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According to present views, the crustal terranes of the Anabar province of the Siberian craton were initially independent blocks, separated from the convecting mantle at 3.1 (Daldyn terrane), 2.9 (Magan terrane) and 2.5 Ga (Markha terrane) (Rosen, 2003, 2004; Rosen et al., 1994, 2005, 2009). Previous studies of zircons in a suite of crustal xenoliths from kimberlite pipes of the Markha terrane concluded that the evolution of the crust of the Markha terrane is very similar to that of the Daldyn terrane. To test this conclusion we present results of U-Pb and Hf-isotope studies on zircons in crustal xenoliths from the Zapolyarnaya kimberlite pipe (Upper Muna kimberlite field), located within the Daldyn terrane, and the Botuobinskaya pipe (Nakyn kimberlite field) in the center of the Markha terrane. The data on xenoliths from the Botuobinskaya kimberlite pipe record tectonothermal events at 2.94, 2.8, 2.7 and 2 Ga. The event at 2 Ga caused Pb loss in zircons from a mafic granulite. U-Pb dating of zircons from the Zapolyarnaya pipe gives an age of 2.7 Ga. All zircons from the studied crustal xenoliths have Archean Hf model ages ranging from 3.65 to 3.11 Ga. This relatively narrow range suggests that reworking of the ancient crust beneath the Nakyn and Upper Muna kimberlite fields was minor, compared with the Daldyn and Alakit-Markha fields (Shatsky et al., 2016). This study, when combined with dating of detrital zircons, implies that tectonic-thermal events at 2.9–2.85, 2.75–2.7 and 2.0–1.95 Ga occurred everywhere on the Anabar tectonic province, and could reflect the upwelling of superplumes at 2.9, 2.7 and 2 Ga. The presence of the same tectonic-thermal events in the Daldyn and Markha terranes (Rosen et al., 2006a,b) supports the conclusion that the identification of the Markha terrane as a separate unit is not valid.

It is widely accepted that granulite xenoliths from kimberlites provide a record of granulite facies metamorphism at the basement of cratons worldwide. However, application of the phase equilibria modeling for seven representative samples of mafic granulites from xenoliths of the Udachnaya kimberlite pipe, Yakutia, revealed that a granulitic garnet + clinopyroxene + plagioclase ± orthopyroxene ± amphibole ± scapolite mineral assemblage was likely formed in the middle crust under amphibolite facies conditions (600–650 °C and 0.8–1.0 GPa) in a deficiency of fluid. Clinopyroxene in the rocks is characterized by elevated aegirine content (up to 10 mol.%) both in the earlier magmatic cores and in the later metamorphic rim zones of the grains. Nevertheless, the phase equilibrium modeling for all samples indicates surprisingly reduced conditions, i.e. oxygen fugacity 1.6–3.3 log units below the FMQ (Fayalite-Magnetite-Quartz) buffer. In contrast, the coexistence of Fe-Ti oxides indicates temperatures of 850–990 °C and oxygen fugacity about lg(FMQ) ± 0.5, conditions which correspond to earlier stages of rock evolution. Reduction of oxygen fugacity during cooling is discussed in the context of the evolution of a complex fluid. The reconstructed P-T conditions for the final equilibration in the mafic granulites indicate that temperatures were ~250 °C higher than those extrapolated from the continental conductive geotherm of 35–40 µW/m2 deduced from peridotite xenoliths of the Udachnaya pipe. Although the granulites resided in the crust for a period for at least 1.4 Ga, they did not re-equilibrate to the temperatures of the geotherm, likely due to the blocking of mineral reactions under relatively low temperatures and fluid-deficient conditions

U–Pb age and Hf-isotope data were collected on zircons from crustal xenoliths from the Late Devonian kimberlite pipes of Markha terrane. The xenoliths include mafic garnet granulites (Gt+Pl+Cpx±Opx±Amp±Bt±Scp) and garnet–biotite gneisses (Grt+Bt+Pl+Kfs+Qtz±Scp). The data from this study demonstrate that the crust of the Markha terrane experienced several tectonothermal events. Zircons with Archean Hf model ages (TDM = 3.13–2.5 Ga) are predominant in all xenoliths with one exception. These data imply that most of the lower and middle crust beneath the Markha terrane was produced in the Archean time. Later this Paleoarchean crust was significantly reworked in several tectonothermal events, including a Neoarchean stage (2.9–2.5 Ga), and several Paleoproterozoic metamorphic stages (1.98, 1.9 and 1.8 Ga). There is very little evidence for generation of juvenile crust associated with these metamorphic events. Importantly, crustal xenoliths from kimberlite pipes of the Markha terrane record all the same events that occurred in the adjacent Daldyn and Magan terranes.

