B Cochain

C Sanloup

C De Grouchy

C Crépisson

H Bureau

C Leroy

I Kantor

T Irifune

Bromine speciation in hydrous silicate melts at high pressure

Br speciation in hydrous silicate melts at high pressure has been investigated up to 7.6 GPa using Xray Absorption Spectroscopy (XAS) at the Br K-edge in a Paris-Edinburgh press. Br in silicate melts is surrounded by an average of 6 Na cations, a number slightly increasing with pressure (5.8 to 6.6), with a Br-Na distance increasing from 3.49 to 3.72 Å. Two oxygens, either from a water, an -OH molecule or from the tetrahedral silicate network, with an average Br-O distance of 1.80 Å, form the closest coordination shell around Br ions. The persistence of an alkali shell around Br, in a structure similar to crystalline NaBr, throughout the pressure range investigated shows that Br can be retained in the melt structure at relatively high pressure and supports the idea of its deep recycling. Finally, our results confirm that Br could be efficiently degassed with water at low pressures and that Br may also have been efficiently degassed along with water during the early stages of an oxidized magma ocean.

Introduction

The halogens (fluorine, chlorine, bromine and to a lesser extent iodine) influence the properties of silicate melts and play an important role in a range of magmatic and hydrothermal processes, from the evolution of magmatic systems to the transport of metals in fluids and the environmental impact of atmospheric emissions during degassing processes (e.g., [START_REF] Aiuppa | Halogens in volcanic systems[END_REF][START_REF] Baasner | Compositional dependence of the rheology of halogen (F, Cl) bearing aluminosilicate melts[END_REF][START_REF] Chevychelov | Experimental study of chlorine and fluorine partitioning between fluid and subalkaline basaltic melt[END_REF][START_REF] Edmonds | Halogen degassing during ascent and eruption of water-poor basaltic magma[END_REF][START_REF] Pyle | Halogens in igneous processes and their fluxes to the atmosphere and oceans from volcanic activity: A review[END_REF]. In order to predict the physical and chemical properties of silicate melts, the fluids that they exsolve, and the glasses that they form, a detailed knowledge of the solubility and speciation of halogens in silicate melts at relevant conditions of pressure and temperature is essential. Most previous experimental studies have focussed on the determination of their solubility, partitioning behaviour or diffusion at pressures relevant for degassing processes (P < 0.3 GPa) (Aletti et al., 2007;[START_REF] Baker | Halogen diffusion in magmatic systems: Our current state of knowledge[END_REF][START_REF] Bureau | Volcanic degassing of bromine and iodine: experimental Fluid/melt partitioning data and applications to stratospheric chemistry[END_REF]Bureau andMétrich, 2003, Signorelli andCaroll 2002;[START_REF] Webster | Fluid-melt interactions involving Cl-rich granites: experimental study from 2 to 8 kbar[END_REF]. In a more recent investigation conducted at pressures of up to 1.7 GPa, [START_REF] Bureau | Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells[END_REF] suggested that the Br cycle in subduction zones is divided in two parts: one superficial cycle, with Br being returned to the atmosphere via volcanism, and another deeper cycle, with Br being recycled back to the mantle via silicate melts. This raises the question of the Br local environment in high-pressure silicate melts as a function of pressure, which is currently virtually unknown. Knowledge of the local structure is particularly important for activity-composition models, which are used to calculate the effects of mixing on the thermodynamic properties of a system. Experimental measurements are therefore needed to constrain the local structure around the halogens in order to further quantify their chemical behaviour (solubility, partitioning behaviour and diffusion) in the subducting slab, mantle wedge and Earth's mantle. In addition, such measurements will ultimately help to model halogen mobilization, transport and degassing in subduction zones or during the degassing of the magma ocean.

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3

In this context, X-ray absorption spectroscopy (XAS), and more particularly extended X-ray absorption fine structure (EXAFS) spectroscopy can play an important role as it is extremely sensitive to the short-range structure around selected atomic sites in both solid and liquid phases.

Indeed, in situ XAS measurements have previously been performed in hydrothermal diamond-anvil cells (HDAC) or autoclaves to characterize the speciation of diverse elements in geologically relevant environments at pressures of up to 2.4 GPa [START_REF] Louvel | Trace elements in subduction zone fluids[END_REF]Louvel et al. 2012;[START_REF] Mayanovic | Investigation of the structural environment of Ta in a silicate glass and water system under high P-T conditions[END_REF][START_REF] Testemale | In-situ X-ray absorption study of Iron(II) speciation in brines up to supercritical conditions[END_REF]. The preliminary in situ XAS work of [START_REF] Louvel | Trace elements in subduction zone fluids[END_REF] in HDAC on Br speciation in aqueous fluids, hydrous haplogranitic and sodium disilicate melts at up to 2.2

GPa has shown that water molecules in the coordination shell of Br in the fluids are gradually replaced by Na ions as the amount of dissolved alkali silicates in the fluid increases. In the present work, we investigated the Br speciation in a hydrous alkali silicic melt at high pressure using XAS at the Br K-edge and a Paris-Edinburgh press. Here, the use of the Paris-Edinburgh press has enabled us to record high-quality data with stable experimental conditions at higher pressures and temperatures relevant to subduction zones and the upper mantle. We therefore focussed our study on the speciation of Br in a hydrous silicic melt up to 7.6 GPa and 1400 °C. XAS (EXAFS and XANES) analysis were conducted on the parent Br bearing glass at ambient conditions, on the melt at 2.1, 3.4 and 7.6 GPa at 1400 ± 70 °C, and on the resulting high-pressure quenched glasses. Six crystalline standards (CaBr 2 , FeBr 2 , NaBr, KBr, KBrO 3 , NaBrO 3 ) were measured to facilitate the modelling of the possible Br valences and chemical environments that may be present in the investigated melts and glasses.

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Materials and Methods

Generation of high-pressure high-temperature conditions

For the in situ measurements, high pressure-high temperature (high P-T) conditions of up to 7.6

GPa and 1400 °C were generated using a Paris-Edinburgh press. We used a modified cell assembly calibrated by [START_REF] Van Kan Parker | Calibration of a diamond capsule cell assembly for in situ determination of liquid properties in the Paris-Edinburgh press[END_REF], consisting of a 7/2.4 mm boron epoxy gasket, a graphite heater and an hBN pressure transmitting medium. We used nano-polycrystalline diamond (NPD) capsules synthesized at Geodynamics Research Center, Ehime University, Matsuyama, Japan [START_REF] Irifune | Ultrahard polycrystalline diamond from graphite[END_REF] instead of single crystal diamond or polycrystalline diamond capsules in order to eliminate the serious interference of the diamond Bragg peaks in the EXAFS spectra. Pt-Rh5% lids were also inserted on either side of the nano-polycrystalline diamond capsule to prevent the loss of volatiles. The NPD cylinder (1.5 mm in height and 0.75 mm inner diameter) and Pt-Rh5% lids were enclosed between two hBN caps on both ends acting as P-transmitting media. High T was achieved by resistive heating through the graphite heater. A Pt foil was inserted between the diamond capsule and the graphite heater as a pressure marker. Pressure transmission to the sample inside the rigid nano-polycrystalline diamond capsule is fully achieved for temperature above 1000 °C [START_REF] Van Kan Parker | Calibration of a diamond capsule cell assembly for in situ determination of liquid properties in the Paris-Edinburgh press[END_REF]. Experiments were conducted by cold compression of the sample to a given pressure, followed by gradual heating to 1400 °C at constant oil pressure. The

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Samples and characterization of materials

Silicic andesite samples from recent eruptions of Mt. Pelée [START_REF] Martel | Magma Storage conditions and control of eruptions regime in silicic volcanoes: experimental evidence from Mt[END_REF] were first melted at 1450°C under atmospheric conditions for one hour before quenching to a glass in distilled water.

The glass was ground in an agate mortar under ethanol and re-melted to ensure chemical homogeneity. It was then doped with 4 wt% NaBr and 4 wt% H 2 O in a internally heated pressure vessel pressurized with an Ar-H 2 gas mixture, holding for forty-two hours at 1250°C and 0.2 GPa thus ensuring the presence of iron in its reduced form, Fe 2+ , in the parent glass. The composition of the parent glass and the quenched products recovered from the 2.1 and 3.4 GPa runs, as specified in Table 1, were determined with a CAMECA SX100 electron microprobe at the EMMAC centre (The Edinburgh Materials and Micro-Analysis Centre), University of Edinburgh. It was not possible to retrieve and analyse the quenched sample from the 7.6 GPa run as a blowout occurred before quenching. The microprobe analyses were performed under "soft" operating conditions, in order to avoid any loss of Na and volatiles, with a 15 kV accelerating voltage, a defocused beam of 10 m and a current of 15 nA. We note that the parent glass and the run products have similar chemical compositions, given the analytical uncertainties, with the exception of the lack of iron in the run products, a result of the reaction between the Fe 2+ present in the parent glass with the Pt-Rh5% lids of the Paris-Edinburgh cell assemblies. The electron microprobe analysis of Br is hindered by the high ionization potential for the K-lines of Br, resulting in low count rates and the overlapping of the L-lines of Br and the K-lines of Al. The Br concentration of the parent and glasses quenched from high pressure was instead determined by Proton-induced X-ray emission (PIXE) analyses performed using a nuclear microprobe (LEEL, CEA/DSM/IRAMIS/SIS2M, CEA Saclay, France), using 3  3 µm 2 incident beams of protons at 3.2 and 2.5 MeV. Br was detected based on the K and K X-rays (11.92 and 13.29 KeV respectively). The details of the procedure are described in [START_REF] Bureau | Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells[END_REF]. The PIXE analysis yielded a Br concentration of 2.20 ± 0.13 wt% for the starting glass, which is identical to the Br concentration determined by electron microprobe analysis [START_REF] Khodja | The Pierre Süe Laboratory nuclear microprobe as a multi-disciplinary analysis tool[END_REF][START_REF] Bureau | Determination of hydrogen content in geological samples using elastic recoil detection analysis (ERDA)[END_REF]. Raman spectra were acquired at the IMPMC using the 1500 grooves/mm grating of the spectrometer and a 514 nm wavelength laser and are shown on Fig. 1b. ERDA measurements were carried out using a Van de Graff accelerator (LEEL, CEA/DSM/IRAMIS/SIS2M, CEA Saclay, France) producing a 3 MeV 4 He + micro-beam with a final incident beam size of approximately 16  4 µm 2 (horizontal  vertical).

