Formation and accretionary evolution of the Kokchetav complex, northwestern Kazakhstan: Insights from structural styles, and detrital zircon geochronology and Lu-Hf isotopes
Jia X. Xiao W. Sang M. Zhai M. Huang P. Li L. Mao Q. Gan J. Yogibekov D. Tileuberdi N.
August 2025Elsevier B.V.
Lithos
2025#506-507
Understanding how subduction processes incorporate continental fragments into accretionary complexes is important for constraining the formation of accretionary orogenic belts. The Kokchetav Complex is a distinctive geological unit in the northwestern Altaids of northwestern Kazakhstan that is ideal for investigating such processes. It hosts microcontinental fragments, and accretionary and (ultra)high-pressure ([U]HP) metamorphic rocks. We undertook U-Pb dating and Lu-Hf isotopic analyses of detrital zircons from quartzites, schists, gneisses, and sandstones in the metasedimentary belt, gneissic basement rocks, (U)HP metamorphic belt, and ophiolitic mélange in the Kokchetav Complex. The quartzite–schist rocks yield three primary zircon age clusters: middle–late Paleoproterozoic (1.8–1.6 Ga), middle Mesoproterozoic to early Neoproterozoic (1.4–0.8 Ga), and latest Neoproterozoic to Early Devonian (544–406 Ma), with a few isolated zircons dated between 3.6 and 2.8 Ga. These rocks have diverse detrital zircon U-Pb age spectra (unimodal to multi-modal) with variable Hf isotope ratios (−10.9 to +22.0). The zircons have a mixed origin from the early Paleozoic Stepnyak Arc and Precambrian continental fragments, and were not derived from the gneissic basement, indicating an affinity with the Proterozoic Musgrave–Albany Orogen in Australia. Consequently, these zircons reveal that a continent fragment from the northwestern Rodinia supercontinent exists within the Kokchetav Complex, which retained its original nature from the Neoproterozoic to early Paleozoic and was later incorporated into the accretionary complex as tectonic sheets and slices during convergence between the Kokchetav microcontinent and Stepnyak Arc. Our results further indicate that, rather than being part of a unified Precambrian block, the Kokchetav Complex incorporated continental fragments and younger accreted materials that formed in an early Paleozoic supra-subduction zone setting.
Central Asian Orogenic Belt , Early Paleozoic , Kokchetav complex , Tectonic evolution , Zircon U-Pb-Hf isotopes
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National Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, 830011, China
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xian, 710069, China
Satbayev University, Institute of Geological Sciences Named after K.I.Satpaev, Almaty, 050010, Kazakhstan
National Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands
Institute of Geology and Geophysics
College of Earth and Planetary Sciences
State Key Laboratory of Continental Dynamics
Satbayev University
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