Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Advances in groundwater storage monitoring are crucial for water resource management and hydrological processes understanding. The evaluation of water storage changes (WSC) often involve point measurements (observation wells, moisture probes, etc.), which may be inappropriate in heterogeneous media. Over the past few years, there has been an increasing interest in the use of gravimetry for hydrological studies. In the framework of the GHYRAF (Gravity and Hydrology inAfrica) project, 3 yr of repeated absolute gravity measurements using a FG5-type gravimeter have been undertaken at Nalohou, a Sudanian site in northern Benin. Hydrological data are collected within the long-term observing system AMMA-Catch. Once corrected for solid earth tides, ocean loading, air pressure effects, polar motion contribution and non-local hydrology, seasonal gravity variations reach up to 11 μGal, equivalent to a WSC of 260-mm thick infinite layer of water. Absolute temporal gravity data are compared to WSC deduced from neutron probe and water-table variations through a direct modelling approach. First, we use neutronic measurements available for the whole vertical profile where WSC occur (the vadose zone and a shallow unconfined aquifer). The RMSD between observed and modelled gravity variations is 1.61 μGal, which falls within the error bars of the absolute gravity data. Second, to acknowledge for the spatial variability of aquifer properties, we use a 2-D model for specific yield (Sy) derived from resistivity mapping and Magnetic Resonance Soundings (MRS). The latter provides a water content (θMRS) known to be higher than the specific yield. Hence, we scaled the 2-D model of θMRS with a single factor (α). WSC are calculated from water-table monitoring in the aquifer layer and neutronic measurements in the vadose layer. The value of α is obtained with aMonte-Carlo sampling approach, minimizing the RMSD between modelled and observed gravity variations. This leads to α = Sy/θMRS = 0.63 ± 0.15, close to what is found in the literature on the basis of pumping tests experiments, with a RMSD value of 0.94 μGal. This hydrogeophysical experiment is a first step towards the use of time-lapse gravity data as an integrative tool to monitor interannual WSC even in complicated subsurface distribution.
ISSN: 0956-540X

hal-00821181
https://hal.archives-ouvertes.fr/hal-00821181
DOI : 10.1093/gji/ggt146

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New structural, geochronological and paleomagnetic data were obtained on dolerite dikes of the Nola region (Central African Republic) at the northern border of the Congo craton. In this region metavolcanic, successions were thrust southward onto the craton during the Panafrican orogenic events. Our structural data reveal at least two structural klippes south of the present-day limits of the Panafrican nappe suggesting that it has once covered the whole Nola region, promoting the pervasive hydrothermal green-schist metamorphism observed in the underlying cratonic basement and also in the intrusive dolerite dikes. Paleomagnetic measurements revealed a stable dual-polarity low-inclination magnetization component in nine dikes (47 samples), carried by pyrrhotite and magnetite. This component corresponds to a paleopole at 304.8 degrees E and 61.8 degrees S (dp = 5.4, dm = 10.7) graded at 2 = 6. Both metamorphism and magnetic resetting were dated by the Ar-40/Ar-39 method on amphibole grains separated from the dikes at 571 +/- 6 Ma. The Nola pole is the first well-dated paleomagnetic pole for the Congo craton between 580 and 550 Ma. It marks a sudden change in direction of the Congo craton apparent polar wander path at the waning stages of the Panafrican orogenic events.
ISSN: 0301-9268

hal-00321120
https://hal.archives-ouvertes.fr/hal-00321120
DOI : 10.1016/j.precamres.2008.05.005

Éditeur(s) : HAL CCSD Integrated Ocean Drilling Program
Résumé : International audience
A detailed study of magnetic properties was carried out on ~60 samples from three holes cored during Integrated Ocean Drilling Program Expedition 324, Shatsky Rise. The measurements include scanning electron microscopy (SEM), hysteresis, and first-order reversal curve (FORC) diagrams, as well as measurements of susceptibility at high and low temperatures and variation of saturation isothermal magnetization at low temperature. SEM measurements show the presence of a complex mixture of Fe-Ti oxides with various Ti content x, which is confirmed by the measurements of susceptibility variation with temperature and low-temperature measurements. According to FORC diagrams, the magnetization is carried by single-domain to pseudosingle-domain grains.
ISSN: 1930-1014

hal-00795484
https://hal.archives-ouvertes.fr/hal-00795484
DOI : 10.2204/iodp.proc.324.201.2013

