Equilibrium-disequilibrium relations in the Monte Rosa Granite,Western Alps: Petrological,Rb-Sr and stable isotope data     

Martin Frey  Johannes C. Hunziker  James R. O'Neil  Hans W. Schwander 《Contributions to Mineralogy and Petrology》1976,55(2):147-179

Nine samples from the Monte Rosa Granite have been investigated by microscopic, X-ray, wet chemical, electron microprobe, stable isotope and Rb-Sr and K-Ar methods. Two mineral assemblages have been distinguished by optical methods and dated as Permian and mid-Tertiary by means of Rb-Sr age determinations. The Permian assemblage comprises quartz, orthoclase, oligoclase, biotite, and muscovite whereas the Alpine assemblage comprises quartz, microcline, albite+epidote or oligoclase, biotite, and phengite. Disequilibrium between the Permian and Alpine mineral assemblages is documented by the following facts: (i) Two texturally distinguishable generations of white K-mica are 2 M muscovite (Si=3.1–3.2) and 2 M or 3 T phengite (Si=3.3–3.4). Five muscovites show Permian Rb-Sr ages and oxygen isotope fractionations indicating temperatures between 520 and 560 ° C; however, K-Ar ages are mixed or rejuvenated. Phengite always shows mid-Tertiary Rb-Sr ages, (ii) Two biotite generations can be recognized, although textural evidence is often ambiguous. Three out of four texturally old biotites show mid-Tertiary Rb-Sr cooling ages while the oxygen isotopic fractionations point to Permian, mixed or Alpine temperatures, (iii) Comparison of radiogenic and stable isotope relations indicates that the radiogenic isotopes in the interlayer positions of the micas were mobilized during Alpine time without recrystallization, that is, without breaking Al-O or Si-O bonds. High Ti contents in young muscovites and biotites also indicate that the octahedral (and tetrahedral) sites remained undisturbed during rejuvenation. (iv) Isotopic reversals in the order of O¹⁸ enrichment between K-feldspar and albite exist. Arguments for equilibrium during Permian time are meagre because of Alpine overprinting effects. Texturally old muscovites show high temperatures and Permian Rb-Sr ages in concordancy with Rb-Sr whole rock ages. For the tectonically least affected samples, excellent concordance between quartz-muscovite and quartz-biotite Permian temperatures implies oxygen isotope equilibrium in Permian time which was undisturbed during Alpine metamorphism. Arguments for equilibrium during the mid-Tertiary metamorphism are as follows: (i) Mid-Tertiary Rb-Sr mineral isochrons of up to six minerals exist, (ii) Oxygen isotope temperatures of coexisting Alpine phengites and biotites are concordant.The major factor for the adjustment of the Permian assemblages to Alpine conditions was the degree of Alpine tectonic overprinting rather than the maximum temperatures reached during the mid-Tertiary Alpine metamorphism. The lack of exchange with externally introduced fluid phases in the samples least affected by tectonism indicates that the Monte Rosa Granite stewed in its own juices. This seems to be the major cause for the persistence of Permian ages and corresponding temperatures.  相似文献   

Gefüge und Entstehung der Ringdünen in den grauen Tuffen des Laacher Vulkans     

Wilhelm Meyer  Johannes Stets  Paul Wurster 《International Journal of Earth Sciences》1974,63(3):1113-1132

The last products of the pleistocene Laach volcano (Eifel, about 40 kms SW of Bonn, Germany) are grey tuffs. Outcrops in the rim show characteristic cross-bedding in these tuffs. It is in discussion whether these structures are produced by wind or by phreato-magmatic outbursts. At all larger outcrops in the rim we measured numerous depositional elements of the tuffs, and analyzed their geometrical structure. So we are able to reconstruct shape, structure and orientation of dunes in the tuffs. They show transport vectors in centrifugal orientation, radially to the vent. The dunes are orientated concentrically to the vent, we intruduce the term “concentrical dune” for this dune type. This points out that the dunes in the Laach tuffs are of volcanic origin. But our geometrical results give no authorization to assume phreato-magmatic processes during the activity of the Laach volcano. We think that the grey Laach tuffs are no base surge deposits, but products of gas-rich eruptions in the phase of decreasing volcanic energy.  相似文献   

Tracing variability of run‐off generation in mountainous permafrost of semi‐arid north‐eastern Mongolia          下载免费PDF全文

Jens Lange  Benjamin Johannes Kopp  Matthias Bents  Lucas Menzel 《水文研究》2015,29(6):1046-1055

