Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : We propose to assess the error done when temperature is considered as a conservative tracer in fluviokarst studies. As a matter of fact, heat exchanges occur between karstic Conduit System (CS) and Porous Fractured Matrix (PFM) that prevents from using this approximation without caution. The conservative tracer approximation boils down to consider the cooling of CS water by PFM flow in an open thermodynamic system where the CS is bounded by an Adiabatic Wall (AW). The resulting CS water temperature contrasts with the one obtained from more complete models (CW), which also take into account heat conduction within the CS, within the PFM, and from the CS to PFM through CS a Conductive Wall. In order to assess first orders of this error, the dimensionless equations, characteristic of CS cooling by PFM, have been solved thanks to Alternate Finite Difference Implicit methods both in AW and CW configurations. Four groups of dimensionless numbers appear in the various terms of energy and mass equations among which the Peclet and Reynolds numbers depict the large morphologic and hydrologic variability of natural karstic systems. A parametric exploration of the differences between AW and CW models has then been conducted vs. Peclet numbers (Pe numbers varying from 106 to 109, at constant CS Reynolds number) and vs. Reynolds numbers (Red varying from 103 to 107, at constant Peclet number). The error curves bound finite volumes in the Peclet–Reynolds space that converge uniformly to zero for the extreme values of these parameters. However, for Peclet and Reynolds numbers characteristic of realistic fluviokarst configurations, the errors reach finite values, that give first order information assessing the error done by considering temperatures as conservative tracers. Maximum relative errors around 10−2 (in fact 0.0092) have been found varying Pe; while it remained slightly lower than 0.7 × 10−2 varying Red. An illustrative example of the temperature conservative tracer AW approximation is presented with the data obtained from the main morphologic and hydrologic properties of the Cent–Font resurgence (Hérault, France). According to the results, the error reached at the output of the fluviokarst is 0.00613 (for Pe = 1.4993 × 108 and Red = 4.2969 × 104). When rescaled to the physical domain, this error leads to a temperature difference of 1.77 K between the CW and AW configurations.
ISSN: 1812-2108

hal-01358348
https://hal.archives-ouvertes.fr/hal-01358348
https://hal.archives-ouvertes.fr/hal-01358348/document
https://hal.archives-ouvertes.fr/hal-01358348/file/hessd-11-169-2014.pdf
DOI : 10.5194/hessd-11-169-2014

Éditeur(s) : Academia Brasileira de Ciencias
Résumé : During the Geobrésil cruise of the R. V. Jean Charcot (1973) several marine geophysical lines, including bathymetry, magnetism, continuous seismic as well as sonobuoy profiles have been run across a deep marginal plateau extending on the southeastern Brazilian margin and known as the Sao Paulo Plateau. These data indicate the presence of a thick sedimentary cover (more than 4s DTT) on the upper slope and up to 3s DTT thick on the lower slope and rise. The entire slope is highly disturbed by salt diapiric structures mostly apparent between the 2 000-3 000 bathymetriclines and comparable to the ones described in the western Mediterranean sea. The Sao Paulo scarp, bordering the deep marginal plateau to the South-West, is believed to be a discontinuous and "en échelon» structure probably related to numerous and closely spaced early fracture zones. The overal structures Of two areas - the Sao Paulo and the Angolan margin - are briefly cOmpared and Preliminary results of DSDP holes 356 and 364 suggest a similar sedimentary history, during mesozoic times, for both margins. [NOT CONTROLLED OCR]
Anais da Academia Brasileira de Ciencias (Academia Brasileira de Ciencias), 1976 , Vol. 48 , N. Supp. , P. 187-198

Droits : Academia Brasileira de Ciencias
http://archimer.ifremer.fr/doc/1976/publication-4990.pdf
http://archimer.ifremer.fr/doc/00000/4990/

