Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Microbathymetry data, in situ observations, and sampling along the 13°20′N and 13°20′N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high-angle fault, scarps show extensive mass wasting that reduces their slope. Flexural rotation further lowers scarp slope, hinders mass wasting, resulting in morphologically complex chaotic terrain between the breakaway and the denuded corrugated surface. Extension and drag along the fault plane uplifts a wedge of hangingwall material (apron). The detachment surface emerges along a continuous moat that sheds rocks and covers it with unconsolidated rubble, while local slumping emplaces rubble ridges overlying corrugations. The detachment fault zone is a set of anostomosed slip planes, elongated in the along-extension direction. Slip planes bind fault rock bodies defining the corrugations observed in microbathymetry and sonar. Fault planes with extension-parallel stria are exposed along corrugation flanks, where the rubble cover is shed. Detachment fault rocks are primarily basalt fault breccia at 13°20′N OCC, and gabbro and peridotite at 13°30′N, demonstrating that brittle strain localization in shallow lithosphere form corrugations, regardless of lithologies in the detachment zone. Finally, faulting and volcanism dismember the 13°30′N OCC, with widespread present and past hydrothermal activity (Semenov fields), while the Irinovskoe hydrothermal field at the 13°20′N core complex suggests a magmatic source within the footwall. These results confirm the ubiquitous relationship between hydrothermal activity and oceanic detachment formation and evolution.
ISSN: 1525-2027

hal-01571973
https://hal.archives-ouvertes.fr/hal-01571973
https://hal.archives-ouvertes.fr/hal-01571973v2/document
https://hal.archives-ouvertes.fr/hal-01571973/file/Escart-n_et_al-2017-Geochemistry%2C_Geophysics%2C_Geosystems.pdf
DOI : 10.1002/2016GC006775

Éditeur(s) : Gauthier-Villars
Résumé : Cyprideis torosa (Crustacea, Ostracoda), which is well known for its ability to live in a wide range of salinity and for the variability of its ornamentation, was sampled in the paralic environment. in the Camargue (France) and in the area of Santa-Pola (south-east Spain), in ambient waters whose salinity varies from 1 to 120 g/l. The collected valves. which are smooth, punctuated, reticulated or have nodes on their surface, were analyzed by means of spark-source mass spectrometry. We detected twenty-six chemical elements, and found a clear relationship between the chemical composition, the ornamentation of the valves and the environmental parameters. In the oligohaline environment, the carapaces are thick, reticulated or node-bearing ; they are enriched in Si, Al, Fe, Mn and Ba which are terrigenous elements introduced by fresh water. In an open hypersaline environment, the carapaces are reticulated or punctuated ; they are chemically characterized by P, Sr and Li, typical for concentrated seawater. Finally, in a closed hypersaline environment. the collected individuals are smooth, and their carapaces are very thin ; their content S is related to the abundant organic matter provided by the development of algal and cyanobacterial mats. Salinity and confinement, which are the main parameters characteristic of the studied ecosystems, are also the two factors that control the ornamentation of the valves. The chemical analysis and the field observations reveal that the granulometric characteristics of the microhabitats must be considered because they control the exchanges at the water-sediment interface. The anthropic influences on the chemical composition of the carapace must be emphasized: it is possible to detect industrial and domestic wastes. But the ornamentation of the carapace is not related to these pollutants - chiefly heavy metals (Pb, Ni Sn) - and depends mainly on the open or closed character of the ambient environment. The present method highlights, on the basis of the chemical composition, a relationship between ornamentation and environmental parameters. It is particularly efficient in the interpretation of the morphology of the valves in relation to the palaeoenvironment.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1991 , Vol. 14 , N. 5 , P. 505-514

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00103/21378/18978.pdf
http://archimer.ifremer.fr/doc/00103/21378/

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100-220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45 degrees rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises similar to 70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge.
ISSN: 0148-0227

hal-00617528
https://hal.archives-ouvertes.fr/hal-00617528
https://hal.archives-ouvertes.fr/hal-00617528/document
https://hal.archives-ouvertes.fr/hal-00617528/file/2010JB007931.pdf
DOI : 10.1029/2010JB007931

