Clara Solaro

Georges Boudon
email: boudon@ipgp.fr

Anne Le Friant

Hélène Balcone-Boissard

Laurent Emmanuel

Martine Paterne

New insights into the recent eruptive history of Montagne Pelée (Lesser Antilles Arc) from offshore marine drilling site U1401A (IODP Expedition 340)

Keywords: Montagne Pelée, Tephrochronology, eruptive history, flank-collapse, IODP expedition

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Introduction

(Fig. 1a). The objectives of the project were 1/ to characterize the voluminous chaotic units identified off the islands associated with the volcanic island landslides [START_REF] Brunet | Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank-collapse to seafloor sediment failure?[END_REF][START_REF] Friant | Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340[END_REF]; 2/ to obtain a complete volcanological history of the surrounding volcanoes and to include the large mass wasting events in the evolution of the volcanoes [START_REF] Wall-Palmer | Late Pleistocene stratigraphy of IODP Site U1396 and compiled chronology offshore of[END_REF][START_REF] Cassidy | Rapid onset of mafic magmatism facilitated by volcanic edifice collapse[END_REF][START_REF] Coussens | The relationship between eruptive activity, flank collapse, and sea level at volcanic islands: A long-term (>1 Ma) record offshore Montserrat, Lesser Antilles[END_REF] The aim of this paper is to provide new insights on the last tens of thousands of years of Montagne Pelée's evolution based on the tephrochonological study of site U1401, sampled during the 340 IODP expedition and located west off Martinique Island, 28 km from the coastline (Fig. 1b). By drilling through the DAD the objectives were to characterize and date the setting of the debris avalanche with associated erosional processes. Although it was not possible to drill through the DAD because of the heterogeneity of the deposit and the presence of large blocks [START_REF] Friant | Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340[END_REF], the pelagic sediments and volcanic deposits that covered the DAD were successfully sampled. They thus offer a good opportunity to study the post DAD volcanoclastic sedimentation processes and to better constrain the volcano's recent evolution.

Geological setting

Martinique Island is located in the southern part of the Lesser Antilles arc that result from the subduction of the northern and southern Atlantic plates beneath the Caribbean plate with a relatively slow rate of 2 cm/yr [START_REF] Wadge | Comparison of volcanic production rates and subduction rates in the Lesser Antilles and Central America[END_REF]. This southern part of the arc is bordered to the west by the 3000 m deep back-arc Grenada Basin (Fig. 1a). Montagne Pelée, the sole active volcano of Martinique island and one of the twelve active volcanoes of the arc, is located in the northern part of Martinique, north of the old Morne Jacob -Pitons du Carbet volcano, (Fig. 1b). It is a famous and tragic volcano as during the first months of the 1902-1905 domeforming eruption the towns of St. Pierre and Morne Rouge were destroyed by a series of laterally directed explosions killing 30 000 inhabitants [START_REF] Lacroix | La Montagne Pelée et ses Eruptions[END_REF]. The last eruptive activity was the 1929-1932 lava dome-forming eruption [START_REF] Perret | The Eruption of Mt. Pelée 1929-1932[END_REF].

Previous works: In the last decades and especially after the 1902-1905 eruption a lot of studies were carried out on Montagne Pelée. Exclusively terrestrial studies were performed until 1998 [START_REF] Roobol | Mount Pelée, Martinique: A pattern of alternating eruptive slyles[END_REF]Westercamp and Traineau, 1983a, b;[START_REF] Bourdier | Magma mixing in a main stage of formation of Montagne Pelée: the Saint Vincent-type scoria flow sequence (Martinique, F.W.I.)[END_REF][START_REF] Bourdier | Stratigraphy of the 1902 and 1929 nuée ardente deposits, Montagne Pelée, Martinique[END_REF]Boudon and Lajoie, 1989;Boudon, 1993) whereas, after this date, combined onland and marine data were obtained through several cruises, field work and laboratory studies [START_REF] Deplus | Submarine evidence for large-scale debris avalanches in the Lesser Antilles Arc[END_REF][START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF], 2015;[START_REF] Boudon | Martinique[END_REF][START_REF] Boudon | Volcano flank instability in the Lesser Antilles Arc: diversity of scale, processes, and temporal recurrence[END_REF][START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF][START_REF] Brunet | Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank-collapse to seafloor sediment failure?[END_REF].

Based on previous works, the volcanological evolution of Montagne Pelée was divided in three eruptive phases. The first two phases ended in a large flank collapse. (Fig. 1c, [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF][START_REF] Boudon | Martinique[END_REF][START_REF] Boudon | Volcano flank instability in the Lesser Antilles Arc: diversity of scale, processes, and temporal recurrence[END_REF][START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF][START_REF] Brunet | Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank-collapse to seafloor sediment failure?[END_REF].

The first eruptive phase resulted in a first volcanic edifice that was destroyed by a large flank collapse (Le Prêcheur event) that produced a 8 x 6 km large horseshoe-shaped structure (without the invisible southern rim) and a debris avalanche of ~25 km 3 that flowed into the Grenada basin [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF][START_REF] Boudon | Volcano flank instability in the Lesser Antilles Arc: diversity of scale, processes, and temporal recurrence[END_REF]. Using K-Ar ages acquired from lava domes and lava flows on the northern volcanic edifices of Montagne Pelée and Mont Conil this event was dated at ~127 ka (Germa et al., 2011a).

The second eruptive stage created a new volcanic edifice inside and on the southern rim of the first flank-collapse structure. Dome-forming eruptions and associated block-and ash pyroclastic density currents involving acid magmas were the dominant activity of this period. This volcanic edifice was destroyed by a second flank collapse (St Pierre event), which generated a horseshoe-shaped structure, 6 x 4 km in size, and a debris avalanche (~13 km 3 ) that flowed like the first one into the Grenada basin. By correlating stratigraphy and magmatology of on-land deposits with tephra layers identified in a piston core (CAR-MAR 4) drilled during the Caraval cruise northwest of Martinique (Fig. 1a), [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF] proposed a minimum age of 32 ka cal BP for this flank collapse.

