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Building on previous work aimed at identifying and characterizing the potential mechanical trigger controlling eruptions and destabilization at Piton de la Fournaise, we study the mechanical behavior of the volcanic edifice on a crustal scale. Do the recurrent earthquake pattern correspond to a destabilization structure, precursor of a large-scale flank sliding? Or instead to a reactivated area of magma storage (partially crystallized “sill”)? To answer these questions, we design numerical models which estimate the stress field associated with the volcanic complex. We use the ADELI finite element method in three dimensions, which handles elasto-visco-plastic rheologies. In these models, we take into account 1) the topographic load, 2) the major density and resistance heterogeneities within the volcano obtained from previous studies, and 3) the overpressure induced by the intrusion of a dike of arbitrary geometry.The modeled dike injection generates deformation and stress fields such that their isocontours highlight an ellipsoidal cup structure extending from the central cone to a depth close to 0 and reaching the ends of the eastern flank. This zone could be assimilated to the zone of seismicity observed and described previously. Together with several systematic test cases, we will discuss the significance of these results, such as whether it reveals a rheological delimitation zone of the hydrothermalized bedrock, resulting from the combined influence of the topographic load and that of a magmatic injection.

The Chilean margin is amongst the most active seismic and volcanic areas on Earth. It hosts active and fossil geothermal and mineralized systems of economic interest documenting significant geofluid migration through the crust. By comparing numerical models with field and geophysical data, we aim at pinning when and where fluid migration occurs through porous domains, fault zone conduits, or remains stored at depth awaiting a more appropriate stress field. Dyking and volcanic activity occur within fault zones along the SAVZ, linked with stress field variations in spatial and temporal association with –short therm- seismicity and -long term- oblique plate convergence. Volcanoes and geothermal domains are mostly located along or at the intersection of margin-oblique fault zones (Andean Transverse Faults), and along margin-parallel strike slip zones, some which may cut the entire lithosphere (Liquiñe-Ofqui fault system). Whereas the big picture displays fluid flow straight to the surface, at close look significant offsets between crustal structures occur. 3D numerical models using conventional elasto-plastic rheology provide insights on the interaction of (i) an inflating magmatic cavity, (ii) a slipping fault zone, and (iii) regional tectonic stresses. Applying either (i) a magmatic overpressure or (ii) a given fault slip can trigger failure of the intervening rock, and generate either i) fault motion or ii) magmatic reservoir failure, respectively, but only for distances less than the structures' breadth even at low rock strength. However, at greater inter-distances the bedrock domain in between the fault zone and the magmatic cavity undergoes dilatational strain of the order of 1-5x10-5. This dilation opens the bedrock’s pore space and forms «pocket domains» that may store up-flowing over-pressurized fluids, which may then further chemically interact with the bedrock, for the length of time that these pockets remain open. These porous pockets can reach kilometric size, questioning their parental link with outcropping plutons along the margin. Moreover, bedrock permeability may also increase as fluid flow diminishes effective bedrock friction and cohesion. Comparison with rock experiments indicates that such stress and fluid pressure changes may eventually trigger failure at the intermediate timescale (repeated slip or repeated inflation). Finally, incorporating far field compression (iii) loads the bedrock to a state of stress at the verge of failure. Then, failure around the magmatic reservoir or at the fault zone occurs for lower loading. Permanent tectonic loading on the one hand, far field episodic seismic inversion of the stress field on the other, and localized failure all together promote a transient stress field, thus explaining the occurrence of transient fluid pathways on seemingly independent timescales. These synthetic models are then discussed with regards to specific cases along the SVZ, particularly the Tatara-San Pedro area (~36°S), where magnetotelluric profiles document conductive volumes at different depths underneath active faults, volcanic edifices and geothermal vents. We discuss the mechanical link between these deep sources and surface structures.

