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1.
Guangjian Wu Baiqing Xu Chenglong Zhang Shaopeng Gao 《Environmental Earth Sciences》2010,61(6):1227-1237
This study measured the major element concentrations and compositions of atmospheric dust aerosol samples collected weekly
for nearly 2 years at Mt. Muztagata, a remote and high-elevation site (38°17′N, 75°01′E, 4,430 m) in the Eastern Pamirs. Inductively
coupled plasma mass spectroscopy (ICP–MS) results show that on the weekly timescale, air at Muztagata contained average element
Al concentrations of 842 ng m−3 between June 2004 and December 2005, and 509 ng m−3 between June 2005 and April 2006. The dust load over the Eastern Pamirs appears to be far lower (by more than an order of
magnitude) than those in northern China. The Muztagata dust aerosols show Ca/Al ratios (~0.7) and Fe/Al ratios (~0.7) that
differ from that in northern China. The general homogeneity exists in the major element compositions, expect Ca/Al ratios
which show minor but clear seasonal variations. Element ratios vary with aerosol concentration. Results indicate that concentrations
and compositions of Asian dust change significantly between different emission regions, and confirm that major element ratios
can be used to efficiently characterize the dust aerosols composition at different sites in northern China. 相似文献
2.
A case study for the ion–aerosol interactions is presented from the simultaneous measurements of mobility spectra of atmospheric
ions in the mobility range of 2.29 to 2.98 × 10 − 4 cm2 V − 1 s-1^{-1}(diameter range 0.41–109 nm) and of size distribution of atmospheric aerosol particles in the size ranges of 4.4–700 nm and
500–20,000 nm diameters made at Maitri (70°45′52′
′S, 11°44′2.7′
′E; 130 m above mean sea level), Antarctica, on two days January 17 and February 18, 2005, with contrasting meteorological
conditions. In contrast to January 17, on February 18, winds were stronger from the morning to noon and lower from the noon
to evening, atmospheric pressure was lower, cloudiness was more, the land surface remained snow-covered after a blizzard on
February 16 and 17 and the airmass over Maitri, descended from an altitude of ~3 km after an excursion over ocean. On these
days mobility spectra showed two modes, corresponding to intermediate ions and light large ions and an indication of additional
one/two maxima for small/cluster ions and heavy large ions. The small ions generated by cosmic rays, and the nucleation mode
particles generated probably by photochemical reactions grew in size by condensation of volatile trace gases on them and produced
the cluster and intermediate ion modes and the Aitken particle mode in ion/particle spectra. Particles in the size range of
9–26 nm have been estimated to grow at the rate of 1.9 nm h − 1 on February 18, 2005. Both, ions and aerosol particles show bimodal size distributions in the 16–107 nm size range, and comparison
of the two size distributions suggests the formation of multiple charged ions. Attachment of small ions to particles in this
bimodal distribution of Aitken particles together with the formation of multiple charged ions are proposed to result in the
light and heavy large ion modes. Growth of the nucleation mode particles on February 18, 2005 is associated with the passage
of the airmass over ocean. In contrast, though the ion size distributions were not much different, the aerosol size distributions
did not show a dominant peak for the formation and growth of nucleation mode particles on January 17. More measurements are
needed before the conclusion of this case study is generalized. 相似文献
3.
Arne P. Willner Axel Gerdes Hans-Joachim Massonne Alexander Schmidt Masafumi Sudo Stuart N. Thomson Graciela Vujovich 《Contributions to Mineralogy and Petrology》2011,162(2):303-327
The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is
composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde
garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s2-foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2σ) was determined from three four-point Lu–Hf
mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are
followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration
of mineral compositions at the rims and also aided Ar diffusion. An 40Ar/39Ar plateau age of white mica at 353 ± 1 Ma (1σ) indicates the time of cooling below 350–400°C. These temperatures were attained
at pressures of 0.2–0.3 GPa, indicative of an average exhumation rate of ≥1 mm/a for the period 390–353 Ma. Late hydrous influx
at 0.1–0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica.
At 284–295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid
intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm
of 10–12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent–continent
collisional setting. 相似文献
4.