Éditeur(s) : HAL CCSD IODP
Résumé : The Superfast Spreading Crust campaign, echoing long-standing ocean lithosphere community endeavors, was designed to help us understand the formation, architecture, and evolution of ocean crust formed at fast spreading rates. Integrated Ocean Drilling Program (IODP) Expedition 335, "Superfast Spreading Rate Crust 4" (13 April-3 June 2011), was the fourth scientific drilling cruise of the Superfast Spreading Crust campaign to Ocean Drilling Program (ODP) Hole 1256D. The expedition aimed to deepen this basement reference site several hundred meters into the gabbroic rocks of intact lower oceanic crust to address the following fundamental scientific questions: Does the lower crust form by subsidence of a crystal mush from a high-level magma chamber (gabbro glacier), by intrusion of sills throughout the lower crust, or by some other mechanism? How does melt percolate through the lower crust, and what are the reactions and chemical evolution of magmas during migration? Is the plutonic crust cooled by conduction or hydrothermal circulation? What are the role and extent of deeply penetrating seawater-derived hydrothermal fluids in cooling the lower crust and the chemical exchanges between the ocean crust and the oceans? What are the relationships among the geological, geochemical, and geophysical structure of the crust and, in particular, the nature of the seismic Layer 2-3 transition? What is the magnetic contribution of the lower crust to marine magnetic anomalies?
https://hal.archives-ouvertes.fr/hal-00688990

hal-00688990
https://hal.archives-ouvertes.fr/hal-00688990
DOI : 10.2204/iodp.pr.335.2011

Éditeur(s) : HAL CCSD
Résumé : International audience
South-east Iran is the site of a rare case of young transition between subduction and collision. We synthesized recent results in geodesy, tectonics, seismology and magnetism to understand the structure and kinematics of the Zagros-Makran transition. Surface observations (tectonics, magnetism and geodesy) draw a transpressive discontinuity consisting of several faults striking obliquely to the convergent plate motion, whereas deeper observations (seismology) support a smooth transition across the fault system. No lithospheric transform fault has been created, even though the transition already behaves like a major boundary in terms of tectonic style, seismic structure, lithology and magnetism. The Zendan-Minab-Palami fault system consists of several faults that accommodate a transpressive tectonic regime. It is the surface expression of a southward propagation of the N-trending right-lateral strike-slip fault system of Jiroft-Sabzevaran. Within each system the numerous faults will coalesce into a single, lithospheric, wrench fault.
ISSN: 0375-6440

hal-00356532
https://hal.archives-ouvertes.fr/hal-00356532
https://hal.archives-ouvertes.fr/hal-00356532/document
https://hal.archives-ouvertes.fr/hal-00356532/file/Regard_MinabSynthese_revised_AvecFigs.pdf
DOI : 10.1144/SP330.4

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : The acquisition of reliable data sets representative of hydrological regimes and their variations is a critical concern for water resource assessment. For the subsurface, traditional approaches based on probe measurements, core analysis, and well data can be laborious, expensive, and highly intrusive, while only yielding sparse data sets. For this study, an innovative field survey, merging relative microgravimetry, magnetic resonance soundings, and hydrological measurements, was conducted to evaluate both surface and subsurface water storage variations in a semiarid Sahelian area. The instrumental setup was implemented in the lower part of a typical hillslope feeding to a temporary pond. Weekly measurements were carried out using relative spring gravimeters during 3 months of the rainy season in 2009 over a 350 × 500 m2 network of 12 microgravity stations. Gravity variations of small to medium amplitude (≤220 nm s−2) were measured with accuracies better than 50 nm s−2, revealing significant variations of the water storage at small time (from 1 week up to 3 months) and space (from a couple of meters up to a few hundred meters) scales. Consistent spatial organization of the water storage variations were detected, suggesting high infiltration at the outlet of a small gully. The comparison with hydrological measurements and magnetic resonance soundings involved that most of the microgravity variations came from the heterogeneity in the vadose zone. The results highlight the potential of time lapse microgravity surveys for detecting intraseasonal water storage variations and providing rich space-time data sets for process investigation or hydrological model calibration/evaluation
ISSN: 0043-1397

hal-00857351
https://hal.archives-ouvertes.fr/hal-00857351
DOI : 10.1002/wrcr.20235