International audience; Underthrusting is a typical process at compressive margins responsible for nappe stacking and sediment subduction. In nature, underthrusting is often associated with weak basal faults, although static mechanical analysis (critical taper theory) suggests that weak basal faults promote accretion while strong basal faults promote underthrusting. We perform mathematical analyses and numerical simulations to determine whether permanent fault weakening promotes or inhibits underthrusting. We investigate the control of permanent fault weakening on the dynamics of a strong-based ( (1 − λ ∗ b )μ b ≈ (1 − λ ∗ )μ ) non-cohesive wedge ( μ and μ b are internal and basal friction, respectively). We control the wedge material strength by a spatially constant fluid overpressure factor ( λ ∗ ), and fault strength by a plastic strain weakening factor ( χ ). First, we use the critical taper theory to determine a mechanical mode diagram that predicts structural styles. Then, we perform numerical simulations of accretionary wedge formation to establish their dynamical structural characteristics. We determine a continuum of structural styles between three end-members which correspond to the theoretical mechanical mode transitions. Style 1 is characterized by thin tectonic slices and little to no underthrusting. Style 2 shows thick slices, nappe stacking, and shallow gravity-driven tectonics. Style 3 displays the complete underthrusting of the incoming sediments, that are exhumed when they reach the backstop. We conclude that in the condition of an initially strong wedge base, permanent fault weakening promotes underthrusting. Thus, this contribution enlightens the control of the dynamic evolution of material properties on the formation of subduction channels, slope instabilities, and antiformal nappe stacks.

Magma is transported through the lithosphere as dykes which, during periods of unrest, may feed eruptions at the surface. The propagation path of dykes is influenced by the crustal stress field and can be disturbed by crustal heterogeneities such as contrasting rock units or faults. Moreover, as dykes propagate, they themselves influence the surrounding stress field through processes of stress transfer, crustal deformation and seismic failure. The result is the formation of arrested dykes, as well as contrasting strike and dip angles and dyke segmentation. Here, we study the mechanisms of dyke injection and the role played in modifying the stress field and potential propagation paths of later dyke injections. To do this we combine field data from an eroded and well-exposed shallow feeder dyke swarm with a suite of two-dimensional FEM numerical models. We mapped 35 dyke segments over a similar to 1 km long dyke swarm exposed similar to 5 km to the East of Pellado Volcano, in the Tatara-San Pedro-Pellado (TSPP) volcanic complex, Southern Volcanic Zone of the Andes. Detailed mapping of the swarm elucidates two preferential strike orientations, one similar to N80 degrees E and the other similar to N60 degrees E. Our numerical models simulate both the TSPP volcanic complex and the studied dyke swarm as zones of either magmatic excess pressure or as a rigid inclusion. The crustal segment hosting the volcanic complex and dykes is modelled using an elastic domain subjected to regional compression in select model cases. Model outputs provide the stress and strain fields resulting from the different geometries and applied boundary loads. The model results indicate that individual dyke injections can locally rotate the principal stresses such as to influence the range of orientations over which later dykes will form. The orientation of sigma(1) at the dyke tip ranges over 60 degrees (+/- 30 degrees either side of the dyke tip) indicating that the strike orientation of later dykes will fall within this range. The effect of adding a bulk regional compression is to locally increase the magnitude of favorably oriented tensile stresses in the bedrock but to reduce the range of sigma(1) orientations to 40 degrees (+/- 20 degrees). This implies that under a far-field transpressive stress regime, as is common in Andean settings, regional dyke swarms will tend to maintain their strike orientation parallel to the regional bulk stress. These results should be accounted for when studying periods of volcanic unrest in order to discern the location and orientation of potential fissure eruptions in active volcanic areas such as the Southern Volcanic Zone of the Andes.

