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921.
Ma?gorzata?Ba?magaEmail author Jan?Kucharski Jadwiga?Wyszkowska Agata?Borowik Monika?Tomkiel 《Environmental Earth Sciences》2014,72(7):2251-2262
A greenhouse pot experiment was conducted at the University of Warmia and Mazury in Olsztyn, with the aim of describing the influence of metazachlor on counts and biodiversity of soil microorganisms, soil enzymatic activity, physicochemical properties of soil and yield of spring oilseed rape. The first experimental factor was soil contamination with increasing rates of metazachlor: 0 (soil without the herbicide), 0.333 (recommended by the manufacturer), 6.666, 13.332, 26.665, 53.328, 106.656 and 213.312 mg kg?1 dm of soil, while the second factor comprised two dates of determination: 30 and 60 days after starting the experiment. The tested herbicide had an adverse effect on reproduction of all analyzed microorganisms: oligotrophic bacteria and their endospore forms, Azotobacter spp. bacteria, organotrophic bacteria, actinomycetes and fungi. The values of the colony development and eco-physiological diversity indices decreased under the influence of excessive doses of the herbicide. Also, significant fluctuation in the enzymatic activity of soil was observed in response to the higher doses of metazachlor and depending on the date of determinations. The herbicide had an invariably negative influence on the activity of soil enzymes, causing the inhibition of dehydrogenases, catalase, urease, acid phosphatase, alkaline phosphatase, arylsulfatase and β-glucosidase. The physicochemical status of soil depended significantly on the degree of soil contamination with the herbicide, same as the yield of spring oilseed rape. 相似文献
922.
Some of the world’s deepest goldmines operate below dolomitic karst aquifers in the Far West Rand (FWR) goldfield, South Africa. Associated impacts include the continuous dewatering of karst aquifers for over six decades and irreversible changes of the hydrogeological setting. Affecting an area of approximately 400 km2 by drawing down the water table up to 700 m, these impacts, and the large amounts of data generated in the process, are used as unique research opportunities to better understand the complex karst hydrology. The focus of this study is on predicting final water table elevations in rewatered aquifers after mining ceases taking the fact that mines hydraulically linked previously disconnected aquifers into account. While part 1 of this series develops the conceptual model, this second part utilises large sets of pertinent data to calculate actual flow rates for predicting the fate of dried up springs after mine closure. Following a Darcy-based approach first applied by Swart et al. (Environ Geol 44:751–770, 2003a) it is not only predicted that the springs will flow again but also shown that linear relationships exist between flow rates through a combined system of karst-fractured aquifers overlying the mine void and the associated hydraulic head driving them. This suggests that—at this scale—porous media-based equations can be meaningfully used to predict flow in non-porous media. 相似文献
923.
Paulo?J.?HidalgoEmail author Tyrone?O.?Rooney 《Contributions to Mineralogy and Petrology》2014,168(3):1011
The origin of adakite magmas remains controversial because initially the term adakite had petrogenetic significance implying an origin by direct melting of the eclogitized subducting oceanic crust. Many models have been produced for their origin, and until now there has not been a straightforward method to discriminate between these models in a given adakite suite. Here, we use detailed chronological and geochemical studies of selected adakitic edifices that allows for the determination of the magmatic output rate parameter (Qe), which has been correlated with the rates of magma generation deep within subduction zones. By providing temporal and eruption rate estimates, we provide constraints on the possible petrogenetic processes involved in the generation of adakite-like signatures. Adakite magmas derived from the melting of the subducting slab should be volumetrically insignificant when compared to the adakite-like magmas produced by typical arc magma generation processes. In this study, we use this observation and the extraordinary stratigraphic exposure from Miocene to present in an adakitic volcano in Panama and to study the temporal and chemical variation in erupted magmas to estimate rates of magma generation. Detailed chemical and geochronological analyses of Baru volcano indicate that the volcanic edifice was constructed in its entirety during the Quaternary and magmas display adakite-like features such as steep rare earth elements patterns, pronounced depletions in the heavy rare earth elements, low Y, high Sr, and high Sr/Y. The magmatic output rates (Qe) that we have calculated show that compared to other typical adakitic volcanoes, most of the volcanic edifice of Baru volcano was constructed extremely rapidly (<~213 k.a.) and in time frames that are similar to typical arc volcanoes. The observed chemical and mineralogical variation, coupled with the high magma production rates, indicate that Baru volcano is more representative of a typical arc volcano than a small-volume melt of the subducting oceanic crust. The technique we outline may have broader application in determining the petrogenetic conditions of other adakite suites. 相似文献
924.
