; Metamorphic temperature estimates using the Zr-in-rutile geothermometer at 13 kbar [START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF] versus detrital rutile U-Pb age; n = 735. For comparison, fields for low, high and intermediate T/P are plotted from [START_REF] Brown | Secular change in metamorphism and the onset of global plate tectonics[END_REF] and fields dividing temperature ranges for the different metamorphic facies (amph: amphibolite; ecl: eclogite; bs: blueschist; gs: greenschist). Dashed blue line corresponds to the new inferred field for low T/P based on both the detrital rutile and rock record. Yellow symbols correspond to log(Cr/Nb) < 0 and Nb > 800 ppm (metafelsic; a -quartz = 1) whereas blue symbols correspond to log(Cr/Nb) > 0 or Nb < 800 ppm (metamafic; a -quartz = unknown) following [START_REF] Meinhold | Rutile chemistry and thermometry as provenance indicator: An example from Chios Island, Greece[END_REF]. Data sources can be found in the text. 1-sigma data uncertainties fall within the symbol used for plotting.

Figure 1 .

 1 Figure 1. Comparison between temperature estimates based on Zr-in-rutile[START_REF] Kohn | A refined zirconium-in-rutile thermometer[END_REF] and on mineral equilibria for 45 samples from 14 published studies (appendix 1). For Zr-in-rutile estimates, average Zr concentrations were used. Uncertainty on the Zr-in-rutile temperatures was calculated using mineral equilibria determined pressure variation and the Zr concentration standard deviation of each sample. A) correlation between both methods using average estimates; B) correlation between both methods adjusting the temperature estimate of mineral equilibria taking into account its variation from classical thermometry.

  Mg, 45 Sc, 51 V, 52 Cr, 87 Sr, 89 Y, 90 Zr, 93 Nb, 95 Mo, 118 Sn, 121 Sb, 139 La, 140 Ce, 141 Pr, 146 Nd, 147 Sm, 153 Eu, 157 Gd, 159 Tb, 165 Ho, 166 Er, 169 Tm, 172 Yb, 175 Lu, 177 Hf, 181 Ta, 182 W, 208 Pb, 232 Th and 238 U.

	Trace elements in rutile were determined using an ASI RESOlution 193nm ArF excimer
	laser coupled to the ANALYTIK JENA Plasma Quant Elite quadrupole ICP-MS at the
	University of Portsmouth (UoP). Rutiles were ablated with laser beam diameters between 25
	2 and a repetition rate of 5 Hz. Analyses
	consisted of 20 s background, 30 s ablation and sample acquisition, and 5 s of washout,
	resulting in 55 s per analysis. Instrumental parameters and ablation conditions are
	summarized in the supplementary file A. The following isotopes were analysed: 49 Ti, 29 Si,

25

ACKNOWLEDGEMENTS

We would like to thank Geoff Long for amazing technical support during sample preparation and Mike Dunk for assistance during sampling. We thank Michael Brown for his valuable comments on an earlier version of this manuscript. We are also thankful to Matthew Kohn and an anonymous reviewer for their constructive comments during peer-review and Alex Webb for his editorial handling. Funding: IP wants to thank the University of Portsmouth for providing a PhD bursary, technical support and for funding all analytical work. HM thanks CNPq -Brazil grant 234610/2014-0. PAC acknowledges support from Australian Research Council grant FL160100168.

Author s contributions: IP undertook sample collection and processing, SEM and LA-ICPMS work, data handling and interpretation, and has written the main parts of the manuscript. CS supervised the project and data processing, has discussed data interpretation, and substantively revised the manuscript. JD provided support during SEM and LA-ICPMS work. HM has been involved with data compilation, discussion and manuscript revision. RS and PAC have provided feedback and discussions related with the background research and have substantively revised the manuscript. All coauthors have contributed to the final version of this manuscript.


Clément Colin

Antoine Martin

How low-techs challenge ergonomics?

This article is a

Introduction

Ergonomics (or human factors) is the discipline that aims at understanding the interactions between humans and artefacts1 with the goal of improving human well-being and the performance of the human-artefact system2 .

Ergonomics has largely developed with industrialization and the concern to produce machines adapted to the work situations of the humans who use them. Since the 1970s, these machines have become digital machines, thus ergonomics has been increasingly devoted to "high-tech" products and services. Industry 4.0, remote work and autonomous vehicles are some of the most prominent topics within the community today. Logically, many of the theories and tools of ergonomics have been developed for digital interfaces (e.g. Bastien & Scapin's or Nielsen's usability heuristics).

