Éditeur(s) : Amer Geophysical Union
Résumé : The Algerian margin has originated from the opening of the Algerian basin about 25-30 Ma ago. The central margin provides evidence for large-scale normal faults of Oligo-Miocene age, whereas transcurrent tectonics characterizes the western margin. A set of NW-SE oriented dextral transform faults was active during basin opening and divided the 600 km long central margin into segments of similar to 120-150 km. The upper Miocene, Plio-Quaternary, and present-day tectonic setting is, however, compressional and supports the occurrence of a margin inversion, a process still poorly documented worldwide. We show that the central Algerian margin represents a rare example of inverted margin, where the process of subduction inception is particularly well expressed and helps understand how extensional and transtensive structures are involved in margin shortening. Using multibeam bathymetry and multichannel seismic reflection sections from the MAR-ADJA 2003 and 2005 cruises, we evidence Pliocene-Pleistocene shortening with contrasting styles along the margin between west (Khayr Al Din bank) and east (Boumerdes-Dellys margin) of Algiers. Pre-Miocene structures such as basement highs and transform faults appear to control changes of the deformation pattern along this part of the margin, resulting in different widths, geometries, and relative positions of folds and faults. Plio-Quaternary and active blind thrust faults do not reuse Oligo-Miocene normal and transform faults during inversion, but instead grow within the continental margin (as testified for instance by the 21 May 2003 M-w 6.8 Boumerdes-Zemmouri earthquake), at the foot of the continental slope and at the northern sides of basement highs interpreted as stretched continental blocks of the rifted margin. The inherited structures of the margin appear, therefore, to determine this deformation pattern and ultimately the earthquake and tsunami sizes offshore. The complex geometry of the fault system along the Algerian margin suggests a process of initiation of subduction in its central and eastern parts.
Tectonics (0278-7407) (Amer Geophysical Union), 2010-03 , Vol. 29 , N. TC2008 , P. 1-22

Droits : 2010 American Geophysical Union
http://archimer.ifremer.fr/doc/00008/11883/9286.pdf
http://archimer.ifremer.fr/doc/00008/11883/9287.pdf
DOI:10.1029/2009TC002547
http://archimer.ifremer.fr/doc/00008/11883/

Éditeur(s) : Elsevier
Résumé : High P-wave velocities (7.1-7.8 km/s) lower crustal bodies (LCBs) imaged along volcanic margins are commonly interpreted as plume and break-up-related thick mafic underplating. This interpretation is partly challenged in this paper based on new seismic observations and modelling of the outer Voring Basin (Norway). An exceptional strong amplitude reflection, the T Reflection, is particularly well defined below the North Gjallar Ridge (NGR) between 7 and 8 s TWT. The T Reflection is located near the volcanic lava flows emplaced during the NE Atlantic breakup (similar to 55-54 Ma ago) and coincides with the top of the LCB, forming a mid-crustal dome. Based on structural and temporal relationships, we show that the dome clearly influences the structural development of the NGR and predates the continental breakup at least by 10-15 Ma. Using a thermo-kinematical model, we tried also to investigate and quantify the relationships between the extension, LCB and the magmatic production. Modelling suggests that significant Paleocene-Early Eocene magmatism can be produced without any temperature anomaly in the mantle if differential stretching occurs during the break-up initiation. The conclusion of 2D thermo-kinematical parametric analysis is that the magmatic model predicts, either little extension (beta < 2) with no melting or high extension (beta > 5) with significant melting along the outer Voring Basin. We suggest that the continental part of the LCB could not necessarily be breakup-related and so magmatic, as has often been stated previously. It is concluded here that the continental part of the LCB observed beneath the outer Voring Basin may be partly (or fully) attributed to inherited, high-pressure granulite/eclogite lower crustal rocks. The real amount of mafic material emplaced along the outer Voring Basin could be 20-40% less than thought.
Tectonophysics (0040-1951) (Elsevier), 2006 , Vol. 412 , N. 3-4 , P. 255-278

Droits : 2005 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-1042.pdf
DOI:10.1016/j.tecto.2005.10.038
http://archimer.ifremer.fr/doc/00000/1042/

