Éditeur(s) : HAL CCSD
Résumé : International audience
The geology of the North Pyrenean Zone in the central Pyrenees allows for the observation in the field of theentire section of the Pyrenean rift, from the mantle to the crust and the Mesozoic cover (pre, syn and post rift).The good knowledge we have of the pre-Alpine history of the Pyrenees allows us to properly constrain the Alpinegeological evolution of the pre-Triassic rocks which record both Variscan and Alpine orogenic cycles.The mantle outcrop as kilometric to centimetric fragments of peridotite dispersed within a carbonate metamorphicbreccia. The study of peridotite serpentinisation shows several events of low-temperature serpentinisation, incontact with seawater. In some locallities, we can observe a mixture of fragments of variously serpentinizedperidotites. This suggests a tectonic context where fragments of peridotites from different structural levels weresampled more or less synchronously.The granulitic basement is characterized by a Variscan syndeformational HT event (300-280 Ma). So farwe have not found any trace of a Cretaceous HT event (> 500C). On the other hand, the basement is affectedby a regional metasomatism that began during the Jurassic and became more spatially focused with time until itwas restricted to the Pyrenean rift during the Aptien, Albian and Cenomanian. The talc-chlorite metasomatism(120-95 Ma) shows an evolution from a static toward a syn-deformation hydrothermal event, under a more or lessnormal geothermal gradient. Extensional deformation is recorded by the reworking of several inherited low-angleVariscan tectonic contacts, but also by dispersed high-angle extensional shear zones formed under greenshistconditions.The metamorphic Mesozoic cover of the basement massifs, which constitute the so-called Internal MetamorphicZone, is an allochtonous unit made of lenses of Mesozoic rocks enclosed into the breccia, whichlocally contains peridotite and basement clasts. The Mesozoic metamorphic carbonates show a first phase ofsyn-metamorphic (450-600C, P < 2 kb) ductile deformation, and subsequent phases of folding and fracturing.The datation of neoformed minerals give a 108-85 Ma time span for the metamorphism. We interpret this brecciaas an abandonment breccia which marks the emergence of the main detachment. The basal contact of the Mesozoiccover has a complex 3D geometry traced by Triassic evaporites. It corresponds to a major pre- and synorogenicpolyphased tectonic contact.All these data show a geometrically complex hyper-extended rift where the crust was not stretched under ahigh geothermal gradient but thinned by the tectonic extraction of relatively thin lenses and perhaps cut by highangle low-grade shear zones. The 3D geometry, as well as the strain records and the breccia lithologies stronglysuggest a non-cylindricity for the exhumation process, probably within a transtentional system
Geophysical Research Abstracts
Vienne, Austria

insu-01510371
https://hal-insu.archives-ouvertes.fr/insu-01510371

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Geochronological studies of samples from continuous crustal sections of fossil intra-oceanic arcs are paramount for determining the precise timing of major processes that took place during the building of an oceanic island-arc crust. In this study, laser ablation ICP-MS U-Pb zircon (and conventional Rb-Sr) analyses pinpoint the timing of major events responsible for crustal growth of the Kohistan paleo-island arc (Northern Pakistan). Inheritance in magmatic rocks is evidence for recycling of intra-arc material and indicates that the Kohistan arc may have formed as early as 135 +/- 4 Ma. One older inherited grain indicates that the arc developed on a young oceanic lithosphere whose remnants include a c. 175 Ma old component. An interesting consequence is that intra-oceanic arc magmas can yield inherited zircons, which can be much older than the arc system itself without requiring recycling back into the mantle by subduction processes. In the case of the Kohistan arc, ante-arc Neotethys oceanic lithosphere was tapped by arc magmas during their way upward into the arc crust. The oldest magmatic ages measured in this study fall in the range 101-102 Ma (100.9 +/- 0.6 and 102.1 +/- 0.4 Ma). This period corresponds to arc build-up and thickening of the arc crust. Leucogranitic melts dated at 89.9 +/- 0.4 Ma and 90.9 +/- 1.0 Ma are considered as produced by dehydration/melting reaction accompanying granulitisation of the thickened lower arc crust. A maximum age for this event is 97.7 +/- 0.7 Ma, the age of emplacement of a garnet meta-tonalite affected by granulite facies metamorphism. Magmatic activity was still ongoing during and after the granulitisation as testified by emplacement of a diorite and a gabbro dated at 89.1 +/- 0.6 and 88.2 +/- 0.9 Ma respectively. The upper part of the metaplutonic sequence contains diorite samples dated at 84.6 +/- 0.5 Ma and 84.3 +/- 0.5 Ma and as young as 81.1 +/- 0.7 Ma. During this period, and based on the present day outcropping sequences, the mean crustal growth rate varied from 32 to 65 km(3)/km/Ma (volume per unit width along the strike of the arc) which is comparable to the range for present day arcs of the Western Pacific region. The correspondence of crustal growth rates observed for present-day island arcs and the good preservation of the crustal section in the Kohistan arc, make this area an exceptional natural laboratory to study arc related processes and to check models of continental crust formation by arc accretion.
ISSN: 0012-821X

hal-00644555
https://hal.archives-ouvertes.fr/hal-00644555
DOI : 10.1016/j.epsl.2011.07.016