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Progress in seismic methodology and ambitious large-scale seismic projects are enabling high-resolution imaging of the continental crust. The ability to constrain interpretations of crustal seismic data is based on laboratory measurements on rock samples and calculations of seismic properties. Seismic velocity calculations and their directional dependence are based on the rock microfabric, which consists of mineral aggregate properties including crystallographic preferred orientation (CPO), grain shape and distribution, grain boundary distribution, and misorientation within grains. Single-mineral elastic constants and density are crucial for predicting seismic velocities, preferably at conditions that span the crust. However, high-temperature and high-pressure elastic constant data are not as common as those determined at standard temperature and pressure (STP; atmospheric conditions). Continental crust has a very diverse mineral composition; however, a select number of minerals appear to dominate seismic properties because of their high-volume fraction contribution. Calculations of microfabric-based seismic properties and anisotropy are performed with averaging methods that in their simplest form takes into account the CPO and modal mineral composition, and corresponding single crystal elastic constants. More complex methods can take into account other microstructural characteristics, including the grain shape and distribution of mineral grains and cracks and pores. Dynamic or active wave propagation schemes have recently been developed, which offer a complementary method to existing static averaging methods generally based on the use of the Christoffel equation. A challenge for the geophysics and rock physics communities is the separation of intrinsic factors affecting seismic anisotropy, due to properties of crystals within a rock and apparent sources due to extrinsic factors like cracks, fractures, and alteration. This is of particular importance when trying to deduce crustal composition and the state of deformation from seismic parameters.
ISSN: 8755-1209

Droits : info:eu-repo/semantics/OpenAccess
hal-01685568
https://hal.archives-ouvertes.fr/hal-01685568
https://hal.archives-ouvertes.fr/hal-01685568/document
https://hal.archives-ouvertes.fr/hal-01685568/file/Almqvist_et_al-2017-Reviewssur Geophysics.pdf
DOI : 10.1002/2016RG000552

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The brittle structures of a Hercynian granite (La Borne, French Massif Central) observed at several scales, from regional to microscopic, are presented and interpreted on mechanical terms. Emphasis is placed on strike slip faults, joints, and cracks related to incipient shear fracturing during horizontal compression. Three compressive tectonic phases have been identified according to their brittle structures and characterised by the burial depth at the time of their generation.The two first phases (H1, H2) are Hercynian and occurred while the granite was deeply buried (∼5 to 3 km depth) whereas the last phase (P) is Pyrenean and occurred at very low depth. The geometric organizations of cracks, joints and faults are clearly similar at various scales from about 10 μm to several m.These field observations are strong arguments for the occurrence of shear structures at microscopic to macroscopic scales during tectonic events. Following this inference, it is proposed that, at least in the case of Hercynian phases, cracks, joints and macroscopic strike slip faults have been generated by the same mechanical process under high overburden weight. Therefore, incipient fractures seem to be generated as shearing structures and to evolve by coalescence with neighbouring ones with the same direction.
ISSN: 0191-8141

hal-01115718
https://hal.archives-ouvertes.fr/hal-01115718
DOI : 10.1016/j.jsg.2014.05.002

Éditeur(s) : Elsevier Science Bv
Résumé : The opening of the Equatorial and South Atlantic Oceans is still a matter of debate, particularly as concerns the locations of the intraplate deformation. We propose here a critical review of the kinematic models published since Bullard et al., 1965, based on a series of constraints: new interpretation of the magnetic anomalies, seafloor isochrons, flow lines, fracture zones, continental and oceanic homologous structures and radiometric dating of igneous rocks. All of these models present numerous unexplained misfits (gaps, overlaps and misalignments). We present here a new evolution of the Equatorial and South Atlantic Ocean from the tightest reconstruction to Chron C34. This new model confirms the hypothesis of a northward propagation of the South American deformation proposed by Eagles, but rejuvenates slightly the ages for this propagation and refines the plate reconstructions. In particular, we highlight the role of the kinematic "buffer" Santos block, located between the salty Aptian Central segment in the North and the Volcanic Hauterivian Austral segment in the South. The new initial fit presented in this study represents the tightest reconstruction that could be obtained and constitutes the base canvas on which the problem of the continental margin genesis should be addressed.
Earth Science Reviews (0012-8252) (Elsevier Science Bv), 2010 , Vol. 98 , N. 1-2 , P. 1-37

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00000/11160/7883.pdf
DOI:10.1016/j.earscirev.2009.08.001
http://archimer.ifremer.fr/doc/00000/11160/