The third eruptive stage, just after this flank collapse, generated more basic magmas (basaltic andesite), with a high production rate, over several thousand years. After a decrease in the magma production, activity resumed and the magma emitted, after and up to the historic activity of Montagne Pelée, were again as acid as during the second eruptive stage.

Plinian to subplinian events and dome-forming eruptions were the two main eruptive styles that occurred during this period. On-land studies recognized 10 plinian to subplinian events and 18 dome-forming eruptions, including the two last historic eruptions, during the last 15 000 years of eruptive activity [START_REF] Roobol | Mount Pelée, Martinique: A pattern of alternating eruptive slyles[END_REF]Westercamp and Traineau, 1983a, b;[START_REF] Traineau | The recent pumiceeruptions of Mt. Pelée volcano, Martinique. Part I: Depositional sequences, description of pumiceous deposits[END_REF][START_REF] Smith | Mt Pelée, Martinique; A Study of an Active Island-arc Volcano[END_REF][START_REF] Michaud-Dubuy | Dynamique des éruptions pliniennes : réévaluation de l'aléa volcanique en Martinique[END_REF]. But tephrochronological studies of the CAR-MAR 4 piston core showed that the number of volcanic events identified on-land was underestimated particularly for the period prior to 5 000 years BP [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF].

During this third stage, a new flank-collapse occurred on the southwestern flank of the volcano (Rivière Sèche event). Lower in volume than the previous ones (~2 km 3 ), the debris avalanche flowed and stopped at the base of the submarine flank and exhibits a typical hummocky morphology. U-Th dating on lava dome located inside the structure gives an age of ~9 ka for this event [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF].

On the basis on IODP core analysis, Le [START_REF] Friant | Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340[END_REF] and [START_REF] Brunet | Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank-collapse to seafloor sediment failure?[END_REF] stated that for the first flank collapse affecting Montagne Pelée volcano the debris avalanche entered the sea, flowed over the submarine volcano slope, to stop and deposit around the slope break. This first -and the largest -debris avalanche deposit loaded, weakened seafloor sediment.

Resulting submarine landslide propagates along a decollement surface, deforming in situ alternation of hemipelagic sediments and turbidity deposits (Fig 1b). The debris avalanche deposit generated by the second flank collapse may have locally remobilized sediments within the submarine landslide deposit, by exerting normal stress that triggered the deformation process.

Materials and analytical methods

Coring and on-board observations

The site U1401 consists of four different holes drilled along a transect 900 m long, NW-SE direction, above the debris avalanche deposits (DAD) associated with the last flank collapse generated by Montagne Pelée volcano (Fig. 1b). The hole U1401A, (14°39.10′N, 61°25.08′W; 2590 mbsl), is the longest of the four drilled holes at 15.61 m recovered length, and has been chosen for this study. For each hole (example: U1401A), several 9 m long cores were collected (example U1401A-1H) and were cut in sections with a maximum length of 1.5 m (example: U1401A -1H1). Each section was sawn lengthwise. One half was stored as an archive (GCR -USIO, Texas A & M University College Station, Gulf Coast Repository) and the other half was used for physical properties (magnetic susceptibility, gamma-ray attenuation density, P-wave velocity), chemical analysis and lithological descriptions. Onboard each core was precisely described by sedimentologists and volcanologists in terms of sedimentology, lithology and volcanic structures.

Sampling

For specific analysis, samples were taken according to their position in each section of the core (example U1401A -1H4, 93/95cm). A systematic sampling (every 10 cm) of the hemipelagic sediments was carried outall along the core for δ 18 O chronostratigraphy. For lithological and chemical analyses of volcanic deposits, samples were taken from each deposit that was visually identified within the core. In case of thick turbidity deposit, two or three samples were taken, at the base, the middle and the top of the deposit, to observe potential lithological variations.

On board physical properties

Magnetic susceptibility measurements were realized with the multisensor track (MST) aboard the Joides Resolution. Closely spaced measurements (one point every 3cm) were collected on the four cores of the site U1401. Magnetic susceptibility measurements provide information on the content of magnetic minerals of each measured lithological level. Thus it is possible to distinguish hemipelagic mud, characterized by a low amount of magnetic and paramagnetic particles, from tephra layers and volcanic turbidity deposits, significantly enriched with magnetic particles.

Gamma -ray attenuation density measurements were performed with the DSDP GRAPE hardware and software. The system consists of a specific instrument that moves a section of core in between a gamma-ray source and a detector. Measurements are based on the direct correlation between the gamma-ray attenuation and the bulk density of the sample, which is an indicator of lithological changes (minerals, grain size, porosity). The higher the bulk density of the sample is, the higher is the attenuation.

Physical properties data need to be corrected due to data related to technical problems occurring during measurements when moving from one section to another (i.e. aberrant density values lower than 1 g/cm 3 ). For this reason, acquired measurements on a slice of 20 cm at the boundary between two successive sections were systematically removed.

We focused on magnetic susceptibility data as they exhibit more sensitive variations along the core. Detailed information about lithological changes at a small scale (1 to 10 cm) and identification of tephra layers within each section can be obtained using this dataset.

18 O stratigraphy

To assess chronology of the volcanic deposits, hemipelagic sediment was sampled every 10 cm all along the core. However, the presence of thick turbidity deposits prevented us from keeping a constant sampling interval all along the core. Turbidity deposits will be taken into account in the interpretation of δ 18 O curves. After being dried for about 12 hours at 70°C, each sample was divided in two equal parts, one used for measurements and the other saved as an archive. The former fraction was then weighed, sieved under water in a 40 µm stainless steel sieve to remove fine particles, then dried again and finally weighed a second time. This fraction was then divided in two halves, one for δ 18 O chronostratigraphy and 14 C dating, the second for lithological and mineralogical analysis.