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
The association of experimental data showing that the plastic deformation of olivine, the main constituent of the upper mantle, is highly anisotropic and the ubiquitous seismic anisotropy in the upper mantle, which indicates that olivine crystals show coherent orientations over scales of tens to hundreds of kilometers, implies that the long-term deformation in the upper mantle is anisotropic. We propose a multiscale approach, based on a combination of finite element and homogenization techniques, to model the deformation of a lithospheric plate while fully considering the mechanical anisotropy stemming from a strain-induced orientation of olivine crystals in the mantle. This multiscale model explicitly takes into account the evolution of crystal preferred orientations (CPO) of olivine and of the mechanical anisotropy during the deformation. We performed a series of numerical experiments simulating the uniaxial extension of a homogeneous (100% olivine) but anisotropic plate to test the role of the olivine CPO on the plate mechanical behavior and the link between CPO and mechanical anisotropy evolution. Even for this simple solicitation, different orientations and intensity of the initial olivine CPO result in variable plate strengths and deformation regimes. A plate with an initial CPO where the olivine [100] and [010] axes are concentrated at 45 degrees to the extension direction has high resolved shear stresses on the easy (010)[100] and (001)[100] slip systems of olivine. This results in low strength and in deformation by transtension. Plates with an initial CPO where the maximum of [100] axes is parallel or normal to the extension direction show a high initial strength. Isotropic plates have an intermediate behavior. The progressive rotation of olivine [100] axes toward the imposed stretching direction results in hardening in all models, except in those characterized by an initial concentration of olivine [100] axes normal to the imposed extension, in which softening is followed by hardening.
ISSN: 1525-2027

hal-00420063
https://hal.archives-ouvertes.fr/hal-00420063
DOI : 10.1029/2009GC002423

Éditeur(s) : Amer Geophysical Union
Résumé : The origin of the Algerian margin remains one of the key questions still discussed in the Western Mediterranean sea, due to the imprecise nature and kinematics of the associated basin during the Neogene. For the first time, the deep structure of the Maghrebian margin was explored during the SPIRAL seismic survey. In this work, we present a N-S transect off Tipaza (west of Algiers), a place where the margin broadens due to a topographic high (Khayr-al-Din Bank). New deep penetration seismic profiles allow us to image the sedimentary sequence in the Algerian basin and the crustal structure at the continent-ocean boundary. Modeling of the wide-angle data shows thinning of the basement, from more than 15km in the continental upper margin to only 5–6km of oceanic-type basement in the Algerian basin, and reveals a very narrow or absent transitional zone. Analysis of the deep structure of the margin indicates features inherited from its complex evolution: (1) an oceanic-type crust in the deep basin, (2) similarities with margins formed in a transform-type setting, (3) a progressive deepening of the whole sedimentary cover, and the thickening of the Plio-Quaternary sediments at the margin foot, coeval with (4) a downward flexure of the basement in the basin. These features argue for a multiphased evolution of the margin, including (1) an early stage of rifting and/or spreading, (2) a late transcurrent episode related to the westward migration of the Alboran domain, and (3) a diffuse Plio-Quaternary compressional reactivation of the margin.
Journal Of Geophysical Research-solid Earth (0148-0027) (Amer Geophysical Union), 2013-08 , Vol. 118 , N. 8 , P. 3899-3916

Droits : 2013. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00152/26333/24412.pdf
DOI:10.1002/jgrb.50318
http://archimer.ifremer.fr/doc/00152/26333/

Éditeur(s) : Gauthier-Villars
Résumé : The analysis of humic compounds by elemental analysis, PY-GC-MS and HPLC techniques permitted determination of the origin of organic inputs, essentially terrestrial, and the effects of environmental conditions in the deposits along a north-south transect through the Rhone delta, from the river mouth to the open sea. In the prodelta the sedimentation of fine particles enriches the sediments in organic matter. The humic compound contents were relatively low in sediments, perhaps due to a rapid burying of organic matter which leads to anoxic conditions. In sediments fulvic acids are more abundant than humic acids. Elemental analysis indicated that fulvic acids were enriched in hydrogen and nitrogen as compared to humic acids. Furthermore, H/C and N/C ratios increased in the fulvic and humic acids towards the open sea, related to a more marine character. Pyrolysis analysis showed some differences between the chemical composition of fulvic acids which correspond to low molecular weights enriched in carbohydrates, and that of humic acids, high molecular weight compounds which are enriched in phenols and aromatic hydrocarbons. The pyrolysis-derived phenols were abundant near the river mouth, decreasing towards the open sea as nitrogen-containing-compounds increased. Near the river mouth, the abundance of phenolic aldehydes demonstrated by HPLC emphasized the existence of fresh organic matter. On the other hand, off the mouth, an increase in phenolic acids could indicate a more degraded organic material. The fractionation of humic acids in various classes of molecular weight species using ultrafiltration (Amicon membranes) and their analysis showed that, close to the river mouth, the large proportion of the high molecular weight humic compounds observed was enriched in phenols and carbohydrates, probably inherited from the terrestrial ligno-cellulosic complex. This process seemed to be superimposed on the increase of molecular weights which is usually observed as the environment becomes purely marine. These humic compounds would derived either from organic matter from terrestrial soils swept along by the river flow, after deposition on its bed or, more probably, from high molecular weight compounds which, associated with the mineral phase, flocculated when reaching the fluvio-marine front. Generally, the low molecular weight fractions were enriched in hydrogen and nitrogen. Near the river mouth, nitrogen-containing compounds were concentrated in the low molecular weight classes which correspond to organic molecules regarded as humic precursors. Off the mouth, they were incorporated into the high molecular weight complexes, certainly of marine origin.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 1 , P. 61-74

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00101/21187/18804.pdf
http://archimer.ifremer.fr/doc/00101/21187/