Cr and Al diffusion in chromite spinel: experimental determination and its implication for diffusion creep 总被引:1,自引:0,他引:1
Diffusion coefficients of Cr and Al in chromite spinel have been determined at pressures ranging from 3 to 7 GPa and temperatures
ranging from 1,400 to 1,700°C by using the diffusion couple of natural single crystals of MgAl2O4 spinel and chromite. The interdiffusion coefficient of Cr–Al as a function of Cr# (=Cr/(Cr + Al)) was determined as D
Cr–Al = D
0 exp {−(Q′ + PV*)/RT}, where D
0 = exp{(10.3 ± 0.08) × Cr#0.54±0.02} + (1170 ± 31.2) cm2/s, Q′ = 520 ± 81 kJ/mol at 3 GPa, and V* = 1.36 ± 0.25 cm3/mol at 1,600°C, which is applicable up to Cr# = 0.8. The estimation of the self-diffusion coefficients of Cr and Al from
Cr–Al interdiffusion shows that the diffusivity of Cr is more than one order of magnitude smaller than that of Al. These results
are in agreement with patterns of multipolar Cr–Al zoning observed in natural chromite spinel samples deformed by diffusion
creep. 相似文献
5.
Ryan M. Morelli Chris C. Bell Robert A. Creaser Antonio Simonetti 《Mineralium Deposita》2010,45(5):461-480
The Homestake gold deposit, located in the Black Hills, South Dakota, USA, is one of the largest known hydrothermal gold deposits
globally, with total mining production exceeding 40 Moz Au. Rhenium–osmium geochronology of ore-associated arsenopyrite and
pyrrhotite was performed in an effort to delineate the timing of gold mineralization in relation to known tectonothermal events
in the northern Black Hills. Arsenopyrite yields a rhenium–osmium (Re–Os) age of 1,736 ± 8 Ma (mean squared weighted deviation = 1.6),
consistent with existing age constraints for gold mineralization, whereas Re–Os pyrrhotite data are highly scattered and do
not yield a meaningful mineralization age. This is taken to indicate that the Re–Os arsenopyrite chronometer is robust to
at least 400°C, whereas the Re–Os pyrrhotite chronometer is likely disturbed by temperatures of 300–350°C. The Re–Os arsenopyrite
age and initial Os ratio (0.28 ± 0.15) are interpreted to indicate that gold was introduced at ca. 1,730 Ma, coincident with
the onset of exhumation of crustal blocks and, possibly, the earliest intrusive phases of Harney Peak granite magmatism. New
in situ U–Pb monazite analyses from an aplite dike in the east-central Black Hills indicate that granite magmatism was a protracted
event, persisting until at least ca. 1,690 Ma. 相似文献
6.
The thermal stabilities and decay kinetics of three peroxy radicals (Centers #1, B and B′) and three other radiation-induced
defects (#3, C′ and E1′) in natural quartz from the high-grade McArthur River uranium deposit (Athabasca basin, Canada) have been investigated by
isochronal and isothermal annealing experiments and electron paramagnetic resonance (EPR) spectroscopy. Single-crystal EPR
spectra of isochronally (2 h) annealed quartz show that these centers all grow in intensity to 280°C and then decay with further
increase in temperature, but their disappearance temperatures differ markedly and depend on the initial concentrations (e.g.,
Center #1 in a dark smoky quartz is annealed out at 380°C, B and B′ at 420°C and #3 and C′ at 580°C). The isothermal decay
processes of these centers are all of the second order type. The calculated activation energies for the peroxy radicals [#1
and B + B′ at 0.36 (9) and 0.83 (8) eV, respectively] are smaller than those of Centers #3, C′ and E1′ [1.09 (8), 1.24 (8) and 1.45 (7) eV, respectively]. Gamma-ray irradiations of thermally bleached quartz restore a fraction
of the peroxy radicals, suggesting that their diamagnetic precursors are stable up to at least 800°C. The unusual decay characteristics
of “peroxy radicals” in quartz reported in the literature are shown to most likely arise from multiple radiation-induced defects.
These results have implications for not only applications of peroxy radicals in quartz for EPR dating but also better understanding
of thermoluminescence and cathodoluminescence spectra of this mineral. 相似文献
7.
Haimanti Biswas Mitali Dey Dipnarayan Ganguly Tarun K. De Sandip Ghosh Tapan K. Jana 《Estuaries and Coasts》2010,33(2):395-398
Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along
with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′
N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007.
Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal
variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods
and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered
by long-term changes in climate. 相似文献
8.
