Cambrian supra-subduction and intraplate oceanic complexes in the Dzhalair-Naiman ophiolite zone (Southern Kazakhstan): age, geochemistry and tectonic implication

The Kokchetav-North Tien Shan region in the west of the Central Asian Orogenic Belt (CAOB) comprises early Paleozoic island-arc volcanic-sedimentary and flysch strata, dismembered ophiolites, cherts, and basalts, composing Neoproterozoic terranes and Ediacaran-Cambrian cover. The Dzhalair-Naiman ophiolite zone located in the southwest of the Kokchetav-North Tienshan region, mainly hosts Cambrian plutonic and volcanogenic-sedimentary complexes of diverse tectonic affinities, and Lower Ordovician terrigenous strata. The oldest formations (Cambrian, Terreneuvian - Series 2) are referred to the Andassai-Dulankara supra-subduction ophiolites, comprised by the dunite-harzburgite and dunite-wehrlite-gabbro complexes along with differentiated volcanics, tonalites, and plagiogranites aged 519-521 Ma. Cambrian, Miaolingian-Furongian complexes here are represented by the Ashchisu oceanic intraplate basalts Formation with interlayers of cherts containing conodonts, as well as the East Dulankara island arc volcanic Formation. Cambrian, upper Furongian Sulusai tuffaceous-volcanic Formation is composed of tuffaceous siltstones, tuffaceous sandstones, and tuff conglomerates with rare flows of rhyolites aged ca. 490 Ma. The youngest (Lower Ordovician, Tremadocian) Dzhambul terrigenous Formation made up by predominant quartz-feldspar sandstones and siltstones, contains detrital zircons with ages ranging from 525 to 2500 Ma. The evolution of the Dzhalair-Naiman zone and adjacent complexes hence record three main stages: (i) Cambrian, Terreneuvian - early Furongian stage of the emergence and development of an intra-oceanic island arc and oceanic islands with OIB basalts; (ii) Cambrian, late Furongian stage of the accretion of the island arc and oceanic islands to the Chu-Kendyktas microcontinent, whose complexes underwent highpressure metamorphism, and switch of the subduction polarity with the formation of a new island arc with a heterogeneous basement; (iii) Early Ordovician stage of the cessation of magmatism, accumulation of thick terrigenous strata possibly in response to a change in the kinematics of the converging plates, and conversion of their boundary into a transform fault. (c) 2024 International Association for Gondwana Research. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.