International audience; Alpha satellite is the major repeated DNA element of primate centromeres. Specific evolutionary mechanisms have led to a great diversity of sequence families with peculiar genomic organization and distribution, which have till now been studied mostly in great apes. Using high throughput sequencing of alpha satellite monomers obtained by enzymatic digestion followed by computational and cytogenetic analysis, we compare here the diversity and genomic distribution of alpha satellite DNA in two related Old World monkey species, Cercopithecus pogonias and Cercopithecus solatus, which are known to have diverged about 7 Ma. Two main families of monomers, called C1 and C2, are found in both species. A detailed analysis of our data sets revealed the existence of numerous subfamilies within the centromeric C1 family. Although the most abundant subfamily is conserved between both species, our fluorescence in situ hybridization (FISH) experiments clearly show that some subfamilies are specific for each species and that their distribution is restricted to a subset of chromosomes, thereby pointing to the existence of recurrent amplification/homogenization events. The pericentromeric C2 family is very abundant on the short arm of all acrocentric chromosomes in both species, pointing to specific mechanisms that lead to this distribution. Results obtained using two different restriction enzymes are fully consistent with a predominant monomeric organization of alpha satellite DNA that coexists with higher order organization patterns in the C. pogonias genome. Our study suggests a high dynamics of alpha satellite DNA in Cercopithecini, with recurrent apparition of new sequence variants and interchromosomal sequence transfer.

International audience; The Southern Andes margin hosts active and fossil volcanic, geothermal, and mineralized systems documenting intense geofluid migration through the crust. Fluid flow is also spatially associated with crustal faults that accommodate the bulk deformation arising from oblique plate convergence. Although recognized, the precise local mechanical interaction between faults and crustal reservoirs is yet to be better understood. Here we present 3D numerical models of a magmatic reservoir and a fault zone set about 4 km apart, inspired by the Tatara-San Pedro volcanic complex in the Southern Volcanic Zone (~36°S), which displays a geothermal field and a margin-parallel dextral active fault zone constrained by published magnetotelluric profiles and crustal seismicity respectively. We investigate elasto-plastic deformation and stress patterns in the intermediate bedrock space between the reservoir and the fault zone and test how shear stress, volumetric strain, and plastic strain develop. We also test the potential of enabling brittle failure of their counterpart by imposing either (1) a strike-slip displacement along the fault zone, or (2) a magmatic overpressure at the cavity walls. Parametric tests of Young's modulus and frictional strength provide the conditions for macro-scale brittle failure and show the development of diffuse domains of dilational strain of the order of 10−5 –10−3 in the intervening bedrock. This dilation is a proxy to the opening of voids or volumetric cracking in the bedrock, which tends to increase porosity and permeability allowing over-pressurized geofluids to migrate within these domains. Our results show that a minimum of 60 m of fault displacement is required to trigger brittle failure of an upper crustal cavity if the bedrock is stiff, whereas, for a more compliant bedrock, more than 100 m of localized slip motion is required. This implies that it is rather the accumulated effect of repeated crustal fault displacement that potentially favors fluid pathways upwards, rather than a single seismic event. On the other hand, a minimum of 7.5 MPa of fluid overpressure is required for a mid-crustal cavity (15 km depth) to trigger brittle failure of the fault zone. This threshold overpressure increases up to 50 MPa when the cavity is shallower (6 km depth). Our results show that in general, shallow reservoirs must be very close to fault zones (less than 1–2 km apart) to reactivate them. The models show that localized strike-slip tectonics and magma intrusions build a dilational stress field at the scale of several kilometers, that promotes fluid pathways to the surface. Further combining this interaction with the regional transpressional stress field may explain observations of transient fluid pathways on seemingly independent timescales along the Andean margin.

Recent studies have reported evidence suggesting that portions of contemporary human genomes introgressed from archaic hominin populations went to high frequencies due to positive selection. However, no study to date has specifically addressed the post-introgression population dynamics of these putative cases of adaptive introgression. Here, for the first time, we specifically define cases of immediate adaptive introgression (iAI), in which archaic haplotypes rose to high frequencies in humans as a result of a selective sweep that occurred shortly after the introgression event. We define these cases as distinct from instances of selection on standing introgressed variation (SI), in which an introgressed haplotype initially segregated neutrally and subsequently underwent positive selection. Using a geographically diverse dataset, we report novel cases of selection on introgressed variation in living humans and shortlisted among these cases those whose selective sweeps are more consistent with having been the product of iAI rather than SI. Many of these novel inferred iAI haplotypes have potential biological relevance, including three introgressed haplotypes that contain immune-related genes in West Siberians, South Asians, and West Eurasians. Overall, our results suggest that iAI may not represent the full picture of positive selection on archaically introgressed haplotypes in humans and that more work needs to be done to analyze the role of SI in the archaic introgression landscape of living humans.

