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Résumé. Les questionnements abordés dans cet article portent sur l’homogénéité et les relations spatiales entre l’ensemble belloisien et le Laborien. Nous avons pris pour cadre géographique d’étude, la (réputée) marge méridionale du Belloisien : la France centrale. Cet espace est jalonné par plusieurs gisements clés de la transition Pléistocène-Holocène, notamment Muides-sur-Loire, Champ-Chalatras et le Cuze de Sainte-Anastasie. C’est à travers l’étude de l’industrie lithique de ces trois sites que nous questionnons les réseaux de relations à l’extrême fin du Paléolithique. Cet espace est également situé à l’écart des grandes dynamiques de recherche universitaire. Il nous faut donc interroger la notion de frontière à travers l’œil du « préhistorique » ou du « préhistoriens », suivant une analyse pétrotechno-typologique. Les résultats mettent en évidence une fréquentation de gîtes communs et une gestion économique des matériaux parfois semblables entre les trois sites étudiés. Ce réseau de relations complexes met en exergue la porosité entre les appellations préhistoriennes. De plus, l’identification de savoir-faire laboriens, à partir de silicites du sud du Bassin parisien, ainsi que la circulation de grands supports laminaires au sein de sites laborien, confirme cette perméabilité. Ces premières observations alimentent l’hypothèse d’une imbrication d’un sous-système technique belloisien à une tradition plus large : le Laborien. Abstract. The aim of this paper is about discussing to the homogeneity and relationship of the Belloisian tradition with the more southern Laborian. In this regard, we choose central France, the reputed southern margin of Belloisian, to be the geographical framework of this study. It is punctuated by key sites belonging to the Pleistocene-Holocene transition: Muides-sur-Loire, Champ-Chalatras and Cuze de Sainte-Anastasie. What we are questioning in this article are the networks relationships between the Belloisian and the Laborian traditions through the study of lithic industry. This research area is on the fringes of the major dynamic’s university programs too and involves research traditions that differ regionally. We therefore also question the notion of “prehistoric” or “prehistorian” boundaries through a petro-techno-typological analysis of lithic series. In this case study, the techno-economic data shows a frequentation of common outcrops and economic management of the silicites for the three sites. This complex network of relationships between groups shows the porosity between the prehistorian designation. The identification of laborian “know-how” from silicites in the south of the Paris Basin and the circulation of large laminar supports corroborate this fact. So finally, these results lead us to propose the hypothesis of an interweaving of a Belloisian technical sub-system with a Laborian tradition, now well defined.

The Main Ethiopian Rift represents a unique insight into process of continental rifting and its comprehensive research can provide partial clarification of open questions such are the causes, mechanisms, and timing of overall tectonic and magmatic evolution. The Main Ethiopian Rift is an intermediary between the Afar triple junction to the north and Kenyan Rift to the south, representing incipient plate boundary between Nubian and Somalian plates. Based on comprehensive geological research of the northern flank of the Southern Main Ethiopian Rift including field geological and structural mapping, petrological and geochemical description of individual lithologies, morphotectonic analysis of Digital Elevation Model, paleostress analysis and gravity pattern assessment including calculation of Linsser indices, some aspects in geodynamic evolution of northern flank of the Southern Main Ethiopian Rift is interpreted. The area recorded typical continental rift-related tectonic and magmatic evolution including "pre-rift" (Eocene to Oligocene) volcanic activity initiated by extensive flood (plateau) alkaline basalt to trachybasalt basalt eruptions due to crustal thinning and mantle plume(s) ascent, followed by fault-dominated "early-rift" (Miocene) bimodal volcanism associated with origin of the rift...

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Subduction zones are active sites of chemical exchange between the Earth’s surface and deep interior and play a fundamental role in regulating planet habitability. However, the mechanisms by which redox sensitive elements (e.g., iron, carbon and sulfur) are cycled during subduction remains unclear. Here we use Fe stable isotopes (δ56Fe), which are sensitive to redox-related processes, to examine forearc serpentinite clasts recovered from deep sea drilling of mud volcanoes formed above the Mariana subduction zone in the Western Pacific. We show that serpentinisation of the forearc by slab-derived fluids produces dramatic δ56Fe variation. Unexpected negative correlations between serpentinite bulk δ56Fe, fluid-mobile element concentrations (e.g., B, As) and Fe3+/ƩFe suggest a concomitant oxidation of the mantle wedge through the transfer of isotopically light iron by slab-derived fluids. This process must reflect the transfer of either sulfate- or carbonate-bearing fluids that preferentially complex isotopically light Fe.

This article presents an overview of recent research on dolia (large storage jars) from the former province of Narbonese Gaul. It aims to bring to light a poorly known aspect of the Roman period, namely the production and diffusion of dolia, thought archaeometrical evidences. Thus, the largest workshop of dolia in Narbonese Gaul has been recognized by combining archaeometrical, geological and archaeological data. Cet article présente une synthèse des récentes recherches menées sur les dolia (grandes jarres de stockage) du territoire de l’ancienne province de Gaule narbonnaise. Il vise à mettre en lumière un phénomène méconnu, à savoir la production et la diffusion des dolia à l’époque romaine par le biais des données archéométriques. Cette étude démontre comment le croisement des données archéométriques, géologiques et archéologiques ont permis de révéler l’existence de l’une des plus grandes zones de production de dolia de Gaule Narbonnaise.

