Éditeur(s) : John Wiley & Sons
Résumé : Based on all available seismic refraction data, the seismic structure of the Western Approaches to the English Channel and the South Armorican continental shelf has been established. The correlation of seismic velocities showed a three-fold structure, related to geological layers as follows: 1. High-velocity, deep sequence (4.4-6.6km/sec): metamorphic basement and Lower to Middle Palaeozoic. 2. Intermediate sequence (3.6-4.3km/sec): Permo-Triassic (and Jurassic?) and possibly also Lower Cretaceous on the margin of the Western Approaches. 3. Upper sequence (1.9-3.6km/sec): Cretaceous and Cenozoic sediments. An acoustic unconformity appears to be present between the Upper sequence and the High velocity and Intermediate sequences. Different geomorphology characterizes these layers: the Palaeozoic is tectonized and generally follows the Hercynian structural trends; mainly Permo-Triassic sediments fill the depressions of the Palaeozoic floor, but only in the Western Approaches; eastwards-transgressive Cretaceous and Cenozoic sediments cover discordantly the preceding layers. [NOT CONTROLLED OCR]
Petroleum and the continental shelf of North-west Europe (John Wiley & Sons), 1975 , P. 29-43

Droits : John Wiley & Sons
http://archimer.ifremer.fr/doc/1975/publication-5465.pdf
http://archimer.ifremer.fr/doc/00000/5465/

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
Late Jurassic coral reefs are present in the Western High Atlas of Morocco along the eastern paleomargin of the young Atlantic Ocean. The Izwarn section shows two reef units made of scleractinian corals and microbialites, included in a progradational shallowing-upward succession. Changes in reefal composition and structure observed in a ca. 50 cm-thick interval at the base of the reef unit 1 are interpreted to represent the first well-documented ecological succession in Late Jurassic reefs. Bioclastic deposits, sparse and poorly diversified corals (five genera) preserved in life position, and finally a more diversified coral assemblage (11 genera) building a reef framework with stromatolitic crusts reflect pioneer, colonization and diversification stages, respectively. A specific depth window, where light was reduced but sufficient for a catch-up growth mode and below the erosive action of waves, probably at the lower slope of a fore-reef area, has made possible the development and the record of this ecological succession. With a more diversified coral assemblage (16 genera), the reef unit 2 reflects shallower and well-agitated waters of a fore-reef area. Overlaying this second reef unit, the upper part of the section reveals back-reef deposits made of reworked reef elements, whereas a putative reef crest area is not recorded.
ISSN: 0016-6995

hal-00795549
https://hal.archives-ouvertes.fr/hal-00795549
DOI : 10.1016/j.geobios.2012.05.002

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd system, in the Gobi-Altay, since the Middle Mesozoic to the Late Cenozoic. The region was firstly affected by a Lower-Middle Jurassic tectonic phase, characterized by a vertical crustal movement larger than 2 km. Then followed a protracted period without major crustal vertical movements until the last uplift phase. The peneplanation of the Jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 Ma. This same surface corresponds to the present summit plateaux of the massifs, standing about 2000 m above the surrounding region, which corresponds to the vertical movement produced by the ongoing uplift. Modelling of fission track data from the massifs of Ih Bogd and Baga Bogd shows that this uplift phase probably started at 5 ± 3 Ma. The Gobi-Altay mountain range appears therefore as one of the youngest mountain ranges in Central Asia, which is consistent with the idea of a northward propagation of the transpressional deformation from the Himalayan front to the Siberian craton. The Cenozoic uplift rate of the massifs is estimated to be between 0.25 and 1 mm/yr, which is slightly higher than the upper Pleistocene vertical slip rates of the bordering faults. This suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries.
ISSN: 0012-821X

insu-00191116
https://hal-insu.archives-ouvertes.fr/insu-00191116
DOI : 10.1016/j.epsl.2007.04.047

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present in this study the first data on Ra isotopes, 222Rn, and 210Pb in waters from the Lez karst system, one of the main ground-water resources in the South of France. The low Ra isotope activities of the Lez system waters (from 0.35 to 3.45 mBq/L of 226Ra) were measured by gamma spectrometry using the method developed in our previous work. Our data reveal the coherent behavior of 226Ra in Lez spring waters, well correlated to other major and trace elements, like Cl, Na, K, Mg, Li, Rb and Ba. The (228Ra/226Ra) ratios are distinct between the Lez spring (0.60 to 0.72) and two neighboring springs (0.52 to 0.65), showing the spatial variability in karst systems. In spite of their small variations in the Lez spring, it was possible to trace different water components and mixing processes from Lower-Cretaceous, Upper-Jurassic and Middle Jurassic end-members, in agreement with previous studies based on major and trace elements. Data obtained on waters derived from the Upper-Jurassic karst reveal that their (228Ra/226Ra) ratios are not related to the Th/U ratio of the Jurassic limestone, but are rather influenced by the soil and alterite cover of the recharge area.222Rn activities in the Lez spring are relatively low (0.5 to 3.7 Bq/L) compared to other karst regions. The highest 222Rn activities are found in diluted waters following heavy rainfall episodes, suggesting a subsurface origin of Rn. Soil and alterite samples that have much higher 226Ra activities (from 51 to 130 Bq/kg), compared to those from the main aquifer rocks (from 2.9 to 16 Bq/kg), are probably the main source of Rn, rather than the rocks of the karst itself. The study of several flood episodes reveals the correlation between Rn peak-values or total activity discharged at the spring with cumulative rainfall. Finally, 222Rn dissolved in water decays to 210Pb, and our data show that constraints on transfer times of underground waters can potentially be obtained from their coupled measurement.
ISSN: 0009-2541

hal-01622749
https://hal.archives-ouvertes.fr/hal-01622749
DOI : 10.1016/j.chemgeo.2017.06.022

