Differential behavior of components of the <Superscript>238</Superscript>U-<Superscript>206</Superscript>Pb and <Superscript>235</Superscript>U-<Superscript>207</Superscript>Pb isotopic systems in polymineralic U ores

U-Pb systems were examined in samples (ranging from 4 to 10 cm³ in volume) of ore material taken from along a 3.5-m profile across a zone of U mineralization exposed in an underground mine at the Strel’tsovskoe U deposit in eastern Transbaikalia. The behaviors of two isotopic U-Pb systems (²³⁸U-²⁰⁶Pb and ²³⁵U-²⁰⁷Pb) are principally different in all samples from our profile. While the individual samples are characterized by a vast scatter of their T(²⁰⁶Pb/²³⁸U) age values (from 112 to 717 Ma), the corresponding T(²⁰⁷Pb/²³⁵U) values vary much less significantly (from 127 to 142 Ma) and are generally close to the true age of the U mineralization. The main reason for the distortion of the U-Pb system is the long-lasting (for tens of million years) migration of intermediate decay products in the ²³⁸U-²⁰⁶Pb(RD²³⁸U) in the samples. This process resulted in the loss of RD²³⁸U from domains with high U concentrations and the subsequent accommodation of RD²³⁸U at sites with low U concentrations. The long-term effect of these opposite processes resulted in a deficit or excess of ²⁰⁶Pb as the final product of ²³⁸U decay. The loss or migration of RD²³⁸U are explained by the occurrence of pitchblende in association with U oxides that have higher Si and OH concentrations than those in the pitchblende and a higher ⁺⁶U/⁺⁴U ratio. The finely dispersed character of the mineralization and the loose or metamict texture of the material are the principal prerequisites for RD²³⁸U loss and an excess of ²⁰⁶Pb in adjacent domains with low U concentrations. Domains with low U contents in the zone with U mineralization serve as geochemical barriers (because of sulfides contained in them) at which long-lived RD²³⁸U(²²⁶Ra, ²¹⁰Po, ²¹⁰Bi, and ²¹⁰Pb) were accommodated and subsequently caused an excess of ²⁰⁶Pb. The ²³⁵U-²⁰⁷Pb system remained closed because of the much briefer lifetime of the ²³⁵U decay products. This may account for the significant discrepancies between the T(²⁰⁶Pb/²³⁸U) and T(²⁰⁷Pb/²³⁵U) age values. RD²³⁸U was most probably lost via the migration of radioisotopes at the middle part and end of the ²³⁸U family (starting with ²²⁶Ra). The heavy Th, Pa, and U radioisotopes (²³⁴Th, ²³⁴Pa, ²³⁴U, and ²³⁰Th) that occur closer to the beginning of ²³⁸U decay, before ²²⁶Ra, only relatively insignificantly participated in the process. Our results show that the loss and migration of RD²³⁸U are, under certain conditions, the main (or even the only) process responsible for the distortion of the U-Pb system.     

Fault structures and their geoelectric parameters in the epicentral zone of the 27 September 2003 Chuya earthquake (Gorny Altai) from resistivity data

This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part.     

Bioindication of water and bottom sediment pollution in the Kondopozhskaya Bay of Lake Onega

The situation in the Kondopozhskaya Bay of Onega Lake, polluted by wastewater of a pulp-and-paper mill is considered. The dynamics of wastewater input over 80 years is analyzed; the rate of such input varied widely in this period because of changes in cellulose production processes. A close correlation was found to exist between the characteristics of the state of aquatic organism communities and the environmental physicochemical characteristics. The pollution indices of water mass and the bed are evaluated, including biological and physicochemical data. Those indices can be used to identify polluted zones of water and bottom sediments in Onega Lake subject to the discharge of wastewaters from pulp-and-paper mill.     

