Paleoproterozoic anorogenic granitoids of the Zheltav sialic massif (Southern Kazakhstan): Structural position and geochronology

The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U–Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural–geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm–Nd isotopic—geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan.     

Heterogenity of planetesimal collisional plume probed by glass inclusions in metal globules of Sierra Gorda 013, an unusual CBa-like chondrite

Metal-rich carbonaceous CB chondrites are generally assumed to be materials accreted from the gas–dust plume formed in catastrophic collisions of planetesimals, at least one of which was differentiated into a metal core and silicate shell. Micron-sized inclusions of siliceous alkali-rich glasses associated with sulfides were found in the metal globules of the Sierra Gorda 013 (SG 013), a CBa-like chondrite. These inclusions are unusual carriers of volatile alkalis which are commonly depleted in CB chondrites. The inclusions are presented by two types: (1) Al-bearing Nb-poor glass associated with daubréelite and (2) Nb-bearing Ca,Al,Mg-poor glass associated with an unknown Na-bearing Cr-sulfide. The glass compositions do not correspond to equilibrium condensation, evaporation, or melting. The Nb-bearing glass has a superchondritic Nb/Ta ratio (31) most likely indicating the fractionation of Nb and Ta in the high-temperature gas–dust impact plume due to condensation from vapor or evaporation of precursor Nb-rich particles. The glasses are interpreted as reaction products between refractory plume condensate particles (or possibly planetary or chondritic solids) with relatively low-temperature K-Na-Si-rich gas in oxidized conditions, possibly in a common plume vapor reservoir. Compositional differences indicate that the glasses and sulfides originated from several different sources under different fO₂, fS₂, and T conditions and were likely combined together and transported to the metal globule formation region by material flows in the heterogeneous impact plume. The glass–sulfide particles were enclosed in the globules aggregated from smaller solid or molten metal grains. The metal globules were further melted during transport to the high-temperature plume region or by plume shockwave heating. Thus, the composition of the glasses, the host metal, and the main mass of SG 013 shows dynamic heterogeneity of physical conditions and impact plume composition after a large-scale planetesimal collision.     

U-Pb age of detrital zircons from neoproterozoic placers of the Erementau-Niyaz massif as a reflection of stages of Precambrian tectono-magmatic evolution of northern Kazakhstan

A typical feature of the Precambrian complexes of the Kokshetau, Ishkeolmess, Erementau-Niyaz, and Aktau-Dzhungaria massifs of Northern and Central Kazakhstan is the presence of the end Mesoproterozoic-beginning of the Neoproterozoic quartzite-schist sequences in these sections. The lower and upper parts of these sequences are mostly composed of schists with interlayers of quartzites and marbles and of quartzitic sandstones, respectively. It is suggested that the quartzite-schist sequences represent the sub-platform cover of a large continental block and were formed in the regressive basin with widely abundant facies of submarine deltas and a littoral shoal. The presence of horizons and the lenses enriched in zircon-rutile heavy concentrate with the amount of accessory minerals of 10-70% characterizes the quartzite-schist sections of the Kokshetau and Erementau-Niyaz massifs. The U-Pb age of zircons from one such locality in the central part of the Erementau-Niyaz massif was analyzed by LA-ICP-MS. The Concordia ages of zircons are in the intervals 1041 ± 13-1519 ± 14, 1623 ± 14-1931 ± 14, and 2691 ± 14-2746 ± 14 Ma. One age was 2850 ± 14 Ma. The age distribution is characterized by clear peaks of 1.08, 1.20. 1.34, 1.46, 1.65, 1.89, and 2.70 Ga and weak peaks of 1.13 and 1.68 Ga. The age of the majority of zircons ranges from 1309 ± 14 to 1519 ± 14 Ma. Our data indicate that mostly Neoproterozoic rocks with a subordinate role of Paleoproterozoic and Neoarchean complexes served the feeding sources for the quartzite-schist sequence of the Erementau-Niyaz massif. The Mesoproterozoic and Paleoproterozoic events identified for the detrital zircons of the Erementau-Niyaz massif are completely manifested only in Laurentia. In the first approximation, these events coincide with the assembly and breakup of the Columbia/Nuna supercontinent (～1650–1580 and 1450–1380 Ma) and assembly of the Rodinia supercontinent (1300–900 Ma).     

A New-Generation Borehole Electrodynamic Seismometer for Seismological Research

This paper reports the development of a new-generation short-period borehole electrodynamic seismometer designed for research, with special emphasis on seismology and volcanology (Sobisevich et al., 2008) and for important applications (Bashilov, 2001), e.g., developing special monitoring and security systems, as well as the search for and monitoring of hydrocarbon exploration.     

The Oldest Vendian (Ediacaran) Fossils of Eurasia: U–Pb Isotope Age of the Basa Formation (Asha Group,Southern Urals)

Doklady Earth Sciences - U–Th–Pb (SHRIMP II) isotopic dating of accessory zircons from Vendian (Ediacaran) ash tuffs of the Basa formation section (Asha Group, Southern Ural) was...     

Paleozoic Age of Metaterrigenous Sequences of the Maksyutov Metamorphic Complex (Southern Urals): Results of U–Pb Dating of Detrital Zircons

Doklady Earth Sciences - The first U–Pb (LA–ICP–MS) isotope dating of detrital zircons from quartzites of two strata of the Maksyutov metamorphic complex (Southern Urals) was...     

Enigmatic cathodoluminescent objects in the Dhofar 025 lunar meteorite: Origin and sources

Dhofar 025 is a lunar highland breccia consisting mainly of anorthositic, with less common noritic, gabbronoritic, and troctolitic material. Rare fragments of low-Ti basalts are present as well, but no KREEP (component enriched in incompatible elements) was found in the meteorite. The cathodoluminescence study of this meteorite showed that its impact–melt matrix contains unusual cathodoluminescent (CL) objects of feldspathic composition, which frequently contain microlites of Fe-Mg spinel (pleonaste). They were presumably formed by impact mixing and melting of olivine and plagioclase with subsequent rapid quenching of the impact melts. Such mixing could happen either during assimilation of anorthosites by picritic/troctolitic magmas or during impact melting of troctolites. The enrichment of CL objects of Dhofar 025 in incompatible trace elements suggests that the mafic component of the impact mixture may be related to the high-magnesium suite rocks, which are frequently enriched in KREEP component. The depletion of CL objects in alkalis indicates their possible relation with residual glasses formed by evaporation. However, the presence of FeO in most objects points to the insignificant extent of evaporation. Thus, evaporation cannot explain the enrichment of the CL objects in Al₂O₃ and other refractory components, although this process definitely took place in their formation. Their similarity to the lunar pink spinel anorthosites, whose existence was predicted from orbital data, serves as an argument in support of the possible formation of the latters by impact mixing.     

Olivine-garnet, olivine-spinel, and orthopyroxene metamorphic rocks of the Kokchetav Massif, northern Kazakhstan

Errata

Olivine-garnet, olivine-spinel, and orthopyroxene metamorphic rocks of the Kokchetav Massif, northern Kazakhstan