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This work presents the results of integrated micropaleontological and lithogeochemical analysis of Upper Oligocene continental deposits of the Turtas Formation from the Zyryanskaya-1 borehole (southwestern part of the Tyumen Region, Western Siberia). The predominance of freshwater planktonic diatoms at the subordinate significance of benthic species, as well as the presence of gemmuloscleres of sponges, indicates the coastal sedimentation conditions in a freshwater basin varying in depth from 3 to 50 m. The studied palynocomplex is similar to the spore-and-pollen spectra of the Turtas Formation of the Lower Ob Region, but differs from palynocomplexes of the same formation spread over the southern regions of Western Siberia in a low amount of Taxodiaceae/Cupressaceae and Betulaceae pollen, as well as the absence of Fagaceae pollen and Pseudokomewuia freshwater dinocysts. The revealed differences can be explained both by facies features and by variations in the volume of the Turtas Formation in the currently known localities. The data on the microelemental composition of samples, as well as geochemical and petrogeochemical modules, indicate that the accumulation of the Turtas Formation occurred in the coastal areas of a low-mineralized basin under relatively warm humid climatic conditions.

Palaeoproterozoic amphibole-biotite orthogneisses with a protolith age of ~ 1840 Ma and Neoproterozoic muscovite-chlorite orthogneisses with an estimated protolith age of ~ 790 Ma have been identified in the structure of the Zheltau terrane (Southern Kazakhstan; west Central Asian Orogenic belt). In addition, metasedimentary complexes represented by prevailing garnet-mica schists and subordinate muscovite-chlorite schists with obtained detrital zircon ages in the range of 604 - 2819 Ma (with two peaks at ~ 991 Ma and ~ 1082 Ma) also comprise the Zheltau terrane. In accordance with the Sm-Nd whole-rock isotopic compositions, the protolith of the observed Palaeoproterozoic orthogneisses formed as a result of a mixing of the Neoarchean crustal source with a juvenile source, whereas the formation of the Neoproterozoic orthogneisses protolith may have been related to the melting of Palaeoproterozoic crustal material. In turn, Late Mesoproterozoic – Early Neoproterozoic granitoids or felsic volcanic rocks, which formed as a result of the melting of Palaeoproterozoic continental crust, are considered as possible sources for the studied detrital zircons obtained from the schists. The terrigenous protolith of the schists from the Zheltau terrane accumulated in the range of ~ 600 to ~ 490 Ma, corresponding to the Ediacaran-Cambrian. Subduction processes in the Early Palaeozoic led to the burial of different horizons of the Zheltau terrane continental crust to significant depths; some of the complexes experienced high-pressure metamorphism at P 15 – 18 kbar; T 750 – 850 °C (high-pressure granulites), whereas most of the rocks were evidently metamorphosed at maximum amphibolite facies and avoided high-pressure re-equilibration. The spatial proximity of the studied metamagmatic and metasedimentary crustal complexes and similar metamorphic changes during the latest stages of retrogression imply their possible mutual exhumation from different levels during the period between 490 and 470 Ma and their following juxtaposition as a package of tectonic slices.

Spinel-bearing ultramafic rocks, metamorphosed in high-pressure conditions, are described from the metamorphic complexes of the western part of the Central Asian Orogenic Belt (CAOB) in the Chu-Yili region in Southern Kazakhstan. They comprise small bodies of magnetite-bearing serpentinites, Cr-spinel-bearing serpentinized and amphibolitized dunites and peridotites enclosed by strongly retrogressed kyanite-bearing paragneisses. Apart from serpentinization, the ultramafic rocks were also overprinted by later rodingitization expressed in the development of the index-minerals hydrogrossular, prehnite and vuagnatite. Cr-spinel-bearing peridotites are characterized by extensive development of symplectitic and coronitic microtextures, which are interpreted to have been formed after garnet breakdown during decompression (i.e. exhumation). Calculated pressure (P) and temperature (T) obtained by phase diagram modeling and conventional geothermobarometry for the symplectites were P 11.5–14.5 kbar for a wide temperature range of T 600–850 °C, which followed the transition from garnet to spinel peridotite. Major and trace element whole-rock geochemical characteristics of the spinel-bearing ultramafic rocks as well as their structurally close relations indicate their mutual origin as parts of an oceanic cumulate complex of an arc-basin system. The protoliths were probably plagioclase-bearing (thus shallow, crustal) ultramafic rocks and troctolites, subducted to eclogite facies conditions and then exhumed along with other metamorphic complexes of the Zheltau massif. These spinel-bearing ultramafic rocks could be classified as crustal formations in accordance with the inferred depths of their origin (