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XAS data acquisition

XAS measurements at ambient and high P-T conditions were performed in transmission mode across the Br-K edge (13.47 keV) on the BM23 beamline at the European Synchrotron Radiation Facility (ESRF -Grenoble, France). Details of the beamline layout are reported elsewhere [START_REF] Filipponi | An experimental station for advanced research on condensed matter under extreme conditions at the European Synchrotron Radiation Facility -BM29 beamline[END_REF]. The storage ring was operating in the 16-bunch mode with an average current of 200 mA. X-rays were generated using a bending magnet, and monochromatised with a double-crystal, fixed exit Si(111) monochromator. The beamsize was 0.1  0.5 mm 2 . The energy of the EXAFS spectra was calibrated using a pellet of NaBr powder (Alfa Aesar) and no significant drift of the energy was observed for the duration of the measurements. EXAFS spectra of the Brbearing reference compounds listed in Table 2 (NaBrO 3 , KBrO 3 , NaBr, KBr, CaBr 2 and FeBr 2 ), the

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Br-doped parent glasses and the glasses quenched from high-pressure (Table 3) were recorded in transmission from 13.30 to 14.30 keV with a total scan time of about 20 minutes. For the in situ measurements (Table 3), the spectra were recorded in transmission between 13.30 and 13.71 keV with a total scan time of about 15 minutes.

EXAFS data analysis

The extended X-ray absorption fine structure (EXAFS) signal (χ) was first extracted using the ATHENA and ARTEMIS packages based on the IFEFFIT program [START_REF] Ravel | HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT[END_REF].

An average of 3 to 5 EXAFS spectra were first normalized to the absorption edge height. We used an automated background subtraction method (AUTOBK) developed by Newville et al. [START_REF] Newville | EXAFS analysis using FEFF and FEFFIT[END_REF] and implemented in the ATHENA software. This method systematizes the k-space placement of the cubic spline function that is used to approximate the post-edge absorbance from an isolated atom. The placement of the spline is chosen so as to minimize the R-space features at distances that are well below the first atom-atom contact distance. This minimum R-space distance, R bkg , was chosen as 1.4 Å [START_REF] Wallen | Hydration of Bromide Ion in Supercritical Water: An X-ray Absorption Fine Structure and Molecular Dynamics Study[END_REF]Evans et al., 2007[START_REF] Evans | The effect of CO2 on the speciation of RbBr in solution at temperatures to 579°C and pressures to 0.26GPa[END_REF]. The intensity of the jump was normalised to 1 and the position of the edge, E 0 , was calculated as the first maximum of the first derivative of the absorption spectra (~ 13.478 keV). EXAFS interference functions, (k), multiplied by k 2 to increase the signal at high k values, were exported into ARTEMIS. These data were Fourier transformed via a Hanning window and fit to the EXAFS equation [START_REF] Newville | EXAFS analysis using FEFF and FEFFIT[END_REF]) over a variable k-range depending on the sample analysed, the experimental conditions and the signal to noise ratio of the EXAFS spectra. A k-range of 2.25-10 Å -1 was used for the crystalline references, except for the NaBr and FeBr 2 model compounds for which a k-range of 2.25-8 Å -1 was used due to the lower quality of the data at high energy. For the glasses at ambient and the melts at high P-T conditions, we used a k-range of 2-7 Å -1 , except for the glass quenched from high pressure recovered from the 2.1 GPa run for which a k-range of 2-6.5 Å -1 was used. The shorter k-range used for the fitting of

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the glasses and melts EXAFS spectra ensures that all the different contributions to the Fourier transforms arise from neighbouring atoms and are not artefacts from the data treatment. For all compositions, the fit parameters included the number of neighbouring atoms, N, around the central Br atom, the average distance, d, to the central Br atom, the Debye-Waller factor,  2 , characterizing the degree of disorder present in the signal, the amplitude reduction factor, S 0 2 , and the difference between the initial model nearest neighbour distance and the real distance, E 0 . All the fits were conducted with a k-weighting of 1 and 2 to decrease correlations between N and  2 [START_REF] Pokrovski | Silver in geological fluids from in situ X-ray absorption spectroscopy and first-principles molecular dynamics[END_REF]. The fits were also performed assuming that the theoretical backscattering amplitude and phase shift functions could have absorber-scatterer distances that differ from the original model by a distinct number of Angstroms. The Debye-Waller factor,  2 , was fitted for all experimental spectra and set to the best fitted values for each spectrum to minimize errors and correlations between the derived structural parameters. The fitted values of E 0 never exceed 6 eV, confirming the validity of the fitting procedure. Finally, the third order anharmonic cumulant-expansion fitting parameter,  3 , which is a measure of the asymmetry in the signal disorder, was included in the fitting of the melts EXAFS spectra in order to partially compensate for the structural disorder due to the high P-T conditions. The goodness of the fits is expressed by the R-factor, which is a sum-of-squares of the fractional misfit between the model and EXAFS data [START_REF] Newville | EXAFS analysis using FEFF and FEFFIT[END_REF].

Spectroscopic results

Reference materials

Fig. 2 shows the normalized XANES spectra, k 2 -weighted EXAFS oscillations, k 2 (k), and their Fourier transforms collected for the crystalline reference materials used to fingerprint the local structural environment of Br. Quantitative analyses of the XANES data were not performed in this study and only a qualitative description is presented. The XANES spectra absorption edge is found

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at E 0 = 13478 ± 0.5 eV for the bromide reference compounds and E 0 = 13480 ± 0.5 eV for the bromate oxides reflecting a change in Br formal charge from Br 2-(CaBr 2 , FeBr 2 ) and Br -(NaBr, KBr) to Br 5+ for the oxides. All the XANES spectra present a relatively broad white line that peaks at a 13482 ± 0.5 and 13484 ± 0.5 eV for the bromides and the bromate oxides respectively. They also exhibit noticeable differences in the shape of the absorption edge crest relative to the Br structural environment. The intensity of the absorption edge is greater for the Br oxides NaBrO 3 and KBrO 3 , while it is smaller for the bromide compounds with a minimum for NaBr bromide. The absorption edge crest of the KBr XANES spectrum splits into two components, as previously observed by [START_REF] Soldatov | X-ray absorption fine-structure investigation of the ionic compounds NaBr, KBr and RbCl: full multiple-scattering analysis[END_REF] and [START_REF] Freund | Extended x-ray-absorption fine-structure study of alkali-metal halides under high pressure[END_REF]. These differences in the XANES spectra point to distinct structural environments of Br, which are also reflected in the corresponding EXAFS oscillations (Fig. 2b) where the frequency of the oscillations varies with the Br environment. We note that the period of the EXAFS oscillations is larger for the two oxides NaBrO 3 and KBrO 3 than for the bromide compounds. The differences in the k 2 (k) oscillations result in distinct Fourier transforms (FT), as shown in Fig. 2c for distances up to 5 Å. It should be noted that the spectra are uncorrected for the phase shift of the photoelectron wave. The peaks at ~1.30, 2.18, 2.33, 2.42 and 2.7 Å correspond to the distances of the first coordination shell of Br by O, Fe, Na, Ca and K atoms respectively, as explained hereafter. The position of each peak in the FT is phase-shifted to lower r by approximately 0.5 Å with respect to the actual average bond distance that corresponds to each peak. Theoretical backscattering amplitude and phase shift functions for Br-O, Br-alkali (Na and/or K), Br-Fe, and Br-Ca were calculated using the crystallographic structures of NaBrO 3 [START_REF] Abrahams | Remeasurement of optically active NaClO 3 and NaBrO 3[END_REF][START_REF] Templeton | Tensor X-ray optical properties of the bromate ion[END_REF], KBrO 3 [START_REF] Templeton | Tensor X-ray optical properties of the bromate ion[END_REF][START_REF] Szafranski | Refinements of the crystal structures and UV-absorption properties of KBrO3, RbBrO3 and CsBrO3[END_REF], KBr (Meisalo and Inkinen, 1963;[START_REF] Szafranski | Refinements of the crystal structures and UV-absorption properties of KBrO3, RbBrO3 and CsBrO3[END_REF], NaBr [START_REF] Rao | Structural and elastic properties of sodium halides at high pressure[END_REF], FeBr 2 [START_REF] Wilkinson | Neutron Diffraction Investigations of the Magnetic Ordering in FeBr2, CoBr2, FeCl2 and Cocl2[END_REF][START_REF] Haberecht | Refinement of the crystal structure of iron dibromide, FeBr2[END_REF] and CaBr 2 [START_REF] Brackett | The crystal structure of calcium bromide[END_REF][START_REF] Kennedy | Synchrotron x-ray powder diffraction study of the structural phase transition in CaBr2[END_REF]. The fitting routine was tested on the crystalline standards and the structural parameters derived from the

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EXAFS analysis (Table 2) were found to be consistent with the relevant EXAFS literature (NaBrO 3 :

Feiters, 2004; KBrO 3 : [START_REF] Templeton | Tensor X-ray optical properties of the bromate ion[END_REF]NaBr and KBr: Lagarde et al., 1976;[START_REF] Freund | Extended x-ray-absorption fine-structure study of alkali-metal halides under high pressure[END_REF]KBr: Di Cicco et al., 1996). The EXAFS fitting models successfully identify the main contributions of O, Na, K, Fe and Ca in the first coordination shell around the Br atom for the reference compounds of interest. The coordination numbers, average distance to Br, Debye-Waller factor  2 , energy shift E 0 , amplitude reduction factor S 0 2 and R-factor determined for the reference compounds are presented in Table 2 and compare favourably with previous XRD structure refinements and XAS data. The analyses for these standards provided the atom pair correlations (or paths) for the atom clusters Br-O, Br-Na, Br-K, Br-Fe and Br-Ca which were used in the fitting routines for the high-pressure glasses and melts. The amplitude reduction factor, S 0 2 , was fitted for all crystalline references (Table 2) and set to the value obtained for NaBrO 3 (0.82 ± 0.04) for the analysis of the silicate glasses and high-pressure silicate melts.

