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61.
Kevin L. Shelton Justin M. Beasley Jay M. Gregg Martin S. Appold Stephen F. Crowley James P. Hendry Ian D. Somerville 《Mineralium Deposita》2011,46(8):859-880
A newly discovered, extensive sphalerite-bearing breccia (~7.5 wt.% Zn) is hosted in dolomitised Carboniferous limestones
overlying Ordovician–Silurian metasedimentary rocks on the Isle of Man. Although base metal sulphide deposits have been mined
historically on the island, they are nearly all quartz vein deposits in the metamorphic basement. This study investigates
the origin of the unusual sphalerite breccia and its relationship to basement-hosted deposits, through a combination of petrographic,
cathodoluminescence, fluid inclusion, stable isotope and hydrogeologic modelling techniques. Breccia mineralisation comprises
four stages, marked by episodes of structural deformation and abrupt changes in fluid temperature and chemistry. In stage
I, high-temperature (T
h > 300°C), high-salinity (20–45 wt.% equiv. NaCl) fluid of likely basement origin deposited a discontinuous quartz vein. This
vein was subsequently dismembered during a major brecciation event. Stages II–IV are dominated by open-space filling sphalerite,
quartz and dolomite, respectively. Fluid inclusions in these minerals record temperatures of ~105–180°C and salinities of
~15–20 wt.% equiv. NaCl. The δ34S values of sphalerite (6.5–6.9‰ Vienna-Canyon Diablo troilite) are nearly identical to those of ore sulphides from mines
in the Lower Palaeozoic metamorphic rocks. The δ18O values for quartz and dolomite indicate two main fluid sources in the breccia’s hydrothermal system, local Carboniferous-hosted
brines (~0.5–6.0‰ Vienna standard mean ocean water) and basement-involved fluids (~5.5–11.5‰). Ore sulphide deposition in
the breccia is compatible with the introduction and cooling of a hot, basement-derived fluid that interacted with local sedimentary
brines. 相似文献
62.
Martin Fahey Matthew Helinski Andy Fourie 《Geotechnical and Geological Engineering》2011,29(5):709-723
Paste backfill used to provide ground support in underground mining is generated from full-stream tailings and is almost always
placed underground with cement. For the backfill, both the rate of strength development and the final strength are important
considerations for design, particularly when the backfill is subsequently exposed in the stope-mining sequence. There is strong
evidence that strengths measured on specimens obtained from coring the in situ cemented backfill are much greater than laboratory-cured
specimens with the same cement content. The paper reviews some of the experimental evidence showing that one of the major
reasons for the different strength is the difference in effective stress acting on the backfill during curing. Laboratory
specimens are (almost) always cured under zero total stress, so no effective stress develops. In contrast, backfill in a stope
may cure under high effective stress, which develops due to either “conventional” consolidation in free-draining backfills,
or to the so-called “self-desiccation” mechanism in fine-grained fills. Evidence is presented showing how the final strength
is affected by applying stress to specimens at different stages of curing and at different rates. It is shown that a fully-coupled
analysis of the filling behaviour is required to determine the appropriate effective stress regime to apply in curing laboratory
specimens, where “fully-coupled” in this context means taking account of the interaction of consolidation/drainage rate, filling
rate and cement hydration rate. Curing protocols for laboratory specimens are proposed, which would ensure that the strengths
obtained are representative of in situ conditions. 相似文献
63.
Michael Wiederkehr Romain Bousquet Martin A. Ziemann Alfons Berger Stefan M. Schmid 《International Journal of Earth Sciences》2011,100(5):1029-1063
This study monitors regional changes in the crystallinity of carbonaceous matter (CM) by applying Micro-Raman spectroscopy
to a total of 214 metasediment samples (largely so-called Bündnerschiefer) dominantly metamorphosed under blueschist- to amphibolite-facies
conditions. They were collected within the northeastern margin of the Lepontine dome and easterly adjacent areas of the Swiss
Central Alps. Three-dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature
contours associated with the Miocene Barrow-type Lepontine metamorphic event cut across refolded nappe contacts, both along
and across strike within the northeastern margin of the Lepontine dome and adjacent areas. Further to the northeast, the isotemperature
contours reflect temperatures reached during the Late Eocene subduction-related blueschist-facies event and/or during subsequent
near-isothermal decompression; these contours appear folded by younger, large-scale post-nappe-stacking folds. A substantial
jump in the recorded maximum temperatures across the tectonic contact between the frontal Adula nappe complex and surrounding
metasediments indicates that this contact accommodated differential tectonic movement of the Adula nappe with respect to the
enveloping Bündnerschiefer after maximum temperatures were reached within the northern Adula nappe, i.e. after Late Eocene
time. 相似文献
64.