Éditeur(s) : HAL CCSD Springer
Résumé : The analysis of three different regions of the South- Pyrenean fold-and-thrust belt reveals that during the Tertiary compression the hydrological system was compartmentalised in time and space. During the early-middle Eocene, when the thrust front affected marine soft-sediments in the Ainsa basin, the thrust fault zones were dominated by formation fluids derived from Eocene marine waters trapped in the underlying Eocene marls, although influences of meteoric waters were also present. During the middle-late Eocene, when the thrust front emplaced marine rocks over continental redbeds in the eastern Catalan basin (L'Escala thrust), the thrust fault zones were dominated by meteoric fluids. These fluids flowed preferentially along these faults, draining laterally the meteoric fluids and acting as barriers hindering their flowing towards more external parts of the belt. During the Oligocene, the most external part of the fold-and-thrust belt in the eastern Catalan basin developed on top of a salt detachment horizon. The thrust front affected continental materials of late Eocene-Oligocene age. At this moment, the thrusts were conduits for meteoric fluids arriving from the surface and also for evolved meteoric fluids migrating over short distance upwards after being in contact with the underlying evaporitic beds. Most of the fractures show a similar sequence of microfractures. Microfractures of stage 1 formed when the sediment was poorly lithified. Microfractures of stage 2 represent the main episode of vein formation which developed when a progressive induration of the host sediment occurred. During microfracture stage 3, formed in an extensional regime, the host sediment was more indurated. The repetition of this sequence of microfractures in different fracture generations of the same outcrop indicates that the sediment induration was restricted to the vicinity of the vein. Away from the veins, the sediment remained poorly lithified during the entire deformation cycle. Calcite cement within the host rock precipitated later than the syn-compressive veins, when the sediment was more indurated. Elemental geochemistry and stable isotopes of the calcite veins indicates that early generation of microfractures is infilled by local fluids (either marine or meteoric), whereas external fluids (meteoric or evolved meteoric) infilled the main compressive stage of microfractures. The hot temperature of these fluids (157°C to 183°C in the Atiart-Arro example) indicates their circulation through deep parts of the thrust belt. The progressive increase of the 87Sr/86Sr ratio through time is due to the progressive uplift, exposure and erosion of the internal Pyrenean Axial Zone.
Thrust belts and foreland basins, from fold kinematics to hydrocarbon systems

hal-00408001
https://hal.archives-ouvertes.fr/hal-00408001
DOI : 10.1007/978-3-540-69426-7_5

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
We explore the tectono-magmatic processes in the western West Philippine Basin, Philippine Sea Plate, using bathymetric data acquired in 2003 and 2004. The northwestern part of the basin formed through a series of northwestward propagating rifts. We identify at least five sequences of propagating rifts, probably triggered by mantle flow away from the mantle thermal anomaly that is responsible for the origin of the Benham and Urdenata plateaus. Gravitational forces caused by along-axis topographic gradient and a ∼30° ridge reorientation appear to also be driving the rift propagations. The along-axis mantle flow appears to be reduced and deflected along the Luzon-Okinawa fracture zone, because the spreading system remained stable west of this major fault zone. North-east of the Benham plateau, a left-lateral fracture zone has turned into a NE–SW-trending spreading axis. As a result, a microplate developed at the triple junction.
ISSN: 0954-4879

insu-00304360
https://hal-insu.archives-ouvertes.fr/insu-00304360
DOI : 10.1111/j.1365-3121.2008.00824.x

Éditeur(s) : HAL CCSD
Résumé : To study the dynamics of an orogen-foreland system and more particularly the impact of surface processes on its development, we base our work on two main axes. In a first part, using analogue tapered wedge models, we investigate the interplay between tectonics, erosion and sedimentation during the orogenic growth. The basis model mimics the evolution of a wedge section extending from the orogen to its foreland basin, with both the structural and the lithological heritages simulated. In a second part, the focus is on the recent tectonic and geomorphologic processes affecting the Swiss Prealpes klippen belt and surrounding structural units (Molasse basin and Jura fold-and-thrust belt). Remote sensing analyses allow to evaluate the impact of tectonics on the drainage pattern and landscape morphology. In addition, local field investigations in the Prealpes provide information on the nature and kinematic of brittle fractures and the paleostress fields.
Afin d'étudier la dynamique d'un système orogène/avant-pays et plus particulièrement l'impact des processus de surface sur son développement, notre travail se base sur deux axes principaux. Dans une première partie, à l'aide de modèles analogiques de prisme d'accrétion, nous analysons les interactions entre la tectonique, l'érosion et la sédimentation au cours de la croissance de l'orogène. Le modèle de base reproduit l'évolution d'une section de prisme, qui s'étend de l'orogène au bassin d'avant-pays, et où les héritages à la fois structural et lithologique sont simulés. Dans une seconde partie, l'accent est mis sur la tectonique récente et les processus géomorphologiques qui affectent la klippe des Préalpes suisses et les unités structurales environnantes (le bassin molassique et le Jura). Des analyses de télédétection permettent d'évaluer l'influence de la tectonique sur le réseau de drainage et la morphologie du paysage. De plus, des analyses de terrain menées localement dans les Préalpes fournissent des informations sur la nature et la cinématique des fractures cassantes et des champs de paléocontraintes.
https://tel.archives-ouvertes.fr/tel-00138836

tel-00138836
https://tel.archives-ouvertes.fr/tel-00138836
https://tel.archives-ouvertes.fr/tel-00138836/document
https://tel.archives-ouvertes.fr/tel-00138836/file/These_Bonnet_2007.pdf