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Serpentinites from subduction environments represent an important sink for fluid-mobile elements. In order to constrain geochemical behavior of fluid-mobile elements hosted by serpentine phases during subduction processes, we carried out a geochemical study (trace elements and Pb isotopes) of a series of serpentinites and cumulates from the accretionary wedge of Greater Caribbean (Cuba and Dominican Republic). The trace element compositions of the primary and alteration-related phases were analyzed in situ using LA-HR-ICP-MS techniques. The studied samples represent parts of the subducted proto-Atlantic oceanic lithosphere, which has experienced low to high grade metamorphism (greenschist to eclogite facies), before being exhumed; a subset of these samples were derived from the mantle wedge. This sampling provides the opportunity to trace the chemical mobility of fluid-mobile elements during prograde metamorphism along a cold geotherm in an oceanic subduction setting.
ISSN: 0009-2541

hal-00720895
https://hal.archives-ouvertes.fr/hal-00720895
DOI : 10.1016/j.chemgeo.2012.04.009

Éditeur(s) : HAL CCSD CRC Press Taylor & Francis Group
Résumé : aucun
Water-Rock Interaction XIII

hal-00857370
https://hal.archives-ouvertes.fr/hal-00857370

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault's base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 M w 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.
ISSN: 0012-821X

insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932/document
https://hal-insu.archives-ouvertes.fr/insu-01557932/file/EPSL-2006-escartin.pdf
DOI : 10.1016/j.epsl.2016.06.024

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : International audience
The Cerro del Almirez massif (Spain) represents a unique fragment of serpentinized oceanic lithosphere that has been first equilibrated in the antigorite stability field (Atg-serpentinites) and then dehydrated into chlorite–olivine–orthopyroxene (Chl-harzburgites) at eclogite facies conditions during subduction. The massif preserves a dehydration front between Atg-serpentinites and Chl-harzburgites. It constitutes a suitable place to study redox changes in serpentinites and the nature of the released fluids during their dehydration. Relative to abyssal serpentinites, Atg-serpentinites display a low Fe3+/FeTotal(BR) (=0.55) and magnetite modal content (=2.8–4.3 wt%). Micro-X-ray absorption near-edge structure (μ-XANES) spectroscopy measurements of serpentines at the Fe–K edge show that antigorite has a lower Fe3+/FeTotal ratio (=0.48) than oceanic lizardite/chrysotile assemblages. The onset of Atg-serpentinites dehydration is marked by the crystallization of a Fe3+-rich antigorite (Fe3+/FeTotal = 0.6–0.75) in equilibrium with secondary olivine and by a decrease in magnetite amount (=1.6–2.2 wt%). This suggests a preferential partitioning of Fe3+ into serpentine rather than into olivine. The Atg-breakdown is marked by a decrease in Fe3+/FeTotal(BR) (=0.34–0.41), the crystallization of Fe2+-rich phases and the quasi-disappearance of magnetite (=0.6–1.4 wt.%). The observation of Fe3+-rich hematite and ilmenite intergrowths suggests that the O2 released by the crystallization of Fe2+-rich phases could promote hematite crystallization and a subsequent increase in fo2 inside the portion of the subducted mantle. Serpentinite dehydration could thus produce highly oxidized fluids in subduction zones and contribute to the oxidization of the sub-arc mantle wedge.
ISSN: 0010-7999

hal-01172310
https://hal.archives-ouvertes.fr/hal-01172310
DOI : 10.1007/s00410-015-1130-y

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
GenMol (TM) code is used to simulate Atomic Force Microscopy (AFM) tests at a kaolinite/brine/kaolinite contact, the confined fluid in sub-nanometre interspaces being in equilibrium with an external multi-species solution. The attraction/repulsion effort, i.e. the derivative versus the interspace aperture h of the interaction energy between both kaolinite faces, is computed versus the variable composition of the confined fluid (see for the method Part I of this work). Two external solutions are tested. Solution Si is a neutral brine (pH=7.5) leading to a possible attraction for apertures lower than 7 angstrom. Solution S2 is an acidified brine (pH=3.2) leading to repulsion whatever may be the aperture h. These two AFM simulations prove the existence of a critical pH value (3.2 < pH(crit) < 7.5) of the external solution, below which the acidification of a natural brine in a CO2 confinement inhibits adhesion between kaolinite aggregates.
ISSN: 0022-0248

hal-00544678
https://hal.archives-ouvertes.fr/hal-00544678
DOI : 10.1016/j.jcrysgro.2010.08.012