For δ 18 O chronostratigraphy, 3 to 4 planktotic foraminifera from the specific species of Globigerinoides ruber (Alba White, D'Orbigny, 1839) were hand-picked in the fraction 250-315 µm. Isotopic δ 18 O analyses of foraminifera samples were performed at ISTeP (Sorbonne Université), with a 3kV-Delta V Advantage IRMS attached to a Kiel IV Carbonate Device.

Isotope values are reported in conventional delta (δ) notation as per mil (‰) deviations of the isotopic ratios ( 18 O/ 16 O) calculated to the VPDB scale using an inhouse standard (Carrara Marble) calibrated against NBS-19. Standard deviation (1σ) for δ 18 O measurements is 0.07 ‰.

14 C dating

On the basis of the δ 18 O curve, 14 C dates allow us to obtain absolute ages on key points of the curve to "calibrate" the timescale. For 14 C dating, 1000 planktonic foraminifera (about 14 mg required for spectrometer detection limit) were hand-picked in the fraction 250-315 µm of each sample. The 14 C analyses were performed at the French National AMS-ARTEMIS-LMC14 facility (Artemis Accelerator Mass Spectrometer, Saclay Laboratory, Université Paris-Saclay, France). The 14 C dating have been converted into calendar years using the Intcal 09 calibration record [START_REF] Reimer | IntCal09 and Marine09 radiocarbon age calibration curves, 0-50,000 years cal BP[END_REF][START_REF] Hughen | Marine 04 marine radiaacarbon age calibration, 0-26 cal kyr BP[END_REF] taking into account the marine reservoir age correction of 400 years.

Lithological data

Lithologic analyses of turbidity deposits and tephra layers were performed on selected samples, chemically attacked with HCl (0.1 mol) to disaggregate all carbonate microfossils and carbonate non biogenic particles, rinsed with de-ionized water, dried and weighed. To remove all remnant fine particles, samples were then sieved in de-ionized water with a 40 µm stainless steel sieve, dried again for about 24 hours at 70°C, and weighed a second time. Each sample was divided in two equal parts, one fraction used for lithology and the other for geochemistry. Counting for lithology was done on 46 samples on the fraction > 125µm on a basis of at least 400 particles/sample on a quadri plate under a binocular microscope. Five classes of clasts were identified: pumice and glass shard particles, scoria clasts, lava dome clasts, oxidized and hydrothermalized clasts and crystals (feldspars, orthopyroxenes, clinopyroxenes, amphiboles, oxides). The objective of counting is to identify the peak of abundance of the different volcanic clasts (scoria, pumice or lava domes clasts); They allow us to link the deposit to a specific eruptive style (pumices with plinian eruptions, scorias with explosive eruptions with more basic magma, and dense clasts with lava dome eruptions) and find some benchmark levels in the core. Counting precision has been estimated counting 6 times 6 different samples. The error linked to the operator is of about 10% based on the counting of the same sample by three different operators. The background signal was estimated counting about 400 clasts in some hemipelagic fractions of the core.

Moreover, detailed textures of volcanic clasts (vesicularity, microcristallinity) have been investigated using Back-Scattered Electron (BSE) images of pumice, scoria and lava dome clasts with a ZEISS-Supra 55 SEM (ISTeP, Sorbonne Université, Paris). Imaging was performed with an acceleration voltage of 15kV and a probe current of 5 nA.

Geochemical data: glass composition

Pumice and scoria clasts from each peak of abundance along the core were hand-picked in the sample fraction reserved for geochemistry, embedded in resin and polished. Major element composition of matrix glass was determined in 10 different tephra layers and 10 turbiditic levels using a CAMECA-SX 100 electron microprobe (Service Camparis, Paris, France). Analyses were performed with an acceleration voltage of 15 kV and a beam current of 4 nA. Counting time was of 5s on Na to limit Na migration, 10s for Si, Ti, Al, Fe, Mn,Mg,Ca, K, P and 15s for Cl. As recommended, we analyzed a minimum of 20 different glass shards per level. However, depending on the level, between 5 and 30 glass shards were kept after detailed investigations of glass composition to discard analyses that represent bias data due to microlite composition.

The purpose of analysing chemical composition of pumice and scoria peaks is to precisely identify the chemical composition of tephra along the core in order to compare them with those of on-land products known for recent Montagne Pelée activity (Westercamp and Traineau, 1983b;[START_REF] Fichaut | .I.). II: petrology of gabbroic and dioritic cumulates[END_REF]. No data has been acquired on lava dome clasts since they are too microcrystallized.

Results

Core description

Cores from hole U1401A, 15.61 m long, were described using core logs and photos obtained on-board during the cruise. The close-up photograph of the section U1401A-1H and a synthetic core description of the whole core are presented in Fig. 2. It consists of a series of volcanoclastic sediments intercalated in hemipelagic mud made of silt and clays (Fig. 2a). We can distinguish two types of volcanoclastic deposits: volcanoclastic turbidity deposits and tephra layers.

Turbidity deposits are a few tens of centimeters to several meters thick. They are of dark color, massive or normally graded, with various grain-sizes depending on the position in the core. 10 turbidity deposits are present in the core, named T1 to T10, from top to bottom (Fig. 2a,b). In the upper part of the core down to 5 m, turbidity deposits are few, thin, fine-grained and massive, with thickness ranging from 15 cm to 130 cm. The upper one, T1, is 50 cm thick, massive and dark deposit at the top of the core. It covers unconsolidated brown hemipelagic mud which corresponds to the recent hemipelagic mud observed generally at the top of cores. Below 5 m, turbidity deposits are thicker, coarse-grained, normally graded and more abundant. Below 10 m, the whole core is made of turbidity deposits without intercalated hemipelagic mud. The last four turbidity deposits (T7 to T10) are significant not only for their thickness but also for their grain-size. These turbidity deposits are normally graded, with large size particles (up to 5 cm) at the bottom and small size particles at the top.

24 tephra layers were identified in the first 8 m of the core. They are of dark color, sandy, a few cm thick, mainly interbedded in hemipelagic levels or more rarely in turbidity deposits.

