Éditeur(s) : HAL CCSD
Résumé : International audience
Seismic anisotropy is a ubiquitous feature of the subcontinental mantle. This can be inferred both from direct seismic observations of shear wave splitting from teleseismic shear waves, as well as the petrofabric analyses of mantle nodules from kimberlite pipes. The anisotropy is principally due to the strain-induced lattice preferred orientation (LPO) of olivine. The combined use of these mantle samples, deformation experiments on olivine, and numerical modeling of LPO, provides a critical framework for making inferences about mantle deformation from observed seismic anisotropy. In most cases there is a close correspondence between mantle deformation derived from seismic observations of anisotropy, and crustal deformation, from the Archean to the present. This implies that the mantle plays a major, if not dominant role in continental deformation. No clear evidence is found for a continental asthenospheric decoupling zone, suggesting that continents are probably coupled to general mantle circulation.
Mantle Petrology: Field Observations and high Pressure experimentations: a Tribute to Francis R. (Joe) Boyd

hal-01391514
http://hal.univ-reunion.fr/hal-01391514
http://hal.univ-reunion.fr/hal-01391514/document
http://hal.univ-reunion.fr/hal-01391514/file/Silver_et_al_BoydVolume 1999_hal.pdf

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
New evolutionary models for the Pyrenean orogeny must consider feedbacks between the Mid-Cretaceous hyperextension postulated recently and the Pyrenean inversion. We present a new crustal section of the Pyrenees through the Jaca Basin, the western Axial Zone and the Chaînons Béarnais, which allows identifying the ancient continental margins of the Iberian and European plates and a suture. A sequential restoration allows a reassessment of the style of convergence through time. Restoration leads to a progressively thinned crust in narrow continental margins separated by a domain of exhumed mantle peridotite and overlain by a detached sedimentary lid. Early convergence during the Late Cretaceous and the Earliest Paleogene was accommodated by subduction of the peridotite domain. This was followed in the Eocene by initial collision involving overriding of the Iberian margin onto the European margin along the deep ramp of the North-Pyrenean Frontal thrust, which defines the suture. Subsequent full collision and strong relief generation from the late-Mid or Late Eocene to the Early Miocene were associated with thrust accretion of the Iberian plate, underlain by wedging and northward subduction of the decoupled Iberian lower crust.
ISSN: 1631-0713

insu-01291223
https://hal-insu.archives-ouvertes.fr/insu-01291223
https://hal-insu.archives-ouvertes.fr/insu-01291223/document
https://hal-insu.archives-ouvertes.fr/insu-01291223/file/The%20crustal%20evolution%20of%20the%20west-central%20Pyrenees%20-%20postprint.pdf
DOI : 10.1016/j.crte.2015.10.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We compile field data collected along the eastern part of the North Pyrenean Zone (NPZ) to point to a tectonic evolution under peculiar thermal conditions applying to the basin sediments in relation with the opening of the Cretaceous Pyrenean rift. Based on this compilation, we show that when thinning of the continental crust increased , isotherms moved closer to the surface with the result that the brittle-ductile transition propagated upward and reached sediments deposited at the early stage of the basin opening. During the continental breakup, the pre-rift Mesozoic cover was efficiently decoupled from the Paleozoic basement along the Triassic evaporite level and underwent drastic ductile thinning and boudinage. We suggest that the upper Albian and upper Creta-ceous flysches acted as a blanket allowing temperature increase in the mobile pre-rift cover. Finally, we show that continuous spreading of the basin floor triggered the exhumation of the metamorphic, ductily sheared pre-rift cover, thus contributing to the progressive thinning of the sedimentary pile. In a second step, we investigate the detailed geological records of such a hot regime evolution along a reference-section of the eastern NPZ. We propose a balanced restoration from the Mouthoumet basement massif (north) to the Boucheville Albian basin (south). This section shows a north to south increase in the HT Pyrenean imprint from almost no metamorphic recrystallization to more than 600 °C in the pre-and syn-rift sediments. From this reconstruction, we propose a scenario of tectonic thinning involving the exhumation of the pre-rift cover by the activation of various detachment surfaces at different levels in the sedimentary pile. In a third step, examination of the architecture of current distal passive margin domains provides confident comparison between the Pyrenean case and modern analogs. Finally, we propose a general evolutionary model for the pre-rift sequence of the Northeastern Pyrenean rifted margin.
ISSN: 0040-1951

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01355131
https://hal-insu.archives-ouvertes.fr/insu-01355131
https://hal-insu.archives-ouvertes.fr/insu-01355131/document
https://hal-insu.archives-ouvertes.fr/insu-01355131/file/TECTO10807-Incorporated%20changes-rev2.pdf
DOI : 10.1016/j.tecto.2016.07.022

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
Although they are famous among Earth scientists, the Lherz peridotites are exposed within geological formations of the North Pyrenean Zone (NPZ) still lacking detailed investigations. Our study focuses on the metasediments of the Aulus basin hosting the Lherz peridotite body and associated ultramafic fragments of smaller size. The new data set comprises of structural analysis and detailed geological mapping of the massive Mesozoic marbles that form the prerift sequence typical of the NPZ and of the ultramafic-rich clastic breccia formations surrounding the peridotite bodies. The massive marbles display an evolution from hot and ductile to cold and brittle deformation, indicative of an exhumation process ending with the sedimentary reworking of both the deformed Mesozoic metasediments and the exhumed ultramafic rocks. Crystal Preferred Orientations (CPO) measured in the marbles support a deformation mechanism by dislocation creep of calcite, which is dominant between 400 8C and 600 8C; these deformation temperatures are within the range determined earlier by Clerc et al. (2015), using RSCM (Raman Spectroscopy of Carbonaceous Material) geothermometry. As a consequence, we better describe the transition from ductile to brittle deformation in the prerift marbles and clarify the origin of the syn-rift breccias. Due to continuous exhumation along detachments' faults, the brecciated metamorphic carbonates of the prerift NPZ sedimentary cover were passively uplifted towards shallower levels and progressively unroofed, while transported passively on the back of the exhumed ultramafic footwall. These results are consistent with the recent interpretations of the North Pyrenean peridotites as remnants of subcontinental mantle rocks exhumed within the pre-Pyrenean rift system. We emphasize the importance of tectonic decoupling between the Mesozoic sedimentary cover and the Palaeozoic basement, which leads to the juxtaposition of metamorphosed and deformed Mesozoic Please cite this article in press as: Lagabrielle Y, et al. Very high geothermal gradient during mantle exhumation recorded in mylonitic marbles and carbonate breccias from a Mesozoic Pyrenean palaeomargin (Lherz area, North Pyrenean Zone, France). C. R. Geoscience (2016), http://dx.
ISSN: 1631-0713

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01285079
https://hal-insu.archives-ouvertes.fr/insu-01285079
https://hal-insu.archives-ouvertes.fr/insu-01285079/document
https://hal-insu.archives-ouvertes.fr/insu-01285079/file/1-s2.0-S1631071315002060-main.pdf
DOI : 10.1016/j.crte.2015.11.004