Geochemical features of the two Early Paleozoic ophiolitic zones and the volcanic rocks in the central-southern Tianshan region, Xinjiang.

Abstract : This paper deals with the geochemical features of the two Early Paleozoic ophiolite zones in the central-southern Tianshan region and the central Tianshan igneous rock belt between them. Study results suggest that the central Tianshan belt was an Ordovician volcanic arc with an affinity of continental crust, and the Kumux-Hongliuhe ophiolitic zone that is located on the southern margin of central Tianshan has a crustal affinity to back-arc marginal sea. The Aqqikkudug-Weiya ophiolitic zone is an accretionary boundary between the Tuha continental block and the central Tianshan volcanic arc during Late Silurian to Devonian; Ordovician ophiolitic blocks, Silurian flysch sequence and HP metamorphic rock relics are distributed along the Aqqikkudug-Weiya zone. Geochemically, ophiolitic rocks in the Aqqikkudug-Weiya zone have an affinity to oceanic crust, reflecting a tectonic setting of paleo-trench or subduction zone. The Early Carboniferous red molasses were deposited unconformably on the pre-Carboniferous metamorphosed and ductile sheared volcanic and flysch rocks, providing an upper limit age of the central and southern Tianshan belts.