Antal?Embey-IsztinEmail author Gábor?Dobosi Jean-Louis?Bodinier Delphine?Bosch G.?A.?Jenner Simone?Pourtales Olivier?Bruguier 《Contributions to Mineralogy and Petrology》2014,168(3):1054
Peridotite xenoliths erupted by alkali basaltic volcanoes in the western Pannonian Basin can be divided into two fundamentally contrasting groups. Geochemical characteristics of the abundant protogranular, porphyroclastic and equigranular nodules suggest that these samples originate from an old consolidated and moderately depleted lithospheric mantle domain. In contrast, the geochemical features of the worldwide rare, but in the Pannonian Basin relatively abundant, poikilitic xenoliths attest to a more complex evolution. It has been argued that the origin of the peculiar texture and chemistry may be intimately linked to melt/rock reactions at successively decreasing liquid volumes in a porous melt flow system. The most likely site where such reactions can take place is the asthenosphere–lithosphere boundary. In this context, poikilitic xenoliths may provide petrological and geochemical evidence for reactions between magmatic liquids issued from the uprising asthenosphere and the solid mantle rocks of the lithosphere. These reactions are important agents of the thermal erosion of the lithosphere; thus, they could have considerably contributed to the thinning of the lithosphere in the Pannonian region. We suggest that in the Pannonian Basin, there could be a strong relation between the unusual abundance of poikilitic mantle xenoliths and the strongly eroded lithosphere. 相似文献
925.
Frank?S.?SpearEmail author Jay?B.?Thomas Benjamin?W.?Hallett 《Contributions to Mineralogy and Petrology》2014,168(3):1059
The consequences of overstepping the garnet isograd reaction have been investigated by comparing the composition of garnet formed at overstepped P–T conditions (the overstep or “OS” model) with the P–T conditions that would be inferred by assuming garnet nucleated in equilibrium with the matrix assemblage at the isograd (the equilibrium or “EQ” model). The garnet nucleus composition formed at overstepped conditions is calculated as the composition that produces the maximum decrease in Gibbs free energy from the equilibrated, garnet-absent, matrix assemblage for the bulk composition under study. Isopleths were then calculated for this garnet nucleus composition assuming equilibrium with the matrix assemblage (the EQ model). Comparison of the actual P–T conditions of nucleation (the OS model) with those inferred from the EQ model reveals considerable discrepancy between the two. In general, the inferred garnet nucleation P–T conditions (the EQ model) are at a lower temperature and higher or lower pressure (depending on the coexisting calcic phase(s)) than the actual (OS model) nucleation conditions. Moreover, the degree of discrepancy increases with the degree of overstepping. Independent estimates of the pressure of nucleation of garnet were made using the Raman shift of quartz inclusions in garnet (quartz-in-garnet or QuiG barometry). To test the validity of this method, an experimental synthesis of garnet containing quartz inclusions was made at 800 °C, 20 kbar, and the measured Raman shift reproduced the synthesis conditions to within 120 bars. Raman band shifts from three natural samples were then used to calculate an isochore along which garnet was presumed to have nucleated. Model calculations were made at several temperatures along this isochore (the OS model), and these P–T conditions were compared to those computed assuming equilibrium nucleation (the EQ model) to estimate the degree of overstepping displayed by these samples. A sample from the garnet isograd in eastern Vermont is consistent with overstepping of around 10 degrees and 0.6 kbar (affinities of around 2 kJ/mole garnet). A sample from the staurolite–kyanite zone in the same terrane requires overstepping of around 50 °C and 2–5 kbar (affinities of around 10–18 kJ/mole garnet). A similar amount of overstepping was inferred for a blueschist sample from Sifnos, Greece. These results indicate that overstepping of garnet nucleation reactions may be common and pronounced in regionally metamorphosed terranes, and that the P–T conditions and paths inferred from garnet zoning studies may be egregiously in error. 相似文献
926.
Veena U. Joshi 《Journal of the Geological Society of India》2014,83(6):613-624
Nearly 4 million hectares of land in India is affected by rill and gully erosion. It is a severe form of soil erosion rendering vast tracts of lands into wastelands giving rise to the formation of badlands. Rate of land degradation through gullying is triggered recently due to the ill-advised landuse practices all over the country. The study area represents one such badland locality along the banks of Pravara river and two of its tributaries in the Deccan trap region, Maharashtra. The area is extensively reclaimed in the last two decades for agricultural practices. The rates in the cross profile changes as well as land lowering were measured with the help of a self fabricated micro-profilometer and erosion pin method. Five first order gullies were monitored using the micro-profilometer. Results of the micro-profilometer technique reveal considerable changes in the cross-sectional areas of individual gullies in this area, which shows the dynamic soil removal mechanism operating in this region. In addition to this, two well developed gully catchments were surveyed using a theodolite and erosion pins were installed in these basins in May 2007. After one year, the exposed pinheads were measured and net gain and net loss in the volume of the sediments were calculated for both the basins. The same practice continued in May 2009. After two years of monitoring the sediment yields were calculated. Average of these two years indicates an annual sediment yield of 1.79 kg/m2 for sample basin 1 and 0.76 kg/m2 for sample basin 2. The calculated yield was compared with the threshold values of soil tolerance limits and it was found that the area has crossed the threshold limit of soil tolerance. 相似文献
927.