Éditeur(s) : HAL CCSD Mineralogical Society of America
Résumé : International audience
Accessory phases are important hosts of trace elements; allanite may contain >90% of the REE in a bulk rock. The mobility and redistribution of several trace elements, notably HREE, Th, U, and Y is thus controlled by reactions involving allanite and other REE phases, as well as several rock-forming minerals. As these elements are commonly concentrated in mature elastic sediments, a suite of impure quartzite was studied. Two eclogite facies samples from the Monometamorphic Cover Complex of the Sesia Zone (Western Italian Alps) are presented in some detail, as they reveal a remarkably rich spectrum of reaction relationships that involve REE phases.;Two allanite-forming reactions were inferred from textures and phase compositions;(1) monazite + Ca-silicate(?) + fluid -> allanite + apatite + thorite;;(2) monazite + thorite + Ca-silicate(?) + fluid -> Th-rich allanite + auerlite +/- apatite.;Petrographic observations and thermodynamic models suggest that allanite entered the HP assemblage at similar to 530 degrees C and 17-18 kbar during prograde metamorphism.;In one sample, allanite is rimmed by epidote rich in Y and HREE that grew at the expense of xenotime. Two net transfer reactions were derived;(3) xenotime + allanite + fluid -> Y-rich epidote + apatite + thorite;;(4) xenotime + allanite + fluid -> Y-rich epidote + aeschynite + thorite + (phosphate?).;Textural relationships and trace element analyses of coexisting allanite/monazite and xenotime/Y-rich epidote reveal systematic partitioning of the REE. Partition coefficients for the HREE are compatible with equilibrium fractionation, whereas those for the LREE show patterns that seem to be inherited from the precursor phases, in this case zircon with variable LREE composition.
ISSN: 0003-004X

hal-00745674
https://hal.archives-ouvertes.fr/hal-00745674
DOI : 10.2138/am.2012.3832

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
[1] Zircons and monazites from 6 samples of the North Ayilari dextral shear zone (NAsz), part of the Karakorum fault zone (KFZ), have been dated with the U-Th-Pb method, using both ID-TIMS and SIMS techniques. The ages reveal (1) inheritance from several events spanning a long period between the late Archean and the Jurassic; (2) an Eocene-Oligocene magmatic event (similar to 35-32 Ma); (3) an Oligo-Miocene magmatic event (similar to 25-22 Ma), at least partly synkinematic to the right-lateral deformation; and (4) a period of metamorphism metasomatism (similar to 22-14 Ma) interpreted as thermal and fluid advection in the shear zone. The Labhar Kangri granite located similar to 375 km farther Southeast along the KFZ is dated at 21.1 +/- 0.3 Ma. Such occurrence of several Oligo-Miocene granites along the KFZ, some of which show evidence for synkinematic emplacement, suggests that the fault zone played an important role in the genesis and /or collection of crustal melts. We discuss several scenarios for the onset and propagation of the KFZ, and offset estimates based on the main sutures zones. Our preferred scenario is an Oligo-Miocene initiation of the fault close to the NA range, and propagation along most of its length prior to similar to 19 Ma. In its southern half, the averaged long-term fault-rate of the KFZ is greater than 8 to 10 mm/a, in good agreement with some shorter-term estimates based on the Indus river course, or Quaternary moraines and geodesy. Our results show the KFZ cannot be considered as a small transient fault but played a major role in the collision history.
ISSN: 0278-7407

hal-00412570
https://hal.archives-ouvertes.fr/hal-00412570
DOI : 10.1029/2007TC002184

Éditeur(s) : Elsevier
Résumé : Emplacement of post-glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity. On the continental rise of the Gulf of Lions (Western Mediterranean), an aseismic area, we identified turbiditic beds deposited during the rising stage and highstand of sea level. Swath bathymetry, sediment cores, in situ Cone Penetrating Tests (CPTU), heavy mineral associations and radiocarbon dating determined the source, composition, distribution and age of the turbiditic beds. Turbidites are composed of homogeneous to positively graded silts to medium sand with quartz (up to 90%), shell debris and shelfal benthic faunas. Their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms. Their source is found in relict regressive sands at the outershelf. Their deposition occurred just after the onset of the post-glacial sea level rise and the concomitant sediment starvation of the Rhone deep sea turbiditic system until recently. Whilst canyons are fed with sand by strong seasonal hydro-sedimentary dynamics on the outershelf, the emplacement of post-glacial turbidites is not controlled by sea level changes but probably by the periodic flushing of the canyons. Our study revealed that this low energy aseismic margin undergoes significant transport of sand, down to the base of slope, during the sea-level rise and the Holocene highstand.
Marine Geology (0025-3227) (Elsevier), 2009-02 , Vol. 257 , N. 1-4 , P. 65-86

Droits : 2009 Published by Elsevier Ltd.
http://archimer.ifremer.fr/doc/2009/publication-6316.pdf
DOI:10.1016/j.margeo.2008.10.013
http://archimer.ifremer.fr/doc/00000/6316/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Aegean domain is a key area for understanding the processes of back-arc extension. Observed deformation pattern and present day kinematics result from the interaction between the southward retreat of the Hellenic trench and the westward escape of Anatolia. Lithosphere-scale analogue models were employed to display that the overall pattern of Aegean extension requires not only the combination of trench retreat and Anatolia escape since middle Miocene but also the presence of an inherited lithosphere-scale mechanical discontinuity: the Vardar Suture Zone (VSZ). The reactivation in dextral shear of the eastern branch of the VSZ accommodates both the trench retreat (NS stretching) and the westward escape of Anatolia (EW shortening) in the Cyclades area since middle Miocene. Additionally, our model shows that the North Anatolian Fault (NAF) is a late structure in the evolution of the Aegean, initiated around 10 Ma after the onset of Anatolia escape. The displacement field at the surface of the model allows the identification of sub-domains, which result from strain partitioning instead of being "rigid microplates", directly comparable to the present-day displacement field (GPS) of the Aegean and western Anatolia. Our model provides a simple but powerful way to look at the dynamics of Aegean extension in two main stages. From middle Eocene to middle Miocene, extension was only driven by the southward retreat of the Hellenic trench at a rate lower than 1 cm*y− 1. Since middle Miocene, the combination of slab rollback with Anatolia westward escape resulted in a southwest direction of trench retreat, with an accelerating rate of up to 3 cm*y− 1.
ISSN: 0040-1951