High-pressure glasses and melts

The normalised Br K-edge XANES spectra of the parent glass, the in situ melts (M) at 2.1, 3.4 and 7.6 GPa and the corresponding glasses quenched from high pressure (Q) are shown in Fig. 3a.

Unfortunately it was not possible to record a spectrum on the glass quenched from 7.6 GPa as the cell blew out just before quenching. All the spectra exhibit a constant absorption edge at E 0 = 13478 ± 0.5 eV with a relatively broad white line with a maximum at 13482 ± 1.5 eV. The XANES spectrum of the parent glass is similar to those previously published for alkali bromide aqueous solutions [START_REF] Evans | The effect of CO2 on the speciation of RbBr in solution at temperatures to 579°C and pressures to 0.26GPa[END_REF][START_REF] Ferlat | Hydration of the bromine ion in a supercritical 1:1 aqueous electrolyte[END_REF][START_REF] Louvel | Trace elements in subduction zone fluids[END_REF]. Changes in the shape of the XANES spectra are observed between the parent glass, the melts and the glasses quenched from high pressure, which suggests substantial differences in the local structure of Br at different P-T conditions. In general, the white line intensity increases with pressure. For example, the white line intensity increases from 1.32 for the parent glass to 1.51 for the quenched 3.4 GPa glass, and from

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1.18 for the 2.1 GPa melt to 1.31 for the 7.6 GPa melt. In contrast, temperature has the opposite effect as a result of the larger disorder around Br at high temperature.

The EXAFS oscillations for the glasses and melts are relatively weak and complex (Fig. 3b). The damping of the EXAFS amplitude at high temperature probably arises from the structural disorder induced by the high temperature conditions. Due to the small amplitudes of these oscillations, the k 2 (k) have significant noise levels, especially for some of the high-pressure melts. As for the XANES spectra, the k 2 (k) EXAFS data vary between the parent glass, the in situ melts and the glasses quenched from high pressure. The EXAFS oscillations of the in situ melts and of the glasses [START_REF] Abrahams | Remeasurement of optically active NaClO 3 and NaBrO 3[END_REF][START_REF] Templeton | Tensor X-ray optical properties of the bromate ion[END_REF]Templeton, 1985, Feiters, 2004) were preferentially used to model the first peak in the Fourier transform of the EXAFS spectra for the glasses quenched from high pressure and the melts due to the similarities in the EXAFS signal and because a better fit was obtained. We then fitted the first Br-O contribution

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and the Br-alkali peak successively, using the theoretical Br-Na and Br-K backscattering amplitudes, phase shift functions and amplitude reduction factors calculated for the crystallographic structure of NaBr [START_REF] Rao | Structural and elastic properties of sodium halides at high pressure[END_REF] and KBr (Meisalo and Inkinen, 1963;[START_REF] Szafranski | Refinements of the crystal structures and UV-absorption properties of KBrO3, RbBrO3 and CsBrO3[END_REF]. The best results were obtained with the Br-Na contribution from the NaBr structure.

We therefore suggest that Br is preferentially surrounded by Na atoms instead of K atoms. We also fitted the EXAFS data with the theoretical Br-O and Br-Na backscattering amplitudes, phase shift functions and amplitude reduction factors calculated for the crystallographic structure of NaBrO 3 [START_REF] Abrahams | Remeasurement of optically active NaClO 3 and NaBrO 3[END_REF][START_REF] Templeton | Tensor X-ray optical properties of the bromate ion[END_REF]Templeton, 1985, Feiters, 2004) and obtained similar results. The EXAFS data along with the final fits are plotted in Fig. 3b&c. The results of the EXAFS analysis, including the fitting parameters, are reported in Table 3.

The EXAFS parameters derived for the melts show that the first coordination sphere of Br is composed of oxygen atoms with a coordination number of ~ 2. The Br-O distance increases from 1.67 to 1.91 Å with the increase in pressure, as shown by the shift in distance of the corresponding peak (Fig. 3c). The second coordination sphere is composed of an increasing number of Na atoms (from 5.8 to 6.6) situated at an increasing Br-Na distance of 3.49 to 3.72 Å with increasing pressure, which is also shown by the shift in distance of the corresponding peak (Fig. 3c). The EXAFS parameters derived for the glasses quenched from high pressure show that the Br local environment of the glasses is not directly comparable to the melts. The two contributions Br-O and Br-Na have a lower coordination number and a slightly shorter distance from the central Br atom (Fig. 5a&b). For the glass quenched from 2.1 GPa, the presence of a peak at 1.5 Å in the Fourier transform of the EXAFS oscillations clearly indicates the presence of a Br-O contribution but since it is relatively weak it was impossible to obtain a reasonable fit. The EXAFS results were therefore only modelled with a Na contribution, giving a slightly greater coordination and bond distance for the Na shell around Br than if the Br-O contribution could have been included.

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Because our EXAFS model does not reproduce the shoulder peak observed at 3.8 Å, we tested the possible presence of Ca, Si and Br atoms in the local environment of Br using Br-Ca correlations from the reference compounds, Br-Si correlations and Br-Br correlations respectively. However, these fitting models either did not give a reasonable fit to the experimental data or the fit quality was even worse. We cannot therefore attribute any of the above correlations to the peak that increases with pressure at 3.8 Å in the Fourier transform of the EXAFS data. The presence of Si in the immediate environment of Br is unlikely according to MAS-NMR and XAFS studies on analog high pressure Cl-bearing (alumino)silicate glasses [START_REF] Evans | A preliminary investigation of chlorine XANES in silicate glasses[END_REF][START_REF] Mckeown | X-ray absorption studies of chlorine valence and local environments in borosilicate waste glasses[END_REF][START_REF] Sandland | Structure of Cl-containing silicate and aluminosilicate glasses: A 35Cl MAS-NMR study[END_REF][START_REF] Stebbins | Chloride ion sites in silicate and aluminosilicate glasses: A preliminary study by 35Cl solid-state[END_REF] that indicate that Cl is mainly coordinated to the network-modifying cations (e.g., alkali and alkaline-earth). In addition, [START_REF] Dalou | The effect of H 2 O on F and Cl solubility and solution mechanisms of in aluminosilicate melts at high pressure and high temperature[END_REF] explained in a recent study that there is no interaction between Si 4+ and Cl -in hydrous aluminosilicate glasses quenched from 1.5 GPa. Even if we cannot undoubtedly rule out the presence of minor amounts of Br bonded to network cations (Si An alternative fitting strategy was applied to the parent glass at ambient pressure because the above fitting procedure did not give a reasonable fit to the experimental data. The EXAFS Fourier transform shows two resolved peaks at ~0.90 Å and ~2.60 Å with a shoulder at 1.75 Å. Following

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ACCEPTED MANUSCRIPT [START_REF] Louvel | Trace elements in subduction zone fluids[END_REF], the fitting model combined the structure of a hydration shell [Br(H 2 O)n] and the structure from crystalline NaBr, with the Na-Br distance determined from the reference analyses.

The hydration shell was modelled by considering that Br is coordinated by 6 water molecules [Br(H 2 O) 6 ] -with a mean Br-O distance of 3.40 Å [START_REF] Ferlat | Hydration of the bromine ion in a supercritical 1:1 aqueous electrolyte[END_REF][START_REF] D'angelo | Hydration Properties of the Bromide Aqua Ion: the Interplay of First Principle and Classical Molecular Dynamics, and X-ray Absorption Spectroscopy[END_REF]. The EXAFS spectrum of the parent glass at ambient pressure is accurately modelled with a first hydration shell with 3.5 ± 0.7 water molecules (N Br-O (--H) ) at a mean Br-O (oxygen of solvating H2O molecules) distance of 3.36 ± 0.09 Å (Table 3) and a Br-Na shell with a coordination of 2.5 ± 1 and a mean Br-Na distance of 2.91 ± 0.37 Å. We attempted to apply this fitting procedure to the spectra of the other glasses and melts but were unable to obtain a reasonable fit to the experimental data.

This suggests that the direct environment of Br in the parent glass is hydrous.

Discussion

Bromine speciation at depth

Our EXAFS results shed light on the bromine speciation and its local environment in silicic melts at pressures of up to 7.6 GPa. Figures 5a andb consistent with the enhanced solubility of halogens in silicate melts with an increase in the concentration of modifier cations [START_REF] Webster | Fluid-melt interactions involving Cl-rich granites: experimental study from 2 to 8 kbar[END_REF]de Vivo, 2002, Bureau et Métrich, 2003). In addition, Br is gradually surrounded by an increasing number of Na atoms at higher pressures (Fig. 5). In the melts and their quenched products, the Na coordination indeed increases from 5.8 to 6.6

with Br-Na relative distances increasing from 3.49 to 3.72 Å. A similar increase in coordination has

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been reported for the oxygen coordination of major elements (Si, Al, Fe) in glasses [START_REF] Meade | High-pressure X-ray diffraction of SiO 2 glass[END_REF][START_REF] Poe | Al and Si coordination in SiO2-A1203glasses and liquids: A study by NMR and IR spectroscopy and MD simulations[END_REF] and was later confirmed in silicate melts (Sanloup et al., 2013a(Sanloup et al., , 2013b)). We report here a similar behaviour for a minor and volatile element.

