Reconstruction of the Silurian to Devonian stratigraphic succession along the northeastern margin of the Junggar block, Xinjiang, NW China, and its tectono-paleogeographic implications for the southwestern Central Asian Orogenic Belt

Abstract

The Paleozoic sediments on micro-blocks in the southwestern Central Asian Orogenic Belt record the tectonic evolution of the Paleo-Asian Ocean and accretionary processes of the south Siberian Craton. However, the absence of detailed stratigraphic studies and sedimentary basin analyses has led to disputes on Paleozoic arc-basin relationships and the tectonic evolution of the Junggar block and East Junggar belt. In this contribution, some Devonian marine-dominated lithostratigraphic units are recognized from the previously identified Huangcaopo Group, using zircon U-Pb data and fossils. To constrain the tectonic setting of the sedimentary basin between the Junggar block and Eastern Junggar belt, seven facies associations including 14 lithofacies were identified from two lithostratigraphic units of the Hongliugou Formation and Kalamaili Formation by detailed petrological and sedimentological studies. Combined with interpretations of detrital provenance and regional contemporaneous magmatism, the Silurian to Devonian successions located along the northeastern margin of the Junggar block could be considered as back-arc basin sediments. Integrated geological characteristics suggest that the Tuva-Altai-Junggar orogenic collage located on the southern margin of Siberian craton was formed during the Ordovician, and the spatial-temporal distribution of the ophiolitic mélange, subduction zone and back-arc extension zone indicate that opening of the Kalamaili Ocean developed on this collage and was related to northward subduction of the North Tianshan Ocean during the Silurian to Devonian.