Éditeur(s) : Wiley-blackwell Publishing, Inc
Résumé : We present the results from processing and interpreting five lines from the 1992 Erable multichannel seismic reflection experiment extending from the southeastern margin of Flemish Cap into the northern Newfoundland Basin. These profiles reveal significant along strike variations in the rifting styles experienced by Flemish Cap. In the southwest, a 100-km-wide transition zone is identified between thinned continental crust and thin oceanic crust. Similar to the conjugate Galicia Bank and Iberian margins, this transition zone contains a section of deep basement adjacent to a series of shallower ridges and is interpreted as exhumed serpentinized mantle. Along strike towards the northeast, this transition zone pinches out completely within 100 km and is replaced by thin oceanic crust directly adjacent to thinned continental crust. By interpreting nearby seismic profiles and profiles on the conjugate margins using the same classification criteria, we construct regional maps of the distribution of crustal domains on both sides of the North Atlantic. These maps reveal significant variations in rifting style on the conjugate margins and along strike of each margin and also highlight the role of ancient transfer zones in compartmentalizing these rifting variations into four distinct regions. We propose that the limited localization of shallow topographically high serpentinized peridotite ridges on the Newfoundland-Iberia and Flemish Cap-Galicia Bank conjugate margins, was directly related to an increase in the rate of extension following the separation of Flemish Cap and Galicia Bank which exhumed deeper, less serpentinized mantle.
Geophysical Journal International (0956-540X) (Wiley-blackwell Publishing, Inc), 2010-03 , Vol. 180 , N. 3 , P. 976-U4

Droits : 2010 RAS
http://archimer.ifremer.fr/doc/00001/11202/7876.pdf
DOI:10.1111/j.1365-246X.2009.04477.x
http://archimer.ifremer.fr/doc/00001/11202/

Éditeur(s) : HAL CCSD
Résumé : The spreading ridge subduction is an unavoidable process during the subduction-related belt elovution. The aim of this thesis concerns the evolution of the Central Patagonian Cordillera, at the latitude of the Chile triple junction, in relation with the Chile spreading ridge subduction inducing the opening of a slab-window beneath the South American plate. By a morphologic, and a structural analysis, coupled with the analysis of satelittes and topographic images, we show the influence of the slab-window development at 3 Ma on the morphostructural evolution of the Central Patagonia. During the Pliocene, the Central Patagonian Cordillera experiences a major extensional phase inducing the formation of transverse and internal depressions. Negative tectonic inversion, responsible to the rift-type topography, induces the inversion of the morphotectonic front and the disruption of the volcano-sedimentary piedmont with the rest of the Cordillera at 3 Ma. Radial extensional regime is characterized by a magnitude comprises between 800 m and 3500 meters and vertical movements are localized along polyphazed faults. We suggest that the Plio-Quaternary morphostructural evolution is related to the opening of the slab-window at 3 Ma beneath the Central Patagonia. The upwelling of asthenospheric hot mantle through the slab window induces the regional collapse of the Central Patagonian Cordillera.
La subduction d'une dorsale active sous un continent est un processus inévitable dans l'évolution des chaînes de subduction. Le travail de cette thèse concerne l'évolution de la Cordillère de Patagonie Centrale, à la latitude du point triple du Chili, en relation avec la subduction de la dorsale active du Chili induisant le développement d'une fenêtre asthénosphérique sous la plaque sudaméricaine. A l'aide d'une approche morphologique, structurale, couplée à l'analyse d'images satellites et topographiques, nous montrons l'influence de la fenêtre asthénosphérique depuis 3 Ma sur l'évolution morphostructurale de la Patagonie Centrale. Au cours du Pliocène, la Cordillère de Patagonie Centrale est marquée par une phase d'extension majeure induisant la formation de dépressions transverses et internes à la chaîne. L'inversion négative du relief responsable de la topographie générale de type rift induit l'inversion du front morphotectonique et la déconnexion du piedmont volcano-sédimentaire du reste de la Cordillère à partir de 3 Ma. L'extension radiale dont l'amplitude est comprise entre 800 mètres et 3500 mètres, se localise dans la plupart des cas au niveau de failles polyphasées. L'évolution morphostructurale plioquaternaire proposée est directement reliée à l'ouverture de la fenêtre asthénosphérique à 3 Ma sous la Patagonie et à la remontée de matériel asthénosphérique chaud induisant la collapse régionale de la Cordillère de Patagonie Centrale.
https://tel.archives-ouvertes.fr/tel-00557618