insu-01066042
https://hal-insu.archives-ouvertes.fr/insu-01066042
https://hal-insu.archives-ouvertes.fr/insu-01066042/document
https://hal-insu.archives-ouvertes.fr/insu-01066042/file/Philippon-brun-tect-2014-HAL.pdf
DOI : 10.1016/j.tecto.2014.04.039

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen’s segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal & India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes.
ISSN: 2045-2322

hal-01420404
https://hal.archives-ouvertes.fr/hal-01420404
https://hal.archives-ouvertes.fr/hal-01420404/document
https://hal.archives-ouvertes.fr/hal-01420404/file/hetenyi2016.pdf
DOI : 10.1038/srep33866

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : L’objectif de cette étude est d’analyser les impacts et les limites d’une expérience de lutte contre la pauvreté par le tourisme au travers d’une étude de cas dans le village d’Anse-la-Raye, à Sainte-Lucie.Depuis son indépendance en 1979, Sainte-Lucie a tenté de diversifier la structure économique héritée de son passé colonial, en développant notamment des sources alternatives de recettes. Au début, il y a eu un certain succès avec l'industrie de confection et le tourisme qui ont émergé comme des activités viables en dehors de l'agriculture d'exportation.À la fin des années 1980, le pays avait même atteint un taux de croissance qui aurait été considéré comme raisonnable. Sainte-Lucie a d’ailleurs été l’île ayant connu la plus grande croissance économique des Etats du CARICOM. L’exportation de la banane a contribué pour beaucoup à ces résultats, et les nouveaux secteurs ont permis la création d’emplois ainsi que des revenus et des recettes d'exportation supplémentaires.Mais comme tous les Petits Etats Insulaires en Développement (PEID), Sainte-Lucie est caractérisée par sa vulnérabilité économique face aux catastrophes naturelles et crises extérieures. Ainsi, deux des secteurs principaux de son économie se sont affaiblis ces dernières années (l’agriculture et l’industrie), avec pour résultat principal une aggravation de la pauvreté à Sainte-Lucie malgré les bons résultats du secteur touristique devenu le pilier principal de l’économie de l’île.Dans ce contexte de faible croissance économique, le gouvernement et les partenaires sociaux se sont rassemblés pour identifier les politiques susceptibles d’accélérer la croissance économique de Sainte-Lucie. Ainsi, trois axes principaux ont été retenus : l’augmentation de la production locale, la réduction du crime et la réduction de la pauvreté. Dans ce dernier cadre, le gouvernement a lancé plusieurs stratégies de lutte contre la pauvreté notamment l’aide au développement d’activités touristiques.L’étude s’intéresse plus particulièrement au village d’Anse-la-Raye et à une expérience de tourisme pro-pauvre qui y a été développé en 2000 : l’Anse-la-Raye Seafood Friday, une sorte de festival qui permet aux visiteurs de déguster les produits de la mer tous les vendredis. Ce festival a-t-il eu réellement des répercussions sur la population pauvre de la communauté d’Anse-la-Raye ? Est-il viable? Quel est son devenir?
The objective of this study is to analyse the impacts and limitations of attempts to combat poverty using tourism through a case study in the village of Anse-la-Raye, in St. Lucia.Since its independence in 1979, St. Lucia has attempted to diversify the economic structure it inherited from its colonial past, in particular developing alternative sources of revenue. Initially there was some success with the clothing industry and tourism, which emerged as viable business activities outside of agricultural exports.At the end of the 1980s, the country had reached a growth which was considered reasonable. Of all the states of CARICOM, St. Lucia has moreover experienced the greatest economic growth. Banana exports have contributed significantly to these results, and new sectors have led to the creation of jobs and income to supplement export income.But like all Small Island Developing States (SIDS), St. Lucia is characterized by vulnerability to natural disasters and external economic shocks. Two major sectors of the economy have weakened in recent years (agriculture and industry), resulting in an increase in poverty in St. Lucia despite favourable outcomes in the tourism sector, which became the primary pillar of the island.In the context of low economic growth the government and social partners gathered together to identify policies and accelerate economic growth in St. Lucia. Three main themes were identified: Increasing local production; reducing crime and reducing poverty. In this context, the government launched several strategies to combat poverty including assistance for the development of tourism.The study focuses on the village of Anse-la-Raye and the experiences of pro-poor tourism that was developed in 2000: Anse-la-Raye Seafood Friday, a kind of festival that allows visitors to taste the seafood on Fridays. Has this festival really had an impact on the poor of the community of Anse-la-Raye? Is it viable? And what is its future?
Sainte-Lucie

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.6525
http://journals.openedition.org/etudescaribeennes/6525

