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1.
An example of identifying karst groundwater flow 总被引:3,自引:2,他引:1
Hydrogeological investigations for the purpose of regulating the karst aquifer were carried out in the mountain massif of
Kucaj in the Carpatho-Balkan range of eastern Serbia. Different geophysical methods were applied in order to identify the
position of karstified zones with active circulation of karst underground streams. Especially good results were obtained by
using the spontaneous potential method for the exploration and construction of boreholes and wells. In the valleys of Crni
Timok and Radovanska reka the measurements have been carried out upstream along the whole width of the alluvium to the limestone
periphery. A number of positive and negative anomalies have been recorded. In the centres of positive anomalies several boreholes
were located: HG-19 (centre of anomaly +30 mV, total length of the biggest cavern is 9 m); HG-1 (+20 mV, cavern of 2 m); HG-15
(max. +114 mV, effective cavernousness is 17%).
Received: 20 February 1995 · Accepted: 12 September 1997 相似文献
2.
Orthopyroxene porphyroblasts zoned to interiors abnormally low in Al and Cr and containing numerous inclusions of olivine
occur in some spinel peridotite xenoliths from the Colorado Plateau. Rims of these orthopyroxene grains contain 2.5–3.0 wt%
Al2O3, consistent with equilibration in spinel peridotite at temperatures near 850 °C, but interiors contain as little as 0.20
wt% Al2O3 and 0.04 wt% Cr2O3. The Al-poor compositions are inferred to have equilibrated in chlorite peridotite, before porphyroblast growth during heating
and consequent reactions that eliminated talc, tremolite, and chlorite. The distinctive orthopyroxene textures are inferred
to have formed during reaction of talc and olivine. Rare intergrowths of orthopyroxene plus diopside are attributed to olivine-tremolite
reaction. Al and Cr have gradients at grain rims that appear little modified by diffusion, but divalent elements are almost
homogeneous throughout the porphyroblasts. Judging from the relative gradients, diffusion of Ca was at least 100 times faster
than that of Al and Cr at the temperatures near and below 850 °C. Diffusion of Al and Cr was most effective along subgrain
boundaries, and along these boundaries it appears to have been at least ten times faster than within the lattice: diffusion
along such boundaries may be a dominant mechanism for re-equilibration of orthopyroxene at low mantle temperatures. Orthopyroxene
with similar low Al and Cr occurs in chlorite peridotite xenoliths from the Navajo field, 300 km east of the Grand Canyon
localities, and in spinel peridotite xenoliths from the Sierra Nevada, 500 km west across the extended Basin and Range province.
Chlorite peridotite may therefore have been a significant minor component in much of the mantle lithosphere of western North
America, although evidence for it would be erased at the higher temperatures recorded by xenoliths from the Basin and Range.
Chemical changes during hydration may have been important in the evolution of these mantle volumes, and the case for addition
of Sr is particularly strong. Dehydration reactions during heating could have influenced patterns of extension and crustal
magmatism.
Received: 1 July 1996 / Accepted: 2 December 1996 相似文献
3.
E. Hejl D. Coyle Nand Lal P. Van den Haute G. A. Wagner 《International Journal of Earth Sciences》1997,86(1):210-219
Since 1985, apatite fission-track analysis was applied to more than 70 samples from surface outcrops and shallow boreholes
at the western margin of the Bohemian massif. Apatite ages were determined by the grain-population method. Additional information
from the frequency distributions of fully confined spontaneous tracks was used for modelling of t–T paths in the low-temperature
range (<120 °C). Seven zircon samples were dated by the external detector method. Zircon ages between 283 and 215 Ma indicate
unroofing during the Permian molasse stage and the Triassic. Tectonic quiescence and slow subsidence prevailed from the Jurassic
until the middle Cretaceous. In the basement area south of Weiden, a Mesozoic partial annealing zone (for apatite fission
tracks) is now exposed at the surface. Farther north, the basement was affected by stronger Cretaceous and Palaeogene erosion,
which yielded cooling ages between 110 and 49 Ma. This second period of post-Variscan denudation was correlated to reverse
faulting along the Franconian Line.
Received: 30 June 1996 / Accepted: 24 October 1996 相似文献
4.