Éditeur(s) : Elsevier
Résumé : We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysis of the combined dataset accurately highlights those portions of the seafloor shaped by active tectonic, depositional and/or erosional processes. The greatest slope gradients are located in the frontal 30 km of the forearc, at the toe of the accretionary wedge. This suggests that long-term deformation rates are highest here and that probably only minor amounts of slip are accommodated by other thrust faults further landward. Obvious N-S oriented lineaments observed on the incoming oceanic plate are aligned sub-parallel to the fracture zones associated with the Wharton fossil spreading center. Active strike-slip motion is suggested by recent deformation with up to 20-30 m of vertical offset. The intersection of these N-S elongated bathymetric scarps with the accretionary wedge partly controls the geometry of thrust anticlines and the location of erosional features (e.g. slide scars, canyons) at the wedge toe. Our interpretation suggests that these N-S lineaments have a significant impact on the oceanic plate, the toe of the wedge and further landward in the wedge. Finally, the bathymetric data indicate that folding at the front of the accretionary wedge occurs primarily along landward-vergent (seaward-dipping) thrusts, all unusual style in accretionary wedges worldwide. The N-S elongated lineaments locally act as boundaries between zones with predominant seaward versus landward vergence.
Earth and Planetary Science Letters (0012-821X) (Elsevier), 2008-11 , Vol. 275 , N. 3-4 , P. 201-210

Droits : 2008 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2008/publication-5166.pdf
DOI:10.1016/j.epsl.2008.04.053
http://archimer.ifremer.fr/doc/00000/5166/

Éditeur(s) : Université de Bretagne Occidentale
Résumé : ln Java island, a number of quaternary volcanoes are Iocated in a back-arc position relative to the Sunda arc volcanie axis. These volcanie centers show an important variability in the petrologic composition of their products (potassic calc-alkali, shoshonitie, alkali potassie and alkali u/trapotassie leucitic series).
L'île de Java comporte, à l'arrière de l'axe volcanique de l'arc de la Sonde, un grand nombre de volcans quaternaires dont les laves présentent une grande diversité pétrologique (séries calco-alcalines potassiques, shoshonitiques, alcalines potassiques, alcalines ultrapotassiques à leucite). Ces édifices arrière-arc, mis en place à la faveur de fractures majeures obliques par rapport à l'axe de l'arc, se situent à des distances très variables de la fosse (profondeurs du plan de Benioff comprises entre 200 et 650 km). Le but de ce travail est la caractérisation géochimique (éléments en trace et isotopes Sr-Nd-Pb) des laves arrière-arc de cette région, leur comparaison avec celles des magmas de l'axe de l'arc, et la discussion de l'origine des variations observées.

Droits : UBO
http://archimer.ifremer.fr/doc/00034/14540/11815.pdf
http://archimer.ifremer.fr/doc/00034/14540/

Éditeur(s) : American Geophysical Union
Résumé : The Fairway Ridge is a buried continental structure that separates the Fairway Basin from the New Caledonia Basin. The proposed Cretaceous age of the Fairway Basin has remained highly hypothetical to date. Deep offshore petroleum exploration wells revealed well-dated Mesozoic carbonaceous sedimentary rocks in the Taranaki Basin at the southern end of the Aotea Basin. In this paper we use geophysical data to confirm the continuity of the 2000 km long Fairway-Aotea Basin connecting New Caledonia to New Zealand and prove its early Late Cretaceous age. Analysis of seismic reflection profiles together with newly compiled gravity and magnetic maps reveals Late Cretaceous NE–SW trending lineaments projecting northeastward from major Tasman Sea fracture zones and the Bellona Trough, which demonstrate that the opening of the Fairway-Aotea Basin predates the opening of the Tasman Sea. This result combined with observations of the Mesozoic regional geology suggests that the Lord Howe, Fairway, and Norfolk ridges are part of a remnant late Early Cretaceous continental arc, which was fragmented into three pieces by the late Early to early Late Cretaceous. This event might be contemporaneous with a plate motion change between the Gondwana and Pacific plates and/or the arrival of the Hikurangi plateau in the subduction zone around 105 Ma, which caused the cessation of subduction along this plate boundary. We interpret either of those two events as being possible trigger events for the post–Early Cretaceous fragmentation of the eastern Gondwana margin in a slab retreat process.
Geochemistry Geophysics Geosystems - G3 (1525-2027) (American Geophysical Union), 2009-12 , Vol. 10 , N. 12 , P. 1-24