Mesosiderite meteorites consist of a mixture of crustal basaltic or gabbroic material and metal. Their formation process is still debated due to their unexpected combination of crust and core materials, possibly derived from the same planetesimal parent body, and lacking an intervening mantle component. Mesosiderites have experienced an extremely slow cooling rate from ca. 550 °C, as recorded in the metal (0.25-0.5 °C/Ma). Here we present a detailed investigation of exsolution features in pyroxene from the Antarctic mesosiderite Asuka (A) 09545. Geothermobarometry calculations, lattice parameters, lamellae orientation, and the presence of clinoenstatite as the host were used in an attempt to constrain the evolution of pyroxene from 1150 to 570 °C and the formation of two generations of exsolution lamellae. After pigeonite crystallization at ca. 1150 °C, the first exsolution process generated the thick augite lamellae along (100) in the temperature interval 1000-900 °C. By further cooling, a second order of exsolution lamellae formed within augite along (001), consisting of monoclinic low-Ca pyroxene, equilibrated in the temperature range 900-800 °C. The last process, occurring in the 600-500 °C temperature range, was likely the inversion of high to low pigeonite in the host crystal, lacking evidence for nucleation of orthopyroxene. The formation of two generations of exsolution lamellae, as well as of likely metastable pigeonite, suggest non-equilibrium conditions. Cooling was sufficiently slow to allow the formation of the lamellae, their preservation, and the transition from high to low pigeonite. In addition, the preservation of such fine-grained lamellae limits long-lasting, impact reheating to a peak temperature lower than 570 °C. These features, including the presence of monoclinic low-Ca pyroxene as the host, are reported in only a few mesosiderites. This suggests a possibly different origin and thermal history from most mesosiderites and that the crystallography (i.e. space group) of low-Ca pyroxene could be used as parameter to distinguish mesosiderite populations based on their cooling history., SCOPUS: ar.j, info:eu-repo/semantics/published

Goal – The reconstruction of past topographies remains challenging and only a few methods allow accurate determination of past surface elevations. We propose here a new technique for deriving paleo-elevations, in which multiple cosmogenic nuclides are measured in the same geological sample exposed at the Earth's surface. This method relies on the altitude dependence of the cosmogenic nuclides' production rates combined with the radioactive decays of nuclides with different half-lives. Theory – The position of the two cosmogenic nuclide exposure curves ( 26 Al/ 10 Be vs 10 Be or 10 Be/ 21 Ne vs 10 Be) depends on the altitude of exposure. If the studied surfaces have been exposed for sufficiently long durations (>500 ka), or have been affected by low erosion rates (500 ka), or low erosion rates (, SCOPUS: ar.j, info:eu-repo/semantics/published

The Temagami Anomaly is one of the largest unexplained magnetic features in North America. It is similar in size and shape to the geophysical anomaly that marks the 1.85 Ga Sudbury Igneous Complex (SIC) in its immediate vicinity but its geological cause and potential link to the Sudbury impact structure have remained elusive. Here we report on a 2200 m deep diamond drill core intersecting the area of maximum magnetic anomaly and provide evidence of diorite dykes therein being most likely related to the Sudbury impact event. The fine-grained, strongly altered biotite-amphibole diorite occurs below 2000 m, is intrusive into Archaean basement rocks and has the same major- and trace element geochemistry as the SIC, which approximates the bulk composition of the local continental crust that was hit by the impact. A crustal affinity analogous to SIC impact-melt rocks is further supported by whole-rock Nd and Pb isotopes. Low ɛ Nd 0 between −27.6 and −18.7, as well as Nd model ages of 2.75 Ga are considered as inherited from the crustal precursor rocks that became largely homogenized in the course of impact melt formation. The 206 Pb/ 204 Pb ratios are between 15.77 and 19.38, 207 Pb/ 204 Pb between 15.22 and 15.59 (corresponding to initial 207 Pb/ 204 Pb at 1850 Ma between 15.14 and 15.22), yielding an “isochron age” of 1780 +320/−330 Ma, and the 208 Pb/ 204 Pb ranges from 35.47 to 41.15, all values that compare well with published data on SIC impact-related igneous rocks of mainly quartz dioritic composition, locally referred to as Offset Dykes, and that are distinctly different to those reported for other magmatic units in the wider region. Although several such dykes have been well known to occur both radially and concentrically around the SIC, none have been described so far from the area east of the SIC. The recognition of former intrusive impact melt at an even greater distance (50 km) from the SIC than has been known so far increases the extent of the impact structure but also the exploration potential of the area of the Temagami magnetic anomaly for Ni-Cu-PGE-sulfide deposits. The actual cause of the Temagami Anomaly remains open to debate., SCOPUS: ar.j, info:eu-repo/semantics/published

