Deformation of accretionary wedges in response to seamount subduction: Insights from sandbox experiments

International audienceSandbox experiments, using a two-dimensional and a three-dimensional approach, are used to study the deformation of margins in response to seamount subduction. Successive mechanisms of deformation are activated during the subduction of conical seamounts. First, reactivation of the frontal thrusts and compaction of the accretionary wedge is observed. Then, back thrusting and, conjugate strike-slip faulting develops above the leading slope of the subducted seamount. The basal d6collement is deflected upward in the wake of the subducting high, and a large shadow zone develops behind the seamount trailing slope. Consequently, frontal accretion is inhibited and part of the frontal margin is dragged into the subduction zone. When the main d6collement returns to its basal level in the wake of the seamount, the margin records a rapid subsidence and a new accretionary wedge develops, closing the margin reentrant. The sediments underthrusted in the wake of the seamount into the shadow zone, are underplated beneath the rear part of the accretionary wedge. Substantial shortening and thickening of the deformable seaward termination of the upper plate basement, associated with basal erosion is observed. Seamount subduction induces significant material transfer within the accretionary wedge, favors large tectonic erosion of the frontal margin and thickening of the rear part of the margin. The subduction and underplating of relatively undeformed, water-ladden sediments, associated with fluid expulsion along the fractures affecting the margin could modify the fluid pressure along the basal ddcollement. Consequently, significant variations of the effective basal friction and local mechanical coupling between the two plates could be expected around the subducting seamount

Western European Populations of the Ichneumonid Wasp Hyposoter didymator Belong to a Single Taxon

Hyposoter didymator (Hymenoptera, Ichneumonidae) is a generalist solitary endoparasitoid of noctuid larvae. In the present work, we tested whether populations of H. didymator were divided in several genetically distinct taxa as described for many other generalist parasitoid species, and whether differences in H. didymator parasitism rates were explained by the insect host species and/or by the plant on which these hosts were feeding on. The genetic analysis of natural populations collected in different regions in France and Spain on seven different insect hosts and seven different host plants (775 individuals) showed that H. didymator populations belong to a unique single taxon. However, H. didymator seems to be somewhat specialized. Indeed, in the fields it more often parasitized Helicoverpa armigera compared to the other host species collected in the present work. Also, H. didymator parasitism rates in field conditions and semi-field experimental studies were dependent on the host plants on which H. armigera larvae are feeding. Still, H. didymator can occur occasionally on non-preferred noctuid species. One hypothesis explaining the ability of H. didymator to switch hosts in natura could be related to fluctuating densities of the preferred host over the year; this strategy would allow the parasitoid to avoid seasonal population collapses

Aragonite-grossular in eclogite-facies marble, Alpine Corsica

The occurrence and preservation of aragonite in eclogite-facies rocks of north-eastern Corsica is linked to an uncommon microtexture. Aragonite exclusively occurs as oriented fibres in garnet crystals of a graphitic, more or less siliceous marble that immediately overlies a serpentinite body of the meta-ophiolitic unit. The arrangement of the fibres is grossly radial, but more clearly sectoral in subhedral garnet, the fibres growing perpendicular to the garnet/matrix interface. Raman mapping reveals that the carbonate is calcite in the matrix and in poikiloblastic garnet cores, and that the fibres in the garnet mantle are aragonite alone in the case of a carbonate matrix, and both aragonite and quartz (in distinct fibres) in a quartz–carbonate matrix. These features are interpreted as prograde intergrowths, the result of garnet nucleation and growth in a calcite and then aragonite matrix (±quartz). Upon further heating and/or decompression, the aragonite matrix transformed back to calcite while the carbonates included in garnet retained their original structure, in spite of the relatively high temperature attained (ca. 500 °C). These aragonite relics are one more example of the preservation of a high-pressure polymorph through mechanical shielding of inclusions in a rigid host. The aragonite–garnet intergrowths are similar to quartz–garnet intergrowths described in amphibolite-facies graphitic schists. They are evidence that oriented inclusions in garnet are not necessarily precipitates (‘exsolutions'). Unlike precipitates, their orientation is controlled more by the shape of the garnet growth front than by symmetry constraints

Cyclical behavior of thrust wedges: Insights from high basal friction sandbox experiments

Scaled sandbox experiments with high basal friction, simulating the growth of accretionary wedges, display cycles alternating between frontal imbricate thrusting and underthrusting of long, undeformed sheets. By contrast, low basal friction experiments with otherwise similar and constant, initial conditions produce a classic frontal imbricate fan through repeated failure along frontal thrusts. The cyclical behavior observed in high basal friction experiments is expressed by three quantities: (1) the average spacing between frontal thrusts, (2) the advance and retreat of the deformation front, and (3) the frontal slope (Alpha) of the actively deforming wedge. As a long sheet is underthrust, the front is steepened through slumping until the maximum critical angle is reached. Then frontal thrusting resumes and the accretion of imbricate slices builds the wedge forward, thereby lowering the taper to the minimum critical angle. At shallow tapers, a long unit is underthrust and subsequently uplifts, shortens, and steepens the overlying wedge through backthrust deformation, thus completing the cycle. Underthrusting of long units offers a simple mechanism for underplating overlying units. It also provides a possible explanation for temporally and spatially varying wedge geometries in nature, when basal frictions attain 80%–90% of the internal friction