Although a minority, work on low-tech tools exists within ergonomics even if it does not bear this name. For example, Rudolph Drillis [START_REF] Drillis | Folk Norms and Biomechanics[END_REF] has collected design standards from popular culture that are applicable to what we would now call "low-tech" tools. Unfortunately, these works focus mainly on biomechanical and anthropometric aspects (minimization of pain-causing gestures, etc.) and less on the overall experience of using a low-tech tool. For example, they do not propose recommendations to (among other things) include hedonic aspects or an empowerment potential in a low-tech tool, yet these concerns are central to the modern lowtech approach. Are contemporary ergonomics ill-equipped to accompany the development of low-techs?

This commentary first presents a study conducted by questionnaire with 400 people, which aimed at evaluating 10 low-techs (experimented or catalogued by the Low-tech Lab). Secondly, it presents the reflections that emerged from this study and that question ergonomics in the light of the low-tech approach: i) the need for a critical theory of needs within ergonomics, ii) the relevance of developing a method that allows for a behavioural assessment that is complementary to "classic" life-cycle assessments methods, and iii) the importance of updating our knowledge of physical tools. We hope that these will be interesting avenues of research for the ergonomics community and beyond.

Presentation of our study on 10 low-techs

The study took the form of a questionnaire distributed to 400 people in the summer of 2020.

The goal was to collect their representations on the low-tech approach and to measure their attitudes towards 10 low-techs (Rocket mass heater, Pantry, Solar heater, Oyster mushrooms cultivation, Hydraulic ram, Black soldier fly larvae, Solar water heater, Dry toilets, Hydroponics, Solar lamp; see image below). Before the pandemic, the study was supposed to take place in the physical presence of said low-techs in trade shows, this was not possible but remains an ideal for a future study.

The idea that sparked the study is a comment by one of the co-founders of the Low-tech Lab: "There is a lot of designing to be done to make these systems, which often use recycled materials, more aesthetic and (especially) more ergonomic" 4 . Another starting point was a first measurement of the ergonomic qualities of low-tech prototypes during a recent experimentation on low-tech housing. [START_REF] Lévêque | Habitat low-tech[END_REF] The overall results of the study are a visualization of the structure of the respondents' representations on low-techs, a ranking of the 10 low-techs by intention of use, requirements in terms of mode of access, and a categorization of the reported problems (across all 10 lowtechs). Finally, the study explored the perceived user experience of each low-tech. These results are summarized in the table below and detailed (in French) in the report available here [link]. • These results give a first idea of which technologies are ready to be disseminated and which require either improvements or a more specific target.

Main results

Structure

Requirements in terms of access modes

• The access modes to low-techs can be categorized in 3 groups based on the responses collected: self-directed access, access through purchase, and access through direct learning.

• These results allow to visualize and quantify 3 types of access modes that associations and companies could offer.

Most frequent problems across all 10 low-techs

• The study collected 692 problems across all low-techs.

They were classified in 15 categories: compatibility problems (171), information/knowledge/skills problems (98), missing functionality problems (74), manufacturing/installation problems (57), performance problems (55), usability problems (40), redundancy problems (34), safety/health problems (31), maintenance/servicing problems (25), hedonic problems (23), compatibility with values problems (22), utility problems (21), aesthetic problems (19), environmental impact problems (15), social problems (7).

• These categories could become points of attention for designers of low-techs. They can be used as a starting point for questionnaires, user testing, activity and task analyses etc.

Exploration of user experience dimensions for each low-tech

• We collected respondents' perception of 4 user experience dimensions (usefulness, usability, hedonism, social aspect) for each of the 10 low-techs.

• These results allow us to evaluate each low-tech in details and to identify specific areas for improvement.

Towards a critical theory of needs: designing for authentic needs

The term "need" is everywhere in ergonomics. Indeed, the users' needs determine their activity and are therefore the starting point of the ergonomic approach. The primary meaning of the word is that of a specification ("requirement") implying a design imperative. If the requirements collected during the "user research" phase are sometimes criticized or put aside, it is mainly for feasibility reasons (budgetary, temporal, strategic) that are external to the ergonomist. Indeed, the theories used in ergonomics do not offer a critical perspective on the notion of "need" which would allow us to go further in putting them into perspective.

A need can be defined as "a configuration of psychological and physical characteristics that is felt as a lack or a tension" [START_REF] Colin | Besoin[END_REF] . Needs motivate human activity [START_REF]The object of the activity is the motive that gives it a conscious and specific orientation, and behind which is necessarily a need or a desire that the activity must allow to reach" Leontiev[END_REF] and their expression depends on the context in which they are expressed (place, history etc.).

To meet the needs of users, the ergonomist classically acts on the characteristics of the artefact (e.g., position of the buttons) to ensure a good quality of interaction (usefulness, accessibility and usability) and a pleasure of use.

