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81.
McMahon K Bengtson Nash S Eaglesham G Müller JF Duke NC Winderlich S 《Marine pollution bulletin》2005,51(1-4):325-334
Low concentrations of herbicides (up to 70 ng l(-1)), chiefly diuron (up to 50 ng l(-1)) were detected in surface waters associated with inter-tidal seagrass meadows of Zostera muelleri in Hervey Bay, south-east Queensland, Australia. Diuron and atrazine (up to 1.1 ng g(-1) dry weight of sediment) were detected in the sediments of these seagrass meadows. Concentration of the herbicides diuron, simazine and atrazine increased in surface waters associated with seagrass meadows during moderate river flow events indicating herbicides were washed from the catchment to the marine environment. Maximum herbicide concentration (sum of eight herbicides) in the Mary River during a moderate river flow event was 4260 ng l(-1). No photosynthetic stress was detected in seagrass in this study during low river flow. However, with moderate river flow events, nearshore seagrasses are at risk of being exposed to concentrations of herbicides that are known to inhibit photosynthesis. 相似文献
82.
Jochen Kolb Sven Sindern Alexander F. M. Kisters F. Michael Meyer Stephan Hoernes Jens Schneider 《Mineralium Deposita》2005,40(5):473-491
Gold mineralization at Kochkar (Urals, Russia) is hosted mainly by quartz lodes, which developed at lithological contacts
between mafic dikes and granitoids of the Plast massif during late Carboniferous to early Permian, regional E–W compression
in the East Uralian Zone (EUZ). The alteration mineralogy in mafic dikes comprises biotite, actinolite, albite, K-feldspar,
quartz, epidote, tourmaline, sericite, pyrite, arsenopyrite, chalcopyrite, sphalerite, fahlores, galena, bismuthinite, and
gold, and in Plast granitoids quartz, sericite, calcite, epidote, and ore minerals. Geochemically, an enrichment of Si, K,
Rb, Ba, S, base metals, W, and Au can be observed. The ore fluid had δ18O values between 8.2‰ and 9.5‰ typical for metamorphic or deep magmatic fluids. The tectonometamorphic evolution of the EUZ
is marked by peak metamorphic conditions at 635±40°C and 5–6 kbar through 500±20°C during gold mineralization, and 300–350°C
and 2–3 kbar. The last event was dated on a late, barren quartz vein formed during greenschist facies metamorphism at 265±3 Ma
by the Rb–Sr method. Fluids related to this overprint had a δ18O value of 5.2‰ and an initial 87Sr/86Sr ratio of 0.70685 indicating that they are largely equilibrated with metamorphic lithologies of the EUZ. The Plast granitoids
and the adjacent Borisov granite, which was dated at 358±23 Ma (U–Pb zircon age), have an adakitic character. This, together
with the arc-signature of the mafic dikes, supports the setting of the EUZ within the Valerianovsky continental arc. Eastward
subduction of the Uralian Ocean below this arc began during the late Devonian to early Carboniferous. Between 320 and 265 Ma,
the oblique closure of the ocean resulted in doming of granitoid massifs in a sinistral transpressional regime, subsequent
retrograde gold mineralization during E–W compression and a later greenschist facies overprint. This long-lasting retrograde
evolution of the EUZ was caused by the lack of postcollisional collapse. Heat for a “deep-later" type of metamorphism and
triggering the auriferous fluid system was supplied by radiogenic heating of an overthickened crust. The greenschist facies
overprint at Kochkar and coeval crustal melting in the EUZ was additionally initiated by local external heating of the terrane.
This could have been caused by syn- to postcollisional slab rollback or delamination resulting in magmatic underplating of
the EUZ, which postdates orogenic gold mineralization at Kochkar. The tectonic interpretation of the EUZ indicates that gold
mineralization at Kochkar formed in a mid-crustal environment of a continental magmatic arc at the cessation of active subduction
predating post orogenic plutonism. 相似文献
83.
Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling 总被引:32,自引:1,他引:31
Yilin Xiao Jochen Hoefs Alfons M. van den Kerkhof Jens Fiebig Yongfei Zheng 《Contributions to Mineralogy and Petrology》2000,139(1):1-16
This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive
H2O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater
and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 14C years Before Present (14C years b.p.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H2O contents of 3 to 6 wt% H2O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding
episodes of mafic magmatism (from 10,600 to ∼3000 14C years b.p.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H2O (<0.2 wt%), lower LILE abundance and different isotopic characteristics. Thus, the mantle-derived inputs into the Medicine
Lake system have not always been low H2O, primitive HAOT, but have alternated between HAOT and hydrous subduction related, calc-alkaline basalt. This influx of hydrous
mafic magma coincides temporally and spatially with rhyolite eruption at Glass Mountain and Little Glass Mountain. The rhyolites
contain quenched magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence
of H2O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined
to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization
of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H2O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to
the liquidus. These combined effects generate SiO2-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H2O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted
granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by
hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H2O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes.
Received: 4 January 1999 / Accepted: 30 August 1999 相似文献
84.
Cochran Anita Veverka Joseph Bell James Belton Michael Benkhoff Johannes Benkhoff Andrew Clark Benton Feldman Paul Kissel Jochen Mahaffy Paul Malin Michael Murchie Scott Neimann Hasso Owen Tobias Robinson Mark Schwehm Gerhard Squyres Steve Thomas Peter Whipple Fred Yeomans Donald 《Earth, Moon, and Planets》2000,89(1-4):289-300
In 1997, the COmet Nucleus TOUR (CONTOUR) was selected byNASA for a new start as part of the Discovery line. In this paper, we review the status of the mission, the mission timeline and the instruments to be flown. Detail is given of the science goals and how they are to be accomplished. 相似文献
85.
Influence of melt‐freeze‐cycles on the radionuclide transport in homogeneous laboratory snowpack 下载免费PDF全文
Radionuclides released to the environment and deposited with or onto snow can be stored over long time periods if ambient temperature stays low, particularly in glaciated areas or high alpine sites. The radionuclides will be accumulated in the snowpack during the winter unless meltwater runoff at the snow base occurs. They will be released to surface waters within short time during snowmelt in spring. In two experiments under controlled melting conditions of snow in the laboratory, radionuclide migration and runoff during melt‐freeze‐cycles were examined. The distribution of Cs‐134 and Sr‐85 tracers in homogeneous snow columns and their fractionation and potential preferential elution in the first meltwater portions were determined. Transport was associated with the percolation of meltwater at ambient temperatures above 0 °C after the snowpack became ripe. Mean migration velocities in the pack were examined for both nuclides to about 0.5 cm hr?1 after one diurnal melt‐freeze‐cycle at ambient temperatures of ?2 to 4 °C. Meltwater fluxes were calculated with a median of 1.68 cm hr?1. Highly contaminated portions of meltwater with concentration factors between 5 and 10 against initial bulk concentrations in the snowpack were released as ionic pulse with the first meltwater. Neither for caesium nor strontium preferential elution was observed. After recurrent simulated day‐night‐cycles (?2 to 4 °C), 80% of both radionuclides was released with the first 20% of snowmelt within 4 days. 50% of Cs‐134 and Sr‐85 were already set free after 24 hr. Snowmelt contained highest specific activities when the melt rate was lowest during the freeze‐cycles due to concentration processes in remaining liquids, enhanced by the melt‐freeze‐cycling. This implies for natural snowpack after significant radionuclide releases, that long‐time accumulation of radionuclides in the snow during frost periods, followed by an onset of steady meltwater runoff at low melt rates, will cause the most pronounced removal of the contaminants from the snow cover. This scenario represents the worst case of impact on water quality and radiation exposure in aquatic environments. 相似文献
86.
87.
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
88.
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
89.
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
90.
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