Dating of magmatic rocks from paleo-island arcs of orogenic belts helps to define the precise timing of subduction processes that took place during the formation of the orogen. Within the central (East Trans-Baikal) part of the Mongol-Okhotsk orogenic belt, the Kamensk island-arc terrane is an example of such paleo-island-arc complex. Its intrusive part is included into the Bereinsky complex, represented by a gabbro-diorite-tonalite-plagiogranite series of rocks demonstrating subduction geochemical characteristics. The dating of zircons from acidic rocks of this complex by the U–Pb classical method showed that they were produced in a narrow time interval – 203±1–205±1 Ma, which corresponds to Norian/Rhaetian boundary of the Late Triassic. Taking into account the previously obtained age of the diorites (254±5 Ma), the timing of formation of the entire series of intrusive rocks is about 50 Ma, thus indicating in the Late Permian – Late Triassic the subduction along the northern (in modern coordinates) margin of the Mongol-Okhotsk Paleocean beneath the Siberian paleocontinent. Diorites of the first phase have positive values ɛND(254MA) = 3.2–3.6 (TNd(DM) = 879–994 Ma), and plagiogranites – ɛND(205MA) = 2.3–3.5 (TNd(DM) = 859–1028 Ma), which points to the connection of these rocks with the substance of the depleted mantle source and is consistent with the Sm-Nd isotope characteristics of the juvenile crust of the Central Asian orogenic belt. This study was supported by Russian Science Foundation, grant no. 22-27-00775. The resources of the Shared Use Center for Isotope-Geochemical Research (Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk) were used in this work.

This work presents new U–Pb ID-TIMS geochronological data obtained for the rocks of the metagabbro–diorite–tonalite complex of the Olondo fragment of the Tokko–Khani greenstone belt of the Aldan Shield, Siberian Craton. Wide development of ultramafic and mafic volcanics associated with felsic volcanics has been recognized only within this fragment. It was established that the protoliths of metagabbro–diorite and quartz metadiorite intruding metavolcanic and metasedimentary rocks were crystallized at 3002 ± 5 and 3005 ± 7 Ma, respectively. The obtained age estimates determine the upper age boundary of the formation of the Olondo supracrustal rocks (3012–2997 Ma). The Nd model ages of the Olondo metaandesites and metadacites are close to 3.0 Ga, which, to the first approximation, determines the lower age boundary of their formation. Thus, the sedimentary–volcanogenic sequence of the Olondo fragment are about 3.0 Ga old, and their formation, including superimposed structural and metamorphic transformations, occurred within a short period (a few million years).

— Detrital zircons from quartzite–schist sequences of the Aktau–Mointy Massif (Central Kazakhstan), which occur in various structural positions relative to the Early Neoproterozoic felsic volcanics, were studied. The obtained U–Pb zircon dating results suggest similarity of detrital zircon age populations with a lower limiting depositional age of 1220 Ma in all quartzite–schist sequences. The different positions of quartzite–schist sequences relative to the felsic volcanics are due to subsequent deformations. The ages of detrital zircons studied fall mostly within the intervals of 1149–2105 and 2354–3159 Ma with major peaks at 1218, 1338, 1468, 1581, 1628, 1743, 1851, and 2520 Ma and minor peaks at 2016, 2619, 2696, 2791, 2823, and 3114 Ma. The structural features of quartzite–schist sequences and the presence of heavy minerals that are unstable during long-term transport indicate the predominance of local source areas, which either form the buried part of the basement of the Aktau–Mointy Massif or have been eroded completely. Within the Aktau–Mointy Massif, it enables us to use the U–Pb ages and Lu–Hf isotope compositions of detrital zircons from quartzite–schist sequences to reconstruct the history of Precambrian continental crust formation. Results suggest that the production of juvenile continental crust prevailed only during Middle Mesoproterozoic, while formation during the Mesoarchean–Neoproterozoic time accompanied magmatic reworking of the older crustal complexes.

U-Pb geochronological studies of detrital zircons from quartzite-schist sequences of the Akbastau Formations of the Chu block (northwest of the Chu-Kendyktas terrane, Southern Kazakhstan) have been provided. The concordant ages of detrital zircons are predominantly within the intervals of 1672-2115 Ma with peaks at 1697, 1780, 1857 and 2066 Ma. Individual zircon grains display ages of 2291-2332 Ma with peaks at 2303 and 2322 Ma. Neoarchean ages 2608-2747 with peak at 2681 Ma characterize another significant zircon population. The lower limit of deposition for the Akbastau Formations of the Chu block, corresponding to the youngest statistically significant zircon population, is estimated at 1,7 billion years.

The complex of Ky-Grt paragneisses, granitic to tonalitic orthogneisses, migmatitic gneisses and homogeneous to layered amphibolites was intruded by dioritic-gabbroic more or less concordant dykes and sills during the synmetamorphic extension in the host regional metamorphic rocks. They now have the character of dioritic orthogneisses. Tile whole lithological sequence was then structurally unified during the late-metamorphic cooling and exhumation within the deep-crustal shear zone. The dioritic orthogneisses bear the features of pre-metamorphic compositional layering into cumulate-like hornblendite(+/- Px), gabbro-diorite, tonalite to trondhjemite. Magmatic layering has been transformed to subsolidus high-temperature layering along the extensional meso-shear bands filled with leucotonalitic melt seggregates crosscutting former magmatic structures at acute to medium angles. A new ductile strain relocalization enhanced mechanical differentiation of dark and felsic minerals into often isoclinally folded layers, with the crystallographic preferred orientation fabrics of amphibole, plagioclase and quartz indicating a layer parallel shear. The U-Pb zircon age of porphyric metadiorites 346 +/- 1 Ma (Early Carboniferous) is related to their magmatic emplacement, immediately followed by the high-temperature mylonitization. We also dated zircon of metatrondhjemitic orthogneiss from the layered amphibolite. An upper intercept age 514 +/- 24 Ma (Late Cambrian) is interpreted as dating the magmatic compositional differentiation of a gabbro-dioritic complex into cumulate-like hornblenditic, gabbrodioritic, tonalitic to trondhjemitic layers, which is an inherited feature in layered amphibolites (with blastic textures). The lower intercept age 348 +/- 31 Ma (Early Carboniferous) obviously reflects the time of regional-metamorphic event and formation of layered amphibolites. The whole composite (VZP-CB) structural complex is crosscut by plagiogranite-aplitic veins dated 233 +/- 4 Ma (Early Triassic).