Identification of drought tolerance maize populations among the French Maize network of genetic resource collection

International audienc

Neuf régions du génome sont impliquées dans la composition et la dégradabilité de la paroi dans des scénarios d'irrigation contrastés chez une population de maïs précoce

International audienceLa valorisation de biomasses lignocellulosiques dans un système économiquement et écologiquement viable passe par la mise en culture de plantes produisant des biomasses au rendement suffisant et à la qualité adaptée à la valorisation visée, que ce soit de la digestibilité chez l'animal ou des procédés industriels, tels que la bioraffinerie, les biomatériaux et la chimie. Ces plantes doivent également pousser dans des systèmes de culture respectueux de l'environnement. Il a été rapporté que les variations de la qualité et de la composition de la biomasse sont impactées par des facteurs génétiques [1] mais aussi environnementaux, tel que le déficit hydrique [2]. De ce fait, la sélection variétale doit conduire à proposer des idéotypes associant le rendement, la qualité de la biomasse et la tolérance au déficit hydrique. L'approche retenue dans notre étude est l'identification de régions chromosomiques impliquées dans la variation de la dégradabilité et de la composition pariétales, ainsi que dans la réponse au déficit hydrique.Dans ce contexte, une population de lignées recombinantes (RILs ; environ 200 individus) issue du croisement entre deux lignées de maïs différant pour la dégradabilité des parois (F271 et Cm484), a été cultivée pendant trois années consécutives près de Montpellier en condition irriguée ou en condition de déficit hydrique par arrêt de l'irrigation à un stade précoce du développement des plantes et jusqu'à leur floraison. La dégradabilité et les composants pariétaux ont été estimés sur les 1300 échantillons récoltés en utilisant des équations NIRS disponibles au sein de l'équipe (cf poster M. Reymond). En combinant ces estimations et l'établissement d'une carte génétique, nous a permis d'identifier 286 QTLs dans les deux scénarios hydriques, localisés sur un nombre restreint de régions chromosomiques (9 régions principales). Ainsi, des QTLs de dégradabilité pariétale co-localisent avec des QTLs de la composition pariétale, telle que la teneur en lignine et/ou en acides p-hydroxycinnamiques. De plus, il apparait que quatre régions chromosomiques présentent une co-localisation de QTLs spécifiques d'un scénario hydrique donné. Remerciements : ces recherches sont soutenues financièrement par l'ANR (projet Biomasse pour le futur, ANR-11-BTBR-0006-BFF). Références bibliographiques [1] C

Neuf régions du génome sont impliquées dans la composition et la dégradabilité de la paroi dans des scénarios d'irrigation contrastés chez une population de maïs précoce

International audienceLa valorisation de biomasses lignocellulosiques dans un système économiquement et écologiquement viable passe par la mise en culture de plantes produisant des biomasses au rendement suffisant et à la qualité adaptée à la valorisation visée, que ce soit de la digestibilité chez l'animal ou des procédés industriels, tels que la bioraffinerie, les biomatériaux et la chimie. Ces plantes doivent également pousser dans des systèmes de culture respectueux de l'environnement. Il a été rapporté que les variations de la qualité et de la composition de la biomasse sont impactées par des facteurs génétiques [1] mais aussi environnementaux, tel que le déficit hydrique [2]. De ce fait, la sélection variétale doit conduire à proposer des idéotypes associant le rendement, la qualité de la biomasse et la tolérance au déficit hydrique. L'approche retenue dans notre étude est l'identification de régions chromosomiques impliquées dans la variation de la dégradabilité et de la composition pariétales, ainsi que dans la réponse au déficit hydrique.Dans ce contexte, une population de lignées recombinantes (RILs ; environ 200 individus) issue du croisement entre deux lignées de maïs différant pour la dégradabilité des parois (F271 et Cm484), a été cultivée pendant trois années consécutives près de Montpellier en condition irriguée ou en condition de déficit hydrique par arrêt de l'irrigation à un stade précoce du développement des plantes et jusqu'à leur floraison. La dégradabilité et les composants pariétaux ont été estimés sur les 1300 échantillons récoltés en utilisant des équations NIRS disponibles au sein de l'équipe (cf poster M. Reymond). En combinant ces estimations et l'établissement d'une carte génétique, nous a permis d'identifier 286 QTLs dans les deux scénarios hydriques, localisés sur un nombre restreint de régions chromosomiques (9 régions principales). Ainsi, des QTLs de dégradabilité pariétale co-localisent avec des QTLs de la composition pariétale, telle que la teneur en lignine et/ou en acides p-hydroxycinnamiques. De plus, il apparait que quatre régions chromosomiques présentent une co-localisation de QTLs spécifiques d'un scénario hydrique donné. Remerciements : ces recherches sont soutenues financièrement par l'ANR (projet Biomasse pour le futur, ANR-11-BTBR-0006-BFF). Références bibliographiques [1] C

