Scanning electron microscopy and Raman spectroscopy as combined methods for studying zoning in minerals: The case of spinels from Archean komatiites

Several types of both magmatic and metamorphic spinels have been found in Archean komatiites of the Sovdozero and Kostomuksha greenstone belts in the eastern part of the Fennoscandian Shield. Scanning electron microscopy and Raman spectroscopy revealed relics of cores of primary magmatic chrome-spinels with high Cr and Al contents. In the Sovdozero structure, the relics are better retained than those in the Kostomuksha structure, which is caused by a different degree of metamorphic transformation. The comparable 100 · Cr/(Al + Cr) values of spinel cores from Sovdozero and Kostomuksha reflect similar conditions of partitional melting in the mantle. These data agree with the fact that both komatiite complexes belong to the Al-undepleted petrogenic type. Wide variations in the Cr and Al contents in primary chrome-spinel cores together with a constant Mg/(Fe²⁺ + Mg) ratio correspond to low oxygen fugacity during magma crystallization. In general, the composition of these primary chrome-spinels is similar to that of accessory phases in peridotites from suprasubduction zones and agrees with hypothesis of komatiite complex formation in back-arc basins.     

Geochemical features of the utilization of buried wastes of the Tyrnyauz Tungsten–Molybdenum Plant using acid leaching

The decontamination of buried wastes of the Tyrnyauz Tungsten–Molybdenum Plant is complicated by the geochemical features of the waste composition: low sulfide and high carbonate content, polyelemental composition, and considerable amounts of technogenic admixtures (kerosene, oils, soda, and soluble glasses). These circumstances result in sufficient complication of the suggested technology of waste treatment, including the sulfuric-acid leaching and separate sorption recovery of hazardous and useful elements from the working solution.     

The second version of the OCARS catalog of optical characteristics of astrometric radio sources

A new version of the Optical Characteristics of Astrometric Radio Sources (OCARS) catalog is presented. The catalog includes a list of radio sources observed in astrometric and geodetic VLBI programs since 1979, their redshifts, photometric data in 13 bands in the visible and near infrared, and a table indicating identifications btween the OCARS objects and objects in other catalogs. The main sources of information for the OCARS catalog are the NED and SIMBAD databases, as well as a variety of publications. Targeted observing programs designed to supplement the optical data for the astrometric radio sources have also been organized. The catalog currently contains 9956 sources, of which 5449 have redshifts and 7473 have photometric data. The catalog is updated, on average, once every several weeks, and is continuously augmented with new sources and new optical data.     

Design and simulation of a vertical broadband seismometer

In this paper, a new vertical broadband seismometer is designed, simulated, and evaluated. The proposed seismometer has a bandwidth from 40 s to 50 Hz and sensitivity to ground velocity of 1500 V’/m/s. The mechanical suspension used in the proposed design is a mass-leaf spring rotational pendulum. The displacement of the seismic mass is sensed by a laser interferometer and then forwarded to an electronic force feedback system which feeds a linear actuator to keep the mass almost fixed in its position. The current needed to fix the mass in its position is an indication of the ground acceleration. The performance of the simulated seismometer is evaluated by applying a data record of two actual earthquakes to the simulated model and comparing its response to the earthquakes with that of a real seismometer (Trillium-40) having the same bandwidth and sensitivity. The proposed seismometer has performed within 0.4 % residual variance for the local event and 0.03 % residual variance for the regional one compared to Trillium-40.     

The oldest (~ 1.9 Ga) metadolerites of the southern Siberian craton: age,petrogenesis, and tectonic setting

Geological, geochronological, and isotope-geochemical studies of the metadolerites of the Angaul complex, widespread in the Urik-Iya graben of the southern Siberian craton, were carried out. The metadolerites forming separate conformal bodies (sills) among the metasandstones of the Ingash Formation were studied in detail. U-Pb zircon (SHRIMP) dating of metadolerites yielded an age of 1913 ± 24 Ma, and U-Pb baddeleyite (ID-TIMS) dating of these rocks yielded an age of 1914.0 ± 1.7 Ma. Thus, the date of 1914 ± 2 Ma can be taken as the most precise age estimate for the studied rocks. The metadolerites of the Angaul complex correspond in chemical composition to the normal-alkaline tholeiitic basalts. Metadolerites are differentiated rocks with mg# of 36 to 58. They show fractionated REE patterns: (La/Yb)_n = 1.2-3.5. All metadolerites, independently of their mg# value, have low contents of Nb (1.6-10.2 ppm) and show well-pronounced negative Nb-Ta anomalies in multielement patterns (Nb/Nb* = 0.19-0.54). The metadolerites are characterized by positive ε_Nd(T) values ranging from 0.4 to 5.2, which correlate well with their SiO₂ content and mg# value. The isotope-geochemical parameters of the metadolerites of the Angaul complex indicate that fractional crystallization, along with the assimilation of the host rocks (AFC), might have been the main process during the formation of the most differentiated metadolerites. The geochemical characteristics of metadolerites with the maximum mg# values of 57-58 and ε_Nd(T) = 5.2 suggest that the parental mantle source of the metadolerites resulted from mixing of predominant depleted mantle material with the subcontinental-lithosphere material. Intrusion of the dolerites of the Angaul complex, as well as the deposition of the sedimentary strata of the Ingash Group, took place at the Paleoproterozoic stage of intracontinental extension caused by the collapse of the orogen resulted from the collision of the Biryusa block with the Tunguska superterrane in the southern Siberian craton.     

Rainfall thresholds for the triggering of landslides considering previous soil moisture conditions (Asturias,NW Spain)

Given its geological and climatic conditions and its rugged orography, Asturias is one of the most landslide prone areas in the North of Spain. Most of the landslides occur during intense rainfall episodes. Thus, precipitation is considered the main triggering factor in the study area, reaching average annual values of 960 mm. Two main precipitation patterns are frequent: (i) long-lasting periods of moderate rainfall during autumn and winter and (ii) heavy short rainfall episodes during spring and early summer. In the present work, soil moisture conditions in the locations of 84 landslides are analysed during two rainfall episodes, which represent the most common precipitation patterns: October–November 2008 and June 2010. Empirical data allowed the definition of available water capacity percentages of 99–100% as critical soil moisture conditions for the landslide triggering. Intensity-duration rainfall thresholds were calculated for each episode, considering the periods with sustained high soil moisture levels before the occurrence of each analysed landslide event. For this purpose, data from daily water balance models and weather stations were used. An inverse relationship between the duration of the precipitation and its intensity, consistent with published intensity-duration thresholds, was observed, showing relevant seasonal differences.