Synchronous deformation and hydrothermal activity in the shear zone hosted high-sulphidation Au-Cu deposit at Peak Hill, NSW, Australia 总被引:1,自引:0,他引:1
A. Allibone 《Mineralium Deposita》1998,33(5):495-512
Altered and mineralised rocks at Peak Hill, are confined to a 300–500 m wide, north-south striking, steeply dipping, shear
zone that is flanked by the Mingelo Volcanics along its western side, and Cotton Formation siltstones along its eastern side.
This shear zone is defined by extensive zones of cataclasite and strongly foliated micaceous schists in marked contrast to
the largely undeformed nature of the adjacent rocks. Advanced argillic assemblages (quartz-kaolinite-pyrite ± alunite ± illite)
occur throughout the core of the Peak Hill deposit. Propylitic assemblages, including albite, quartz, interlayered chlorite-smectite,
illite and ankerite, and a narrow discontinuous zone of argillic (quartz-illite-pyrite) alteration are developed in the Mingelo
Volcanics along the western side of the deposit. Propylitic, argillic and advanced argillic assemblages are overprinted by
an internally zoned phase of phyllosilicate alteration that grades inwards from a peripheral sericite-clay-chlorite assemblage,
through phyllic assemblages (muscovite/illite-pyrite ± paragonite) to a pyrophyllite-pyrite ± diaspore ± andalusite altered
core. Au-Cu mineralisation is hosted by barite-pyrite veins that cut the advanced argillic assemblage, but pre-date the phyllosilicate-dominated
alteration. Native Au (lacking Ag), calaverite, Te-rich tennantite-tetrahedrite (goldfieldite), chalcopyrite, covellite and chalcocite occur in the barite-pyrite veins. No ore-bearing minerals were detected in any of
the alteration assemblages. The total gold content of the Peak Hill deposit is currently 720 K ounces and this includes 100 K
ounces of unmined reserves. Within the shear zone phyllosilicate minerals are developed in strain shadows and partly define
the stretching lineation associated with dip-slip movement. The zonation within the phyllosilicate assemblages mimics the
geometry of bends in the shear zone and minor internal structures. These textures indicate that the phyllosilicate alteration
developed synchronous with movement on the shear zone. Earlier advanced argillic alteration and mineralisation are developed
in rocks derived from both sides of the shear zone. Hydrothermal activity associated with the earlier advanced argillic alteration
was therefore either synchronous with juxtaposition of these distinct rock units, or occurred during a later phase of movement
on the shear zone. Cross-cutting fibrous textures in the auriferous barite-pyrite veins indicate that repeated fracturing
of the advanced argillic altered rocks accompanied development of successive generations of auriferous veins. Concentrations
of auriferous veins are localised in steeply plunging shoots that are oriented parallel to the stretching lineation in the
shear zone. These features all indicate movement on the host shear zone accompanied each phase of hydrothermal activity in
the Peak Hill deposit. The location, alteration zonation and distribution of mineralised veins within the deposit are intimately
controlled by deformation on the host shear zone synchronous with hydrothermal activity. The development of high-sulphidation
hydrothermal systems synchronous with deformation along brittle-ductile shear zones is a predictable consequence of intrusive
activity during deformation in areas characterised by a high geothermal gradient. The close relationship between tectonism
and hydrothermal activity indicates that these deposits are likely to be located in the vicinity of regional-scale shear zones.
Deposits are likely to be aligned parallel to the regional-scale structural “grain” and restricted to areas of conspicuous
deformation as is the case at Peak Hill (and Temora, NSW). Aluminous alteration zones concentrated in the vicinity of regional-scale
structures in the Carolina Slate Belt may be a further example of this style of hydrothermal activity.
Received: 30 September 1996 / Accepted: 28 August 1997 相似文献
5.