Hydrogeochemical study of the thermal and mineralized waters of the Banaz (Hamamboğazi) area,western Anatolia,Turkey 总被引:1,自引:1,他引:0
The Hamamboğazi spa in western Turkey was built around natural hot springs with discharge temperatures in the range of 30–54°C;
the waters have near neutral pH values of 6.50–7.10 and a TDS content between 2,694 and 2,982 mg/l. Thermal water with a temperature
of 47.5–73°C has been produced at 325 l/s from five wells since 1994, causing some springs to go dry. A management plan is
required in the study area to maximize the benefits of this resource, for which currently proposed direct uses include heating
in the district and greenhouses, as well as balneology in new spas in the area. The best use for the water from each spring
or well will depend on its temperature, chemistry and location. The thermal waters are mixed Na–Mg–HCO3–SO4 fluids that contain a significant amount of CO2 gas. The chemical geothermometers applied to the Hamamboğazi thermal waters yield a maximum reservoir temperature of 130°C.
Isotope results (18O, 2H, 3H) indicate that the thermal waters have a meteoric origin: rainwater percolates downward along fractures and faults, is heated
at depth, and then rises to the surface along fractures and faults that act as a hydrothermal conduit. The basement around
the Banaz Hamamboğazi resort is comprised of Paleozoic metamorphic schist and marbles exposed 8 km south and 15 km north of
Banaz. Mesozoic marble, limestone and ophiolitic complex are observed a few km west and in the northern part of Banaz. These
units were cut at a depth of 350–480 m in boreholes drilled in the area. Overlying lacustrine deposits are composed of fine
clastic units that alternate with gypsum, tuff and tuffites of 200–350 m thickness. The marble and limestones form the thermal
water aquifer, while lacustrine deposits form the impermeable cap. 相似文献
9.
In the present paper, an environmental analysis of Manikpur area, Korba coalfield, Bilaspur, M.P., India is undertaken. The
area lies in the Geological Survey of India Toposheet no. 64J/11 Latitude 82°42′54″–82°45′10″ North; Longitude 22°18′46″–22°19′46″
East. The paper deals with pollution and its control measures through the natural plants found in the vicinity of the coalmines,
namely Mangifera indica, Eucalyptus spp., Cassia siamea, Delbergia sissoo, etc. The plants control the Suspended Particulate Matter (SPM), Nitrous Oxides (NOx), Sulphur Oxides (SOx) of the mines
and mining site. Therefore, plantation in the mining site should be encouraged.
Received: 12 May 1998 · Accepted: 6 October 1998 相似文献
10.
E. Chongyi Wang Yong Yang Taibao Han Jiankang Hu Hongchang Yang Fengmei 《Environmental Geology》2009,56(7):1281-1293
Chongce Ice Cap (35°14′N, 81°07′E), located in the south margin of Taklimakan Desert, West Kunlun Mts. of China was sampled
by coring in 1992, and this provides us with climate proxy of high altitudes (6,530 m). Through analyzing the weather observation
stations surrounding Taklimakan Desert, the climate record of Hotan station was chosen to be the representative of low altitudes.
Wavelet analysis were used to investigate the climatic variations of patterns, cycles and frequencies of different altitudes
from 1954 to 1992, and different responses of different altitude surrounding Taklimakan Desert to global warming were recorded:
(1) coherent decline of snow accumulation rate and dust deposition of high altitude recorded in Chongce ice core; (2) coherent
increase of summer half-year precipitation and SAT of Hotan; (3) consistent variation tendency between dust deposit recorded
in Chongce ice core and Hotan spring sandstorm days; (4) opposite variation tendency between Hotan precipitation and Chongce
ice core snow accumulation rate and consistent cycles in general. By analyzing the mechanism of different responses, the predominant
factors were determined of different altitudes: (1) at the low altitude, the vapor supply is predominant, and more vapor supplying
means more precipitation; (2) at the high altitude, probably the population of dust aerosols which act as cloud ice nuclei
in high altitude takes advantage over the vapor supply to affect the precipitation, and so the dust aerosol population reducing
results in the wet deposition being reduced, thus the dust aerosol is the predominant factor. 相似文献
11.
Mualla Cengiz Çinku 《International Journal of Earth Sciences》2011,100(7):1633-1645
The Jurassic paleogeographic position of the Pontides is not well studied because of insufficient paleomagnetic data. For
this reason, a paleomagnetic study was carried out in order to constrain the paleolatitudinal drift of the Turkish blocks
during the Jurassic period. A total of 32 sites were sampled from volcanic and volcanoclastic rocks of the Lower/Middle Jurassic
Kelkit formation (Eastern Pontides), Mudurnu formation (Sakarya continent) and Upper Jurassic–Lower Cretaceous Ferhatkaya
formation exposed around Amasya region (Eastern Pontides). Rock magnetic experiments demonstrate that the main ferromagnetic
mineral is pseudo-single-domain titanomagnetite in these rocks. Paleomagnetic analysis revealed two main components of the
natural remanent magnetization during stepwise thermal and alternating field demagnetization. The first component is a low-coercivity
(unblocking temperature) component with a direction sometimes similar to that of the earth’s present field or a viscous component.