Quartz–amphibole–pyroxene gneiss from the island of Akilia, Southwest Greenland has been claimed to contain the earliest traces
of life on Earth in the form of biogenic carbonaceous matter encapsulated as inclusions in apatite crystals. Various lines
of evidence, including petrography, geochronology, field relations, and geochemistry, have, however, been presented that challenge
this interpretation. Textural relationships and geochemical signatures in this controversial gneiss presented here manifest
a complex, spatially variable metamorphic history that includes granulite- and amphibolite-facies overprints and metasomatism.
A peak metamorphic, granulite-facies, quartz–orthopyroxene–clinopyroxene–amphibole–magnetite assemblage is preserved in only
a few centimeter-scale layers within the 5-m-thick, quartz–amphibole–pyroxene gneiss unit. Calcite veinlets that appear to
postdate the peak metamorphism occur in pyroxene. The quartz–amphibole–pyroxene gneiss unit has subsequently experienced isochemical
(except hydration) amphibolite-facies alteration during which pyroxenes were retrogressed to amphiboles and magnetite, and
calcite was consumed. Parts of the quartz–amphibole–pyroxene gneiss that contain texturally late hornblende have experienced
metasomatic alteration by Al-carrying fluids. These fluids controlled the alteration of pyroxenes and amphiboles to hornblende,
and modified the trace-element composition by remobilizing LREE and Eu. Apatite has variable REE composition and 87Sr/86Sr in the quartz–amphibole–pyroxene gneiss, but on the local scale (cm) is in equilibrium with co-existing silicates. Effective
recrystallization of apatite crystals as well as co-existing silicates during several stages of the metamorphic history makes
the intact preservation of diagenetic apatite with encapsulated primary carbonaceous matter implausible. Hence, it is highly
unlikely that Akilia apatite could serve as repository of the earliest traces of life on Earth. 相似文献
65.
It is widely believed that successful colonization of ecosystems by non-native species will have catastrophic consequences
for the recipient system. Within the Mobile–Tensaw Delta, AL, exotic Eurasian milfoil (Myriophyllum spicatum) has been reported to trigger degradation of ecosystem structure and function. We evaluated the impacts of structurally complex
milfoil on food web structure and predator-prey interactions via comparisons with two native grasses, structurally simple
wild celery (Vallisneria americana) and the more complex water stargrass (Heteranthera dubia). While significant differences were not detected in the faunal compositions of milfoil and stargrass habitats, significant
differences between milfoil and wild celery were found. Laboratory experiments showed that rainwater killifish, a key contributor
to these differences, preferred milfoil over wild celery, but did not occupy milfoil more than stargrass. Subsequent experiments
indicated that survivorship was drastically lower in wild celery. Though many of the documented impacts of Eurasian milfoil
have been cast as detrimental, shelter-seeking organisms may perceive milfoil in the same way as other complex native species. 相似文献
66.
János Kovács Szabolcs Á. Fábián Gábor Varga Karoly Németh Corina Risso Francisco Nullo Gabor Kereszturi Titusz Bugya Szabolcs Á. Fábián Noémi L. Görcs István P. Kovács Bertalan Radvánszky Gabriella Barta Rudolf Musil Alice Ghiselli Marzio Merazzi Andrea Strini Roberto Margutti Michele Mercuriali Rauf Gardashov Daria Gushchina Boris Dewitte Martin Michálek Marián Putiš Christoph A. Hauzenberger Jindřich Šancer Martin Štrejbar Aneta Maleňáková George Migiros George D. Bathrellos Hariklia D. Skilodimou Theodoros Karamousalis 《Central European Journal of Geosciences》2011,3(2):229-229
67.
Alexandre Forest Jean-Éric Tremblay Yves Gratton Johannie Martin Jonathan Gagnon Gérald Darnis Makoto Sampei Louis Fortier Mathieu Ardyna Michel Gosselin Hiroshi Hattori Dan Nguyen Roxane Maranger Dolors Vaqué Cèlia Marrasé Carlos Pedrós-Alió Amélie Sallon Christine Michel Colleen Kellogg Jody Deming Elizabeth Shadwick Helmuth Thomas Heike Link Philippe Archambault Dieter Piepenburg 《Progress in Oceanography》2011,91(4):410-436
Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m−2 calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m−2, which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m−2, a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m−2), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m−2). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain. 相似文献
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