To accurately measure the pH, Eh, EC and temperature of groundwater retrieved from boreholes, a deep groundwater sampling
apparatus was developed which provided sensory measurements both in situ and in a flow-through cell at ground level. Under
a pressure of 1×106 Pa the in situ accuracy of the apparatus sensor was within the following limits: pH ±0.2, temperature ±0.1°C, Eh ±10 mV,
and EC ±2.4%. The measuring and sampling of deep groundwater from a borehole of more than 1000 m in depth was performed continuously
for 30 days. Values of pH were the same for the in situ sensor, the flow-through cell sensor and the laboratory measurements
of the sampled water. At the beginning of the sampling period, Eh values of the in situ sensor indicated deep groundwater
conditions. The apparatus is particularly useful for Eh measurement. Chemical composition and stable isotope ratios indicated
that the groundwater sampled from more than 1000 m depth was a connate water with a chemical composition slightly different
from seawater of the present time, and the groundwater retrieved from 800 m depth was a meteoric water. Natural radioactive
elements are thought to be the origin of the tritium in the groundwater retrieved from the 1000 m depth.
Received: 6 August 1996 / Accepted: 22 October 1996 相似文献
6.
A. Pavese 《Physics and Chemistry of Minerals》1999,26(8):649-657
Numerical simulations, using empirical interatomic potentials within the framework of lattice dynamics and quasi-harmonic
approximation, have been carried out to model the behaviour of the structure and of some thermoelastic properties of pyrope
at high pressure and high temperature conditions (0–50 GPa, 300–1500 K). Comparison with observed data, available as a function
either of P or of T, suggests that the pressure effects are satisfactorily modelled, whilst the effect of T on the simulations is underestimated. The cell edge, bond lengths and polyhedral volumes have been studied as a function
of P along five isotherms, spaced by 300 K steps. These isotherms tend to converge at high pressure, which demonstrates that the
pressure effects become dominant compared to those of thermal origin in affecting the structural properties far from ambient
conditions. The cell parameter, bond distances, and other structural and thermoelastic quantities determined through simulations
have been parametrised as a function of P and T by polynomial expansions. Bulk modulus and thermal expansion have been discussed in the light of the high-temperature-Birch-Murnaghan
and of the Vinet P – V – T equations of state. The predictions of the bulk modulus versus P and T from the present calculations and from the Vinet-EOS agree up to 10 GPa, but they differ at higher pressure.
Received: 23 October, 1998 / Revised, accepted: 23 April, 1999 相似文献
7.
Mobility of components in metasomatic transformation and partial melting of gneisses: an example from Sri Lanka 总被引:2,自引:1,他引:1
L. L. Perchuk O. G. Safonov T. V. Gerya B. Fu D. E. Harlov 《Contributions to Mineralogy and Petrology》2000,140(2):212-232
Reaction textures, fluid inclusions, and metasomatic zoning coupled with thermodynamic calculations have allowed us to estimate
the conditions under which a biotite–hornblende gneiss from the Kurunegala district, Sri Lanka [hornblende (NMg=38–42) + biotite (NMg=42–44) + plagioclase + quartz + K-feldspar + ilmenite + magnetite] was transformed into patches of charnockite along shear
zones and foliation planes. Primary fluid inclusion data suggest that two immiscible fluids, an alkalic supercritical brine
and almost pure CO2, coexisted during the charnockitisation event and subsequent post-peak metamorphic evolution of the charnockite. These metasomatic
fluids migrated through the amphibolite gneiss along shear zones and into the wallrock under peak metamorphic conditions of
700–750 °C, 5–6 kbar, and afl
H2O=0.52–0.59. This resulted in the formation of charnockite patches containing the assemblage orthopyroxene (NMg=45–48) + K-feldspar (Or70–80) + quartz + plagioclase (An28) in addition to K-feldspar microveins along quartz and plagioclase grain boundaries. Remnants of the CO2-rich fluid were trapped as separate fluid inclusions. The charnockite patches show the following metasomatic zonation patterns:
– a transition zone with the assemblage biotite (NMg= 49–51) + hornblende (NMg = 47–50) + plagioclase + quartz + K-feldspar + ilmenite + magnetite;
– a KPQ (K-feldspar–plagioclase–quartz) zone with the assemblage K-feldspar + plagioclase + orthopyroxene (NMg=45–48) + quartz + ilmenite + magnetite;
– a charnockite core with the assemblage K-feldspar + plagioclase + orthopyroxene (NMg = 39–41) + biotite (NMg=48–52) + quartz + ilmenite + magnetite.