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
Age constraints on the protoliths, deformation, metamorphism and melting events are key parameters when correlating different continental lithospheric remnants among each other and disentangling their evolution within large-scale orogens. In situ U-Th-Pb chemical dating on monazites using Electron Probe Micro-Analyser (EPMA) has been performed on eight samples throughout the Variscan Maures-Tanneron massif (SE France) in order to date the medium to high-tectonothermal events related to the Variscan orogeny.Results indicate a polyphased crustal evolution : (i) U-Th-Pb ages obtained in polygenetic monazite grain cores gave inherited Upper Ordovician (456 ± 11 Ma) age, highlighting the large scale occurrence of the Ordovician magmatic activity in the North Gondwanian margin. An Early Devonian (404 ± 10 Ma) age may date a protolith emplacement related to calc-alkaline supra-subduction magmatism or could be associated to an early medium-grade metamorphism, prior to collisional stage. (ii) The crustal thickening stage has been further recorded in prograde metamorphic monazites formed during the underthrusting and subsequent nappe stacking events, under amphibolite facies conditions. This stage is dated between 382 ± 11 (Middle Devonian) and 331 ± 5 Ma (Late Visean). (iii) An orogenic partial melting event took place during Middle Carboniferous and is accompanied by the crystallization of crustal peraluminous magmas (Plan-de-la-Tour granite, 329 ± 3 Ma).This contribution demonstrates the capacity of monazite to record the prograde path of rocks during increasing metamorphic conditions related to stages of crustal thickening, and the robustness of the U-Th-Pb chronometer in monazite despite the overprinting of high-grade thermal events, including partial melting. The age ranges of the different orogenic stages reported in this study are in good agreement with those reported in adjacent Variscan Corsica and Sardinia; while correlations with other nearest Variscan massifs like the Argentera massif in the southwestern Alps or the French Massif Central remain more hypothetic. The Internal Zone of the Maures-Tanneron massif, and more widely the Internal Zone of the Maures-Tanneron-Corsica-Sardinia segment, is part of the southern orogenic root system of the Variscan belt.
EISSN: 1777-5817

insu-01140973
https://hal-insu.archives-ouvertes.fr/insu-01140973
DOI : 10.2113/gssgfbull.186.2-3.145

Éditeur(s) : HAL CCSD Elsevier
Résumé : Understanding chemical element mobility during high-pressure metamorphism is paramount to the knowledge of the transformations occurring during the course of eclogite-facies metamorphism. In particular, the role of deformation and fluid circulation appear essential. In order to better decipher this role, we investigated two eclogite-facies samples from the Lindas Nappe in the Bergen arcs (Norwegian Caledonides), which are related to a fluid/deformation metamorphic event. This study, based on detailed microtextural investigations, coupled with major and trace element analyses, either in situ EMPA and LA-ICP-MS or by conventional ICP-MS nebulisation on mineral fractions, illustrates the complexity of chemical reactions accompanying the eclogite- and amphibolite-facies metamorphism. A single eclogite-facies mineral species two eclogite-facies (i.e. phengite and epidote) depicts various chemical features depending on its textural location at thin-section scale. The correlation with the mineralogical reaction occurring in each textural site demonstrates that the compositional variations are inherited from the precursor minerals. Thus, the composition of eclogite-facies minerals is locally controlled by the composition of few hundred-micron domains. On the contrary, alteration phases of the amphibolite facies (symplectite and calcic amphibole) display clear enrichment in LILE, Pb, Sr and LREE compared to their precursor minerals (omphacite and garnet). This supports that the transport of elements at hand-sample scale was enhanced during the retrogression and elements were efficiently delocalised from one textural site to another. The contrasting behaviour of element mobility between peak eclogite-facies metamorphism and retrogression can be explained in terms of rate processes and fluid/deformation activity. During eclogitisation,deformation allows the formation of textural and mineralogical microdomains. Contemporaneously the fluid circulation favours the development of heterogeneities by transport of elements in excess towards areas protected from deformation where phengite-bearing quartz lenses crystallise. This, together with the very fast recrystallisation of eclogite-facies minerals, results in a heterogeneous redistribution of elements at sample scale and in a chemical disequilibrium between different microdomains of hundred-micron size. During retrogression in the amphibolite facies, coeval with long-term ductile deformation, the fluids act as an efficient vector to redistribute the elements from a given textural site to another and, thus, allow to reach, at hand-sample scale, a new chemical equilibrium between the different crystallising phases.
ISSN: 0024-4937

hal-00404602
https://hal.archives-ouvertes.fr/hal-00404602
DOI : 10.1016/j.lithos.2006.10.001

