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Analysis of new geochemical information of distribution of petrogenetic and rare, including rare-earth, elements in Fe- and Al-rich metapelites of the Korda (Yenisei Ridge) and Amar (Kuznetsk Alatau) Formations gave a clue to the reconstruction of the composition and origin of their protoliths. It has been established that these rocks are the redeposited and metamorphosed products of the Precambrian kaolinite-type crusts of weathering, while petro- and geochemical differences between them are due, chiefly, to different conditions of formation. The protolith of the Korda Formation metapelites was produced by erosion of the post-Archean complexes of rocks chiefly of granitoid composition and accumulation in continental-margin shallow basins in the conditions of humid climate. Geochemical characteristics of deeper primary deposits of the Amar Formation suggest a dominating role of volcanogenic material of basic composition in the erosion zone. These results agree with data of lithological-facies analysis and geodynamic reconstructions of evolution of geological complexes of the Yenisei Ridge in the Middle Riphean and of the Kuznetsk Alatau in the Vendian. A conclusion is made that rare-earth elements had limited migration mobility during contact and collisional metamorphism.

Cr-diopside group mantle xenoliths from Late Cenozoic basaltoids of the Udokan volcanic field located at the boundary of the Aldan Shield and Baikal-Vitim terrane have been studied. Slightly depleted lherzolites are predominant xenoliths in the central part of the field (Pliocene basanites of Lake Kuas), whereas depleted harzburgites prevail in its northern part. The composition of the Udokan peridotites suggests that they are components of the Phanerozoic oceanic mantle subducted beneath the Siberian craton rather than the Archean mantle of the Aldan Shield.
Xenoliths of Lake Kuas are divided into two series: harzburgite-lherzolite and lherzolite-websterite. The latter series probably represents ancient mantle, whereas the former might have been formed through the later interaction of peridotites with a hypothetic silicate melt, which was probably accompanied by Na-amphibole metasomatism. The Kuas spinel harzburgites and dunites are characterized by higher equilibrium temperatures (1000-1050

A specific complex of metaultrabasites and metabasites has been first mapped and comprehensively studied in the central part of the Aldan-Stanovoi Shield. The complex rocks break through granulites (Kurumkan, Nimnyr, and Fedorov Formations) of the Nimnyr terrane of the Paleoproterozoic collision belt. The age of granulite metamorphism is estimated at 2.0-1.9 Ga, and the age of syncollisional granites, at 1907-1920 Ma. The structure of the southern part of the terrane was determined from successive changes of two types of deformational parageneses of collisional genesis, early domal and late slip. It has been established that metabasite and metaultrabasite bodies intruding into syncollisional granites were deformed by asymmetric folds with steep bends formed during slip motions. The metamorphism grade of metabasites and metaultrabasites corresponds to granulite facies. ⁴⁰Ar/³⁹Ar dating of high-temperature amphiboles from two metabasite samples yielded 1903 ± 16 and 1908 ± 15 Ma. In chemical composition the complex rocks correspond to normal rocks of tholeiitic series. The REE pattern (strong enrichment with LREE, La/Yb = 2-9.5), REE ratios, and LILE and HFSE enrichment of these rocks due to the primitive mantle show their similarity to rocks of plume magmatism. Great variations in contents of HREE (3 to 20 times higher relative to chondrite) seem to be due to the melting of compositionally different mantle rock materials with the participation of asthenospheric or lower-crustal matter. Models for the lithosphere delamination and slab detachment are proposed for the explanation of plume magmatism during the collision of Precambrian terranes.

A specific complex of different types of mineralization (early Cu-Ni-Pt and Ni-Co-As and late Hg, Au-Hg, and porphyry Cu-Mo) has been revealed in the areas of influence of the Siberian and Tarim mantle plumes. In some regions, Mo-W, Sn-W, Ag-Sb, hydrothermal Fe-skarn, Fe-Ti (apatite), REE-Ta-Nb-carbonatite, and other types of mineralization have been found. The central parts of the areas host large Cu-Ni-Pt deposits, whereas the peripheries are made up of Ni-Co-As, Hg, Au-Hg, and Cu-Mo ores. In some ore districts, the largest commercial deposits are confined to rift structures or deep-fault zones. Formation of large ore deposits was determined by the spatial co-occurrence of plume magmatism and within-plate rifting and the active mantle-crust interaction.