Antarctic blue ice zones, the most productive locations for meteorite recovery on Earth, contain old ice that is easily accessible and available in large quantities. However, the mechanisms behind these meteorite traps remain a topic of ongoing debate. Here, we propose an interdisciplinary approach to improve our understanding of a meteorite trap in Dronning Maud Land (East Antarctica) on the Nansen blue ice field meteorite trap (2600–3100 m above sea level), where more than half of the Asuka meteorites have been collected. Based on 185 surface blue ice samples, one of the largest observed spatial patterns in oxygen isotopic variation to date is found. Relying on meteorites for which the terrestrial ages are determined using 14C and 36Cl, this surface ice is interpreted to date from the Last Interglacial up to the present-day. By combining state-of-the-art satellite derived surface velocities, surface mass balance modelling and ice flow modelling, we estimate that about 75–85% of the meteorites found on the ice field were supplied by ice flow after entering the ice sheet in an accumulation area of a few hundred square kilometres located south (upstream) of the ice field. Less than 0.4 new meteorites per year are supplied to the ice field through ice flow, suggesting that the hundreds of meteorites found 25 years after the first visit to this ice field mostly represent meteorites that were previously not found, rather than newly supplied meteorites. By combining these findings, the infall rate of meteorites from space is estimated, which is in line with values from the literature, but situated at the higher end of the range. A comparison of the oxygen isotopic variation of the surface blue ice to that of the European Project for Ice Coring in Antarctica (EPICA), Dronning Maud Land (EDML) ice core (located 750 km to the west, at the same elevation), suggests that the regional changes in topography have been relatively limited since the Last Interglacial, supporting theories of an overall stable East Antarctic Ice Sheet (EAIS) over this time period., SCOPUS: ar.j, info:eu-repo/semantics/published

The Mariana forearc is a unique setting on Earth where serpentinite mud volcanoes exhume clasts originating from depths of 15 km and more from the forearc mantle. These peridotite clasts are variably serpentinized by interaction with slab derived fluid, and provide a record of forearc mantle dynamics and changes in geochemistry with depth. During International Oceanic Discovery Program (IODP) Expedition 366, we recovered serpentinized ultramafic clasts contained within serpentinite muds of three different mud volcanoes located at increasing distance from the Mariana trench and at increasing depth to the slab/mantle interface: Yinazao (distance to the trench: 55 km / depth to the slab/mantle interface: 13 km), Fantangisña (62 km / 14 km) and Asùt Tesoru (72 km / 18 km). Four different types of ultramafic clasts were recovered: blue serpentinites, lizardite-serpentinites, antigorite/lizardite- and antigorite-serpentinites. Lizardite-serpentinites are primarily composed of orange serpentine, forming mesh and bastite textures. Raman and microprobe analyses revealed that these textures contain a mixture of Fe-rich brucite (XMg ~ 0.84) and lizardite/chrysotile. Antigorite/lizardite- and antigorite-serpentinites record the progressive recrystallization of mesh and bastite textures to antigorite, magnetite and pure Fe-poor brucite (XMg ~ 0.92). Oxygen isotope compositions of clasts and pore fluids showed that the transition from lizardite to antigorite is due to the increase in temperature from 200 °C to about 400 °C within the forearc area above the slab/mantle interface. Lizardite-, antigorite/lizardite- and antigorite-serpentinites displayed U-shaped chondrite normalized Rare Earth Element (REE) patterns and are characterized by high fluid mobile element concentrations (Cs, Li, Sr, As, Sb, B, Li) relative to abyssal peridotites and/or primitive mantle. The recrystallization of lizardite to antigorite is accompanied by a decrease in Cs, Li and Sr, and an increase in As and Sb concentrations in the bulk clasts, whereas B concentrations are relatively constant. Some clasts are overprinted by blue serpentine, often in association with sulfides. Most of these blue serpentinites were recovered at Yinazao and the uppermost units of Fantangisña and Asùt Tesoru suggesting alteration in the shallower portions of the forearc, possibly during exhumation of the clasts. This episode of alteration resulted in a flattening of REE spectra and an increase of Zn concentrations in serpentinites. Otherwise, no systematic changes of ultramafic clasts chemistry or mineralogy were observed with increasing depth to the slab. The samples document previously undescribed prograde metamorphic events in the shallow portions of the Mariana subduction zone, consistent with a continuous burial of the serpentinized forearc mantle during subduction. Similar processes, induced by the interaction with fluids released from the downgoing slab, likely occur in subduction zones worldwide. At greater depth, breakdown of brucite and antigorite will result in the massive transfer of fluids and fluid mobile elements, such as As, Sb and B, to the source of arc magmas., SCOPUS: ar.j, info:eu-repo/semantics/published

