The article is dedicated to review of structural and evolutionary peculiarities of the southern part of central sector of the Indian ocean. Study is based on analyses of global digital models, distribution of fractures, global and regional lithosphere evolution models and published geological and geophysical data. As a result of study, tectonic regionalization of oceanic crust of the area is presented and main evolution stages of the region are distinguished.
The article describes the geological structure of the Turgoyak granitoid massif (γϬС1–2ts), Urenga (RF2ur) and Uytash (RF3uš) suites. In the Late Vendian time the rocks first experienced regional metamorphism under the conditions of the cummingtonite-amphibolite facies at a temperature of 550–595 °C and a pressure of 250400 МПа, and then in local areas — diaftoresis (T=520530 °C and P=130170 МПа). During the formation of the Turgoyak massif (T=770810 °C and P=210250 МПа), the rocks of the Urengin and Uytash suites were subjected to contact metamorphism. This metamorphic processes made the black shale gold to remove from the black shale zone of the amphibole-hornfels facies and caused its redeposition within the albite-epidote-hornfly zone.
Xenoliths from the Mir pipe and from Shandong and Liaoning provinces were studied according to electron microbeam analysis and ICP-MS. Their mineralogical, geochemical and genetic features are revealed. Minerals of diamondiferous paragenesis were established in xenoliths of the Mir pipe, but not in xenoliths of China. All xenoliths have secondary changes. They are stronger in the xenoliths of China. The distribution of REE shows the involvement of subduction processes in the formation of xenoliths from the Mir pipe. They are not found in xenoliths from China; the influence of metasomatism is clearly manifested in them. РТparameters were calculated: Т=600700 °С, Р=22,5 GPa. They do not correspond to mantle settings and reflect the conditions of metasomatic processes.
The Xishimen skarn iron deposit was confined to a deep fault and locates at the contact of small intrusions of monzodiorites with Pz–Mz carbonate rocks. It is represented by several banding and lenticular forms. The formation of ores is associated with the recycling processes of ore matter.
The process proceeded in several stages. Primary sedimentary and volcanogenic-sedimentary ores were formed in Ar–Prt1 time. Then followed several stages of tectonic-magmatic activation, among which the most significant was Anshan stage (Jurassic-Cretaceous). Monzodiorite magma in the process of recycling was enriched by siderophilic elements of early Precambrian and formed a series of Fe deposits in the zone of deep faults.
This paper discusses the use of geophysical well logging for the interpretation of complex structure oil-saturated intervals of the Lower and Middle Jurassic horizons with high average number of permeable intervals, the content of minerals — semiconductors (pyrite, siderite, glauconite, et al.) for structuring a complex of geological and geophysical information and developing a researching methodology of areas with hard to recover reserves on example of deposits which was in operation for an extended period of time.
Reservoir layers were located within the Nepa horizon according to the log data interpretation of 26 wells. Porosity and gas saturation were calculated within these layers. The research provides an opportunity to determine reservoir potential of sediments and to identify further research lines.
Scheelite from the Kekura gold deposit in the Western Chukchi Peninsula is reported for the first time. Three generations of the mineral have been identified. According to the LA–ICP–MS data, the Mo content in scheelite does not exceed 0,2 ppm and total REE ranges from 20 to 150 ppm. The REE distribution patterns of all three scheelite generations have a strong positive Eu anomaly (Eu/Eu*=4,455,6), which is typical of scheelite from intrusion-related and orogenic gold deposits. The high Sr concentration (1300–12000 ppm) is characteristic of the hypabyssal intrusion-related Au deposits. According to the fluid inclusion data, the minimal crystallization temperature of scheelite and associated quartz is 200–250 °С.
The trace element composition of the vertical section of the Black Sea bottom sediments was studied. Based on the calculated enrichment factors relative to the average composition of the earth’s crust, it was shown that a lithogenic source is predominant for most trace elements. Significant enrichment was obtained for Ca and Sr (due to bioaccumulation) and for S, As and Mo (as a result of hydrogen sulfide contamination processes and the influence of mud volcanoes). A specific conditions of sedimentation were estimated based on the elements’ ratios which indicate: a presence of exhalation components in the deposits (Fe+Mn/Ti), a range of transport of terrigenous material (Ti/Zr) were estimated; paleoreconstruction of salinity (Corg/S), as well as redox conditions in the bottom water layer (Mn/Fe, Mo/Mn, V/(V+Ni), V/Mn).
Data on the content of major ions (Na+, K+, Mg2+, Ca2+, Cl–, SO42–, HCO3–) and dissolved trace elements (Rb, Cs, Be, Sr, Ba, B, Si, Pmin, V, Cr, Ge, As, Mo, W, Sb, Te, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ag, Sn, Pb, Al, Ga, Ti, Zr, U) in the waters of 30 springs in Moscow during the winter low water period are presented. The geometric mean values and ranges of concentration of the studied components, as well as correlations between them, were established. The presence of hydrochemical anomalies of dissolved iron and manganese in the north-east of Moscow with an excess of maximum allowable concentration (MAC) for these elements was revealed, whereas in the rest of the city their concentration almost everywhere correspond to the natural background.
Information on recharge value is necessary for solving different classes of hydrogeological problems. One of the methods of recharge estimation is simulation of flow in vadose zone. Soil hydraulic parameters are used to estimate recharge by flow in vadose zone. One of the hydraulic parameters is the pore connectivity parameter l. The sensitivity of estimated recharge to the value of pore connectivity parameter, especially under humid climate conditions, is studied insufficiently. In present study, the experimental values of soil hydraulic parameters of samples from two different sites with various landscape conditions and vadose zone structure (forest landscape on sand and field landscape on loam) were used to estimate recharge.Recharge estimation was also carried for the value of l=0,5 and for reported values of l parameter for certain type of sediment. Analysis of calculation results demonstrated that using fixed value of l=0,5 leads to significant overestimation of calculated recharge both for forest and filed landscapes, which emphasizes the importance of experimental definitions of soil hydraulic parameters for recharge estimation. The analysis of the water balance components showed that the increase of estimated recharge with enhancement of l value is mainly associatedwith the decrease of evaporation from the upper soil layer.
A study of the distribution of rare-earth elements in surface and underground waters, waterbearing rocks, as well as secondary mineral formed by the thermal waters of the Paratunka and Viluchinsky hydrothermal systems of Kamchatka was carried out. It was found that the REE content, their distribution and fractionation differ depending on the geochemical type of water, as well as the pH–Eh of the aquifer. All waters are characterized by the predominance of the dissolved form of the REE water transfer, which exceeds the transfer of REE with colloids by a factor of a thousand. It has been shown that in the discharge areas of the studied thermal waters carbonates, sulfates and silicates, including calcite, gypsum, and amorphous opal, are widespread. The intensity of the REE redistribution process in the rock-water-secondary deposits system is very weak in waters where REEs are associated with sulfates. At the same time, REEs bound in water with carbonate complexes most actively accumulate in newly formed mineral phases.
