Lithology and Mineral Resources最新文献

The results of a comparison of various ratios of trace elements-indicators of the composition of provenances for clay rocks of the Middle Riphean Avzyan Formation and the Upper Riphean Biryan Subformation of the Zilmerdak Formation (Bashkirian meganticlinorium, Southern Urals) are analyzed. The formation of these two objects is separated by a hiatus, with the maximum duration up to 250 Ma. The study is based on materials related to the content of trace elements in clay/fine-grained clastic rocks, respectively, of the Avzyan Formation (28 samples) and Biryan Subformation (16 samples) from the collections of E.Z. Gareev and the author, obtained by the ICP-MS method at the IGG Ural Branch of the Russian Academy of Sciences (Yekaterinburg). Distribution of individual and average data points of clay rocks of the named objects on La/Sc–Th/Co, Sc–Th/Sc, Eu/Eu*–Th/Sc, Ni–V–10Th, Th–La–Sc, Y/Ni–Cr/V, Cr/Th–Th/Sc, and Hf–La/Th diagrams are significantly comparable. The chondrite-normalized spectra of rare earth elements (REE) are also comparable. Only on the Th–Th/U diagram, the distribution of data points has a slightly different form, suggesting that either the provenance composition was invariable for almost 250 Ma, the duration of the pre-Upper Riphean hiatus was not so long, the author’s analytics are “lame”, or there are other reasons.

Chromites are a common component of the heavy fraction of sedimentary cover deposits in the platform areas, and their contents usually do not exceed some percents. Commonly, economic chromite placers are formed in vicinity of bedrock sources. Within the Lukoyanov placer district (Nizhny Novgorod region), high chromite contents (up to 100 kg/m³) were found in Middle Jurassic complex coastal-marine rare metal–titanium placers of economic importance. Placer bodies are localized on the periphery of domes in the sedimentary cover. The placers can be sourced from Upper Permian and Lower Jurassic rocks, which were eroded in the zone of positive tectonic structures of the cover and platform basement and within the adjacent land. The revealed patterns can serve as a basis for forecasting similar deposits within promising areas.

A new approach is proposed to assess the degree of defect density of kaolinite minerals using their IR spectra in the OH-stretching vibration region. Three linear equations were obtained that relate the ratios of spectroscopic parameters to each other: (frac{{Aleft( {{{nu }_{3}}} right)}}{{Aleft( {{{nu }_{3}}} right) + Aleft( {{{nu }_{2}}} right)}} = - {kern 1pt} 0.2177frac{{FWHMleft( {{{nu }_{1}}} right)}}{{FWHMleft( {{{nu }_{4}}} right)}}) + 1.247; (frac{{FWHMleft( {{{nu }_{3}}} right)}}{{FWHMleft( {{{nu }_{2}}} right)}} = - 0.5804frac{{FWHMleft( {{{nu }_{1}}} right)}}{{FWHMleft( {{{nu }_{4}}} right)}}) + 2.8696; (frac{{FWHMleft( {{{nu }_{3}}} right)}}{{FWHMleft( {{{nu }_{2}}} right)}} = 2.636frac{{Aleft( {{{nu }_{3}}} right)}}{{Aleft( {{{nu }_{3}}} right) + Aleft( {{{nu }_{2}}} right)}} - 0.4437), where: FWHM(ν_i) is a full width at half maximum and A(ν_i) is the integral intensity of Lorentzian absorption bands at ν₁ ~ 3697 cm^–1, ν₂ ~ 3670 cm^–1, ν₃ ~ 3652 cm^–1 and ν₄ ~ 3620 cm^–1, respectively. These equations made it possible to establish criteria for decomposing the IR spectra into individual bands (ν_i) and determining the optimal values for the FWHM(ν_i) and A(ν_i) parameters used for calculating the contents of high-ordered kaolinite (HOK) and low-ordered kaolinite (LOK) phases in natural samples with an accuracy of ~5%.

