Fracture sealing of quartzite under a temperature gradient: experimental results     

Christoph Hilgers  Eric Tenthorey 《地学学报》2004,16(4):173-178

Veined lithologies are formed by fracturing and sealing processes, with the veins representing former fluid conduits through the rock. Although detailed fieldwork and numerical simulations have provided a better understanding of vein growth, few studies have attempted to seal fractures and generate veins experimentally. In this pilot study, we subjected fractured quartzite to temperature gradients of 45–125 °C under hydrothermal conditions in a static fluid, with the aim of precipitating secondary quartz in the cooler portions of the fracture. Results show that secondary quartz precipitates due to the imposed temperature gradient, causing the initial fracture to seal locally. Although no systematic sealing pattern was observed along the fracture, samples subjected to higher temperatures exhibit a smaller fracture width and appear to have reacted more extensively. Electron microprobe mapping visualizes the spatial distribution of secondary quartz, which contains elevated concentrations of aluminium.  相似文献   

Exposure dating and reinterpretation of coarse debris accumulations (‘rock glaciers’) in the Cairngorm Mountains,Scotland     

Colin K. Ballantyne  Christoph Schnabel  Sheng Xu 《第四纪科学杂志》2009,24(1):19-31

Relict rock glaciers have considerable potential for contributing to palaeoclimatic reconstruction, but this potential is often undermined by lack of dating control and problems of interpretation. Here we reinvestigate and date four proposed ‘rock glaciers’ in the Cairngorm Mountains and show that the morphology of only one of these appears consistent with that of a true rock glacier produced by creep of underlying ice or ice‐rich sediment. All four features comprise rockslide or rock avalanche runout debris, and the possibility that all four represent unmodified runout accumulations cannot be discounted. Surface exposure dating of the four debris accumulations using cosmogenic ¹⁰Be produced uncertainty‐weighted mean ages of 15.4 ± 0.8 ka, 16.2 ± 1.0 ka, 12.1 ± 0.6 ka and 12.7 ± 0.8 ka. All four ages imply emplacement under cold stadial conditions, two prior to the Windermere Interstade of ca. 14.5–12.9 cal. ka BP and two during the Loch Lomond Stade of ca. 12.9–11.5 cal. ka BP. The above ages indicate that paraglacial rock‐slope failure on granite rockwalls occurred within a few millennia after deglaciation. The mean exposure ages obtained for runout debris at two sites – Strath Nethy (16.2 ± 1.0 ka) and Lairig Ghru (15.4 ± 0.8 ka) – are consistent with basal radiocarbon ages from Loch Etteridge, 22 km to the southwest (mean = 15.6 ± 0.3 cal. ka BP) and imply widespread deglaciation of the Cairngorms and adjacent valleys before 15 ka and possibly 16 ka. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

One hundred years of mountain hydrology in Switzerland by the WSL     

Christoph Hegg  Brian W. McArdell  Alexandre Badoux 《水文研究》2006,20(2):371-376

In 1903 the Swiss Federal Research Institute WSL started its first forest hydrology measurements with the aim to deliver a sound scientific basis for the implementation of new forest legislation introduced in Switzerland in 1876. This legislation was triggered by several large floods that occurred in Switzerland, for which a major cause was widely seen as the poor condition of forests at that time. Consequently, hydrologic research at WSL first focused on the influence of forests on floods. In the second half of the 20th century, other hydrological issues such as water quality, snow hydrology and sediment transport complemented the hydrologic research at WSL. Some recent results of this work are presented in three papers joining this introductory paper to mark the 100th anniversary of hydrologic research at WSL. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Transfer factors of contamination between the German Bight and its tributary waters derived from measured tritium and Cs-137 activity concentrations     