At present, it is difficult to determine precisely the origin of the ~1.80 Å oxygen contribution. It may originate either from a water molecule, an -OH group or an oxygen from the silicate melt network as seen for Cl in Cl-bearing borosilicate glasses [START_REF] Mckeown | X-ray absorption studies of chlorine valence and local environments in borosilicate waste glasses[END_REF]. Although the small increase with pressure in the white line intensity of the melts spectra could be consistent with a change of Br environment from bromide to bromate, there is no other evidence for such a dramatic change with pressure. A more likely explanation is that it is due to an increase in the local order around Br with pressure. For example, there is no change in the oxidation state of Br as the position of the edge of the EXAFS spectra, E 0 , remains at 13478 ± 0.5 eV for all the glasses and melts. The Br formal charge therefore remains the same and cannot be used to decipher the bonding origin of the oxygen contribution. The presence of a H 2 O "hydration shell" around Br in the melt at high pressure appears plausible as the melts contain about 4 wt% dissolved H 2 O. However, this hypothesis is not supported by results from NMR studies on hydrous Cl-bearing (alumino)silicate glasses quenched from 0.8 GPa [START_REF] Sandland | Structure of Cl-containing silicate and aluminosilicate glasses: A 35Cl MAS-NMR study[END_REF] which show no evidence for the replacement of Na + by H 2 O (or OH groups) in the neighbouring shell around the halide ions in glasses containing up to 5.5 wt% H 2 O. The presence of the oxygen atom from a water or -OH molecule at such a short distance from Br could also be due to the proximity of a water molecule linked to the alkali "salt-like" structure of Br atoms in the melt. Indeed, 29 Si, 27 Al and 23 Na NMR studies of hydrous aluminosilicate glasses indicate that the hydration sites in the structure are preferentially located around alkali ions (Kohn, 2000;[START_REF] Schmidt | Quantitative determination of water speciation in aluminosilicate glasses: a comparative NMR and IR spectroscopic study[END_REF]. The fact that the oxygen coordination remains constant and equal to 2 within uncertainties while the Br-O distance increases from 1.67 to 1.81 Å could be another indication that this oxygen contribution arises from the proximity of a water molecule linked to one of the alkali ions of the salt-like structure with the greater Br-O distance observed with pressure being due to the increasing distance of the Br-Na bonds.

Finally, the quantitative EXAFS results presented here suggest that there is a slight structural difference between the melts and their glasses quenched from high pressure. The results reveal a slightly larger coordination of Br by Na and O atoms and slightly longer bond distances for the in situ melts than for the glasses quenched from high pressure, notably for the 3.4 GPa run. The greater distances observed for the melts are most likely due to thermal disorder and the thermal expansion of the bond distances [START_REF] Mysen | Silicate glasses and melts : Properties and structure[END_REF]. However, we note that the overall alkali "salt-like" structure of Br in the melts and in their quenched product remains comparable.

Geological implications

In a recent state-of-the-art study on the role of halogen elements in igneous processes, [START_REF] Pyle | Halogens in igneous processes and their fluxes to the atmosphere and oceans from volcanic activity: A review[END_REF] clearly pointed out the lack of knowledge of the heavy halogens Br and I, compared to Cl or even F. Br has a low abundance in Earth's volcanic and mantle rocks [START_REF] Newsom | Composition of the solar system, planets meteorites and major terrestrial reservoirs[END_REF], from ppb to ppm in order of magnitude. These low abundances partly explain why it has been poorly studied and why much remains to be learned about it. Our results on the speciation of Br in high-pressure melts emphasize the influence of pressure on the speciation of Br in geologically relevant silicate melts. The changes observed in Br speciation with pressure and the observed Br-Na complexation in melts are consistent with the available experimental data for Br partitioning between fluids and melts and with the enhanced solubility of halogens in silicate melts with increasing concentration of network modifying cations [START_REF] Bureau | An experimental study of bromine behaviour in water-saturated silicic melts[END_REF]. Indeed, Br solubility has been shown to be very high in hydrous alkali silicic melts (thousands of ppm to wt.% depending on the bulk composition), which is similar to Cl solubility in hydrous silicic melts (Bureau and Metrich, 2003). In addition, Br (halogens) complexation with alkalis may be an efficient mechanism for the transport and recycling of halogens, although "diluted" fluids produced

A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT
by the dehydration of the slab may be the main carriers of halogens in subduction zones [START_REF] Louvel | Trace elements in subduction zone fluids[END_REF][START_REF] Bureau | Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells[END_REF]. Our results suggest that if part of the halogen elements are retained in the slab after the first dehydration steps liberating aqueous fluids, they could later be partially removed by hydrous melts produced at greater depths or by complex fluids with a high fraction of dissolved silicates [START_REF] Hermann | Aqueous fluids and hydrous melts in high-pressure and ultrahigh pressure rocks: Implications for element transfer in subduction zones[END_REF][START_REF] Kessel | Trace element signature of subduction-zone fluids, melts and supercritical liquids at 120-180 km depth[END_REF][START_REF] Manning | The chemistry of subduction-zone fluids[END_REF], contributing to recycling an important fraction of halogens in subduction zones. Although the silicic melt investigated is different from the magma produced by mantle melting upon fluid release, as we had to investigate a composition with a great Br solubility to record good EXAFS spectra, we suggest that the incorporation of Br in the structure of silicate melts at high pressure should favour their transport from the slab to the mantle wedge and most likely to the volcanic arc. Halogens in the volcanic arc are strongly involved in mantle fertilization processes [START_REF] John | Dehydration of subducting serpentinite: Implications for halogen mobility in subduction zones and the deep halogen cycle[END_REF] and may play a critical role in volcanic degassing by influencing the properties of the magmas (e.g. viscosity, phase relations, diffusion) [START_REF] Aiuppa | Halogens in volcanic systems[END_REF]. Indeed, natural volcanic products related to subduction zone volcanism are enriched in halogen elements [START_REF] Roggensack | Explosive basaltic volcanism from Cero Negro volcano: influence of volatiles on eruptive style[END_REF][START_REF] Wallace | Volatiles in subduction zone magmas: concentrations and fluxes based on melt inclusion and volcanic gas data[END_REF][START_REF] Straub | The systematics of chlorine, fluorine, and water in Izu arc front volcanic rocks: implications for volatile recycling in subduction zones[END_REF]Layne, 2003, Kent et al., 2002) and it has recently been confirmed that subduction zones may be a major source of halogen elements in the Earth's mantle [START_REF] Kendrick | Subductionrelated halogens (Cl, Br and I) and H2O in magmatic glasses from Southwest Pacific Backarc Basins[END_REF].

The presence of Br in the melt structure at high pressure and the increasing number of Na atoms in its local environment with increasing pressure show that Br has the potential to be stored deeper in Earth's mantle than previously supposed. This could explain the traces of Br detected in inclusions trapped in ultra deep eclogitic diamonds [START_REF] Johnson | Noble gas and halogen geochemistry of mantle fluids: comparison of African and Canadian diamonds[END_REF][START_REF] Burgess | Constraints on the age and halogen composition of mantle fluids in Siberian coated diamonds[END_REF]. Finally, the differences observed between the parent glass quenched under low pressure (0.2 GPa) and the melts or glasses quenched from high-pressure implies that glasses quenched from ambient pressure may not be good candidates to represent the local environment of volatile elements in silicate melts at high pressure. It also confirms the high values of Br partitioning between fluid and glass obtained by [START_REF] Bureau | Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells[END_REF] that showed that almost all of the Br contained in the melt was exsolved into the aqueous fluid during the experimental quench at low pressures (< 1.7 GPa). Such results could indicate that the shallow repartitioning of the halogens, during the Hadean when the Earth was a magma ocean, was determined by water degassing. Indeed, if we assume that the halogen cycle is linked to the Earth's water cycle, halogen elements may have been efficiently degassed during the early stages of an oxidized magma ocean.

Conclusion

Our results show that Br anions form NaBr complexes in the hydrous melts under pressure. BrOH complexes are also probably formed but further investigation is needed to elucidate the origin of the Br-O contribution present in our work. The increase with pressure of the mean coordination of Na ions around Br, a minor and volatile element, is similar to that observed for the oxygen coordination of major elements. In addition, our results confirm that Br can be more concentrated in the hydrous silicate melt or supercritical melt as compared to aqueous fluid when pressure (i.e. depth) increases [START_REF] Bureau | Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells[END_REF] and support the idea of a deep recycling of Br, at least at depths of >150 km in the upper mantle, i.e. deeper than the location of arc magma genesis where the presence of Br has been found in saline inclusions in natural diamonds from the upper mantle [START_REF] Johnson | Noble gas and halogen geochemistry of mantle fluids: comparison of African and Canadian diamonds[END_REF].

Furthermore, the results suggest that Br, and by extension Cl and I, are efficiently degassed with water during eruption and that Br may also have been efficiently degassed with water during the early stages of an oxidized magma ocean.