Benjamin?J.?AndrewsEmail author Michael?Manga 《Contributions to Mineralogy and Petrology》2014,167(1):961
Magma mixing can occur in a fluid manner to produce banded pumice or in a brittle manner to form enclaves. We propose that the critical control on mixing style is a competition between developing networks of crystals in the intruding magma that impart a strength to the magma and melting and disrupting those networks in the host. X-ray computed tomography analysis demonstrates that banded pumice from the 1915 Mt. Lassen eruption lacks crystal networks. In contrast, rhyodacite hosts with mafic enclaves from Chaos Crags contain well-developed networks of large crystals. We present a one-dimensional conductive cooling model that predicts mixing style, either ductile or brittle, as a function of magma compositions, temperatures, and the size of the intruding dike. Our model relies on three assumptions: (1) Mixing is initiated by the injection of a hot dike into a cooler magma body with a yield strength; (2) when magma crystallinity exceeds a critical value, 13 vol% plagioclase, the magma develops a yield strength; and (3) when total crystallinity exceeds 40 vol%, the magma has a penetrative crystal network and is effectively solid. Importantly, because the two magmas are of different compositions, their crystallinities and viscosities do not have the same variations with temperature. As the intruding magma cools, it crystallizes from the outside in, while simultaneously, host magma temperature near the intruder rises. Mixing of the two magmas begins when the host magma is heated sufficiently to (1) disrupt the crystal network and (2) initiate convection. If the shear stress exerted by the convecting host magma on the dike is greater than the yield strength of the dike margin (and dike crystallinity does not exceed 40 %), then fluid mixing occurs, otherwise enclaves form by brittle deformation of the dike. Application of the model to magma compositions representative of Lassen and Chaos Crags shows that emplacement of dikes <1 m thick should produce enclaves, whereas thicker dikes should generate fluid mixing and form banded pumice within days to weeks of emplacement. Similar relationships apply to other modeled magmatic systems, including Pinatubo, Unzen, and Ksudach/Shtuybel’ volcanoes. For all studied systems, the absolute size of the intruding dike, not just its proportion relative to the host, influences mixing style. 相似文献
928.
Takeshi?KuritaniEmail author Takeyoshi?Yoshida Jun-Ichi?Kimura Toshiro?Takahashi Yuka?Hirahara Takashi?Miyazaki Ryoko?Senda Qing?Chang Yoshinori?Ito 《Contributions to Mineralogy and Petrology》2014,167(2):969
The conditions under which rear-arc magmas are generated were estimated using primary basalts from the Sannome-gata volcano, located in the rear of the NE Japan arc. Scoriae from the volcano occur with abundant crustal and mantle xenoliths, suggesting that the magma ascended rapidly from the upper mantle. The scoriae show significant variations in their whole-rock compositions (7.9–11.1 wt% MgO). High-MgO scoriae (MgO > ~9.5 wt%) have mostly homogeneous 87Sr/86Sr ratios (0.70318–0.70320), whereas low-MgO scoriae (MgO < ~9 wt%) have higher 87Sr/86Sr ratios (>0.70327); ratios tend to increase with decreasing MgO content. The high-MgO scoriae are aphyric, containing ~5 vol% olivine microphenocrysts with Mg# [100 × Mg/(Mg + Fe2+)] of up to 90. In contrast, the low-MgO scoriae have crustal xenocrysts of plagioclase, alkali feldspar, and quartz, and the mineralogic modes correlate negatively with whole-rock MgO content. On the basis of these observations, it is inferred that the high-MgO scoriae represent primary or near-primary melts, while the low-MgO scoriae underwent considerable interaction with the crust. Using thermodynamic analysis of the observed petrological features of the high-MgO scoriae, the eruption temperature of the magmas was constrained to 1,160–1,220 °C. Given that the source mantle was depleted MORB-source mantle, the primary magma was plausibly generated by ~7 % melting of a garnet-bearing spinel peridotite; taking this into consideration, and considering the constraints of multi-component thermodynamics, we estimated that the primary Sannome-gata magma was generated in the source mantle with 0.5–0.6 wt% H2O at 1,220–1,230 °C and at ~1.8 GPa, and that the H2O content of the primary magma was 6–7 wt%. The rear-arc Sannome-gata magma was generated by a lower degree of melting of the mantle at greater depths and lower temperatures than the frontal-arc magma from the Iwate volcano, which was also estimated to be generated by ~15 % melting of the source mantle with 0.6–0.7 wt% H2O at ~1,250 °C and at ~1.3 GPa. 相似文献
929.
