Crystal chemistry and OH defect concentrations in spodumene from different granitic pegmatites

Thirty spodumene samples of distinct paragenetic types (primary magmatic, secondary after petalite and hydrothermal) from variety of granitic pegmatites were characterized by electron microprobe, polarized FTIR spectroscopy and Mössbauer spectroscopy. The FTIR spectra of OH (weak sharp pleochroic bands at 3,425, 3,410, 3,395 cm⁻¹ and in the 3,500–3,470 spectral region) are strongly polarized with maximum absorption parallel to n_γ. The majority of OH dipoles are presumably generated by a partial replacement of O2 oxygen atoms with an orientation pointing above the Li vacancy site. The separation of the bands probably resulted from a replacement of the coordinating Al by Fe and Si by Al. Homogeneous spodumene mostly close to its ideal formula LiAlSi₂O₆ shows Fe (0.00–0.10 apfu as Fe³⁺; Fe³⁺ >> Fe²⁺) and Na (0.00–0.04 apfu) as the only minor cations and Fe³⁺Al₋₁ substitution up to 10 mol% of the LiFe³⁺Si₂O₆ component. Hydrogen concentrations (from 0.1 up to <5 ppm H₂O by weight) vary as a function of genetic type with the highest amounts in high-temperature magmatic spodumene. Differences among particular genetic types of spodumene are related to maximum solubility of OH in spodumene structure at given P–T conditions and at actual chemical composition of spodumene. OH defect concentrations in spodumene follow a trend, LT/LP pyroxenes containing lower hydrogen contents compared to HT/HP ones. The hydrogen contents in particular genetic types of spodumene and their decrease with decreasing T and P are consistent with petrologic models of the pegmatite (sub)types formations.     

The effect of acquisition error and level of detail on the accuracy of spatial analyses

There has been a great deal of research about errors in geographic information and how they affect spatial analyses. A typical GIS process introduces various types of errors at different stages, and such errors usually propagate into errors in the result of a spatial analysis. However, most studies consider only a single error type thus preventing the understanding of the interaction and relative contributions of different types of errors. We focus on the level of detail (LOD) and positional error, and perform a multiple error propagation analysis combining both types of error. We experiment with three spatial analyses (computing gross volume, envelope area, and solar irradiation of buildings) performed with procedurally generated 3D city models to decouple and demonstrate the magnitude of the two types of error, and to show how they individually and jointly propagate to the output of the employed spatial analysis. The most notable result is that in the considered spatial analyses the positional error has a much higher impact than the LOD. As a consequence, we suggest that it is pointless to acquire geoinformation of a fine LOD if the acquisition method is not accurate, and instead we advise focusing on the accuracy of the data.     

Spatial analysis of high-resolution urban thermal patterns in Vojvodina,Serbia

Main objective of this study was to establish a relationship between land cover and land surface temperature (LST) in urban and rural areas. The research was conducted using Landsat, WorldView-2 (WV-2) and Digital Mapping Camera. Normalised difference vegetation index and normalised difference built-up index were used for establishing the relation between built-up area, vegetation cover and LST for spatial resolution of 30 m. Impervious surface and vegetation area generated from Digital Mapping Camera from Intergraph and WV-2 were used to establish the relation between built-up area, vegetation cover and LST for spatial resolutions of 0.1, 0.5 and 30 m. Linear regression models were used to determine the relationship between LST and indicators. Main contribution of this research is to establish the use of combining remote sensing sensors with different spectral and spatial resolution for two typical settlements in Vojvodina. Correlation coefficients between LST and LST indicators ranged from 0.602 to 0.768.     