Studies of the Fe, Cu, and Zn isotopic compositions of volcanic rocks and sulfides provide an important tool for understanding magmatic, hydrothermal, and alteration processes, thereby enabling the determination of both transition metal sources and the quantification of the petrologic environmental impacts of hydrothermal activities. In this study, the δ56Fe and δ57Fe values of the mid-ocean ridge basalts (MORBs) are higher than those of the seafloor hydrothermal fluids, while the reverse is true for the δ66Zn and δ68Zn values, suggesting that basalt-fluid interactions preferentially incorporate isotopically light Fe and heavy Zn into the fluids, resulting in the relative enrichment of heavier Fe and lighter Zn isotopes in altered basaltic rocks. Most of the δ56Fe values (−1.96 to +0.11‰) of the sulfide minerals are within the range of the vent fluids, but they are significantly lower than those of the MORBs and back-arc basin basalts (BABBs), suggesting that the Fe in the sulfides was mainly derived from the fluids. However, the majority of the chalcopyrite δ56Fe and δ57Fe values are higher than those of the sphalerite and pyrite. This suggests that high-temperature sulfide minerals are enriched in 56Fe and 57Fe, whereas medium- and low-temperature sulfides are depleted in 56Fe and 57Fe. Moreover, the δ65Cu (−0.88 to −0.16‰) and δ66Zn (−0.39 to −0.03‰) values of the sulfide minerals are significantly lower than those of the MORBs, BABBs, and fluids, suggesting that 63Cu and 64Zn were preferentially removed from the fluids and incorporated into the chalcopyrite and sphalerite, respectively. Consequently, vent fluid injection and deposition can cause the heavier Cu and Zn isotopic compositions of hydrothermal plumes, seawater, and sediments., SCOPUS: ar.j, info:eu-repo/semantics/published

Rare Earth Elements (REE) are used in numerous industrialized products. The main sources of REE are carbonatite lavas and intrusions. Carbonatites are rare, carbonate-rich lavas, whose origin remains underconstrained: either directly derived from the melting of a C-rich mantle, or formed by protracted differentiation and immiscibility from silicate magmas. This project is focused on the petro-geochemical study of mantle xenoliths gathered around the Oldoinyo Lengai (OL; Tanzania), the only active volcano emitting carbonatites on Earth. Thanks to a multi-mineral approach integrating chemical data of all the mineral phases present in mantle xenoliths, this study shows that the Tanzanian lithospheric mantle is heterogeneous, with a complex metasomatic history. In addition, some xenoliths contain carbonates similar to those previously observed in the lithospheric mantle from the area. The isotopic compositions of carbonates from this study and of two samples from the literature reanalyzed herein display δ18O and δ13C isotopic compositions that support the pedogenic formation of these carbonates. This refutes an overall carbon enrichment, in the form of mantle carbonates, of the lithospheric mantle under the only active volcano emitting carbonatites. These results support the formation of Tanzanian carbonatites by extreme differentiation from alkaline magmas produced by the partial melting of a relatively C-poor mantle. In addition, alkaline silicate magmas (melilitite, Mg-nephelinite) are considered to be the potential parental magmas of carbonatites currently produced by the OL. Previous studies on these magmas have shown that they can potentially be generated by the partial melting of pyroxenite metasomatic lithologies carrying volatile-rich phases (CO2, H2O). Hence, the melting of a natural metasomatic vein from our sample set forms the most volatile-rich silicate alkaline magmas experimentally produced from a natural protolith. The melting of metasomatic phlogopite-rich pyroxenites veins produces magmas which compositions strongly suggest their involvement in the genesis of the primitive magmas of the area. Thus, these results suggest that the partial melting of the fertile veins of a metasomatized mantle participates in the formation of the parental magmas of carbonatites., Les Terres Rares (REE) sont utilisés dans de nombreux produits industrialisés. Les principales sources de REE sont les laves et intrusions carbonatitiques. Les carbonatites sont des laves rares, riches en carbonates, dont les modèles pétrogénétiques font débat: soit une formation directe par la fusion partielle d'un manteau enrichi en carbone, soit par différenciation extrême puis immiscibilité à partir d'un magma silicaté alcalin. Ce projet se base sur une étude pétro-géochimique des xénolithes mantelliques recueillis autour de l'Oldoinyo Lengai (OL; Tanzanie), le seul volcan actif émettant des carbonatites, pour mieux contraindre la genèse des magmas carbonatitiques et alcalins associés. Grâce à une approche multi-minérale intégrant l'ensemble des données chimiques de toutes les phases minérales des xénolithes, cette étude montre que le manteau lithosphérique Tanzanien est hétérogène avec une histoire métasomatique complexe. Par ailleurs, certains xénolithes contiennent des carbonates similaires à ceux observés précédemment dans le manteau de la région. Les compositions des carbonates de cette étude et de deux échantillons de la littérature réanalysés ici documentent des δ18O et δ13C qui soutiennent la formation pédogénique de ces carbonates et réfutent donc un enrichissement global en carbone, sous forme de carbonates mantelliques, du manteau lithosphérique N-Tanzanien. Ces résultats soutiennent une formation des carbonatites de la région par une différenciation extrême de magmas alcalins produits par la fusion partielle d'un manteau lithosphérique relativement pauvre en carbone. Par ailleurs, les magmas silicatés alcalins (mélilitite, Mg-néphélinite) sont considérés comme les potentiels magmas parents des carbonatites actuellement produites par l'OL. Les études sur ces magmas ont montré qu'ils peuvent être générés par la fusion de lithologies métasomatiques pyroxénitiques porteuses de phases riches en éléments volatils (CO2, H2O). Ainsi, la fusion d'une veine métasomatique naturelle provenant de nos échantillons forme les magmas alcalins silicatés les plus riches en CO2 et H2O expérimentalement produits depuis un protolithe naturel. La fusion des veines de pyroxénites à phlogopites forme donc des magmas dont les compositions suggèrent leur implication dans la genèse des magmas primitifs de la région. Ces résultats suggèrent que la fusion partielle des veines fertiles d'un manteau métasomatisé participe à la formation des magmas parents des carbonatites.

