Slow slip in subduction zones: Reconciling deformation fabrics with instrumental observations and laboratory results

Cataclasites are a characteristic rock type found in drill cores from active faults as well as in exposed fossil subduction faults. Here, cataclasites are commonly associated with evidence for pervasive pressure solution and abundant hydro­ fracturing. They host the principal slip of regular earthquakes and the family of so­called slow earthquakes (episodic slip and tremor, low to very low frequency earthquakes, etc.). Slip velocities associated with the formation of the different types of cataclasites and conditions controlling slip are poorly constrained both from direct observations in nature as well as from experimental research. In this study, we explore exposed sections of subduction faults and their dominant microstructures. We use recently proposed constitutive laws to estimate deformation rates, and we compare predicted rates with instrumental observations from subduction zones. By identifying the maximum strain rates using fault scaling relations to constrain the fault core thickness, we find that the instrumental shear strain rates identified for the family of “slow earthquakes” features range from 10−3s−1 to 10−5s−1. These values agree with estimated rates for stress corrosion creep or brittle creep possibly controlling cataclastic deformation rates near the failure threshold. Typically, pore­fluid pressures are suggested to be high in subduction zones triggering brittle deformation and fault slip. However, seismic slip events causing local dilatancy may reduce fluid pressures promoting pressure­solution creep (yielding rates of <10−8 to 10−12s−1) during the interseismic period in agreement with dominant fabrics in plate interface zones. Our observations suggest that cataclasis is controlled by stress corrosion creep and driven by fluid pressure fluctuations at near­lithostatic effective pressure and shear stresses close to failure. We posit that cataclastic flow is the dominant physical mechanism governing transient creep episodes such as slow slip events (SSEs), accelerating preparatory slip before seismic events, and early afterslip in the seismogenic zone

Shattered Veins Elucidate Brittle Creep Processes in the Deep Slow Slip and Tremor Region

Deep Slow Slip and Tremors (SSTs) are a combination of transient clusters of tectonic tremors and slow slip associated with extremely elevated fluid pressures. SSTs are thought to reflect a transition from viscous to brittle plate interface rheology and likely exert a first-order control on megathrust seismicity. Nevertheless, the deformation mechanisms governing the source of SSTs remain elusive. We herein document the occurrence of vein networks precipitated and brecciated within the deep SST region under blueschist-facies conditions. These lawsonite-rich vein sets exhibit extensive evidence of brittle deformation and are spatially related to localized, finely milled (cataclastic) shear bands. Petro-geochemical data reveal that brittle deformation was accompanied by the injection of several ultramafic-, mafic- and metasedimentary-derived fluid pulses, imprinting characteristic Cr, high field strength elements, and light over heavy rare earth elements positive anomalies in the vein breccias while leaching light rare earth elements from the cataclastic blueschist host. Our results suggest that metamorphic veins represent zones of mechanical anisotropy within the rock volume prone to localized shearing, brittle deformation and episodic injection of externally derived fluids. These networks demonstrate the importance of former vein sets as structural heterogeneities in triggering fluid-controlled brittle creep events. The combined effects of high pore fluid pressures and rheological heterogeneities in the form of metamorphic veins could trigger the nucleation and propagation of SSTs at the margins of this mechanically anisotropic environment, and thus determine where slip will take place along deep subduction interfaces.INSU/CNRS Grant (Tellus program)IDEX research chairIDEX Universite de Paris ANR-18-IDEX-0001Eidgenossische Technische Hochschule Zuric