Christoph Wedekind  Günter Främcke 《Ocean Dynamics》1991,44(2):59-75

Summary Evaluation of the results of radioactivity monitoring in the southern North Sea between 1977 and 1987 has shown that in the water of the German Bight three areas stand out due to their different ratios between salinity and concentration of dissolved Cs-137 and tritium. While salinity steadily increases with greater distance from the coast, the Cs-137 concentration above 34 PSU (Practical Salinity Unit) increases sharply and shows how far water from the western and central North Sea, contaminated by nuclear reprocessing in Sellafield (Irish Sea), reaches into the German Bight. In the 34 to 32.5 PSU range, the influence can be seen of water contaminated by tritium originating in the rivers Rhein, Maas and Schelde, precipitation and the nuclear reprocessing plant at La Hague (Channel). Below 32.5 PSU, the influence of the influx from the rivers Elbe, Weser and Ems becomes apparent. These rivers are less contaminated with tritium.Assuming that Cs-137 and tritium, like the salinity of sea water, behave conservatively and that the decay-time of these two isotopes is long compared with the time-scale of water exchange in the southern North Sea, the concentration values measured are used to calculate the structure of the water masses in the three areas of the German Bight mentioned above using the mixing principle. Evaporation is taken into account. Results show that beyond 34 PSU, about half the sea water originates in the western central North Sea while the other half comes from the Channel. Below 34 PSU, the first mentioned share amounts only to a few per cent. Results also show that fresh water from the Rhein delta and precipitation, increasing with a decrease in salinity from 34 to 32.5 PSU, accounts for a maximum of 5% each. The fresh water influx into the German Bight via the rivers Elbe, Weser and Ems amounts to app. 11% when the PSU value reaches 29. The calculated portions are the mean values for the observation period. The number of measurements available makes it impossible to distinguish more exactly between the temporal and spatial variability of the amounts of the individual components.The quantity of each calculated portion of sea water also represents the transfer factor of concentration between the nuclide concentration in the source (e. g. the Rhein) and the concentration in the German Bight. In addition, these factors are used to calculate the transfer factors of discharge using the annual drainage rates of the sources. Thus a radioactive discharge rate of 10¹⁵ Bq per year into the Rhein would produce a mean activity concentration of 0.34 Bq/l in the German Bight (at a salinity of 33.5 PSU). To verify the calculated transfer factors, tritium concentrations in the German Bight are derived from existing environmental tritium data and the results are compared with the values actually measured.

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Transferkaktoren zwischen der Deutschen Bucht und ihren Zuflüssen abgeleitet aus der Tritium- und Cs-137-Aktivitätskonzentration in den beteiligten Gewässern

Zusammenfassung Eine zusammenhängende Auswertung der Meßergebnisse der Radioaktivitätsüberwachung in der südlichen Nordsee über den Zeitraum 1977 bis 1987 hat gezeigt, daß im Wasser der Deutschen Bucht deutlich drei durch den Salzgehalt des Meerwassers und die Konzentration der gelösten Radionuklide charakterisierte Bereiche zu unterscheiden sind.Während der Salzgehalt mit wachsender Entfernung von der Küste stetig zunimmt, steigt die Cs-137-Konzentration oberhalb 34 PSU (Practical Salinity Unit) sprunghaft an und signalisiert die Grenze, bis zu der das durch die Kernbrennstoff-Wiederaufarbeitung in Sellafield (Irische See) kontaminierte Meerwasser der westlichen und mittleren Nordsee in die Deutsche Bucht vordringt. Im Bereich 34 bis 32,5 PSU ist das von Westen zugeführte, stärker Tritium-kontaminierte Wasser aus Rhein, Maas, Schelde und atmosphärischem Niederschlag zu erkennen, an das sich unterhalb 32,5 PSU der geringer mit Tritum kontaminierte Zufluß aus Elbe, Weser und Ems anschließt.Davon ausgehend, daß sich Cs-137 und Tritium wie der Salzgehalt im Meerwasser konservativ verhalten und daß weiterhin die Halbwertzeit des radioaktiven Zerfalls dieser beiden Nuklide lang ist gegenüber den Wasseraustauschzeiten im betrachteten Meeresgebiet, wurden die in der südlichen Nordsee gemessenen sowie aus der Literatur für den Süßwasserbereich entnommenen Konzentrationswerte dazu genutzt, um rechnerisch mit Hilfe des Mischungsgesetzes den Wassermassenaufbau in den drei genannten Salinitätsbereichen in der Deutschen Bucht quantitativ zu bestimmen. Es zeigte sich, daß oberhalb von 34 PSU das Meerwasser aus etwa gleichen Teilen aus der westlichen/mittleren Nordsee und dem Kanal stammt, während unterhalb dieser Salzgehaltsgrenze nur noch mit wenigen Prozentanteilen Wasser aus der mittleren Nordsee zu finden ist. Ferner ergab sich, daß das aus dem Rheinmündungsbiet bzw, aus dem atmosphärischen Niederschlag stammende Süßwasser — mit sinkendem Salzgehalt steigend — bei 32,5 PSU einen maximalen Anteil von jeweils 5% an Meerwasser hat. Der direkte Süßwasserzufluß aus Elbe, Weser und Ems beträgt in die Deutsche Bucht bei 29 PSU ca. 11%.Die berechneten Anteile sind Mittelwerte über den gesamten Beobachtungszeitraum; die Anzahl der Messungen läßt eine genauere Unterscheidung in zeitliche und räumliche Variabilität der Zusammensetzung nicht zu.Die Größe des jeweils bestimmten Anteils am Meerwasser stellt gleichzeitig den Transferfaktor der Konzentration zwischen der Nuklidkonzentration im Ursprungsgewässer (z. B. dem Rhein) und der sich daraus einstellenden Konzentration in der Deutschen Bucht dar. Ferner wurden die Transferfaktoren der Konzentration in Verbindung mit aus der Literatur entnommenen Größen der jährlichen Abflußmengen der Ursprungsgewässer genutzt, um auch die Transferfaktoren der jährlichen Einbringung zu ermitteln. So ergibt die jährliche Einbringung von 10¹⁵ Bq eines Nuklides z. B. in den Rhein bei 33,5 PSU in der Deutschen Bucht eine mittlere Konzentration von 0,34 Bq/l.Als Anwendungsbeispiel und zur Überprüfung der Richtigkeit der Transferfaktoren wird die Auswertung des Tritiumauslasses bei La Hague auf die Deutsche Bucht berechnet und mit den gemessenen Werten verglichen.