Éditeur(s) : HAL CCSD
Résumé : International audience
Mylonite bodies are exhumed extensions at depth of shallow structural level brittle faults. They are characterised by intense strain localisation involving large volumes of middle to lower continental crust. The analysis of shear zone geometry and microstructures is a useful tool to decipher deformation kinematics, though finite strain estimation is still relatively qualitative. Timing of the deformation has also been the focus of numerous studies using the complete spectrum of geochronometers. However, only rare examples provide geochronological data that can be unambiguously interpreted and cooling, recrystallisation and neocrystallisation are difficult to tell from each other. Thus, time-scales over which major mylonite zones develop and remain active under ductile conditions as well as their strain rate often remain poorly documented. We investigated two sections across the South-Armorican Shear Zone (SASZ), a crustal-scale pluri-km thick dextral shear zone active during a single tectonic event of late-Variscan age and associated with syntectonic granite emplacement.. Finite strain profiles on these cross-sections, quantified from average Quartz grain-size in 34 samples, show a strong deformation partitioning towards the center of the SASZ, with a decrease, for each section, from 150µm in slightly deformed zones to less than 7-5 µm in the core of the ultramylonite. Furthermore, toward the core of the SASZ, development of a penetrative shear band network progressively eliminates lenses of less deformed rocks and results in homogenisation of the Quartz grain sizes. In parallel, we performed in-situ UV-laser Ar/Ar dating on the fabric-forming white micas. White micas population can be decomposed into inherited muscovites carried by the folation and newly-formed, syn-tectonic substituted phengites located along the shear bands yielding 2 age groups for each sample. Along the profiles, the difference between these two ages evolves from 10-15 Ma in weakly deformed domains to zero toward the SASZ core. In addition, mylonite-forming phengites yielded the same age irrespectively of their position on the section or of the rock strain.. On the regional point of view, this study brings deformation-ages for the late-orogenic evolution of the South Armorican domain. Strain accumulated along the SASZ in a time-span extending to 300-298 Ma, i.e. contemporaneously with the activity of nearby major extensional shear zones. These results support a new model of crustal-scale shear zone activity, where the whole body of the shear zone is active throughout its history (defined as the largest age difference through the section), i.e. the actively deforming zone does not get progressively narrower. The strain distribution nevertheless evolves with time, with an increasingly large fraction partitioned in the ultramylonitic core.
EGU General Assembly
Vienne, Austria

insu-00839320
https://hal-insu.archives-ouvertes.fr/insu-00839320
BIBCODE : 2010EGUGA..12.9881A

Éditeur(s) : HAL CCSD Oxford University Press
Résumé : International audience
The epigenetic events imposed during germline reprogramming and affected by harmful exposure can be inherited and transferred to subsequent generations via gametes inheritance. In this study, we examine the transgenerational effects promoted by widely used herbicide atrazine (ATZ). We exposed pregnant outbred CD1 female mice and the male progeny was crossed for three generations with untreated females. We demonstrate here that exposure to ATZ affects meiosis, spermiogenesis and reduces the spermatozoa number in the third generation (F3) male mice. We suggest that changes in testis cell types originate from modified transcriptional network in undifferentiated spermatogonia. Importantly, exposure to ATZ dramatically increases the number of transcripts with novel transcription initiation sites, spliced variants and alternative polyadenylation sites. We found the global decrease in H3K4me3 occupancy in the third generation males. The regions with altered H3K4me3 occupancy in F3 ATZ-derived males correspond to altered H3K4me3 occupancy of F1 generation and 74% of changed peaks in F3 generation are associated with enhancers. The regions with altered H3K4me3 occupancy are enriched in SP family and WT1 transcription factor binding sites. Our data suggest that the embryonic exposure to ATZ affects the development and the changes induced by ATZ are transferred up to three generations.
ISSN: 0305-1048

hal-01477213
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01477213
DOI : 10.1093/nar/gkw840
PUBMED : 27655631

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : We present whole-rock major- and trace-element and Nd–Sr–Pb radiogenic isotope data for Cretaceous igneous suites from eastern Cuba. These rocks are related to the Greater Antilles paleo-island arc magmatism and have three different igneous styles. Group 1 consists of tholeiitic basalts and rare basaltic andesites that have normal mid-ocean ridge basalt (N-MORB)-like compositions similar to those found in back-arc basin basalts (TiO2 = 1·2–2·9 wt%; La/Yb(N) = 0·7–0·9, Th/Nb = 0·06–0·08, and initial 208Pb/ 204Pb = 37·65–37·74). Group 2 comprises basaltic and rare basaltic andesitic subvolcanic dykes with major- and trace-element and isotopic compositions similar to those of island arc tholeiites (TiO2 = 0·7–1·4 wt%; La/Yb(N) = 0·6–0·9, Th/Nb = 0·06–0·68, and initial 208Pb/ 204Pb = 37·74–38·25). Group 3 is composed of low-Ti (TiO2 = 0·3–0·9 wt%) calcalkaline igneous rocks that have an unambiguous subduction-related character (La/Yb(N) = 1·1–5·0, Th/Nb = 0·35–1·55, and initial 208Pb/ 204Pb = 37·94–38·39). The parental magmas of the three groups formed by variable melting degrees (< 5–25%) of spinel lherzolite, with more depleted mantle sources for Groups 2 and 3 than Group 1. The trace-element and radiogenic isotope compositions of primitive Group 3 samples are strongly bimodal. One subgroup of samples is characterized by low Ta/Yb (0·02–0·03) and Th/La (0·10–0·13), slightly subchondritic Nb/Ta (13·3–17·3), and relatively high initial 206Pb/204Pb (18·57–18·62) and {varepsilon}Nd (7·6–9·4). The remaining primitive Group 3 samples have higher Ta/Yb (0·06–0·11) and Th/La (0·24–0·32), and highly subchondritic Nb/Ta (7·6–9·1), coupled with lower initial 206Pb/204Pb (18·24–18·29) and {varepsilon}Nd (3·4–5·5). These signatures were induced by two distinct slab components that mainly reflect the contributions of Cretaceous Atlantic marine and North American continental sediments, respectively. Nb/Ta in the first subgroup was influenced by melting of rutile-bearing subducted crust, whereas in the second it was inherited from recycled continental sediments. The involvement of Atlantic and North American sediments in Cuban Cretaceous magmatism indicates that the Proto-Caribbean (North American-Proto Atlantic) lithosphere subducted beneath the Greater Antilles arc during the Late Cretaceous (pre-Campanian), consistent with geotectonic models involving onset of SW-dipping subduction beneath the Greater Antilles paleo-arc during the Aptian. The variable mantle source depletion and magnitude of the subduction component probably reflect different settings across the arc, from the arc front to a back-arc spreading ridge.
ISSN: 0022-3530

hal-00406373
https://hal.archives-ouvertes.fr/hal-00406373
DOI : 10.1093/petrology/egm040