Figures

Figure 1: a) SEM image of the glass quenched from 3.4 GPa recorded at IMPMC, CNRS, Paris showing the homogeneity of the quenched sample as well as the lack of large scale crystallization of the high-pressure recovered quenched sample. The 0.1  0.5 mm 2 EXAFS beam was centred in the middle of the capsule. b) Raman spectrum of the glass quenched from 3.4 GPa plotted after baseline subtraction. The water content was determined after calculating the ratio, Rw/s, between the "silicate" region's area, As, and the "water" region's area, Aw, as Rw/s = Aw/As, then correlating it with the empirical calibration of Le Losq et al. (2010). 3. 3.

  temperature was determined from previous calibration measurements of the cell-assembly[START_REF] Van Kan Parker | Calibration of a diamond capsule cell assembly for in situ determination of liquid properties in the Paris-Edinburgh press[END_REF] and the pressure was derived from the cell volume of Pt. Estimated error bars are ± 0.25 GPa on P, and ± 70 °C on T. Before recording the EXAFS spectra, the molten state of the sample was assessed by the disappearance of crystalline Bragg peaks in the diffraction patterns recorded on a MAR detector. X-ray radiographic images of the sample were systematically recorded before and after collection of XAS data to check for homogeneity/ heterogeneity of the sample and the lack of crystallization.

  quenched from high pressure appear to be composed of at least two sinusoidal signals with one having a phase shift twice as large as the other one. This is not completely reproduced in the EXAFS oscillations for the parent glass. These differences indicate that several pair correlations contribute to the EXAFS spectra of the glasses and melts, resulting in the distinct Fourier transforms which are shown uncorrected for the phase shift of the electron wave in Fig.3c. The Fourier transforms all exhibit the same features except for the parent glass. For the glasses quenched from high pressure and the melts, two main peaks are discernable at ~1.20 Å and ~2.70 Å with a shoulder at ~3.80 Å. The first peak at 1.20 Å approximately corresponds to the Br-O position determined for the oxide standards, while the second peak corresponds to the Br-alkali (Na or K) position determined for the reference compounds. As the literature on X-ray absorption of Br bearing compounds is relatively scarce, the aforementioned EXAFS results on crystalline references were used to model the local structure around Br in the glasses and the melts. The theoretical Br-O backscattering amplitude, phase shift function and amplitude reduction factor calculated for the crystallographic structure of NaBrO 3

  4+ and Al 3+ ), our structural model, represented in Figure4, shows that Br in silicate melts at high pressure is surrounded by an average of 6 Na cations at an average Br-Na distance of 3.61 Å in a structure similar to crystalline NaBr [or (Na,K)Br]. Similar structures have been suggested for Cl in Ca-bearing silicate melts by[START_REF] Evans | A preliminary investigation of chlorine XANES in silicate glasses[END_REF] where Ca-Cl species could be found in a salt-like atomic arrangement and ionic bonding. Two oxygens form the closest coordination shell around Br ions. They originate either from a water molecule, an -OH molecule or from the tetrahedral silicate network at an average Br-O distance of 1.80 Å. The large errors on the coordination numbers are associated with the high Rfactor, which characterizes the quality of the fit, and may result from the in situ conditions, particularly the disorder induced by the high temperature.

  respectively show the Br coordination number by O and Na atoms and their corresponding Br-O and Br-Na distances as a function of pressure. The present results confirm the transition in Br speciation from a Br[Na x (H 2 O) y ] complex at low pressure (parent glass) to an alkali structure at around 2 GPa as evidenced by Louvel (2011) and shown schematically in Figure 4. Br association with Na and by extension Cl-Na association, are

Figures 2 :

 2 Figures 2: Normalized X-ray absorption spectra (a), k 2 -weighted (k) EXAFS oscillations (b) and Fourier transforms (c) for crystalline bromine model compounds at ambient conditions. The spectra have been shifted in the vertical direction for clarity. Red dashed lines are least-square fits performed using IFEFFIT. Contributions around the Br atom arising from the first neighbours are labelled. Peak positions are uncorrected from backscattering phase shift (c). The corrected interatomic distances are reported in Table2. For reason of clarity the amplitude of the k 2 -weight NaBrO 3 and KBrO 3 reference compounds have been divided by two.

Figures 3 :

 3 Figures 3: Normalized X-ray absorption spectra (a), k 2 -weighted (k) EXAFS oscillations (b) and Fourier transforms (c) for the starting glass at ambient pressure, the glasses quenched from high pressure (Q) and the melts (M) at the pressure indicated in GPa. Red dashed lines are least-square fits performed using IFEFFIT. Peak positions are uncorrected from backscattering phase shift (c). The corrected interatomic distances are reported in Table3.

Figure 4 :

 4 Figure 4: Schematic representation of the Br speciation in high pressure silicate melts. The proposed model obtained from the EXAFS experiments shows a transition in Br speciation from a Br[Na x (H 2 O) y ] complex at low pressure (parent glass) to a Br atom surrounded by an increasing number of Na ions with two oxygen atoms at P ≥ 2 GPa. Colour code is the following: Br (large green), Na (large purple), O (light blue) and H(pink). The lines between the Na atoms are guides to the eyes.

Figure 5 :

 5 Figure 5: Evolution of (a) bromine coordination numbers (N Br -O..H , N Br-O and N Br-Na ) and (b) distances (Br -O..H, Br-O and Br-Na) as a function of pressure for the melts (open symbols and dashed lines) and the glasses quenched from high pressure (plain symbols and line).

Figures 2 :Figures 3 :

 23 Figures 2: Normalized X-ray absorption spectra (a), k 2 -weighted (k) EXAFS oscillations (b) and Fourier transforms (c) for crystalline bromine model compounds at ambient conditions. The spectra have been shifted in the vertical direction for clarity. Red dashed lines are least-square fits performed using IFEFFIT. Contributions around the Br atom arising from the first neighbours are labelled. Peak positions are uncorrected from backscattering phase shift (c). The corrected interatomic distances are reported in Table 2. For reason of clarity the amplitude of the k 2 -weighted (k) EXAFS oscillations and Fourier transforms of NaBrO 3 and KBrO 3 reference compounds have been divided by two.

Figure 4 :

 4 Figure 4: Schematic representation of the Br speciation in high-pressure silicate melts. The proposed model obtained from the EXAFS experiments shows a transition in Br speciation from a Br[Na x (H 2 O) y ] complex at low pressure (parent glass) to a Br atom surrounded by an increasing number of Na ions with one or two oxygen atoms at P ≥ 2 GPa. Colour code is the following: Br (large green), Na (large purple), O (light blue) and H (pink). The lines between the Na atoms are guides to the eyes.

Figure 5 :

 5 Figure 5: Evolution of (a) bromine coordination numbers (N Br -O..H , N Br-O and N Br-Na ) and (b) distances (Br -O..H, Br-O and Br-Na) as a function of pressure for the melts (open symbols and dashed lines) and the glasses quenched from high pressure (plain symbols and line).

  Hayward for his help with electron microprobe analyses, J.W.E. Drewitt and O. Mathon for their help with the EXAFS experiments, M. Roberge, C. Raepsaet and the LEEL staff who helped us during PIXE sessions, J.W.E. Drewitt and J. Hudspeth for proofreading this manuscript.

	Constructive reviews from an anonymous reviewer and the AE improved the manuscript. The SEM
	facility of IMPMC is supported by Region Ile de France Grant SESAME 2006 NOI-07-593/R,
	INSU-CNRS, UPMC and ANR grant ANR-07-BLAN-0124-01. This work was supported by the
	European Research Council under the European Community's Seventh Framework Programme
	(FP7/20072013 Grant Agreement No. 259649 to C.S.).

Table 1 :

 1 Chemical composition a (wt %) of the starting material and of the recovered glass samples

	_______________________________________________
		Parent	Quenched	Quenched
		Glass	Glass	Glass
			2.1 GPa	3.4 GPa
	_______________________________________________
	SiO 2	73.27 (70)	71.29 (58)	71.50 (72)
	TiO 2	0.30 (1)	0.29 (7)	0.28 (1)
	Al 2 O 3	12.20 (30)	11.93 (25)	13.23 (33)
	FeO b	0.83 (16)	0.04 (12)	0.02 (10)
	MgO	0.41 (4)	0.40 (19)	0.41 (5)
	MnO	0.08 (1)	0.09 (2)	0.04 (1)
	CaO	2.29 (14)	2.19 (13)	2.26 (14)
	Na 2 O	4.19 (21)	4.79 (29)	4.85 (23)
	K 2 O	1.60 (13)	1.62 (18)	1.73 (14)
	P 2 O 5	0.01 (1)	0.01 (1)	0.01 (1)
	Cl	0.01 (1)	0.01 (2)	0.01 (1)
	Br c/d	2.20 (22) / 2.28 (13) 2.27 (31) / 2.21 (15) 2.27 (22) /1.97 (12)
	H 2 O e/f 3.50 (50) / 3.72 (36)	4.20 (50) / -	3.80 (50) / 4.41 (43)
	________________________________________________
	a Average of 10 analyses given with the standard deviation
	(number in brackets) in terms of the least unit cited.
	b Total iron reported as FeO
	c determined by PIXE analysis
	d determined by electron microprobe analyses
	e determined by Raman spectroscopy
	f determined by ERDA analysis

Table 2 :

 2 EXAFS-derived structural parameters for the crystalline reference compounds ________________________________________________________________________________________________________ Difference between the initial model nearest neighbour distance and the real distance d Amplitude reduction factor

		Bond type	C.N. a	d(Å)	R-factor  2 (Å -2 10 -3 ) b	E 0 (eV) c	S 0 2 d	literature (see text)
	________________________________________________________________________________________________________
	CaBr 2	Br-Ca	3.1 ± 0.3 2.90 ± 0.02	0.002	0.01 ± 0.002	4.12 ± 0.55	0.49 ± 0.04	3*Ca at 2.89 Å
	FeBr 2	Br-Fe	2.8 ± 0.7 2.77 ± 0.03	0.007	0.13 ± 0.008	0.47 ± 1.19	0.92 ± 0.03	3*Fe at 2.63 Å
	NaBr	Br-Na	6.1 ± 0.4 2.97 ± 0.01	0.007	0.03 ± 0.01	-1.40 ± 0.82	0.43 ± 0.05	6*Na at 2.98 Å
	KBr	Br-K	6.3 ± 0.6 3.24 ± 0.06	0.024	0.01 ± 0.002	1.64 ± 0.85	0.56 ± 0.08	6*K at 3.30 Å
	KBrO 3	Br-O	3.0 ± 0.3 1.67 ± 0.01	0.019	0.01 ± 0.001	1.42 ± 0.99	0.69 ± 0.05	3*O at 1.66 Å
	NaBrO 3	Br-O	3.2 ± 0.2 1.69 ± 0.04	0.018 0.005 ± 0.001 1.84 ± 0.82	0.82 ± 0.04	3*O at 1.66 Å

a Average coordination number b Debye-Waller factor c

Table 3 :

