Three Generations of Basins of the Early Turkestan Ocean: Ediacaran–Silurian of the South and Middle Tian Shan

The results of U–Pb dating of detrital zircon from volcano-terrigenous Ediacaran–Silurian deposits, mainly from grauwacke turbidites, after accretion of which the “Caledonian” basement of the Paleozoic structure was formed in Kyzylkum and in the ridges of the Southwestern Tian Shan, including Northern Ferghana, allowed us to clarify the age correlation and show the dynamics of the formation of this complex. It consists of deposits associated with the opening, filling and subsequent convergent development of three generations of oceanic basins, including the emergence and destruction of island arcs. The earliest of these basins was formed at the active volcanic margin of the eastern Rodinia/Gondwana, which included the Karakum-Tajik massif. Sandy turbidites (Besapan Formation, etc.), the age of which is not younger than the beginning of the Cambrian, were deposited here on top of siliceous (Taskazgan) Ediacaran sediments. The second generation is represented by Ordovician basins, in which radiolarian flints of the Lower Ordovician form the bathyal part of the sediments, and the main filling is turbidites of the Middle Ordovician–Rhuddanian. The newly opened Silurian oceanic basins and their margins were filled with sediments of the third Caledonian generation, mainly graptolite aleuropelites and turbidites, starting from the end of the Llandovery. Incomplete preservation of the Ediacaran–Silurian sedimentary series is due to their partial absorption (tectonic erosion) during further subduction and collision, mainly already in the Carboniferous.