Neogene tectonostratigraphic history of the southern Neuquén basin (39°–40°30′S,Argentina): implications for foreland basin evolution

Although the Neuquén basin in Argentina forms a key transitional domain between the south‐central Andes and the Patagonian Andes, its Cenozoic history is poorly documented. We focus on the sedimentologic and tectonic evolution of the southern part of this basin, at 39–40°30′S, based on study of 14 sedimentary sections. We provide evidence that this basin underwent alternating erosion and deposition of reworked volcaniclastic material in continental and fluvial settings during the Neogene. In particular, basement uplift of the Sañico Massif, due to Late Miocene–Pliocene intensification of tectonic activity, led to sediment partitioning in the basin. During this interval, sedimentation was restricted to the internal domain and the Collon Cura basin evolved towards an endorheic intermontane basin. From stratigraphic interpretation, this basin remained isolated 7–11 Myr. Nevertheless, ephemeral gateways seem to have existed, because we observe a thin succession downstream of the Sañico Massif contemporaneous with the Collon Cura basin‐fill sequence. Comparisons of stratigraphic, paleoenvironmental and tectonic features of the southern Neuquén basin with other foreland basins of South America allow us to classify it as a broken foreland with the development of an intermontane basin from Late Miocene to Late Pliocene. This implies a thick‐skinned structural style for this basin, with reactivation of basement faults responsible for exhumation of the Sañico Massif. Comparison of several broken forelands of South America allows us to propose two categories of intermontane basins according to their structural setting: subsiding or uplifted basins, which has strong implications on their excavation histories.     

A Study of Spatial Distribution of Induced Seismicity in the Upper Silesian Coal Basin

The Upper Silesian Coal Basin (USCB) is a region where high seismic activity is observed. Most of these seismic events have a local magnitude not exceeding 2.3. Their location and type of focal mechanism suggest that they are connected with new discontinuities in the rock mass caused by mining activity. Shocks with higher magnitude are also observed but their frequency is much lower. The strong events have a different focal mechanism than the low energetic events. The spatial distribution of shock epicentres is not uniform in the USCB area and shows the fractal character of seismic phenomena. Despite extensive mining activity throughout the area, the epicentres of strong events are concentrated in four regions belonging to different geological units. The temporal variability of epicentre co-ordinates and the general decrease of seismic activity points to the migration of seismicity across the investigated area. Analysing the spatial and temporal distributions of the strongest shocks, one can suppose this area to be critically self-organised. These facts suggest that induced seismicity in the USCB is triggered by a nonlinear dynamic process, having regional character and connected with recent tectonic activity.     

The Siwaliks of western Nepal: I. Geometry and kinematics

The Siwalik Group which forms the southern zone of the Himalayan orogen, constitutes the deformed part of the Neogene foreland basin situated above the downflexed Indian lithosphere. It forms the outer part of the thin-skinned thrust belt of the Himalaya, a belt where the faults branch off a major décollement (MD) that is the external part of the basal detachment of Himalayan thrust belt. This décollement is located beneath 13 Ma sediments in far-western Nepal, and beneath 14.6 Ma sediments in mid-western Nepal, i.e., above the base of the Siwalik Group. Unconformities have been observed in the upper Siwalik member of western Nepal both on satellite images and in the field, and suggest that tectonics has affected the frontal part of the outer belt since more than 1.8 Ma. Several north dipping thrusts delineate tectonic boundaries in the Siwalik Group of western Nepal. The Main Dun Thrust (MDT) is formed by a succession of 4 laterally relayed thrusts, and the Main Frontal Thrust (MFT) is formed by three segments that die out laterally in propagating folds or branch and relay faults along lateral transfer zones. One of the major transfer zones is the West Dang Transfer Zone (WDTZ), which has a north-northeast strike and is formed by strike-slip faults, sigmoid folds and sigmoid reverse faults. The width of the outer belt of the Himalaya varies from 25 km west of the WDTZ to 40 km east of the WDTZ. The WDTZ is probably related to an underlying fault that induces: (a) a change of the stratigraphic thickness of the Siwalik members involved in the thin-skinned thrust belt, and particularly of the middle Siwalik member; (b) an increase, from west to east, of the depth of the décollement level; and (c) a lateral ramp that transfers displacement from one thrust to another. Large wedge-top basins (Duns) of western Nepal have developed east of the WDTZ. The superposition of two décollement levels in the lower Siwalik member is clear in a large portion of the Siwalik group of western Nepal where it induces duplexes development. The duplexes are formed either by far-travelled horses that crop out at the hangingwall of the Internal Décollement Thrust (ID) to the south of the Main Boundary Thrust, or by horses that remain hidden below the middle Siwaliks or Lesser Himalayan rocks. Most of the thrusts sheets of the outer belt of western Nepal have moved toward the S–SW and balanced cross-sections show at least 40 km shortening through the outer belt. This value probably under-estimates the shortening because erosion has removed the hangingwall cut-off of the Siwalik series. The mean shortening rate has been 17 mm/yr in the outer belt for the last 2.3 Ma.     

