Thermal evolution of an extensional detachment as constrained by organic metamorphic data and thermal modeling: Graz Paleozoic Nappe Complex (Eastern Alps)   总被引：1，自引：0，他引：1  

Gerd Rantitsch  Reinhard F. Sachsenhofer  Christian Hasenhüttl  Barbara Russegger  Thomas Rainer 《Tectonophysics》2005,411(1-4):57-72

Following Early Cretaceous nappe stacking, the Eastern Alps were affected by late-orogenic extension during the Late Cretaceous. In the eastern segment of this range, a Late Cretaceous detachment separates a very low- to low-grade metamorphic cover (Graz Paleozoic Nappe Complex, GPNC) above a low- to high-grade metamorphic basement. Synchronously, the Kainach Gosau Basin (KGB) collapsed and subsided on top of the section.Metamorphism of organic material within this section has been investigated using vitrinite reflectance data and Raman spectra of extracted carbonaceous material. In the southern part of the GPNC, vitrinite reflectance indicates a decrease in organic maturity towards the stratigraphic youngest unit. The remaining part of the GPNC is characterized by an aureole of elevated vitrinite reflectance values and Raman R2 ratios that parallels the margins of the GPNC. Vitrinite reflectance in the KGB shows a steep coalification gradient and increases significantly towards the western basin margin. The observed stratigraphic trend in the southern GPNC is a result of deep Paleozoic to Early Cretaceous burial. This maturity pattern was overprinted along the margins by advective heat and convective fluids during Late Cretaceous to Paleogene exhumation of basement rocks.During shearing, the fault zone was heated up to ca. 500 °C. This overprint is explained by a two-dimensional thermal model with a ramp-flat fault geometry and a slip rate of 1 to 1.5 cm/year during 5 Ma fault movement. The collapse basin above the detachment subsided in a thermal regime which was characterized by relaxing isotherms.  相似文献   

Argon isotope fractionation induced by stepwise heating     

Mario Trieloff  Martina Falter  Ekaterina V. Korochantseva  Rainer Altherr 《Geochimica et cosmochimica acta》2005,69(5):1253-1264

Noble gas isotopes are widely used to elucidate the history of the rocks in which they have been trapped, either from distinct reservoirs or by accumulation following radioactive decay. To extract noble gases from their host rocks, stepwise heating is the most commonly used technique to deconvolve isotopically different components, e.g., atmospheric, in situ radiogenic, or excess radiogenic from mantle or crustal reservoirs. The accurate determination of the isotopic composition of these different components is of crucial importance, e.g., for ages obtained by ⁴⁰Ar-³⁹Ar stepheating plateaus. However, diffusion theory-based model calculations predict that the stepwise thermal extraction process from mineral phases induces isotope fractionation and, hence, adulterates the original composition. Such effects are largely unconsidered, as they are small and a compelling experimental observation is lacking. We report the first unequivocal evidence for significant mass fractionation of argon isotopes during thermal extraction, observed on shungite, a carbon-rich Precambrian sedimentary rock. The degree of fractionation, as monitored by ³⁸Ar/³⁶Ar and ⁴⁰Ar/³⁶Ar ratios, very well agrees with theoretical predictions assuming an inverse square root dependence of diffusion coefficient and atomic mass, resulting in easier extraction of lighter isotopes. Hence, subatmospheric ⁴⁰Ar/³⁶Ar ratios obtained for argon extracted at low temperatures may not represent paleoatmospheric argon. Shungite argon resembles modern atmospheric composition, but constraints on the timing of trapping appear difficult to obtain, as shungites are multicomponent systems.In ⁴⁰Ar-³⁹Ar stepwise heating, the isotope fractionation effect could cause systematic underestimations of plateau ages, between 0.15 and 0.4% depending on age, or considerably higher if samples contain appreciable atmospheric Ar. The magnitude of this effect is similar to the presently achieved uncertainties of this increasingly precise dating technique. Our results also indicate the importance of thermally activated diffusion as a possible fractionation mechanism, e.g., for hydrothermal gas exhalations, or for carbonaceous carrier phases such as “Q” in meteorites that have been suggested as carriers of highly fractionated noble gas residues from the early solar nebula.  相似文献   

Assessing vulnerability: an integrated approach for mapping adaptive capacity,sensitivity, and exposure     

Shawn W. Margles Weis  Vera N. Agostini  Lynnette M. Roth  Ben Gilmer  Steven R. Schill  John English Knowles  Ruth Blyther 《Climatic change》2016,136(3-4):615-629

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Ionic conductivity in gem-quality single-crystal alkali feldspar from the Eifel: temperature,orientation and composition dependence     

Hamid El Maanaoui  Fabian Wilangowski  Aditya Maheshwari  Hans-Dieter Wiemhöfer  Rainer Abart  Nicolaas A. Stolwijk 《Physics and Chemistry of Minerals》2016,43(5):327-340