Droits : 2009 American Geophysical Union
http://archimer.ifremer.fr/doc/2009/publication-7322.pdf
DOI:10.1029/2009GC002612
http://archimer.ifremer.fr/doc/00000/7322/

Éditeur(s) : HAL CCSD
Résumé : Juin 2003
Dans le contexte actuel de mondialisation, de changement climatique et de forte anthropisation de la biosphère, les Petites Antilles s'érigent en monde marginal ou encore en anti-monde. Fracturées du point de vue politique, économique, linguistique et à certains égards culturel, ces territoires insulaires du Bassin caraïbe recèlent de richesses environnementales (physiques, écosystèmiques et paysagères). Comme partout ailleurs dans le monde humanisé, la survie de ces sociétés implique le rétablissement des grands équilibres écologiques consubstantiels à une articulation efficiente entre le naturel, l'urbain et l'agricole. Compte tenu de la pression démographique, variable d'une île à l'autre, la pérennité des écosystèmes en covariance avec un développement économique profitant au plus grand nombre ne peut se concevoir à l'échelle insulaire. Il semble judicieux d'imaginer un développement à l'échelle de l'archipel basé sur la complémentarité, puisque au sein de chaque composante les diverses ressources biologiques terrestres et marines sont insuffisantes pour assurer une autosuffisance en termes de produits de premières nécessités et d'énergie. Le développement des Petites Antilles s'il doit être durable et prendre comme ossature les directives de Rio (Brésil, 1992) et de Johannesburg (Afrique du Sud, 2002), il devra s'inscrire dans une gestion administrative, scientifique, technique et agricole commune dans le cadre d'une Caraïbe fonctionnellement unifiée. A l'unité floristique, faunistique et biocénotique doivent correspondre des stratégies et donc des politiques, similaires mais diversifiées, d'utilisation des ressources abiotiques (énergie éolienne, hydroélectrique et photovoltaïque) et biotiques (écosystèmes terrestres et marins, flore, faune, sols). Malheureusement dans le présent, la compartimentation économique et politique de la Caraïbe rend ces propos profondément utopiques. Néanmoins dans le futur la survie des peuples des Petites Antilles, impliquera un développement durable signifié par des rapports équilibrés entre hommes et milieux.
–––––
In the nowadays context of "globalization", climatic variation and great anthropization of the biosphere, the Lesser Antilles appear as a marginal world. In a political point of view, those islands offer a greatly distinct and fractured image. The same fact can also be observed in an economic, linguistic and, in a certain measure, cultural perspective. Despite of such a statement, those territories of the Caribbean basin keep economic and landscape resources whom survival depends on the re-establishment of the great ecologic structures implying a productive articulation between the natural, the urban and the agricultural. It seems pertinent to imagine a development on the level of the archipelago based upon complementarity since each constituent presents a limited number of earth and marine biologic reserves which do not guarantee an autosubsistance in energy and first nessecity productivity. A lasting development of the Lesser Antilles supposes a necessary and commun administrative, scientific, technical and agricultural management within the setting of a Caribbean functionally unified. Facing the biocenotic unity, a useful strategy, based on a similar and diversified organization in the exploitation of biophisic resources, must be erected. Such statements could be considered as utopic, regarding the situation of politic and economic division in the Caribbean nowadays. However, in the future, the survival of those insular societies will imply a lasting development lying upon an efficient relationship between Man and environment.
https://halshs.archives-ouvertes.fr/halshs-00003054

Droits : info:eu-repo/semantics/OpenAccess
halshs-00003054
https://halshs.archives-ouvertes.fr/halshs-00003054
https://halshs.archives-ouvertes.fr/halshs-00003054/document
https://halshs.archives-ouvertes.fr/halshs-00003054/file/Devpt-durable_JOSEPH-PHILIPPE.pdf

