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81.
82.
Yilin Xiao Jochen Hoefs Zhenhui Hou Klaus Simon Zeming Zhang 《Contributions to Mineralogy and Petrology》2011,162(4):797-819
In order to better understand the role of fluids during subduction and subsequent exhumation, we have investigated whole-rock
and mineral chemistry (major and trace elements) and Li, B as well as O, Sr, Nd, Pb isotopes on selected continuous drill-core
profiles through contrasting lithological boundaries from the Chinese Continental Scientific Drilling Program (CCSD) in Sulu,
China. Four carefully selected sample sets have been chosen to investigate geochemical changes as a result of fluid mobilization
during dehydration, peak metamorphism, and exhumation of deeply subducted continental crust. Our data reveal that while O
and Sr-Nd-Pb isotopic compositions remain more or less unchanged, significant Li and/or B isotope fractionations occur between
different lithologies that are in close contact during various metamorphic stages. Samples that are supposed to represent
prograde dehydration as indicated by veins formed at high pressures (HP) are characterized by element patterns of highly fluid-mobile
elements in the veins that are complementary to those of the host eclogite. A second sample set represents a UHP metamorphic
crustal eclogite that is separated from a garnet peridotite by a thin transitional interface. Garnet peridotite and eclogite
are characterized by a >10% difference in MgO, which, together with the presence of abundant hydroxyl-bearing minerals and
compositionally different clinopyroxene grains demonstrate that both rocks have been derived from different sources that have
been tectonically juxtaposed during subduction, and that hydrous silicate-rich fluids have been added from the subducting
slab to the mantle. Two additional sample sets, comprising retrograde amphibolite and relatively fresh eclogite, demonstrate
that besides external fluids, internal fluids can be responsible for the formation of amphibolite. Li and B concentrations
and isotopic compositions point to losses and isotopic fractionation during progressive dehydration. On the other hand, fluids
with isotopically heavier Li and B are added during retrogression. On a small scale, mantle-derived rocks may be significantly
metasomatized by fluids derived from the subducted slab. Our study indicates that during high-grade metamorphism, Li and B
may show different patterns of enrichment and of isotopic fractionation. 相似文献
83.
Some of the oldest, indisputably indigenous, and thermally exceptionally well preserved biomarkers occur in the uppermost sections of the 1.64 billion year old (Ga) Barney Creek Formation (BCF) of the McArthur Basin in northern Australia. These rocks preserve more than 22 different C40 carotenoid derivatives, including the saturated hydrocarbons β-carotane, γ-carotane and lycopane. However, in deeper sections of the BCF, saturated carotenoid derivatives were not detected. To determine whether their absence from the deeper sections is a primary biological phenomenon or the result of degradation, we simulated the catagenesis of β-carotane in the laboratory by way of hydrous pyrolysis. Using breakdown products as elution standards, we were able to confirm the presence of β- or γ-carotane derivatives in the deeper sections, where the C40 parent compounds had been degraded. 相似文献
84.
Jochen J. Brocks 《Geochimica et cosmochimica acta》2011,75(11):3196-3213
Archean shales from the Pilbara in Western Australia contain biomarkers that have been interpreted as evidence for the existence of cyanobacteria and eukaryotes 2.7 billion years (Ga) ago, with far reaching implications for the evolution of Earth’s early biosphere. To re-evaluate the provenance of the biomarkers, this study determined the spatial distribution of hydrocarbons in the original drill core material. Rock samples were cut into millimeter-thick slices, and the molecular content of each slice was analyzed. In core from the Hamersley Group (∼2.5 Ga), C<13 alkanes had gradually increasing concentrations from the surfaces to the center of the rock while the abundance of steranes, hopanes and C15+ alkanes decreased with distance from the outer surfaces. In samples from the Fortescue Group (∼2.7 Ga), hydrocarbons were overwhelmingly concentrated on rock surfaces.Two mechanisms are proposed that may have caused the inhomogeneous distribution: diffusion of petroleum products into the rock (contamination model), and leaching of indigenous hydrocarbons out of host shales driven by pressure release after drilling (‘live-oil’ effect). To test these models, the hydrocarbon distributions in the Archean shales are compared with artificially contaminated rocks as well as younger mudstones where leaching of live-oil had been observed.The results show that chromatographic phenomena associated with live-oil escape and contaminant diffusion have strong effects on molecular ratios and maturity parameters, potentially with broad implications for oil-source rock correlation studies and paleoenvironmental interpretations.For the Archean shales, the live-oil effect is consistent with some of the observed patterns, but only the contamination model fully explains the complex chromatographic fingerprints. Therefore, the biomarkers in the Pilbara samples have an anthropogenic origin, and previous conclusions about the origin of eukaryotes and oxygenic photosynthesis based on these samples are not valid.However, the study also identified indigenous molecules. The spatial distribution of particular aromatic hydrocarbons suggests they are syngenetic. Although devoid of biological information, these aromatics now represent the oldest known clearly-indigenous terrestrial liquid hydrocarbons. 相似文献
85.