In the lower part of the core, tephra layers are scarce or totally absent.

19 levels of hemipelagic sediments can be recognized in the first 10 m (Fig. 2a,b); they have clear sand color and thickness ranging from ~2-6 cm to ~70 cm. They are usually deformed or distorted, probably due to coring effects.

Physical properties analyses

Results from magnetic susceptibility and GRA (Gamma Ray Attenuation) density evidence adequate correlations between the two sets of values (Fig. 3). Turbidity deposits exhibit important variations in magnetic susceptibility (2500 to 4000 *10 -5 SI) and GRA density (0.5 to 2 g/cm 3 ) (Fig. 3a). This is likely related to the coarse-grained characteristic of the basal part of the turbidity deposits leading to the poor ability of large size particles to ensure compaction and a lack of mineralogical sorting. Hemipelagic sediments show the largest amplitude in variations in physical properties with low values of about 1000-1500 *10 - variations at a centimeter scale. Six negative peaks are identified for hemipelagic parts of the section, one main positive peak for turbidity deposit and six correspond to thin tephra layers (Fig. 3b).

Lithology

Counting of 46 samples of tephra layers and turbidity deposits along the core were performed in order to characterize the lithological composition of the different volcanoclastic deposits (Fig. 2b). The most representative type of particles in the tephra layers are lava dome clasts. 16 different peaks can be recognized and their abundance is mostly higher than 30%, with maximum values at about ~96%.

Abundance of pumice clasts ranges from 0 to 95% all along the core. 6 pumiceous peaks can be identified: 4 in the shallow part of the core with pumice content of 88-95 % (at a depth of 95, 163, 240 and 300 cm respectively) and 2 in its deeper part (at a depth of 700 and 800 cm) showing pumice percentages of less than 50%. Scoria clasts are in low abundance (10-15%) except for three scoria peaks (45-60%) at a depth of 688, 713 and 766 cm. Lithology of the major volcanoclastic turbidity deposits is dominated by lava dome clasts (80 to 98 %).

δ 18 O stratigraphy and 14 C dating

δ 18 O analyses on planktonic foraminifera (Globigerinoides ruber -white) of hemipelagic sediments exhibit fluctuations ranging from -2.52‰ (at 286 cm depth) to a maximum value of 0.07‰ (at 650 cm depth; Fig. 2c). 3 remarkable points were chosen for 14 C dating (red dots in Fig. 2c) : a steep negative peak of -0.75‰ (at 290 cm depth), the maximum positive peak of 0.07‰ (at 650 cm depth) and the final last hemipelagic layer of the core of -0.60‰ (at 965 cm depth). For these three points, 14 C dating returned estimated ages of 8082 ± 86 years cal. BP, 24677 ± 172 years cal. BP and 36425 ±191 years cal. BP respectively (after calibration with intcal 09.14c, [START_REF] Reimer | IntCal09 and Marine09 radiocarbon age calibration curves, 0-50,000 years cal BP[END_REF].

SEM observations

Textures of pumice, scoria and lava dome clasts were obtained by BSE imaging (Fig. 4).

Clasts present large differences in size, shape and vesicularity. Lava dome clasts (Fig. 4a) are poorly vesiculated, with highly microcrystallized matrix glass. On the contrary, pumice clasts (Fig. 4b) are vesiculated with glassy matrix glass and thin bubble walls. Scoria clasts (Fig. 4c) are moderately vesiculated, with more contorted vesicle shape, larger bubble walls and more microcrystallized matrix glass than in pumice clasts.

Geochemistry

Major element compositions were measured in the main pumiceous and scoriaceous tephra layers and their matrix glasses exhibit few variations in composition (Table 1). For pumice clasts, silica content is centered at rhyolitic values of about 73-78 wt% SiO 2 (Fig. 5a) with a total alkali content of about 5 wt%. Contrariwise, scoria clasts from tephra layers and turbidity deposits (T8, T9 and T10) show an extended compositional variability from andesite (67 wt% SiO 2) to rhyolite (74 wt% SiO 2 ) with 6-7 wt% alkali content (Fig. 5a).

Discussion

Marine chronostratigraphic framework of the core U1401A

The chronostratigraphical record of core U1401A is first compared to a previous wellestablished tephrochronological one from a deep-sea sediment core CAR-MAR 4, collected 50 km northwest and downwind off Martinique Island (Fig. 1b) during the CARAVAL cruise in 2002 [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF]. This core is in a steadier environment for sedimentation than that of the core U1401A, on a high point and outside the flow zones of debris avalanche and turbidity currents. For these reasons it may be used as a reference for our tephrochronological study in order to estimate the time period registered by the core U1401A. As the base of the core U1401A is located on the roof of the debris avalanche deposit related to the third flank collapse of Montagne Pelée, the tephrochronogical investigations will also provide constrains on a minimum age of the flank collapse.

CAR-MAR 4 is a 10.6 m long core, characterized, from top to bottom, by 7 m of continuous sedimentation with thick hemipelagic layers, tephra layers and no turbidity deposits followed by 3.6 m of disturbed and unstructured sedimentation [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF].

Only the first 7 meters were investigated for tephrochronological studies. CAR-MAR 4 δ 18 O results have already been correlated with a well-dated nearby deep-sea core (EN32-PC6, [START_REF] Broecker | Accelarator mass spectroscopic radiocarbon measurements on foraminifera shell from deep-sea cores[END_REF]. The correlation shows that CAR-MAR 4 covers the last 32 cal. ka BP (Fig. 6). We can use it as a reference curve for U1401A because the two cores are spatially close and analyses have been realized on the same planktonic foraminifera species and with the same analytical protocol for both. Owing to the presence of thick turbidity deposits in the core U1401A, to establish an adequate correlation with the CAR-MAR 4 δ 18 O curve, it is necessary to subtract the thickness of the turbidity deposits. This allows us to obtain a real chronostratigraphic scale for hemipelagic deposits.