The Siilinjärvi phosphate deposit (Finland) is hosted by an Archean carbonatite complex. The main body is composed of glimmerite, carbonatite and combinations thereof. It is surrounded by a well-developed fenitization zone. Almost all the rocks pertaining to the glimmerite-carbonatite series are considered for exploitation of phosphate. New petrological and in-situ geochemical as well as spectroscopic data obtained by cathodoluminescence, Raman and laser-induced breakdown spectroscopy make it possible to constrain the genesis and evolution of apatite through time. Apatite in the glimmerite-carbonatite series formed by igneous processes. An increase in rare earth elements (REE) content during apatite deposition can be explained by re-equilibration of early apatite (via sub-solidus diffusion at the magmatic stage) with a fresh carbonatitic magma enriched in these elements. This late carbonatite emplacement has been known as a major contributor to the overall P and REE endowment of the system and is likely connected to fenitization and alkali-rich fluids. These fluids - enriched in REE - would have interacted with apatite in the fenite, resulting in an increase in REE content through coupled dissolution–reprecipitation processes. Finally, a marked decrease in LREE is observed in apatite hosted by fenite. It highlights the alteration of apatite by a REE-poor fluid during a late-magmatic/hydrothermal stage. Regarding the potential for REE exploitation, geochemical data combined with an estimation of the reserves indicate a sub-economic potential of REE to be exploited as by-products of phosphate mining. Spectroscopic analyses further provide helpful data for exploration, by determining the P and REE distribution and the enrichment in carbonatite and within apatite., SCOPUS: ar.j, info:eu-repo/semantics/published

Bogoslof volcano, Alaska, experienced at least 70 explosive eruptions between 12 December 2016 and 31 August 2017. Due to its remote location and limited local monitoring network, this eruption was monitored and characterized primarily using remote geophysical and satellite techniques. SO2 emissions from Bogoslof were persistently detected by the Infrared Atmospheric Sounding Interferometer (IASI) satellite sensors. Of Bogoslof’s 70 explosive events, 50% produced measurable SO2 masses ranging from 0.1 to 21.5 kt, with a median and standard deviation of 0.7 ± 4.0 kt SO2, respectively. Here, we compare IASI-derived SO2 masses from Bogoslof events to complementary geophysical datasets to provide insights into eruption source processes, namely the degree of seawater scrubbing of water-soluble SO2 and variations in magma flux. Correlations with the number of lightning strokes and infrasound energy are expected to indicate magma-flux as a controlling process, while correlations with infrasound frequency index are expected to indicate variations in vent-water content as a controlling factor. These comparisons suggest that the measured SO2 masses are primarily a function of eruption magnitude (degassed magma mass) and that scrubbing of SO2 emissions by vent seawater may have exerted a minor effect on the observed SO2 masses. SO2 masses were combined with petrologic constraints on melt inclusion and matrix glass S concentrations to calculate degassed magma masses and volumes. The cumulative SO2-derived degassed magma mass and estimated volume (dense-rock equivalent) for the full Bogoslof eruption were found to be 2.8 × 1010 kg and 9.3 × 106 m3, respectively. When individual event masses are compared against event masses calculated using an empirical plume-height method, a strong correlation is found (R2 = 0.83), with better than order-of-magnitude agreement in most cases. These estimates of eruption masses provide useful information on the magnitude, behavior, and associated hazards of the 2016–2017 eruption, and potentially future unrest at Bogoslof volcano., SCOPUS: ar.j, info:eu-repo/semantics/published