We measured the ion conductivity of single-crystal alkali feldspar originating from two different locations in the Eifel/Germany, named Volkesfeld and Rockeskyller sanidine and having potassium site fractions \(C_\mathrm{K}\) of 0.83 and 0.71, respectively. The dc conductivities resulting from electrochemical impedance spectroscopy over the temperature range of 300–900 \(^{\circ }\hbox {C}\) show a weak composition dependence but pronounced differences between the b-direction [\(\perp (010)\)] and \(c^{*}\)-direction [\(\perp (001)\)] of the monoclinic feldspar structure. Conductivity activation energies obtained from the observed linear Arrhenius plots are close to 1.2 eV in all cases, which is closely similar to the activation energies of the \(^{22}\mathrm{Na}\) tracer diffusivity in the same crystals. Taking into account literature data on K tracer diffusion and diffusion correlation effects, the present results point to a predominance of the interstitialcy mechanism over the vacancy mechanism in mass and charge transport on the alkali sublattice in potassium-rich alkali feldspar.  相似文献   

Probabilistic Analysis of Rock Slopes Involving Correlated Non-normal Variables Using Point Estimate Methods     

Morteza Ahmadabadi  Rainer Poisel 《Rock Mechanics and Rock Engineering》2016,49(3):909-925

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Modern modes of provenance and dispersal of terrigenous sediments in the North Pacific and Bering Sea: implications and perspectives for palaeoenvironmental reconstructions   总被引：1，自引：0，他引：1  

Rong Wang  Boris K. Biskaborn  Arne Ramisch  Jian Ren  Yongzhan Zhang  Rainer Gersonde  Bernhard Diekmann 《Geo-Marine Letters》2016,36(4):259-270

During expedition 202 aboard the RV Sonne in 2009, 39 seafloor surface sediment sites were sampled over a wide sector of the North Pacific and adjoining Bering Sea. The data served to infer land–ocean linkages of terrigenous sediment supply in terms of major sources and modes of sediment transport within an over-regional context. This is based on an integrated approach dealing with grain-size analysis, bulk mineralogy and clay mineralogy in combination with statistical data evaluation (end-member modelling of grain-size data, fuzzy cluster analysis of mineralogical data). The findings on clay mineralogy served to update those of earlier work extracted from the literature. Today, two processes of terrigenous sediment supply prevail in the study area: far-distance aeolian sediment supply to the pelagic North Pacific, and hemipelagic sediment dispersal from nearby land sources via ocean currents along the continental margins and island arcs. Aeolian particles show the finest grain sizes (clay and fine silt), whereas hemipelagic sediments have high abundances of coarse silt. Exposed sites on seamounts and the continental slope are partly swept by strong currents, leading to residual enrichment of fine sand. Four sediment sources can be distinguished on the basis of distinct index minerals revealed by statistical data analysis: dust plumes from central Asia (quartz, illite), altered materials from the volcanic regions of Kamchatka and the Aleutian Arc (smectite), detritus from the Alaskan Cordillera (chlorite, hornblende), and fluvial detritus from far-eastern Siberia and the Alaska mainland (quartz, feldspar, illite). These findings confirm those of former studies but considerably expand the geographic range of this suite of proxies as far south as 39°N in the open North Pacific. The present integrated methodological approach proved useful in identifying the major modern processes of terrigenous sediment supply to the study region. This aspect deserves attention in the selection of sediment core sites for future palaeoenvironmental reconstructions related to aeolian and glacial dynamics, as well as the recognition of palaeo-ocean circulation patterns in general.  相似文献   

The St. Gallen Fault Zone: a long-lived,multiphase structure in the North Alpine Foreland Basin revealed by 3D seismic data     

Stefan Heuberger  Philippe Roth  Olivier Zingg  Henry Naef  Beat P. Meier 《Swiss Journal of Geoscience》2016,109(1):83-102

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Surface mapping of the Milh Kharwah salt diapir to better understand the subsurface petroleum system in the Sab’atayn Basin,onshore Yemen     

Gabor Tari  Leslie Jessen  Patrick Kennelly  Adel Salman  Thomas Rainer  Peter Hagedorn 《Arabian Journal of Geosciences》2018,11(15):428

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Climate change policies,natural resources and conflict: implications for development     

Esteve Corbera  Dik Roth  Courtney Work 《Climate Policy》2019,19(6):S1-S7

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A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains,Australia     

Stephen P. Carey  Aaron B. Camens  Matthew L. Cupper  Rainer Grün  John C. Hellstrom  Stafford W. McKnight  Iain Mclennan  David A. Pickering  Peter Trusler  Maxime Aubert 《Quaternary Science Reviews》2011,30(5-6):591-610

A diverse assemblage of late Pleistocene marsupial trackways on a lake bed in south-western Victoria provides the first information relating to the gaits and morphology of several megafaunal species, and represents the most speciose and best preserved megafaunal footprint site in Australia. The 60–110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid Diprotodon optatum, a macropodid (probably Protemnodon sp.) and a large vombatid (perhaps Ramsayia magna or ‘Phascolomys’ medius) and possible prints of the marsupial lion, Thylacoleo carnifex. The footprints were imprinted within a short time period, demonstrating the association of the taxa present, rather than the time-averaged accumulations usually observed in skeletal fossil deposits. Individual manus and pes prints are distinguishable in some trackways, and in many cases some digital pad morphology is also present. Several parameters traditionally used to differentiate ichnotaxa, including trackway gauge and the degree of print in-turning relative to the midline, are shown to be subject to significant intraspecific variation in marsupials. Sexual dimorphism in the trackway proportions of Diprotodon, and its potential for occurrence in all large bodied, quadrupedal marsupials, is identified here for the first time.  相似文献