This chapter covers archaeological and biological studies that have been insightful in the understanding of dairying history and the evolution of lactase persistence in humans. More specifically, we report results from lipid residue analyses on archaeological pottery vessels, ancient and modern human DNA and explain the biology and genetics of lactase persistence. Available data suggests that domesticated animals were used for milk consumption by humans early in the Neolithic, while contemporaneous populations seem to have been mainly lactose intolerant. This contrasts with modern European populations, which show a generally high proportion of lactase persistence.

Surface volcanism at la Reunion and Hawaii occurs with an offset of 150-180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis: (i) it is 20 km thick, (ii) it has a 150 km radius, (iii) it lays at the base of the elastic part of the lithosphere, i.e., around, similar to 50-70 km depth where the temperature varies from similar to 600 degrees C to similar to 750 degrees C, (iv) it lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, and (vi) it is controlled by the visco-elastic relaxation time at 50-70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively. This indicates that this basal compression is actually a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., similar to 150 km away from the plume head. There, melts propagate through dikes upwards to similar to 35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30-35 km depth may thus host a magmatic reservoir where melts transported by dykes pond. Only after further magmatic differentiation can dykes resume their ascension up to the surface and begin forming a volcanic edifice. As the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards, inducing extra tensile stress at 30-35 km depth and compression at 15 km depth (induced by the edifice load). It implies that now the melts pond at similar to 15 km and form another magmatic reservoir lying just underneath the crust. These processes explain the ponding of primary (shield) melts at similar to 35 km and similar to 15 km depths as recorded below La Reunion, Mauritius or Hawaii volcanoes, all shifted by similar to 150 km with respect to the plume axis.

International audience; ilicic systems generate the most explosive eruptions on Earth. In contrast to basaltic systems, they can accumulate large volumes of magma without systematically erupting, confronting the classical interpretation that a volcano inflates when a magmatic intrusion occurs. Understanding the mechanisms of volcanic inflation and unrest is thus one of the most important challenges in volcanic risk assessment. Laguna del Maule (LdM) in the Southern Volcanic Zone (SVZ) of Chile, is one of the most active Holocene silicic complexes in the world and it has been inflating since 2007, accumulating 2 m of uplift without erupting. Several geophysical and geochemical studies conclude that a large crystal rich reservoir would be residing beneath LdM, in consistency with other multi-disciplinary studies showing that such crystal-rich reservoirs (“mush zones”) can be maintained beneath silicic volcanoes, fed by mafic magma recharge from below. Nevertheless, the mechanical state of such reservoirs remains unclear. Here, we characterize for the first time the mechanical properties of such a mush reservoir, able to promote large surface displacements such as those measured at LdM. Using a 3D finite element method we simulate a recharge of magma at the base of a crystal rich reservoir, by assuming an overpressurized source surrounded by a large viscoelastic shell. Inversion results show that this model fits the observed temporal and spatial evolution of ground displacements measured with InSAR data and GNSS data between 2007 and 2017. We interpret the temporal behavior of ground displacement at LdM as resulting from two contributions. A magma recharge occurred within the first 4 yr of the active inflation, followed by the viscous response of the large viscoelastic shell, set to a viscosity of 1017 Pas. Compared to a purely elastic solution, our model suggests that up to 50% of the accumulated surface displacement during the ten-year period can be explained by this viscous response, and predicts ongoing displacements 50 yr after the onset of inflation. This model agrees with geophysical and geochemical observations and offers a simple explanation of the temporal evolution of surface displacements. It further allows to reconsider the mechanical behavior of large partially crystallized domains in the upper crust; such significant transient stress transfer over large viscoelastic areas should thus be accounted for in other studies of silicic volcanic complexes.