A new type of gas chimney exhibiting an unconventional linear planform is found. These chimneys are termed "Linear Chimneys", which have been observed in 3-D seismic data offshore of Angola. Linear Chimneys occur parallel to adjacent faults, often within preferentially oriented tier-bound fault networks of diagenetic origin (also known as anisotropic polygonal faults, PFs), in salt-deformational domains. These anisotropic PFs are parallel to salt-tectonic-related structures, indicating their submission to horizontal stress perturbations generated by the latter. Only in areas with these anisotropic PF arrangements do chimneys and their associated gas-related structures, such as methane-derived authigenic carbonates and pockmarks, have linear planforms. In areas with the classic "isotropic" polygonal fault arrangements, the stress state is isotropic, and gas expulsion structures of the same range of sizes exhibit circular geometry. These events indicate that chimney's linear planform is heavily influenced by stress anisotropy around faults. The initiation of polygonal faulting occurred 40 to 80m below the present day seafloor and predates Linear Chimney formation. The majority of Linear Chimneys nucleated in the lower part of the PF tier below the impermeable portion of fault planes and a regional impermeable barrier within the PF tier. The existence of polygonal fault-bound traps in the lower part of the PF tier is evidenced by PF cells filled with gas. These PF gas traps restricted the leakage points of overpressured gas-charged fluids along the lower portion of PFs, hence controlling the nucleation sites of chimneys. Gas expulsion along the lower portion of PFs preconfigured the spatial organisation of chimneys. Anisotropic stress conditions surrounding tectonic and anisotropic polygonal faults coupled with the impermeability of PFs determined the directions of long-term gas migration and linear geometries of chimneys. Methane-related carbonates that precipitated above Linear Chimneys inherited the same linear planform geometry, and both structures record the timing of gas leakage and palaeo-stress state; thus, they can be used as a tool to reconstruct orientations of stress in sedimentary successions. This study demonstrates that overpressure hydrocarbon migration via hydrofracturing may be energetically more favourable than migration along pre-existing faults., SCOPUS: ar.j, info:eu-repo/semantics/published

The 176Lu–176Hf isotopic system is widely used for dating and tracing cosmochemical and geological processes, but still suffers from two uncertainties. First, Lu–Hf isochrons for some early Solar System materials have excess slope of unknown origin that should not be expected for meteorites with ages precisely determined with other isotopic chronometers. This observation translates to an apparent Lu decay constant higher than the one calculated by comparing ages obtained with various dating methods on terrestrial samples. Second, unlike the well constrained Sm/Nd value (to within 2%) for the chondritic uniform reservoir (CHUR), the Lu/Hf ratios in chondrites vary up to 18% when considering all chondrites, adding uncertainty to the Lu/Hf CHUR value. In order to better understand the Lu–Hf systematics of chondrites, we analyzed mineral fractions from the Richardton H5 chondrite to construct an internal Lu–Hf isochron, and set up a numerical model to investigate the effect of preferential diffusion of Lu compared to Hf from phosphate, the phase with the highest Lu–Hf ratio in chondrites, to other minerals. The isochron yields an age of 4647±210 million years (Myr) using the accepted 176Lu decay constant of 1.867±0.008×10−11yr−1. Combining this study with the phosphate fractions measured in a previous study yields a slope of 0.08855±0.00072, translating to a 176Lu decay constant of 1.862±0.016×10−11yr−1 using the Pb–Pb age previously obtained, in agreement with the accepted value. The large variation of the Lu/Hf phosphates combined with observations in the present study identify phosphates as the key in perturbing Lu–Hf dating and generating the isochron slope discrepancy. This is critical as apatite has substantially higher diffusion rates of rare earth elements than most silicate minerals that comprise stony meteorites. Results of numerical modeling depending of temperature peak, size of the grains and duration of the metamorphic event, show that diffusion processes in phosphate can produce an apparently older Lu–Hf isochron, while this effect will remain negligible in perturbing the Sm–Nd chronology. Our results suggest that only type 3 chondrites with the lowest metamorphic grade and large minerals with minimal diffusive effects are suitable for determination of the Lu–Hf CHUR values and the Lu decay constant respectively., SCOPUS: ar.j, info:eu-repo/semantics/published

The present work aims to study the variability of the petrological and geotechnical properties of lateritic gravel developed under the same climate, the same vegetation, the same gneissic bedrock, but located under different hydric conditions, with a view to their use in road construction. The study was conducted on a rock quarry and 18 lateritic gravels quarries. After a detailed macroscopic description of the materials, the samples taken were the subject of petrological and geotechnical studies. The mineralogy of the powders of rock and lateritic gravels samples was determined by optical microscopy and X-ray diffractometry. The chemical determinations of the major elements of the materials were carried out by X-ray fluorescence and the determination of ferrous iron FeO, by titrimetry. Geotechnical studies focused on identification and compaction tests and on mechanical rock tests only. The results obtained show that the rocks of the Obala-Mandjock area are amphibole and epidote gneisses. Gray in color and granonatoblastic texture, these gneisses are composed of quartz, biotite, amphibole, pyroxene, orthoclase, microcline and epidote. Geochemically, this rock is predominantly composed of SiO2 (55.76 %) and Al2O3 (16.46 %). The lateritic gravels developed on these gneisses are subdivided into 02 zones, according to the water character. Those of humid savannah, yellowish with clay-sandy matrix and, those of dry savannah, red, with clay matrix. They are formed in acid (pH= 5.7) and reducing (Eh= 0.07 mV) environments, the environment being more reducing in humid savannah than in dry savannah. These materials are composed of quartz, kaolinite, hematite, goethite, and sometimes gibbsite and anatase. Hematite, goethite, are predominant in dry savannah while quartz is more abundant in humid savanna. The contents of Fe2O3 and Al2O3, respectively 31.41 % and 18.04 %, are higher in dry savannah while those in SiO2, 51.13 %, are predominate in humid savannah. These materials are silico-ferrugino-aluminous. The interpretation of these geochemical indices CIA, MIA(O) and IOL, respectively associated with A–CN–K, A–L–F and SAF diagrams as well as the AF–CNK–M diagram show that the decrease of the labile elements (Ca, Na, K and Mg), very important in the lateritic gravel of the Obala - Mbandjock zone, is accompanied by a moderate to strong lateritization phenomenon. The lateritic gravels of humid savannah are kaolinitized to moderately lateritized, while those of dry savannah are moderately to strongly lateritized. Alterological charts indicate that alteration is low to medium in humid savannah and medium in dry savannah. Ferruginization, allitization and monosilitization prevail in these materials, with a prevalence of ferruginization in lateritic gravels of dry savannah. With LA < 30 %, MDE ≤ 20 %, CA ≤ 25 % and CBR ≥ 100 % values, aggregates from Obala - Mbandjock gneiss can be used as base layer and wearing course. The results of the Principal Component Analysis (PCA) and through Agglomerative Hierarchical Clustering (AHC) reveal the existence of 03 groups of materials, (1) the lateritic gravels of a humid savannah (< 75 µm = 32.9 %, Plasticity Index (PI) = 27 %, maximal dry density (MDD) = 1.9 g/cm3, Californian Bearing ratio (CBR) = 31 %), (2) intermediate lateritic gravels (