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 × 200 km2 area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15–18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a mid-lithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho but with a more slanting direction (NE–SW) compared to the NS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8–9 per cent. We relate this interface to melt ponding, possibly favouring here deformation process such as grain-boundary sliding (EAGBS) due to lithospheric strain. Its geometry might have been controlled by inherited lithospheric fabrics and heterogeneous upper mantle structure. We evidence that crustal and mantle magmatic processes represent first order mechanisms to ease and locate the deformation during the first stage of a cratonic lithospheric breakup.
ISSN: 0956-540X

hal-01622078
https://hal.archives-ouvertes.fr/hal-01622078
https://hal.archives-ouvertes.fr/hal-01622078/document
https://hal.archives-ouvertes.fr/hal-01622078/file/plasmanGJI2017.pdf
DOI : 10.1093/gji/ggx177

Éditeur(s) : HAL CCSD
Résumé : To understand the effect of inherited lithospheric structures on the continental plates deformation process, we have developed a multi scale model that explicitly takes into account an anisotropic viscosity due to the Crystal Preferred Orientation (CPO) of olivine in the mantle by coupling a viscoplastic self-consistent simulation of the deformation at the polycrystalline aggregate to a 3D Finite Element code. Using this tool, we calculate the mechanical behavior of a continental lithosphere submitted to extension for various initial structures. The first set of experiments investigates the deformation of a plate with a homogeneous initial olivine CPO. Results show that the macroscopic anisotropy is strongly dependent on the initial orientation of the olivine CPO relative to the solicitation and to its evolution. The second set of experiments aims to analyze the deformation of a continental plate containing pre-existing lithospheric scale shear zones. These multi-domain models show that the olivine mechanical anisotropy may induce the reactivation of pre-existing lithospheric scale shear zones in a plate submitted to rifting. In both cases, the results shows that the macroscopic mechanic anisotropy induced by the evolution of olivine CPO in the upper mantle is a key parameter to understand the deformation of the continental plates and to explain the observed reactivation of inherited structure from past tectonics events
Afin de comprendre l'effet des structures préexistantes sur la déformation des plaques continentales, nous avons développé une méthode de modélisation mécanique multi-échelle utilisant une viscosité anisotrope induite par les Orientations Préférentielles du Réseau (OPR) des cristaux d'olivine présents dans le manteau. Cette méthode en couple le calcul viscoplastique autocohérent de la déformation d'un agrégat d'olivine à un code éléments finis 3D. Elle a été utilisée pour le calcul du comportement mécanique d'une plaque continentale soumise à une extension. Une première série d'expériences numériques sur l'extension de plaque lithosphérique présentant des OPR initiales d'olivine homogènes a permis de montrer que l'anisotropie mécanique macroscopique est fortement dépendante de l'orientation initiale de l'OPR. La seconde série de simulations analyse l'extension d'une plaque continentale présentant une zone présentant des OPR d'olivine héritées d'un événement tectonique précédant. Les résultats de ces calculs multi-domaines que l'anisotropie mécanique de l'olivine peut expliquer la réactivation des zones de cisaillement héritées lors du rifting. Les résultats obtenus dans les deux séries de modèles montrent que l'anisotropie mécanique macroscopique induite par l'évolution des OPR d'olivine dans le manteau supérieur est un paramètre clé pour la compréhension de la déformation des plaques continentales et pour expliquer la réactivation observée de structures tectoniques, tels que les grands décrochements, lors des épisodes tectoniques ultérieurs.
https://tel.archives-ouvertes.fr/tel-00369463

tel-00369463
https://tel.archives-ouvertes.fr/tel-00369463
https://tel.archives-ouvertes.fr/tel-00369463/document
https://tel.archives-ouvertes.fr/tel-00369463/file/KnollThese09.pdf

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Reactivation of structures inherited from previous collisional or rifting events, especially lithospheric-scale faults, is a major feature of plate tectonics. Its expression ranges from continental break-up along ancient collisional belts(1,2) to linear arrays of intraplate magmatism and seismicity(3,4). Here we use multiscale numerical models to show that this reactivation can result from an anisotropic mechanical behaviour of the lithospheric mantle due to an inherited preferred orientation of olivine crystals. We explicitly consider an evolving anisotropic viscosity controlled by the orientation of olivine crystals in the mantle. We find that strain is localized in domains where shear stresses on the inherited mantle fabric are high, and that this leads to shearing parallel to the inherited fabric. During rifting, structural reactivation induced by anisotropy results in oblique extension, followed by either normal extension or failure. Our results suggest that anisotropic viscosity in the lithospheric mantle controls the location and orientation of intraplate deformation zones that may evolve into new plate boundaries, and causes long-lived lithospheric-scale wrench faults, contributing to the toroidal component of plate motions on Earth.
ISSN: 1752-0894

