Geomorphological processes and landforms in the southern part of the Polická vrchovina Highland (Czech Republic)

The paper examines relations among geomorphological processes and the landforms of the Polická vrchovina Highland in the Bohemian Massif. Geologically, the Polická vrchovina Highland is a part of the Intra-Sudetic Basin on the boundary between Bohemia and Poland. The basin structure of the Highland developed during the neotectonic period. In the outer parts of the Highland, Mesozoic rocks dip gently to the centre of the basin to form cuestas. In the central part, layers are horizontal or subhorizontal. Mesas (Hejda and Osta Mesa) provide evidence of the erosion of the Mesozoic deposits. The relative uplift of the Highland resulted in the incision of the Metuje River and its tributaries. Unloading of rocks and erosion initiated typical geomorphological processes such as deep- seated creep, cambering, rockfalls, landslides and pseudokarst processes. These processes produced some typical forms controlled by rock properties, jointing, relative differences in height and climatic changes in the Tertiary and Quaternary.     

Carbonate alteration of the Upper Mount McRae Shale beneath the martite-microplaty hematite ore deposit at Mount Whaleback, Western Australia

The formation of large martite-microplaty hematite ore deposits in northwest Australia remains a contentious topic in part because important evidence supporting a unifying genetic model has not been observed at all deposits. Carbonate replacement of silica has been found along normal faults below ore at the Mount Tom Price and Giles Mini deposits, which suggests an early hypogene process during ore formation. However, such rocks have not been identified at the largest martite-microplaty hematite deposit, Mount Whaleback. In this study, samples of the Mount McRae Shale are examined for their chemistry, mineralogy and petrography. These samples were collected from several key locations, including an area that immediately underlies ore along the Mount Whaleback fault at Mount Whaleback. Compared to unaltered black Mount McRae Shale from Wittenoom Gorge in the north and altered black and red Mount McRae Shale at Mount Whaleback, reddish-green Mount McRae Shale along the Mount Whaleback fault is greatly enriched in MgO and CaO and depleted in SiO₂. This chemistry arises from significant amounts of fine- to medium-grained ferroan-dolomite and ankerite and cross-cutting chlorite and carbonate veins. The composition is distinct from that produced during regional metamorphism, and most likely represents hydrothermal alteration after metamorphism. The lack of carbonate-rich, silica-poor rocks in the overlying Dales Gorge Member at Mount Whaleback is consistent with pervasive oxidation of most rocks in the region during or after ore genesis, a process that removed carbonates. Although several questions remain unanswered, these results support models that invoke an early hypogene stage during the formation of the martite-microplaty hematite deposits in the Hamersley Province.Editorial Handling: B. Lehmann     

Storm Surges from Extra-Tropical Cyclones

The possible influence of climate change on the tracks of the extra-tropical cyclones as well as storm surges is studied. Two differentdata bases have been used: one for the Great Lakes of North America and the otherfor the German Bight in the North Sea of Europe. For the Great Lakes region,significant east-west and north-south shifts in the tracks of ETC'S with decadal periodicities have been observed. However, there was no trend in the amplitudes of storm surges. The most important result for the Great Lakes is that, depending upon its position relative to the constantly shifting storm tracks, a given location could eitherexperience a major storm surge or could miss out completely.The storm surges in the German Bight in general, and at Cuxhaven in particular, appear to show a slightly increasing trend in the latterpart of the 20th century. However, the most significant result for the German Bightis that the number of storm tides (i.e., multiple peaks in a given storm surge event)definitely has shown an increase in the second half of the 20th century. This increase isinterpreted as due to the influence of meso-scale weather systems embedded in the synoptic scale ETCs.     

On the occurrence of critical levels in solar magnetohydrodynamics

It is shown that the singular behaviour exhibited by a solution of the magnetoatmospheric wave equation for motion in the presence of a horizontal magnetic field is a special case of the valve type critical level discussed by Acheson (1973), with the difference that the valve effect does not strictly occur; waves are captured as they approach the singular level from either side and are neither reflected or transmitted, but constrained to propagate along the field line. This effect is also likely to occur for purely vertical fields. The possible importance of such critical levels to solar physics is discussed.     

Dating granulite-facies structures and the exhumation of lower crust in the Moldanubian Zone of the Bohemian Massif

Deformation of granulite-facies rocks in the Moldanubian Zone of the southern Bohemian Massif is expressed in two intersecting planar fabrics - steeply disposed (S₁) and flat-laying (S₂) - which correspond to two deformation stages (D₁) and (D₂). The existing Sm-Nd garnet ages from banded granulite gneisses, new U-Pb zircon data from deformed granite intrusions within the granulite gneisses, and the P-T and field structural relations constrain the ages and P-T conditions of the two deformation phases. The early deformation (D₁) was associated with a HP-HT metamorphic stage with a minimum age of ca. 354 Ma which was followed by a near-isothermal decompression. A concordant U-Pb zircon age of 318ǃ Ma dates the emplacement of intrusions of deformed granite into the granulite gneisses and constrains deformation phase (D₂). This phase was associated with an LP-HT metamorphism dated in the region at ca. 340-330 Ma. The available structural and isotopic data indicate that granulites in the southern Bohemian Massif were exhumed from lower to middle crust during compression. The structural relations and P-T-t data for the studied granulites are consistent with their exhumation by near-vertical extrusion of the softened orogenic root.     

Sources and extractibility of chromium and nickel in soil profiles developed on Czech serpentinites

Soil profiles developed on serpentinites from several localities in the Czech Republic were investigated by a combination of geochemical and mineralogical methods (selective extractions, XRD, SEM/EDS) to determine the partitioning and mobility of chromium (Cr) and nickel (Ni). Whereas Cr is released from pyroxenes, amphiboles and Cr-spinels present in the bedrock, Ni is primarily mobilized from olivines and small Fe-Ni sulphide inclusions. The results of extraction methods indicated significant differences in the availability and mobility of Cr and Ni in soils. Chromium is almost not phytoavailable, as indicated by the DTPA extractions. The selective extractions showed that Cr is tightly bound to well-crystallised Fe-oxides and primary rock-derived phases. In contrast, Ni is substantially more mobile in soil, being mainly controlled by Mn-oxides and amorphous/less crystallised Fe-oxides. The DTPA extraction indicated that up to 10% of total Ni might be phytoavailable.