tel-00557618
https://tel.archives-ouvertes.fr/tel-00557618
https://tel.archives-ouvertes.fr/tel-00557618/document
https://tel.archives-ouvertes.fr/tel-00557618/file/scalabrinothese.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The East Sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far-field effects of the India-Asia collision and the extension linked to the opening of the Baikal Rift System. The active deformation that affects this range is very recent (around 5 Ma) but occurs in a very complex morphotectonic setting and the understanding of the Tertiary deformation relies entirely on a detailed knowledge of the pre-deformation situation. Using apatite fission track thermochronology, cosmogenic 10Be and morphological study on Tertiary lava flows we demonstrate that prior to the Oligocene the morphology of the East Sayan area was characterized by a wide, constantly rejuvenated erosion surface. Apatite fission track thermal modelling indicates that this surface started to form at least in Late Jurassic-Early Cretaceous (140-120 Ma). The long-term exhumation rates (several tens of million years) derived from apatite fission track data (17.5 m/Ma) and the short-term erosion rates (over a few hundred thousand years) derived from cosmogenic 10Be data (12-20 m/Ma) are coherent implying a near constant mean erosion rate since Late Jurassic. This constant, slow erosion prevented the formation of a lateritic-kaolinic weathering crust on the planation surface. By Oligocene-early Miocene times a long wavelength uplift that remains to be explained, induced incision that created shallow valleys later filled by basaltic lava flows. Finally, the present short-wavelength topography initiated during the Pliocene.
ISSN: 0743-9547

insu-00805603
https://hal-insu.archives-ouvertes.fr/insu-00805603
DOI : 10.1016/j.jseaes.2011.09.017

Éditeur(s) : Geological Society of America
Résumé : A seismic-refraction study of the sedimentary structure of the South West African continental shelf was carried out between lat 17°S and 24°S using expendable sonobuoys. Striking differences exist both in the topography and sedimentary structure between the shelf north and south of the Walvis Ridge. South of the ridge, as far as lat 23°S, the shelf consists of a prograded series, whereas north of the ridge, at least as far as lat 17°S, east-trending canyons cut the shelf sedimentary cover. The steep northem scarp of Walvis Ridge can be traced eastward under the sediment of the continental margin. The southern flank of the ridge is buried under a thicker sedimentary cover and could only be traced eastward to long. 10°E on seismic-reflection records. This flank probably parallels the northern scarp under the continental margin. Two-dimensional structural models, built with the help of seismic-retlection and seismic-refraction results and based on the hypothesis of local isostatic equilibrium, account for the obsewed gravity profiles. A compensating root consists of light material (density 2.95 g/cm3) and reaches a depth of about 25 km. Gravity results also suggest that the Walvis Ridge does not constitute a superimposed load on the lithosphere; rather, the ridge and its underlying compensating mass were created at approximately the same time as the adjacent ocean basins. The creation of the two aseismic ridges of the South Atlantic - the Rio Grande Rise and Walvis Ridge - by a mantle hot spot and plume is accepted; this theory seems to explain most of the peculiar features of the Walvis Ridge. However, it is probable that the surface expression of the mantle hot spot was controlled by the presence of weak zones in the lithosphere such as transform faults. [NOT CONTROLLED OCR]
Geological Society of America Bulletin (Geological Society of America), 1975 , Vol. 86 , P. 1713-1724

Droits : Geological Society of America
http://archimer.ifremer.fr/doc/1975/publication-4978.pdf
http://archimer.ifremer.fr/doc/00000/4978/