The second component, which is interpreted as the characteristic remanent magnetization (ChRM) direction, has low to high
coercivity properties between 20 and 100 mT or unblocking temperatures between 300 and 580°C. A positive fold test at the
95% level of confidence proved that the ChRM of the sites is primary. Paleomagnetic directions calculated for the Kelkit formation
in the Eastern Pontides have a mean direction of D = 334.8°, I = 49.7°, α
95 = 7.1° after tilt-correction. A mean direction of D = 332.2°, I = 48.5°, α
95 = 14.6° was obtained from the volcanoclastic rocks of the Mudurnu formation, and D = 324.3°, I = 43.3°, α
95 = 9.5° was calculated for the Upper Jurassic–Lower Cretaceous limestones/Ferhatkaya formation of the Amasya region. The Jurassic
rocks in the Eastern Pontides and Mudurnu region are considered to represent products of the rifted Neo-Tethys ocean, while
the Upper Jurassic–Lower Cretaceous sediments in Amasya are related to basin-filling materials. The data suggest that the
Kelkit formation was formed at 30.5°N paleolatitude and the equivalent Mudurnu formation at 29.5°N paleolatitude. The paleolatitude
of the Eastern Pontides indicates that this rifting block was separated from Eurasia by a marginal basin instead of being
a part of Eurasia. The lower paleolatitude of the Amasya region at 24.8°N in the Upper Jurassic to Lower Cretaceous clearly
indicates southward drift of the Turkish blocks during the Jurassic to Lower Cretaceous period together with the motion of
Eurasia. 相似文献
12.
Dehydration behavior of muscovite flake was investigated at 760–860°C by using in situ high-temperature IR microspectroscopy
for the OH absorption band around 3,620 cm−1. Isothermal kinetic heating experiments at each temperature gave detailed decrease curves of the OH band area with time.
These curves have been simulated by the first and second order reactions or mono- and two-dimensional diffusion processes.
The mono-dimensional diffusion was found to give the best fit to the experimental data and apparent diffusion coefficients
D were determined at 760–860°C with the activation energy of 290 ± 20 kJ/mol. The apparent diffusion coefficients D varied with the sample thickness L. This variation can be explained by an m layers model with a unit length of L′ with a constant diffusion coefficient D′. Therefore, the dehydration process might be rate-limited by mono-dimensional diffusion through tetrahedral silicate sheet
perpendicular to (001) planes of muscovite with a unit length of L′. 相似文献
13.
A. Kontny R. Engelmann J. C. Grimmer R. O. Greiling A. Hirt 《International Journal of Earth Sciences》2012,101(3):671-692
Magnetite-bearing mylonitic garnet–micaschists close to the major suture between the Baltica and Iapetus terranes (Seve Nappe
Complex, Scandinavian Caledonides) show very high anisotropy of magnetic susceptibility (AMS) with corrected degree of anisotropy
(P′) up to 4.8. Three different magnetic fabric types can be distinguished. They correspond to protomylonite (type I, P′ < 2), mylonite (type II, 2 < P′ < 3), and ultramylonite (type III, P′ > 3), respectively. The orientation of the ellipsoid axes from all applied magnetic fabric methods in this study is similar
with shallow dips of the metamorphic foliation toward WSW and subhorizontal, mostly NW–SE trending mineral lineation. Differences
between subfabrics were minimized under high shear strain as all markers tend to align parallel with the shear plane. The
very high anisotropies and mostly oblate ellipsoid shapes of type III correlate with high magnetic susceptibility (k
mean up to 55 × 10−3 SI units) and are related to the concentration of magnetite aggregates with shape-preferred orientation. They show a distinct
field dependence of magnetic susceptibility of up to 10% in the k
max-direction. We attribute this field dependence to a “memory” of high strains in the domain walls of the crystals acquired
during synkinematic magnetite growth during shear zone fabric development at temperatures of 550–570°C. 相似文献
14.