Éditeur(s) : HAL CCSD
Résumé : This historical perspective provides an overall view of the main steps that led to the acceptance of the concept of mantle exhumation accompanying lithosphere stretching and extreme crustal thinning. We first remember that the presence of exposures of mantle rocks along oceanic spreading ridges was early reported in the 60's due to the results of sediment cores and dredge hauls collected along the Mid-Atlantic Ridge. In the meantime, detailed analysis of the relationships between oceanic sediments of Late Jurassic age and their primary basement in the Apennine ophiolites led many authors to point to the importance of exhumation of mantle rocks on ancient seafloors. By contrast to the thick sections of classical ophiolites (e.g. Oman), the Alpine-Corsican-Appennine ophiolites are characterized by a relatively small amount of mafic rocks (gabbros and basalts), by the absence of any sheeted dyke complex and by the frequent occurrence of oceanic sediments stratigraphically overlying mantle-derived peridotites and associated gabbroic intrusions. They display some of the characteristics of slow-spreading ridge systems, but, due to their highly tectonized character, they have been interpreted successively either as remnants of oceanic fracture zones of normal ocean or as remnants of very-poorly organized, abnormal oceanic basement. This review shows how the concept of mantle exhumation has been elaborated more or less in the same period both by marine geoscientists and by geologists conducting investigations in ophiolitic units of the Alps-Apennines mountain belt. Dredging and diving results from the Gorringe Bank, the Iberia margin, the Thyrrenian Sea and the Central Atlantic in the 1980's and 1990's provided additional proofs that the mantle is currently exhumed in various oceanic environments, including distal continental margins, back-arc basins and slow-spreading ridges of wide oceans. It is shown finally how renewed cross-information from mountain belts and the oceans, multiplying the examples of sedimentary reworking of mantle material, help better constrain the mechanisms of mantle exhumation. This mechanism progressively appeared as a fundamental step during the processes of extension of both continental and oceanic lithospheres in numerous geological situations worldwide.
Bollettino della Società Geologica Italiana

hal-00475653
https://hal.archives-ouvertes.fr/hal-00475653
DOI : 10.3301/IJG.2009.128.2.279

Éditeur(s) : HAL CCSD
Résumé : International audience
The Achmmach tin mineralization (NE of theMoroccan Central Massif) is associated with tourmaline-richalteration halos, veins, and faults hosted in sandstones andmetapelites of the Upper Visean-Namurian. These depositsare reported to be late Hercynian in age and related to theemplacement of late-orogenic granite not outcropping in thestudied area. Structural and paragenetic studies of theAchmmach tin deposit were conducted in order to establisha general model of the mineralization. From field constraints,the late Hercynian phase is marked by a transition fromtranspression to extension with deformation conditions evolvingfrom ductile to brittle environments. The transpression(horizontal shortening direction roughly trending E-W) is coevalwith the emplacement of the first tourmaline halos alongseveral conjugated trends (N070, N020, and N120).Thereafter, a tourmaline-rich breccia formed in response tothe fracturing of early tourmaline-altered rocks.Subsequently, during the extensional phase, these structureswere reactivated as normal faults and breccias, allowing theformation of the main tin mineralization (cassiterite) associatedwith a wide variety of sulfides (arsenopyrite, chalcopyrite,sphalerite, galena, pyrrhotite, bismuthinite, pyrite, and stannite). This evolution ends with fluorite and carbonate deposition.The hydrothermal fluid flow velocity, calculated byapplying statistical measures on the tourmaline growth bands,varies with the lithology. Values are lower in metapelites andhigher in breccia. In the general evolution model proposedhere, tourmaline alteration makes the rock more competent,allowing for brittle fracturing and generation of open spacewhere the main Sn mineralization was precipitated.
Mineralium Deposita

insu-01240481
https://hal-insu.archives-ouvertes.fr/insu-01240481
DOI : 10.1007/s00126-015-0613-0

Éditeur(s) : HAL CCSD Elsevier
Résumé : The slow advance of a crack in soda-silicate glasses was studied at nanometer scale by in-situ and real-time atomic force microscopy (AFM) in a well-controlled atmosphere. An enhanced diffusion of sodium ions in the stress-gradient field at the sub-micrometric vicinity of the crack tip was revealed through several effects: growth of nodules in AFM height images, changes in the AFM tip–sample energy dissipation. The nodules patterns revealed a dewetting phenomenon evidenced by ‘breath figures'. Complementary chemical micro-analyses were done. These experimental results were explained by a two-step process: (i) a fast migration (typical time: few milliseconds) of sodium ions towards the fracture surfaces as proposed by Langford et al. [J. Mat. Res. 6 (1991) 1358], (ii) a slow backwards diffusion of the cations as evidenced in these AFM experiments (typical time: few minutes). Measurements of the diffusion coefficient of that relaxing process were done at room temperature. Our results strengthen the theoretical concept of a near-surface structural relaxation due to the stress-gradient at the vicinity of the crack tip. The inhomogeneous migration of sodium ions might be a direct experimental evidence of the presence of sodium-rich channels in the silicate structure [A. Meyer et al., Phys. Rev. Let. 93 (2004) 027801].
ISSN: 0022-3093

hal-00407634
https://hal.archives-ouvertes.fr/hal-00407634
DOI : 10.1016/j.jnoncrysol.2006.09.034