Éditeur(s) : HAL CCSD Centre National de la Recherche Scientifique
Résumé : Une étude stratigraphique, sédimentologique et magnétique a été réalisée sur la partie supérieure d'une terrasse alluviale de l'oued Adaila, dansla plaine d'El Ma Labiod (nord-est de l'Algérie). Cette terrasse renferme un niveau très riche en matériel archéologique appartenant à la civilisation atérienne, dont l'âge dépasse 35 000 ans. Du point de vue sédimentologique, les sédiments sont dominés par la fraction limoneuse suivie par les sables fins et grossiers. Du point de vue stratigraphique, la succession de dépôts à éléments grossiers recouverts par des éléments fins correspond à des niveaux fluviatiles avec des mises en place à débit contrasté. Les courbes cumulatives ont un faciès dit " parabolique " et témoignent d'un sédiment immature et peu évolué. Les résultats de l'étude magnétique concordent avec les précédents. Ils révèlent une forte concentration en grains magnétiques dans la partie médiane de la coupe (foyer) et une faible concentration à la base (Unité L) contemporaine d'un climat sec. Les grains magnétiques, de taille variable (polydomaine, monodomaine et superparamagnétique), sont portés par la magnétite et la maghémite de faible champ coercitif, ainsi que par la goethite et l'hématite de fort champ coercitif. Les courbes de la susceptibilité magnétique en fonction de la température et les courbes de la décomposition de l'ARI (spectres de coercivité) confirment ces résultats.
ISSN: 1142-2904

hal-00750185
https://hal.archives-ouvertes.fr/hal-00750185

Éditeur(s) : HAL CCSD IODP
Résumé : Integrated Ocean Drilling Program (IODP) Expedition 335 (14 April–4 June 2011) will be the fourth ocean cruise of the "Superfast" campaign to drill a deep hole into intact oceanic basement and will return to Ocean Drilling Program (ODP) Hole 1256D to deepen this scientific reference penetration a significant distance into cumulate gabbros. Cores and data recovered during the Superfast 4 expedition will provide hitherto unavailable observations that will test models of the accretion and evolution of the oceanic crust. Site 1256 was specifically located on oceanic crust that formed at a superfast spreading rate (>200 mm/y) to exploit the observed relationship between spreading rate and depth to axial low velocity zones, thought to be magma chambers, seismically imaged at active mid-ocean ridges. This was a deliberate strategy to reduce the drilling distance to gabbroic rocks because thick sequences of lavas and dikes have proved difficult to penetrate in past. ODP Leg 206 (2002) initiated operations at Site 1256, including the installation in Hole 1256D of a reentry cone with 16 inch casing inserted through the 250 m thick sedimentary cover and cemented into basement to facilitate deep drilling. The hole was then cored ~500 m into basement. IODP Expeditions 309 and 312 (2005) successfully completed the first sampling of an intact section of upper oceanic crust from lavas, through the sheeted dikes, and into the upper gabbros. Hole 1256D now penetrates >1500 meters below seafloor (mbsf) and >1250 m subbasement and currently resides in the dike–gabbro transition zone. The first gabbroic rocks were encountered at 1407 mbsf. Below this lies a ~100 m complex zone of fractionated gabbros intruded into contact metamorphosed dikes. Although previous cruises achieved the benchmark objective of reaching gabbro in intact ocean crust, critical scientific questions remain. These include the following: 1. Does the lower crust form by the recrystallization and subsidence of a high-level magma chamber (gabbro glacier), crustal accretion by intrusion of sills throughout the lower crust, or some other mechanism? 2. Is the plutonic crust cooled by conduction or hydrothermal circulation? 3. What is the geological nature of Layer 3 and the Layer 2/3 boundary at Site 1256? 4. What is the magnetic contribution of the lower crust to marine magnetic anomalies? Hole 1256D is poised at a depth where samples that should conclusively address these questions can be obtained, possibly with only a few hundred meters of drilling. Importantly, as of the end of Expedition 312, the hole was clear of debris and open to its full depth. Increased rates of penetration (1.2 m/h) and enhanced core recovery (>35%) in the gabbros indicate that this return to Hole 1256D could deepen the hole >300 m into plutonic rocks, past the transition from dikes to gabbro, and into a region of solely cumulate gabbroic rocks.
https://hal.archives-ouvertes.fr/hal-00564953

hal-00564953
https://hal.archives-ouvertes.fr/hal-00564953
DOI : 10.2204/iodp.sp.335.2010

