Diurnal precipitation cycle in Austria

A back-trajectory clustering method was developed to identify synoptic patterns associated with heavy precipitation in Austria. Extending this work from daily precipitation sums to accumulation intervals from 12 to 48 hours, an unexpected problem was encountered related to the observation schedule of data. To modify available data to our specific needs, evening precipitation falling between 19 and 21 LT (Local Time) was studied. Hourly precipitation data for the period of 1950 to 2005 from 132 weather stations over Austria were used. It was found that the evening precipitation fraction has its maxima in the central Alps in all seasons, except in autumn when maxima shift more towards the south of the Alps. These results encouraged us to analyse the variation of diurnal precipitation for different seasons in Austria as well. A total of 119 stations with sixteen years (1990?C2005) of data were used for this purpose. Mean hourly precipitation values were calculated, which were then normalised, smoothed and were finally clustered to find regions with homogeneous diurnal cycles. The diurnal cycles of precipitation of the centres exhibit systematic patterns and seasonal cycles, reflecting intensity and timing of convective activity over these regions. The winter season is relatively dry and summer is associated with the highest precipitation. The areas inside the Alps receive higher amplitudes of precipitation in summer. Interesting features such as bimodal distributions, nocturnal maxima and early morning maxima were also observed in many regions.     

On a nonlinear hybrid method for multiscale analysis of a bearing-capacity test of a real-scale segmental tunnel ring

A nonlinear hybrid method is developed for multiscale analysis of a bearing-capacity test of a real-scale segmental tunnel ring subjected to point loads. The structural analysis consists of two parts. Part I refers to modeling of bending-induced tensile cracking of the segments, resulting from the external loading. The segments are subdivided into elements, according to the crack spacing. Each element is either intact or contains one central crack band, flanked by lateral undamaged domains. A multiscale model for tensile softening of concrete is used to describe the progressive deterioration of the crack bands. After iterative determination of their state of damage, the effective bending and extensional stiffnesses of the corresponding elements are quantified by means of Voigt-Reuss-Hill estimates. The effective stiffnesses are used for linear-elastic simulations of the segmental tunnel ring. Part II refers to the relative rotation angles at the joints, which are estimated from monitoring data, using the Bernoulli-Euler hypothesis. Since the validity of this hypothesis is questionable for neck-like joints, the relative rotation angles are post-processed such that they refer to rigid body displacements of the segments. The following conclusions are drawn: The presented approach yields good estimates of crack widths. Relative rotation angles at the joints mainly result in rigid body displacements of the segments, governing the convergences. Because realistic interface models are lacking, hybrid analysis based on displacement-monitoring data allows for performing ultimate-load analysis of segmental tunnel rings.     

Geochemical exploration for gold in the Nile Valley Block (A) area,Wadi Allaqi,South Egypt

The present work aims to estimate Au-anomalous distribution patterns, the optimum grain size fraction and pathfinder elements for gold placer. The obtained data of analyzed elements (Au, Ag, As, Ba, Cd, Co, Cr, Cu, Fe, Ga, Hg, Li, Mn. Mo, Ni, Pb, Rb, Sb, Se, Sr, Te, Ti, V, Y and Zn) in both the fine (?0.25 mm) and coarse (?1 mm+0.25 mm) grain size fractions of 32 dry stream sediment samples, which have been derived from metamorphosed Island Arc volcanic rocks of Late Proterozoic age, revealed that most of the analyzed elements in both grain size fractions are asymmetrically distributed and did not pass the tests of normality. The coarse grain size fraction appears to be the better size fraction for Au detection and can be considered as the optimum grain size fraction for future application in regional stream sediment surveys. The presence of Au anomalies in the upper part of the stream and beside the mine is either sourced by the main Au-mineralization or new potential extension of the mineralization in the study area. Silver, Cd, Se, Zn and Te can be considered as useful pathfinder elements for Au in the coarse grain size fraction, and they may be used for future geochemical exploration for Au in the area. Recommendation of the authors is pointing to perform lithogeochemical survey in the eastern and western parts of the mine.     