Éditeur(s) : HAL CCSD
Résumé : The evolution of mountain belt piedmont is controlled by interactions between tectonics, erosion and sedimentation. To study coupling between these processes, we analyze morphometric data collected in the eastern Tian Shan piedmont (NW China) and develop a new analogue modelling technique. The modeling approach uses an experimental set-up and analog material specifically designed to study simultaneously tectonic structures (faults, folds), detailed morphology (drainage basins, channels, alluvial fans, etc.) and stratified sedimentation. Measurement techniques based on laser interferometry and image correlation are also developed to quantify the topographic and kinematic evolution of models.
Our experiments allow a new approach for the study of piedmont morphotectonic evolution. Our results indicate that tectonics mainly controls this evolution. The propagation of deformation and the formation of relief both significantly influence the development of drainage networks, the evolution of drainage basins and the formation of morphotectonic markers. Particularly, a study of alluvial fans and watershed metrics suggests that there is a dynamical equilibrium between uplift, erosion and morphology. In addition, our results show that terrace nucleation is controlled by thrust activity and hydrography adjustments. Folding of terraces responds to a homothetic deformation pattern.
This new methodology brings promising perspectives in the fields of geomorphology, seismotectonics and sedimentology.
L'évolution d'un piémont de chaîne de montagnes est contrôlée par les interactions entre la tectonique, l'érosion et la sédimentation. Pour étudier ces processus, nous avons analysé des données morphométriques issues des piémonts orientaux du Tian Shan (NW Chine) et développé un nouveau type de modélisation analogique. Cette approche utilise un dispositif et un matériau expérimental spécialement conçus pour modéliser simultanément des structures tectoniques (failles, plis), une morphologie détaillée (bassins versants, rivières, cônes alluviaux, etc.) et une sédimentation stratifiée. Des techniques de mesure optique ont été également mises en oeuvre afin de quantifier l'évolution topographique et cinématique des modèles.
Les expériences réalisées offrent une opportunité inédite d'étudier l'évolution morphotectonique d'un piémont. Nos résultats montrent que la tectonique exerce un contrôle de premier ordre sur cette évolution. La propagation de la déformation et la formation des reliefs influencent en effet significativement le développement du réseau de drainage, l'évolution des bassins versants et la formation des marqueurs morphotectoniques. En particulier, l'analyse de la morphométrie des cônes alluviaux et de leurs bassins versants suggère qu'un équilibre dynamique s'installe entre la surrection, l'érosion et la morphologie. Nos résultats montrent également que l'apparition des terrasses est guidée par l'activité des chevauchements et les adaptations de l'hydrographie. Leur modèle de plissement répond à une déformation homothétique.
Cette nouvelle approche ouvre des perspectives d'étude prometteuses en géomorphologie, sismotectonique et stratigraphie.
https://tel.archives-ouvertes.fr/tel-00339145

tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145v2/document
https://tel.archives-ouvertes.fr/tel-00339145/file/These_Graveleau08.pdf

Éditeur(s) : Springer
Résumé : The Håkon Mosby mud volcano is a 1.5-km-diameter geological structure located on the Southwest Barents Sea slope at a water depth of 1,270 m. High-definition seabed mapping of the mud volcano has been carried out in 2003 and 2006. A comparative analysis of the bathymetry and backscatter maps produced from the two surveys shows subtle morphological changes over the entire crater of the mud volcano, interpreted to be the consequence of mud eruption events. Mud temperature measurements point to a persistently warm mud at shallow depth in the crater. This is explained by upward fluid advection, rather than conductive cooling of mud flows. The small-scale spatial variability in the temperature distribution may be related to mud outflows or changes in the fluid flow regime. Furthermore, the locations of free gas venting observed in 2006 were found to differ from those of 2003. Our observations of overall similar topographic profiles across the mud volcano in 2003 and 2006 suggest that eruption events would have been modest. Nevertheless, the data bring evidence of significant change in activity even over short time intervals of only 3 years. This may be a characteristic shared by other submarine mud volcanoes, notably those considered to be in a quiescent stage.
Geo-marine Letters (0276-0460) (Springer), 2010-06 , Vol. 30 , N. 3-4 , P. 157-167

Droits : Springer-Verlag 2010
http://archimer.ifremer.fr/doc/00004/11527/10261.pdf
DOI:10.1007/s00367-010-0193-z
http://archimer.ifremer.fr/doc/00004/11527/

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
P>Tehran is one of the largest cities in the world (12 million people) facing seismic hazard. Standing at the foothills of Alborz Mountains, the capital of Iran is exposed to potential earthquakes associated with several nearby active faults. Classically mentioned as active features, the Kahrizak, the North Rey and the South Rey scarps cross the town itself and would be the sources of several destructive historical earthquakes. However, the nature of these topographic scarps remains uncertain. To assess whether these features correspond to active faults, we carried out a morphological and stratigraphic study. Our results show that the three scarps define horizontal scarp lines that follow contour lines matching ancient shorelines further East. This point, associated with other morphological characteristics such as the flatness of the upper and the lower surfaces, the long and regular streams that incised the upslope upper surfaces and the fact that the deposits are horizontal and without deformations, suggests in fact that the Kahrizak, the North Rey and the South Rey scarps correspond most likely to ancient shore lines and are not fault scarps.
ISSN: 0954-4879

hal-00496390
https://hal.archives-ouvertes.fr/hal-00496390
DOI : 10.1111/j.1365-3121.2010.00938.x