Éditeur(s) : North-Holland Publishing Company
Résumé : The Rift Valley between 36° 42'N and 36° 55'N in the Atlantic Ocean is 31 km wide, with half-widths of 12 and 19 km for the western and eastern sides respectively. Both outer edges of the Rift Valley stand about 1500 m above an Inner Floor where very fresh pillow lavas occur. The Inner Floor probably includes the locus of new crust ; and its bordering slopes, which are particularly well-defined on the western side, limit to less than about 2.5 km the width of the zone over which new crust may have evolved with little or no vertical displacement. The width of the locus of new crust may be less than 0.5 km between 36° 45'N and 36° 47'N, where the deepest slopes of the Rift Valley walls nearly merge. Near 36° 50'N, the Inner Floor accommodates an approximately 1 km wide, 4 km long Central High, with a height of up to 250 m. In this area, the locus of new crust may also occupy a very narrow zone ; it may lie either along the Central High or along a trough flanking the Central High. The magnetic anomaly pattern indicates that, since the beginning of the Brunhes epoch (6.9 X 10(5) yr B.P.), the eastern limb has grown approximately twice as fast as the western limb. Using extrapolated spreading rates, the ages of the outer edges of the Rift Valley are 1.3 and 1.7 m.y. for the eastern and western sides respectively. Comparison with data for the Rift Valley in other parts of the ocean further suggests that the residence time of new crust in the Rift Valley is about 1.5 m.y. Uplift of crust from the Inner Floor, which may be dominated by lithospheric thickening, may thus be primarily a function of age. [NOT CONTROLLED OCR]
Earth and Planetary Science Letters (North-Holland Publishing Company), 1974 , Vol. 22 , P. 29-43

Droits : North-Holland Publishing Company, Amsterdam
http://archimer.ifremer.fr/doc/1974/publication-5159.pdf
http://archimer.ifremer.fr/doc/00000/5159/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present new shear-wave splitting measurements performed at 16 stations on the East European Craton, and discuss their implications in terms of upper-mantle anisotropy for this geophysically poorly-known region. Previous investigations of mantle anisotropy in Central Europe have shown fast directions aligning smoothly with the craton's margin and various suggestions have been proposed to explain their origin such as asthenospheric flow or lithospheric frozen-in deformation.;Here, we aim at investigating the continuation of this shear-wave splitting pattern further to the East, into the East European Craton For the craton, the interpretation appears to be less ambiguous than for central Europe since several arguments support lithospheric anisotropy in this region 1) The large-scale coherence within either of the four constituting blocks and the significant variations between the blocks on a small-scale, 2) the weak correlation with absolute plate motion vectors, and 3) the good correlation between anisotropy and crustal features, for which we use magnetic field alignments as a proxy. Rattler good correlation of these magnetic features with seismic fast orientations strongly supports the idea of vertically coherent deformation throughout upper mantle and crust. The observed splitting orientations thus reflect the last tectonic events of each block. frozen-in into the lithosphere for hundreds of millions of years
ISSN: 0040-1951

hal-00475647
https://hal.archives-ouvertes.fr/hal-00475647
https://hal.archives-ouvertes.fr/hal-00475647/document
https://hal.archives-ouvertes.fr/hal-00475647/file/Wuestefeld_EEC_craton_SKS_Tphy2010_hal.pdf
DOI : 10.1016/j.tecto.2009.01.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Evidence of anomalous volcanism is readily observed in the Gulf of Aden, although, much of this oceanic basin remains as yet unmapped. In this paper, we investigate the possible connection of the Afar hotspot with a major off-axis volcanic structure and its interpretation as a consequence of a the anomalous presence of melt by integrating several data sets, both published and unpublished, from the Encens-Sheba cruise, the Aden New Century (ANC) cruise and several other onshore and marine surveys. These include bathymetric, gravity, magnetic, magneto-telluric data, and rock samples. Based upon these observations, interpretations were made of seafloor morphology, gravity and magnetic models, seafloor age, geochemical analyses and tectonic setting. We discuss the possible existence of a regional melting anomaly in the Gulf of Aden area and of the probability of its connection to the Afar plume. Several models that might explain the anomalous volcanism are taken into account, such as a local melting anomaly unrelated to the Afar plume, an anomalously large volume of melt associated with seafloor spreading, and interaction of the ridge with the Afar plume. A local melting anomaly and atypical seafloor spreading prove inconsistent with our observations. Two previously proposed models of plume-ridge interactions are examined: the diffuse plume dispersion called pancaked flow and channelized along-axis flow. We conclude that the configuration and structure of this young ocean basin may have the effect of channeling material away from the Afar plume along the Aden and Sheba Ridges to produce the off-axis volcanism observed on the ridge flanks. This interpretation implies that the influence of the Afar hotspot may extend much farther eastwards into the Gulf of Aden than previously believed. The segmentation of the Gulf of Aden and the configuration of the Aden-Sheba system may provide a potential opportunity to study channeled flow of solid plume mantle from the plume along a segmented ridge and nearby continental margins.
ISSN: 0012-821X