Éditeur(s) : HAL CCSD Elsevier
Résumé : In this study, I examine the strain modes of the forearc, arc and back-arc domains in arc-continent collisional settings leading to arc material subduction, delamination and/or accretion. The study focusses on two well-documented colliding island arcs: the Izu–Bonin–Mariana (IBM) arc in Japan and the Luzon arc in Taiwan, both carried by the Philippine Sea plate. Firstly, there is a body of evidence that both the IBM and the Luzon arcs were built on the same Late Jurassic to Early Cretaceous “proto-Philippine Sea Plate” crust. Their internal structure is thus more heterogeneous than expected from Paleogene or Neogene supposedly “intra-oceanic” island arcs. Secondly, those arc systems and proximal “back-arcs” have similar seismic characteristics attesting either for the presence of a middle crust with continental velocities and/or serpentinized uppermost mantle that facilitate crustal shortening/slivering and subsequent decoupling from the rest of the subducting plate. It is shown that the proximal back-arc domain (called “rear-arc” in case of paleoarc activity), overlying the mantle wedge and the subducting slab, may lose its strength if slab-derived hydration occur. Decoupling then occurs below the Moho. Arc delamination likely occurs in mid-crustal levels because middle-crust, heated by nearby magmatism, becomes weak. Accretion of arc material onto the upper plate depends on the characteristics of the arc itself and the geodynamic configuration. Most of the accreted material is probably underplated rather than frontally accreted.
ISSN: 0743-9547

hal-01243080
https://hal.archives-ouvertes.fr/hal-01243080
DOI : 10.1016/j.jseaes.2013.07.043

Éditeur(s) : HAL CCSD Springer/Terra Scientific Publishing Company
Résumé : International audience
Samples were obtained from three baked contacts and one lava flow along the upper Turonian-lower Coniacian Tovuz section, two baked contacts along the upper Coniacian-lower Santonian Paravakar section in the northern part of Armenia, and three baked contacts along the Titonian-Valanginian Kafan section in southern Armenia. A total of 130 samples were studied. Updated mean paleomagnetic poles were calculated for the Upper Cretaceous Tovuz-Paravakar sections (65.6 degrees N, 162.2 degrees E, A(95) = 4.3, paleolatitude = 27.0 +/- 3.4 degrees) and the Upper Jurassic-Lower Cretaceous Kafan section (61.7 degrees N, 158.9 degrees E, A(95) = 4.8 degrees, paleolatitude = 24.7 +/- 3.8 degrees). Paleointensity determinations could be estimated from two of the upper Cretaceous and three of the Upper Jurassic-Lower Cretaceous baked contacts, corresponding to a 30% success rate. The mean virtual dipole moments obtained were low (1.7-5.5 x 10(22) A m(2)), which is in agreement with data published by Bol'shakov and Solodovnikov (1981a, 1983) for the same sections (3.0-4.4 x 10(22) A m(2)). Our results support the hypothesis of the Mesozoic Dipole Low, even though the overall data arc widely dispersed.
ISSN: 1343-8832

hal-00413047
https://hal.archives-ouvertes.fr/hal-00413047

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The basis of this study is a new bathymetric map of the northeast Atlantic compiled from previously published maps made from conventional echosounder data, plus all Sea Beam data acquired on board the R/V JEAN CHARCOT since 1977. As most of the Sea Beam data have been obtained on the continental margin from Porcupine Seabight to the south of the Iberian Peninsula, a precise picture of the continental slope is given. A statistical analysis of the canyons, based on 750 measurements, reveals that many of the canyons present sharp changes in their direction, indicating a structural control mainly linked to the late Hercynian trends, especially around the Iberian Peninsula. Nevertheless, the paths of canyons may merely reflect recent gravity processes, as in the Porcupine Seabight. Canyons locally follow the directions of listric and associated transecting faults (Permian to Triassic and upper Jurassic to lower Cretaceous), as on the Celtic
ISSN: 0278-7407

hal-01261558
https://hal.archives-ouvertes.fr/hal-01261558
https://hal.archives-ouvertes.fr/hal-01261558/document
https://hal.archives-ouvertes.fr/hal-01261558/file/Lallemand1986-Tectonics.pdf
DOI : 10.1029/TC005i007p01125

