Mécanismes et évolution des chaînes d'accrétion : exemple des chaînes paléozoïques d'Asie Centrale (Ouest Junggar, N-O de la Chine)

Abstract : Accretionary orogens develop at sites of oceanic subduction and they largely contribute to continentalcrust growth. The Altaids tectonic collage covers the whole Central Asia, exposing numerousaccretionary orogens that can account for the Palaeozoic continental crust growth. Multidisciplinaryapproach, using geochronological, geochemical, structural and palaeomagnetic tools was carried out toreveal the architecture of a past accretionary belt (West Junggar, Northwestern China) and to decipher thetiming of continental crust growth in Central Asia. A polycyclic geodynamical evolution is inferred from thedetrital zircon studies and field observation. Continuous recycling of the Palaeozoic juvenile crust is coevalwith episodic addition of mantle-derived materials into the crust and this supports a geodynamic control ofthe continental crust growth. The Early Palaeozoic cycle is characterized by the closure of two oceanicdomains bounding island-arc systems. Early Devonian subduction jamming results from the successivecollisions of an island arc and a microcontinent, which are documented by thrusting, sedimentation coevalwith tectonics and alkaline intraplate magmatism. From Middle Devonian, two active continental marginsdeveloped upon the Early Palaeozoic basement, in response to the subductions of Ob-Zaisan Ocean, to thenorth and Junggar-Balkash Ocean, to the south. Accretionary complexes growth results from the accretion ofoceanic and terrigenous materials. Development of the Late Palaeozoic Kazakh orocline led to obliquesubduction of the Junggar-Balkash Ocean. Consequently, transpression affected the West Junggaraccretionary complex as indicated by folds with vertical axes. Progressive buckling of the orocline gives riseto Late Carboniferous to Permian strike-slip faults, which accommodate lateral unit transport. Relativerotations of the blocs continue after Late Triassic, due to diachronous intraplate reactivation.
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Flavien Choulet. Mécanismes et évolution des chaînes d'accrétion : exemple des chaînes paléozoïques d'Asie Centrale (Ouest Junggar, N-O de la Chine). Sciences de la Terre. Université d'Orléans, 2011. Français. ⟨NNT : 2011ORLE2036⟩. ⟨tel-00658776v2⟩

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