Amongst 15 bird species, representative of 7 orders, recurrent breakages evocating the presence of fragile sites were detected in the chromosomes of the 5 species belonging to Passeriformes. These breaks appeared when 5-bromodeoxyuridine (BrdU) was added to the cell culture medium at a dose inefficient for inducing chromosome structure alterations in other birds and mammals. They involved, similarly in male and female, 3 loci on the Z chromosome of 3 Turdus species (Turdidae). Labeling by BrdU antibody confirmed the correlation between BrdU incorporation into DNA and breakage, especially around and in the sites of breakage. Thus, 3 BrdU-sensitive fragile sites were present in the Z chromosomes of these birds. Three fragile sites were also detected at different locations in the Z chromosomes of the European robin (Erithacus rubecula, Muscicapidae), suggesting that a structural rearrangement occurred during the evolution of Turdidae and Muscicapidae. Chromosome banding confirmed this interpretation. Finally, in the more distantly related species Parus major (Paridae), the almost acrocentric Z chromosome displayed a single BrdU-sensitive fragile site in its short arm, and the W appeared to be pulverized by BrdU incorporation. Although it cannot be excluded that the BrdU-sensitive fragile sites may be involved in rearrangements, their conservation in many species, and possibly all Passeriformes, provides evidence that they do not constitute a pejorative character during evolution.

International audience; Since nearly 20 years, huge transient thermal warm anomalies have been observed in different regions worldwide. The main peculiarity of these thermal anomalies is their close relationship with the occurrence of earthquakes of magnitude > 5. Most of the thermal anomalies appear tens of days before the earthquake and reach a maximum positive value of 10 K few hours before the main shock. They are located at hundreds kilometres from the epicentres and can cover areas of 10,000 km2. Some hypotheses have already been proposed to explain these thermal anomalies, e.g., variation of the groundwater level, release of greenhouse gases creating a localised greenhouse effect or air ionisation. This study focuses on the Boumerdes-Zemmouri earthquake (M = 6.8) that hit Algeria in 2003. This earthquake was preceded by a thermal anomaly observed by AVHRR (Advanced Very High Resolution Radiometer; 1 km/pixel) thermal sensor on the NOAA-15 satellite. This region is very adapted to a preliminary study as 1) the tectonic is less complex than in other regions, 2) the semi-arid environment allows high temporal coverage as cloud cover is not significant, and 3) vegetation is excessively sparse. The objective of this study is to interpret this excess temperature and to improve our understanding of the processes behind their development. The thermal anomaly was located in a sedimentary basin 400 km south from the epicentre and covered a maximal surface of 41,000 km2. It appeared ten days before the earthquake and reached a maximum temperature anomaly of +7 °C a few hours before the main shock. The results obtained from a combination of MODIS thermal infrared data with climate reanalyses from ECMWF (European Center for Medium Range Weather Forecasts) demonstrated first that this thermal anomaly cannot be explained by meteorological variations, neither by changes in the physico-chemical properties of the surface. We suggest that this earthquake-related thermal anomaly in Algeria can be explained by subsurface alterations induced by the pre-seismic stresses (Lopez et al, in preparation). Publications have shown that pre-seismic stresses may change the groundwater circulation and/or its physico-chemical properties. Development of thermal anomalies prior to an earthquake suggests that pre-seismic stresses change the vertical permeability of the system and thus have an influence on the groundwater circulation. This leads to a short-term increase of the aquifers and the atmosphere connexion. Indeed, the southern limit of the thermal anomaly seems to be controlled by the extension of aquifer artesianism (Lopez et al, submitted). Moreover, the transfer of elastic stresses might explained the distance observed between the thermal anomaly and the epicentre. The original combination of thermal infrared images with other EO dataset and geophysical data may lead to a new vision of a subject so far very little studied. In that context, the thermal infrared sensor might play a future key role in understanding the development and transfer of pre-seismic loading or unloading stresses in (semi)-arid regions.