Systematic changes in the bulk chemistry and mineralogy across the four zones suggest that along with metasomatic transformation,
this process may have been complicated by partial melting in the charnockite core. This melting would have been coeval with
metasomatic processes on the periphery of the charnockite patch. There is also good evidence in the charnockitic core that
a second mineral assemblage, consisting of orthopyroxene (NMg= 36–42) + biotite (NMg=50–51) + K-feldspar (Or70–80) + quartz + plagioclase (An28–26), could have crystallised from a partial melt during cooling from 720 to 660 °C at decreasing afl
H2O from 0.67 to 0.5. Post-magmatic evolution of charnockite at T < 700 °C resulted in fluids being released during the crystallisation
of the charnockitic core. These gave rise to the formation of late stage rim myrmekites along K-feldspar grain boundaries
as well as late stage biotite, cummingtonite, and carbonates.
Received: 15 September 1999 / Accepted: 8 June 2000 相似文献
8.
M. I. Kuzmin E. B. Karabanov A. A. Prokopenko V. F. Gelety V. S. Antipin D. F. Williams A. N. Gvozdkov 《International Journal of Earth Sciences》2000,89(2):183-192
With this paper we present a first attempt to combine the direct results on lithology, composition and age dating in the
boreholes BDP-93, BDP-96 and BDP-97 with geological and seismic data from the areas where those sections were drilled. The
sedimentary environments represented by the BDP boreholes are markedly different and possess characteristic lithological features.
The results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions
of the Lake Baikal rifting dynamics. Neither the basin-wide unconformity interpreted from seismic data, nor the interpreted
change from shallow-water to deep-water facies at the boundary of the seismic stratigraphic complexes were found in the BDP-96
boreholes on Academician Ridge. Also, lithology does not support the proposed reconstructions of intense lake level fluctuations
and transgressions during the Pliocene at Academician Ridge. The continuous deep-water hemipelagic sedimentation at Academician
Ridge has existed for the past 5 Ma. The beginning of an intense rifting phase of the Neobaikalian sub-stage and related drastic
changes in sedimentation processes were interpreted on seismic sections as the basin-wide unconformity B10. Different age
estimates for this boundary ranged from Late Pliocene (3.5 Ma) to Plio-Pleistocene boundary. As shown by BDP-96 borehole,
B10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact.
The new age for this boundary in BDP-96 is approximately 2.5 Ma. This new age constraint suggests that the upper sedimentary
strata of Northern Baikal (1.5–1.7 km thick) have formed during the past 2.5 Ma with average sedimentation rates of 60–70 cm/ka.
The BDP-93 boreholes at Buguldeika suggest that uplift in Primorsky Range took place prior to 1.07–1.31 Ma, a date which exceeds
the age of previous geological models.
Received: 12 March 1999 / Accepted: 10 February 2000 相似文献
9.
Marine contamination of groundwater may be caused by seawater intrusion and by salt spray. The role of both processes was
studied in the Cyclades archipelago on four small islands (45–195 km2) whose aquifers consist essentially of fractured, weathered metamorphic rocks. Annual rainfall ranges from 400 to 650 mm
and precipitation has high total dissolved solids contents of 45–223 mg l–1. The chemical characteristics of the groundwater, whose salinity is from 0.4 to 22 g l–1, are strongly influenced by seawater intrusion. However, the effect of atmospheric input is shown in certain water sampling
locations on high ground elevation where the dissolved chloride contents may attain 200 mg l–1.
Received: 14 November 1995 · Accepted: 9 September 1996 相似文献
10.
Alfons M. van den Kerkhof Geoffrey H. Grantham 《Contributions to Mineralogy and Petrology》1999,137(1-2):115-132
In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10 m in width in the normally
garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous
pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration
reaction Bt + Qtz → Opx + Kfs + H2O and the reaction of Grt + Qtz → Opx + Pl were responsible for the charnockitization. The compositions of fluid inclusions
show systematic variation with: (1) the Port Edward Enderbite being dominated by CO2 and N2 fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18–23 EqWt% NaCl; (3) the charnockitic
aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity
with minor CO2. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range
(up to 390 °C) compared to the fluid inclusions in granite (mostly <250 °C). Contrary to fluid-controlled charnockitization
(brines, CO2) which may have taken place along shear zones away from the intrusive body, the present “proximal” charnockitized granite
formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of “dry”
enderbitic magma into “wet” granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing
textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the
Port Edward Enderbite suggests intrusion at temperatures of ∼1000–1050 °C into country rock with temperature of <700 °C. The
temperature of aureole formation must have been between ∼700 °C (breakdown of pyrite to form pyrrhotite) and ∼1000 °C. Charnockitization
was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the
release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed
to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions
and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity
inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an
isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred.