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : Normal faulting mechanisms observed in the northern foothills of the Central–Western Pyrenees are remarkable, since one expects thrust faults at a convergent plate boundary. To understand the mechanisms involved, we used numerical modeling and investigated the impact of the following processes: gravitational potential energy associated with topography and dense crustal blocks; isostatic compensation in response to denudation and/or sedimentation. To decipher the effects of each process, we designed three model geometries and added a pre-existing weak fault where most of the seismicity occurs. To evaluate our model results, we derived the fault slip rate from the focal mechanisms in the region where we have the fault in our model. We found a slip rate of ∼15 m/Ma, which is in agreement with our modelling results. We conclude that flexural rebound induced by surface processes is able to explain the seismicity in Central–Western Pyrenees.
ISSN: 1631-0713

hal-01346028
https://hal.archives-ouvertes.fr/hal-01346028
https://hal.archives-ouvertes.fr/hal-01346028/document
https://hal.archives-ouvertes.fr/hal-01346028/file/Genti.pdf
DOI : 10.1016/j.crte.2015.08.004

Résumé : SODACAL prawn farm which was set up as a pilot farm for the development of a prawn industry in New Caledonia, saw its production exponentially rise from 1984 to 1992 (to 400 t/year, then experienced a sharp drop in 1993 (250 t/year) which carried on until 1997, and finally rose back to a stabilizing level around 400 t/year until 1999. The study analyses the difficulties observed before and during the drop of production. Among them, mortality outbreaks, other biological perturbations (benthic mat clearing and crab and fish mortality) and focus on the noxious state of the bottom (reduced and smelling sulfide hydrogen). It particularly shows that Syndrome 93 outbreaks could be observed on this farm from 1990. The analysis highlights the particular climatic conditions in New Caledonia from 1990 to 1995 (drought) and their potential impact on the production. The development of this very particular process of physical and topographic differential evolution of the pond bottom under wind action (accumulation and digging) and its consequences on pond preparation is explained. This work takes a close look at the grow-out management : age and quality of post larvae, pond stocking with pre-grown animals, feed characteristics and management, water exchange management and pumping capacity, strategy on density and size of harvested animals. The results have been assessed using a distinctive tool, the "survival differential", allowing inter-pond comparisons within a site, inter-farms comparisons over pluri-annual periods of time. >From the commented farm results over a 20 year period, we could distinguish the principal factors responsible for the drop of grow-out capacity of some ponds. We have outlined a conceptual description of the different parameters leading to the decrease of survival, an epidemiological scenario and a synoptic table of the history of events and their relative severity. The study draws the hypothesis of a cumulative effect of positive factors, which could have led back to satisfying production results: a physical and biochemical restoration of pond bottoms, a modified and standardized grow-out management, an appropriate pumping capacity and the come back of adequate climatic conditions. This case study illustrates the concept of « flexibility » of the farming capacity and the sustainability of prawn farming in New Caledonia. The clear objective of this 20 year historic investigation was to get relevant information, in order to improve the understanding on the "summer syndrome" which hits two farms at the moment, and to participate in the hypothesis under study by the DAC (2005). We also tried to make the new farmers aware of the fragility of the pond ecosystem, and give some common-sense advices in the hope that such problems will not happen again in other places.
La ferme de SODACAL, conçue à l'origine comme une ferme de démonstration pour le développement d'une filière d'aquaculture exportatrice de crevettes en Nouvelle-Calédonie a connu une phase de croissance exponentielle de sa production de 1984 à 1992 (jusqu'à 400 t/an), puis une chute brutale en 1993 (250 t/an) qui s'est prolongée jusqu'en 1997 et enfin une reprise à partir de 1998 pour arriver à une stabilisation autour de 420 t/an depuis 1999. L'étude inventorie les dysfonctionnements observés avant et pendant la crise de production. Parmi ceux-ci sont évoqués les épisodes de mortalité de crevettes, d'autres désordres biologiques (décollements de tapis benthique et « hécatombes » de crabes et de poissons), l'état délétère des fonds (sédiments réduits et odeur d'hydrogène sulfuré). Elle permet notamment de montrer que des épisodes de mortalité typiques du Syndrome 93 pouvaient être observés sur cette ferme dès 1990. L'étude met en évidence les conditions climatiques remarquables qui ont sévi en Nouvelle-Calédonie de 1990 à 1995 (sécheresse) et leur impact probable sur les élevages. La genèse du phénomène très particulier d'évolution physique et topographique des fonds des bassins par l'effet du vent (accumulation et creusement) et des conséquences sur la préparation des bassins est explicitée. Ce travail aborde la gestion zootechnique : l'âge et la « qualité » des post larves, la pratique des ensemencements à partir d'animaux pré grossis, la gestion de l'alimentation et la nature de la provende, le contrôle du renouvellement d'eau et la capacité de pompage, le choix des densités et du calibre des animaux récoltés. Les résultats ont pu être évalués à travers un outil original «le différentiel de survie », permettant des comparaisons inter-bassins au sein du site, inter-fermes à des périodes pluri annuelles distinctes. A partir des résultats commentés de la ferme obtenus sur 20 années, on a pu distinguer les principaux facteurs qui ont provoqué cette chute d'aptitude culturale de certains bassins. Un schéma conceptuel des différents paramètres ayant conduit à la baisse des survies, un scénario épidémiologique ainsi qu'un tableau synoptique de la chronologie des évènements et de leur relative sévérité sont esquissés. Le rapport ébauche l'hypothèse d'un cumul de causes favorables qui ont permis le retour à des résultats zootechniques satisfaisants : une réhabilitation physique et biochimique des fonds de bassins, une zootechnie modifiée et standardisée, une capacité de pompage adéquate et une climatologie de nouveau favorable. Cette étude de cas permet ainsi d'illustrer les notions d « élasticité » de l'aptitude culturale et de durabilité de la crevetticulture en Nouvelle-Calédonie. Le but de cette enquête historique sur 20 ans est l'acquisition d'informations pertinentes permettant d'améliorer la compréhension du « Syndrome d'été » qui affecte actuellement deux fermes de production et ainsi aider à compléter le scénario hypothétique avancé par le Dac (2005). Enfin, au travers de cet historique, on a cherché également à sensibiliser les nouveaux opérateurs de la filière sur la fragilité de l'écosystème-bassin et présenter quelques conseils de bon sens pour éviter que de tels phénomènes ne se reproduisent ailleurs.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2005/rapport-718.pdf
http://archimer.ifremer.fr/doc/00000/718/

