LINKING SOUTHERN WEST JUNGGAR TO KAZAKHSTAN CONTINENT: INSIGHTS FROM THE OLDEST ACCRETIONARY COMPLEXES OF WEST JUNGGAR, NW CHINA

The West Junggar is known to tectonically correlate with East Kazakhstan. However, link of its southern part is still uncertain, and its accretionary process with Kazakhstan continent is accordingly controversial. We examine here the oldest but distinct accretionary complexes in the southern West Junggar to constrain its tectonic evolution and links to adjacent regions during Early-Middle Paleozoic. Overall these complexes have obvious distinctions in lithological, geochemical, geochronological features, and thus sedimentary provenances and tectonic settings. The Laba Formation originated from Late Ordovician-Early Devonian (peak ages at 450-420 Ma) continental arc systems and Precambrian terranes, which formed as early as Early Devonian instead of Ordovician and metamorphosed due to Permian transcurrent tectonic; whereas the Kekeshayi Formation includes Cambrian to Middle Silurian intra-oceanic subunit from local sources and Late Silurian continental subunit from similar provenance to that of Laba Formation. The southern West Junggar shows a strong provenance link to the northern Yili Block during Late Silurian to Early Devonian on the basis of their similar Gondwana ages, zircon age spectra and continental origins of Early Devonian Laba Formation and Late Silurian accretionary complexes. This provenance link argues against models invoking the southern West Junggar as extension of northern limb of the Kazakhstan Orocline, and thus the southern and northern West Junggar might evolve separately. Combined with previous data, a new southern West Junggar-Kazakhstan continent linking model is proposed in which the southern West Junngar first evolved individually, and then collided with Yili Block to constitute the Kazakhstan continent before Late Silurian, prior to final amalgamation of the West Junggar during Late Carboniferous. The independent, contrasting southern West Junggar intra-oceanic arc and Yili northern continental margin arc also exclude presence of a long-lived single arc and further argue for archipelago-type evolution of West Junggar and Central Asian Orogenic Belt during Paleozoic.