 3 EXAFS-derived structural parameters for the parent glass, the melts and the glasses quenched from high pressure Difference between the initial model nearest neighbour distance and the real distance d Third order anharmonic cumulant-expansion fitting parameter

		Bond type	C. N. a	d (Å)	 2 (Å -2 10 -3 ) b	R-factor	E 0 (eV) c	 3 d
		Br-Na	2.5 ± 1	2.91 ± 0.37
	Parent glass				0.02 ± 0.02	0.02	4.39 ± 0.61	-
		Br-O (--H)	3.5 ± 0.7	3.36 ± 0.09
	Glasses
	Q -2.1 GPa	Br-Na	6.5 ± 0.4	3.63 ± 0.18	0.09 ± 0.01	0.12	-4.58 ± 0.11	0.008
		Br-O	1.5 ± 0.6	1.68 ± 0.33	0.03 ± 0.02
	Q -3.4 GPa					0.04	3.25 ± 1.02	0.024
		Br-Na	5.3 ± 0.3	3.54 ± 0.87	0.01 ± 0.07
	Melts
		Br-O	2.0 ± 0.2	1.67 ± 0.02	0.07 ± 0.03
	M -2.1 GPa					0.02	3.79 ± 1.19	0.005
		Br-Na	5.8 ± 0.2	3.49 ± 0.05	0.05 ± 0.01
		Br-O	2.2 ± 0.3	1.83 ± 0.18	0.19 ± 0.02
	M -3.4 GPa					0.03	5.95 ± 2.42	0.012
		Br-Na	6.1 ± 0.4	3.63 ± 0.38	0.06 ± 0.03
		Br-O	2.1 ± 0.6	1.91 ± 0.23	0.05 ± 0.03
	M -7.6 GPa					0.19	1.90 ± 0.92	0.001
		Br-Na	6.6 ± 0.7	3.72 ± 0.57	0.03 ± 0.01

a Average coordination number b Debye-Waller factor c

ACCEPTED MANUSCRIPT

Acknowledgments

The EXAFS experiments were conducted at ESRF (proposals HC776 and HD563). We thank C.

Martel for supplying the parent glass, R. Champalier and G. Prouteau for glass synthesis, C.

The water content was determined after calculating the ratio, Rw/s, between the "silicate" region's area, As, and the "water" region's area, Aw, as Rw/s = Aw/As, then correlating it with the empirical calibration of Le Losq et al. (2010).

Highlights

-Br speciation has been investigated in hydrous silicate melts up to 7.6 GPa by EXAFS spectroscopy -Br is surrounded by increasing number of Na cations (5.8 to 6.6), with an increasing Br-Na distance (3.49 to 3.72 Å) -Two oxygens form the closest coordination shell around Br ions -Br can be retained in the melt structure at relatively high pressure which supports the idea of its deep recycling -Br could also be efficiently degassed with water at low pressures


Estelle Leroux
email: stll.leroux@gmail.com

Daniel Aslanian

Marina Rabineau

Maryline Moulin

Didier Granjeon

Christian Gorini

Laurence Droz

Sedimentary markers in the Provençal Basin (western Mediterranean): a window into deep geodynamic processes

Keywords: stratigraphy, sedimentary marker, geodynamic, subsidence, passive margin

come   L'archive ouverte pluridisciplinaire

INTRODUCTION

Whilst the link between deep Earth dynamics and surface geologic processes appears more and more as a key parameter, deep Earth research, encompassing fields such as seismology and mantle geodynamics, has traditionally operated distinctly from fields focusing on surface dynamics, such as sedimentology and geomorphology [START_REF] Cloetingh | TOPO-EUROPE: Understanding of the coupling between the deep Earth and continental topography[END_REF]. Nevertheless, the formation of passive continental margins -namely the process by which the continental lithosphere thins and subsides that remains one of the main challenges in Earth Science-, allows recording in its sedimentary layers the main steps of the Earth dynamic processes (subsidence, uplift, erosion, paleoclimate…). Passive margins represent a sink for sediments resulting from climate and tectonic erosive actions on the continents. Sedimentary layers also record the effects of eustasy, subsidence and isostasy, so that sediment appears as a storyteller of the Earth.

We present here a quantification of the post-rift vertical movements of the Provence Basin (West Mediterranean) based on the interpretation of sedimentary paleomarkers using a large 3D grid of seismic data, correlations with existing drillings, refraction data and validation by numerical stratigraphic modelling with Dionisos [START_REF] Granjeon | Concepts and applications of a 3-d multiple lithology, diffusive model in stratigraphic modelling[END_REF]. The results of this 3D analysis emphasize the strong link between deep Earth dynamic processes and surface geologic processes.

Geological Setting

The Provence Basin reveals a structure and evolution corresponding to a young pair of rifted margins formed by the counter-clockwise rotation of the Corso-Sardinian micro-blocks with respect to the Ibero-European plate from the Late Eocene (Priabonian,33.7 Ma), in a general context of collision between Africa and Europe (Figure 1-A). The opening took place at the southern end of the intra-European rift system, in a back-arc situation, in response to SE rollback of the slab of the African plate subducting beneath the European plate during an extensional phase. This Corso-Sardinian micro-continent rotation resulted in the emplacement of oceanic crust, starting in the Late Aquitanian (23 Ma to 19 Ma) and ending in the Langhian (about 15 Ma) [START_REF] Olivet | La cinématique de la plaque ibérique[END_REF].

Thanks to its recent history, the subsidence in the Provence Basin is still underway at present and continually creates a large amount of space which favours a progressive filling that preserves the record of both the comings and goings of shorelines associated with the rise and fall of sea levels as well as the vertical movements of the margin [START_REF] Rabineau | Sedimentary sequences in the gulf of lions : A record of 100,000 years climatic cycles[END_REF]. This fact, together with the substantial seismic database available on the Provence margin, including conventional standard seismic lines, high-resolution multi-channel data, very highresolution profiles and industrial drillings make this basin ideal for constraining evolutionary and subsidence models of rifted continental margins using the sedimentary record.

DATA AND METHODS

Many global, regional and local factors have long been recognised to control the overall geometry and deposition of sediments but defining and quantifying the relative part of parameters interacting to produce the final sedimentary architecture of basins (subsidence, eustasy, sediment supply) is not a simple task. This has been one of the main goals of Seismic and Sequence Stratigraphy, as developed in the late 70's [START_REF] Mitchum | Seismic stratigraphy and global changes of sea level, part 2: the depositional sequence as a basic unit for stratigraphic analysis[END_REF]Posamentier, 1988a]. At the same time, the development of quantitative techniques for geological analysis of sedimentary basins (geohistory analysis) were developed [START_REF] Van Hinte | since 20 Ma) = 500 m/Myr Top of Salt Base of Salt Base of Mb Base of M unit Substratum Q5 Q10 P11 Top of UU Sea oor PXX Interpretated LRM18 seismic reflection profile. The offlap-breaks are represented with white dots; Inset: the overall geometry of Pliocene-Quaternary strata shows prograding clinoforms (or prisms) with a clear geometrical change in the Late Pliocene to Quaternary clinoforms (after yellow horizon p11), from essentially prograding (green) to prograding-aggrading (yellow[END_REF][START_REF] Jervey | Quantitative geological modelling of siliclastic rock sequences and their seismic expressions[END_REF][START_REF] Allen | Basin analysis, Principles and Applications[END_REF][START_REF] Robin | Mesure des signaux eustatiques et tectoniques au sein de l'enregistrement sédimentaire d'un bassin intracratonique. Application au Lias du bassin de Paris[END_REF]. They aim to produce a curve for subsidence and sediment accumulation rates through time. This is reached after a number of corrections (decompaction, paleobathymetry and absolute sea-level fluctuations) based on available datasets. The total subsidence is therefore partitioned into contributions from tectonic driving forces, thermal evolution, sediment loading and sea-level fluctuations [START_REF] Steckler | Subsidence of the Atlantic-type continental margin off New York[END_REF][START_REF] Allen | Basin analysis, Principles and Applications[END_REF]. This backstripping depends on strong assumptions: the isostatic response of the lithosphere (e.g. Airy vs regional flexure), theoretical law for porosity, paleobathymetries, sea-level changes, densities of mantle and crust and thermal subsidence. Moreover, lateral and longitudinal variations along a margin are important and 1D modeling cannot be applied to the entire margin. [START_REF] Leroux | Stratigraphic simulation on the shelf of the Gulf of Lions : testing subsidence rates and sea-level curves during Pliocene and Quaternary[END_REF] presented a new method to quantify the post-rift subsidence by the direct use of sedimentary geometries. In this paper, we apply this method in a 3D analysis of sedimentary geometries. In a first step, seismic stratigraphy and borehole data have been used to interpret and date the paleosurfaces on all profiles. Those have been correlated at a regional scale and converted in depth using ESP and sonic data from wells to generate isobath and isopach maps and to quantify sediment fluxes through time [START_REF] Leroux | Quantification des flux et de la subsidence du bassin Provençal (Méditerranée occidentale)[END_REF]. In a second step, 10 fictitious regional lines were extracted from this set of isobath maps (Figure 1-B). We then built vertical dip and strike sections in order to quantify the 3D vertical evolution and potential tectonic deformation of the margin. On each profile, we adjusted paleosurfaces to straight lines, to mesure their subsidence rates (Figure 1-C). This method highlights not only the evolution of subsidence through time but also its spatial segmentation along the margin.

