New constraints on the pre-Permian continental crust growth of Central Asia (West Junggar, China) by U-Pb and Hf isotopic data from detrital zircon.

Abstract : In-situ U-Pb geochronology of detrital zircons from various Palaeozoic sedimentary rocks of West Junggar accretionary complexes (Central Asia) suggests two distinct episodes of arc magmatism, and an evolution in three steps: i) Ordovician-Silurian subduction generating juvenile arc crust; ii) Late Silurian subduction jamming, erosion and intraplate magmatism, iii) development of two new opposed Devonian-Carboniferous subductions recycling the Early Palaeozoic crust. Zircon Hf isotopes document three pre-Permian episodes of mantle-derived magmatic input into the crust: 1) Neoproterozoic (850-550 Ma), 2) Early Palaeozoic (530-450 Ma) and 3) Late Palaeozoic (380-320 Ma). Zircons also record the recycling of Neoproterozoic and Early Palaeozoic juvenile crusts during the Early and Late Palaeozoic. These data support a model of episodic continental crust growth in Central Asia.