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : The Latest Cretaceous/Paleocene paleokarsts from Bas-Languedoc (South of France) are characterized by : 1) exokarstic paleosurfaces (sink holes, pinnacles, canyons) which are mostly superimposed onto the Late Jurassic limestones and partly filled up with breccias and sandy clays containing Paleocene planktonic foraminifera; 2) endokarstic cavities filled up by sandy pelites and laminated mudstones with similar micropaleontological assemblage. All these cavities constitute three cut-and-filled paleokarstic systems. A general model of formation for this polyphase system is proposed. These paleosurfaces are generated by a Latest Cretaceous tectonic phase and Paleocene movements associated with eustatic rises inducing rapid floodings. During Upper Danian-Lower Selandian times three successive base levels drops, whose cumulated duration could be as long as 3 Ma, have induced several hundred metres of incisions within the exposed Jurassic carbonate series. A paleogeographic reconstruction shows three main marine gulfs which extend towards NE the EW Pyrenean thrust belt ("Pyrenean Paleocene Trough", PPT) located on the axis of the future Pyrenees. The similarity of the facies and micropaleontological content in the two domains suggests connexions between the marine Paleocene deposits of Bas-Languedoc and the PPT. It could thus explain the succession of the same tectono-eustatic events. We propose, as an hypothesis, that the rapid sea-level changes, as recorded by the imbricated karstic paleomorphologies, could be induced by the closing and the opening of a strait in the Eastern part of the PPT acting as a sill. This would be controlled by tectonic movements along the active orogenic axis of the Pyrenean Range and eustatic variations of the Paleocene World Ocean. The karstic systems developed during these low-stand episodes may have been later reactivated after the Early Selandian and more specifically during the Messinian desiccation event. This late evolution may have generated deep flooded karsts, now situated below the present sea level. Such karsts, partly inherited from Paleocene, could be important aquifers of economic interest.
ISSN: 0985-3111

hal-00407601
https://hal.archives-ouvertes.fr/hal-00407601
DOI : 10.3166/ga.20.301-326

Éditeur(s) : HAL CCSD Société Géologique de France
Résumé : International audience
The seaward extension of onshore formations and structures were previously almost unknown in Provence. The interpretation of 2D high-resolution marine seismic profiles together with the integration of sea-bottom rock samples provides new insights into the stratigraphic, structural and paleogeographic framework of pre-Messinian Salinity Crisis (MSC) deposits of the Provence continental shelf. Seven post-Jurassic seismic units have been identified on seismic profiles, mapped throughout the offshore Provence area and correlated with the onshore series. The studied marine surface and sub-surface database provided new insights into the mid and late Cretaceous paleogeography and structural framework as well as into the syn-and post-rift deformation in Provence. Thick (up to 2000 m) Aptian-Albian series whose deposition is controlled by E-W-trending faults are evidenced offshore. The occurrence and location of the Upper Cretaceous South-Provence basin is confirmed by the thick (up to 1500 m) basinal series downlaping the Aptian-Albian unit. This basin was fed in terrigenous sediments by a southern massif (" Massif Méridional ") whose present-day relict is the Paleozoic basement and its sedimentary cover from the Sicié imbricate. In the bay of Marseille, thick syn-rift (Rupelian to Aquitanian) deposition occurred (>1000 m). During the rifting phase, syn-sedimentary deformations consist of dominant N040 to N060 sub-vertical faults with a normal component and N050 drag-synclines and anticlines. The syn-rift and early post-rift units (Rupelian to early Burdigalian) are deformed and form a set of E-W-trending en echelon folds that may result from sinistral strike-slip reactivation of N040 to N060 normal faults during a N-S com-pressive phase of early-to-mid Burdigalian age (18-20 Ma). Finally, minor fault reactivation and local folding affect post-rift deposits within a N160-trending corridor localized south of La Couronne, and could result from a later, post-Burdigalian and pre-Pliocene compressive phase.
Cadre tectonostratigraphique des formations anté-pliocènes du plateau continental de Provence (golfe du Lion oriental, SE France) Mots-clés. – Géologie marine, Tectonostratigraphie, Stratigraphie sismique, Paléogéographie crétacée, Rifting oligo-miocène, Compression post-rift Résumé. – Le prolongement en mer des formations et des structures provençales était jusqu'alors largement inconnu.L'interprétation de profils de sismique-réflexion marine 2D et l'intégration de dragages et carottages du fond-marin ont permis d'apporter des éléments nouveaux concernant le cadre stratigraphique, structural et paléogéographique des dé-pôts anté-Messiniens du plateau continental de Provence. Sept unités sismiques post-jurassiques ont été identifiées sur les profils sismiques, cartographiées à travers le plateau continental et corrélées avec les séries affleurant à terre. Une épaisse unité apto-albienne (jusqu'à 2000 m) dont le dépôt est contrôlé par des failles E-W a été mise en évidence en mer. L'existence d'un bassin subsident au Crétacé supérieur sur le plateau continental de Provence a été confirmée par le développement d'une épaisse série de bassin (jusqu'à 1500 m) reposant en downlap sur l'Apto-Albien. Le socle mé-tamorphique de l'écaille de Sicié et sa couverture sédimentaire peut être considéré comme une relique allochtone du « Massif Méridional » ayant alimenté le Bassin sud-provençal en éléments terrigènes au Crétacé supérieur. Dans la rade de Marseille, une épaisse unité syn-rift (Rupélien à Aquitanien) a été mise en évidence (>1000 m), structurée en une série de synformes en échelon d'axe E-W et affectée par des failles d'orientation dominante N040 à N060. Sur le flanc sud des synformes, la formation de plis d'axe N050 est associée à une déformation syn-sédimentaire. La formation des synformes en échelon d'axe E-W résulterait d'une réactivation en décrochement des failles N040 à N060 pendant une phase de compression N-S dont l'âge est compris entre le Burdigalien inférieur et moyen (18-20 Ma). Enfin, les dépôts post-rift sont affectés par des déformations mineures (réactivation de failles et plis associés), le long d'un couloir d'orientation N160 à l'ouest de la baie de Marseille, attribuables à une phase de compression post-burdigalienne et anté-pliocène.
ISSN: 0037-9409

