Temperature Range for Metasomatism at the Bakalskoe Siderite Deposits with Use of Geochemical Data

На основе количественных микрозондовых определений состава парагенезов анкерит-сидерит в семи точках, приуроченных к разным частям Бакальского рудного поля, показано, что околорудные анкериты в западной и центральной частях рудного поля отличаются по средним концентрациям FeCO 3 (соответственно 14,21 и 20,84 мас. %), в то время как в составе сидероплезита этих объектов нет выраженных различий. Расчет температур магнезиально-железистого метасоматоза на основе анкерит-сидеритового и анкерит-брейнеритового геотермометров показал их совпадение при 250°С и выше. Средние температуры сидеритового метасоматоза составляют в центральной части Бакальского рудного поля 250−270°С, в периферической части - не выше 190−220°С и не зависят от положения сидеритовой залежи в стратиграфическом разрезе бакальской свиты.The data obtained with the quantitative microprobe ankerite–siderite composition analysis of seven samples from the different parts of Bakalskoe field showed that the wallrock ankerites in the western and central parts of the ore field differ in average concentrations of FeCO 3 (respectively 14.21 and 20.84 wt.%). However, there is no significant difference in composition of siderites. The calculation of the Mg-Fe metasomatism temperatures based on ankerite-siderite and ankerite-breinerite geothermometers showed the close agreement of the values of both methods at temperatures of 250 °C and above. The average temperatures of siderite metasomatism in the central part of the Bakalskoe ore field are in range 250-270 ° C, and, in the peripheral part, the determined temperature does not exceed 190-220 ° C. These values do not depend on the position of the siderite deposits in stratigraphic level of the Bakalskaya Suite

Quartz Reef from Gold Occurrences in Riphean Deposits of the Avzyan Ore Region (South Urals): Mineralogical and Thermocriometric Features

Жильный кварц из золотосульфидно-кварцевого месторождения Горный Прииск и золотокварцевых малосульфидных рудопроявлений Улюк-Бар и ВосточноАкташское имеет сходные температуры гомогенизации первичных флюидных включений (228–382°С) и солевой состав, в котором преобладают хлориды магния и калия. Солёность варьирует в интервале 5,4–15,8 мас. % NaCl экв. Его формирование обусловлено миграцией магматогенных флюидов в связи с тектонотермальным этапом на границе среднего и позднего рифея. Безрудный жильный кварц из вмещающих рифейских отложений характеризуется более низкими Тгом (128–238°С), преобладанием хлоридов железа в солевом составе и более высокой солёностью (12,9–22,8 мас. % NaCl экв.). В золотосульфидном проявлении Богряшка образование кварца, имеющего Тгом 152–292°С и преобладание хлоридов кальция и магния в составе солей, связаны с дорудным процессом магнезиальножелезистого метасоматоза.Quartz reefs from the gold-sulfide-quartz deposit Gorny Priisk and gold-quartz sulfide bearing ore occurrences Ulyuk-Bar and Vostochno-Aktashskoe have the similar temperatures of homogenization of primary fluid inclusions (228-382 ° C) and salt composition, in which magnesium and potassium chloride predominate. Salinity varies in the range of 5,4-15,8 wt. % NaCl equiv. Generation of gold- bearing quartz reefs was caused by the migration of magmatogene fluids connected with the tectono-thermal stage between the Middle and Late Riphean. Barren vein quartz from the host Riphean rocks is characterized by lower temperatures of homogenization (128-238 ° C), predominance of the iron chlorides in salt composition and higher salinity (12,9-22,8 wt% NaCl equiv.). The generation of quartz in the gold-sulphide ore occurrence Bogryashka, which have temperatures of homogenization of 152-292 ° C and the predominance of calcium and magnesium chlorides in the salts, is associated with the pre-ore process of magnesian-ferruginous metasomatism

Nanoscale Real-Time Detection of Quantum Vortices at Millikelvin Temperatures

Since we still lack a theory of classical turbulence, attention has focused on the conceptually simpler turbulence in quantum fluids. Can such systems of identical singly-quantized vortices provide a physically accessible "toy model" of the classical counterpart? That said, we have hitherto lacked detectors capable of the real-time, non-invasive probing of the wide range of length scales involved in quantum turbulence. However, we demonstrate here the real-time detection of quantum vortices by a nanoscale resonant beam in superfluid $^4$He at 10 mK. The basic idea is that we can trap a single vortex along the length of a nanobeam and observe the transitions as a vortex is either trapped or released, which we observe through the shift in the resonant frequency of the beam. With a tuning fork source, we can control the ambient vorticity density and follow its influence on the vortex capture and release rates. But, most important, we show that these devices are capable of probing turbulence on the micron scale