The low-tech approach wants to target "essential needs" in priority. How to define and recognize this class of needs? The ideal car, in the need expressed by the user or determined by the designer, is perhaps the one that brings no friction, no constraint, no effort. Should the hoverchairs imagined in the dystopian society of Wall-E 8 be design goals? The temptation to answer in the negative is all the greater if we take into account the "ratchet effect" and the "Collingridge dilemma": it is difficult to predict the impact of a new technique before its massive deployment, which makes it difficult to control or redirect it afterwards. This difficulty is characteristic of our cumulative culture, which operates by trial and error and thus, makes planned sustainability difficult.

To help us distinguish between essential needs and others, the critical theory of needs (developed by the philosophers and sociologists Agnes Heller and André Gorz on the basis of the work of Marx) opposes "authentic" 9 needs to "artificial" needs:

-The first (authentic needs) are composed of absolute biological needs which are universal and "on which the survival of the organism depends: eating, drinking and protecting oneself from the cold, for example" 10 . Authentic needs can also be psychological. The psychologists Ryan & Deci distinguish three basic psychological needs that are universal, unfulfillable and non-hierarchical: autonomy, relationship with others and competence. Their satisfaction is necessary for well-being -Artificial needs, on the other hand, are alienating, i.e., they lead to a loss of autonomy or dispossess the human being of his or her life. They imply mass production (mass production, standardization, diversification and complexity) which destroys the human being and his or her environment 11 It is up to the ergonomics or human factors specialist to seize this distinction to make a critical diagnosis and try to meet the authentic needs first. In practical terms, here are some concrete actions to implement:

identify the authentic need behind the artificial need and make a priority to address it first, for example by recognizing and eliminating needs that will bring about only marginal comfort 12 ; -do not determine new artificial needs via a technological solution;

be better at helping users in knowing and expressing their needs (a task that is among the most difficult for both the user and the designer 13 ); -make a priority to identify and design "desirable" activities (e.g., consuming less energy in winter) in order to make them simpler and more satisfying to carry out, and thus allow their dispersion in the general population;

in order to avoid the alienation of the user, use the recommendations of the philosopher Ivan Illich 14 on the characteristics of the fair tool ("it generates efficiency without degrading personal autonomy, it creates neither slaves nor masters, it widens the radius of personal action") and those of the sociologist Razmig Keucheyan 15 for emancipated goods (they are robust/stable, dismountable/modular, interoperable, evolutive); -include in our approaches the necessary negotiations between manufacturers and users so that they can determine together "acceptable" needs 16 .

Towards "behavioural assessment": designing for desirable uses

Life-cycle assessments (or LCAs) are methods for measuring the environmental footprint of a product or service from its production to its end of life: extraction of raw materials, water, transportation, etc. However, LCAs forget one important variable. The environmental impact of a technical system depends strongly on the use that will be made of it. For example, in the building sector, experiments aimed at reducing energy consumption have taken place by focusing on the energy efficiency of buildings and equipment. Yet, the expected reductions in consumption have not been observed 17 . This discrepancy can be explained by the difference between the representation that the designers have of the inhabitants and the behaviour of inhabitants, which leads to a discrepancy between the intended use and the real use of the building and equipment [START_REF] Zélem | Pas de « smart cities » sans « smart habitants[END_REF] , thus limiting its energy efficiency. This example reveals that systems, however efficient they may be from an LCA point of view, are only really efficient if they generate sustainable behaviours. It is therefore essential to design the uses that accompany technical systems to ensure that they are desirable.

Currently, ergonomics proposes to analyse user behaviours and knowledge to ensure that they are taken into account at the design stage. Similarly, it sometimes studies behaviour during use, but is often limited to the analysis of errors and safety risks. The compliance of the generated behaviours with sustainability objectives is only very rarely studied. For example, the ergonomist does not observe whether new users of electric vehicles (EVs) behave in an energyefficient manner or whether the purchase of an EV leads them to drive more often. Moreover, these "compliant" behaviours are not defined at the start of the project.

Given the strong emphasis on sustainability in the low-tech approach, adapted ergonomics should i) identify the actual behaviours generated by the low-tech object and ii) help to modify the object to reduce undesirable behaviours (e.g., early disposal, misuse) and facilitate desirable ones (e.g., repair, sharing knowledge).