hal-00486140
https://hal.archives-ouvertes.fr/hal-00486140
DOI : 10.1016/j.epsl.2010.02.036

Éditeur(s) : Gauthier-Villars
Résumé : Multichannel seismic reflection profiling has revealed that the basalt layer on the Outer Voring Plateau is underlain in places by steeply dipping layered reflectors. Two opposing theories have been considered for the origin of the layered reflectors: (1) They are Mesozoic sediments deposited before the Tertiary opening of the Norwegian Sea. (2) They are Tertiary deposits formed during the early stage of opening of the Norwegian Sea by seafloor spreading. The authors find that: (a) magnetic anomaly 24 can be traced continuously from the Lofoten Basin on to the Voring Plateau, associated with the oldest seafloor generated in the opening of the Norwegian Sea; (b) the layered reflectors form a characteristically shaped wedge that coincides with anomaly 24; (c) the material comprising the wedge possesses seismic velocities which increase from about 2.6 km/sec. in the upper part to about 6.4 km/sec. in the lower part. The above observations strongly support a Tertiary age for the material comprising the wedge, which consists of basalic flows and volcanogenic sediments and which is associated with sea floor created a few million years after the start of spreading.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1981

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00245/35669/34177.pdf
http://archimer.ifremer.fr/doc/00245/35669/

Éditeur(s) : HAL CCSD Springer/Terra Scientific Publishing Company
Résumé : International audience
The laboratory of paleomagnetism of Montpellier (France) has developed a new one-axis vibrating thermal magnetometer dedicated to the Study of physical properties of natural rocks remanence. Among its key characteristics, this apparatus allows both measurement or the magnetization moment on the interval from room temperature to 700 degrees C with a precision of 2 x 10(-9) A m(2) and acquisition of a total or a partial thermo-remanent magnetization using a steady field from - 100 up to 100 mu T. Another point that is worth noting is that one can apply a controlled atmosphere by means of argon flux to prevent oxidation of the studied sample during heating. We report here a technical description of this new instrument and review some specific applications in absolute paleointensity surveys.
ISSN: 1343-8832

hal-00413078
https://hal.archives-ouvertes.fr/hal-00413078
https://hal.archives-ouvertes.fr/hal-00413078/document
https://hal.archives-ouvertes.fr/hal-00413078/file/Poidras-CatVTM.pdf

Éditeur(s) : HAL CCSD Institute of Electrical and Electronics Engineers Inc.
Résumé : International audience
An important issue in epilepsy research is to understand the structural and functional modifications leading to chronic epilepsy, characterized by spontaneous recurrent seizures, after initial brain insult. To address this issue, we recorded and analyzed electroencephalography (EEG) and quantitative magnetic resonance imaging (MRI) data during epileptogenesis in the in vivo mouse model of Medial Temporal Lobe Epilepsy (MTLE, kainate). Besides, this model of epilepsy is a particular form of drug-resistant epilepsy. The results indicate that high-field (4.7T) MRI parameters (T2-weighted; T2-quantitative) allow to detect the gradual neuro-anatomical changes that occur during epileptogenesis while electrophysiological parameters (number and duration of Hippocampal Paroxysmal Discharges) allow to assess the dysfunctional changes through the quantification of epileptiform activity. We found a strong correlation between EEG-based markers (invasive recording) and MRI-based parameters (non-invasive) periodically computed over the 'latent period' that spans over two weeks, on average. These results indicated that both structural and functional changes occur in the considered epilepsy model and are considered as biomarkers of the installation of epilepsy. Additionally, such structural and functional changes can also be observed in human temporal lobe epilepsy. Interestingly, MRI imaging parameters could be used to track early (day-7) structural changes (gliosis, cell loss) in the lesioned brain and to quantify the evolution of epileptogenesis after traumatic brain injury. © 2016 IEEE.
38th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC 2016
Unknown, Unknown or Invalid Region

hal-01467552
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01467552
DOI : 10.1109/EMBC.2016.7591605