Basaltic eruptions are increasingly studied in a lot of active volcanoes around the world. Yet, their pre- and syn-eruptive processes are not fully understood. In order to characterize and understand the set of mechanisms occurring from the shallow magmatic system to the surface, this thesis is focused on the study of the eruptive products of Piton de la Fournaise volcano (La Réunion Island, France), which is one of the most active volcano in the world. Integrated textural and chemical analysis on tephra and lava are performed to identify some key parameters which can be related to major magmatic processes, eruptive dynamics and fragmentation processes. When it is available and relevant, these interpretations are integrated with pre- and syn-eruptive monitoring measurements acquired by ground-based and remote sensing observation systems.The first objective of this integrated study is to gain insight on the magmatic overpressure, conduit and eruptive dynamics during basaltic dyke eruptions. During the June 2014 eruption, eruptive triggers and syn-eruptive transitions from Hawaiian-style to mild Strombolian-style activities, associated with a decreasing of the lava flux, have been related to a second boiling mechanism and a pre-eruptive pressurization which was indirectly evidenced by golden pumice emission (highly vesicular and glassy tephra). On the contrary, the July 2015 eruption (relatively scarce golden pumice emission) was triggered by a shallow magmatic input that was tracked in the textural and chemical features of the eruptive products.On year later, another short-lived eruption occurred on September 2016, which emitted a lot of golden pumice. However, this eruption, dominated by Hawaiian fountaining, behaved atypically with an increase in lava flux associated with uncommon ash emission the last day of the eruptive activity. Thus, the second objective of the thesis is to improve our comprehension on the transition from Hawaiian-style (associated with golden pumice and fluidal scoria) to more explosive activities (associated with dense, crystal-rich opaque scoria and ash emission). The integrated study on this eruption supports the hypothesis that the opaque scoria and ash were inherited from the sub-surface cooling and degassing of the golden pumice material. This suggests the formation of a low-permeable plug, which modulated overpressure pulses at shallow levels and transient explosive activity under the late input of a relatively undegassed and ascending magma. It is commonly accepted that effusive activity represents the main emitted magmatic volume in basaltic shield volcanoes. However, the September 2016 eruption reminded us that basaltic eruptions can sometime produce hazards related to ash-dominated events. Therefore, the third purpose of the thesis is to bring together a comprehensive sampling of tephra from major historical and recent eruptions at Piton de la Fournaise and Karthala (Ngazidja Island, Comoros) volcanoes. The study of these different deposits reveals very different textural characteristics reflecting different fragmentation processes, as ductile fragmentation, brittle fragmentation (triggered by syn-eruptive crystallization of the juvenile magma), interactions between magma and external fluids, high magma ascent velocities and shear-induced fragmentation mechanisms during caldera collapse events.All these insights expose a lot of different magmatic and fragmentation processes which highlight the complexity of the mechanisms driving such basaltic eruptions. This thesis only represent a part of the research possibilities on basaltic eruptions. In the future, many additional laboratory studies and real-time monitoring of the eruptive activity can be performed in order to even better understand and better predict the change in eruptive activity than can represent unexpected threats to the environing populations., Les éruptions basaltiques sont de plus en plus étudiées au sein de nombreux volcans. Cependant, les processus pré- et syn-éruptifs gouvernant ces éruptions ne sont pas entièrement compris. Dans le but de caractériser et comprendre l’ensemble des mécanismes opérant depuis le système magmatique superficiel jusqu’à la surface, cette thèse est principalement axée sur l'étude des produits éruptifs du Piton de la Fournaise (île de la Réunion, France), qui est l'un des volcans les plus actifs au monde. Des analyses texturales et géochimiques sur les pyroclastes et les laves sont conjointement réalisées dans le but d’identifier des paramètres clés pouvant être reliés à des processus magmatiques majeurs, à des dynamiques éruptives et à des mécanismes de fragmentation. Lorsque cela est pertinent, ces interprétations sont intégrées à des données de surveillance pré- et syn-éruptives acquises au sol ou par télédétection.Le premier objectif de cette étude intégrée est de mieux comprendre les mécanismes à l’origine des surpressions