hal-01463727
https://hal-amu.archives-ouvertes.fr/hal-01463727
https://hal-amu.archives-ouvertes.fr/hal-01463727/document
https://hal-amu.archives-ouvertes.fr/hal-01463727/file/Fournier_et_al_Provence_2016.pdf
DOI : 10.2113/gssgfbull.187.4-5.187

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
The Jurassic Mirdita ophiolite crops out in the western branch of the Hellenide-Dinaride ophiolite belt in the Balkan Peninsula; it represents a remnant of the Tethyan oceanic lithosphere developed between the Apulian and Pelagonian microcontinents. Emplaced during the Cretaceous on the western margin of Pelagonia, the Mirdita ophiolite was involved in southwestward thrusting of the Hellenide-Dinaride tectonic units during the Eocene alpine tectonics. It was little affected, however, by these alpine events as marked by nearly horizontal Cretaceous limestone deposits overlying the ophiolite. A continuous section of Middle Jurassic oceanic crust, including thin gabbros, a N-S-trending sheeted dike complex, and extrusive rocks, is exposed in the central part of the ophiolite and thickens eastward within a regional, N-S-trending synform. Peridotite massifs exposed along the western and eastern edges of this synform show major structural and petrological differences. The eastern ultramafic domain has a harzburgitic mantle exhibiting a high-temperature asthenospheric foliation dipping steeply to moderately to the west. Major chromite deposits are restricted to these eastern ultramafic massifs. The western ultramafic domain has a zoned mantle, with asthenospheric harzburgite exposed at its western margin, progressively replaced eastward by plagioclase-peridotites that were highly strained at low temperatures, and that are bounded by amphibole-peridotites along with crustal rocks. The occurrence of plagioclase is ascribed to melt impregnation processes that occurred immediately before or during intense lithospheric deformation. The gabbros in the eastern massifs are thicker (1-2 km and layered, whereas they are highly thin and discontinuous in the western massifs. Mantle peridotites of the western massifs locally are in direct contact with the overlying diabase and volcanic rocks along ductile shear zones. Development of epidote-amphibolite facies metamorphism in upper-crustal rocks was produced by hydrothermal alteration in the oceanic realm, and was intense and widespread in the western domain. The Mirdita ophiolite likely originated in a short-lived, narrow ocean basin, which was closed during the Middle Jurassic by eastward overthrusting of the western domain, and westward subduction of the eastern domain. This constrictional phase was followed by dextral oblique convergence between the Pelagonian and Apulian microcontinents. This model implies a parautochtonous origin of the Mirdita ophiolite between these two microcontinents.
ISSN: 0020-6814

hal-00456063
https://hal.archives-ouvertes.fr/hal-00456063
DOI : 10.1080/00206810902823982

Éditeur(s) : HAL CCSD
Résumé : The northern Mirdita ophiolite massifs in Albanian Dinarides formed at a slow-spreading ridge, active during the Jurassic (160–165 Ma). They share a common horizontal Jurassic–Lower Cretaceous sedimentary cover showing that they were not deeply and intrinsically affected by later Alpine thrusting. The western massifs of Mirdita, first oceanic core complex (OCC) and detachment shear zone described in ophiolites, compare with OCCs in slow-spreading ridges and provide continuous exposure of the deep internal structure of this system, revealing its kinematics, thanks to detailed structural mapping in peridotites and gabbros. The Mirdita detachments root in the Moho transition zone (MTZ), a weak zone at the top of asthenospheric mantle, where basaltic melts impregnate dunites. The OCC domes are plagioclase-amphibole–bearing mylonitic peridotites, ∼400 m thick, grading downward within 200 m to harzburgitic mantle. The mylonitic detachments crossed Moho beneath a NNE-SSW–trending ridge. On the western side of OCC domes, the hanging wall of the ridge, crustal gabbros, and basalts are still preserved, despite being deeply affected by hydrothermal alteration. From there, the partially molten MTZ was detached as a shear zone, mixing with lower gabbros. The OCC emerged, migrating upsection and eastward over 5 km. Finally, the OCC front is observed in hornblende-rich syntectonic mylonites derived from upper gabbros and from the overlying former lid. Serpentinization is static within these mylonites. A low-temperature detachment fault is expressed as a sheared antigoritic mélange at the margin of the mylonitic shear zone. Asthenospheric flow in the harzburgitic mantle beneath the ridge of origin has been preserved below the OCC rooting. The dominant asthenospheric flow direction trends parallel to the ridge axis. This mantle flow rotates over 200 m into the low-temperature mylonitic detachments, where OCC motion turns transversal to the ridge. Crystal preferred orientation measurements on six samples point to brown hornblende crystal growth during mylonitic flow and illustrate the change of olivine intra-crystalline slip system in mylonites compared to porphyroclastic harzburgite.
ISSN: 1553-040X