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Torsion experiments (inline image =3 × 10−4 s−1) were performed to investigate the large strain (γmax = 15) rheology on quartz-muscovite aggregate as analogue to pelitic rocks undergoing melting and crystallization during deformation at 300 MPa confining pressure and 750°C temperature. Microstructures reveal four distinct but gradational stages of crystal-melt interactions during deformation--(a) solid state deformation, (b) initiation and domination of partial melting, (c) simultaneous partial melting and crystallization, and (d) domination of crystallization. The microstructural stages are linked to the rheology of the deforming samples. Partial melting starts at relatively low finite shear strains (γ = 1-3) showing approximately 60% strain softening. At γ = 4-10 the partially molten bulk material shows a steady state flow at low stress. Further crystallization of new crystals at the expense of melt between γ = 10 and 15 causes weak strain hardening until the material fails by developing brittle fractures. The stress exponent (n), calculated at γ = 1, 5, and 10, increases from ∼ 3 to ∼ 43, indicating a transition from power to power law breakdown or exponential flow of the bulk system. Hydrostatic experiments for equivalent times and conditions of the torsion experiments were also conducted to evaluate the reaction kinetics and microstructures under static conditions. The new experimental data establish that partially molten rock does not flow according to a constant strain rate-dependent power law (steady state) rheology. The rheological transition from strain rate sensitive to strain rate insensitive flow is interpreted as a function of melt-crystal ratio, their mutual interactions, and the evolution of microstructures in the partially molten rock.
ISSN: 0148-0227

hal-01053709
https://hal.archives-ouvertes.fr/hal-01053709
DOI : 10.1002/2013JB010777

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Madeira Sn-Nb-Ta deposit corresponds to the albite-enriched facies of Madeira granite (Madeira Suite) that is part of a NE-SW alignment of three granitic bodies. Structural analyses suggest that the albite-enriched granite emplacement and development of related structures occurred in a different tectonic setting than earlier facies of the granitic bodies in the NE-SW alignment and that the structure was dominated by a N-NE-trending shortening related to a left-lateral motion along a NE-SW corridor within a Riedel shear. Three types of structures (flat-lying, near vertical fractures, and geodes/miaroles) concentrated the last magmatic-related fluid in the albite-enriched granite. U-Pb in situ zircon dating of the albite-enriched granite yielded an age of 1,822 ± 22 Ma. The other granitic plutons of the Madeira Suite, Água Boa granite (topaz-granite facies), and Europa per-alkaline granite formed at 1,825 ± 14 Ma, 1,831± 11 Ma, and 1,839 ± 10 Ma, respectively. The granite bodies of the Madeira Suite occur in an area occupied by a cauldron complex composed of volcanic sequences (Iricoumé Group) and associated A-type granites (Mapuera Suite), and their formation was controlled by the reactivation of the cauldron structures and the pre-existing structures. The gap between the cauldron complex and the Madeira Suite is no greater than 35 Ma. The geological evolution was reanalyzed from the perspective of an entire extensional environment where three successive episodes of A-type magmatism and basin formation (Urupi Formation) occurred. The data and interpretations of this work imply crucial constraints on the petrologic models proposed for the albite-enriched granite and, consequently, on the genesis of the Madeira deposit
ISSN: 0301-9268

insu-00939888
https://hal-insu.archives-ouvertes.fr/insu-00939888
https://hal-insu.archives-ouvertes.fr/insu-00939888/document
https://hal-insu.archives-ouvertes.fr/insu-00939888/file/BastosNeto-PrecambrianResearch-2014.pdf
DOI : 10.1016/j.precamres.2013.12.021

