Ductile to brittle fault zone evolution in Austroalpine units to the southeast of the Tauern Window (Eastern Alps)     

Andreas Wölfler  Wolfgang Frisch  Harald Fritz  Martin Danišik  Anke Wölfler 《Swiss Journal of Geoscience》2015,108(2-3):239-251

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U–Pb ages and Hf isotopic composition of zircons in Austrian last glacial loess: constraints on heavy mineral sources and sediment transport pathways     

Gábor Újvári  Urs Klötzli 《International Journal of Earth Sciences》2015,104(5):1365-1385

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Experimental study of the carbonation of partially serpentinized and weathered peridotites   总被引：1，自引：0，他引：1  

Jörn Hövelmann  Håkon Austrheim  Andreas Beinlich  Ingrid Anne Munz 《Geochimica et cosmochimica acta》2011,75(22):6760-6779

Carbonation of partially serpentinized and weathered peridotites was studied experimentally under hydrothermal conditions (T: 200 °C, P_CO2: 130-180 bars). Experiments were performed in a closed system using whole rock drill core samples (height: 1 cm, diameter: 1 cm) as starting material. The initial samples were composed mainly of meshwork serpentine, relicts of primary olivine and an olivine weathering product (deweylite assemblage). Two types of solutions, each with a total salt content corresponding to that of average seawater (35 g/L dissolved salts), were used: (1) a Na-Ca-Cl solution (12.5 g/L CaCl₂ + 22.5 g/L NaCl) and (2) a NaCl solution (35 g/L NaCl). After 15-25 days of experimental treatment, the samples were partly covered with carbonates. In addition, noticeable carbonation reactions had occurred below the sample surfaces within zones with thicknesses up to 250 μm. In the Na-Ca-Cl solution, both the olivine relicts and the deweylite assemblage were partly replaced by calcite along the surrounding serpentine veins. However, the extent of calcitization was found to be considerably larger for the deweylite assemblage than for the olivine. Bulk fluid analyses show an increase in the Mg and Si concentrations with reaction time. In the NaCl solution, the deweylite assemblage was partly dissolved resulting in large voids within the reaction zone. In contrast, the olivine was replaced by magnesite. Under the conditions of our experiments, the meshwork serpentine was not reactive, but aided fluid infiltration into the rock samples. The experimentally produced microtextures closely resemble those found in natural examples. Our study elucidates the mechanisms by which carbonates form in ultramafic rocks under relatively high P_CO2-T conditions and particularly in the presence of Ca-bearing aqueous solutions. The existence of a serpentine meshtexture and the presence of weathering products formed from primary Mg-silicates may have significant beneficial effects on in situ CO₂ mineral sequestration in ultramafic rocks.  相似文献   

60Fe–60Ni systematics in the eucrite parent body: A case study of Bouvante and Juvinas     

Ghylaine Quitté  Christopher Latkoczy  Maria Schönbächler  Alex N. Halliday  Detlef Günther 《Geochimica et cosmochimica acta》2011,75(23):7698-7706

Eucrites are basaltic meteorites that cooled rapidly but are in many instances thermally metamorphosed and impact brecciated. The exact timing of these events remains unclear. In this study, Ni isotopic compositions and Fe/Ni elemental ratios are presented for two non-cumulate eucrites, Bouvante and Juvinas, including mineral separates from the latter. The samples are characterized by variable, well-resolved ⁶⁰Ni-excesses consistent with the former presence of live ⁶⁰Fe (t_1/2 = 2.62 Ma) at the time of eucrite crystallization. A significant fraction of Ni with a terrestrial-like composition appears to be surface correlated. This Ni may be the product of terrestrial contamination or was introduced by a chondritic impactor during brecciation. Altogether, the data provide evidence for a complex and probably multi-stage history of Fe and/or Ni redistribution, which impedes the interpretation of the chronological data.  相似文献   