Analysis of geological and isotope-geochronological data on the Sayan-Baikal-Muya belt has shown that subduction and the subsequent collision of microcontinents with island arc were essential in the Neoproterozoic-Early Paleozoic. They influenced the formation, localization, and preservation of gold mineralization in ophiolite belts and the formation of ore clusters with diverse types of precious-metal deposits and mineralization: gold-PGE, in blueschist rocks; high-temperature (>400

A semi-empirical model is presented, which describes the processes of formation, migration, and accumulation of radiogenic lead (Pb_Rn) in opals deposited in open cavities. In contrast to lead that forms in situ through radioactive decay of uranium trapped by opal, Pb_Rn is produced from uranium disseminated in the rock enclosing the cavities. Its incorporation into the opal is described by the following chain of processes: decay of parental uranium to yield radon - emanation and diffusion migration of radon from the rock into the cavity - decay of radon to yield lead - diffusion migration of lead in the cavity - adsorption of lead on colloidal silica particles - coagulation and settling of the colloidal particles - formation of opal. Besides the colloidal adsorption, Pb_Rn can also be incorporated into the growing opal through direct diffusion flow onto its surface. The latter mechanism is also relevant to minerals crystallizing from ionic solutions; it is less efficient than the mechanism of colloidal adsorption.
Distribution of Pb_Rn isotopes throughout a cavity depends on the cavity geometry and the half-life of the parental Rn isotope. In cavity filled with stagnant water, the concentration profiles of Pb_Rn show maxima at some distance from the cavity wall. The movement of water through a cavity leads to a more complex distribution of Pb_Rn isotopes. The model describes accumulation of Pb_Rn on silica micelles during their growth until the critical size of coagulation (5-10 nm) is reached and during the subsequent coagulation. For micelles 5-50 nm in size, the calculated concentrations of Pb_Rn agree with those in young (Miocene and younger) natural opals.
Opals formed in open cavities in acidic volcanic rocks (with U = 4-5 ppm) can trap significant amounts of Pb_Rn. Applying standard U-Pb dating equations, which ignore Pb_Rn, will yield an overestimated age of such opals. This is true for young opals (younger than ≈30 Ma). As the age of opal increases, the share of radiogenic Pb formed in situ also grows, and the PbRn correction becomes negligible.

The paper deals with the petrography and geochemistry of graphite-bearing granitoids (garnet-biotite granites, leucogranites, pegmatoid granites, pegmatites, plagioclasites, and syenites) composing up to 2 m thick veins among blastomylonites and blastocataclasites in the southeast of the Main Sayan Fault, at the boundary between the Sharyzhalgai uplift of the basement of the Siberian Platform and the Caledonian Slyudyanka crystalline complex. The granitoids are the products of crystallization of low-temperature (760-710

The Keping basalts occur on the western margin of the Tarim plate and are confined to the Kupukuziman and Kaipaizileike Formations of Early Permian age. They are enriched in Fe₂O₃, TiO₂, and P₂O₅ and are undersaturated in SiO₂. The overwhelming majority of the explored specimens belong to the alkali basalt series, and only one specimen, to the tholeiite series. Rare-earth and trace elements are geochemical signatures of the basalts that appeared under the conditions of within-plate extension. They have the following characteristics: ε _Nd ( T ) from -1.73 to -3.69, ε _Sr ( T ) from +27.56 to +56.87; ²⁰⁶Pb/²⁰⁴Pb = 17.87-18.02, ²⁰⁷Pb/²⁰⁴Pb = 15.45-15.53, ²⁰⁸Pb/²⁰⁴Pb = 38.22-38.49. Nd, Sr and Pb isotopic compositions suggest that the Keping basalts have been derived from the Precambrian enriched-type continental lithospheric mantle. This is also typical of the mafic igneous rocks, which are the most abundant in the Tarim basin and on its margin. For this reason, the Xinjiang Uigur Autonomous Region is divided into two obviously different geochemical provinces, southern and northern. The southern and northern provinces are characterized by isotopic compositions of enriched and depleted mantle, respectively. The Late Paleozoic igneous rocks in these two provinces seem to be produced by different geologic processes.

Exemplified by one of the diamond deposits (Guaniamo, Venezuela), it has been shown that the complex study of the internal structure of diamond crystals by the Laue-SR method yields new information on diamond formation in deep-seated zones of continental lithosphere. The diamonds initially grown as sufficiently large crystals underwent several stages in their postgrowth history, owing to changes in both pressure and temperature and to mechanical actions. In their ultimate state, the crystals are flat cleavage platelets, slightly dissolved (or etched), or chips of other configurations with obvious traces and figures of plastic deformation. The weakening of brown color usually observed in deformed but nonannealed diamond crystals and typical traces of polygonization revealed by the Laue-SR method suggest long-lasting annealing, which occurred after the chips subparallel to sliding plane {111} had been separated from the crystals. The applied technique is useful to study diamond crystals in situ and to obtain additional genetic information.

The paper addresses the structure and stress field of faulted upper crust on the eastern side of Lake Baikal. The reported structural map of the study area provides details of crustal heterogeneity and images major fault-bounded blocks. The regional stress field was studied along the mapped faults by structural and tectonophysical methods. The obtained stress pattern indicates faulting in shear and extension environments.