A. H. M. Selim Reza Jiin-Shuh Jean Ming-Kuo Lee Shang-De Luo Jochen Bundschuh Hong-Chun Li Huai-Jen Yang Chia-Chuan Liu 《Environmental Earth Sciences》2011,63(5):955-967
Two boreholes and ten piezometers in the Ganges flood plain were drilled and installed for collecting As-rich sediments and
groundwater. Groundwater samples from the Ganges flood plain were collected for the analysis of cations (Ca2+, Mg2+, K+, Na+), anions (Cl−, NO3
−, SO4
2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction was
performed to characterize the major mineral contents of aquifer sediments and X-ray fluorescence (XRF) to analyze the major
chemical composition of alluvial sediments. Results of XRF analysis clearly show that fine-grained sediments contain higher
amounts of trace element because of their high surface area for adsorption. Relative fluorescence index (15–38 QSU) of humic
substance in groundwater was measured using spectrofluorometer, the results revealed that groundwater in the Ganges flood
plain contains less organic matter (OM). Arsenic concentration in water ranges from 2.8 to 170 μg/L (mean 50 μg/L) in the
Ganges flood plain. Arsenic content in sediments ranges from 2.1 to 14 mg/kg (mean 4.58 mg/kg) in the flood plains. TOC ranges
from 0.49 to 3.53 g/kg (mean 1.64 g/kg) in the Ganges flood plain. Arsenic is positively correlated with TOC (R
2 = 0.55) in sediments of this plain. Humic substances were extracted from the sediments from the Ganges flood plain. Fourier
transform infrared analysis of the sediments revealed that the plain contains less humic substances. The source of organic
carbon was assigned from δ13C values obtained using elemental analysis-isotope ratio mass spectrometry (EA-IRMS); the values (−10 to −29.44‰) strongly
support the hypothesis that the OM of the Ganges flood plain is of terrestrial origin. 相似文献
86.
Jochen Eislöffel 《Astrophysics and Space Science》1994,216(1-2):135-136
Proper motion measurements have been carried out for the HH 46/47 outflow system. The results of these measurements and some implications for the physics of the outflow and its modelling are discussed. 相似文献
87.
Francesca Bacciotti Thomas P. Ray Jochen Eislöffel Jens Woitas Josef Solf Reinhard Mundt Christopher J. Davis 《Astrophysics and Space Science》2003,287(1-4):3-13
Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow. 相似文献
88.
89.
90.
Jochen Schanze Johanna Trümper Cornelia Burmeister Dirk Pavlik Ivan Kruhlov 《Environmental Earth Sciences》2012,65(5):1405-1414
The paper presents a methodology on how to consistently deal with the future change and management options in integrated water
resources management (IWRM). It is based on a conceptual framework with a five step procedure for the formulation and analysis
of a so-called ‘parameterised regional futures’. Developing and testing the approach for IWRM is realised for the upper part
of the Western Bug River catchment (Ukraine). Special attention is paid to scenarios of change covering climate and land use.
The future regional climate is downscaled with the model CCLM. Land cover is projected after retrospective change detection
and the derivation of prospective algorithms. Parameters of the interrelations between land use and the water cycle are tackled
through using the concept of the model PWF-LU. The methodology is currently being tested to analyse the impacts of mid-term
regional change and management options on the water cycle of the catchment. 相似文献