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1.
Stress Sensitivity of Seismic and Electric Rock Properties of the Upper Continental Crust at the KTB
We test the hypothesis that the general trend of P-wave and S-wave sonic log velocities and resistivity with depth in the pilot hole of the KTB site Germany, can be explained by the progressive
closure of the compliant porosity with increasingly effective pressure. We introduce a quantity θc characterizing the stress sensitivity of the mentioned properties. An analysis of the downhole measurements showed that estimates
of the quantitiy θc for seismic velocities and electrical formation factor of the in situ formation coincide. Moreover, this quantity is 3.5 to 4.5 times larger than the averaged stress sensitivity obtained from
core samples. We conclude that the hypothesis mentioned above is consistent with both data sets. Moreover, since θc corresponds approximately to the inverse of the effective crack aspect ratio, larger in situ estimates of θc might reflect the influence of fractures and faults on the stress sensitivity of the crystalline formation in contrast to
the stress sensitivity of the nearly intact core samples. Finally, because the stress sensitivity is directly related to the
elastic nonlinearity we conclude that the elastic nonlinearity (i.e., deviation from linear stress-strain relationship i.e.,
Hooke's law) of the KTB rocks is significantly larger in situ than in the laboratory. 相似文献
2.
Katharina Marquardt Elena Petrishcheva Rainer Abart Emmanuel Gardés Richard Wirth Ralf Dohmen Hans-Werner Becker Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(10):751-760
In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion
couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical
analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method,
we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential
influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal
substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film
diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is
small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG
can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results.
At 1,450°C and 1 bar, we infer log D
Yb (m2/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated
with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect
cannot generally be ignored. 相似文献
3.
Katharina?MarquardtEmail author Gregory?S.?Rohrer Luiz?Morales Erik?Rybacki Hauke?Marquardt Brian?Lin 《Contributions to Mineralogy and Petrology》2015,170(4):40
Rocks consist of crystal grains separated by grain boundaries that impact the bulk rock properties. Recent studies on metals and ceramics showed that the grain boundary plane orientation is more significant for grain boundary properties than other characteristics such as the sigma value or disorientation (in the Earth’s science community more frequently termed misorientation). We determined the grain boundary character distribution (GBCD) of synthetic and natural polycrystalline olivine, the most abundant mineral of Earth’s upper mantle. We show that grain boundaries of olivine preferentially contain low index planes, in agreement with recent findings on other oxides (e.g. MgO, TiO2, Al2O3 etc.). Furthermore, we find evidence for a preferred orientation relationship of 90° disorientations about the [001] direction forming tilt and twist grain boundaries, as well as a preference for the 60° disorientation about the [100] axis. Our data indicate that the GBCD, which is an intrinsic property of any mineral aggregate, is fundamental for understanding and predicting grain boundary related processes. 相似文献
4.
We studied 14 presolar SiC mainstream grains for C‐, Si‐, and S‐isotopic compositions and S elemental abundances. Ten grains have low levels of S contamination and CI chondrite‐normalized S/Si ratios between 2 × 10?5 and 2 × 10?4. All grains have S‐isotopic compositions compatible within 2σ of solar values. Their mean S isotope composition deviates from solar by at most a few percent, and is consistent with values observed for the carbon star IRC+10216, believed to be a representative source star of the grains, and the interstellar medium. The isotopic data are also consistent with stellar model predictions of low‐mass asymptotic giant branch (AGB) stars. In a δ33S versus δ34S plot the data fit along a line with a slope of 1.8 ± 0.7, suggesting imprints from galactic chemical evolution. The observed S abundances are lower than expected from equilibrium condensation of CaS in solid solution with SiC under pressure and temperature conditions inferred from the abundances of more refractory elements in SiC. Calcium to S abundance ratios are generally above unity, contrary to expectations for stoichiometric CaS solution in the grains, possibly due to condensation of CaC2 into SiC. We observed a correlation between Mg and S abundances suggesting solid solution of MgS in SiC. The low abundances of S in mainstream grains support the view that the significantly higher abundances of excess 32S found in some Type AB SiC grains are the result of in situ decay of radioactive 32Si from born‐again AGB stars that condensed into AB grains. 相似文献
5.