hal-00413033
https://hal.archives-ouvertes.fr/hal-00413033
DOI : 10.1038/ngeo528

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) : HAL CCSD
Résumé : International audience
In the external Western Alps, the collision started with the shortening of the proximal European (Dauphinois) margin. One peculiar feature is the crustal thickening that finally led to the exhumation of the basement External Crystalline Massifs (ECM) during the Neogene. In these massifs, various age of shortening, structural style and sequence of deformation have been proposed leading to different kinematics along the Alpine arc that in turn do not imply the same crustal/lithospheric strength. In this contribution, we present new structural and microstructural data along with Ar/Ar ages from field studies in the Oisans-Grandes Rousses massifs, between Grenoble and Briançon). From balanced cross-sections, we show that about half of the external zone crustal shortening is accommodated within the ECM with similar Ar/Ar ages in all massifs. Furthermore, the shear zones present very large thicknesses (several hundred meters) and do not reactivated either the inherited Liassic normal faults or the Variscan foliation. Finally, the main shortening structures are localized beneath inherited Liassic syn-rift basins. These results suggest that the crust was weak during its shortening. Such behavior is most likely due to the combination of several factors: the crust burial (below the overthrusting internal units) down to about 10km, the presence of weak inherited syn-rift basins, and the strain softening in shear zones that evolve in mica-rich phyllonites. These results are consistent with the studies in the Aar massif and should most likely apply to the Mont Blanc massif, whose relationships with its cover are still debated.
EGU General Assembly
Vienne, Austria

insu-00839426
https://hal-insu.archives-ouvertes.fr/insu-00839426
BIBCODE : 2013EGUGA..15.8837B

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : La venue de Benoît XVI à Cuba du 26 au 28 mars 2012 a représenté un temps fort de la vie politique de l’île. Si cette rencontre n’a pas eu la même portée que celle de Jean Paul II en 1998 et qu’aucune déclaration cruciale n’a marqué la visite papale, elle n’en demeure pas moins un événement diplomatique majeur révélateur des évolutions historiques à l’œuvre au sein de l’Église catholique et de la société cubaine. L’absence de discours politique critique d’un pape à la réputation anticommuniste a surpris les journalistes occidentaux. Ceux-ci n’en ont tiré aucune conclusion. Pourtant, les silences du souverain pontife montrent la volonté du Vatican de pallier aux faiblesses structurelles de l’Église catholique cubaine héritée du XIXème siècle tandis que l’accueil réservé par l’administration cubaine rend manifeste la volonté des autorités d’inclure les croyants dans une Patrie cubaine dont ils furent longtemps exclus. Cet article tente de revenir, à partir d’une enquête de terrain minutieuse, sur les implications des discours des différents acteurs au cours de cette rencontre.
The arrival of Benedict XVI to Cuba from March 26 to 28, 2012 represented a high point in the political life of the island. If this meeting does not have the same scope as that of John Paul II in 1998 and no critical statement marked the papal visit, it nonetheless reveals a major diplomatic event of historical developments in work within the Catholic Church and the Cuban society. The lack of critical political discourse of a pope to anti reputation which surprised Western journalists. They do not have any conclusion. Yet the silence of the Pope will show the Vatican to overcome the structural weaknesses of the Cuban Catholic Church inherited from the nineteenth century while the reception by the Cuban government makes manifest the will of the authorities to include believers in Cuban homeland whose they were long excluded. This article attempts to come back from a thorough field investigation on the implications of the speeches of the various actors in this game.
La visita de Benedicto XVI a Cuba, del 26 al 28 de marzo de 2012, representó un momento clave de la política cubana. Aunque no tuvo el mismo impacto que la visita de Juan Pablo II y ninguna declaración crucial marcó la visita papal, constituye un acontecimiento diplomático de suma importancia revelador de las evoluciones históricas que tienen lugar en el seno de la iglesia católica y la sociedad cubana. La ausencia de un discurso político de un papa de reputación anticomunista sorprendió a los periodistas occidentales. Estos últimos no se pronunciaron al respecto. Sin embargo, los silencios del soberano pontífice muestran la voluntad del Vaticano de paliar las debilidades estructurales de la iglesia católica cubana heredadas del siglo XIX. La acogida de la administración cubana, por su parte, revela la voluntad de las autoridades de incluir a los creyentes en una patria cubana de la cual fueron excluidos durante largo tiempo. Este artículo pretende abordar, a partir de una investigación minuciosa en Cuba, las implicaciones de los discursos de los diferentes actores durante este encuentro.
Cuba