Éditeur(s) : HAL CCSD
Résumé : International audience
The complexity of the Lesser Antilles vegetation must be linked to the variety of topographic features that influence the structure of some climatic parameters, particularly the rainfall. The above mentioned environmental factors influence a plurality of biotopes colonized by specific phytocenoses. Using survey transects of different minimal areas, we highlighted the specific, biocenotic, structural and architectural heterogeneity of the survey stations. This spatio-temporal differentiation of plant groupings is strongly guided by the activities of the successive human societies. These elements show that the anthropized vegetation of the Lesser Antilles represents a true laboratory for the study of plant succession using the synchronic approach.
ISSN: 2320-5407

hal-01376445
https://hal.univ-antilles.fr/hal-01376445
DOI : 10.21474/IJAR01/1322

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : We examined tree-soil habitat associations in lowland forest communities at Paracou, French Guiana. We analyzed a large dataset assembling six permanent plots totaling 37.5 ha, in which extensive LIDAR-derived topographical data and soil chemical and physical data have been integrated with precise botanical determinations. Map of relative elevation from the nearest stream summarized both soil fertility and hydromorphic characteristics, with seasonally inundated bottomlands having higher soil phosphate content and base saturation, and plateaus having higher soil carbon, nitrogen and aluminum contents. We employed a statistical test of correlations between tree species density and environmental maps, by generating Monte Carlo simulations of random raster images that preserve autocorrelation of the original maps. Nearly three fourths of the 94 taxa with at least one stem per ha showed a significant correlation between tree density and relative elevation, revealing contrasted species-habitat associations in term of abundance, with seasonally inundated bottomlands (24.5% of species) and well-drained plateaus (48.9% of species). We also observed species preferences for environments with or without steep slopes (13.8% and 10.6%, respectively). We observed that closely-related species were frequently associated with different soil habitats in this region (70% of the 14 genera with congeneric species that have a significant association test) suggesting species-habitat associations have arisen multiple times in this tree community. We also tested if species with similar habitat preferences shared functional strategies. We found that seasonally inundated forest specialists tended to have smaller stature (maximum diameter) than species found on plateaus. Our results underline the importance of tree-soil habitat associations in structuring diverse communities at fine spatial scales and suggest that additional studies are needed to disentangle community assembly mechanisms related to dispersal limitation, biotic interactions and environmental filtering from species-habitat associations. Moreover, they provide a framework to generalize across tropical forest sites.
ISSN: 1932-6203

hal-01260289
https://hal.archives-ouvertes.fr/hal-01260289
PRODINRA : 342930
DOI : 10.1371/journal.pone.0141488