The Baikal–Muya Foldbelt is one of the oldest and the most enigmatic terrain among the Central Asian Orogenic Belt. During the Early (1.0–0.8 Ga) and Late (0.8–0.6 Ga) Neoproterozoic orogenic cycles a notable amount of juvenile crust has been formed in subduction–collision settings along with the reworking of the existing Early Precambrian continental crust. The latter is perfectly presented within the North Muya metamorphic block (Anamakit–Muya zone) including the oldest high-pressure subduction-related rocks in the Central Asia. In order to evaluate the process of the juvenile crust formation in the Precambrian continental unit, whole-rock trace elements along with zircon U–Pb ages and Hf-isotopic composition were analyzed in granites of unknown age that intrude the Precambrian volcanic-sedimentary rocks of the Parama series in the southern North Muya Block. Combined geochemical and zircons isotopic studies indicate the formation of granites with the main pulse at ∼810 Ma due to partial melting of a juvenile mafic crust accompanied by reworking of the older crustal material from the continental arc basement. The composition of the granites was controlled by processes of intracrustal differentiation together with a probable contamination by older crustal substrate. Geochemistry and age of the studied granites are comparable to the granites of the Muya complex observed in the volcano–plutonic Kelyana–Irokinda zone. It is assumed that the Muya block and the Kelyana–Irokinda zone (terrane) had possibly been parts of the large continental-arc system beyond the Siberia margins.

U–Pb dating and Hf-isotope analysis of zircons and whole-rock Nd-isotope analyses were carried out on country rocks of the eclogite–gneiss complex of the North Muya dome in the Anamakit-Muya zone of the Baikal Muya accretionary fold belt. Zircons from garnet–biotite gneisses (Qtz + Kfsp + Pl + Bt + Grt) and garnet–biotite–muscovite schist (Pl + Kfsp + Bt + Mu + Grt + Qtz) were dated using the LA-ICP-MS technique. Based on U–Pb isotope data and CL images zircon grains were divided into three groups: detrital, magmatic and metamorphic zircons. Metamorphic zircons display no zoning or the cloudy zoning. The grains morphology together with the well-developed oscillatory zoning clearly identifies the igneous origin of magmatic zircons. The metamorphic zircons (ages 576–680 Ma) have Th/U ratios varying from 0.271 to 0.004, whereas the ratio in magmatic zircons ranges from 0.779 to 0.11. Magmatic zircons from granite-gneisses of the North Muya dome exhibit a relatively narrow spread in the crystallization age with the major peak at ca 764 Ma. Younger ages are interpreted as due to the partial resetting of U–Pb system during the subsequent metamorphic evolution. Detrital zircons from two-mica schist sample Mu-93-10 give ages of 1.88–2.66 Ga. The oldest detrital zircon from this sample plots near concordia and has a 207 Pb/ 206 Pb age of 3.2 Ga. Zircons from this sample are characterized by the widest scatter of ɛ Hf ( t ) values (from +13.9 to −15.3) and T DM C model ages (0.82–3.86 Ga). Zircons from other samples have a much narrower ranges of ɛ Hf ( t ) (+11.6 to −0.7) and T DM C (0.85–1.52 Ga). The involvement of older crustal material is also evident from the whole-rock Nd isotopic compositions. The gneisses and schists exhibit a range of Nd isotopic compositions with ɛ Nd ( t ) values ranging from −3.5 to +3.6 and t Nd(DM) from 1.64 to 1.09 Ga. The integration of the Hf-isotope data with the age spectra provides with the first evidence for the existence of Mesoarchean crust in the Baykal-Muya sector of the Central Asian Orogenic Belt.

To clarify the tectonic-thermal evolution of the Anabar tectonic province in the central Siberian Craton, we performed an isotope-geochemical study of 20 xenoliths from the Udachnaya, Zarnitsa, and Komsomolskaya kimberlite pipes to represent different crustal levels. Most mafic granulites have Proterozoic Nd model ages and geochemical characteristics close to those of intraplate basalts, whereas some mafic and intermediate granulites with Archean model ages exhibit geochemical features of supra-subduction ophiolitic basalts. Analysis of U-Pb ages and hafnium isotopic composition of zircon indicates that the main tectonic-thermal events modified the crust at 2.7 and 1.9–1.8 Ga, which is consistent with ages of mantle depletion events from previous studies. All zircons have Archean Hf model ages ( T DM C 3.6 - 3.2 Ga). Overall, thermal events with ages of 2.9–2.8, 2.7, 2.4, 1.97 and 1.8 Ga have remarkable influence on the studied zircons. Tectono-thermal events at 2.4 1.97, 1.9 and 1.8 Ga with no addition of juvenile material are recorded by zircons from xenoliths of mafic and intermediate granulites and metadiorites. A compilation of isotope-geochemical data demonstrates that instead of age-stratified, the crust of the Anabar tectonic province consists of variably reworked Paleoarchean rocks and juvenile Proterozoic rocks at all crustal levels. Hence the crust and mantle of the Siberian Craton has been coupled since the Paleoarchean.