The Ereendavaa Range (north-eastern Mongolia): an additional argument for Mesozoic extension throughout eastern Asia

Mesozoic rift basins locally bounding metamorphic core complexes have been recognized in Transbaikalia and northern China. Numerous basement outcrops located between these two regions, in eastern Mongolia, are considered as pre-Palaeozoic in age. One of these, the Ereendavaa Range, appears as a gneissic core marked by amphibolite-facies metamorphic conditions. The range is overlain to the NW by the unmetamorphosed Mesozoic Onon Basin. Below the basin, the upper part of the range consists of a gently NW-dipping shear zone associated with top-to-the-NW motion. The structural pattern is consistent with syn-extensional exhumation of the range. Preliminary geochronological data indicate that the shear zone is late Jurassic to early Cretaceous in age, coeval with the Onon Basin. These new data from eastern Mongolia constitute a link between Transbaikalia and northern China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region.     

Electrical Resistivity Imaging technique to delineate coal seam barrier thickness and demarcate water filled voids

Exploration and exploitation of coal seams is one of the major resources for the energy sector in any country but at the same time water filled voids/water logged areas in the old workings of these seams are very critical problems for the coal mining industry. In such situations, disasters like inundation, landslides, collapsing of the old seams may occur. In this regard, it is necessary to find out the water saturated/water filled voids and zones in the mining areas. Since no established technique is available to find such zones, an experimental study using Electrical Resistivity Imaging (ERI) has been carried out in one of the coal mining areas near Dhanbad, to find out the feasibility of finding the barrier thickness and the water logged area in underground coal mines. The area under study forms part of Jharia coalfield in Dhanbad district, Jharkhand state. The coal bearing rocks of Barakar Formation of Lower Permian age (Gondwana period) occur in the area under a thin cover (10 m to15 m) of soil and or alluvium. Coal bearing Barakar Formations consist mainly of sandstone of varying grain size, intercalation of shale and sandstone, grey and carbonaceous-shale and coal seams. Since the water saturation reduces the resistivity of a formation to a large extent, water filled voids and old coal workings are expected to have significant resistivity contrast with the surrounding host rock. Hence, ERI technique was applied in such an environment as this technique uses high-density data acquisition both laterally and vertically by using multiple number of electrodes. Along with ERI, mise-à-la-masse (also called charged body) technique was also employed at one of the promising sites to find out the connectivity of water logged areas and also detection of these old workings from the surface measurements was analyzed. The interpreted 2D resistivity sections have clearly indicated the water bearing zone(s) along the profile which was well confirmed with the existing water level in the nearby borewells. On the other hand, this technique did not identify the size of the coal pillar and gallery (air filled voids), which might be due to the small size of the voids (i.e. about 2 m × 2 m) below a depth of 15m and more but have indicated altogether as a high resistive zone ranging from 600–1000 Ohm-m.     

Field evidences of secondary surface ruptures occurred during the 20 February 1956 Eskişehir earthquake in the NW Anatolia

Surface rupture and source fault of the 20 February 1956 Eskişehir earthquake have been a matter of debate that potentially contributes towards the understanding of the active deformation and seismic risk in the highly populated NW Anatolia. Field observations on the two fault segments (namely Kavacık and Uludere faults) in the north of the Eskişehir graben revealed evidences of co-seismic surface rupture and mass movements during the Eskişehir earthquake. Surface rupture was observed as a 2.5m wide, a 100m long and ca. 20 cm deep asymmetric depression in the Gümüşlü valley, 2 km east of the Uludere village. A trench dug on this depression confirms a prominent high-angle south dipping fault (dominantly left lateral strike slip) and two faint north-dipping antithetics as clear noticeable shear zones in organic-rich thick soil. Mass failures are particularly observed in spring depressions filled with loose torrent and carbonaceous material in front of the fault scarp. Some rock slides of several tens of meters in size that obviously require significantly high ground shaking were also developed on steep fault scarps. The orientation of the principal stress tensor as deduced from the surface rupture of the Eskişehir earthquake displays clear inconsistency with the geometry of prominent faults in the area. We concluded that this disagreement may be explained by a curved surface rupture. The western and eastern tips of this rupture are EW trending and the probable NW-running part in the middle would correspond to the bounding zone between two right-stepping faults.     

Examining potential genetic links between Jurassic porphyry Cu–Au ± Mo and epithermal Au ± Ag mineralization in the Toodoggone district of North-Central British Columbia,Canada

