Precambrian stratigraphy of northeastern part of Yenisey ridge

In the area between the Uvolga, Chapa, and Vorogovka rivers, all of the Tungusik, Oslyanka, and a part of the Sukhoy Pit series are missing in the Precambrian section, which consists of the following series, from the bottom up: Teya, parts of Sukhoy Pit, and Chingasan. -- V.P. Sokoloff     

New insights into the nature of the Late Riphean Eosolenides

Studies of a morphologically diverse population of Eosolenides, organic-walled macrofossils from the Upper Mesoproterozoic (1015–1025 Ma) Lakhanda Group of southeastern Siberia, suggest that these elongate fossils may be remains of soft-bodied organisms having tube-grade organization. The compressed, originally cylindrical fossils, of more or less constant diameter along their length, are subdivided by transverse membranes into a regular series of distinct chamber-like segments. The lateral walls of the segmented tubes are double-layered, the outer sheath- or cuticle-like layer of which was originally flexible and commonly exhibits very fine and closely spaced transverse striations. The presence of structures inferred to be basal attachment disks suggests a benthic habit, whereas the morphological variability of the population can be interpreted as showing that their body shape changed as the organisms grew and increased markedly in length. Reproduction may have been by budding. An important peculiarity exhibited by these tubular fossils is the presence within many specimens of small spherical unicells, interpreted possibly to be algal endosymbionts. Although in some respects these fossils resemble cnidarians, the biological affinities of Eosolenides tubes remain enigmatic.     

Plant assemblage from Opole,southern Poland: New data on Late Cretaceous vegetation of the northern part of the European Province

This paper presents the results of studies on plant macroremains found in the upper Turonian of the Folwark Quarry, Opole, Poland, associated with palynological studies of the host rocks. In addition to a few macrofossils (gymnosperm wood, conifer Geinitzia reichenbachii and fern ?Didymosorus) rich sporomorphs (bryophyte, lycopod and fern spores, conifer and angiosperm pollen grains) and marine palynomorphs (mainly dinoflagellate cysts) were recorded. The palynological analysis revealed that the vegetation on the neighbouring land (the East Sudetic Island) in the late Turonian was much more diverse than could be reconstructed based on only macrofossil remains. The latter are taxonomically restricted and dominated by one gymnosperm species (Geinitzia reichenbachii), which make them similar to most neighbouring, coeval Central European assemblages. Its over representation is, thus, a result of taphonomy.     

Gabbro-peridotite sills of the Late Riphean Dovyren plutonic complex (northern Baikal area,Russia)

We report data on the geology, mineralogy, petrography, and chemistry of 733 Ma gabbro-peridotite sills from the Late Riphean Dovyren plutonic complex. Thick sills were differentiated into plagiolherzolite to olivine gabbronorite compositions by fractional crystallization of the K-Na series high-Mg low-alkali low-Ti picritic parental magma. The magma already contained up to 5% of intratelluric olivine crystals when entering the reservoir. The sills emplaced before the whole complex, judging by the presence of their fragments as plagiolherzolite xenoliths in the gabbro zone of the Yoko-Dovyren layered pluton. The gabbro-peridotite sills are products of high-temperature within-plate magmatism. High heat flow during the generation of the magma, evident from its high-Mg composition, was likely maintained by the activity of a mantle plume associated with the Neoproterozoic Franklin large igneous province.     

Late Riphean Sedimentation in the Central Russian Aulacogen

Result of the analysis of combined structural, facies, mineralogical, and micropaleontological data suggest that the formation of the Central Russian Aulacogen was related to the evolution of a major strike-slip system in the Late Riphean on the Russian Plate. The strike-slip system led to the formation of parageneticaly interrelated structures: central anticlinal uplift framed by two troughs (structurally isolated echelon of lake-type sedimentary basins). The structural pattern of Late Riphean riftogenesis was responsible for the isolation of the sedimentation system. The variable intensity of extension at opposite flanks of the aulacogen is reflected in the fanlike form of the present-day structure and composition of sedimentary complexes, particularly the presence of red-colored molasse in the widest (southwestern) part of the study region. The growth of the central uplift is inferred from the enrichment of heavy fraction in epidote from blastomylonites derived from the lithostructural framing (rocks of the tectonic melange).     

First finding of nepheline rocks in northern Yenisey Range

Alkalic nepheline rocks were discovered in the Srednyaya and Pravaya Noyba interstream areas, as alluvial-deluvial piles at different altitudes, in proximity of outcrops of quartz and alkalic syenites to which they may be related genetically. The alumina potential of this part of the range is augmented particularly by the associated rare-metals mineralization. — IGR Staff.     

Sources of the Late Riphean carbonatite magmatism of Northern Transbaikalia: Geochemical and isotope-geochemical data

New major and trace element and Nd-Sr isotope results are reported for the carbonatites of the Veseloe and Pogranichnoe occurrences, Northern Transbaikalia. The carbonatites from both these occurrences are enriched in Sr, Ba, LREE, Th, U, and depleted in Ti, Cr, and V relative to primitive mantle. As compared to the “average dolomite carbonatite”, the rocks from the Northern Transbaikalia have higher contents of Ni, Cr, and low contents of Ba, Ti, and V. The rocks are characterized by ⁸⁷Sr/⁸⁶S in the range of 0.7037–0.7043 and ɛNd from + 0.6 to + 2.05. Obtained geochemical and isotope data indicate that the carbonatites were derived from moderately depleted source with a contribution of enriched component.     