QUANTIFICATION OF SUBSIDENCE

For each profile, three domains of different subsidence were identified by dips and slopebreaks of each horizon 1 (Figure 1-C). Subsidence on the shelf is characterised by a Plio-Quaternary tilt of 0.16°/Myr about a rotational axis located 15 km landward of the presentday coastline (Hinge Line 1, HL1). This Plio-Quaternary subsidence is constant through time [START_REF] Leroux | Stratigraphic simulation on the shelf of the Gulf of Lions : testing subsidence rates and sea-level curves during Pliocene and Quaternary[END_REF]. During the Miocene, this rate varies spatially: 0,12°/Myr on the western sections and 0.06°/Myr on the eastern sections, using the same hinge line 1.

Seawards of the hinge line 3 (HL3), in the distal part of the margin, Miocene and Plio-Quaternary reflectors are flat and parallel to the substratum, indicating a purely vertical subsidence. The strong early erosion at the top of the synrift deposits or directly on the substratum suggests a subaerial position of the substratum before the first post-rift deposit [START_REF] Bache | Evolution of rifted continental margins : The case of the gulf of lions (western mediterranean basin)[END_REF]. This erosional surface is observed on the entire margin and allows us to consider a high position of the entire margin (with a paleobathymetry above sea-level) at the end of rifting. Considering an age of 20 Ma for the end of rifting [START_REF] Séranne | The Gulf of Lion continental margin (NW MEditerranean) revisited by IBS: an overview[END_REF], we can then calculate the mean post-rift vertical subsidence rate in the deep basin of 500 m/Myr. Between these two domains, the slope accommodates vertical movements of either side.

Whilst the slope break between the slope and the deep basin (hinge line 3) is fixed in space through time, the hinge line 2 (HL2) between the shelf and the slope varies during the Pliocene within an area of less than 20 km, which mainly reflects the prograding-aggrading 1 Plio-Quaternary key reflectors labelled MES (Margin Erosional Surface in pink), P11 (yellow), PXX (turquoise-blue), Q10 (red), Q5 (purple) and seafloor (marine-blue) are respectively dated at 5.33 Ma, 2.6 Ma, 1.6 Ma, 0.9 Ma, 0.5 Ma and 0 Ma [START_REF] Leroux | Stratigraphic simulation on the shelf of the Gulf of Lions : testing subsidence rates and sea-level curves during Pliocene and Quaternary[END_REF]. The substratum (brown) and Miocene markers such as the base of the MSC (Messinian Salinity Crisis in red), the base of Mb -interpretated as an evaporitic unit-(orange), the base and top of salt (green and light green) and the top of UU (Upper Unit in grey) are from [START_REF] Bache | Messinian erosional and salinity crisis: View from the Provence basin (Gulf of Lions, Western Mediterranean)[END_REF].

sedimentary system on the shelf [START_REF] Leroux | Stratigraphic simulation on the shelf of the Gulf of Lions : testing subsidence rates and sea-level curves during Pliocene and Quaternary[END_REF] rebuilding the margin after the Messinian erosional event [START_REF] Lofi | Plio-quaternary prograding clinoform wedges of the Western Gulf of Lion continental margin (NW Mediterranean) after the messinian salinity crisis[END_REF]. This 3D quantification of subsidence in three domains was then tested with Dionisos [START_REF] Granjeon | Concepts and applications of a 3-d multiple lithology, diffusive model in stratigraphic modelling[END_REF] using the quantitative constraints on sediment supply inferred from a 3D stratigraphic analysis [START_REF] Leroux | Quantification des flux et de la subsidence du bassin Provençal (Méditerranée occidentale)[END_REF], Leroux et al., 2014, Fig S1. in Supplementary Material) and the eustatic curve of [START_REF] Haq | Chronology of fluctuating sea levels since the Triassic (250 million years ago to present)[END_REF], modified by a 1500 m drawdown during the MSC [START_REF] Clauzon | Le canyon messinien du rhône : une preuve décisive du dessicated deep-basin model[END_REF] (Fig S1 . in Suppl. Material).

Figure 2 demonstrates that the 3D modelling successfully restores the stratigraphic record with the sedimentary geometries and thicknesses observed from seismic data. This modelling is coherent with micropaleontological data from Miocene borehole samples on the shelf [START_REF] Cravatte | Les sondages du golfe du lion : Stratigraphie, sédimentologie[END_REF] that reveals a deepening of the depositional environment at this time (see Figures S1,S2, S3 and movies S4, S5, S6 in Suppl. Material). The aggrading shelf-slope geometries during the Early to Middle Miocene indicate that the morphology of the margin and the subsidence pattern changed after this early erosion and led to the creation of accommodation. After rifting, the entire Gulf of Lions margin was thus affected by strong post-rift subsidence leading to thick post-rift (Miocene to Quaternary) sedimentary accumulations. After the MSC we can observe a Pliocene progradation trend followed by a Pleistocene progradation-aggradation trend (after 2.6 Ma). All these elements are well reproduced by our simulation.

Western Mediterranean basins and margins have undergone a transition into Late Neogene basin inversion (e.g. [START_REF] Roure | Mesozoic and Cenozoic Basins Formation and Deformation along the North African Margin. Search and Discovering Article #30276[END_REF]. Increase in the level of intraplate compression in the Northern Atlantic region could explain the observed rapid phases of Plio-Quaternary subsidence after a phase of quiescence [Cloetingh & Kooi, 1992]. Moreover, in the Gulf of Lion, sediment flux during Pliocene (after 5.33 Ma) is 3 times higher than the flux in the Miocene (Figure S1 in Suppl. Material). This increasing sediment load, driven by climate or tectonic, may therefore play an important role in the increasing subsidence. However, since 2004, many studies on passive margins, which are not in back-arc setting nor in inversion, have shown delayed subsidence which increases long after the breakup, as on Spitzberg Margin [START_REF] Rabineau | A deep seismic transect from Hovgard Ridge to northwestern Svalbard across the continental-ocean transition: A sheared margin study[END_REF], on Iberia-Newfoundland Margins [START_REF] Peron-Pinvidic | The final rifting evolution at deep magma-poor passive margins from Iberia-Newfoundland: a new point of view[END_REF], on Morocco Margin [START_REF] Labails | Crustal structure of the SW Moroccan margin from wide-angle and reflection data (the Dakhla experiment). Part B., The tectonic heritage[END_REF], on Brazilian margins [Aslanian et al., 2009), on Angola margin [START_REF] Moulin | Geological constraints on the evolution of the angolan margin based on reflection and refraction seismic data (ZaïAngo project)[END_REF] or on the Gulf of Lion margin [START_REF] Bache | Evolution of rifted continental margins : The case of the gulf of lions (western mediterranean basin)[END_REF]Aslanian et al., 2012;Moulin et al., in press]. In some margins, the presence of carbonates overlying the salt layer shows that a shallow environment lasted after the break-up.

The subsidence rate then seems to increase rapidly. The general character of the delayed subsidence followed by an increased subsidence rate implies probably a deep contribution like a lithosphere driven process (as proposed by Aslanian et al., 2009;[START_REF] Huismans | Depth-dependant extension, two-stage breakup and cratonic underplating at rifted margins[END_REF][START_REF] Van Hinte | since 20 Ma) = 500 m/Myr Top of Salt Base of Salt Base of Mb Base of M unit Substratum Q5 Q10 P11 Top of UU Sea oor PXX Interpretated LRM18 seismic reflection profile. The offlap-breaks are represented with white dots; Inset: the overall geometry of Pliocene-Quaternary strata shows prograding clinoforms (or prisms) with a clear geometrical change in the Late Pliocene to Quaternary clinoforms (after yellow horizon p11), from essentially prograding (green) to prograding-aggrading (yellow[END_REF]Aslanian et al., 2012), whithout excluding basin inversion process and/or sediment overloading".

CORRELATION WITH THE UNDERLYING CRUSTAL DOMAINS

Four structural domains extending from the coast to the oceanic crust have been highlighted on the basis of gravity, magnetic, reflection and wide-angle seismic data (Figure 3) [START_REF] Pascal | The ocean-continent boundary in the Gulf of Lions from analysis of expanding spread profiles and gravity modelling[END_REF][START_REF] Gailler | Crustal structure of a young margin pair: new results accross the liguro-provencal basin from wide-angle seismic tomography[END_REF], Aslanian et al., 2012, Moulin et al., in press;Afilhado et al., in press]: a) a 20 km thick continental crust (thinned crust), b) a highly thinned continental zone (the continental necking zone as described by [START_REF] Kooi | Lithospheric Necking and Regional Isostasy at Extensional Basins. 1. Subsidence and Gravity Modeling with an Application to the Gulf of Lions margin (SE France)[END_REF][START_REF] Cloetingh | Role of pre-rift rheology in kinematics of extensional basin formation: constraints from thermomechanical models of Mediterranean and intracratonic basins[END_REF], which is marked by a prominent reflector (T) easily recognised at depth [START_REF] De Voogd | First deep seismic reflection transect from the Gulf of Lions to Sardinia (ECORS-CROP profiles in Western Mediterranean)[END_REF]Moulin et al., in press], c) a 5 km thin domain of unknown crust and complex nature (called a transitional domain), and last d) a thin oceanic crust. The limit between the necking and the transitional domains corresponds to the French-side limit of the pre-rift paleogeography [START_REF] Olivet | La cinématique de la plaque ibérique[END_REF]. The base of the necking and transitional domains presents a 4 km thick layer with anomalous seismic velocities (6.8 -7.5 km/s) which are neither typical of continental crust nor oceanic crust [START_REF] Pascal | The ocean-continent boundary in the Gulf of Lions from analysis of expanding spread profiles and gravity modelling[END_REF][START_REF] Gailler | Crustal structure of a young margin pair: new results accross the liguro-provencal basin from wide-angle seismic tomography[END_REF]Moulin et al, in press, Afilhado et al., in press.]. The nature of the transitional domain was a matter of debate [START_REF] De Voogd | First deep seismic reflection transect from the Gulf of Lions to Sardinia (ECORS-CROP profiles in Western Mediterranean)[END_REF][START_REF] Pascal | The ocean-continent boundary in the Gulf of Lions from analysis of expanding spread profiles and gravity modelling[END_REF][START_REF] Séranne | The Gulf of Lion continental margin (NW MEditerranean) revisited by IBS: an overview[END_REF][START_REF] Gailler | Crustal structure of a young margin pair: new results accross the liguro-provencal basin from wide-angle seismic tomography[END_REF][START_REF] Bache | Evolution of rifted continental margins : The case of the gulf of lions (western mediterranean basin)[END_REF]Aslanian et al., 2012] but the recent results of wide-angle seismic analysis seem in favour of an exhumed lower continental crust nature [Moulin et al., in press; Afilhado et al., in press]. This is beyond the scope of this paper, but a consensus does exist on the very different nature of this crust compared to the crustal domains observed on both sides, and the transitional crust may have different physical behaviour.