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 Elsevier
Résumé : International audience
Piton des Neiges basaltic volcano (La Réunion) has been deeply dissected by erosion, exposing large volumes of debris avalanche deposits. To shed light on the factors that led to volcano flank destabilizations, we studied the structure, the crystallographic and magnetic fabrics of the substratum of a debris avalanche unit. This substratum is a complex of N50 seaward-dipping sills that has been exposed by the avalanche. Structural observations show that the sill plane in contact with the avalanche is one of the latest intrusions in the sill complex. In this uppermost sill, the anisotropy of magnetic susceptibility (AMS) is correlated to the crystallographic preferred orientation of magmatic silicate minerals, allowing us to use AMS as a proxy to infer the magmatic flow. The AMS fabric across the intrusion is strongly asymmetric, which reveals that the contact sill was emplaced with a normal shear displacement of its hanging wall. The shear displacement and the magma flow in the intrusion are both directed toward the NNE, i.e. toward the sea, which is also the direction of the slope and of the debris avalanche runout. Because all the sills in the intrusion complex have a similar dip and dip direction, it is likely that several of them also underwent a cointrusive slip toward the NNE. We conclude that this cointrusive normal slip, repeated over many intrusions of the sill complex, increased the flank instability of the volcano. This incre-mental instability may have ended up into the observed debris avalanche deposit. At Piton de la Fournaise, the active volcano of La Réunion, sill intrusion and cointrusive flank displacement have been inferred from geophys-ical studies for the April 2007 eruption. By providing direct evidence of sheared sills, our study substantiates the idea that repeated sill intrusions may eventually trigger flank destabilizations in basaltic volcanoes.
ISSN: 0040-1951

hal-01351758
http://hal.univ-reunion.fr/hal-01351758
http://hal.univ-reunion.fr/hal-01351758/document
http://hal.univ-reunion.fr/hal-01351758/file/2016-Tectonopgysics-Berthod.pdf
DOI : 10.1016/j.tecto.2016.02.017

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : International audience
Carbonation of ultramafic rocks in geological reservoirs is, in theory, the most efficient way to trap CO2 irreversibly; however, possible feedback effects between carbonation reactions and changes in the reservoir permeability must be considered to realistically assess the efficiency and sustainability of this process. We investigated changes in the hydrodynamic properties of sintered dunite samples by means of percolation experiments, under conditions analogous to that of in situ carbonation. Our results show that carbonation efficiency is controlled by the local renewal of the reactants and the heterogeneity of the pore structure. Preferential flow zones are characterized by the formation of magnetite and of a silica-rich layer at the olivine surfaces, which eventually inhibits olivine dissolution. Conversely, sustainable olivine dissolution together with coprecipitation of magnesite, siderite, and minor Mg-TOT-phyllosilicates, occur in reduced-flow zones. Thus carbonate precipitation only decreases porosity in zones where diffusion-controlled transport is dominant. Consequently, while high flow rates will decrease the carbonation efficiency of the reservoir and low flow rates may reduce the permeability irreversibly close to the injection point, moderate injection rates will ensure a partial carbonation of the rock and maintain the reservoir permeability.
ISSN: 0013-936X

hal-00424540
https://hal.archives-ouvertes.fr/hal-00424540
DOI : 10.1021/es8018429

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Numerous archeomagnetic studies have provided high quality data for both the direction and the intensity of the geomagnetic field, essentially in Europe for the last 10 millennia. In particular, Greece supplies a lot of archeological materials due to its impressive cultural heritage and volcanic activity, so that numerous data have been obtained from burnt clays or historical lava flows. The most recent Greek secular variation curves are available for the last 8 millennia for the intensity and the last 6 millennia for the direction. Nevertheless, the coverage still presents several gaps for periods older than 2500 BC. In an effort to complete the Greek curve and extend it to older times, we present the archeointensity results from three Neolithic settlements in Northern Greece. The samples are of two different natures: burnt structures from Avgi (5250 ± 150 BC) and Vasili (4800 ± 200 BC), as well as ceramics from Dikili Tash (4830 ± 80 BC) and Vasili (4750 ± 250 BC). The samples have been subjected to standard rock magnetic analyses in order to estimate the thermal stability and the domain state of the magnetic carriers before archeointensity measurements. Surprisingly, very few ceramic samples provided reliable archeointensities whereas samples from burnt structures presented a very good success rate. Complementary studies showed that a detailed examination of the matrix color, following archeological information and classification standards can be a decisive test for pre-selection of sherds. In spite of these unsuccessful measurements from ceramics, we obtained an intensity value of 73.5 ± 1.1 μT for Dikili Tash, a higher value than the other data obtained in the same area, during the same period. However we do not have evidences for a technical artefact during the experiment. The burnt structures yielded two reliable archeointensities of 36.1 ± 1.8 μT and 46.6 ± 3.4 μT for Avgi and Vasili, respectively. Finally, we achieved a new archeomagnetic dating for these sites by comparing these new archeointensity values, combined to the directional measurements already published, with the Bulgarian secular variation curve. These new results contribute to extend the Greek secular variation reference curve towards older periods.
ISSN: 0031-9201