Clay minerals were studied in Pleistocene sediments from Hole 1038А (114.50 m deep) and Hole 1038Н (192.80 m deep) drilled near a hydrothermal vent with a temperature of 217°C on Central Hill, 275 m east of Hole 1038B. In sediments from Hole 1038A, at a depth of 8.52 m, <0.001-mm fraction consists completely of chlorite. In the rest of the sediment section in Hole 1038A, clay minerals consist of chlorite (from ~64 to ~98%) and illite. In sediments from Hole 1038H, clay minerals also consist of chlorite and illite. They were formed under conditions related to the intrusion of a basaltic melt as laccolith into the Escanaba Trough and the heating under its influence of a solution, during the interaction of which with sediments at a high-temperature stage biotite was formed. During the subsequent slow cooling of the laccolith and fluid, the newly formed biotite was replaced completely by chlorite. Illite was precipitated from a hydrothermal solution. At a depth of 183 m, in sediments from Hole 1038H, clay minerals consist of biotite, chlorite, and dioctahedral smectite, just as in sediments from Hole 1038B during their formation under conditions of rapid cooling of the laccolith flank and penetration of sea water into the sediments. The paper shows similarities and dissimilarities in the formation of clay minerals in Pleistocene sediments of the Central Hill, located above the slowly cooling part of the laccolith (Holes 1038A and 1038H) and in sediments located above the rapidly cooling laccolith flank (Hole 1038B).

The crystal chemical characteristics and causes of their variations in the weakly and strongly modified by epigenetic processes dolomites of the Middle Riphean Avzyan Formation in the Bashkir meganticlinorium have been determined. The studies were accomplished by the X-ray diffraction, X-ray fluorescence, and SEM/EDS analysis methods. The Avzyan dolomites are marked by increased parameters of the crystal lattice (a_av = 4.8105 Å, c_av = 16.0211 Å) and reduced values of the substructural reflection (K_av = 0.66) in comparison with stoichiometric dolomites. The average content of elements is as follows: Fe(II) 4545 ppm, Mn 423 ppm, and Sr 124 ppm. Increase in parameters of the crystal lattice of the Avzyan dolomites shows direct correlation with increase in the contents of Fe and Mn, whereas values of the substructural reflection have an inverse correlation. Rocks of all studied sections include two generations of dolomite and calcite. The calcite–dolomite veinlets were formed at 260–530°C and 0.3–2.3 kbar. In dolomites of different subformations, the average value of parameters of the crystal lattice a and c decreases from the early (Kataskin subformation) to the late Avzyan (Tyul’men subformation). In the same direction, average values of the coefficient K of the dolomite structure ordering increase. Dolomites of different stratigraphic levels of the Avzyan Formation underwent intense epigenetic transformations caused by the impact of medium- and high-temperature Fe- and Mn-containing fluids on rocks. Change in the crystal chemical characteristics of the Avzyan dolomites is associated not so much with the process of regional metamorphism, as with the activity of postmagmatic (sections near the Veselovka Settlement and on the Tyul’men River) and catagenetic (sections near the Islambaevo Settlement and on the Bol’shoi Avzyan River) of fluids, which percolated along the fracture zones.

The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the Laptev Sea shelf leads to the development of a thick alluvial fan at the continental rise, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western flank of which is complicated by terraces. The presence of fault structures, bottom subsidence, extensive sediment supply, and the widespread development of subaqueous slump processes indicate the high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate rocks have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. The palynological and micropaleontological analysis of the carbonate rocks indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and oxidation products of gases and organic matter. The authigenic carbonates were precipitated mainly in an isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between ⁸⁷Sr/⁸⁶Sr and δ¹³C indicates the presence of at least two different sources of carbonate-forming solutions.