A model of lunar evolution

There have been many models describing the evolution of our sister planet. As information from the intensive exploration by the Apollo program has accumulated, more constraints on these models have emerged. We specifically consider a hypothesis in which there is a present day asthenosphere, a heat flow between 24 and 32 ergs cm⁻² s⁻¹ and a crust which developed early in the Moon's history by melting of the outer 100 to 200 km. We have also introduced a constraint which keeps the deep interior below the Curie point of iron for the first 1 to 1.5 b.y. so that it is able to carry the memory of an early field which magnetized the cold interior. The magnetized mare basalts and breccias cooled in this field from above the Curie point of iron (≈800°C.) and acquired a thermoremanent magnetization. While fully recognizing that some of these constraints are subject to other interpretations, it is nevertheless instructive to consider the thermal history that follows from such a model. First, the initial temperature must be high enough to cause melting in the outer 100–200 km, while the interior temperature must be cool enough to be below the Curie point of iron. Second, the crust in this model cools off so rapidly that the mare basalts could not be developed as late as indicated in lunar history. Rather we propose that the mare basalts result from local remelting associated with giant impacts. Third, the Moon's deep interior must have warmed up enough to erase the memory of the ancient magnetic field from the deep interior and to develop the asthenosphere which has been detected seismically. Fourth, if this asthenosphere is real, the viscosity of the Moon as a function of temperature must be high enough to have prevented convective cooling until the temperature increased to a value near the solidus temperature. At this temperature, the Moon would then likely cool by convection in the solid state. It is, therefore, a consequence of this model that solid body convection tool place late in lunar history. This may well have contributed to the lunar center of figure and center of mass offset, to the low order terms in its gravity field and to, its disequilibrium moment of inertia differences.     

Results of monitoring of the changes in the hydrochemical structure of the central and Southern Caspian Sea over 1995–2005

The results of decennial monitoring of the Caspian Sea were summarized, which allowed revealing the “pumping” of nutrients from the euphotic layer to deepwater depressions of the Central and Southern Caspian Sea. In parallel, in the deepwater depressions, growth of hypoxia to values of 0.2–0.5 ml O₂/l proceeds. In 2006, hydrogen sulfide was registered in the near-bottom layer of the South Caspian Sea Basin. It is shown that the transformation of the hydrochemical structure was directed towards the conditions observed at the times of Bruevich (1933–1934), but no complete coincidence has yet been reached.     

“7.20”华北特大暴雨过程中低涡发展演变机制研究

利用中国地面加密自动站观测资料、北京地区雷达探测资料、NCEP （1°×1°） FNL资料、ECMWF ERA Interim （0.125°×0.125°）逐日再分析资料等,对造成2016年7月19-20日华北极端暴雨中的低涡系统发展演变的结构特征和加强机制进行了研究。华北地区这次特大暴雨过程出现了3个阶段降水,其中与低涡系统强烈发展对应的第2阶段降水是本次华北暴雨过程的主要降水阶段。针对该低涡的分析表明：（1）850 hPa以西南低涡为中心的低压带中,在河南西北部新生低涡系统,并且其在向华北地区移动过程中显著加强,该低涡系统在空间结构上,从倾斜涡柱逐渐发展成近乎直立的、贯穿整个对流层的深厚低涡系统;（2）中低层低涡系统快速发展过程与高低空系统构成耦合作用有关：低层低涡系统显著加强之前,对流层上层（300-200 hPa）首先出现高空槽异常加深并向南发展,该高空槽发展的开始阶段与其本身冷暖平流造成的斜压发展过程对应;而后,随着高纬度平流层高位涡沿等熵面向南运动,造成华北地区对流层上层涡度增强,形成正位涡异常区;当这一正位涡异常区叠加在对流层中低层锋区上空时,造成对流层中低层气旋快速发展并向下伸展,诱发河南西北部的新生气旋;低涡系统的发展进一步强化了低空暖平流,促使低空气旋向东北方向发展"移动"（本质上是暖平流前端造成的气旋发展）,这一动力学过程反过来使高层的涡度增强;这一正反馈过程形成的耦合环流不仅造成了整个涡度柱强度增强,而且垂直结构上逐渐由倾斜涡柱演变为近乎于直立的涡柱;（3）随着低涡系统增强,极大地加强了垂直上升运动并触发了对流,形成大范围的强降水,大量的凝结潜热释放,造成了低层低涡系统在强降水开始阶段的快速发展和增强;20日00时（世界时）以后,虽然对流活动显著减弱,但低涡系统的加深维持了大范围强降水过程的持续。强降水与低涡发展的正反馈过程是这次华北暴雨得以长时间维持的重要机制之一,这一过程形成的持续性潜热释放也是对流层中上层低涡系统热力结构发生改变的重要原因。     