magmatiques et des dynamiques éruptives lors des éruptions récentes du Piton de la Fournaise. Au cours de l’éruption de Juin 2014, les déclenchements éruptifs ainsi que les transitions syn-éruptives d’un régime hawaiien vers un régime strombolien relativement faible, associés à une diminution du flux lavique, ont été liés à une vésiculation et à une surpression pré-éruptive du magma qui furent indirectement mises en évidence par l’émission de pyroclastes de type golden pumice (pyroclastes très vésiculés et vitreux). Au contraire, l’éruption de Juillet 2015 (émission de golden pumice relativement rare) a été déclenchée par un apport magmatique superficiel qui a pu être identifié au sein des signatures texturales et géochimiques des produits éruptifs.Un an plus tard, une autre éruption de courte durée s'est produite en Septembre 2016, produisant beaucoup de pyroclastes de type golden pumice. Cependant, cette éruption dominée par des fontaines de lave, se comporta de manière atypique et fut associée à une augmentation du flux lavique et d’une émission inhabituelle de cendres lors du dernier jour de l’activité éruptive. Le deuxième objectif de la thèse est donc d’améliorer nos connaissances sur la transition d’une activité hawaiienne (associée à l’émission de pyroclastes de type golden pumice et fluidal scoria) vers une activité plus explosive associée à l’émission de scories et de cendres relativement denses et riches en cristaux, de type transitional et opaque. Les analyses texturales et chimiques des produits éruptifs confirment l'hypothèse selon laquelle ces scories et cendres denses sont issues du refroidissement et du dégazage à pression ambiante du magma initialement vésiculé et peu cristallisé. Il est donc possible de former un bouchon faiblement perméable, provoquant des impulsions magmatiques pressurisées à faible profondeur et une activité explosive transitoire sous l’influence et la remontée tardive d’un magma relativement peu dégazé. Il est communément admis que l’activité effusive représente la majorité du volume magmatique émis au sein des volcans boucliers basaltiques. Cependant, l’éruption de Septembre 2016 a montré que les éruptions basaltiques peuvent parfois produire des aléas liés à des émissions de cendres non-négligeables. Par conséquent, le troisième but de la thèse est de rassembler une série d’échantillons correspondant aux principales éruptions historiques et récentes des volcans du Piton de la Fournaise et du Karthala (île de Ngazidja, Comores). L’étude de ces différents dépôts cendreux révèle des caractéristiques texturales très différentes suggérant différents processus de fragmentation, à savoir la fragmentation ductile, la fragmentation fragile (provoqué par la cristallisation syn-éruptive du magma juvénile), des interactions entre le magma et des fluides externes, des vitesses de remontée magmatiques élevées ou encore la fragmentation par cisaillement pendant l’effondrement de calderas.Toutes ces connaissances exposent de nombreux processus magmatiques et de fragmentation qui mettent en évidence la complexité des mécanismes à l'origine de telles éruptions basaltiques. Ces travaux de thèse ne représentent qu’une partie des possibilités de recherche sur les éruptions basaltiques. Dans le futur, de nombreuses études de laboratoire supplémentaires et de surveillance de l’activité en temps-réel pourront être réalisées pour encore mieux comprendre et mieux prévoir l'évolution de l’activité éruptive en surface qui peut présenter des risques inattendus pour les populations environnantes.

Selenium is a chalcophile, moderately volatile and redox-sensitive element. The Se isotopic and elemental systematics of mantle-derived rocks and melts may therefore provide new approaches to study the terrestrial volatile origin and evolution as well as secular changes of redox conditions across the surface and mantle reservoirs. Selenium is significantly depleted in mantle samples (at ng/g levels), posing analytical challenges for Se isotopic studies of the igneous system. This study presents an analytical protocol suitable for precise and accurate determination of Se isotope and Se–Te abundances of igneous rocks. The Se–Te elemental systematics provide a petrogenetic context for interpreting Se isotope systematics. The new method was used to analyze a suite of basaltic glasses from the Pacific–Antarctic ridge (PAR) and the Mid-Atlantic ridge (MAR). The magmatic differentiation involving concurrent sulfide segregation results in significant chalcophile element fractionation but no measurable Se isotopic variation. Because of the demonstrated lack of Se isotopic fractionation between sulfides and silicate melt, the Se isotope systematics of MORB reflects a source signature. The southern MAR displays a significant source heterogeneity due to the localized interaction between the ridge and Shona and Discovery mantle plumes that incorporate recycled components.