Physicochemical parameters of the formation of hydrothermal deposits: A fluid inclusion study. I. Tin and tungsten deposits 总被引:1,自引:0,他引:1
The author’s database, which presently includes data from more than 18500 publications on fluid and melt inclusions in minerals
and is continuing to be appended, was used to generalize results on physicochemical parameters of the formation of hydrothermal
deposits and occurrences of tin and tungsten. The database includes data on 320 tin and tin-tungsten deposits and occurrences
and 253 tungsten and tungstentin deposits around the world. For most typical minerals of these deposits (quartz, cassiterite,
tungsten, scheelite, topaz, beryl, tourmaline, fluorite, and calcite), histograms of homogenization temperatures of fluid
inclusions were plotted. Most of 463 determinations made for cassiterite are in the range of 300–500°C with maximum at 300–400°C,
while those for wolframite and scheelite (453 determinations) fall in the range of 200–400°C with maximum at 200–300°C. Representative
material on pressures of hydrothermal fluids included 330 determinations for tin and 430 determinations for tungsten objects.
It was found that premineral, ore, and postmineral stages spanned a wide pressure range from 70–110 bar to 6000–6400 bar.
High pressures of the premineral stages at these deposits are caused by their genetic relation with felsic magmatism. Around
50% of pressure determinations lie in the range of 500–1500 bar. The wide variations in total salinity and temperatures (from
0.1 to 80 wt % NaCl equiv and 20–800°C) were obtained for mineral-forming fluids at the tin (1800 determinations) and tungsten
(2070 determinations) objects. Most of all determinations define a salinity less than 10 wt % NaCl equiv. (∼60%) and temperature
range of 200–400°C (∼70%). The average composition of volatile components of fluids determined by different methods is reported.
Data on gas composition of the fluids determined by Raman spectroscopy are examined. Based on 180 determinations, the fluids
from tin objects have the following composition (in mol %): 41.2 CO2, 39.5 CH4, 19.15 N2, and 0.15 H2S. The volatile components of tungsten deposits (190 determinations) are represented by 56.1 CO2, 30.7 CH4, 13.2 N2, and 0.01 H2S. Thus, the inclusions of tungsten deposits are characterized by higher CO2 content and lower (but sufficiently high) contents of CH4 and N2. The concentrations of tin and tungsten in magmatic melts and mineral-forming fluids were estimated from analysis of individual
inclusions. The geometric mean Sn contents are 87 ppm (+ 610 ppm/−76 ppm) in the melts (569 determinations) and 132 ppm (+
630 ppm/−109 ppm) in the fluids (253 determinations). The geometric mean W values are 6.8 ppm (+ 81/−6.2 ppm) in the magmatic
melts (430 determinations) and 30 ppm (+ 144 ppm/−25 ppm) in the mineral-forming fluids (391 determinations). 相似文献
15.
D. M. Chate 《Natural Hazards》2011,56(1):81-91
A very high number concentration of aerosols in urban locations has a wide impact on health and ecosystem. The evolutions
of urban aerosol distributions at elapse-time 30 and 60 min are simulated at rainfall rates, 0.5 and 0.9 mm h−1 applying scavenging coefficients to initial aerosols number concentrations (before rain). We show how thunderstorm rain scavenges
number concentrations of urban aerosols in the ultrafine and fine modes. Elapsed-time evolutions of urban aerosols presented
in this work show washout of about 50–60 and 70–80% number concentrations of particles in the diameter range 0.02 μm ≤ D
p
≤ 0.1 μm after 30 and 60 min of thunderstorm rain when compared to initial number concentrations (before rain). Assuming
37 and 24% Sulfate and Organic Carbon particles in aerosol distributions in the urban environment and by applying scavenging
coefficients to these initial number concentrations, elapse-time evolutions after 30 and 60 min of thunderstorm rain are presented
in this work. The health impact is addressed in terms of depositions of particles within respiratory system by deposition
fractions as a function of particle size. For D
p
≤ 0.1 μm, 33 and 41% of initial number concentrations of Sulfate and Organic Carbon particles deposits within respiratory
system. Whereas elapsed-time evolutions show 60 and 80% cleansing of initial number concentrations of Sulfate and Organic
Carbon particles after 30 and 60 min of thunderstorm rain. 相似文献
16.
The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation
of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the
columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out
using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th
August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths
covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band
around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99
have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment.
The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance
of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the
present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due
to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal
variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease
during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed
maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater
as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high,
there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols
over the study region. 相似文献
17.
Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada 总被引:1,自引:0,他引:1
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment.