A spectral analysis and a correlation between the two cores have been processed using the free software Analyseries [START_REF] Paillard | Macintosh program performs time-series analysis[END_REF]. This software enables us to compare our δ 18 O data with the selected reference CAR-MAR 4 curve by selecting and comparing a series of calibration points between the two curves. From the calibration points, Analyseries realizes a linear intercalibration to calculate the age of the intermediate points of the curve. It takes into account the age and the depth of the two calibration points up and down the intermediary one, and the depth of the intermediary point, according to the equation:

Age X = [(age A -age B ) / (depth A -depth B )]*[depth X -depth A ] + age A
where X is the intermediary point, A the upper calibration point and B the lower calibration point.

In the final age model (Fig. 6), the two curves are correlated with a coefficient of 0.936 and correlation returns a mean pelagic sedimentation rate of 22cm/ka, consistent with that known for the Grenada basin [START_REF] Reid | Late Quaternary sedimentation in the Lesser Antilles island arc[END_REF][START_REF] Boudon | Volcano flank instability in the Lesser Antilles Arc: diversity of scale, processes, and temporal recurrence[END_REF]. From the modelled ages, the core U1401A covers a period from 0 to ~36 cal. ka BP, with a maximum δ 18 O value (0.07 ‰) at about 25 cal. ka BP. The overlap of the two curves is clear especially in the first part (0-8 ka). However, for recent ages, a small shift is evident between the two cores (Fig. 6):

the modelled ages of the core U1401A are younger than those of CAR-MAR 4. This proves that the core U1401A recorded the largest temporal range, probably because of the presence of a thick turbidity deposit (T1, 50 cm thick) at the top of the core that allowed the preservation of the youngest and not compacted sediments, usually destroyed by drilling processes.

Another difference between the two cores is the sampling frequency used for δ 18 O chronostratigraphy. The sampling interval for the core CAR-MAR 4 is constant at 10 cm while the sampling interval could not be kept constant for the core U1401A. Sampling the core U1401A led to two types of problems: (1) the presence of numerous and thick turbidity deposits and (2) the low content of the planktonic foraminifera Globigerinoides ruber in many samples. These problems can be explained by the particular position of the U1401 site, located on the submarine flank of the volcano. As a result the site is more exposed to clastic and clayey sedimentation related to on-land processes, which induce a decrease in biogenic steady-state sedimentation. Secondly, the presence of thick turbidity deposits has a significant impact on the sedimentary record of U1401A core. The correlation between the two cores is lost when turbidity deposits are present (Fig. 6). In fact, some significant gaps occur, causing a lack of thousands of years in the sedimentary record. A strong erosive power of turbidites can probably be invoked during their deposition process. Three 14 C dates were performed to obtain absolute ages on 3 key positions of the U1401A core (Figs 2c,[START_REF] Kutterolf | Tephrostratigraphy and provenance from IODP Expedition 352, Izu-Bonin arc: Tracing tephra sources and volumes from the Oligocene to recent[END_REF]. They are roughly located at the top, the center and the bottom of the core (respectively at 197, 348.5 and 488.5 cm turbidity deposits off depths). These 3 points have been selected as they represent a particular milestone in the evolution of the δ 18 O curve. In addition, dating the top and bottom of the curve allows us to obtain the entire coverage period of the core and an absolute age for the sediments located on the DAD. The most recent age obtained (8220 cal. ka BP) is well consistent with the model obtained with δ 18 O analysis. It corresponds to a positive peak in the δ 18 O record. The second 14 C age of 24677 cal. ka BP corresponds to the higher value of the δ 18 O obtained in the core U1401A. If we compare with the CAR-MAR 4 curve where the higher value of the δ 18 O curve is obtained at a more recent age (~18 ka), the maximum value of the U1401A δ 18 O curve is probably too high (Fig. 6a). This is likely related to the lack of points in the δ 18 O record due to the erosion by turbidity density currents during the 17-24 ka period where the maximum δ 18 O value is reached. The third 14 C age of 36425 cal. ka BP corresponds to the lowest point sampled in a small hemipelagic deposit interbedded between T7 and T8 turbidity deposits and overlaying the top of the debris avalanche deposit (T8 to T10) of the U1401A core. As this third age is obtained on the lowest hemipelagic level of the core but not really at its physical bottom, our results of ~36 cal. ka BP represents a minimum age for the occurrence of the third flank collapse of Montagne Pelée, that significantly contrasts with what was thought up to now.

Nevertheless below this point three thick turbidity deposits (T8 to T10) are present. They overly the top of the debris avalanche deposit. No hemipelagic sediments are identified between these turbidity deposits or at the top of the debris avalanche deposit. These observations lead us to believe that it is likely that turbidity deposits T8 to T10 formed in a short period of time directly after the flank collapse event.

Tephrochronology, stratigraphy and eruptive styles

Figure 7 shows the complete estimated chronostratigraphic model of the core U1401A.

24 tephra layers and 10 turbidity deposits have been recognized all along the core by cross correlation of photos observations, counting techniques and analysis of physical properties.

The comparison of tephra record between the core U1401A and the core CAR-MAR 4 is showed in Figure 6.

The core U1401A can be divided in three different units. In the first unit, 0-3 m in depth (0 to 9 cal. ka BP), 2 turbidity deposits can be recognized (Fig. 7, T1= 50 cm and T2= 10 cm).

