The Tekturmas ophiolite belt of central Kazakhstan: Geology, magmatism, and tectonics

The Tekturmas ophiolite belt of central Kazakhstan is located in the western Central Asian Orogenic Belt. It consists of three structural-formational zones: Tekturmas (centre), Bazarbai (north), and Sarysui (south). The Tekturmas zone includes igneous and sedimentary rocks of Karamurun, Tekturmas, and Sarytau formations, which are dominated by volcanogenic, deep sea, and clastic deposits, respectively. The Bazarbai zone consists of Kuzek and Basarbai formations dominated, respectively, by basaltic and sedimentary rocks. The Sarysui zone includes terrigenous Airtau and olistostromic Ermek formations. The age of sedimentary rocks was constrained by microfossils. The igneous rocks of the Karamurun and Bazarbai formations are alkaline and subalkaline basalt/dolerite, andesibasalt, and andesite. There are three main groups of rocks: high-Ti, mid-Ti, and low-Ti. The high-Ti Karamurun volcanics and low-Ti Bazarbai are variably enriched in light rare earth element (LREE) showing LREE enriched (high-Ti) and LREE flat (low-Ti) REE patterns. The high-Ti group shows enrichment in Nb, Th, Zr, and Sm compared with the low-Ti group. The low-Ti group is special for the Nb troughs in primitive mantle-normalized multi-element diagrams, which are typical of supra-subduction settings. Both groups yielded positive εNd values, although the averages are 4.6 and 7.5 for the high- and low-Ti rocks, respectively. The geochemical features suggest formation of the igneous rocks in oceanic and supra-subduction (intra-oceanic arc) settings. The geological and geochemical features of the Tekturmas ophiolite belt accord well with the tectonic emplacement of ophiolites and formation of accretionary complex at a Pacific-type convergent margin similar to those of the western Pacific.