Éditeur(s) : HAL CCSD BMJ Publishing Group
Résumé : International audience
BACKGROUND: Mutations in the leucine-rich-repeat kinase 2 (LRRK2) gene have been identified in families with autosomal dominant Parkinson's disease (ADPD), the most common of which is the p.G2019S substitution that has been found at varying frequencies worldwide. Because of the size of the LRRK2 gene, few studies have analysed the entire gene in large series of ADPD families. METHODS: We performed extensive mutation analyses of all 51 coding exons of the LRRK2 gene in index cases from 226 Parkinson's disease families compatible with autosomal dominant inheritance, mostly from France (n = 182) and North Africa (n = 14). RESULTS: We found 79 sequence variants, 29 of which were novel. Eight potentially or proven pathogenic mutations were found in 22 probands (9.7%). There were four novel amino acid substitutions that are potentially pathogenic (p.S52F, p.N363S, p.I810V, p.R1325Q) and two novel variants, p.H1216R and p.T1410M, that are probably not causative. The common p.G2019S mutation was identified in 13 probands (5.8%) including six from North Africa (43%). The known heterozygous p.R1441H and p.I1371V mutations were found in two probands each, and the p.E334K variant was identified in one single patient. Most potentially or proven pathogenic mutations were located in the functional domains of the Lrrk2 protein. CONCLUSION: This study leads us to conclude that LRRK2 mutations are a common cause of autosomal dominant Parkinson's disease in Europe and North Africa.
ISSN: 0022-2593

inserm-00529272
http://www.hal.inserm.fr/inserm-00529272
DOI : 10.1136/jmg.2008.062612
PUBMED : 19357115

Éditeur(s) : HAL CCSD
Résumé : When the upper crust below the mountain ranges shows crustal extension with a direction collinear to the convergence direction, it is generally accepted that it is the result of gravitational collapse. However, recent studies challenge this paradigm by showing that erosion induces uplift and extension in the central part of the low convergent mountain ranges. In this study, we investigate the impact of denudation on the seismotectonic regime of mountain ranges.In order to identify a relationship between seismotectonic regime and erosion, the first part of this work presents a compilation of data in the mountain ranges. Based on these observations, a simple kinematic model is proposed to predict the seismotectonic regime of the study ranges.For low convergence rate and moderate mean elevation ranges, this model predicts an extension regime when the denudation rate is 15% higher than the convergence rate.The second part is devoted to the development of thermomechanical 2D finite element models to study the impact of surface processes on the deformation of the Pyrenees. The results show that the isostatic response to erosion reactivates pre-existing structures. The kinematics of an inherited fault plane can be predicted due to the gradient of the horizontal surface velocity profile. Thus, a plane located in the eroded zone is reactivated in normal fault when near the border of the erosion area, this same plane is reactivated in reverse fault. These results suggest that the current deformation in the North Pyrenean Zone could be the result of surface processes.Given the small number of studies quantifying erosion rates in the Pyrenees, the models developed in the second part suffer from high uncertainty. To remedy this, we study the central Pyrenees through a study that combines two types of data : watershed denudation rates from cosmogenic isotopes concentration, and incision rates from sediments buried in the karst. These results are presented in chapter 3. Denudation profiles obtained are consistent with reactivation of a normal fault plane located in the North Zone of the Central Pyrenees.From our study in the Pyrenees, a good correlation appears between the value of the rate of erosion and the glacier occupation. Given that the glaciers where more developed in the Alps, it raises the question of the impact of the late-würmian deglaciation on the present deformation of this range. A numerical model detailing this relationship is presented in the fourth chapter. Theresults show that deglaciation of the western Alps is controlled by the rheological heterogeneity of the crust. Some of our models predict uplift rates consistent with those highlighted by geodesy.
Lorsque l’extension de la croûte sous les parties hautes des chaînes de montagnes est colinéaire à la direction de convergence, il est traditionnellement admis que le moteur est l’effondrement gravitaire. Pourtant, des études récentes remettent en cause ce paradigme en montrant que l’érosion induit un soulèvement et de l’extension dans la partie centrale des chaînes de montagne à faible taux de convergence. L’objectif de notre étude est d’étudier l’impact de la dénudation de la topographie sur le régime sismo-tectonique des chaînes de montagnes.La première partie de ce travail présente une compilation de données dans les chaînes de montagnes afin de dégager des relations entre régime sismo-tectonique et érosion. Sur la base de ces observations, un modèle cinématique simple permettant de prévoir le régime de la chaîne est proposé. Ainsi, pour les chaînes à faible taux de convergence et d’élévation moyenne, ce modèleprédit de l’extension lorsque le taux de dénudation est 15% plus élevé que le taux de convergence.La deuxième partie est consacrée au développement d’un modèle thermo-mécanique 2D en éléments finis pour étudier l’impact des processus de surface sur la déformation des Pyrénées.Les résultats montrent que la réponse isostatique à l’érosion permet de réactiver des structurespré-existantes. La cinématique d’un plan de faille hérité peut être prédite grâce au gradient du profil des vitesses de surface horizontales. Ainsi, un plan situé dans la zone d’érosion est réactivé en faille normale alors qu’en bordure de cette zone une faille est réactivée en régime inverse. Ces résultats suggèrent que la déformation actuelle des Pyrénées pourrait être la conséquence d’unprocessus d’érosion.Compte tenu du faible nombre d’études quantifiant les taux d’érosion dans les Pyrénées, les modèles développés dans la deuxième partie souffrent d’une forte incertitude. Pour y remédier, nous avons cherché à les quantifier dans les Pyrénées Centrales grâce à une étude qui combine deux types de données : taux de dénudation des bassins versants à partir des isotopes cosmogéniques, et vitesses d’incision à partir des sédiments piégés dans les karsts. Ces résultats sontprésentés dans la troisième partie. Les profils de dénudation obtenus sont compatibles avec unrejeu en faille normale d’un plan situé dans la Zone Nord Pyrénéenne des Pyrénées Centrales.Notre étude dans les Pyrénées, montre une bonne corrélation entre la valeur du taux d’érosion et la cartographie de l’occupation glaciaire. Les glaciers ayant été plus développés dans les Alpes, cela pose la question de l’impact de la déglaciation tardi-Wurmienne sur la déformation actuelle de cette chaîne. Un modèle numérique détaillant cette relation est présenté dans le quatrième chapitre. Les résultats montrent que la déglaciation des Alpes occidentales est contrôléepar l’hétérogénéité rhéologique de la croute. Certains de nos modèles prédisent des vitesses de surrection compatibles avec celles mises en évidence par la géodésie.
https://hal.archives-ouvertes.fr/tel-01262333