Hafnium isotopic variations in East Atlantic intraplate volcanism     

Jörg Geldmacher  Kaj Hoernle  Barry B. Hanan  Janne Blichert-Toft  F. Hauff  James B. Gill  Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2011,162(1):21-36

The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), ¹⁷⁶Hf/¹⁷⁷Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (¹⁷⁶Hf/¹⁷⁷Hf_m up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (¹⁷⁶Hf/¹⁷⁷Hf_m = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower ¹⁷⁶Hf/¹⁷⁷Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat older recycling ages of ≥1 Ga.  相似文献   

The structural vulnerability in the framework of natural hazard risk analyses and the exemplary application for storm loss modelling in Tyrol (Austria)     

Matthias Huttenlau  Johann Stötter 《Natural Hazards》2011,58(2):705-729

In the context of natural hazard-related risk analyses, different concepts and comprehensions of the term risk exist. These differences are mostly subjected to the perceptions and historical backgrounds of the different scientific disciplines and results in a multitude of methodological concepts to analyse risk. The target-oriented selection and application of these concepts depend on the specific research object which is generally closely connected to the stakeholders’ interests. An obvious characteristic of the different conceptualizations is the immanent various comprehensions of vulnerability. As risk analyses from a natural scientific-technical background aim at estimating potential expositions and consequences of natural hazard events, the results can provide an appropriate decision basis for risk management strategies. Thereby, beside the preferably addressed gravitative and hydrological hazards, seismo-tectonical and especially meteorological hazard processes have been rarely considered within multi-risk analyses in an Alpine context. Hence, their comparative grading in an overall context of natural hazard risks is not quantitatively possible. The present paper focuses on both (1) the different concepts of the natural hazard risk and especially their specific expressions in the context of vulnerability and (2) the exemplary application of the natural scientific-technical risk concepts to analyse potential extreme storm losses in the Austrian Province of Tyrol. Following the corresponding general risk concept, the case study first defines the hazard potential, second estimates the exposures and damage potentials on the basis of an existing database of the stock of elements and values, and third analyses the so-called Extreme Scenario Losses (ESL) considering the structural vulnerability of the potentially affected elements at risk. Thereby, it can be shown that extreme storm events can induce losses solely to buildings and inventory in the range of EUR 100–150 million in Tyrol. However, in an overall context of potential extreme natural hazard events, the storm risk can be classified with a moderate risk potential in this province.  相似文献   

Avalanche risk assessment for mountain roads: a case study from Iceland   总被引：2，自引：0，他引：2  

Maria Wastl  Johann Stötter  Hannes Kleindienst 《Natural Hazards》2011,56(2):465-480

This paper presents an assessment of the avalanche hazard potential and the resulting risks on mountain roads for a 38.7-km-long section of road no 76 (Siglufjarearvegur) in northern Iceland following a regional scale approach developed in the Alps. The assessment of the individual avalanche death risk proved applicable to distinguish areas of avalanche hazard with a risk above the accepted level, which should be given priority in following detailed investigations and the planning of possible protective measures, from road sections where the avalanche death risk is low and accepted according to international practice. The cumulative individual and collective avalanche death risks in the investigated road section provide a comparable measure for assessing the avalanche hazard both within the Icelandic public road network and on an international scale. The case study on road no 76 in northern Iceland shows that a standardised regional scale risk-based approach is practical to determine, analyse and assess the avalanche hazard situation on mountain roads in Iceland and guarantees comprehensible, reproducible and comparable results as a basis for a sustainable planning of measures.  相似文献   

First- and second-order adaptation to natural hazards and extreme events in the context of climate change   总被引：3，自引：1，他引：2  

Jörn Birkmann 《Natural Hazards》2011,58(2):811-840

This paper deals with coping and adaptation processes to natural hazards and (potential) climate change impacts. Selected response measures to natural hazards are critically reviewed with respect to the actual and potential consequences that these measures might imply for additional adaptation needs and changes within social-ecological systems. In this context, the author introduces the concept of first- and second-order adaptation processes in order to underline the cascade process that adaptation implies, the potentials for failure, and the limits of adaptation. Important aspects of first- and second-order adaptation processes as well as the issue of the limits of adaptation are illustrated based on observations and empirical work conducted in Vietnam. In its final part, the paper discusses the findings in light of selected theoretical approaches that might help to understand how stabilization and destabilization processes are influenced or even triggered by adaptation measures.  相似文献   