We compared the arithmetic average chemical composition of main types of Pleistocene sediments in the Indian and Atlantic oceans, and average chemical composition of the Pleistocene in both oceans as well. As the base for comparison, we used data from the International project of deep-sea drilling reports (phases DSDP, ODP, IODP) and other references. It was revealed that the results of comparative analyses of the mean weighted chemical composition were determined by masses of the dry sediment matter. Domination of the Atlantic mass accumulation rates over the Indian Ocean ones was due to markedly larger catchment areas, influence of more significant humid climate, and enhanced primary production.

Both tectonic settings and sedimentary environments of the oil- and gas-bearing Triassic sequences in the Caspian region are examined. It is shown that the Scythian and West Turanian plates were located at an active margin of the East European continent in Triassic. A unified thick (up to 3–5 km) cover of sedimentary and volcanosedimentary (mainly tuffaceous) rocks without the characteristic features of rifting was formed. In the northern and eastern parts of the region, the Triassic is composed of variegated continental terrigenous rocks. In many areas of the region (eastern and southern parts of the Pre-Caspian Basin, Eastern Ciscaucasia, Mangyshlak, and Middle Caspian), the Lower Triassic (Olenekian) and Middle Triassic are represented by marine terrigenous–carbonate rocks. The structural features of sequences in the Pre-Caspian Basin are associated with salt tectonics. The maximum thickness (up to 4.5–5 km) of Triassic rocks within the Scythian Plate is recorded in the southwestern part of the Middle Caspian and southeastern part of the Karpinsky Ridge, where they fill up a series of NW-extending graben-shaped troughs. Their absence in the northwestern part of the region is related to the latest shear deformations, as confirmed by their discrepancy with the facies zonation of Triassic deposits. Currently, the Permian and Triassic deposits represent a pre-platform geodynamic seismic sequence unconformably overlying the pre-Kungurian deposits. Triassic deposits of the Scythian and West Turanian plates are disturbed by faults (amplitude up to 2 km) and dislocated in some areas. Folding with faults and strike-slip faults is especially intense on the Karpinsky Ridge. Increased dislocation and Late Triassic magmatism on the Scythian and West Turanian plates are associated with the processes of collision during the closure of the Paleotethys Ocean. Oil and gas prospects of the region are assessed positively.

Several geochemical characteristics ((La/Yb)_N, Eu/Eu*, and Th content) of gray silts of the Volga River, suspended particulate matter of the Lena River, and silt–pelite fraction of bottom sediments in the Yangtze River are analyzed. It has been established that the above parameters of the chondrite-normalized lanthanide spectra and the Th content turn out in almost all cases to be comparable with their values determined for the specially prepared (removal of nonterrigenous carriers of rare earth elements (carbonate minerals, Fe–Mn oxyhydroxides, and organic components) pelite fractions of bottom sediments deposited near the mouths of named major rivers, and are retained over thousands of kilometers upstream from their deltas/mouths. The regulation of the Volga and Yangtze flows does not have a significant impact on parameters of the suspended particulate matter and bottom sediments under consideration.

Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B (120.50 m deep), drilled on the northwestern edge of the Central Hill (Escanaba Trough, Gorda Ridge) near the hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough 5 km south of the Central Hill. The terrigenous clay mineral assemblage in sediments from Hole 1037B consists of the mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. Sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m are composed of terrigenous clay minerals. In the rest of the sedimentary section, clay minerals are represented by the newly formed biotite, chlorite, and dioctahedral smectite. They were formed during the basaltic melt intrusion into the Escanaba Trough with the formation of a laccolith and the subsequent rapid cooling of its flank. The intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, the fine-dispersed biotite was formed in sediments at the high-temperature stage of this interaction due to the primary terrigenous clay minerals, K-feldspar, and amphiboles. The rapid cooling of the hydrothermal fluid to a temperature of presumably 270–330°C promoted the partial replacement of biotite by chlorite. The further rapid cooling of the hydrothermal fluid to 200°C and lower and its mixing with seawater seeping into sediments of the Central Hill fostered the formation of smectite.