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : International audience
The interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts. Here we investigate the modalities of deformation in Central Nepal on a c. 100 ka time scale in response to tectonic and external forcings, through the use of a finite-element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding. We study the complex coupling existing between tectonics and erosion, with special emphasis on the influences of rock strength and rainfall distributions. Our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography. We show that the location of the Main Frontal Thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the Siwaliks Hills. As previously suspected (Burbank et al. 2003), our simulations demonstrate that the pattern of uplift in Nepal is mainly dependent on both erodability and fault geometry, rather than on rainfall distribution.
ISSN: 2041-4927

hal-01543331
https://hal-amu.archives-ouvertes.fr/hal-01543331
DOI : 10.1144/GSL.SP.2006.253.01.18

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
This paper presents a synthetic view of the geodynamic evolution of the Zagros orogen within the frame of the Arabia-Eurasia collision. The Zagros orogen and the Iranian plateau preserve a record of the long-standing convergence history between Eurasia and Arabia across the Neo-Tethys, from subduction/obduction processes to present-day collision (from ~ 150 to 0 Ma). We herein combine the results obtained on several geodynamic issues, namely the location of the oceanic suture zone, the age of oceanic closure and collision, the magmatic and geochemical evolution of the Eurasian upper plate during convergence (as testified by the successive Sanandaj-Sirjan, Kermanshah and Urumieh-Dokhtar magmatic arcs), the P-T-t history of the few Zagros blueschists, the convergence characteristics across the Neo-Tethys (kinematic velocities, tomographic constraints, subduction zones and obduction processes), together with a survey of recent results gathered by others. We provide lithospheric-scale reconstructions of the Zagros orogen from ~ 150 to 0 Ma across two SW-NE transects. The evolution of the Zagros orogen is also compared to those of the nearby Turkish and Himalayan orogens. In our geotectonic scenario for the Zagros convergence, we outline three main periods/regimes: (1) the Mid to Late Cretaceous (115-85 Ma) corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper-plate fragmentation, (2) the Paleocene-Eocene (60-40 Ma) witnesses slab break-off, major shifts in arc magmatism and distributed extension within the upper plate, and (3) from the Oligocene onwards (~ 30-0 Ma), collision develops with a progressive SW migration of deformation and topographic build-up (Sanandaj-Sirjan Zone: 20-15 Ma, High Zagros: ~12-8 Ma; Simply Folded Belt: 5-0 Ma) and with partial slab tear at depths (~10 Ma to present). Our reconstructions underline the key role played by subduction throughout the whole convergence history. We finally stress that such a long-lasting subduction system with changing boundary conditions also makes the Zagros orogen an ideal natural laboratory for subduction processes.
ISSN: 0016-7568

insu-00616582
https://hal-insu.archives-ouvertes.fr/insu-00616582
https://hal-insu.archives-ouvertes.fr/insu-00616582/document
https://hal-insu.archives-ouvertes.fr/insu-00616582/file/692.full.pdf
DOI : 10.1017/S001675681100046X