The first turbidity deposit (T1) is located at the top of the core, covering the recent and not compacted hemipelagic sediments. Its peculiar position allows it to be linked to the last period of volcanic activity characterized by the last 1902-1905 and 1929-1932 dome-forming eruptions. In addition, its lithology (prevalence of lava dome's clasts) is similar to that of onland pyroclastic density current deposits [START_REF] Bourdier | Stratigraphy of the 1902 and 1929 nuée ardente deposits, Montagne Pelée, Martinique[END_REF]. This unit is also characterized by the occurrence of 10 tephra layers (Fig. 7, red lines = 4 pumice clast-rich levels and blue lines = 6 lava dome clast-rich levels) interbedded in the hemipelagic sedimentation. Such alternation of pumice clasts and lava dome clasts-rich levels is consistent with tephrochronological results on the core CAR-MAR 4 (Fig. 6b, [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF] and with observations on on-land deposits that show the well-known alternation between domeforming eruptions and plinian or subplinian eruptions (P1 to P8 eruptions, Westercamp and Traineau, 1983a, b;[START_REF] Traineau | The recent pumiceeruptions of Mt. Pelée volcano, Martinique. Part I: Depositional sequences, description of pumiceous deposits[END_REF][START_REF] Michaud-Dubuy | Dynamique des éruptions pliniennes : réévaluation de l'aléa volcanique en Martinique[END_REF]. The residual glass of the pumice clasts from these tephra layers has rhyolitic composition (about 75 wt% SiO 2 and 5 wt% Na 2 O+K 2 O) which is close to the composition of the residual glass of the pumice clasts from on-land deposits (Fig. 5b). Furthermore their composition is clearly far from that of Dominica island (SiO 2 ~78 wt%, Na 2 O+K 2 O ~5-7 wt%, Balcone-Boissard et al., 2018) and clearly excludes tephra originating from Dominica volcanoes, even though more investigations have to be performed using trace elements proxies. We see that the record of eruptive events is lower in the core U1401A than for the core CAR MAR4 and also for onland record (Fig. 6). This is due to the location of the site U1401 not in the axis of the main local windward direction of the winds (westbound trade) and to the dispersion of the plumes from plinian and subplinian eruptions or ash-clouds associated to block-and ash pyroclastic density currents.

The second unit of the core, 3 to 8 m in depth (9 to 30 cal. ka BP) is characterized by well-spaced turbidity deposits (Fig. 7, T3 to T6) in thick hemipelagic layers. Their thickness varies from 10 cm (T4) to 120 cm (T5). Lithology of T3 and T5 shows the prevalence of lava dome's clasts; they are probably linked with block-and ash pyroclastic density currents associated to dome-forming eruptions. A total of 14 tephra layers can be documented in this unit. Only 3 tephra layers enriched in lava dome clasts are recognized in the first half of the second unit (Fig. 7, blue lines) whereas 11 tephra layers are present in the second half. 6 of them are rich in dome clasts (blue lines), 2 rich in pumice clasts (red lines), whereas 3 of them contain scoria clasts (green lines). In these tephra, the residual glass of scoria clasts is more basic than the residual glass of the pumice clasts (~65 wt% SiO 2 , Fig. 5a), but we also observed some clasts that exhibit a more evolved composition (~75 wt% SiO 2 ) -see explanation in the next section. The lack of tephra records between 5 and 6.7 m in this unit may be related to a decrease in volcanic activity, or the set-up of thick turbidity deposits that eroded a part of the previously deposited sediments.

The third unit of the core, 8 to 15 m in depth (30 to 36 cal. ka BP) is almost exclusively characterized by thick turbidity deposits (T7 to T10). Their thickness varies from 140 cm (T7) to 230 cm (T8). Lithological results highlighted that these turbidity deposits are rich in lava dome's clasts but also in scoria clasts (about 10 to 20 %). The absence of hemipelagic sediments in this part of the core indicates a significant supply of volcanic products in a short time interval.

Origin of the scoria-rich levels

Complete results on U1401A core show that the turbidity deposits and some of the tephra layers from the bottom of the core are rich in scoria clasts (up to 60% of the clasts in the sections between 680 and 820 m depth) of more basic composition (~65 wt% SiO 2 ). The proportion of scoria clasts decreases progressively to the top of the core rarely being over a background content of 5% of clasts.

Based on tephrochronological study of the CAR-MAR 4 core (Fig. 6b) and on-land data, [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF] have proposed that abundant deposits of scoria flows of basaltic andesitic composition were generated after the second flank collapse event, estimated around 32 ka, whereas acid andesitic magma were emitted before this flank collapse event. These changes in composition and eruptive style are explained by the decrease of the threshold effect exerted by the volcanic edifice on the magma plumbing system allowing more basic and denser magmas to reach the surface [START_REF] Pinel | Some consequences of volcanic edifice destruction for eruption conditions[END_REF][START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF][START_REF] Cassidy | Rapid onset of mafic magmatism facilitated by volcanic edifice collapse[END_REF]. This activity occurred over several thousand years, rapidly building a new cone inside the horseshoe-shaped structure. This also shows that the magma production was high just after the flank collapse and gradually decreased during the building of the new cone and progressively exerted a new threshold effect on the plumbing system. The magma production is then probably reduced for a few thousand years before resuming with the production of more acidic and less dense magmas. The ages proposed for this period of basaltic andesite emissions range between 32 cal. ka BP or more and 27 cal. ka BP. A period of weaker magmatic activity occurs between 27 to 22.5 cal. ka BP prior to a new emission of andesites from 22.5 cal. ka BP to present [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF].

The on-land relationship between the horseshoe-shaped structure of the second flankcollapse and the scoria pyroclastic density currents were not clearly established as the scoria pyroclastic density currents which resulted from column collapse of explosive eruptions, covered all the flanks of the volcano inside and outside the horseshoe-shaped structures.

Considering 1) the estimated ages of the on-land scoria pyroclastic density currents (Westercamp and Traineau, 1983a, b), the age of the tephra levels rich in scoria clasts in the CAR-MAR 4 core band the ages obtained on the turbidity deposits and tephra level rich in scoria clasts of the U1401A core; 2) the similar composition of the residual glass of these scoria clasts in the cores and on-land, we can assume that all these deposits belong to the same period of activity of Montagne Pelée and the production of basaltic andesites during this period did not follow the second but the third flank collapse as the site U1401 is located on the third DAD.