Alfred Ngomanda Katharina Neumann Astrid Schweizer Jean Maley 《Quaternary Research》2009,71(3):307-318
The third millennium BP crisis of the central African rainforest is not sufficiently understood. The low resolution of most pollen profiles and a large plateau of the calibration curve aggravate the exact dating of the event, and its causal climatic parameters are debated. We present a high-resolution pollen profile from the swamp site Nyabessan in the southern Cameroonian rainforest, covering the period 3100-2300 cal yr BP. Between 3100 and 2500 cal yr BP, the climate was favourable for a regional evergreen forest with Caesalpiniaceae and Lophira and a local Raphia swamp forest. Around 2500/2400 cal yr BP, a significant decrease of mature forest and swamp forest taxa and an increase of pioneers indicate that the rain forest was seriously disturbed and replaced by secondary formations. The dominance of Trema orientalis, a pioneer well adapted to seasonal desiccation, points to a much more accentuated seasonality after 2500 cal yr BP, which seems to be linked to a southwards shift of the ITCZ during the northern hemisphere winter months. We propose that the rain forest crisis between 2500 and 2200 cal BP created favourable conditions for farming and paved the way for a major expansion of Bantu speaking populations. 相似文献
6.
Katharina Marger Matthieu Harlaux Andrea Rielli Lukas P. Baumgartner Andrea Dini Barbara L. Dutrow Anne‐Sophie Bouvier 《Geostandards and Geoanalytical Research》2020,44(3):593-615
Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ11B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ11B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO2 and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s). 相似文献
7.
Grain boundaries influence many physical and chemical properties of crystalline materials. Here, we perform molecular dynamics simulations to study the structure of a series of [100] symmetric tilt grain boundaries in Mg2SiO4 forsterite. The present results show that grain boundary energies depend significantly on misorientation angle. For small misorientation angles (up to 22°), grain boundary structures consist of an array of partial edge dislocations with Burgers vector $\frac{1}{2}[001]$ associated with stacking faults and their energies can be readily fit with a model which adds the Peach-Koehler equation to the Read-Shockley dislocation model for grain boundaries. The core radius of partial dislocations and the spacing between the partials derived from grain boundary energies show that the transition from low- to high-angle grain boundaries occurs for a misorientation angle between 22° and 32°. For high misorientation angles (32.1° and 60.8°), the cores of dislocations overlap and form repeated structural units. Finally, we use a low energy atomic configuration obtained by molecular dynamics for the misorientation of 12.18° as input to simulate a high-resolution transmission electron microscopy (HRTEM) image. The simulated image is in good agreement with an observed HRTEM image, which indicates the power of the present approach to predict realistic atomic structures of grain boundaries in complex silicates. 相似文献
8.
Simulation of DNAPL infiltration and spreading behaviour in the saturated zone at varying flow velocities and alternating subsurface geometries 总被引：3，自引：1，他引：2
Katharina Erning Sibylle Grandel Andreas Dahmke Dirk Schäfer 《Environmental Earth Sciences》2012,65(4):1119-1131
The influence of varying groundwater flow velocities on DNAPL infiltration and spreading behaviour was investigated by multiphase
modelling using TMVOC and PetraSim. The multiphase models were calibrated by results of previously conducted laboratory experiments
for the complete spatio-temporal range of the experiments. The small scale 2D scenario modelling was applied to qualify and
quantify changes in position, architecture, geometry and dissolution of a TCE body in a fully saturated homogeneous sandy
medium. The applied flow velocities ranging from 0.05 up to 40.00 m/day exhibited that the DNAPL TCE is affected even at the
lowest flow velocity in its position, its size and its architecture. Additionally, several impermeable lenses with simple
geometry were assumed in the model, to investigate the influence of stratified subsoil. In the experimental set-ups, the DNAPL
body reacts more sensitive to the applied groundwater flow velocities than to the geometrical set-up of the scenarios. A possible
consequence can be the transportation and displacement of a DNAPL pool due to natural or anthropogenic induced high groundwater
flow velocities, as by Pump and Treat facilities, complicating site investigation process and planning of remediation activities. 相似文献
9.