hal-01504440
https://hal.archives-ouvertes.fr/hal-01504440
DOI : 10.1130/GES01383.1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The geologic evolution of the South Armenian Block (SAB) in the Mesozoic is reconstructed from a structural, metamorphic, and geochronologic study including U–Pb and 40Ar/39Ar dating. The South Armenian Block Crystalline Basement (SABCB) outcrops solely in a narrow tectonic window, NW of Yerevan. The study of this zone provides key and unprecedented information concerning closing of the Northern Neotethys oceanic domain north of the Taurides-Anatolides platform from the Middle Jurassic to the Early Cretaceous. The basement comprises of presumed Proterozoic orthogneiss overlain by metamorphosed pelites as well as intrusions of granodiorite and leucogranite during the Late Jurassic and Early Cretaceous. Structural, geochronological and petrological observations show a multiphased evolution of the northern margin of the SAB during the Late Jurassic and Early Cretaceous. A south-dipping subduction under the East Anatolian Platform-South Armenian Block (EAP-SAB) is proposed in order to suit recent findings pertaining emplacement of relatively hot subduction related granodiorite as well as the metamorphic evolution of the crystalline basement in the Lesser Caucasus area. The metamorphism is interpreted as evidencing: (1) M1 Barrovian MP–MT conditions (staurolite–kyanite) at c. 157–160 Ma and intrusion of dioritic magmas at c. 150–156 Ma, (2) near-adiabatic decompression is featured by partial melting and production of leucogranites at c. 153 Ma, followed by M2 HT–LP conditions (andalusite–K-feldspar). A phase of shearing and recrystallization is ascribed to doming at c. 130–150 Ma and cooling at 400 °C by c. 123 Ma (M3). Structural observations show (1) top to the north shearing during M1 and (2) radial extension during M2. The extensional event ends by emplacement of a thick detrital series along radial S, E and W-dipping normal faults. Further, the crystalline basement is unconformably covered by Upper Cretaceous-Paleocene series dated by nannofossils, evolving from Maastrichtian marly sandstones to Paleocene limestones.
ISSN: 0743-9547

hal-01174077
https://hal.archives-ouvertes.fr/hal-01174077
DOI : 10.1016/j.jseaes.2014.07.018

Éditeur(s) : HAL CCSD
Résumé : National audience
Crustal-scale models for the Pyrenees based on ECORS reflection profileshave around 20 years now. In recent years, new understandingswere gained on the reconstruction to the preorogenic times, namelya scenario of extreme crustal attenuation and mantle exhumation ; inturn, this has implications on the interpretation of the present-day structure,as new models for the chain must consider feedbacks between themid-Cretaceous hyperextension and the Pyrenean inversion. On the WcentralPyrenean traverse, the southern part comprises 3 S-vergent basementthrust units, the Lakora, Gavarnie and Guarga units, flanked by thedetached cover of the Jaca piggyback basin and the Ebro basin, wherethe Mesozoic is thin and Late Cretaceous-Tertiary synorogenic carbonateand detrital sequences record a southward depocenter migration.To the N, the Chaînons Béarnais belt (CB) is a system of Jurassic to LowerCretaceous carbonate anticline ridges separated by synclines withthick Albian-Cenomanian flysch, covered to the north by Upper Cretaceousflysch sequences. The CB is thrust southwards together with theLakora thrust unit and northwards onto the Aquitaine basin. CB foldinglargely results from the rising and squeezing of diapirs initiated duringthe Jurassic-Early Cretaceous extension. Pieces of crust and mantle liftedin the diapirs attest that the CB derive from a Cretaceous domainof hyperextended continental crust and exhumed mantle. Moho reflectionsin the ECORS-Arzaq profile constrain the present deep structure.Restoration leads to a Mesozoic cover detachment over the N-Iberianand S-European margins. Inversion began by subduction of the exhumedmantle and folding and pop-up thrusting of the CB cover onto themargins. From the mid-late Eocene onwards, continental collision wasaccommodated by wedging and thrust stacking in the Iberian crust, involvingthe piggyback formation of S-vergent basement thrusts in theupper crust, and the northward subduction of the lower crust.
24 ème Réunion des sciences de la Terre 2014
Pau, France

insu-01080831
https://hal-insu.archives-ouvertes.fr/insu-01080831

Éditeur(s) : HAL CCSD Elsevier
Résumé : Obduction processes, though spectacular (dense oceanic ophiolites are emplaced on top of light, continental rocks along thousands of km), have been little elucidated since the advent of plate tectonics. Based on convergence velocities and blueschist formation, we show that the two recent large-scale, Upper Jurassic and Upper Cretaceous obductions coincided with periods during which velocities increased abruptly and more than doubled. The latter obduction also modified the interplate coupling across adjacent subduction zones. We critically propose a mechanism in which large-scale obductions are triggered by intraplate instabilities resulting from sharp plate accelerations, possibly in response to superplume events
ISSN: 0012-821X

hal-00407960
https://hal.archives-ouvertes.fr/hal-00407960
DOI : 10.1016/j.epsl.2007.04.002