National audience; Par sa situation au cœur de Paris, le long des berges de Seine, le Jardin des Plantes représente un îlot de verdure pérenne depuis sa création en 1650. Afin de connaitre la diversité des petits mammifères terrestres de ce parc, nous avons entrepris deux campagnes d’inventaire en 2007-2008 et en 2018 dont nous présentons ici les résultats. Nous avons utilisé des pièges modèles Sherman, INRA, et des ratières grillagées, disposés en lignes dans les Jardins Alpin, Ecologique, et de l’îlot Buffon-Poliveau au printemps et en automne. Les petits mammifères collectés ont été euthanasiés selon les règles éthiques approuvées par le comité d'éthique en matière d'expérimentation animale Cuvier, les mensurations corporelles standard ont été effectuées, ainsi que des prélèvements pour des analyses cytogénétiques et moléculaires. Par ailleurs, trois pièges photographiques ont été disposés à proximité de trois ratières et visant des zones de présence avérée de rats, distant d’environ 150 m l’un de l’autre, afin d’enregistrer des captures vidéos, par segment de 30s espacé d’une seconde, pendant 13-15 jours répartis entre le 19 Novembre et le 16 Décembre 2018.En Avril 2007 pour un effort de piégeage de 30 nuits-pièges (NP) nous avons capturé 2 petits mammifères dans l’îlot Buffon-Poliveau, contre 10 pour 20 NP en avril 2008 et 7 pour 125 NP en avril 2018. Pour la campagne 2007-2008, le mulot sylvestre Apodemus sylvaticus a été le seul rongeur capturé dans l’îlot Buffon Poliveau. Pour la campagne 2018, A. sylvaticus est toujours le rongeur le plus abondant dans ce site mais il y était aussi accompagné de Mus musculus (la souris domestique ; 5 %) et de Rattus norvegicus (rat brun ou surmulot ; 11%). Au jardin alpin, 4 individus ont été capturés pour un effort de 66 NP en août 2008 et 17 individus pour 120 NP en novembre 2018. Apodemus sylvaticus a été le seul rongeur capturé en extérieur et 2 M. musculus en intérieur. Au jardin écologique, 105 NP en août 2008 et 100 NP en novembre 2018 ont livré respectivement 17 captures et 32 évènements de captures pour 19 individus prélevés, le mulot représentant 92% des individus collectés, la souris domestique 4% et le hérisson d’Europe Erinaceus europaeus 4%. Aucune ratière n’a capturé de rat. Les 2 pièges photos du jardin alpin ont enregistré un total de 58 contacts/heure du surmulot sur un total de 648 heures, et celui du jardin écologique 61 contacts/heure pour 360 heures. Pour ce dernier piège photo, 14 contacts/heure de mulots sylvestres ont été obtenus, 2 contacts/heure du hérisson, et 1 contact/heure d’un petit carnivore non identifiable. L’ensemble des contacts de mammifères a été enregistré uniquement de nuit, entre 17h00 et 09h00.Malgré un effort de piégeage plus soutenu il n’a pas été possible de capturer d’autres rongeurs connus en région parisienne comme Micromys minutus, Microtus agrestis, M. arvalis, M. subterraneus, Clethrionomys glareolus. De même aucune musaraigne comme Sorex coronatus, Crocidura russula et C. leucodon n’a pu être capturée malgré des milieux à priori favorables.La description morphologique et morphométrique de ces spécimens, ainsi que leur analyse génétique sont en cours et permettront de caractériser ces populations et leur degré d’isolement par rapport aux autres parcs et jardins de la capitale et de sa petite couronne, dont les échantillonnages seront initiés avec un effort de piégeage plus important.

Les adultes en situation de handicap moteur peuvent rencontrer des changements d’occupation dans leur vie quotidienne induits par les préconisations de l’ergothérapeute. Cette recherche vise à comprendre, à travers les perceptions des ergothérapeutes, comment ils tiennent compte de l’identité occupationnelle d’une personne adulte en situation de handicap moteur pour permettre son engagement dans un changement d’occupation. Par le biais d’une méthode clinique, des entretiens ont été réalisés avec trois ergothérapeutes pour mieux percevoir ce phénomène. Les résultats, traités par une analyse thématique, mettent en lumière le fait que les ergothérapeutes évoquent des indicateurs de l’identité occupationnelle comme les facteurs personnels, l’environnement humain, le vécu occupationnel et le sens donné aux occupations.