Éditeur(s) : HAL CCSD Elsevier
Résumé : LA-ICP-MS and SIMS U–Pb analyses have been performed on detrital zircon grains from four heavy mineral rich metasediments collected at different levels of the Nathorst Land Group (Eleonore Bay Supergroup, Greenland). Zircons from high-grade samples collected in the sillimanite and migmatite zones exhibit modifications to their structure, which are lacking in grains from a low-grade sample (0.3 GPa and 350–400 °C). In the sillimanite zone (0.5 GPa, 650 °C), thin discontinuous rims (<20 μm) plating detrital zircon grains document a metamorphic overgrowth during the Caledonian event dated at 428 ± 25 Ma (2σ). In the migmatite zone (0.4 GPa, 700 °C), zircons underwent severe recrystallisation processes but no new zircon growth. Ilmenite, which constitutes over 50% of the heavy mineral layers, underwent recrystallisation in both high-grade samples and is likely to represent the main source of Zr available for growth of zircon rims in the sillimanite zone. However, in the migmatite zone sample, the metamorphic conditions allowed titanite overgrowth around ilmenite, which acted as a sink for Zr and inhibited new zircon growth. 207Pb/206Pb ages for 152 detrital zircons broadly range between 2800 and 990 Ma. The detrital zircon age signature is characterized by the large predominance of late Paleoproterozoic (1.85–1.60 Ga) grains in all analysed samples and by lesser amounts of Archean (2.7–2.8 Ga) and Mesoproterozoic (1.2–1.0 Ga) zircons. The overall age range indicates that detritus can be sourced from the Labradorian and Makkovikian provinces of northeastern Laurentia. The youngest grain analysed (987 ± 18 Ma) indicates that deposition took place during the Neoproterozoic, in a post-Grenvillian sedimentary environment and was likely coeval with the Mid-Neoproterozoic episode of aborted rifting that affected the eastern margin of Laurentia. The lack of detritus originating from Amazonia or Baltica, placed adjacent to Laurentia during the early stages of Rodinia fragmentation, suggests that these two continental landmasses did not constitute a topographic high during the Neoproterozoic or that the Mid-Neoproterozoic rifting opened toward an open ocean to the north of a combined Laurentia/Baltica, thus resulting in a general south to north direction of transport of the sediments.
ISSN: 0301-9268

hal-00407204
https://hal.archives-ouvertes.fr/hal-00407204
DOI : 10.1016/j.precamres.2007.01.002

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Imaging deep active volcanic areas remains a challenge in our understanding of their activity and evolution, especially in subduction zones. Study of magnetic anomalies is appropriate to access such dynamics in depth. The magnetic anomaly pattern of the Lesser Antilles Arc (LAA) subduction is studied through Curie Point Depth (CPD), interpreted as the depth of the 580 °C isotherm, and developed to better assess the deep thermal structure of the arc. The depth of the estimated CPD exhibits a complex topography. Keeping in mind the overall uncertainty associated with this method, a main doming is evidenced below the Guadeloupe archipelago. Its apex is shifted towards the ancient arc, suggesting a very hot state of the fore-arc/arc domain. To better understand the LAA thermal state, we perform 2D thermo-mechanical simulations of the subduction zone. Recalling that magnetite is a serpentinization by-product, we simulate water transfer triggered by slab dehydration to test the assumption of fore-arc serpentinization suggested by the positive magnetic anomaly in the vicinity of the Guadeloupe archipelago. In this area, the subduction-induced arc lithosphere hydration and related weakening trigger a fast heating of the upper plate by basal convective removal. This process of fast arc lithosphere thinning may apply where simultaneously the volcanic arc is split in two and normal convergence is high enough. As serpentinization strongly decreases P-wave velocity, we propose a new interpretation of a published seismic profile below Guadeloupe. The seismic layer previously interpreted as the arc lower crust may rather be a layer of serpentinized mantle, as supported by spatial correlations between gravimetric and magnetic anomalies. Consequently, at the scale of Guadeloupe Island, the fore-arc Moho would be shallower than initially assumed, with a dome shape more consistent with both the extensive deformation active since the Oligocene in the inner fore-arc and the CPD doming.
ISSN: 0040-1951

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01505300
https://hal-insu.archives-ouvertes.fr/insu-01505300
https://hal-insu.archives-ouvertes.fr/insu-01505300/document
https://hal-insu.archives-ouvertes.fr/insu-01505300/file/Gailler-2017.pdf
DOI : 10.1016/j.tecto.2017.03.014

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
More than 10 years of geodetic measurements demonstrate an uplift rate of 1–3 mm/yr of the high topography region of the Western Alps. By contrast, no significant horizontal motion has been detected. Two uplift mechanisms have been proposed: (1) the isostatic response to denudation responsible for only a fraction of the observed uplift and (2) the rebound induced by the Wurmian ice cap melting which predicts a broader uplifting region than the one evidenced by geodetic observations. Using a numerical model to fit the geodetic data, we show that a crustal viscosity contrast between the foreland and the central part of the Alps, the latter being weaker with a viscosity of 1021 Pa s, is needed. The vertical rates are enhanced if the strong uppermost mantle beneath the Moho is interrupted across the Alps, therefore allowing a weak vertical rheological anomaly over the entire lithosphere.
ISSN: 0094-8276

hal-01332757
https://hal.archives-ouvertes.fr/hal-01332757
DOI : 10.1002/2016GL067821

