Structural-petrologic and isotopic-geochronologic data on magmatic, metamorphic, and metasomatic rocks from the Chernorud zone were used to reproduce the multistage history of their exhumation to...

We present new structural, petrographic, geochemical and geochronological data for the late Paleozoic–early Mesozoic granites and associated igneous rocks of the Taimyr Peninsula. It is demonstrated that large volumes of granites were formed due to the oblique collision of the Kara microcontinent and the Siberian paleocontinent. Based on U-Th-Pb isotope data for zircons, we identify syncollisional (315–282 Ma) and postcollisional (264–248 Ma) varieties, which differ not only in age but also in petrochemical and geochemical features. It is also shown that as the postcollisional magmatism was coming to an end, Siberian plume magmatism manifested in the Kara orogen and was represented by basalts and dolerites of the trap formation (251–249 Ma), but also by differentiated and individual intrusions of monzonites, quartz monzonites and syenites (Early–Middle Triassic) with a mixed crustal-mantle source. We present a geodynamic model for the formation of the Kara orogen and discuss the relationship between collisional and trap magmatism.

The paper presents new geological, mineralogical, and isotope geochronological data for rare-metal pegmatites in the Kalba granitic batholith (Eastern Kazakhstan). Mineralization is especially abundant in the Central-Kalba ore district, where pegmatite bodies occur at the top of large granite plutons and at intersections of deep faults. The pegmatites contain several successive mineral assemblages from barren quartz-microcline and quartz-microcline-albite to Li-Cs-Ta-Nb-Be-Sn-bearing cleavelandite-lepidolite-spodumene. Ar-Ar muscovite and lepidolite ages bracket the metallogenic event between 291 and 286 Ma. The pegmatite mineral deposits formed synchronously with the emplacement of the phase 1 Kalba granites during the evolution of hydrous silicate rare-metal magmas that are produced by the differentiation of granite magma at large sources with possible inputs of F and rare metals with fluids.

The 650–621 Ma plume which impinged beneath the Siberian craton during the breakup of Rodinia caused the formation of several alkaline carbonatite massifs in craton margins of the Angara rift system. The Beloziminsky alkaline ultramafic carbonatite massif (BZM) in the Urik-Iya graben includes alnöites, phlogopite carbonatites and aillikites. The Yuzhnaya pipe (YuP) ~ 645 Ma and the 640–621 Ma aillikites in BZM, dated by ⁴⁰Ar/³⁹Ar, contain xenoliths of carbonated sulfide-bearing dunites, xenocrysts of olivines, Cr-diopsides, Cr-phlogopites, Cr-spinels (P ~ 4–2 GPa and T ~ 800–1250 °C) and xenocrysts of augites with elevated HFSE, U, Th. Al-augites and kaersutites fractionated from T ~ 1100–700 °C along the 90 mW/m² geotherm. Higher T trend for Al-Ti augite, pargasites, Ti-biotites series (0.4–1.5 GPa) relate to intermediate magma chambers near the Moho and in the crust. Silicate xenocrysts show Zr-Hf, Ta-Nb peaks and correspond to carbonate-rich magma fractionation that possibly supplied the massif. Aillikites contain olivines, rare Cr-diopsides and oxides. The serpentinites are barren, fragments of ore-bearing Phl carbonatites contain perovskites, Ta-niobates, zircons, thorites, polymetallic sulphides and Ta-Mn-Nb-rich magnetites, ilmenites and Ta-Nb oxides. The aillikites are divided by bulk rock and trace elements into seven groups with varying HFSE and LILE due to different incorporation of carbonatites and related rocks. Apatites and perovskites reveal remarkably high LREE levels. Aillikites were generated by 1%–0.5% melting of the highly metasomatized mantle with ilmenite, perovskite apatite, sulfides and mica, enriched by subduction-related melts and fluids rich in LILE and HFSE. Additional silicate crystal fractionation increased the trace element concentrations. The carbonate-silicate P-bearing magmas may have produced the concentration of the ore components and HFSE in the essentially carbonatitic melts after liquid immiscibility in the final stage. The mechanical enrichment of aillikites in ore and trace element-bearing minerals was due to mixture with captured solid carbonatites after intrusion in the massif.

New geological, mineralogical, geochemical, and geochronological data have been obtained for Li-bearing pegmatites from the Tochka deposit located within the Karagoin–Saryozek zone in East Kazakhstan. Earlier, the exploration works in this zone were carried out to detect only Ta and Sn mineralization, but other ores (including Li) were not considered. The estimation of lithium resources in pegmatites from the area was methodologically imperfect. Previously, it was believed that the formation of rare-metal pegmatite veins was associated with Late Carboniferous Na-granites. The obtained geological observation confirms that the ore-bearing rare-metal pegmatites at the Tochka deposits cut the Late Carboniferous Na-granites and do not cut the Early Permian Kalba granites. The associations of the accessory minerals in host hornfels, Na-granites, and rare-metal pegmatites are different and the accessory minerals in pegmatites are similar to the accessory minerals in the Kalba granites. Geochemical data show that the behavior of rare elements (Ba, Th, HFSE, and REE) and the levels of accumulation of rare metals prove that pegmatites are similar to the product of the differentiation of the granitic magmas of the Kalba complex. The ⁴⁰Ar/³⁹Ar muscovite age of the Tochka pegmatites (~292 Ma) fits the age range of the Kalba granite complex. Based on the main principles of the generation of rare-metal pegmatites, the Tochka pegmatites formed during the fluid–magmatic fractionation of magma in large granitic reservoirs of the Kalba complex. The Karagoin–Saryozek zone—located between several large granite massifs of the Kalba complex where host rocks play a role as a roof—may be very promising for rare-metal pegmatite mineralization.

We report the first data on ⁴⁰Ar/³⁹Ar dating, trace-element geochemistry, and isotope (Nd, Sr, O) composition of the Belaya Gora gabbro-foidolite-foyaite intrusive massif, one of typical representatives of the alkaline province of the northeastern Kuznetsk Alatau. The established age of rock-forming amphibole, ~ 401-403 Ma, is taken as the time of the pluton formation in the Early Devonian. The distribution and ratios of LILE and HFSE in the rocks suggest that the intrusion took place in the setting of “superposition” of Devonian mantle plume on the Early Paleozoic accretion-collision complexes. Therefore, the source of magmatic products had a heterogeneous composition as a result of mixing of plume material with the substances of suprasubduction and crustal substrates. The mantle component might have been a PREMA + EM combination, which is confirmed by the parameters of the Nd isotope composition (£_NdT - 3.2-4.6; T_Nd(DM) - 0.8 Ga) of alkaline rocks. 87 86 18 The effects of crustal contamination are reflected in the high ratios of strontium and oxygen isotopes ( Sr/ Sr)_T - 0.7046-0.7054; 5 O - 8.5-9.2%c, SMOW).