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The identification of a large OIB-type volcanic sequence on top of an obducted nappe in the Lesser Caucaus of Armenia helps us explain the obduction processes in the Caucasus region that are related to dramatic change in the global tectonics of the Tethyan region in the late Lower Cretaceous. The ophiolitic nappe preserves three distinct magmatic series, obducted in a single tectonic slice over the South Armenian Block during the Coniacian-Santonian (88-83 Ma), the same time as the Oman ophiolite. Similar geological, petrological, geochemical and age features for various Armenian ophiolitic massifs (Sevan, Stepanavan, and Vedi) argue for the presence of a single large obducted ophiolite unit. The ophiolite, shows evidence for a slow-spreading oceanic environment in Lower to Middle Jurassic. Serpentinites, gabbros and plagiogranites were exhumed by normal faults, and covered by radiolarites. Few pillow-lava flows have infilled the rift grabens. The ophiolite lavas have hybrid geochemical composition intermediate between Arc and MORB signatures: (La/Yb)(N) = 0.6-0.9: (Nb/Th)(N) = 0.17-0.57; (Nd-143/Nd-144)(i) = 0.51273-0.51291; (Sr-87/Sr-86)(i) = 0.70370-0.70565; (Pb-207/Pb-204)(i) = 15.4587-15.5411; (Pb-208/Pb-204)(i) = 37.4053-38.2336; (Pb-206/Pb-204)(i) = 17.9195-18.4594. These compositions suggest they were probably formed in a back-arc basin by melting of a shallow asthenosphere source contaminated by a deeper mantle source modified by subducted slab-derived products. Sr-87/Sr-86 ratios and petrological evidence show that these lavas have been intensely altered by mid-oceanic hydrothermalism as well as by serpentinites, which are interpreted as exhumed mantle peridotites. The gabbros have almost the same geochemical composition as related pillow-lavas: (La/Yb)(N) = 0.2-2.3; (Nb/Th)(N) = 0.1-2.8; (Nd-143/Nd-144)(i) = 0.51264-0.51276: (Sr-87/Sr-86)(i) = 0.70386-0.70557; (Pb-207/Pb-204)(i) = 15.4888-15.5391; (Pb-208/Pb-204)(i) = 37.2729-37.8713; (Pb-206/Pb-204)(i) = 17.6296-17.9683. Plagiogranites show major and trace element features similar to other Neo-Tethyan plagiogranites (La/Yb)(N) = 1.10-7.92; (Nb/Th)(N) = 0.10-0.94; but display a less radiogenic Nd isotopic composition than basalts [(Nd-143/Nd-144)(i) = 0.51263] and more radiogenic (Sr-87/Sr-86)(i) ratios. This oceanic crust sequence is covered by variable thicknesses of unaltered pillowed OIB alkaline lavas emplaced in marine conditions. Ar-40/Ar-39 dating of a single-grain amphibole phenocryst provides a Lower Cretaceous age of 117.3 +/- 0.9 Ma, which confirms a distinct formation age of the OIB lavas. The geochemical composition of these alkaline lavas is similar to plateau-lavas [(La/Yb)(N) = 6-14; (Nb/Th)(N) = 0.23-0.76; (Nd-143/Nd-144)(i) = 0.51262-0.51271; (Sr-87/Sr-86)(i) = 0.70338-0.70551; (Pb-207/Pb-204)(i) = 15.5439-15.6158; (Pb-208/Pb-204)(i) = 38.3724-39.3623; (Pb-206/Pb-204)(i) = 18.4024-19.6744].;They have significantly more radiogenic lead isotopic compositions than phiolitic rocks, and fit the geochemical compositions of hot-spot derived lavas mixed with various proportions of oceanic mantle. In addition, this oceanic + plateau sequence is covered by Upper Cretaceous calc-alkaline lavas: (La/Yb)(N) = 2.07-2.31; (Nb/Th)(N) = 0.08-0.15; (Nd-144/Nd-143)(i) = 0.51271-0.51282; (Sr-117/Sr-116)(i) = 0.70452-0.70478), which were likely formed in a supra-subduction zone environment. During the late Lower to early Upper Cretaceous period, hot-spot related magmatism related to plateau events may have led to significant crustal thickening in various zones of the Middle-eastern Neotethys. These processes have likely hindered subduction of some of the hot and thickened oceanic crust segments, and allowed them to be obducted over small continental blocks such as the South Armenian Block.
ISSN: 0024-4937