Éditeur(s) : HAL CCSD PeerJ
Résumé : International audience
Acoustic recording has been recognized as a valuable tool for non-intrusive monitoring of the marine environment, complementing traditional visual surveys. Acoustic surveys conducted on coral ecosystems have so far been restricted to barrier reefs and to shallow depths (10–30 m). Since they may provide refuge for coral reef organisms, the monitoring of outer reef slopes and describing of the soundscapes of deeper environment could provide insights into the characteristics of different biotopes of coral ecosystems. In this study, the acoustic features of four different habitats, with different topographies and substrates, located at different depths from 10 to 100 m, were recorded during daytime on the outer reef slope of the north Coast of Moorea Island (French Polynesia). Barrier reefs appeared to be the noisiest habitats whereas the average sound levels at other habitats decreased with their distance from the reef and with increasing depth. However, sound levels were higher than expected by propagation models, supporting that these habitats possess their own sound sources. While reef sounds are known to attract marine larvae, sounds from deeper habitats may then also have a non-negligible attractive potential, coming into play before the reef itself.
ISSN: 2167-8359

Droits : http://creativecommons.org/licenses/by/
hal-01654685
http://hal.upmc.fr/hal-01654685
http://hal.upmc.fr/hal-01654685/document
http://hal.upmc.fr/hal-01654685/file/peerj-4019.pdf
DOI : 10.7717/peerj.4019

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes1. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre2, 3. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades4, 5. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.
ISSN: 0028-0836

hal-01685757
https://hal.archives-ouvertes.fr/hal-01685757
DOI : 10.1038/nature22355

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
Natural disturbances are the dominant form of forest regeneration and dynamics in unmanaged tropical forests. Monitoring the size distribution of treefall gaps is important to better understand and predict the carbon budget in response to land use and other global changes. In this study, we model the size frequency distribution of natural canopy gaps with a discrete power law distribution. We use a Bayesian framework to introduce and test, using Monte Carlo Markov chain and Kuo–Mallick algorithms, the effect of local physical environment on gap size distribution. We apply our methodological framework to an original light detecting and ranging dataset in which natural forest gaps were delineated over 30 000 ha of unmanaged forest. We highlight strong links between gap size distribution and environment, primarily hydrological conditions and topography, with large gaps being more frequent on floodplains and in wind-exposed areas. In the future, we plan to apply our methodological framework on a larger scale using satellite data. Additionally , although gap size distribution variation is clearly under environmental control, variation in gap size distribution in time should be tested against climate variability.
ISSN: 1726-4170

hal-01590729
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729/document
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729/file/bg-14-353-2017.pdf
DOI : 10.5194/bg-14-353-2017

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Past studies have shown that high coastal uplift rates are restricted to active areas, especially in a subduction context. The origin of coastal uplift in subduction zones, however, has not yet been globally investigated. Quaternary shorelines correlated to the last interglacial maximum (MIS 5e) were defined as a global tectonic benchmark (Pedoja et al. (2011)). In order to investigate the relationships between the vertical motion and the subduction dynamic parameters, we cross-linked this coastal uplift database with the "geodynamical" databases from Heuret (2005), Conrad and Husson (2009) and Müller et al. (2008). Our statistical study shows that: [1] the most intuitive parameters one can think responsible for coastal uplift (e.g., subduction obliquity, trench motion, oceanic crust age, interplate friction and force, convergence variation, dynamic topography, overriding and subducted plate velocity) are not related with the uplift (and its magnitude); [2] the only intuitive parameter is the distance to the trench which shows in specific areas a decrease from the trench up to a distance of ~300 km; [3] the slab dip (especially the deep slab dip), the position along the trench and the overriding plate tectonic regime are correlated with the coastal uplift, probably reflecting transient changes in subduction parameters. Finally we conclude that the first order parameter explaining coastal uplift is small-scale heterogeneities of the subducting plate, as for instance subducting aseismic ridges. The influence of large-scale geodynamic setting of subduction zones is secondary.
ISSN: 0264-3707

hal-00968538
https://hal.archives-ouvertes.fr/hal-00968538
https://hal.archives-ouvertes.fr/hal-00968538/document
https://hal.archives-ouvertes.fr/hal-00968538/file/henryterraces_v2.pdf
DOI : 10.1016/j.jog.2014.04.001