Received: 8 November 1998 / Accepted: 21 June 1999 相似文献
11.
We have analyzed the chemical composition and boron isotope composition of tourmaline from tourmalinites, granite and a quartz-tourmaline
vein from the Deri ore zone and from a pegmatitic band in the Rampura-Agucha ore body. These two Proterozoic massive sulfide
deposits occur in the Aravalli-Delhi orogenic belt, Rajasthan, northwest India. Tourmaline from stratiform tourmalinites closely
associated with the massive sulfides in the Deri deposit have preserved their original chemical compositions despite regional
and thermal metamorphism in the area. These tourmalines have low Fe/(Fe + Mg) ratios (0.19–0.30; mean 0.26) that suggest formation
close to the sediment-sea water interface. The δ11B values (−15.5 and −16.4‰) are compatible with boron derived from leaching of argillaceous sediments and/or felsic volcanics
underlying the original massive sulfide deposit during its formation. Boron isotope compositions measured in tourmaline from
a post-ore granite and quartz-tourmaline vein in the Deri deposit indicate that boron in these tourmalines was derived from
the tourmalinites produced during ore formation. The boron isotope systematics of a coarse brown tourmaline crystal from a
pegmatitic band on the hanging wall contact of the Rampura-Agucha deposit indicate that 45 ± 25% of the boron within the original
tourmaline was lost during upper amphibolite facies regional metamorphism.
Received: 3 April 1996 / Accepted: 11 April 1996 相似文献
12.
J. Garcia-Guinea P. D. Townsend L. Sanchez-Muñoz J. M. Rojo 《Physics and Chemistry of Minerals》1999,26(8):658-667
Laboratory driven ionic thermal exchange of alkali feldspars from K to Na produces samples which are strongly luminescent
in the ultraviolet region near 320 nm. The sites providing this luminescence are suggested as being correlated with the motion
of Na atoms along interface-interphases of the material (i.e. with Na-O bond fracture). The thermoluminescence peaks show
multi-order kinetics. Thermal preheatings of low albite sensitize the feldspar lattice with respect to thermoluminescence
generated by exposure to UV irradiation and heating produces a strong blue luminescence spread over the range 350 nm to 500 nm
band in feldspars. The upper temperature for thermoluminescence in feldspars is ∼300 °C, which is also the point where ionic
conductivity of albite (010) begins, but the 300 °C region is also the starting point of a large second glow peak in adularia.
Whilst it seems appropriate to link the Na motion to the 350–500 nm emission, it is unclear whether these changes are the
result of the large anisotropic thermal vibration of Na atoms or the massive Na jumps that occur when the lattice reaches
300 °C. A speculative model is considered in which the UV TL emissions of natural minerals are linked to different interface-interphases
(grain boundaries, exsolution limits, twinning planes, antiphase domains). Increased interface coherency energies are related
to the kinetic order and the spectral position of luminescence emission peaks.
Received: 3 December 1998 / Revised, accepted: 17 April 1999 相似文献
13.
Molecular dynamics simulations employing a many-body embedding potential model have been conducted to calculate both bulk
and shear viscosity of pure liquid iron at the Earth's outer core conditions. Liquid iron shear viscosity thus obtained is
in the order of 10−2 Pa · s and is in close agreement with previous estimates. In contrast, liquid iron bulk viscosity is in the order of 10−3 to 10−4 Pa · s and is much smaller than previous estimates. Consequently, the ratio of bulk to shear viscosity is close to 0.1. This
value disagrees with both the common speculation that bulk and shear viscosities are equal at ambient pressure, and the previous
inference that bulk viscosity of liquid iron is much larger than shear viscosity at outer core conditions. Potential implications
of present data are also briefly given for the dynamic state of the outer core.
Received: 9 April 1999 / Revised, accepted: 7 June 1999 相似文献
14.