The following is a proposed approach [START_REF] Lilley | Design for sustainable behaviour[END_REF] that delineates this so-called "behavioural assessment":

1. Understand the context of use (existing infrastructure, internal and external factors driving the action).

2. Define target behaviours when using a low-tech.

Modify the object if divergent behaviours appear:

a. Prevent undesirable behaviours: i. Make a behaviour impossible (e.g., limit the heating capacity of a kettle to 80°C).

ii. Improve the user's understanding of the behavioural problem (e.g. feedback). b. Facilitate desirable behaviours: i. Include in the design ways to limit or neutralize socio-cognitive biases.

For example, we are subject to moral compensation bias: when a morally positive action (e.g., investing in energy efficient equipment) is used to legitimize a morally less positive action (e.g., no longer monitoring one's energy consumption). This approach is opposed to the paternalistic logic used in marketing or behavioural economics (e.g., nudging) to induce behaviour and usage.

ii. Designing a positive user experience for the target uses. This strategy has the advantage of putting the burden of user behaviour on the manufacturer of the object. It is the company that is mostly responsible for the generated behaviours and that must act on its technological proposal to limit the undesirable effects of its use.

Designing for less digital interactions

Non-digital tools [START_REF]Defined as a "physical object that is manipulated by users in such a manner as to both affect change in some aspect of the environment and to represent an extension of the users themselves. The manipulation is directed towards a specific goal or purpose, and the associated activity requires a degree of control and coordination[END_REF] represent an important part of low-tech objects (e.g., rocket mass heater).

With them comes the reintroduction of less stereotyped manual interactions (making, handling and repairing). Ergonomics has taken off around digital tools, so the methods and models of ergonomics are often calibrated for them (e.g., usability criteria for interfaces). It is therefore important to reinvest the subject in a different light: from the perspective of ergonomics applied to low-techs. Chris Baber 21 identifies 4 forms of engagement between humans and non-digital tools:

environmental engagement (separate from environment/manufacture) -morphological and motor engagement (manipulation of the tool with the body) -perceptual and cognitive engagement (plan, monitor, feedback) -cultural engagement (community, praxis, rules). These four forms of engagement provide a framework for the ergonomist working to improve a low-tech product (see table below).

•

  The study collected, in the form of short texts, the respondents' opinions on the low-tech approach. A statistical analysis of these texts allowed us to categorize their discourse into 3 themes: the stakes of low-tech (technical and societal transition), the conditions of the transition to the age of low-techs (accessibility, implementation at the individual level, psychological aspects) and the technologies to be abandoned/adopted.• These topics can be used to structure the communications of low-tech associations or companies in accordance with important themes for the public. Ranking of the 10 low-techs by intention of use • The direct measurement of the intention of use of the 10 low-techs allows to establish 3 groups. Low-techs with a high intention of use (solar water heater, dry toilets, pantry). Low-techs with a medium intention of use (solar heating, rocket mass heater, solar lamp, oyster mushrooms cultivation). Low-techs with a low intention of use (hydroponics, hydraulic ram, black soldier fly larvae).

3 .

 3 Measure the actual usage behaviours of the low-tech. 4. Compare target behaviours with actual behaviours.

  Form of engagement Example of questions for the ergonomist Environmental Can the low-tech clearly be associated with a goal by the user? Do the parts of the lowtech correspond to users' goals? Morphological and motor Do the manipulations required to use lowtech correspond to the capacity of these users? Do they allow for the maintenance of proper security?

Clément Colin an ergonomist and PhD Candidate. He volunteers at the Low-tech Lab.

Antoine Martin is a researcher and consultant in ergonomics. He volunteers at the Low-tech Lab.

Acknowledgments

The authors thank Clément Chabot (for his support throughout the study and for his warm welcome to the Low-tech Lab), Solène de Jacquelot (for giving visibility to the results of the study) and Amandine Garnier (for sending out the questionnaire). We warmly thank Nada Negraoui for introducing us to the works of Razmig Keucheyan, André Gorz and Agnes Heller, that are cited in this article. Finally, we would like to thank the 400 people who responded to our questionnaire and thus made the study possible.

Perceptual and cognitive

Can the user get feedback from his use of the low-tech? Can he/she monitor and correct its functioning?

Cultural

In which community will the use of low-tech take place?

In 2020 [START_REF] Osiurak | Technition: When tools come out of the closet[END_REF] , French psychologists and ergonomists proposed a new field of cognitive science, "technition", which could serve as a breeding ground for ergonomics adapted to low-techs.

Their observation: there is a lack of work on the technical skills of humans (tool making, tool selection, tool use, etc.). What is the interest of this for low-techs? This new field supports the idea that tools such as low-techs are not simplistic: in cognitive terms, the technical skills required to make a tool go beyond "simple" manipulation or the use of low-level cognitive skills: imitation, creation, anticipation and problem-solving skills are also involved. It is up to ergonomics to take this work into account to design better low-techs.