Thèse de doctorat en Sciences de la Terre
Soutenue en 2010
à Besançon en cotutelle avec l'Université de Padoue , en partenariat avec Université de Franche-comté. UFR des sciences et techniques (autre partenaire) .
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La méchanique des séismes dans la croûte continentale : apports de l’analyse structurale des pseudotachylytes et des cataclasites
This thesis aims at deciphering the complex and polyphase seismic deformation associated with two major pseudotachylyte-bearing fault zones, the pre-mesozoic Outer Hebrides Fault (OHF) in northwest Scotland, and the Mesozoic to Cenozoic Canavese fault zone and adjacent Ivrea zone in the Italian Alps. For both areas, the deformation was analysed from the field scale to scanning electron microscope scale to scanning electron microscope scale. In addition, Ar:Ar absolute dating was performed on Italian pseudotachylytes. The first part of this thesis shows that the OHF in the south Uist-Barra area is clearly segmented: the northern Stulabhal segment is characterized by quartz-feldspar gneisses (QF gneisses) in the foot wall and by two –pyroxene gneisses (Corodale gneisses) in the hanging-wall. The southern Eriskay segment is characterized by QF gneisses both in the hanging wal. Moreover, the Stulabhal segment is underlined by a continuous and mappable, several meters thick, pseudotachylyte sole at the base of the hanging wall, and by diffuse pseudotachylyte fault vein in the footwall, while the Eriksay segment consists of several faults outlined by pseudotachylyte-rich zones whose thickness never exceeds 1 m. […]In the second part of this thesis, we clarify the spatial and temporal distribution of pseudotachylyte in the Val Sesia area of the Ivrea zone. Pseudotachylytesin the Balmuccia periotite tectonic lens were formed during at least two periods:before Permian times and lateCretaceous to Tertiary. Pseudotachylytes in gabbroic rocks are randomly distributed over two-kilometrer-wide belt and were formed in the early Cretaceous. Pseudotachylytes in paragneisses distributed near the Canavese fault were formed in Eocene Times and are probably related to the thrusting of the Sesia zone over the Ivrea zone. This polyphase formation accompanied the exhumation of the Ivrea crust. […] This comparative analysis between the two fault zones brings information pertaining to the mechanical behavior of the continental crust.