Studies of density and magnetic properties of rocks from Northern Sweden

Summary Over the shield region of Northern Sweden, the Geological Survey runs a low altitude (30 m) aeromagnetic survey and regional gravity surveys cover almost the same areas. The production of detailed geological maps would be almost impossible without these geophysical measurements. To enhance their interpretation, a study of the appropriate petrophysical properties was started by measurements of density, susceptibility and remanence on all rock specimens collected by field geologists. Up to now more than 30,000 specimens have been measured and almost as many in situ susceptibility determinations have been made. About 10% of the samples are oriented. The information obtained is useful not only for the direct interpretation of geophysical surveys but also reflects the effects of various geological processes acting during and after the formation of the rocks considered.In precambrian rocks, density is obviously closely correlated to mineral composition and thus to chemical composition. This is demonstrated for igneous rocks by the correlation trends between density and SiO₂-content and the CM/AF-index.Susceptibility mainly reflects the magnetite content of rocks. As magnetite is an accessory mineral it is seldom considered by geologists. However, a closer study of the magnetic susceptibility of rocks reveals that its extreme complexity reflects the effects of primary and secondary geological processes. The susceptibility spectrum of a certain rock may prove to be a useful classification tool — at least regarding intermediate and basic igneous rocks.The combination of the physical parameters density and susceptibility in 2-dimensional frequency distributions seems to be a promising approach to the understanding of certain petrological processes and makes possible the delineation of local or regional secondary processes. Magmatic differentiation and serpentinization can be demonstrated in this manner.Remanent magnetization plays a secondary role in the majority of precambrian rocks. Still there are places where the natural remanence dominates and shows pronounced directions deviating from today's magnetic field. So far we have only one case where a follow up by demagnetization has been attempted, but intensified paleomagnetic research should most certainly add to our understanding of precambrian geology.Combination of susceptibility and remanance shows some characteristic correlations for highly remanent rocks, reflecting mainly exosolution phenomena among magnetic opaques and grain size distributions. Even these features might be used as diagnostic or classifying tools. They also explain some of the diversity of susceptibility spectra.     

The Precision of Classical Rock Analysis

Three rock reference samples. W-2, DNC-1, and BIR-1, were analysed five times over several months by classical chemical methods using a Youden Square as the experimental design. A significant variation for the data classified by months was found for SiO₂, CaO, H₂O^-, and TiO₂ among the 15 constituents determined. Nevertheless, most standard deviations for the five data for each oxide in any sample, as well as the error standard deviations from the analyses of variance, are less than or approximately equal to the allowable difference between duplicate determinations traditionally used as limits of error. We also determined nine constituents in three portions each of two samples, W-2 and DNC-1, the six portions being analysed concurrently. F ratios for 16 comparisons of the variances of the five data for an oxide obtained over several months and of the three data determined as a group were significant for only one oxide, total iron as Fe₂O₃ in W-2. We conclude that, if a chemist analyses rock samples carefully, the variation of the determinations will be the same for portions analysed as a group, or analysed over a time interval.     

Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska

The Canyon Creek vertebrate-fossil locality is an extensive road cut near Fairbanks that exposes sediments that range in age from early Wisconsin to late Holocene. Tanana River gravel at the base of the section evidently formed during the Delta Glaciation of the north-central Alaska Range. Younger layers and lenses of fluvial sand are interbedded with arkosic gravel from Canyon Creek that contains tephra as well as fossil bones of an interstadial fauna about 40,000 years old. Solifluction deposits containing ventifacts, wedge casts, and rodent burrows formed during a subsequent period of periglacial activity that took place during the maximum phase of Donnelly Glaciation about 25,000–17,000 years ago. Overlying sheets of eolian sand are separated by a 9500-year-old paleosol that may correlate with a phase of early Holocene spruce expansion through central Alaska. The Pleistocene fauna from Canyon Creek consists of rodents (indicated by burrows), Mammuthus primigenius (woolly mammoth), Equus lambei (Yukon wild ass), Camelops hesternus (western camel), Bison sp. cf. B. crassicornis (large-horned bison), Ovis sp. cf.O. dalli (mountain sheep), Canis sp. cf. C. lupus (wolf), Lepus sp. cf. L. othus or L. arcticus (tundra hare), and Rangifer sp. (caribou). This assemblage suggests an open landscape in which trees and tall shrubs were either absent or confined to sheltered and moist sites. Camelops evidently was present in eastern Beringia during the middle Wisconsin interstadial interval but may have disappeared during the following glacial episode. The stratigraphic section at Canyon Creek appears to demonstrate that the Delta Glaciation of the north-central Alaska Range is at least in part of early Wisconsin age and was separated from the succeeding Donnelly Glaciation by an interstadial rather than interglacial episode.     