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
To estimate the seismic hazard, the geometry (dip, length and orientation) and the dynamics (type of displacements and amplitude) of the faults in the area of interest need to be understood. In this paper, in addition to geomorphologic observations, we present the results of two ground penetrating radar (GPR) campaigns conducted in 2010 and 2011 along the Emeelt fault in the vicinity of Ulaanbaatar, capital of Mongolia, located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes. As the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event, the fault location and geometry is difficult to determine precisely. However, by using GPR first, a non-destructive and fast investigation, the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location. GPR was performed with a 50 MHz antenna over 2-D lines and with a 500 MHz antenna for pseudo-3-D surveys. The 500 MHz GPR profiles show a good consistency with the trench observations, dug next to the pseudo-3-D surveys. The 3-D 500 MHz GPR imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m. This is consistent with a right lateral strike-slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6. The 2-D 50 MHz profiles, recorded perpendicular to the fault, show a strong reflection dipping to the NE, which corresponds to the fault plane. Those profiles provided complementary information on the fault such as its location at shallow depth, its dip angle (from 23 • to 35 •) and define its lateral extension. Central Asia is known for its high level of seismic hazards, especially Mongolia, which has been one of the most seismically active intracontinental regions in the world with four large earthquakes (magnitude around 8) along its active faults in the western part of the country during the last century (Khilko et al. 1985). The deformation in Mongolia is located between compressive structures related to the collision and penetration of the Indian plate into the Eurasian plate and extensive structures in the north of the country related with the Baykal rift (Tapponnier & Molnar 1979; Baljinnyam et al. 1993; Schlupp 1996; Bayasgalan & Jackson 1999). The seismic activity observed in the vicinity of Ulaanbaatar (UB), capital of Mongolia, is relatively low compared to the activity observed in western Mongolia. Nevertheless, since 2005, the seismic activity around UB not only has increased, but is also organized (see Fig. 1) at the west of UB along two perpendicular directions, which determine two active faults: Emeelt fault, discovered in 2008 (NNW-SSE direction, 25-km-long minimum and situated about 10 km W of UB) and Hustai fault (WSW–ENE direction, 80 km long, with its NE tip at less than 20 km west of UB); their length and morphology indicate that they can produce earthquakes of magnitude 6.5–7.5 (Schlupp et al. 2012). Most of the Mongolian population (1.2 million over 3 million) is concentrated at UB, which is the main political and economical centre of the country. Hence, the study of seismic hazard and the estimation of the probability of future destructive earthquakes are of primary importance for the country (Dugarmaa et al. 2006). Since the last large earthquake, the faults geomorphology has been highly smoothed by erosional processes and the exact location of the fault plane surface rupture is thus hidden within a several metre wide strip. The GPR method has been proven to give good and useful results to characterize faults by identifying offsets of radar reflections (Malik et al. 2007; Christie et al. 2009; Yalçiner et al. 2013) and
ISSN: 0956-540X

hal-01342629
https://hal.archives-ouvertes.fr/hal-01342629
https://hal.archives-ouvertes.fr/hal-01342629/document
https://hal.archives-ouvertes.fr/hal-01342629/file/Dujardin_Bano_etal_Geoph.%20J.%20Int._2014_final.pdf
DOI : 10.1093/gji/ggu130

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Deep-seated gravitational spreading (DSGS) affects the slopes of formerly glaciated mountain ridges. On Mars, DSGS has played a key role in shaping the landforms of the giant Valles Marineris troughs. Though less spectacular, DSGS is common in terrestrial orogens, where understanding its mechanics is critical in the light of the ongoing climate change because it is a potential source of catastrophic landslides in deglaciated valleys. We conducted parametric numerical studies in order to identify important factors responsible for DSGS initiation. DSGS models are computed using an elastoviscoplastic finite element code. Using ADELI's software, we reproduce topographic ridge spreading under the effect of valley unloading. Two types of spreading topographic ridges are investigated, homogeneous or with horizontal rheological layering. We find that gravitational instabilities are enhanced by high slopes, which increase gravitational stress, and low friction and cohesion, which decrease yield stress. In the unlayered ridge, instability is triggered by glacial unloading with plastic strain concentration inside the ridge and at the base of the high slopes. Vertical fractures develop in the upper part of the slope, potentially leading to fault scarps. Ridge homogeneity promotes a deformation mode controlled by uphill-facing normal faulting and basal bulging. In the second case, the ridge encompasses horizontal geological discontinuities that induce rock mass anisotropy. Discontinuity located at the base of the slope accumulates plastic strain, leading to the formation of a sliding plane evolving into a landslide. The presence of a weak layer at ridge base therefore promotes another slope deformation mode ending up with catastrophic failure. Mechanical conditions and slope height being equal, these conclusions can probably be extrapolated to Earth. Compared with Mars, DSGS on Earth is inhibited because terrestrial topographic gradients are lower than in Valles Marineris, an effect counterbalanced by increased gravitational stress, where the intensity of deformation is enhanced because of the Earth gravity potential.
ISSN: 0169-555X

hal-01420007
https://hal.archives-ouvertes.fr/hal-01420007
DOI : 10.1016/j.geomorph.2016.06.011

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

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