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Fluid entrapment and reequilibration during subduction and exhumation: A case study from the high-grade Nestos shear zone, Central Rhodope, Greece     

Kurt Krenn  Christoph Bauer  Alexander Proyer  Evripidis Mposkos  Georg Hoinkes 《Lithos》2008,104(1-4):33-53

A fluid inclusion study on metamorphic minerals of successive growth stages was performed on highly deformed paragneisses from the Nestos Shear Zone at Xanthi (Central Rhodope), in which microdiamonds provide unequivocal evidence for ultrahigh-pressure (UHP) metamorphism. The correlation of fluid inclusion density isochores and fluid inclusion reequilibration textures with geothermobarometric data and the relative chronology of micro- and macro-scale deformation stages allow a better understanding of both the fluid and metamorphic evolution along the P–T–d path. Textural evidence for subduction towards the NE is recorded by the orientation of intragranular NE-oriented fluid inclusion planes and the presence of single, annular fluid inclusion decrepitation textures. These textures occur within quartz “foam” structures enclosed in an earlier generation of garnets with prolate geometries and rarely within recrystallized matrix quartz, and reequilibrated both in composition and density during later stages of exhumation. No fluid inclusions pertaining to the postulated ultrahigh-pressure stage for microdiamond-bearing garnet–kyanite–gneisses have yet been found. The prolate shape of garnets developed during the earliest stages of exhumation that is recorded structurally by (L  S) tectonites, which subsequently accommodated progressive ductile SW shearing and folding up to shallow crustal levels. The majority of matrix kyanite and a later generation of garnet were formed during SW-directed shear under plane-strain conditions. Fluid inclusions entrapped in quartz during this stage of deformation underwent density loss and transformed to almost pure CO₂ inclusions by preferential loss of H₂O. Those inclusions armoured within garnet retained their primary 3-phase H₂O–CO₂ compositions. Reequilibration of fluid inclusions in quartz aggregates is most likely the result of recrystallization along with stress-induced, preferential H₂O leakage along dislocations and planar lattice defects which results in the predominance of CO₂ inclusions with supercritical densities. Carbonic fluid inclusions from adjacent kyanite–corundum-bearing pegmatoids and, the presence of shear-plane-parallel fluid inclusion planes within late quartz boudin structures consisting of pure CO₂-fluid inclusions with negative crystal shapes, bear witness of the latest stage of deformation by NE-directed extensional shear.This study shows that the textures of early fluid inclusions that formed already during the prograde metamorphic path can be preserved and used to derive information about the kinematics of subduction that is difficult to obtain from other sources. The textures of early inclusions, together with later generations of unaltered primary and secondary inclusions in metamorphic index minerals that can be linked to specific deformation stages and even P–T conditions, are a welcome supplement for the reconstruction of a rather detailed P–T–d path.  相似文献   