M.?Yu.?KoreshkovaEmail author H.?Downes V.?A.?Glebovitsky N.?V.?Rodionov A.?V.?Antonov S.?A.?Sergeev 《Contributions to Mineralogy and Petrology》2014,167(2):973
Garnet granulite and pyroxenite xenoliths from the Grib kimberlite pipe (Arkhangelsk, NW Russia) represent the lower crust beneath Russian platform in close vicinity to the cratonic region of the north-eastern Baltic (Fennoscandian) Shield. Many of the xenoliths have experienced strong interaction with the kimberlite host, but in others some primary granulite-facies minerals are preserved. Calculated bulk compositions for the granulites suggest that their protoliths were basic to intermediate igneous rocks; pyroxenites were ultrabasic to basic cumulates. A few samples are probably metasedimentary in origin. Zircons are abundant in the xenoliths; they exhibit complex zoning in cathodoluminescence with relic cores and various metamorphic rims. Cores include oscillatory zircon crystallized in magmatic protoliths, and metamorphic and magmatic sector-zoned zircons. Recrystallization of older zircons led to the formation of bright homogeneous rims. In some samples, homogeneous shells are surrounded by darker convoluted overgrowths that were formed by subsolidus growth when a change in mineral association occurred. The source of Zr was a phase consumed during a reaction, which produced garnet. Late-generation zircons in all xenoliths show concordant U–Pb ages of 1.81–1.84 Ga (1,826 ± 11 Ma), interpreted as the age of last granulite-facies metamorphism. This event completely resets most zircon cores. An earlier metamorphic event at 1.96–1.94 Ga is recorded by some rare cores, and a few magmatic oscillatory zircons have retained a Neoarchaean age of 2,719 ± 14 Ma. The assemblage of metaigneous and metasedimentary rocks was probably formed before the event at 1.96 Ga. Inherited magmatic zircons indicate the existence of continental crust by the time of intrusion of magmatic protoliths in the Late Archaean. The U–Pb zircon ages correspond to major events recorded in upper crustal rocks of the region: collisional metamorphism and magmatism 2.7 Ga ago and reworking of Archaean rocks at around 1.95–1.75 Ga. However, formation of the granulitic paragenesis in lower crustal rocks occurred significantly later than the last granulite-facies event seen in the upper crust and correlates instead with retrograde metamorphism and small-volume magmatism in the upper crust. 相似文献
930.
Shahrzad?ManoochehriEmail author Max?W.?Schmidt 《Contributions to Mineralogy and Petrology》2014,168(6):1091
The time scales and mechanics of gravitationally driven crystal settling and compaction is investigated through high temperature (1,280–1,500 °C) centrifuge-assisted experiments on a chromite-basalt melt system at 100–1,500g (0.5 GPa). Subsequently, the feasibility of this process for the formation of dense chromite cumulate layers in large layered mafic intrusions (LMIs) is assessed. Centrifugation leads to a single cumulate layer formed at the gravitational bottom of the capsule. The experimentally observed mechanical settling velocity of a suspension of ~24 vol% chromite is calculated to be about half (~0.53) of the Stokes settling velocity, with a sedimentation exponent n of 2.35 (3). Gravitational settling leads to an orthocumulate layer with a porosity of 0.52 (all porosities as fraction). Formation times for such a layer from a magma with initial chromite contents of 0.1–1 vol% are 140–3.5 days, equal to a growth rate of 0.007–0.3 m/day for grain sizes of 1–2 mm. More compacted chromite layers form with increasing centrifugation time and acceleration through chemical compaction: An increase of grain contact areas and grain sizes together with a decrease in porosity is best explained by pressure dissolution at grain contacts, reprecipitation and grain growth into the intergranular space and a concomitant expulsion of intergranular melt. The relation between the porosity in the cumulate pile and effective pressure integrated over time (Δρ · h · a · t) is best fit with a logarithmic function, in fact confirming that a (pressure) dissolution–reprecipitation process is the dominant mechanism of compaction. The experimentally derived equation allows calculating compaction times: 70–80 % chromite at the bottom of a 1-m-thick chromite layer are reached after 9–250 years, whereas equivalent compaction times are 0.2–0.9 years for olivine (both for 2 mm grain size). The experiments allow to determine the bulk viscosities of chromite and olivine cumulates to be of magnitude 109 Pa s, much lower than previously reported. As long as melt escape from the compacting cumulate remains homogeneous, fluidization does not play any role; however, channelized melt flow may lead to suspension and upward movement of cumulate crystals. In LMIs, chromitite layers are typically part of a sequence with layers of mafic minerals, compaction occurs under the additional weight of the overlying layers and can be achieved in a few years to decades. 相似文献