We also observe that even if the emitted magmas are dominantly basaltic andesites, they can be associated with more evolved magmas of dacitic composition with rhyolitic glasses (Fig. 5). This characteristic has already been evidenced on-land for these eruptions [START_REF] Traineau | Mélanges magmatiques à la Montagne Pelée (Martinique). Origine des éruptions de type Saint-Vincent[END_REF][START_REF] Bourdier | Magma mixing in a main stage of formation of Montagne Pelée: the Saint Vincent-type scoria flow sequence (Martinique, F.W.I.)[END_REF] and explained by the presence of more superficial and small pocket of more evolved magmas within the "mushy" plumbing system impacted by the ascent of more basic magmas stored deeper [START_REF] Pichavant | Physical conditions, structure, and dynamics of a zoned magma chamber: Mount Pelée (Martinique, Lesser Antilles arc)[END_REF]. This magma mixing generally occurred at the beginning of the eruptive phases.

Age of the third flank collapse and relationship with the volcanic activity

Our results allow us to propose a significant shift in age of the third flank collapse from 9 ka to ~36 cal. ka BP.

Considering that the drilling operations of the core U1401A reach the top of the third DAD, and on the basis of the δ 18 O age model and on the 14 C ages we can consider that the age of 36425 ± 191 cal. ka BP obtained in the lowest level of hemipelagic mud is a minimum age for the third DAD and the corresponding flank collapse. But a series of turbidity deposits (T8 to T10) are recognized between the last dated hemipelagic mud and the top of the debris avalanche deposits. Thus it is possible to raise the question of the time interval separating this 14 C age from the true age of the flank collapse.

As previously proposed, the decrease of the load exerted by the third flank-collapse has led to the production of scoria rich deposits of basaltic composition and to a high magma production rate. This high magma production rate generated abundant scoria pyroclastic density currents that entered the sea and evolved in turbidity currents. This explains the abundance and the thickness of the turbidity deposits recognized at the base of the U1401A core and on the debris avalanche deposit. This abundance of volcanic products generated after the flank-collapse supports rapid deposition from the turbidity currents (T8 to T10). We can consider that the time between the flank collapse and the ascent of more basic magmas is not too long (probably not more than a few decades) and that the age of 36.425 cal. ka BP obtained on the hemipelagic mud covering these turbidity deposits is a minimum age not so far from the true age of the debris avalanche setup.

The recent eruptive history of Montagne Pelée

Previous studies have described the eruptive history of Montagne Pelée as the succession of three different phases of construction of the volcanic edifice, separated by two flank collapses (Fig. 8a); the third flank collapse, is in fact included in the third stage of building [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF][START_REF] Boudon | Martinique[END_REF][START_REF] Boudon | Volcano flank instability in the Lesser Antilles Arc: diversity of scale, processes, and temporal recurrence[END_REF][START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF]Germa et al., 2011a). On the basis of on-land studies, the three different flank collapses had previously been dated at 127 ka (Germa et al., 2011a) for the first one, 32 ka [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF] and 9 ka (Le [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF], respectively for the second and the third one.

Nevertheless, the results of our study significantly modify the volcanological evolution of Montagne Pelée and allow us to submit a new evolution for the volcano (Fig. 8b). On-land, several rims of flank collapse structures have been identified (Fig. 11 of Le Friant et al., 2003 and Fig 1c). The rims resulting from the first flank-collapse structure are clearly identified, though its southern rim is not visible as it is covered by the products of the most recent volcano activity. Rims of the third flank collapse structures are clearly identifiable as they are the most recent, but they are also partially covered by recent volcanic products. On the contrary, the scars originating from the second flank collapse structure are not clearly visible and remain questionable on the basis of on-land investigations. Recent offshore studies following the IODP expedition 340 have shown that the DADs do not have the extension previously proposed [START_REF] Friant | Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340[END_REF][START_REF] Brunet | Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank-collapse to seafloor sediment failure?[END_REF]. The large chaotic deposits identified on seismic profiles and on bathymetry are deformed sediments pushed by the DAD that stopped at the base of the submarine flank. It is difficult to distinguish the DADs of the first and the second event because they form a unique bulge at the base of the submarine flank of the volcano (Fig 1b). On the contrary, the third DAD is clearly identified on the submarine flank of the volcano with its lobe-shape and its hummocky morphology.

The question of the occurrence of three flank collapse events can thus be addressed in a serious manner. The morphology and the distribution of the valleys indicate that the northern rim of the first flank collapse structure exists. Its age of 127 ka (Germa et al., 2011a) obtained on two lava domes on each part of the rim is reliable. The third flank collapse is now also clearly identified by the presence of submarine DADs, some remnants of hummock morphology on-land and the rims of the horse-shoe shaped structure [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF].

Its age is now confidently set at ~36 ka (this study). The time interval that separated the first (127 ka) from the third flank collapse (~36 ka) is in the order of 90 ka. Is this short period enough to build a new cone destroyed by a second flank collapse and a third cone destroyed again by the third one? It is difficult to answer this question as the data we produce in this study concern the last 40 000 thousand years. However the magma production rate of Montagne Pelée is, although significant, not very high and can be estimated at a few km 3 /10 000 years for the last tens of thousands of years [START_REF] Wadge | Comparison of volcanic production rates and subduction rates in the Lesser Antilles and Central America[END_REF][START_REF] Michaud-Dubuy | Dynamique des éruptions pliniennes : réévaluation de l'aléa volcanique en Martinique[END_REF]. We can consider that the highest magma production rate occurred after the flank collapse event dated now at ~36 ka over a period of 10 000 years. An alternative to the already proposed evolution of the volcano -that must be confirmed by on-land work and additional tephrochronological investigations on other marine cores in the period between the first and the "third" flank collapse -is that only two flank collapses occurred (Fig. 8b): the first one at127 ka, and the last one at 36 ka. Though less voluminous, this last flank-collapse modified the dynamics of the magmatic plumbing system, leading for a short period of time to the ascent of more basic and denser magma than those emitted before the flank collapse.