hal-00443855
https://hal.archives-ouvertes.fr/hal-00443855
DOI : 10.1016/j.lithos.2009.02.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : Different types of fractures and fault rocks occur within the major normal fault zones bordering the NW of the Neogene Penedes basin (NE Spain). In the southwest part of the basin, the main fault is the Baix Penedes fault that places the Upper Jurassic-Lower Cretaceous dolomicrites of the footwall in contact with the Miocene siliciclastic sediments of the hangingwall. Within the footwall damage zone, different fracture systems and their respective associated breccias and cements have been recognized. Using a combination of structural, petrologic and geochemical analyses, we show that these fracture systems evolved from mainly tectonic to mainly karstic features during the progressive development and upward propagation of the fault. The earlier fractures and associated breccias represent the initial stages of the fault propagation, when the process zone formed around the fault tip was dominated by dilatant fracturing (fractures 1 and dilatant breccias B1). The fluid involved in this early deformation precipitated the dolomite cement Cl, in equilibrium with the host-rock in a closed hydrogeological system. Localization of frictional processes generated cataclasites and ultracataclasites along distinct second-order faults (fractures 2). In these fractures, the dolomite cement C2 precipitated in relation to the incipient opening of the hydrological system to percolating meteoric waters. The later fractures and associated breccias represent the late stages of the fault propagation. These structures (fractures 3, fractures 4 and the dilatant breccias B2) were formed when the extensional deformation reached the surface, resulting in an increasingly open hydrogeological system. At these stages, deposition of the dolomitic sediment DS and precipitation of the calcite cements C3, C4 and C5 show the circulation of freshwaters in a vadose meteoric environment, i.e. in karstic conditions.
ISSN: 0375-6742

hal-00512690
https://hal.archives-ouvertes.fr/hal-00512690
DOI : 10.1016/j.gexplo.2009.11.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The behaviour of the four Ra isotopes (measured by gamma spectrometry) and 222Rn (measured with an AlphaGUARD ionisation chamber) has been investigated in NaCl-rich thermal waters of Balaruc-les-Bains on the Mediterranean coast (South of France). This study allows identification of the deep thermal water signature and reveals the influence of seawater or karst water inflows on Ra isotopes and 222Rn. The deep thermal water has 226Ra and 222Rn activities of 840 and 1900 mBq/l, respectively, a (228Ra/226Ra) activity ratio of 0.59, and low (224Ra/228Ra) and (223Ra/226Ra) ratios of 0.67 and 0.025, respectively. Several arguments suggest a dominant role of radioactive decay for short-lived Ra isotopes and Rn during the relatively rapid ascent of thermal water through wide open fractures and drains. The low (223Ra/226Ra) ratio constrains the maximum ascent velocity of thermal water to 8-10 m/h. Seawater inflow into the hydrothermal system results in an enrichment in short-lived Ra isotopes and 222Rn. The high (223Ra/226Ra) ratio (0.23) suggests that 223Ra, 224Ra and 222Rn produced by alpha-recoil in the upper-Jurassic limestone are entrained by seawater percolation through the coastal basement, due to active pumping in one of the near shore production well. This process would be enhanced by a low water/rock ratio (i.e. in a low-porosity, micro-fractured limestone). Mixing of this enriched seawater with thermal water induces barite precipitation with co-precipitation of a large fraction of Ra. Short-lived Ra isotopes may thus be useful tracers of seawater flux towards the continent. Conversely, the inflow and mixing of karst groundwater result in a general dilution of all dissolved elements, only a small enrichment in 224Ra and 223Ra, but a large enrichment in 222Rn (up to 26 Bq/l). The combination of Ra isotopes and 222Rn data provides a good way to trace the dynamics of different water masses along coastal areas.
ISSN: 0016-7037

hal-00795512
https://hal.archives-ouvertes.fr/hal-00795512
DOI : 10.1016/j.gca.2012.09.010

Éditeur(s) : Institut Francais du Pétrole
Résumé : The study of the rock and sediment dredgings carried out on the Armorican margin between 47 and 48° latitude North enables us to precise this latter's paleogeographical and tectonic evolution and to integrate it to the Bay of Biscay's. The microfacies analysis of the rock samples dating back from the Upper Jurassic to the Neogene era demonstrates: - on the one hand, the belonging of the northern edge of the Armorican margin to the Mesogean domain, at least up to the Mid-Cretaceous period; - on the other hand, the persistence of a carbonated platform regime which seems to operate from the Tithonian to the lower Tertiary phase, and on which reef could grow, especially in the Mid-Cretaceous period. Over the whole period, sedimentation compensated for subsidence; - lastly, the increase of subsidence from the Eocene period (accompanied with a decrease in the calcium production?) which is most probably related to the major tectonic phenomena that affected the southern edge of the European plate at that time.
L'étude des dragages de roches et de sédiments effectués sur la marge armoricaine entre 47 et 48° de latitude Nord permet d'en préciser l'évolution paléogéographique et tectonique et de l'intégrer à celle du golfe de Gascogne. L'andyse de microfaciès des échantillons rocheux dont l'âge varie du Jurassique supérieur au Néogène met en évidence : - d'une part, l'appartenance de la bordure nord de la marge armoricaine au domaine mésogéen au moins jusqu'au Crétacé moyen ; - d'autre part, la permanence d'un régime de plate-forme carbonatée qui paraît fonctionner du Tithonique au Tertiaire inférieur, sur laquelle ont pu s'installer des édifices récifaux notamment au Crétacé moyen. Pendant toute cette période la sédimentation a compensé la subsidence ; - enfin, l'accentuation de la subsidence à partir de l'Éocène (accompagnée d'une diminution de la production de calcium ?) qui est vraisemblablement en relation avec les phénomènes tectoniques majeurs qui ont affecté à ce moment la bordure sud de la plaque européenne. [OCR NON CONTRÔLE]
Revue de l'Institut Francais du Pétrole (Institut Francais du Pétrole), 1976-06 , Vol. 31 , N. 3 , P. 401-425

