Toward a unified model of Altaids geodynamics: Insight from the Palaeozoic polycyclic evolution of West Junggar (NW China)
Résumé
The Altaid tectonic collage extends over Central Asia, exposing numerous accretionary orogens that can account for the Palaeozoic
continental crust growth. A pluridisciplinary approach, using geochronological, geochemical, structural and palaeomagnetic
tools was carried out to unravel the architecture and the evolution of West Junggar (Northwestern China), a segment
of the Altaid Collage. A polycyclic geodynamic evolution is inferred and includes: (1) an Early Palaeozoic cycle, characterized
by the closure of two oceanic basins bounded by island-arc systems; (2) an Early Devonian subduction jamming resulting in a
minor-scale collision documented by thrusting, syntectonic sedimentation and subsequent crutal thinning associated with alkaline
magmatism; (3) a Late Palaeozoic cycle, driven by the evolution of two opposite subduction zones developed upon the
Early Palaeozoic basement. Detailed structural analysis and paleomagnetic data provide constraints for the late evolution of
Junggar in the frame of the development of the Late Palaeozoic Kazakh orocline, which led to oblique subduction and transpression
in the West Junggar accretionary complex. Progressive buckling of the Kazakh orocline further resulted in Late Carboniferous
to Permian wrench tectonics, and lateral displacement of lithotectonic units. Block rotations that continued after the
Late Triassic are due to diachronous intraplate reactivation. This scenario mirrors the Palaeozoic geodynamics of the Altaid
Collage. Multiple Early Palaeozoic collisions of intra-oceanic arcs and micro continents have contributed to the formation of
the Kazakhstan Microcontinent. Since the Late Palaeozoic, subductions formed around this microcontinent and the final
oblique closure of oceanic domains resulted in the transcurrent collage of Tarim and Siberia cratons. Palaeozoic strike-slip
faults were later reactivated during Mesozoic intracontinental tectonics.