Pliocene climate change of the Southwest Pacific and the impact of ocean gateways     

Cyrus Karas  Dirk Nürnberg  Ralf Tiedemann  Dieter Garbe-Schönberg 《Earth and Planetary Science Letters》2011,301(1-2):117-124

The transition from the early Pliocene “Warmhouse” towards the present “Icehouse” climate and the role of Gateway dynamics are intensively debated. Both, the constrictions of the Central American Seaway and the Indonesian Gateway affected ocean circulation and climate during the Pliocene epoch. Here, we use combined δ¹⁸O and Mg/Ca ratios of planktonic foraminifera (marine protozoa) from surface and subsurface levels to reconstruct the thermal structure and changes in salinities from the Southwest Pacific Deep Sea Drilling Project (DSDP) Site 590B from 6.5 to 2.5 Ma. Our data suggest a gradual cooling of ~ 2 °C and freshening of the sea surface during ~ 4.6–4 Ma with an increased meridional temperature gradient between the West Pacific Warm Pool and the Southwest Pacific when the closing of the Central American Seaway reached a critical threshold. After ~ 3.5 Ma, the restricted Indonesian Gateway might have amplified the East Australian Current, allowing enhanced heat transport towards the Southwest Pacific with reduced meridional temperature gradients when the global climate gradually cooled. At the same time our data suggest a cooling and freshening of Subantarctic Mode Water (SAMW) or/and an increased northward flow of SAMW towards Site 590B, possibly a first step towards the present Antarctic Frontal System.  相似文献   

Erosion rates and mechanisms of knickzone retreat inferred from 10Be measured across strong climate gradients on the northern and central Andes Western Escarpment     

Luca M. Abbühl  Kevin P. Norton  John D. Jansen  Fritz Schlunegger  Ala Aldahan  Göran Possnert 《地球表面变化过程与地形》2011,36(11):1464-1473

A steep escarpment edge, deep gorges and distinct knickzones in river profiles characterize the landscape on the Western Escarpment of the Andes between ~5°S and ~18°S (northern Peru to northern Chile). Strong north–south and east–west precipitation gradients are exploited in order to determine how climate affects denudation rates in three river basins spanning an otherwise relatively uniform geologic and geomorphologic setting. Late Miocene tectonics uplifted the Meseta/Altiplano plateau (~3000 m a.s.l.), which is underlain by a series of Tertiary volcanic‐volcanoclastic rocks. Streams on this plateau remain graded to the Late Miocene base level. Below the rim of the Meseta, streams have responded to this ramp uplift by incising deeply into fractured Mesozoic rocks via a series of steep, headward retreating knickzones that grade to the present‐day base level defined by the Pacific Ocean. It is found that the Tertiary units on the plateau function as cap‐rocks, which aid in the parallel retreat of the sharp escarpment edge and upper knickzone tips. ¹⁰Be‐derived catchment denudation rates of the Rio Piura (5°S), Rio Pisco (13°S) and Rio Lluta (18°S) average ~10 mm ky^?1 on the Meseta/Altiplano, irrespective of precipitation rates; whereas, downstream of the escarpment edge, denudation rates range from 10 mm ky^?1 to 250 mm ky^?1 and correlate positively with precipitation rates, but show no strong correlation with hillslope angles or channel steepness. These relationships are explained by the presence of a cap‐rock and climate‐driven fluvial incision that steepens hillslopes to near‐threshold conditions. Since escarpment retreat and the precipitation pattern were established at least in the Miocene, it is speculated that the present‐day distribution of morphology and denudation rates has probably remained largely unchanged during the past several millions of years as the knickzones have propagated headward into the plateau. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献