Katharina?Marquardt Elena?Petrishcheva Emmanuel?Gardés Richard?Wirth Rainer?Abart Wilhelm?Heinrich 《Contributions to Mineralogy and Petrology》2011,162(4):739-749
Yb-Y inter-diffusion along a single grain boundary of a synthetic yttrium aluminium garnet (YAG) bicrystal has been studied
using analytical transmission electron microscopy (ATEM). To investigate the diffusion, a thin-film containing Yb as the diffusant
was deposited perpendicular to the bicrystal grain boundary by pulsed laser deposition (PLD). Structural properties and their
change with time in both the diffusant source and the grain boundary are reported. The diffusion profiles are incorporated
in a numerical diffusion model, which is applied to determine the grain boundary diffusion coefficient, D
gb
, at 1.723 K it is equal to 3 × 10−15 m2/s. We find that grain boundary diffusion is 4.85 orders of magnitude faster than volume diffusion, which was determined from
the same diffusion experiment. This result is discussed in the context of special versus general grain boundaries. Finally,
we successfully tested the capability of synchrotron-based nano-X-ray fluorescence analysis to map micro-chemical patterns
in two dimensions with sub-micrometre resolution. 相似文献
10.
Michael Zech Nikolai Pedentchouk Katharina Leiber Slobodan B. Markovi? 《Geochimica et cosmochimica acta》2011,75(17):4917-4928
During the last decade, compound-specific hydrogen isotope analysis of plant leaf-wax and sedimentary n-alkyl lipids has become a promising tool for paleohydrological reconstructions. However, with the exception of several previous studies, there is a lack of knowledge regarding possible effects of early diagenesis on the δD values of n-alkanes. We therefore investigated the n-alkane patterns and δD values of long-chain n-alkanes from three different C3 higher plant species (Acer pseudoplatanus L., Fagus sylvatica L. and Sorbus aucuparia L.) that have been degraded in a field leaf litterbag experiment for 27 months.We found that after an initial increase of long-chain n-alkane masses (up to ∼50%), decomposition took place with mean turnover times of 11.7 months. Intermittently, the masses of mid-chain n-alkanes increased significantly during periods of highest total mass losses. Furthermore, initially high odd-over-even predominances (OEP) declined and long-chain n-alkane ratios like n-C31/C27 and n-C31/C29 started to converge to the value of 1. While bulk leaf litter became systematically D-enriched especially during summer seasons (by ∼8‰ on average over 27 months), the δD values of long-chain n-alkanes reveal no systematic overall shifts, but seasonal variations of up to 25‰ (Fagus, n-C27, average ∼13‰).Although a partly contribution by leaf-wax n-alkanes by throughfall cannot be excluded, these findings suggest that a microbial n-alkane pool sensitive to seasonal variations of soil water δD rapidly builds up. We propose a conceptual model based on an isotope mass balance calculation that accounts for the decomposition of plant-derived n-alkanes and the build-up of microbial n-alkanes. Model results are in good agreement with measured n-alkane δD results. Since microbial ‘contamination’ is not necessarily discernible from n-alkane concentration patterns alone, care may have to be taken not to over-interpret δD values of sedimentary n-alkanes. Furthermore, since leaf-water is generally D-enriched compared to soil and lake waters, soil and water microbial n-alkane pools may help explain why soil and sediment n-alkanes are D-depleted compared to leaves. 相似文献