Following this flank collapse, a lot of explosive eruptions produced scoria fall and density currents covering a large part of the volcano. Numerous turbidity currents were generated by scoria density currents entering into the sea or by the remobilization of scoria density current deposits, covering part of the submarine flank of Montagne Pelée. The eruptive activity was high just after the flank-collapse and decreased progressively. The significant eruptive activity rapidly involved the building of a new volcanic edifice which exerted a new threshold effect on the plumbing system. The volcanic activity decreased and progressively a change in the composition of the emitted magmas occurred; more acidic magmas were generated giving rise to the alternance of plinian or subplinian events and dome-forming eruptions up to this day.

Conclusions

The detailed study of the core U 1401a located on the submarine flank of Montagne Pelée, on the hummocky deposit of the third debris avalanche (DAD 3) has improved our knowledge of the eruptive history. It has allowed us to propose a minimum age of ~36 ka for the last flank collapse. It also indicates that the volcanic activity can be modified in terms of magma production and in terms of magma composition after a flank collapse. Deeper and more basic magmas can erupt for a long time before a new cone exerts a threshold effect on the plumbing system, reducing the magma production rate and changing the composition of the emitted magmas. It also indicates that after a flank collapse, a lot of turbidity currents can occur resulting in the offshore evolution of abundant pyroclastic density currents or the remobilization of on-land deposits. It also shows that a sole core does not enable the reconstruction of all the eruptive history of a volcano for a given period. The core U1401 located on the western submarine flank of Montagne Pelée is well located for the study of the post flank-collapse activity and the pyroclastic density currents as well as tephra layers.

Abundant turbidity deposits have an significant erosive power, destroying part of the lower deposits, but can also preserve recent and not compacted hemipelagic sediments, generally not observed, as was the case for the upper recent turbidity deposits. The core CAR MAR 4 is best located to study tephra layers as it is on a high point without erosion and closer to the direction of the winds (East-West) in the troposphere. But a lot of tephra are dispersed to the East as the eruptive column for Plinian eruptions reaches the stratosphere where the wind direction is generally West-Easterly. A core located to the east of Montagne Pelée will allow us to complete the eruptive history of the volcano. and scoria clasts (purple) from Montagne Pelée [START_REF] Boudon | Role of large flank collapses on magma evolution of volcanoes. Insights from the Lesser Antilles Arc[END_REF] and pumices from the neighboring island of Dominica (orange) [START_REF] Balcone-Boissard | Deep pre-eruptive storage of silicic magmas feeding Plinian and dome-forming eruptions of central and northern Dominica (Lesser Antilles) inferred from volatile contents of melt inclusions Contrib[END_REF]. Hem.

Hem.

Hem.

Hem.

Magnetic Susceptibility

  Figure captions.

Figure 1 .

 1 Figure 1. a) Geodynamic setting of the Lesser Antilles volcanic arc; Predicted bathymetry

Figure 3 .

 3 Figure 3. a) Correlation between GRA density and magnetic susceptibility data along the

Figure 4 .

 4 Figure 4. SEM images of three representative volcanic fragments with a magnification of x35

Figure 5

 5 Figure 5. a) Evolution of the SiO 2 content of volcanic clasts (matrix glasses) along depth in

Figure 6 :

 6 Figure 6: a) Modeled age of the core U 1401 A and correlation with the core CAR-MAR 4

Figure 7 :

 7 Figure 7: Ages of tephra layers depending on the depth in the core. In red pumice layers, in

Figure 8 :

 8 Figure 8 : The recent volcanic history of Montagne Pelée: toward a new model of evolution.

  Figure 1

  Figure2

  Figure 3

  Figure 6

  .1 Sect.2 Sect.3 Sect.4 Sect.5 Sect.6 Sect.7

	340 -U1401A -1H
			t
		t				t
		t				t
						t
	T2		T3	t	t	t
	t
		t	T4			t
					t
	H	t
	t		t
						hemipelagic mud
			t			turbidity deposit
						tephra layer
	H
		t	t

Sect

SI for magnetic susceptibility and < 1.5 g/cm 3 for GRA density (Fig.3a). A detailed view of section U1401A-1H2 (Fig.3b) enables us to precisely analyze magnetic susceptibility

Acknowledgments

We thank the captains, officers, crews of the R/V Joides Resolution and the IODP-340 scientific mission. Major element analyses at the microprobe facility benefited the support of M. Fialin and N. Rividi (Service CAMPARIS). Oxygen stratigraphy analysis benefited the support of N. Labourdette (UPMC). Imaging at SEM was helped by Omar Boudouma (Sorbonne Université). We thank INSU, NERC, ANR-13-BS06-0009 for funding. 14 C dating were performed at LMC14 laboratory (Artemis program). We also thank E. Lebas for her participation and help in the acquisition of planktonic foraminifera samples.

DAD 3. Contour interval is 500 m, (modified from Brunet et al., 2017). Coring site U1401 is located on Deposit 3 and consists of a 900 m transect with four holes (C, A, B, D from East to West); c) Detail of the west flank of Montagne Pelée volcano marked by horseshoe shaped structures deriving from flank collapses. First flankcollapse structure is labeled in red, the second in green and the third in yellow (from [START_REF] Friant | Large scale flank-collapse during the recent activity of Montagne Pelée, Martinique, FWI[END_REF]. In brown: turbidites (T1 to T10); in beige: hemipelagic mud; in orange: tephra layers (t). Abundance of volcanic fragments in each tephra layer and in volcanoclastic turbiditic deposits obtained from counting operations: in green scoria, in red pumices and in blue lava dome clasts; Six peaks of pumices can be recognized along the core, four in the first 300 cm and two others in the deep part of the core at depth of 700 and 800 m. Two peaks of scoria are found at about 700 m. Lava dome clasts prevail all along the core with percentages rarely going lower than 20%; c) Isotopic δ 18 O and 14 C results on core U1401A: in blue δ 18 O results, In red: 14 C dating for the three marker points at 197, 348.5 and 488.5 cm in the core).

δ 18 O values exhibit variations from -2,52 to 0,07 ‰, with high values in the deep part of the hole and isotopic maximum recorded at about 650 cm in depth.