The Toodoggone district comprises Upper Triassic to Lower Jurassic Hazelton Group Toodoggone Formation volcanic and sedimentary rocks, which unconformably overlie submarine island-arc volcanic and sedimentary rocks of the Lower Permian Asitka Group and Middle Triassic Takla Group, some of which are intruded by Upper Triassic to Lower Jurassic plutons and dikes of the Black Lake suite. Although plutonism occurred episodically from ca. 218 to 191 Ma, the largest porphyry Cu–Au ± Mo systems formed from ca. 202 to 197 Ma, with minor mineralization occurring from ca. 197 to 194 Ma. Porphyry-style mineralization is hosted by small-volume (<1 km³), single-phase, porphyritic igneous stocks or dikes that have high-K calc-alkaline compositions and are comparable with volcanic-arc granites. The Fin porphyry Cu–Au–Mo deposit is anomalous in that it is 16 m.y. older than any other porphyry Cu–Au ± Mo occurrence in the district and has lower REEs. All porphyry systems are spatially restricted to exposed Asitka and Takla Group basement rocks, and rarely, the lowest member of the Hazelton Group (i.e., the ca. 201 Ma Duncan Member). The basement rocks to intrusions are best exposed in the southern half of the district, where high rates of erosion and uplift have resulted in their preferential exposure. In contrast, low- and high-sulfidation epithermal systems are more numerous in the northern half of the district, where the overlying Hazelton Group rocks dominate exposures. Cogenetic porphyry systems might also exist in the northern areas; however, if they are present, they are likely to be buried deeply beneath Hazelton Group rocks. High-sulfidation epithermal systems formed at ca. 201 to 182 Ma, whereas low-sulfidation systems were active at ca. 192 to 162 Ma. Amongst the studied epithermal systems, the Baker low-sulfidation epithermal deposit displays the strongest demonstrable genetic link with magmatic fluids; fluid inclusion studies demonstrate that its ore fluids were hot (>468°C), saline, and deposited metals at deep crustal depths (>2 km). Sulfur, C, O, and Pb isotope data confirm the involvement of a magmatic fluid, but also suggest that the ore fluid interacted with Asitka and Takla Group country rocks prior to metal deposition. In contrast, in the Shasta, Lawyers, and Griz-Sickle low-sulfidation epithermal systems, there is no clear association with magmatic fluids. Instead, their fluid inclusion data indicate the involvement of low-temperature (175 to 335°C), low-salinity (1 to 11 equiv. wt.% NaCl) fluids that deposited metals at shallow depths (<850 m). Their isotope (i.e., O, H, Pb) data suggest interaction between meteoric and/or metamorphic ore fluids with basement country rocks.     

Radiation-induced defects in quartz. III. Single-crystal EPR,ENDOR and ESEEM study of a peroxy radical

The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiated natural quartz permit quantitative analysis of a ²⁹Si hyperfine structure (A ~12.6 MHz) and an ²⁷Al hyperfine structure (A ≤ 0.8 MHz) for a previously reported hole-like center. The ²⁹Si hyperfine structure arises from interaction with two equivalent Si atoms and is characterized by the direction of the unique A axis close to a Si–O bond direction. The ²⁷Al hyperfine structure, confirmed by pulsed electron nuclear double resonance and electron spin echo envelope modulation spectra, is characterized by the unique A axis approximately along a twofold symmetry axis. These ²⁹Si and ²⁷Al hyperfine data, together with published theoretical results on peroxy radicals in SiO₂ as well as our own density functional theory (DFT) calculations on model peroxy centers, suggest this hole-like center to have the unpaired spin on a pair of oxygen atoms linked to two symmetrically equivalent Si atoms and a substitutional Al³⁺ ion across the c-axis channel, a first peroxy radical in quartz. The nuclear quadrupole matrix P also suggests that the Al³⁺ ion corresponds closely to the diamagnetic precursor to the [AlO₄]⁰ center. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The influence of topography and land use on water quality of Xiangxi River in Three Gorges Reservoir region

A self-organizing map (SOM) was used to cluster the water quality data of Xiangxi River in the Three Gorges Reservoir region. The results showed that 81 sampling sites could be divided into several groups representing different land use types. The forest dominated region had low concentrations of most nutrient variables except COD, whereas the agricultural region had high concentrations of NO₃N, TN, Alkalinity, and Hardness. The sites downstream of an urban area were high in NH₃N, NO₂N, PO₄P and TP. Redundancy analysis was used to identify the individual effects of topography and land use on river water quality. The results revealed that the watershed factors accounted for 61.7% variations of water quality in the Xiangxi River. Specifically, topographical characteristics explained 26.0% variations of water quality, land use explained 10.2%, and topography and land use together explained 25.5%. More than 50% of the variation in most water quality variables was explained by watershed characteristics. However, water quality variables which are strongly influenced by urban and industrial point source pollution (NH₃N, NO₂N, PO₄P and TP) were not as well correlated with watershed characteristics.     

Application of Fractal Models to Distinguish between Different Mineral Phases

Fractal modeling is demonstrated to be an effective and rapid tool to distinguish between mineral phases in rock samples. It supplements work that previously could be performed only by observing the interpenetrational or metasomatic phenomena between different minerals with the aid of mineralographic microscope. The Gejiu tin district in southwestern China was chosen as a study area for the recognition and characterization of the spatial distribution of two phases (Types I and II) of cassiterite. Vector patterns used for this study were extracted from digital photomicrographs and analyzed with the aid of MapGIS. Perimeter–area fractal dimension, cumulative number–area exponent, and shape index were determined in order to quantify geometrical irregularities and spatial cassiterite phase distribution characteristics. The results show that fractal dimensions based on area and perimeter are larger for crystals of Type I than for those of Type II. The mean shape index (SI) increases from 0.54 (Type I) to 0.64 (Type II), indicating an increase in regularity. The number–area exponent also increases from 0.88 to 1.15, indicating the smaller crystals of Type II. The cumulative number–shape index log–log plot shows two separate straight-line segments. One of these probably represents a background shape realized during the original process of natural crystallization, whereas the other likely represents anomalous shapes because of weathering or other superimposed processes. Two parallel lines can be constructed on the perimeter–area log–log plots. The upper line, with a larger intercept, represents crystals with lower SI. The lower line represents crystals with higher SI, indicating that the intercept provides a measure of the irregularity of grains. By combining the perimeter–area model with cumulative number–area plot and shape index, the two phases of cassiterite can be distinguished and characterized. One phase has fewer crystals of large size, and the other has smaller crystals. This difference can be explained by assuming that under higher-temperature conditions, the large cassiterite crystals formed earlier than the smaller crystals. Consequently, the large cassiterites underwent longer, high-intensive weathering than the small crystals so that their shapes became more irregular. The younger, more abundant small cassiterites retained their original regular shapes.