The headwaters of mountainous, discontinuous permafrost regions in north‐eastern Mongolia are important water resources for the semi‐arid country, but little is known about hydrological processes there. Run‐off generation on south‐facing slopes, which are devoid of permafrost, has so far been neglected and is totally unknown for areas that have been affected by recent forest fires. To fill this knowledge gap, the present study applied artificial tracers on a steppe‐vegetated south‐facing and on two north‐facing slopes, burned and unburned. Combined sprinkling and dye tracer experiments were used to visualize processes of infiltration and water fluxes in the unsaturated zone. On the unburned north‐facing slope, rapid and widespread infiltration through a wet organic layer was observed down to the permafrost. On the burned profile, rapid infiltration occurred through a combusted organic and underlying mineral layer. Stained water seeped out at the bottom of both profiles suggesting a general tendency to subsurface stormflow (SSF). Ongoing SSF could directly be studied 24 h after a high‐intensity rainfall event on a 55‐m hillslope section in the burned forest. Measurements of water temperature proved the role of the permafrost layer as a base horizon for SSF. Repeated tracer injections allowed direct insights into SSF dynamics: A first injection suggested rather slow dispersive subsurface flow paths; whereas 18 h later, a second injection traced a more preferential flow system with 20 times quicker flow velocities. We speculate that these pronounced SSF dynamics are limited to burned slopes where a thermally insulating organic layer is absent. On three south‐facing soil profiles, the applied tracer remained in the uppermost 5 cm of a silt‐rich mineral soil horizon. No signs of preferential infiltration could be found, which suggested reduced biological activity under a harsh, dry and cold climate. Instead, direct observations, distributed tracers and charcoal samples provided evidence for the occurrence of overland flow. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Bounce Rock—A shergottite‐like basalt encountered at Meridiani Planum,Mars     

Jutta ZIPFEL  Bradley L. JOLLIFF  Ralf GELLERT  Kenneth E. HERKENHOFF  Rudolf RIEDER  Robert ANDERSON  James F. BELL III  Johannes BRÜCKNER  Joy A. CRISP  Philip R. CHRISTENSEN  Benton C. CLARK  Paulo A. De SOUZA Jr.  Gerlind DREIBUS  Claude D’USTON  Thanasis ECONOMOU  Steven P. GOREVAN  Brian C. HAHN  Göstar KLINGELHÖFER  Timothy J. McCOY  Harry Y. McSWEEN Jr.  Douglas W. MING  Richard V. MORRIS  Daniel S. RODIONOV  Steven W. SQUYRES  Heinrich WÄNKE  Shawn P. WRIGHT  Michael B. WYATT  Albert S. YEN 《Meteoritics & planetary science》2011,46(1):1-20

Abstract– The Opportunity rover of the Mars Exploration Rover mission encountered an isolated rock fragment with textural, mineralogical, and chemical properties similar to basaltic shergottites. This finding was confirmed by all rover instruments, and a comprehensive study of these results is reported here. Spectra from the miniature thermal emission spectrometer and the Panoramic Camera reveal a pyroxene‐rich mineralogy, which is also evident in Mössbauer spectra and in normative mineralogy derived from bulk chemistry measured by the alpha particle X‐ray spectrometer. The correspondence of Bounce Rock’s chemical composition with the composition of certain basaltic shergottites, especially Elephant Moraine (EET) 79001 lithology B and Queen Alexandra Range (QUE) 94201, is very close, with only Cl, Fe, and Ti exhibiting deviations. Chemical analyses further demonstrate characteristics typical of Mars such as the Fe/Mn ratio and P concentrations. Possible shock features support the idea that Bounce Rock was ejected from an impact crater, most likely in the Meridiani Planum region. Bopolu crater, 19.3 km in diameter, located 75 km to the southwest could be the source crater. To date, no other rocks of this composition have been encountered by any of the rovers on Mars. The finding of Bounce Rock by the Opportunity rover provides further direct evidence for an origin of basaltic shergottite meteorites from Mars.  相似文献   

Mid-Paleocene event at Gabal Nezzazat,Sinai, Egypt: planktonic foraminiferal biostratigraphy,mineralogy and geochemistry     

Mamdouh F. Soliman  Nageh A. Obaidalla  Ezzat A. Ahmed  Ahmed A. Ahmed  Johannes Kurzweil 《Arabian Journal of Geosciences》2014,7(10):4079-4099