Le cinéma d'action américain contemporain : Une abstraction figurative

Motion picture is by nature the art of motion and action: the machine records body motions and put them down as storytelling.Action film becomes a genre by showing excessive and spectacular action. In a way, classical cinema genres (such as western, slapstick, musical, war films) can be seen as an entire class of all action films. They are all driven by the action way which is the way motion pictures tell stories, by motion. From the Seventies or the Eighties, action film becomes an all new genre which converts the old classical genres into an immoderate and spectacular sort of films. Such films are mainly led by physical power and technology. They gave birth to the Hollywoodian movie industry of blockbuster.After having defined action films as a genre, we will analyze its split nature, part abstract and conceptual thinking and part popular storytelling. Narratives are very stylized in contemporary action films and bring low figurative pictures. Contemporary action films pictures are close to Photorealism and some sort of experimental films. But contemporary action films also deal with figuration, muscular bodies and mass destruction which are set into a very recognizable world.Contemporary spectacular direction is found somewhere between these two guidelines that are abstraction and representation. It aims at immersing physically speaking the wiever. He’s like drowned into the movie from his chair. To be immerged in the spectacular movie, viewers willingly give up their rational way of thinking for feeling. Intuition is an other way of perceiving spectacular pictures in motion.Le cinéma est naturellement un art de l’action qui enregistre mécaniquement le mouvement des corps et les inscrit dans un cadre fictionnel. Le genre du film d’action se constitue en présentant une action excessive selon une esthétique spectaculaire. Les genres du cinéma classique (western, burlesque, film musical, film de guerre…) sont tous à leur manière des films d’action. Ils sont tributaires du mode de l’action qui est une façon propre au cinéma de raconter des histoires par le mouvement. De façon plus singulière, le film d’action devient à partir des années soixante/quatre-vingt un genre à part entière qui propose un dépassement excessif et ludique des anciens genres spectaculaires. Ce cinéma de la performance physique et technologique s’est imposé comme le moteur de l’industrie hollywoodienne du blockbuster.Après avoir défini le genre du film d’action, nous analyserons sa double nature, entre l’art conceptuel et la fiction populaire. Les structures narratives stylisées du cinéma d’action contemporain donnent naissance à des images faiblement figuratives, héritières de l’art hyperréaliste et proches de certaines pratiques expérimentales. Mais le film d’action est aussi un fortement incarné, met en valeur des corps musclés et des destructions massives, dans un contexte référentiel marqué.La mise en scène du spectaculaire contemporain équilibre ces deux tendances, entre abstraction et figuration, et aboutit à l’immersion physique du spectateur. Celui-ci est invité à prendre part à l’action, sans bien sûr quitter son siège. Pour ce faire, il doit renoncer à sa rationalité discursive et laisser son intuition percevoir l’enchainement dynamique des images

Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

International audienceThe Monviso ophiolite Lago Superiore Unit constitutes a well-preserved, almost continuous upper fragment of oceanic lithosphere subducted at c. 80 km depth, thereby providing a unique opportunity to study mechanical coupling processes and meter-scale fluid-rock interactions occurring at such depths in present-day subduction zones. It is made of (i) a variably thick (50-500 m) section of eclogitized basaltic crust (associated with minor calcschist lenses) overlying a 100-400 m thick metagabbroic body and of (ii) a c. 1 km thick serpentinite sole. We herein focus on the three major eclogite-facies shear zones found at the top of the unit, at the boundary between basalts and gabbros, and between gabbros and serpentinites, respectively. Strain localization occurred at lithological interfaces, irrespective of material strength. While ductile deformation dominates along the shear zones, local brittle behaviour is demonstrated by the existence of numerous eclogite breccias of Fe-Ti metagabbros and widespread garnet fractures, possibly linked with intermediate-depth eclogite-facies (micro)seismicity. These m- to hm-sized fragments of Fe-Ti metagabbros were later sheared and disseminated within serpentinite schists along the gabbro-serpentinite boundary (Lower Shear zone; LSZ). Pervasive and focused fluid flow is attested in the LSZ by significant alteration of bulk rock compositions, weakening of the rocks and widespread crystallization of hydrous parageneses. By contrast, the Intermediate Shear zone (ISZ) shows evidence for more restricted, short-range fluid flow. The activity of both the ISZ and LSZ ceased during early lawsonite eclogite-facies exhumation, when deformation localized deeper within the serpentinite sole, allowing for the detachment (and preservation) of this large ophiolitic fragment