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.6146
http://journals.openedition.org/etudescaribeennes/6146

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The present-day topography of the Tian Shan range is considered to result from crustal shortening related to the ongoing India-Asia collision that started in the early Tertiary. In this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event. Apatite fission track analysis and (U-Th)/He dating on apatite and zircon indicate that inherited Paleozoic structures were reactivated in the late Paleozoic-early Mesozoic during a Cimmerian orogenic episode and also in the Late Cretaceous-Paleogene (around 65-60 Ma). These reactivations could have resulted from the accretion of the Kohistan-Dras arc or lithospheric extension in the Siberia-Mongolia zone. Activity resumed in the late Mesozoic prior to the major Tertiary orogenic phase. Finally, the ongoing deformation, which again reactivates inherited tectonic structures, tends to propagate inside the endoreic basins that were preserved in the range, leading to their progressive closure. This study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas.
ISSN: 0278-7407

Droits : info:eu-repo/semantics/OpenAccess
hal-00551323
https://hal.archives-ouvertes.fr/hal-00551323
https://hal.archives-ouvertes.fr/hal-00551323/document
https://hal.archives-ouvertes.fr/hal-00551323/file/2010TC002712.pdf
DOI : 10.1029/2010TC002712

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 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) : 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 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) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We use lithospheric-scale analog models to study the reactivation of pre-existing heterogeneities under oblique shortening and its relation to the origin of arcuate orogens. Reactivation of inherited rheological heterogeneities is an important mechanism for localization of deformation in compressional settings and consequent initiation of contractional structures during orogenesis. However, the presence of an inherited heterogeneity in the lithosphere is in itself not sufficient for its reactivation once the continental lithosphere is shortened. The heterogeneity orientation is important in determining if reactivation occurs and to which extent. This study aims at giving insights on this process by means of analog experiments in which a linear lithospheric heterogeneity trends with various angles to the shortening direction. In particular, the key parameter investigated is the orientation (angle α) of a strong domain (SD) with respect to the shortening direction. Experimental results show that angles α ≥ 75° (high obliquity) allow for reactivation along the entire SD and the development of a linear orogen. For α ≤ 60° (low obliquity) the models are characterized by the development of an arcuate orogen, with the SD remaining partially non-reactivated. These results provide a new mechanism for the origin of some arcuate orogens, in which orocline formation was not driven by indentation or subduction processes, but by oblique shortening of inherited heterogeneities, as exemplified by the Ouachita orogen of the southern U.S.
ISSN: 0278-7407

insu-01498544
https://hal-insu.archives-ouvertes.fr/insu-01498544
https://hal-insu.archives-ouvertes.fr/insu-01498544/document
https://hal-insu.archives-ouvertes.fr/insu-01498544/file/Calignano_et_al-2017-Tectonics.pdf
DOI : 10.1002/2016TC004424

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
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 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

