卷 70, 编号 4 (2025)
Articles
Different types of CaSiO3 in the Earth’s mantle and its geochemical heterogeneity: the Juina area in Brazil as an example
摘要
CaSiO3 inclusions in diamonds from the Juina area in Brazil have low Fe (0.08–0.53 wt. % FeO) and Al (0–1.52 wt. % Al2O3) concentrations; they belong to the ultramafic association. Two different types exist among CaSiO3 grains. Type I has a normal REEn pattern, while type II has a sinusoidal REEn pattern. Type I CaSiO3 associates with high-Mg – high-Ni protogenetic ferropericlase, and type II associates with high-Fe – low-Ni syngenetic ferropericlase. Thus, type I CaSiO3 grains are protogenetic, formed, like high-Mg – high-Ni ferropericlase, in the upper part of the lower mantle as davemaoite (CaSi-perovskite), and type II CaSiO3 were formed in the transition zone as breyite. The enrichment of CaSiO3 in REE, particularly in LREE, corresponds to high values of their partition coefficient CaSiO3/melt and shows the Ca-SiO3’s origin from a mantle material under high pressures. The isotope characteristics of the studied CaSiO3 demonstrate strong geochemical heterogeneity in the inclusions. The 87Rb/86Sr ratios in type II CaSiO3 (0.127–3.23) are 3–4 orders higher than in type I (0.0008). Even within a single diamond, different CaSiO3 grains have 87Rb/86Sr ratios varying from 0.014 to 3.23. The same is true for U/Pb isotope systematics (e. g., 238U/206Pb varies in one sample in an order of magnitude from 0.031 to 0.312) and, to some extent, for Sm/Nd ratios. This implies the geo-chemical heterogeneity in Deep Earth on a very small scale.
271-284
Distribution of hydrocarbon biomarkers with depth in marine sediments in the area of the linear depression of the West Kara stage
摘要
Studies of molecular and hydrocarbon composition in marine sediments provide important information on sedimentary organic matter (OM). In this work, the distribution of hydrocarbons and molecular markers along the depth of the sedimentary cover in the region of the linear depression of the West Kara stage was studied. For this, two sediment columns were sampled during the 89th cruise of the R/V “Akademik Mstislav Keldysh”: at station 7444 and at background station 7441. The distribution of n-alkanes was measured by GC-MS analysis and the peculiarities of distribution of the sediment OM in marine sediments of biomarker indices with sediment depth were determined. It was shown that higher terrestrial vegetation was the dominant source to the sediment OM of marine sediments at stations 7444 and 7441. The OM had low maturity as shown by the values of the Ts/(Ts+Tm) ratio. According to the values of H31–S/H31–(S+R) and NAR indices, a small constant inflow of petrogenic hydrocarbons was observed in the study area, while at the background station 7441 the inflow was much less. Based on the distribution of CPI25–33, TAR and NAR indices, the presence of hydrocarbons of anthropogenic origin in the near-surface layers of 0–15 cm sediment at the background station 7441 was assumed.
285-299
Humification of the organic matter in the surface bottom sediments of the East Siberian Sea
摘要
New data on the content of humic substances (HS) in the East Siberian Sea are presented. The results of the studies showed that the degree of humification of organic matter (OM) in the studied samples of the upper layer of bottom sediments of the sea varies from 21 % to 9 % and averages 15 %, which is typical of low-productivity Arctic seas. It was found that the average HA values (for the considered profiles) were 0.16 and 0.20 %, which is typical of oxidized marine sediments. The concentration of organic carbon (Corg) varied from 0.34 % to 1.89 % depending on the granulometric type of sediment. It is shown that the total Corg consists of 10–40 % HS, the HS themselves consist of 12–30 % humic acids (HA) and 70–88 % fulvic acids (FA), which indicates early humification of sediments. НAs were determined only in the sediments of the coastal part of the sea. FAs were determined in all studied bottom sediments.
300-312
A new reaction controlling the composition of oils: hydrogenation of aromatic hydrocarbons
摘要
Analysis of the composition of n-alkyl-substituted monocyclic compounds of Tatarstan oils (n-alkylcyclohexanes, n-alkylcyclopentanes and n-alkylbenzenes) made it possible to prove that during the formation of the composition of the studied oils, hydrogenation reactions of aromatic hydrocarbons, previously not recorded in the rock, took place. It has been directly proven that n-alkylcyclohexanes of petroleums were partially formed from the n-alkylbenzenes present in them. At the same time, catalysts for the hydrogenation of aromatic hydrocarbons known from organic chemistry are either absent in any noticeable quantities in oils (and platinum group metals in the earth’s crust) or are inactive in natural environments. So today it is not possible to indicate a natural catalyst for this reaction. That is, the discovery of this reaction demonstrates the incompleteness of our understanding of the catalysts involved in the formation of the composition of oils. From the literature it follows that Tatarstan is not the only region in whose oils this reaction occurs. It has been shown that during hydrogenation, oils must be in conditions radically different from those that occurred during the formation of their main components (acid catalysts in the first stage and their absence in the second). It follows that the hydrogenation reaction of aromatic hydrocarbons in Tatarstan oils occurs at the later stages of their evolution, when the main composition of the oils has already been formed. It seems reasonable to assume that hydrogenation takes place after the migration of oil from the source rock. That is, this reaction occurs either along the oil migration routes or into deposits.
313-322
Elemental composition and sources of urban dust of а large industrial city (Krasnoyarsk, Russia)
摘要
For the first time, a comprehensive study of urban dust collected in Krasnoyarsk city was carried out. The results obtained enabled the features of elemental composition of urban dust and their natural and anthropogenic sources to be investigated. Dust samples (n = 68) were collected in different functional areas of the city. The content of 70 elements was determined in the collected samples of urban dust. The diagrams of the (CaO + Na2O) – Al2O3 – K2O and (CaO + Na2O + K2O) – Al2O3 – (Fe2O3 + MgO) composition showed that the mineral part of most of the studied Krasnoyarsk dust samples is represented by plagioclases. Values of enrichment factors and geoaccumulation indices showed contamination of Krasnoyarsk dust by Co Sn, Bi, Pb, Mo, Cu, As, Zn, Cd, W, Ag and Sb. Regularities of microelement accumulation depending on sampling locations were found. Sb accumulates to a large extent in samples collected on major highways of Krasnoyarsk, while elevated contents of As, Cu and Co are typical for samples collected in industrial areas of the city. The principal component analysis and Pearson matrix allowed to identify 6 groups of elements in the dust samples, which can be attributed to various natural and anthropogenic sources: Al, Ti, Cr, Fe and Ni – weathering of soils and rocks; Fe, Co, Ni, Cu and As – emissions from metallurgical plants and coal-fired thermal power plants; W, Bi, Zn and Mo – heavy metallurgical and mechanical engineering industries; Cu, Cd, Sn and Pb – emissions from motor and rail transport, as well as wear of metal parts and structures; Sn and Sb – wear of brake pads and tires and industrial emissions; Hg – weathering of soils and rocks.
323-344