Retour vers le futur

Et si l’espace des mobilités du Paris des années 1920 avait déjà des attributs et des qualités que nous recherchons et projetons aujourd’hui pour les espaces métropolitains de demain ? À savoir, un foisonnement des mobilités et des usages au fil de la Seine et des canaux, une voirie partagée ou se croisent piétons, vélos et véhicules sans délimitation stricte au sol, des moyens de locomotion variés et inventifs tant dans leur forme, leur fonction que leur mode de propulsion, la marche urbaine omniprésente et peu canalisée, et même la présence d’ani­maux à chaque coin de rue. Les mobilités participent du façonnement du paysage. Lorsqu’elles disparaissent, elles laissent presque toujours des traces. Cette situation peut être donnée à voir à notre regard d’aujourd’hui grâce aux rares et magnifiques plans cinématographiques réalisés par André Sauvage en 1928 dans Études sur Paris. Retour vers le futur. Serait-il possible d’utiliser avantageusement des documents à caractère historique dans des situations où il est avant tout question de changements à venir ?Do the mobilities of Paris in the 1920’s resemble or presage those that urban planners and designers seek today for the future of metropolitan areas? That period offered a richness of means of movement and of corresponding expe­riences and uses, be it in and alongside the Seine or through the coexistence of a diversity of possibilities for movement-walking, pedaling or motoring-in a common, undifferentiated street space. It associated innovation in the form, use and mechanical design of means of loco­motion with great freedom of movement for those on foot and a rich presence of animal life. Ali mobilities play a raie in the shaping of the urban landscape and those that disappear tend to leave traces. Back to the future. The rare, exceptionally fine cinematic images realized by André Sauvage’s 1928 film Études sur Paris suggest the possibility of considering historical documents as source of ideas for reactivating and redefining the latent qualities of the spaces they portray

Pervasive Eclogitization Due to Brittle Deformation and Rehydration of Subducted Basement: Effects on Continental Recycling?

The buoyancy of continental crust opposes its subduction to mantle depths, except where mineral reactions substantially increase rock density. Sluggish kinetics limit such densification, especially in dry rocks, unless deformation and hydrous fluids intervene. Here we document how hydrous fluids in the subduction channel invaded lower crustal granulites at 50–60 km depth through a dense network of probably seismically induced fractures. We combine analyses of textures and mineral composition with thermodynamic modeling to reconstruct repeated stages of interaction, with pulses of high‐pressure (HP) fluid at 650–670°C, rehydrating the initially dry rocks to micaschists. SIMS oxygen isotopic data of quartz indicate fluids of crustal composition. HP growth rims in allanite and zircon show uniform U‐Th‐Pb ages of ∼65 Ma and indicate that hydration occurred during subduction, at eclogite facies conditions. Based on this case study in the Sesia Zone (Western Italian Alps), we conclude that continental crust, and in particular deep basement fragments, during subduction can behave as substantial fluid sinks, not sources. Density modeling indicates a bifurcation in continental recycling: Chiefly mafic crust, once it is eclogitized to >60%, are prone to end up in a subduction graveyard, such as is tomographically evident beneath the Alps at ∼550 km depth. By contrast, dominantly felsic HP fragments and mafic granulites remain positively buoyant and tend be incorporated into an orogen and be exhumed with it. Felsic and intermediate lithotypes remain positively buoyant even where deformation and fluid percolation allowed them to equilibrate at HP

Thermal evolution of an ancient subduction interface revealed by Lu–Hf garnet geochronology, Halilbagi Complex (Anatolia)