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) : Agrocampus Ouest
Résumé : The origin of fish stocks variability is a key question in fisheries science. The exploitation indeed has an important effect in terms of biomass reduction, but environmental forcing is of central interest as it affects numerous key biological processes. Recent theoretical results have shown that the nature of the environmental fluctuations, the environmental noise, has important ecological consequences on populations and particularly on their fluctuations. In addition the effects of exploitation, that are not a simple removal of individuals but also profoundly modifies the demography, the structure and the trophic interactions of fish stocks, can interact with environmental effects. Through an extensive analysis of time series we aim at understanding the effects of environmental noise on fish stocks variability, according to their biological characteristics (life-history traits) and their exploitation. A technique of time series comparison allows to propose that the fluctuations of Atlantic large pelagics are inherited from the interaction between environmental effects, endogenous dynamics and exploitation. We then show that the colour of environmental noise affects the variability of time series, its effects depending on the life-history traits of species. Finally, preliminary results on bentho-demersal and pelagic stocks from the North Atlantic suggest that the exploitation increases the sensitivity of fish stocks to the colour of environmental noise and affects their variability, according to their life-history traits.
L'origine de la variabilité des stocks de pêche est une question centrale en halieutique. Si l'exploitation tient un rôle important dans la réduction de biomasse, le forçage environnemental affecte de nombreux processus biologiques clés. Des résultats théoriques récents ont montré que la nature des fluctuations environnementales, la couleur du bruit environnemental, avait des implications écologiques importantes sur les populations et notamment sur leurs fluctuations. De plus, les effets environnementaux peuvent agir en interaction avec l'exploitation qui ne consiste pas en un simple prélèvement d'individus, mais qui modifie profondément la démographie, la structure et les interactions trophiques des stocks. Au travers de l'analyse extensive de séries temporelles, on essaye ici de comprendre les effets de la couleur du bruit environnemental sur la variabilité des stocks en fonction de leurs caractéristiques biologiques (traits d'histoire de vie) et de leur état d'exploitation. Le développement d'une technique de comparaison des séries temporelles permet de proposer que les fluctuations des grands pélagiques de l'Atlantique sont héritées de l'interaction entre effets environnementaux, dynamique interne et dynamique de l'exploitation. On montre ensuite que la couleur du bruit environnemental affecte la variabilité des séries temporelles, mais que son effet dépend des traits d'histoire de vie des espèces. Enfin, des résultats préliminaires sur les stocks bentho-démersaux et pélagiques de l'Atlantique Nord, suggèrent que l'exploitation augmente la sensibilité des stocks à la couleur du bruit environnemental et affecte leur variabilité en fonction de leurs traits d'histoire de vie.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2008/these-6596.pdf
http://archimer.ifremer.fr/doc/00000/6596/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fromthe Proterozoic to the Quaternary, the evolution of the Earthwas characterised by recurrent periods of glaciation.However, the margins of many ancient ice-sheets are poorly defined on palaeogeographic reconstructions.The extent and outlines of ancient ice sheets can be better understood through careful documentation ofsediments deposited at the ice-sheet margin. An outstanding example is provided herein based on an end-Ordovician archive in Libya (Tihemboka area, Murzuq Basin). The four sets of structures include: i) subglacialglaciotectonic structures and soft sediment deformations from flowing glacier ice, such as intraformational glacialstriae, intraformational deformation (shear planes, sheath folds), normal microfaults, and large-scaleglaciotectonic folds-and-thrusts; (ii) structures resulting from overpressured subglacial (meltwater) flowssuch as clastic dykes and tunnel valleys; (iii) proglacial depositional structures and facies related to highmagnitudemeltwater floods such as sandstone intraclasts, large-scale bedforms resulting from supercriticalflows, climbing-dune cross-stratification and kettle holes; and (iv) deformation structures resulting from freefloating and nonglacier ice such as ice-keel scours and ice-crystal marks. Such a set of structures points to anice-marginal (essentially continental) depositional setting, and provides an excellent suite of criteria to identifymargins of ancient ice sheets in the stratigraphic record. At a regional scale, a reconstruction through time andspace of the related depositional wedge is proposed. This corresponded to a seismic-scale (N120 m in thickness,40 km in length) ice-marginal wedge in front of an essentially warm-based ice-sheet inducing concomitantlarge-scale glaciotectonic deformation, glacial basin and tunnel valley downcuttings. The related ice-front wasassociated with high-energy meltwater flows feeding a network of deeply incised proglacial channels downstreamand, beyond them, a fluvioglacial deltaic system. Shallow ice-marginal permafrost most likely affectedthe depositional wedge. At a larger scale, the Tihemboka ice-marginal wedge is interpreted as related to a stillstandperiod over the Gondwana platform, developed over an estimated interval of a few thousands of years.Based on these data, the conditions that arose in a particularly favourable context for the development, the preservationand the identification of ice-marginal wedges in the geological record are reviewed. Significantmeltwater-derived sediment deposition and aggradation in an accommodation space resulting either frompreglacial inheritance, glacial downcuttings and/or glacio-isostatic lithospheric flexure, or active tectonic subsidence(>1 Myr) are required for their formation and subsequent preservation.
ISSN: 0012-8252

insu-01184739
https://hal-insu.archives-ouvertes.fr/insu-01184739
DOI : 10.1016/j.earscirev.2015.06.006