Fluid and source magma evolution of the Questa porphyry Mo deposit,New Mexico,USA   总被引：14，自引：1，他引：13  

Leonhard M. Klemm  Thomas Pettke  Christoph A. Heinrich 《Mineralium Deposita》2008,43(5):533-552

Combined fluid inclusion microthermometry and microanalysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) are used to constrain the hydrothermal processes forming a typical Climax-type porphyry Mo deposit. Molybdenum mineralisation at Questa occurred in two superimposed hydrothermal stages, a magmatic-hydrothermal breccia and later stockwork veining. In both stages, texturally earliest fluids were single-phase, of low salinity (~7 wt.% NaCl_equiv.) and intermediate-density. Upon decompression to ~300 bar, they boiled off a vapour phase, leaving behind a residual brine (up to 45 wt.% NaCl_equiv) at temperatures of ~420°C. The highest average Mo concentrations in this hot brine were ~500 μg/g, exceeding the Mo content of the intermediate-density input fluid by about an order of magnitude and reflecting pre-concentration of Mo by fluid phase separation prior to MoS₂ deposition from the brine. Molybdenum concentrations in brine inclusions, then, decrease down to 5 μg/g, recording Mo precipitation in response to cooling of the saline liquid to ~360°C. Molybdenite precipitation from a dense, residual and probably sulphide-depleted brine is proposed to explain the tabular shape of the ore body and the absence of Cu-Fe sulphides in contrast to the more common Cu-Mo deposits related to porphyry stocks. Cesium and Rb concentrations in the single-phase fluids of the breccia range from 2 to 8 and from 40 to 65 μg/g, respectively. In the stockwork veins, Cs and Rb concentrations are significantly higher (45–90 and 110–230 μg/g, respectively). Because Cs and Rb are incompatible and hydrothermally non-reactive elements, the systematic increase in their concentration requires two distinct pulses of fluid exsolution from a progressively more fractionated magma. By contrast, major element and ore metal concentrations of these two fluid pulses remain essentially constant. Mass balance calculations using fluid chemical data from LA-ICPMS suggest that at least 25 km³ of melt and 7 Gt of deep input fluid were necessary to provide the amount of Mo contained in the stockwork vein stage alone. While the absolute amounts of fluid and melt are uncertain, the well-constrained element ratios in the fluids together with empirical fluid/melt partition coefficients derived from the inclusion analyses suggest a high water content of the source melt of ~10%. In line with other circumstantial evidence, these results suggest that initial fluid exsolution may have occurred at a confining pressure exceeding 5 kbar. The source of the molybdenum-mineralising fluids probably was a particularly large magma chamber that crystallised and fractionated in the lower crust or at mid-crustal level, well below the shallow intrusions immediately underlying Questa and other porphyry molybdenum deposits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Shale basins,sulfur-deficient ore brines and the formation of exhalative base metal deposits     

