Detrital-zircon geochronology and provenance of Ediacaran–Silurian rocks of the central to northern Tajikistan traverse: Geodynamic implications for the evolution of the Tian Shan

Abstract

The South and Middle Tian Shan form the marginal part of the Central Asian Orogenic Belt (CAOB) and comprise Paleozoic ocean margins, arcs, and Precambrian continental fragments. We use U-Pb dating of detrital zircons from the Ediacaran–Early Paleozoic sedimentary succession, across a south-north transect of the South Tian Shan (STS) fold belt, to show that the Karakum-Tajik Continent (KTC) of the south-western CAOB margin contains an Early to Late Proterozoic nucleus, overprinted by tectono-magmatic events of Ediacaran–Early Cambrian age. Accretionary-type crust formed between ca. 650–500 Ma, while marginal volcanism of the KTC and microcontinents inside the western STS represented the main provenance for clastic sediments deposited within the young Turkestan ocean basin. Abundant zircon grains with ages of 580–500 Ma are widely presented to the north of KTC suggesting a possible connection between the KTC and Baltica through the south-eastern Urals during the Late Ediacaran–Cambrian. The next major zircon cluster of ca. 460–430 Ma, found within sedimentary cover of the KTC, turbidites of its northern margin in the Kurama Range, as well as inside the STS, indicate that these sediments were derived from erosion of Late Ordovician–Early Silurian continental and/or island arcs at the northern margin of the KTC. Numerous accretionary events that occurred during early-middle Paleozoic in the STS were later overprinted by continental collision during the Carboniferous closure of the Turkestan Ocean. The Paleozoic sedimentary cover of the KTC was deformed into an imbricate thrust structure during the Visean, when the Ediacaran–Cambrian Yagnob turbidites were subducted under the KTC to form the matrix of the accretionary complex.