Experimental study of a biotite-bearing granitic system under water-saturated and water-undersaturated conditions

Phase relationships in haplogranitic melts containing ferromagnesian minerals were investigated in the temperature range 760–850°C, atP _total=2 kbar, =0.25 1.00, and at NNO buffer conditions. The compositions of coexisting biotite, orthopyroxene, magnetite and granitic melt were determined by electron microprobe. Biotite was the only Fe–Mg mineral in the starting material. It disappeared in water-undersaturated melts at temperatures above 830°C and in melts saturated with water above 810°C. Magnetite was present in all runs. Orthopyroxene became stable between 780 and 800°C. The Mg/(Mg+Fe) ratios of biotite (0,63–0,72) and orthopyroxene (0,63–0,71) are similar in water-saturated and undersaturated melts at comparable temperatures and increase slightly with increasing temperature. The solubility of Mg in haplogranitic melts is very low (0,07–0,24 wt% MgO). It increases slightly with temperature and is independent of the prevailing water activity. The solubility of Fe is low (0,91–1,37 wt% FeO); it also increases with increasing temperature, and it is higher in water-saturated than in water-undersaturated melts.     

Estimation of spatially distributed soil information: dealing with data shortages in the Western Bug Basin,Ukraine

Integrated watershed models require spatially differentiated soil information. However, in many regions of the world the limited availability of soil data hinders an appropriate simulation of hydro-ecological processes. Such circumstances lead to unsupported statements, poor statistics, misrepresentations, and, ultimately, to bad resource management. The Western Bug catchment in west Ukraine is an example of such a region. In the former Soviet Union, soil classification primarily focused on soils of agricultural importance, whereas, forested, urban, industrial, and shallow soil territories were left underrepresented in the classification and soil maps. Spatially differentiated soil texture data are required to predict soil hydraulic properties using pedotransfer functions (PTFs), along with soil maps. Furthermore, the Ukrainian soil texture scheme does not match the particle size classes commonly used with PTFs. To overcome these shortcomings, a fuzzy logic methodology was applied, based on terrain and vegetation/land use analysis and soil sampling, to close the information gaps. For the application of PTFs, a procedure was tested to estimate missing values of soil texture distribution. Applied methods were evaluated using recent soil surveys, measured soil texture, and water retention properties, while having in consideration the limitations brought by scarce soil data for integrated watershed modelling purposes.     

WIP: A Web‐based program for indexing planar features in quartz grains and its usage

Planar deformation features (PDFs) in quartz are the most important diagnostic features that allow the unambiguous identification of impact structures on Earth. In order to confirm that these features (that are characterized by planar character and form along specific crystallographic planes) are indeed PDFs, they need to be properly investigated and indexed. Following universal‐stage measurements, the process of indexing is usually performed manually, using a Wulff stereonet and following a strict procedure, which is time consuming and error prone. In this article, we present WIP, a new Web‐based program for indexing planar deformation features in quartz. The correctness of our program is shown by its application to measurements that had previously been indexed manually. The observed minor differences, especially in the absolute frequency percentage of PDFs, are negligible and not significant enough to influence the estimation of shock pressure that could be calculated from the indexed results. Usability of this program is shown using the spatial relationships between a statistically significant number of 278 quartz grains with 409 sets of PDFs analyzed within the area (~35 mm²) of a single thin section of a meta‐greywacke from the Bosumtwi impact structure. Our program is not only more accurate and faster than the manual (graphical) method but also removes the human error from the plotting process and allows control of several parameters, such as the value of estimated measurement error used in the indexing calculation or method of aggregated error handling. The program also provides information about the angles between the planes of the measured PDF sets present in a grain, which allows determination of the angles between (for example) indexed {} and {} sets.     