Quantum state engineering with Josephson-junction devices

We review recent theoretical and experimental progress in quantum state engineering with Josephson junction devices. The concepts of quantum computing have stimulated an increased activity in the field. Either charges or phases (fluxes) of the Josephson systems can be used as quantum degrees of freedom, and their quantum state can be manipulated coherently by voltage and current pulses. They thus can serve as qubits, and quantum logic gates can be performed. Their phase coherence time, which is limited, e.g., by the electromagnetic fluctuations in the control circuit, is long enough to allow a series of these manipulations. The quantum measurement process performed by a single-electron transistor, a SQUID, or further nanoelectronic devices is analyzed in detail.Comment: An article prepared for Reviews of Modern Physics, 46 pages, 23 figure

Collapse-Breccia as a Sign of the Pre-Existing Evaporites (Lower Riphean Satka Suite, South Ural

The presence of pre-existing evaporites in the carbonate unit is considered on example of the Lower Riphean Satka Suite. It is proved by the extensive development of the collapse breccia in the Karagay member of the Upper Satka subsuite. The difference of collapse-breccias from other sedimentary breccias is shown, and the mechanism of their formation due to the bio sulphate reduction processes is proposed. Diagenesis bacterial decomposition of sulphate led to a decrease in the concentration of the sulphates ion in the pore waters and the total dissolution of the gypsum and anhydrite with the formation of the collapse breccia horizons. A low level of oxygenation in the Mesoproterozoic time supported a wide development of biosulphate reduction even in the photic zone of shallow lagoons under conditions of low hydrodynamic activity

Transient deep-water oxygenation recorded by rare Mesoproterozoic phosphorites, South Urals

EES acknowledges start-up funds from the School of Earth & Environmental Sciences at the University of St Andrews. The isotope work was supported by RFBR project 19-05-00623. This contribution is dedicated to Galina Ovchinnikova, a pioneer in U-Pb dating of sedimentary apatite at IPGG RAS (St. Petersburg, Russia).The Mesoproterozoic deep ocean is thought to have been largely anoxic, dominated by ferruginous conditions. Phosphate was scavenged from the water column by iron oxyhydroxides, and dissolved nitrate was rapidly reduced along the redoxcline. Primary productivity was therefore generally low, and eukaryotic life was restricted to oxic marine margins. This model is supported by new nitrogen isotope data from the Lower Riphean (ca. 1.55 Ga) strata of the South Ural Mountains, where we find evidence for strong redox stratification, coupled with low organic carbon content. In contrast, unconformably overlying siliciclastic sedimentary rocks of Middle Riphean age (ca. 1.33 Ga) preserve a rare occurrence of apatite concretions, associated with relatively high concentrations of organic carbon (up to 4 wt%). The Pb-Pb isochron age for the apatite concretions of the Zigazino-Komarovo Formation is 1330 ± 20 Ma (MSWD = 3.7). We measured nitrogen isotope ratios across this interval and found δ15N values up to + 7.6‰, which are similar to those in modern upwelling zones and indicative of a significant nitrate reservoir. These observations are most parsimoniously explained by upwelling of phosphate- and nitrate-bearing waters, suggesting that the deep ocean was at least regionally and temporarily oxygenated. The lack of redox-sensitive trace element enrichment in these strata and the general scarcity of apatite accumulations in the Mesoproterozoic sedimentary record suggest that oxic deep-waters were not a global and persistent phenomenon, but our results confirm that oxic, nutrient-rich refugia existed in Mesoproterozoic oceans and were perhaps important for the radiation of early eukaryotes.PostprintPeer reviewe

Geochemical and Lu/Hf isotopic (LA-ICP-MS) signature of detrital zircons from sandstones of the basal levels of the Riphean stratotype

5 page(s

The First U-Pb (LA-ICP-MS) isotope data of detrital zircons from the basal levels of the Riphean stratotype

5 page(s

Biophysical basis for the geometry of conical stromatolites

Stromatolites may be Earth’s oldest macroscopic fossils; however, it remains controversial what, if any, biological processes are recorded in their morphology. Although the biological interpretation of many stromatolite morphologies is confounded by the influence of sedimentation, conical stromatolites form in the absence of sedimentation and are, therefore, considered to be the most robust records of biophysical processes. A qualitative similarity between conical stromatolites and some modern microbial mats suggests a photosynthetic origin for ancient stromatolites. To better understand and interpret ancient fossils, we seek a quantitative relationship between the geometry of conical stromatolites and the biophysical processes that control their growth. We note that all modern conical stromatolites and many that formed in the last 2.8 billion years display a characteristic centimeter-scale spacing between neighboring structures. To understand this prominent—but hitherto uninterpreted—organization, we consider the role of diffusion in mediating competition between stromatolites. Having confirmed this model through laboratory experiments and field observation, we find that organization of a field of stromatolites is set by a diffusive time scale over which individual structures compete for nutrients, thus linking form to physiology. The centimeter-scale spacing between modern and ancient stromatolites corresponds to a rhythmically fluctuating metabolism with a period of approximately 20 hr. The correspondence between the observed spacing and the day length provides quantitative support for the photosynthetic origin of conical stromatolites throughout geologic time