On possible fluid detection in equivalent transversely isotropic media

We consider a transversely isotropic medium that is long-wave equivalent to a stack of thin, parallel, isotropic layers and is obtained using the Backus average. In such media, we analyse the relations among anisotropy parameters; Thomsen parameters, ε and δ, and a new parameter ϕ. We discuss the last parameter and show its essential properties; it equals 0 in the case of isotropy of equivalent medium and/or constant Lamé coefficient λ in layers. The second property occurs to make ϕ sensitive to variations of λ in thin-bedded sequences. According to Gassmann, in isotropic media the variation of fluid content affects only the Lamé coefficient λ, not μ; thus, the sensitivity to changes of λ is an essential property in the context of possible detection of fluids. We show algebraically and numerically that ϕ is more sensitive to these variations than ε or δ. Nevertheless, each of these parameters is dependent on the changes of μ; to understand this influence, we exhibit comprehensive tables that illustrate the behaviour of anisotropy parameters with respect to specific variations of λ and μ. The changes of μ in layers can be presented by the Thomsen parameter γ that depends on them solely. Hence, knowing the values of elasticity coefficients of equivalent transversely isotropic medium, we may compute ϕ and γ, and based on the aforementioned tables, we predict the expected variation of λ; in this way, we propose a new method of possible fluid detection. Also, we show that the prior approach of possible detection of fluids, proposed by Berryman et al., may be unreliable in specific cases. To establish our results, we use the Monte Carlo method; for the range and chosen variations of Lamé coefficients λ and μ – relevant to sandstones – we generate these coefficients in thin layers and, after the averaging process, we obtain an equivalent transversely isotropic medium. We repeat that process numerous times to get many equivalent transversely isotropic media, and – for each of them  – we compute their anisotropy parameters. We illustrate ϕ, ε and δ in the form of cross-plots that are relevant to the chosen variations of λ and μ. Additionally, we present a table with the computed ranges of anisotropy parameters that correspond to different variations of Lamé coefficients.     

Correlation studies on an RC frame shaking-table specimen

This paper presents the correlation of the results of a new model for the dynamic analysis of reinforced concrete (RC) frames with the experimental time history of a two storey RC frame shaking-table specimen. The frame member model consists of separate subelements that describe the deformations due to flexure, shear and bond slip in RC structural elements. The subelements are combined by superposition of flexibility matrices to form the frame element. A non-linear solution method which accounts for the unbalance of internal forces between different subelements during a given load increment is used with the model. The ability of the proposed model to describe the dynamic response of frame structures under earthquake excitations is evaluated by comparing the analytical results with experimental evidence from a two-storey, one bay reinforced concrete frame tested on the shaking-table. The model parameters for the shaking-table specimen are derived from available experimental evidence and first principles of reinforced concrete. The effect of reinforcing bar slip on the local and global dynamic response of the test structure is assessed. © 1997 John Wiley & Sons, Ltd.     

Response of braiding channel morphodynamics to peak discharge changes in the Upper Yellow River

The braiding intensity and dynamics in large braiding rivers are well known to depend on peak discharges, but the response in braiding and channel–floodplain transformations to changes in discharge regime are poorly known. This modelling study addresses the morphodynamic effects of increasing annual peak discharges in braiding rivers. The study site is a braiding reach of the Upper Yellow River. We estimated the effects on the larger‐scale channel pattern, and on the smaller‐scale bars, channel branches and floodplains. Furthermore, we determined the sensitivity of the channel pattern to model input parameters. The results showed that the dominant effect of a higher peak discharge is the development of chute channels on the floodplains, formed by connecting head‐cut channels and avulsive channels. Widening of the main channel by bank erosion was found to be less dominant. In addition, sedimentation on the bars and floodplains increased with increasing peak discharge. The model results also showed that the modelled channel pattern is especially sensitive to parametrization of the bed slope effect, whereas the effect of median grain size was found to be relatively small. Copyright © 2018 John Wiley & Sons, Ltd.