The drainage pattern of Hansbreen and Werenskioldbreen, two polythermal glaciers in Svalbard

To improve our understanding of Svalbard-type polythermal glacier drainage, hydraulic geometry models of the subglacial hydrology of two contrasting glaciers in Svalbard have been constructed. The models are tested against a uniquely long and rich set of field observations spanning 45 years. Digital elevation models (DEMs) were constructed from bedrock data measured with ground penetrating radar and surface data of two medium-sized polythermal glaciers, Hansbreen and Werenskioldbreen, in south-west Spitsbergen. Hansbreen has a low angle bed with over-deepenings and a calving front, while Werenskioldbreen has steeper bed and terminates on land. Together they are representative of many Svalbard glaciers. The DEMs were used to derive maps of hydraulic potential and subglacial drainage networks. Validation of the models was done using field observations including location mapping and speleological exploration of active moulins, positions of main river outflows, dyetracing and water chemistry studies, and observations of water pressure inside moulins. Results suggest that the water pressure is generally close to ice overburden pressure but varies greatly depending on local conditions such as bed location, the thickness of cold ice layer, the thickness of the glacier and seasonal changes in meltwater input.     

Crustal thickness, discontinuity depth, and upper mantle structure beneath southern Africa: constraints from body wave conversions

The technique of receiver function analysis is applied to the study of crustal and upper mantle structures beneath the Kaapvaal craton in southern Africa and its surroundings. Seismic data were recorded by the seismic array of 82 sites deployed from April 1997 to April 1999 across southern Africa, as well as a dense array of 32 sites near Kimberley, in operation from December 1998 to June 1999. Arrival times for phases converted at the Moho are used to determine crustal thickness. The Moho depth in the south–western section of the craton was found to vary between 37 and 40 km, except for one station that recorded a depth of 43 km (SA23). Farther north along the western block of the craton (into Botswana) the depth increases up to 43 km. The depth increases even further in the north–eastern section of the craton, where results vary from 40 to 52 km. Just north of the Kaapvaal craton, in the neighbouring Zimbabwe craton, the crustal thickness drops significantly. The results obtained there varied from 36 to 40 km. For the Kimberley area, using the dense array, the Moho depth was found to be 37.3 km. Arrivals of the Ps and Ppps phases were used to determine the Poisson’s ratio in the region. This was found to be 0.26±0.01. Arrivals of phases from the 410 and 660 km mantle discontinuities are used to interpret the relative positions of these discontinuities, as well as for comparison of mantle temperatures and seismic velocities in the region with global averages. In the Kimberley area the 410 and 660 km discontinuities were found at their expected depth, implying that mantle temperatures in the region are close to the global average. The seismic velocities above the ‘410’ were found up to 5% faster than the averages from the global iasp91 model, which is fast even by Precambrian standards. In other sections of the Kaapvaal craton, the velocities are also faster than global averages, but not as fast as beneath Kimberley. In these sections, the ‘410’ is also slightly elevated, while the ‘660’ is depressed, which implies a slightly lower mantle temperature relative to the global average. Beneath the Kaapvaal craton we find evidence suggesting the presence of a zone with a reduced wavespeed gradient at an upper bound of approximately 300 km, which may mark the lower chemical boundary of the craton.     

The effects of mafic-felsic magma interaction on magma diversity: insights from an early Paleozoic hornblendite-quartz monzonite suite in the South China block

Mineralogy and Petrology - Understanding the mechanisms responsible for the interplay between mafic and felsic magmas is the key to retrieving information on their sources, and characterizing the...     

On the Use of Weighted Linear Combination Method in GIS: Common and Best Practice Approaches

The weighted linear combination (WLC) technique is a decision rule for deriving composite maps using GIS. It is one of the most often used decision models in GIS. The method, however, is frequently applied without full understanding of the assumptions underling this approach. In many case studies, the WLC model has been applied incorrectly and with dubious results because analysts (decision makers) have ignored or been unaware of the assumptions. This paper provides a critical overview of the current practice with respect to GIS/WLC and suggests the best practice approach.