Fossil subduction recorded by quartz from the coesite stability field

Metamorphic rocks are the records of plate tectonic processes whose reconstruction relies on correct estimates of the pressures and temperatures (P-T) experienced by these rocks through time. Unlike chemical geothermobarometry, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on overstepping of reaction boundaries and to identify other examples of non-equilibrium behavior in rocks. Here we introduce a method that exploits the anisotropy in elastic properties of minerals to determine the unique P and T of entrapment from a single inclusion in a mineral host. We apply it to preserved quartz inclusions in garnet from eclogite xenoliths hosted in Yakutian kimberlites (Russia). Our results demonstrate that quartz trapped in garnet can be preserved when the rock reaches the stability field of coesite (the high-pressure and hightemperature polymorph of quartz) at 3 GPa and 850 \ub0C. This supports a metamorphic origin for these xenoliths and sheds light on the mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that interpreting P and T conditions reached by a rock from the simple phase identification of key inclusion minerals can be misleading

Комплексная переработка бурых углей с получением восков и углеродных адсорбентов. Сообщение 1. Получение восков

The influence of preliminary modifying treatment of brown coal on the properties and yield of resulting brown coal waxes was investigated. The efficiency of coal demineralization by hydrochloric, oxalic and citric acid solutions was studied. A scheme for complex processing of brown coal to obtain waxes was proposed.И сследовано влияние предварительной модифицирующей обработки бурых углей на свойства и выход получаемых восков. Изучена эффективность деминерализации углей растворами соляной, щавелевой и лимонной кислот. Предложена схема комплексной переработки бурых углей с целью получения восков

Effective Use of a Computer Grading System for Teaching Mathematics at a University

In the given work, the technology to create mathematical assignments with an auto-checking system in the MOODLE system to control education was considered. It is shown that due to using the STACK plugin, those assignments can be applied in all main sections of mathematical basics courses for engineering training: vector and matrix algebra, analytical geometry, mathematical analysis. The examples of interactive assignments for the development of mathematical thinking are listed. Two different methods of using auto-checking assignments in the educational program are shown. The first includes work in class with computer facilities and students’ self-studies. Thanks to individual assignments for each student, that methodology allows reaching high results in mathematic training. The second based on the organization of student self-studies and applies mostly to underperforming students and allows them to learn how to solve tasks, which are necessary to pass the math exam. Solution’s auto-check system and the ability to generate hints in automatic mode helps to reduce the load on the teacher, as eliminating a large amount of verification work and after-hours assistance to students

Geochemical and Isotopic Properties of Fluids from Gold-Bearing and Barren Quartz Veins of the Sovetskoye Gold Deposit (Siberia, Russia)

This paper reports on the comparative study of fluids trapped in inclusions in gold-bearing and barren quartz veins at the Sovetskoye gold deposit, Yeniseisky ridge, Siberia, Russia. The host rocks are greenschist facies metasedimentary rocks of Upper Proterozoic age. Within the deposit, some veins contain 10 to 25 ppm of Au (gold-bearing veins); others contain Jess than 1 ppm of Au (barren veins). Fluid inclusions trapped in barren veins are predominantly low-salinity-H20 (4.0—8.0 mass % NaCl equiv.) with variable contents of dissolved C02 (<12.5 mol 070), CH4 (<1.3 mol 0/0), and N2 (<1.7 mol 070). Homogenization temperatures vary from 2000 to 4100C, and the calculated pressures of entrapment are <1.5 kbars. Inclusion fluids trapped in the host schists are predominantly aqueous (97.6 —99.3 mol % HO), with C02 contents below 2.4 mol percent. The fluids trapped in ore-bearing quartz inclusions are different. Inclusions show higher homogenization temperatures (up to 6300C) and salinity (up to 20—25 mass % NaCl equiv). Calculated pressures range from 0.7 to 2.0 kbars. Bulk gas chromatographic data of fluids extracted from native gold have contents of C02 that range from 29.3 to 62.0 mol percent, N2 from 2.7 to 13.2 mol percent, and CH4 from 0.0 to 2.8 mol percent. In gold-bearing quartz the contents of C02 range from 18.0 to 41.0 mol percent, N2 from 0.1 to 0.2 mol percent, and CH4 from 0.3 to 3.0 mol percent. Raman spectroscopic data of fluid from gold-bearing quartz revealed C02 contents of individual inclusions as high as 98.2 mol percent, N2 up to 66.4 mol percent, and CH4 up to 88.7 mol percent. Fluids of the country-rock schists which host gold-bearing quartz veins are also enriched in C02 (up to 49.5 mol 0/0). The host rocks for both barren and gold-bearing quartz veins show consistent REE patterns characterized by a negative Eu anomaly. Fluids from barren quartz veins show similar REE patterns although with a less conspicuous negative Eu anomaly, whereas fluids from gold-bearing quartz show a marked positive Eu anomaly. Similar isotopic values of sulfur in pyrite, pyrrhotite, and arsenopyrite disseminated in country rocks (ð34S = 14.7—21.6%0), and in barren (ð34S = and gold-bearing quartz veins (ô34S = suggest that sulfur in sulfides was derived from the same source, most likely being the adjacent country rocks. C02 trapped in fluid inclusions of barren and gold-bearing quartz has distinct isotopic compositions (ð 13C = —8.1 to —10.2 and —4.9 to +5.2 700, respectively), and the ð 13C values are positively correlated with Au contents in veins. Helium isotope composition of both types of quartz veins (3He/4He = 0.04—0.05 Ra for gold-bearing veins and 3He/4He 0.02 Ra for barren veins) indicates a crustal provenance of mineral-forming fluids. The 40Ar/39Ar dating of sericite demonstrates that the barren veins (890—850 Ma) are significantly older than the gold-bearing veins (830—730 Ma). On the basis of their ages, barren veins are interpreted as symmetamorphic. The age of the gold-bearing veins corresponds to the age of the local granitoids (850—720 Ma), suggesting that the origin of the Sovetskoye deposit is related to the tectonic activity syntetctonic magmatism