The Qreiya Beds that record the ‘mid-Paleocene event’ at Gabal Nezzazat occur within the Igorina albeari (P3b) Zone and constitute part of a 14-m thick shale succession that ranges in age from Early to Late Paleocene. They are composed of four alternating dark grey and brown shale beds, which are thinly laminated, phosphatic, organic-rich and extremely sulphidic. They are characterized by distinct enrichment and high peak anomalies in chalcophiles (Zn, Co, Ni, Cu and Pb) and organic association elements (V and Cr), especially within the brown organic-rich beds. It is concluded that these elements are incorporated into the phosphatic debris, sulphides and organic matter. In contrast, the grey beds are enriched in clay minerals and quartz. Clay mineral assemblages indicate alternating periods of warm/humid climate (high kaolinite) and dry climate (low kaolinite) during the formation of the grey and brown beds, respectively. The sediments of the Qreiya Beds yield lithological, biotic, geochemical and mineralogical data indicative of suboxic/anoxic marine environments as a result of high productivity and/or upwelling. The top metre of the succession below the Qreiya Beds is characterized by a progressive change from faunas dominated by praemurcurids to faunas dominated by Morozovilids, and by a progressive upward decrease in δ¹³C_carb and δ¹⁸O_carb values. The foraminiferal faunal change may reflect shallowing and warming preceding deposition of the Qreiya Beds. The change in isotopic values is inferred to be the result of surface weathering, fluvial input and diagenesis with no evidence of any primary change that could support presence of a hyperthermal event.  相似文献   

Analysis of coprolites from the extinct mountain goat Myotragus balearicus     

Frido Welker  Elza Duijm  Kristiaan J. van der Gaag  Bas van Geel  Peter de Knijff  Jacqueline van Leeuwen  Dick Mol  Johannes van der Plicht  Niels Raes  Jelle Reumer  Barbara Gravendeel 《Quaternary Research》2014

Humans colonized the Balearic Islands 5–4 ka ago. They arrived in a uniquely adapted ecosystem with the Balearic mountain goat Myotragus balearicus (Bovidae, Antilopinae, Caprini) as the only large mammal. This mammal went extinct rapidly after human arrival. Several hypotheses have been proposed to explain the extinction of M. balearicus. For the present study ancient DNA analysis (Sanger sequencing, Roche-454, Ion Torrent), and pollen and macrofossil analyses were performed on preserved coprolites from M. balearicus, providing information on its diet and paleo-environment. The information retrieved shows that M. balearicus was heavily dependent on the Balearic box species Buxus balearica during at least part of the year, and that it was most probably a browser. Hindcast ecological niche modelling of B. balearica shows that local distribution of this plant species was affected by climate changes. This suggests that the extinction of M. balearicus can be related to the decline and regional extinction of a plant species that formed a major component of its diet. The vegetation change is thought to be caused by increased aridity occurring throughout the Mediterranean. Previous hypotheses relating the extinction of M. balearicus directly to the arrival of humans on the islands must therefore be adjusted.  相似文献   

Debating clean energy: Frames,counter frames,and audiences     

Michaël Aklin  Johannes Urpelainen 《Global Environmental Change》2013,23(5):1225-1232

In the United States, both scholars and practitioners have repeatedly emphasized the importance of “issue framing” for garnering public support for climate change policy. However, the debate frequently overlooks the importance of counter frames. For every framing attempt by advocates of climate policy, there will be a counter frame by the opponents of climate policy. How do counter frames influence the effectiveness of issue framing as a communication strategy? To answer this question, we report results from a survey experiment on a nationally representative sample of 1000 Americans on clean energy policy, a key policy issue in the public debate on climate change in the United States. Overall, we find that different combinations of positive and negative frames have remarkably little effect on support for clean energy policy. A follow-up on-line survey experiment with a convenience sample of 2000 Americans suggests that the counter frames are responsible for undermining the effects of the original frames.  相似文献   

Modernizing the ISC location procedures     

Johannes Schweitzer  Dmitry A. Storchak 《Physics of the Earth and Planetary Interiors》2006,158(1):1-3

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Stress anisotropy in natural debris flows during impacting a monitoring structure     

Nagl  Georg  H&#;bl  Johannes  Kaitna  Roland 《Landslides》2022,19(1):211-220

Landslides - The frictional resistance of rock and debris is supposed to induce stress anisotropy in the unsteady, non-uniform flow of gravitational mass flows, including debris flows. Though...  相似文献   

Temporal evolution of backward erosion piping in small-scale experiments     

Pol  Johannes C.  Kanning  Willem  van Beek  Vera M.  Robbins  Bryant A.  Jonkman  Sebastiaan N. 《Acta Geotechnica》2022,17(10):4555-4576

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.

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