Droits : Institut Francais du Pétrole
http://archimer.ifremer.fr/doc/1976/publication-5100.pdf
http://archimer.ifremer.fr/doc/00000/5100/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The continental South Armenian Block – part of the Anatolide–Tauride South Armenian microplate – of Gondwana origin rifted from the African margin after the Triassic and collided with the Eurasian margin after the Late Cretaceous. During the Late Cretaceous, two northward dipping subduction zones were simultaneously active in the northern Neo-Tethys between the South Armenian Block in the south and the Eurasian margin in the north: oceanic subduction took place below the continental Eurasian margin and intra-oceanic subduction resulted in ophiolite obduction onto the South Armenian Block in the Late Cretaceous.The paleolatitude position of the South Armenian Block before its collision with Eurasia within paleogeographic reconstructions is poorly determined and limited to one study. This earlier study places the South Armenian Block at the African margin in the Early Jurassic. To reconstruct the paleolatitude history of the South Armenian Block, we sampled Upper Devonian–Permian and Cretaceous sedimentary rocks in Armenia. The sampled Paleozoic rocks have likely been remagnetized. Results from two out of three sites sampled in Upper Cretaceous strata pass fold tests and probably all three carry a primary paleomagnetic signal. The sampled sedimentary rocks were potentially affected by inclination shallowing. Therefore, two sites that consist of a large number of samples (> 100) were corrected for inclination shallowing using the elongation/inclination method.These are the first paleomagnetic data that quantify the South Armenian Block's position in the Tethys ocean between post-Triassic rifting from the African margin and post-Cretaceous collision with Eurasia. A locality sampled in Lower Campanian Eurasian margin sedimentary rocks and corrected for inclination shallowing, confirms that the corresponding paleolatitude falls on the Eurasian paleolatitude curve. The north–south distance between the South Armenian Block and the Eurasian margin just after Coniacian–Santonian ophiolite obduction was at most 1000 km.
ISSN: 0040-1951

hal-01365871
https://hal.archives-ouvertes.fr/hal-01365871
DOI : 10.1016/j.tecto.2015.01.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper focuses on the analyses of the clastic sedimentary infill of the Coastal Plain of Eastern Mexico, which initiated synchronously with the Laramide orogeny in the vicinity of the Golden Lane. Results of these analyses are used as boundary conditions for calibrating/interpreting seismic profiles across more distal depocenters in the offshore of the Gulf of Mexico, from the sea shore and continental slope in the west to the abyssal plain in the east. The objective of the study is to better predict the reservoir distribution in the Deep offshore Basin of the Gulf of Mexico (DBGM), in order to explore for petroleum. The Coastal Plain is underlain by three morpho-tectonic domains: the tectonic front of the Sierra Madre Orientale (SMO), the Chicontepec deep water flexural basin, and the Tuxpan Platform (also known as the Golden Lane). Each domain is characterized by a distinct, dominantly siliciclastic Cenozoic lithostratigraphy. After a Jurassic rifting episode, followed by thermal subsidence, the oceanic basin and its western passive margin were deformed during the Upper Cretaceous and Paleogene, by far field stresses associated with the Cordilleran-Laramide Orogeny. Starting in the Late Cretaceous-Early Paleogene and during the Early Eocene, the tectonic load associated with the Laramide Orogen (Sierra Madre Oriental, SMO) caused flexural subsidence of the foreland located under the Coastal Plain. During this period, a massive transfer of siliciclastic sediments occurred from the Laramide foothills into the adjacent foreland. Sediments were eroded of the Sierra Madre tectonic wedge. Loading by these sediments pushed source units associated with the former passive margin down ward. The first syn-tectonic sediments of the Laramide orogeny were turbiditic silt layers in submarine fans which record also numerous collapse episodes and gravity slides. During the Late Eocene and Oligocene, the flexural subsidence stopped in the hinterland, whereas the subsidence of the passive margin resumed. This resulted in a change in the overall sedimentary architecture of the basin. Paleo-highs and reefs facies of the Golden Lane were flooded. Clastics by-passed the reefs and progradational clastic stratification formed as sediment moved towards the DBGM in the east. The final depositional environment of the continental platform/Coastal Plain became deltaic, marked by a succession of sand bars, levees and channels systems. From Miocene times onward, a system of gravitational listric faults developed near the platform to slope transition, resulting in a coeval compressional system at the transition between the slope and the abyssal plain. This system is driven by sediments charge. Because the sedimentation rate is larger than the subsidence, a large amount of clastics and slumped sediments are deposited in hangingwall basins.
ISSN: 0264-8172

hal-00424586
https://hal.archives-ouvertes.fr/hal-00424586
DOI : 10.1016/j.marpetgeo.2008.03.009