Okinawa trough backarc basin: Early tectonic and magmatic evolution

International audienceThe Okinawa Trough, lying between Japan and Taiwan, is a backarc basin formed by extension within the continental lithosphere behind the Ryukyu trench-arc system. Stress directions associated with the two last extensional phases in the southwestern Okinawa Trough have been deduced from a comparison with analog modeling: the direction of extension is N150° for the Pleistocene phase of extension (2–0.1 Ma) and N170° for the late Pleistocene-Holocene phase of extension (0.1–0 Ma). The present-day Ryukyu volcanic arc, a narrow continuous feature extending from Japan to Taiwan, is located on the eastern side of the Okinawa Trough, 80–100 km above the Wadati-Benioff zone, the minimum depth for emplacement of arc magmatism. Scarce present-day backarc volcanism appears in the middle and southern Okinawa Trough within linear en echelon bathymetric depressions. A N045° oriented seamount volcanic chain cuts across obliquely the southwestern Okinawa Trough and lies in the direct line of extension of the Gagua ridge, a N-S linear volcanic feature of the Philippine Sea plate. Associated with this extension of the Gagua ridge, a large reentrant located at the base of the Ryukyu prism, the uplift of part of the Nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross-backarc volcanism could be tied to the subduction of the Gagua ridge located there at a depth of 80–100 km beneath the backarc basin. A second area of anomalous volcanism has been identified in the middle Okinawa Trough in the ENE extension of the Daito ridge, a WNW-ESE 400-km-long volcanic feature of the Philippine Sea plate. We suggest that the Gagua and Daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere, allowing magmas with arc affinities to erupt at the seafloor. This excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts. The Okinawa Trough is consequently still in an early stage of evolving from arc type to backarc activity

Exploring the genetic basis of cell wall traits upon contrasted water regimes in maize.

International audienceCell wall digestibility and composition are the major targets for improving both feeding value and industrial valorizations (such as bioethanol) from lignocellulosic biomass. Biomass production should also reach expected yields under environmental-friendly practices. It was brought back that the variations of the biomass quality and composition are not only impacted by genetic, but also by environmental factors, such as water stress episodes. To guide breeding of maize and other dedicated C4 species for biomass production, we evaluated a F271 x Cm484 recombinant inbred population under non-irrigated and irrigated conditions during three consecutive years near in M ontpellier (South of France). We quantified over 1,300 harvested stover samples using dedicated near-infrared spectroscopy equations established with calibrated samples harvested under both water regime conditions. We showed that biomass digestibility and composition varied between irrigated and non-irrigated scenarios. Using a genotyping-by-sequencing approach, we then built a dense genetic map with 1,000 single nucleotide polymorphism (SNP) markers and performed single-marker analyses to identify constitutive quantitative trait loci (QTLs) across years and conditions, and responsive QTLs using the interaction effect between the marker and the treatment. Overall, we identified 16 clusters of constitutive QTLs and 5 clusters of responsive QTLs, of which only one did not co-localized with constitutive QTLs. These results showed that co-localization between traits were different depending on the QTLs, underlying different strategies for breeding

Exploring the genetic basis of cell wall traits upon contrasted water regimes in maize.

International audienceCell wall digestibility and composition are the major targets for improving both feeding value and industrial valorizations (such as bioethanol) from lignocellulosic biomass. Biomass production should also reach expected yields under environmental-friendly practices. It was brought back that the variations of the biomass quality and composition are not only impacted by genetic, but also by environmental factors, such as water stress episodes. To guide breeding of maize and other dedicated C4 species for biomass production, we evaluated a F271 x Cm484 recombinant inbred population under non-irrigated and irrigated conditions during three consecutive years near in M ontpellier (South of France). We quantified over 1,300 harvested stover samples using dedicated near-infrared spectroscopy equations established with calibrated samples harvested under both water regime conditions. We showed that biomass digestibility and composition varied between irrigated and non-irrigated scenarios. Using a genotyping-by-sequencing approach, we then built a dense genetic map with 1,000 single nucleotide polymorphism (SNP) markers and performed single-marker analyses to identify constitutive quantitative trait loci (QTLs) across years and conditions, and responsive QTLs using the interaction effect between the marker and the treatment. Overall, we identified 16 clusters of constitutive QTLs and 5 clusters of responsive QTLs, of which only one did not co-localized with constitutive QTLs. These results showed that co-localization between traits were different depending on the QTLs, underlying different strategies for breeding