Fernando Tornos  Christoph A. Heinrich 《Chemical Geology》2008,247(1-2):195-207

The massive sulfide deposits of the Iberian Pyrite Belt are interbedded with felsic volcanic rocks and shale, and underlain by several thousand meters of siliciclastic sedimentary rocks known as the PQ Group. Isotope geochemistry and regional geology are both consistent with equilibration of the ore-forming fluids with the PQ Group, prior to ore deposition near the former seafloor. The average Cu:Zn:Pb ratio of the PQ Group rocks (ca. 26:55:19) is similar to the weighted average of all the massive sulfide orebodies combined (ca. 25:52:23).The genetic relationship between massive sulfide deposits and a siliciclastic sedimentary metal source is explained here by a thermodynamic model, proposing that mildly reducing redox conditions imposed by equilibration with the sedimentary rocks are most critical for the formation of an effective ore-forming fluid. Relatively metal-rich but organic-poor pyrite-bearing shale undergoing dewatering of saline pore fluids is an effective source for the generation of sulfur-deficient but relatively iron and base metal-rich brines. Thus, we propose that the giant deposits of the Iberian Pyrite Belt owe their existence not to exceptionally metal-enriched (e.g., magmatic) fluids, but to the existence of a fairly ordinary but large metal source in reactive siliciclastic sediments, combined with an underlying igneous heat source and a particularly efficient mechanism of sulfide precipitation by mixing with H₂S-rich fluids at or near the seafloor.Essentially similar mineral equilibria are imposed when saline fluids are buffered by typical continental basement rocks. Leaching of retrograde minerals and possibly residual salts from their magmatic or metamorphic prehistory is expected to generate similar, variably metal-rich but relatively sulfide-deficient fluids. Thus, the existence of mildly reducing rocks can be the dominant chemical control in the source of fluids generating many volcanogenic, Irish-type or sedex deposits, many of which are known to precipitate their metal load in response to biogenic sulfide addition at the ore deposition site.  相似文献   

Geographic variation of golden redfish (Sebastes marinus) and deep-sea redfish (S. mentella) in the North Atlantic based on otolith shape analysis   总被引：1，自引：0，他引：1  

Stransky  Christoph 《ICES Journal of Marine Science》2005,62(8):1691-1698

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The GeoForschungsZentrum Potsdam/Groupe de Recherche de Gèodésie Spatiale satellite-only and combined gravity field models: EIGEN-GL04S1 and EIGEN-GL04C   总被引：2，自引：1，他引：1  

Christoph Förste  Roland Schmidt  Richard Stubenvoll  Frank Flechtner  Ulrich Meyer  Rolf König  Hans Neumayer  Richard Biancale  Jean-Michel Lemoine  Sean Bruinsma  Sylvain Loyer  Franz Barthelmes  Saskia Esselborn 《Journal of Geodesy》2008,82(6):331-346

The recent improvements in the Gravity Recovery And Climate Experiment (GRACE) tracking data processing at GeoForschungsZentrum Potsdam (GFZ) and Groupe de Recherche de Géodésie Spatiale (GRGS) Toulouse, the availability of newer surface gravity data sets in the Arctic, Antarctica and North-America, and the availability of a new mean sea surface height model from altimetry processing at GFZ gave rise to the generation of two new global gravity field models. The first, EIGEN-GL04S1, a satellite-only model complete to degree and order 150 in terms of spherical harmonics, was derived by combination of the latest GFZ Potsdam GRACE-only (EIGEN-GRACE04S) and GRGS Toulouse GRACE/LAGEOS (EIGEN-GL04S) mean field solutions. The second, EIGEN-GL04S1 was combined with surface gravity data from altimetry over the oceans and gravimetry over the continents to derive a new high-resolution global gravity field model called EIGEN-GL04C. This model is complete to degree and order 360 and thus resolves geoid and gravity anomalies at half- wavelengths of 55 km at the equator. A degree-dependent combination method has been applied in order to preserve the high accuracy from the GRACE satellite data in the lower frequency band of the geopotential and to form a smooth transition to the high-frequency information coming from the surface data. Compared to pre-CHAMP global high-resolution models, the accuracy was improved at a spatial resolution of 200 km (half-wavelength) by one order of magnitude to 3 cm in terms of geoid heights. The accuracy of this model (i.e. the commission error) at its full spatial resolution is estimated to be 15 cm. The model shows a reduced artificial meridional striping and an increased correlation of EIGEN-GL04C-derived geostrophic meridional currents with World Ocean Atlas 2001 (WOA01) data. These improvements have led to select EIGEN-GL04C for JASON-1 satellite altimeter data reprocessing. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Late Paleozoic volcanism in the central part of the Southern Permian Basin (NE Germany, W Poland): facies distribution and volcano-topographic hiati     

Marion Geißler  Christoph Breitkreuz  Hubert Kiersnowski 《International Journal of Earth Sciences》2008,97(5):973-989

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