The thermal structure of subduction zones exerts a major influence on deep-seated mechanical and chemical processes controlling arc magmatism, seismicity, and global element cycles. Accretionary complexes exposed inland may comprise tectonic blocks with contrasting pressure–temperature (P–T) histories, making it possible to investigate the dynamics and thermal evolution of former subduction interfaces. With this aim, we present new Lu–Hf geochronological results for mafic rocks of the Halilbagi Complex (Anatolia) that evolved along different thermal gradients. Samples include a lawsonite–epidote blueschist, a lawsonite–epidote eclogite, and an epidote eclogite (all with counter-clockwise P–T paths), a prograde lawsonite blueschist with a “hairpin”-type P–T path, and a garnet amphibolite from the overlying sub-ophiolitic metamorphic sole. Equilibrium phase diagrams suggest that the garnet amphibolite formed at ~0.6–0.7 GPa and 800–850 °C, whereas the prograde lawsonite blueschist records burial from 2.1 GPa and 420 °C to 2.6 GPa and 520 °C. Well-defined Lu–Hf isochrons were obtained for the epidote eclogite (92.38 ± 0.22 Ma) and the lawsonite–epidote blueschist (90.19 ± 0.54 Ma), suggesting rapid garnet growth. The lawsonite–epidote eclogite (87.30 ± 0.39 Ma) and the prograde lawsonite blueschist (ca. 86 Ma) are younger, whereas the garnet amphibolite (104.5 ± 3.5 Ma) is older. Our data reveal a consistent trend of progressively decreasing geothermal gradient from granulite-facies conditions at ~104 Ma to the epidote-eclogite facies around 92 Ma, and the lawsonite blueschist–facies between 90 and 86 Ma. Three Lu–Hf garnet dates (between 92 and 87 Ma) weighted toward the growth of post-peak rims (as indicated by Lu distribution in garnet) suggest that the HP/LT rocks were exhumed continuously and not episodically. We infer that HP/LT metamorphic rocks within the Halilbagi Complex were subjected to continuous return flow, with “warm” rocks being exhumed during the tectonic burial of “cold” ones. Our results, combined with regional geological constraints, allow us to speculate that subduction started at a transform fault near a mid-oceanic spreading centre. Following its formation, this ancient subduction interface evolved thermally over more than 15 Myr, most likely as a result of heat dissipation rather than crustal underplating

Diagnosis Of The Chronic Lymphocytic Leukemia (CLL) Using A Raman-Based Scanner Optimized For Blood Smear Analysis (M3s Project)

Introduction/ Background In hematology, actual diagnosis of B chronic lymphocyte-leukemia (CLL) is based on the microscopic analysis of cell morphology from patient blood smear. However, new photonic technologies appear promising to facilitate and improve the early diagnosis, prognostic and monitoring of personalized therapy. The development of automated diagnostic approaches could assist clinicians in improving the efficiency and quality of health services, but also reduce medical costs. Aims The M3S project aims at improving the diagnosis and prognosis of the CLL pathology by developing a multimodal microscopy platform, including Raman spectrometry, dedicated to the automatic analysis of lymphocytes. Methods Blood smears were prepared on glass slides commonly used in pathology laboratories for microscopy. Two types of sample per patient were prepared: a conventional blood smear and a deposit of “pure” lymphocyte subtypes (i.e. normal B, CLL B, T and NK), sorted out in flow cytometry by using the negative double labeling technique. The second sample is used for the construction of a database of spectral markers specific of these different cell types. The preparations were analyzed with the multimodal machine which combines i) a Raman micro-spectrometer, equipped with a 532nm diode laser excitation source; ii) a microscope equipped with 40x and 150x lenses and a high precision xyz motorized stage for scanning the blood smear, and localizing x-y coordinates of representative series (~100 for each patient) of lymphocyte cells before registering three Raman spectra; these cells of interest being previously localized by an original method based on the morphology analysis. After the Raman acquisitions, the conventional blood smears were submitted to immunolabelling using specific antibodies. For the establishment of the Raman classifiers, this post-acquisition treatment was used as reference to distinguish the different lymphocyte sub-populations. Raman data were then analyzed using chemometric processing and supervised statistical classifiers in order to construct a spectral library of markers highly specific of the lymphocyte type and status (normal or pathological). Results Currently, a total of 60 patients (CLL and healthy) were included in the study. Various classification methods such as LDA (Linear Discriminant Analysis), PLS-DA (Partial Least Square Discriminant Analysis), RF (Random Forest) and SVM (Support Vector Machine), were tested in the purpose to distinguish tumoral B lymphocytes from other cell types. These classification algorithms were combined with feature selection approaches. The best performances were around 70% of correct identification when a three-class model (B-CLL vs B-normal vs T and NK lymphocytes) was considered, and 80% in case of a two-class model (B-CLL vs B-normal lymphocytes). These encouraging results demonstrate the potential of Raman micro-spectroscopy coupled to supervised classification algorithms for leukemic cell classification. The approach can find interest more generally in the field of cyto-hematology. Further developments will concern the integration of additional modality such as Quantitative Phase Imaging on one hand to speed the exploration process of cells of interest to be probed, and on the other hand to extract additional characteristics likely to be informative for CLL diagnosis. In addition, the identification of prognostic markers will be investigated by confronting the photonic data to clinical patient information.