Structural characteristics of deposition of gold ores in parts of Yenisey ridge

Positional and morphological variation in the ore bodies, particularly the remarkable differences in depth-length of gold-quartz veins, are related to structural controls and heterogeneities in host rocks of the ores, and not to tectonic controls of the ore deposition by the meridional “tectonic rupture,” as once believed.     

Late Jurassic-Neocomian volcanism of the northern Okhotsk region: Geology,tectonic settings,and mineralization

The paper deals with new data on the geology, geochronometry, and petrogeochemistry of the Upper Jurassic-Neocomian basaltic andesites constituting the base of the Cretaceous volcanogenic section in the northern Okhotsk region. The geochronometric data confirm the Late Jurassic-Neocomian age of these rocks (147–138 Ma, K-Ar method). Their characteristic features provide grounds for considering these rocks as fragments of the Uda volcanic belt. The comparison of the petrogeochemical characteristics with similar parameters of other different-age tectonic structures of the region under consideration that were formed in different geodynamic environments (intracontiental and continental marginal volcanogenic belts, island arcs) revealed similarity between the conditions of the formation of the Late Jurassic-Neocomian (Uda belt) and Albian-Cenomanian (Okhotsk-Chukotka belt) volcanics: both characterize continental marginal environments. It is assumed that the Late Jurassic-Neocomian volcanism associates with Au-Ag mineralization, which is also expected in other similar although poorly known volcanic structures.     

U–Pb zircon geochronology of Late Devonian to Early Carboniferous extension‐related silicic volcanism in the northern New England Fold Belt

Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of zircons confirm a Late Devonian to Early Carboniferous age (ca 360–350 Ma) for silicic volcanic rocks of the Campwyn Volcanics and Yarrol terrane of the northern New England Fold Belt (Queensland). These rocks are coeval with silicic volcanism recorded elsewhere in the fold belt at this time (Connors Arch, Drummond Basin). The new U–Pb zircon ages, in combination with those from previous studies, show that silicic magmatism was both widespread across the northern New England Fold Belt (>250 000 km² and ≥500 km inboard of plate margin) and protracted, occurring over a period of ～15 million years. Zircon inheritance is commonplace in the Late Devonian — Early Carboniferous volcanics, reflecting anatectic melting and considerable reworking of continental crust. Inherited zircon components range from ca 370 to ca 2050 Ma, with Middle Devonian (385–370 Ma) zircons being common to almost all dated units. Precambrian zircon components record either Precambrian crystalline crust or sedimentary accumulations that were present above or within the zone of magma formation. This contrasts with a lack of significant zircon inheritance in younger Permo‐Carboniferous igneous rocks intruded through, and emplaced on top of, the Devonian‐Carboniferous successions. The inheritance data and location of these volcanic rocks at the eastern margins of the northern New England Fold Belt, coupled with Sr–Nd, Pb isotopic data and depleted mantle model ages for Late Palaeozoic and Mesozoic magmatism, imply that Precambrian mafic and felsic crustal materials (potentially as old as 2050 Ma), or at the very least Lower Palaeozoic rocks derived from the reworking of Precambrian rocks, comprise basement to the eastern parts of the fold belt. This crustal basement architecture may be a relict from the Late Proterozoic breakup of the Rodinian supercontinent.     

New data on the composition and age of granitoids in the northern part of the Tagil structure (Ural Mountains)

The Tagil structure representing a large fragment of the Paleozoic island arc on the eastern slope of the Urals has been sufficiently well studied in its southern part (Middle Urals). In contrast, reliable data on the age and geochemical properties of various, including granitoid, rock complexes available for its northern part are scarce. The first data on the U–Pb LA–ICP–MS age of zircons from quartz diorites of the Man’ya massif of the Petropavlovsk Complex (436 ± 3 Ma, MSWD = 1.3), tonalites of the same complex (439.4 ± 1.3 Ma, MSWD = 1.3), granites of the Yuzhno-Pomur massif of the Severorudnichnyi Complex (422.4 ± 3 Ma, MSWD = 1.5), and titanite of the same massif (423.4 ± 4.4 Ma, MSWD = 0.84) have been obtained. Based on these data combined with the geochemical properties of the host rocks, the conclusion that they were crystallized at the initial stages of the formation of comagmatic volcanic series is supported; by their composition, granitoids correspond to island arc igneous rocks.     

New data on the Early Cenozoic volcanism of the Kolyuchinskii-Mechigmen graben,Chukotka Peninsula

The isotopic-geochemical composition of the Late Paleocene-Early Eocene basalts in the central part of the Kolyuchinskii-Mechigmen graben on the east of the Chukotka Peninsula is studied. The distribution of major and trace elements and the elemental ratios point to the formation of basalts under conditions of marginal-continental rifting. The basalts of Mount Otdel’naya are characterized by a combination of depleted, intraplate, and suprasubduction geochemical features, which differentiates them both from the rocks of suprasubduction volcanic belts and tholeiites and alkaline lavas of the continental rifts and oceanic island arcs. The specific peculiarities of basalts of Mount Otdel’naya are extremely high, relative to similar basalts of spreading zones of the region and the ⁸⁷Sr/⁸⁶Sr ratios, which reflect the involvement of carbonate material in the magma generation zone.