tel-01262333
https://hal.archives-ouvertes.fr/tel-01262333
https://hal.archives-ouvertes.fr/tel-01262333/document
https://hal.archives-ouvertes.fr/tel-01262333/file/these-Genti-2015-postjury.pdf

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
Symbioses with the dinoflagellate Symbiodinium are widespread among marine invertebrates and protists, especially in nutritionally demanding habitats, such as tropical coral reefs, where they play a major role in ecosystem survival. Moreover, apart from corals and sea anemones, many of the Symbiodinium species and clades involved in these partnerships remain to be characterized. This study provides new insights into nudibranch and sponge associations with Symbiodinium by sequencing regions of the Symbiodinium 28S rDNA and the host mitochondrial COI oxidase. Specimens were sampled between 2011 and 2013 from locations around the islands of Moorea and Tahiti, French Polynesia. Our results revealed that some of the sponges and nudibranchs harbored typical Symbiodinium from clade B or C while others harbored new, undescribed Symbiodinium-like dinoflagellates. A detailed analysis of the different life stages of the nudibranch Phestilla lugubris and of its specific coral prey, Porites rus, suggests a prey-predator horizontal transfer of the symbiont and its vertical inheritance from the parent to the eggs.
Les symbioses à zooxanthelles, dinoflagellés du genre Symbiodinium, sont largement répandues chez les invertébrés marins et les protozoaires, notamment dans les eaux oligotrophes, où ils jouent un rôle important dans la survie des récifs coralliens. De plus, excepté chez les coraux et les anémones, les différentes espèces et clades de Symbiodinium impliqués dans ces associations restent à être caractérisés. Notre étude, grâce à l’utilisation des marqueurs génétiques 28S ADNr des Symbiodinium et la sous-unité 1 de la cytochrome oxydase mitochondriale (COI) de l’hôte, procure de nouvelles données quant aux associations des éponges et des nudibranches avec les Symbiodinium. L’échantillonnage a eu lieu autour de Moorea et de Tahiti (Polynésie française), entre 2011 et 2013. Nos résultats révèlent que certaines espèces d’éponges et de nudibranches possèdent les clades B et C communément retrouvés, chez les coraux notamment, alors que d’autres présentent de nouveaux dinoflagellés « Symbiodinium-like ». Une analyses détaillée des Symbiodinium à différents stades du cycle de vie du nudibranche corallivore Phestilla lugubris et de son corail hôte Porites rus suggèrent l’existence d’un transfert horizontal de Symbiodinium proie–prédateur et un transfert vertical du parent P. lugubris à ses œufs.
ISSN: 1631-0691

hal-01145518
https://hal.archives-ouvertes.fr/hal-01145518
DOI : 10.1016/j.crvi.2015.01.005

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
The within-population spatial structure of genetic diversity is shaped by demographic processes, including historical accidents such as forest perturbations. Information drawn from the analysis of the spatial distribution of genetic diversity is therefore inherently linked to demographic-historical processes that ultimately determine the fate of populations. All adult trees and saplings in a 1.4-ha plot within a mixed Norway spruce (Picea abies [L.] Karst) stand were characterised by means of chloroplast (paternally inherited) markers, and a large sub-sample of these were genotyped at mitochondrial (maternally inherited) molecular markers. These data were used to analyse the spatial distribution of genetic variation and to compare the patterns corresponding to the two marker types. The plot presented non-homogeneous local stem density in the younger cohorts, and the indirect effect of this source of variation on the spatial genetic structure was investigated. Results suggest that (i) spatially limited seed dispersal induced patchiness in genotype distribution, while pollen flow had a homogenising effect; (ii) deviations from random spatial structure were stronger in the demographically most stable portions of the stand, while they were weaker where sudden bursts of regeneration occurred; (iii) spatially overlapping adult and sapling cohorts displayed the same spatial genetic structure (stronger on stable areas, weaker in portions of the stand undergoing events of intense regeneration), which was substantiated by the influence of local demographic processes. Regeneration dynamics as modulated by demography thus influences the distribution of genetic diversity within the stand both in the younger life stages and in the adult population.
ISSN: 0378-1127

hal-01032063
https://hal.archives-ouvertes.fr/hal-01032063
DOI : 10.1016/j.foreco.2008.03.023