The Effect of Inhomogeneous Magnetic Permeability on Magnetotelluric Responses: 1D and 2D Models

Izvestiya, Physics of the Solid Earth - Abstract—When solving direct and inverse problems of magnetotellurics, magnetic permeability throughout model medium is conventionally assumed to be...     

What is the source of baseflow in agriculturally fragmented catchments? Complex groundwater/surface‐water interactions in three tributary catchments of the Wabash River,Indiana, USA

Some conceptual models suggest that baseflow in agriculturally fragmented watersheds may contain little, if any, groundwater. This has critical implications for stream quality and ecosystem functioning. Here, we (a) identify the sources and flowpaths contributing to baseflow using ²²²Rn and ⁸⁷Sr/⁸⁶Sr and (b) quantify mean apparent ages of groundwater and baseflow using multiple isotopic tracers (CFC, SF₆, ³⁶Cl, and ³H) in 4 small (0.08 to 0.64 km²) tributary catchments to the Wabash River in Indiana, USA. ²²²Rn activities and ⁸⁷Sr/⁸⁶Sr ratios indicate that baseflow in 3 catchments is sourced primarily from groundwater; baseflow in the fourth is dominated by a source similar to agricultural run‐off. CFC‐12 data indicate that springs in 1 catchment are discharging significant proportions of water that recharged between 1974 (42 ± 2 years) and 1961 (55 ± 2 years). Those same springs have ³⁶Cl/Cl ratios between 1,381.08 ± 29.37 (×10^?15) and 1,530.64 ± 27.65 (×10^?15) indicating that a substantial proportion of the discharge likely recharged between 1975 (41 years) and 1950 (66 years). Groundwater samples collected from streambed mini‐piezometers in a separate catchment have CFC‐12 concentrations indicating that a large proportion of the recharge occurred between 1948 (68 ± 2 years) and 1950 (66 ± 2 years). Repeat sampling conducted in September 2015 after above‐average summer rainfall did not show significant decreases in mean apparent age. The relatively old ages observed in 3 of the catchments can be explained by geological complexities that are likely present in all 4 catchments, but overwhelmed by flow from the shallow phreatic aquifer in the fourth catchment.     

Geology of the volcanic-hosted Brockman rare-metals deposit,Halls Creek Mobile Zone,northwest Australia. l. Volcanic environment,geochronology and petrography of the Brockman volcanics

Summary Rare-metals mineralization of the Brockman deposit (Halls Creek Mobile Zone, NW Australia) is hosted in a fluorite-bearing, rhyolitic volcaniclastic unit informally termed the Niobium Tuff. The Tuff, more correctly described as a tuffaceous volcaniclastic deposit, is the lowermost unit of a sequence of trachyte-to-rhyolite lavas, trachyandesite subvolcanic rocks, and volcaniclastic units of the Brockman volcanics located within the Halls Creek Group, a thick, early Proterozoic volcano-sedimentary sequence. High precision SHRIMP ion-microprobe zircon dating of the Niobium Tuff gives an eruption age of 1870 ± 4 Ma. Regional geochronological constraints indicate the Niobium Tuff was deposited about 15 Ma before major orogenic activity affected the area. Despite folding, faulting and low-grade metamorphism, the Brockman volcanics show excellent preservation of primary volcanological features, including pillow-lavas and pillow-breccias, that suggest a dominantly subaqueous, below-wave-base emplacement environment. The style of eruption products and magma volume constraints suggest the trachyte-dominated volcanics were erupted from a small shield volcanic complex probably in a rift-related basin in a shallow-marine setting. The tectonic setting was intraplate but differs from most Tertiary to recent trachyte volcanic complexes which are largely subaerial, are built on relatively thick continental crust, and show no post-eruptive orogenic history. Brockman-style rare-metal deposits are characterized by preservation of subaqueous volcanics beneath a thick sedimentary sequence, eruption of early incompatible-element enriched products followed by less differentiated magmas, and fine-grained mineralogy influenced by alteration processes. Prospects exist for discovery of analogous deposits, particularly in early Proterozoic mobile belts and Tertiary intraplate shield volcanic provinces.