A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study
on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada,
with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel
originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88
species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution
in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well
as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth
(1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting
(σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay
fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction
as the single best-correlated variable. 相似文献
18.
In this study, reservoir temperatures of Balıkesir geothermal waters in northwestern Turkey are estimated with various geochemical
models. The geothermal fluids in the region are represented by Na–SO4, Na–HCO3 and Ca–HCO3 type waters with discharge temperatures up to 98°C. It was determined that the solubility of silica in most of the waters
is controlled by the chalcedony phase. Equilibrium states of the Balıkesir thermal waters studied by means of Na–K–Mg–Ca diagram,
mineral saturation calculations and activity diagrams in the system composed of Na2O–CaO–K2O–Al2O3–SiO2–H2O phases approximate a reservoir temperature of about 120°C. Most of the waters are found to be equilibrated with calcite,
chalcedony ± quartz and muscovite at predicted temperature ranges, similar to those calculated from the chemical geothermometers. 相似文献
19.
Mantle xenoliths in within-plate Cenozoic alkaline mafic lavas from NE Spain are used to assess the local subcontinental lithospheric
mantle geotherm and the influence of melting and metasomatism on its oxidation state. The xenoliths are mainly anhydrous spinel
lherzolites and harzburgites and gradations between, with minor pyroxenites. Most types show protogranular textures, but transitional
protogranular–porphyroclastic and equigranular lherzolites also exist. Different thermometers used in the estimates provide
higher subsolidus equilibrium temperatures for harzburgites (1,062 ± 29°C) than for lherzolites (972 ± 89°C), although there
is overlap; the lowest temperatures correspond to porphyroclastic lherzolites, whereas pyroxenites give the highest temperatures
(up to 1,257°C). Maximum pressures for subsolidus equilibrium of peridotites are at 2.0–1.8 GPa. Later they followed adiabatic
decompression and harzburgites registered lower pressures (1.02 ± 0.19 GPa) than lherzolites (1.41 ± 0.27 GPa). One pyroxenite
gives values consistent with the spinel lherzolite field (1.08 GPa). The shallowest barometric data are in agreement with
the highest local conductive geotherms, which implies that the lithosphere–asthenosphere boundary is at 70–60 km minimum depth.
Higher equilibrium temperatures for the harzburgites could be explained by the existence of mafic magma bodies or dykes at
the lower crust–mantle boundary. Paleo-fO2 conditions during partial melting as inferred from the covariation between V and MgO concentrations are mainly between QFM−1
and QFM−2 in log units. However, most thermobarometric fO2 estimates are between QFM−1 and QFM+1, suggesting oxidation caused by later metasomatism during uplift and cooling. 相似文献
20.
The revised titanium-in-zircon geothermometer was applied to Paleoproterozoic ultrahigh-temperature (UHT) granulites at Tuguiwula,
Inner Mongolia, North China Craton. The Tuguiwula granulites contain diagnostic UHT mineral assemblages such as sapphirine + quartz
and high alumina orthopyroxene + sillimanite + quartz, suggesting formation under temperatures of ca. 1,000°C and pressures
of up to 10 kbar. Here, we report detailed petrographic studies and ICP-MS data on titanium concentration in zircons associated
with the UHT assemblages. The zircons associated with sapphirine–spinel–sillimanite–magnetite assemblages have the highest
Ti concentration of up to 57 ppm, yielding a temperature of 941°C, and suggesting that the growth of zircons occurred under
ultrahigh-temperature conditions. The maximum temperatures obtained by the revised Ti-in-zircon geothermometer is lower than
the equilibrium temperature of sapphirine + quartz, indicating an interval of cooling history of the granulites from UHT condition
to ca. 940°C. Many of the zircons have Ti concentrations ranging from 10 to 33 ppm, indicating their growth or recrystallization
under lower temperatures of ca. 745–870°C. These zircons are interpreted to have recrystallized during the retrograde stage
indicated by microstructures such as cordierite rim or corona between spinel and quartz, and orthopyroxene–cordierite symplectite
around garnet. Previous geochronological study on the zircons of the Tuguiwula UHT granulites gave a mean U–Pb SHRIMP age
of 1.92 Ga. However, based on the Ti-in-zircon geothermometer results reported in this work, and considering the relatively
slow thermal relaxation of these rocks, we infer that the timing of peak UHT metamorphism in the Tuguiwula area could be slightly
older than 1.92 Ga. 相似文献