Two-feldspar geothermometry: a review and revision for slowly cooled rocks

Recent improvements in the experimental and thermodynamic basis of two-feldspar geothermometry allow one to recover temperatures of coexistence more reliably. Some problems, however, persist: (1) the experimental solvi by Seck (1971a) and Elkins and Grove (1990) differ from each other; (2) it is not known to what extent Na–K–Ca exchange equilibrium is approached; (3) both solvi are probably metastable with regard to Al, Si order; (4) it is difficult to judge how closely high-temperature natural feldspars compare to this situation; (5) the thermodynamic treatment neglects phase transformations; (6) the temperature dependence of the Margules parameters used to model non-ideal mixing behaviour may not be linear; (7) it is not clear which expressions should be used to describe ideal activities. With these caveats in mind we treat the problem of retrograde resetting in high-grade metamorphic rocks that were slowly cooled under essentially dry conditions. Coexisting feldspars from such rocks commonly do not plot on a common isotherm. Thus temperatures derived from such pairs using any of the proposed two-feldspar geothermometers will necessarily be in error. We suggest that the non-equilibrium compositions result from retrograde intercrystalline K–Na exchange. This exchange continues after the plagioclase and alkali feldspar have already become essentially closed systems with respect to Al–Si exchange, which is a prerequisite for (Na,K)–Ca exchange. We use a modified version of the Fuhrman and Lindsley (1988) programme to reverse the K–Na exchange and derive concordant temperatures.     

Slow cooling versus episodic fluid injections: Deciphering the Caledonian orogeny in Vestvågøy,Lofoten islands,Norway

The determination of the thermal (temperature–time) histories of high‐P metamorphic terranes has been commonly based on the concepts of slow cooling and closure temperatures. In this paper, we find that this approach cannot reconcile a geochronological data set obtained from the amphibolite‐facies allochthonous Leknes Group of the Lofoten islands, Norway, which reveals an extremely complex thermal history. Using detailed results from several different geochronometers such as ⁴⁰Ar/³⁹Ar, Rb–Sr and U–Pb, we show that a model invoking multiple, short‐lived thermal pulses related to hot‐fluid infiltration channelized by shear zones can reconcile this complicated data set. This model suggests that hot fluids infiltrated throughout basement shear zones and affected the overlying cold allochthon, partially resetting U/Pb rutile and titanite ages, crystallizing new zircon and produced identical ⁴⁰Ar/³⁹Ar and Rb/Sr ages in muscovite, biotite and amphibole in various rocks throughout the region. This paper shows the enormous potential of coupling laser Ar‐spot data with thermal modelling to identify and constrain the duration of short‐lived events. An optimal P–T–t history has been derived by modelling the age data from a previously dated large muscovite crystal (Hames & Andresen, 1996, Geology, 24 :1005) and using Zr‐in‐rutile thermometry which is consistent with all geochronological data and geological constraints from the basement zones and allochthon cover. This tectonothermal model history suggests that there have been three episodic hot‐fluid and ⁴⁰Ar‐free infiltration events, resulting in the total resetting of Ar ages during the Scandian (425 Ma) for 1 Ma at 650°C and two reheating events at 415 Ma for 400 ka at 650°C and at 365 Ma for 50 ka at 600°C, which are modelled as thermal spikes above an ambient temperature of 300°C. Independent confirmation of these parameters was provided by Pb‐diffusion modelling in rutile and titanite. The model suggests that the amphibolite facies rocks of the Leknes Group probably remained cold before being exhumed for at least 60 Ma (425–365 Ma) and successfully explains the presence of different minerals that crystallized or were totally/partially reset in the allochthon and in the basement. The migration of hot fluids for short periods of times within conduits extending through the basement and allochthon rock units is likely associated with episodic seismic activity during the Caledonian orogeny.