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Geologie der an Vulkanite gebundenen Seltene-Metalle-Lagerstätte Brockman, Halls Creek Mobile Zone, Nordwest-Australien. I. Vulkanologie, Geochronologie und Petrographie der Brockman-Vulkanite

Zusammenfassung Selten-Metall-Vererzung der Brockman-Lagerstätten (Halls Creek Mobile Zone, NW Australien) sitzt in einer Fluorit-führenden, rhyolitischen vulkanoklastischen Einheit auf, die informell als der Niob-Tuff bezeichnet wird. Es handelt sich hier um ein vulkanoklastisches Tuff-Sediment; dieses ist die unterste Einheit einer Abfolge vor Trachyt bis Rhyolit-Laven, trachyandesitischen Subvulkaniten and vulkanoklastischen Einheiten der Brockman Vulkanite innerhalb der Halls Creek Gruppe, einer mächtigen frühproterozoischen vulkanosedimentdren Abfolge. Prüzisionsdatierungen des Niob Tuffs mit der SHRIMP Ionen-Mikrosonde ergeben ein Eruptionsalter von 1870 +-4 Millionen Jahren. Regionale geochronologische Zusammenhänge zeigen, daß der Niob Tuff etwa 15 Millionen Jahre vor einer größeren Orogenese, die das Gebiet betroffen hat, abgelagert wurde. Trotz Faltung, Bruchtektonik and niedriggradiger Metamorphose zeigen die Brockman-Vulkanite einen hervorragenden Erhaltungszustand primärer vulkanologischer Erscheinungen. Diese urnfassen auch Kissenlaven und KissenBreckzien, die eine vorwiegend subaquatische Ablagerung in ruhigem Wasser erkennen lassen. Die Art der Eruptionsprodukte and das Magmavolumen zeigen, daß die Trachytdominierten Vulkanite von einem kleinen Schildvulkan stammer, wahrscheinlich in einem Becken in einer Rift-Situation im seichten marinen Milieu. Die tektonische Situation war intraplate, aber unterscheidet sich von den meisten tertiären bis rezenten trachytischen Vulkan-Komplexen, die hauptsächlich subaerisch sind, auf einer relativ mächtigen kontinentalen Kruste aufsitzen, and keine post-eruptive orogene Entwicklung zeigen. Seltene-Metalle-Lagerstatten des Brockman-Typs rind durch die Erhaltung subaquatischer-Vulkanite unterhalb einer machtigen sedimentdren Abfolge gekennzeichnet; welters durch frühe Eruptionsprodukte, die an inkompatiblen Elementen angereichert sind, auf die dann weniger differenzierte Magmen folgten, und schließlich durch einen feinkörnigen Mineralbestand, der vor Umwandlungsprozessen betroffen war. Es besteht die Möglichkeit der Entdeckung analoger Lagerstätten, besonders in frühproterozoischen mobilen Gürteln und in tertidren intraplate Schildvulkan Provinzen.

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Deceased     

Retrospective Assessment of Bottom Deposits in Kondopoga Bay,Lake Onega

Long-term observations of the chemical composition of bottom sediments in Kondopoga Bay, Lake Onega, are considered. The present-day state of bottom sediments is characterized, and regularities of variations in the composition and properties of sediments occurring in the zone of influence of wastewaters from a pulp and paper plant (PPP).