Figure 3 presents our reconstructed 3D subsidence map and the striking correlation between the three differential subsidence domains described using paleo-markers and the underlying crustal domains highlighted by geophysical data. Up to present day, the crustal limits defined by the passive margin genesis still control, at the very first order, the vertical movements recorded by sedimentary sequences. Not all passive margins exhibit a sag basin, with a « pure » vertical subsidence. Therefore, the use of depositional architecture can give a first approximation for the partitioning of the subsidence (with or without a sag basin) and the basement surface geometry.

In the GOL, the sag basin is described to be allochthonous, with exhumed lower crust near the necking and anomalous thinned oceanic crust in the middle of the basin [Aslanian et al., 2012;Moulin et al., in press;Afilhado et al., in press]. This partitioning, with different magnetic and gravity patterns, fits the palaeogeographic reconstructions and is also observed in the salt geometry (connected /separated domes). Using wide-angle and reflection seismic data, a similar observation was made for the Angola Margin, where the sag basin exhibits a similar mainly vertical, pre-breakup and post-breakup subsidence [START_REF] Moulin | Geological constraints on the evolution of the angolan margin based on reflection and refraction seismic data (ZaïAngo project)[END_REF]Aslanian et al., 2009]. As shown in the Gulf of Lion, the post-break-up subsidence of the Angolan basin uses the same hinge lines that have built and segmented the passive margin [START_REF] Moulin | Geological constraints on the evolution of the angolan margin based on reflection and refraction seismic data (ZaïAngo project)[END_REF]. However, the nature of its basement is different from the GOL, with an autochthonous upper continental crust (just after the necking) and an allochthonous crust that can be exhumed or intruded [START_REF] Moulin | Geological constraints on the evolution of the angolan margin based on reflection and refraction seismic data (ZaïAngo project)[END_REF]Aslanian et al., 2009]. This partitioning is also observed in the salt geometry (connected/separated domes), and fits the initial palaeogeographic reconstruction [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF]Aslanian & Moulin, 2010;[START_REF] Leroux | Quantification des flux et de la subsidence du bassin Provençal (Méditerranée occidentale)[END_REF].

The difference between the two examples shows that a sag basin can occur with different crustal nature as shown by geophysical data. In both cases the exhumed/intruded lower continental crust is involved. The wide angle results in GOL [Afilhado et al., in press] and in the Santos Basin [START_REF] Klingelhoefer | Imaging proto-oceanic crust off the Brazilian Continental Margin[END_REF]Evain et al., accepted] show that the transition between exhumed lower crust to oceanic crust is not abrupt and raises the question on the role of the lower continental crust "flow", that can be gradually recrystallized to build the first atypical oceanic crust [START_REF] Bott | Evolution of young continental margins and formation of shelf basins[END_REF]Aslanian et al., 2009[START_REF] Sibuet | The geodynamic province of transitional lithosphere adjacent to magmapoor continental margins[END_REF]Evain et al., accepted;Afilhado et al., in press].

Anyway, in both cases, whilst the combination of depositional architecture, surface observations and palaeogeographic reconstructions will not give the exact crustal nature, they can give crucial information such as: basement surface geometry, allochthonous/autochthonous nature, and, thanks to magnetism, oceanic nature.

CONCLUSION

Using the new method of [START_REF] Leroux | Stratigraphic simulation on the shelf of the Gulf of Lions : testing subsidence rates and sea-level curves during Pliocene and Quaternary[END_REF] to quantify the post-rift subsidence by the direct use of sedimentary geometries on the 3D analysis of tilts of stratigraphic markers in the Gulf of Lions margin, we individualize three domains of subsidence: on the platform and slope, the subsidence takes the form of a seaward tilting with different amplitudes, whereas the deep basin subsides purely vertically, as in the case of a sag basin. These domains fit with the deeper crustal domains highlighted by previous geophysical data implying that the postbreak-up subsidence re-uses the initial hinge lines of the rifting phase and that the sedimentary record (even the last 5 Ma) is correlated with the underlying structural domains.

This study provides therefore strong evidence for the recognition and importance of the link between deep Earth dynamic processes and surface geological processes [e.g. [START_REF] Braun | The many surface expressions of mantle dynmics[END_REF][START_REF] Cloetingh | TOPO-EUROPE: Understanding of the coupling between the deep Earth and continental topography[END_REF]. The vertical coupling between mantle and surface processes promises new insights into past mantle dynamics through the geological record and the sediments are a precious tool for deciphering the laws of subsidence, even in their recent history, and can be considered as the storyteller of vertical and horizontal movements [START_REF] Leroux | Stratigraphic simulation on the shelf of the Gulf of Lions : testing subsidence rates and sea-level curves during Pliocene and Quaternary[END_REF] and can be used as a window on deep geodynamic processes. and the initial basement at 20 Ma is flat with a paleobathymetry around +100 m (cf text for explanation).

FIGURE CAPTIONS

• Figure S2. Interpretated LRM18 seismic reflection profile. The offlap-breaks are represented with white dots; Inset: the overall geometry of Pliocene-Quaternary strata shows prograding clinoforms (or prisms) with a clear geometrical change in the Late Pliocene to Quaternary clinoforms (after yellow horizon p11), from essentially prograding (green) to progradingaggrading (yellow). Leroux et al., 2014 (in press).

• Figure S3. Comparison between (A) a regional seismic profile from (Bache, 2009) Deposit paleobathymetries and resultant geometries predicted by Dionisos in our 3D stratigraphic modelling of the Gulf of Lion and Provence basin (A). The sedimentary architecture of the margin and final depths of the stratigraphic markers (relative to the substratum) are well reproduced by the model. We can compare this simulation with the NW-SE seismic profile ECORS 1 on (B): on both we observe the deepening of the Miocene depositional environment, the Messinian trilogy and the prograding trend during the Pliocene followed by a prograding-aggrading trend during the Pleistocene (after 2.6 Ma). Note that the vertical scale units are respectively metres in A and secondes (twtt) in B. This explains the relative differences in unit thicknesses, in particular for the pre-Messinian Miocene unit. See also seismic lines corresponding to the black boxes S1 & S2 in the supplementary information.

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Fig1

  Fig1. (A) Location of the study area (black box) on a bathymetric map of the Provence Basin.

Figure 2 .

 2 Figure 2. (A) Deposit paleobathymetries and resultant geometries predicted by Dionisos in

Figure 3 .

 3 Figure 3. (A) 3D post-rift subsidence map drawn after our seismic interpretation and the

  and (B) the same seismic profile extracted by Dionisos from our Messinian modelling. On this synthetic seismic line, the impedance constrasts (in red and blue scale) highlight the same discontinuities we have observed on the seismic profile A. The final simulated present-day topography (in blue-scale) is superimposed on the synthetic section. • Movie S4. 3D stratigraphic model of the Gulf of Lions and Provence basin from 20 to 0 Ma. The movie shows deposit paleobathymetries and resultant geometries predicted by Dionisos. • Movie S5. Evolutional model of the Gulf of Lions and Provence basin through 3D stratigraphic modelling during the Messinian Salinity Crisis. The movie shows deposit paleobathymetries and resultant geometries predicted by Dionisos. • Movie S6. Evolutional model of the Gulf of Lions and Provence basin through 3D stratigraphic modelling during the Messinian Salinity Crisis. The movie shows lithologic facies and resultant geometries predicted by Dionisos.

ACKNOWLEDGEMENTS

Stratigraphic simulations were performed with IFP-Energies Nouvelles Dionisos software kindly made available to the University of Brest. This research was mainly funded by CNRS and IFREMER, with additional support from the French Actions-Marges program (JL Rubino & P. Unternehr) and the GRI "Méditerranée" (Groupement Recherche et Industrie). This work also benefited from the Labex Mer initiative, a State Grant from the French Agence Nationale de la Recherche (ANR) in the Program « Investissements d'avenir » with the reference ANR-10-LABX-19-01, Labex Mer. The authors are grateful to Katalin Kovacs for

post-editing the English style. We also thanks Jim Pindell and an anonymous reviewer for their very fruitful comments that greatly improved this paper, as well as Max Coleman, Scientific Editor and the anonymous associated editor for their reading and encouragements.

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Competing financial interests

The authors declare no competing financial interests.

Supplementary material

Major input parameters (evolution of the eustatic curve and sediment supply) for the 3D simulation of postrift filling of the Provence basin. The simulation was run over the last 20 Ma with a 0.1 Ma time-step. The basin is defined as a rectangular area (250x400 km) and the initial basement at 20 Ma is flat with a paleobathymetry around +100 m (cf text for explanation).

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