hal-00805575
https://hal.archives-ouvertes.fr/hal-00805575
DOI : 10.1016/j.pepi.2012.10.011

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : In the western Mediterranean Sea, the Liguro-Provençal Basin (LPB) is a key area for studying passive margins because of its recent formation and abundance of onshore and offshore data. The Nerthe area located in the northern margin of LPB provides the unique continuous Oligo-Miocene deposits contemporaneous of the transition rifting to drifting. However, the age of the deposits remains debated and the link between outcrops and offshore seismic data is poorly constrained. The purpose of this paper is double. First, we intend to propose a new chronostratigraphic frame based on bio- (planktonic foraminifera, calcareous nannofossils) and magneto-stratigraphy. Second, we aim to make, through the integration of new highly time-resolved seismic data and field works, a coherent onshore-offshore link concretized by a 3D geological model. The new temporal and spatial data presented in this paper allow correlating the Oligo-Miocene sequences, defining their geometry and specifying precisely the timing of syn- and post-rift stages. The first marine transgression is now precisely dated latest Chattian within the syn-rift deposits and appears to be synchronous with the first marine deposits in the offshore wells and other marginal basins. The transition from syn-rift to post-rift appears to last 3.3 Ma at maximum, between 21.8 and 18.5 Ma (late Aquitanian to early Burdigalian). It is underlined by two major erosional unconformities bearing a hiatus of around 1 Ma. The post-rift started with a major marine transgression that is now dated from middle Burdigalian, at around 18.5 Ma, as elsewhere in the LPB. Contrarily to recent proposals, the post-rift deposits are widely represented on the northeastern margin of the "Golfe du Lion". There, the subsidence of the margin was low during the syn-rift and the transitional periods and high during the post-rift. The onset of this high post-rift subsidence appears to be synchronous with the slowdown of the Corsica-Sardinia block (CSb) motion.
EISSN: 1777-5817

hal-00558497
https://hal.archives-ouvertes.fr/hal-00558497
DOI : 10.2113/gssgfbull.181.6.591

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
We surveyed the junction between the central and southern Philippine Trench and the Sangihe Trench near 6øN using swath bathymetry, gravity, and magnetics. These data, along with seismicity, allow us to discuss the genetic relations between these trenches and the forces acting on converging plates. Our final model favors the northern extension of the Halmahera Arc up to 8øN, with three segments offset left-laterally along NW-SE transform faults. Accretion of the northern segment to Mindanao Island 4 to 5 m.y. ago resulted in the failure within the Philippine Sea Plate east of the arc. Initiation of the Philippine Trench between 7øN and 10øN agrees with the maximum recorded depth of the Philippine Trench floor (10,000 m below sea-level) and Philippine Sea slab (200 km). South of 6øN (trench junction), another segment of the arc is being subducted beneath the Sangihe margin, while south of 3øN, the southern segment of the Halmahera Arc is still active. The rapid southward shallowing of the trench floor along the southern Philippine Trench, the type of faulting affecting both sides of the trench, the lack of significant interplate seismicity, and the concentration of the seismicity beneath the Miangas-Talaud Ridge are interpreted as a slowing down of the subduction along this branch of the Philippine Trench compared with the rest of the subduction zone. The Sangihe deformation front has been recognized up to 7øN but seems active only south of 6øN.
ISSN: 2169-9275

hal-01261614
https://hal.archives-ouvertes.fr/hal-01261614
https://hal.archives-ouvertes.fr/hal-01261614/document
https://hal.archives-ouvertes.fr/hal-01261614/file/lallemandJGR1998.pdf