S. J. Appleyard 《Environmental Geology》1996,28(2):106-110
Drilling of 15 boreholes at a disused liquid waste disposal site near Perth, Western Australia, has indicated that a contamination
plume extends about 1000 m in a southerly direction from the site in the direction of groundwater flow. The plume is up to
600 m wide and 5–40 m thick. Chemical and microbiological analyses have indicated that contaminated groundwater contains high
concentrations of ammonia, iron, and bacteria at levels that commonly exceed national drinking water guidelines. It is likely
that a proposed water supply production well in the path of the contamination plume will have to be abandoned, and additional
wells may have to be abandoned if the plume continues to extend in the direction of groundwater flow. There is currently insufficient
information to indicate whether the plume is continuing to expand, but studies on similar plumes in the Perth metropolitan
area have indicated that contaminated groundwater can move at rates up to 100 m yr–1. Several other liquid waste disposal sites are now located in residential areas of Perth where wells are used for garden
irrigation. Further work is required to ensure that there is no potential impact of groundwater contamination on public health
in these areas.
Received: 31 July 1995 · Accepted: 18 September 1995 相似文献
15.
Analyses of deterioration of the Cappadocian tuff, Turkey 总被引:8,自引:3,他引:5
The Cappadocian tuff contains unique erosional features, the so-called fairy chimneys, some of which in the past were dwelled
in and contain valuable wall paintings. These historical heritages, however, are undergoing chemical and physical deterioration
due to atmospheric effects. For the conservation studies, understanding of the deterioration phenomenon of the tuff is essential.
In this study, engineering geological and physicochemical characteristics of the tuff were determined. The durability of the
tuff was assessed through wetting-drying, freezing-thawing, and salt crystallization. The test results suggest that chemical
weathering may be traced to a depth of 2 cm below lichen-covered surfaces and 20 cm adjacent to discolored joint walls. Based
on durability assessment methods, the tuff may be classified as having poor to very poor durability.
Received: 16 December 1996 · Accepted: 3 April 1997 相似文献
16.
Analysis and remedies of landslides of cut slopes due to the presence of weak cohesive layers within stronger formations 总被引:4,自引:0,他引:4
Several cases of instability of cut slopes along major highways in Jordan were reviewed in this study, in some detail. Emphasis
was placed on the Amman-Irbid highway, but some cases along the Na'ur-Dead Sea highway were also reviewed, with the aim of
establishing a wider database of case-studies and examining all possible mechanisms and factors influencing stability. The
study showed that major cut slope failures were caused by the presence of weak cohesive layers (mainly clayey marl) interbedded
within mostly stronger formations, in addition to the steep cutting angles and unfavorable dip of strata combined with relatively
high piezometric surface brought about by poor surface and subsurface drainage. No remedies were implemented to stabilize
major cut slope failures (at km 39+200, 44+300, and 56+400) along the Irbid-Jerash-Amman highway. The three major cut slope
failures require extensive remedial work and probably advanced geotechnology, which is expected to be expensive. To investigate
the influence of various parameters on slope stability, several analyses were performed in addition to back analyses to determine
shear strength parameters; parametric sensitivity studies were also performed on some cases. Data was obtained from previous
investigations by local and international firms and were screened and modified where needed before being used in stability
analyses. Considerable difference between back analysis and test result values for shear strength parameters were observed
in many cases. Failure surfaces and mechanisms were accurately depicted in most cases, allowing back analyses to be performed
with considerable confidence. The effective residual shear strength parameters for clayey marl needed for stability analysis
were found to be: c
r
′=5–18 kPa, and φ
r
′=13°–18°. The relation between total annual rainfall and occurrence of landslides was investigated; it was shown that all
landslides occurred in years of very high rainfall, with values always exceeding 400 mm. The probability of exceeding the
average total annual rainfall was found to be approximately 0.42 for the three gauging stations considered.
Received: 28 October 1996 · Accepted: 23 September 1997 相似文献
17.
Tidal freshwater marshes exist at the interface between watersheds and estuaries, and thus may serve as critical buffers
protecting estuaries from anthropogenic metal pollution. Bi-weekly samples of newly deposited marsh sediments were collected
and analyzed for Cu, Zn, and Fe concentrations over 21 months from July 1995 to March 1997 in five distinct habitats at the
head of Bush River, Maryland. Bi-weekly anthropogenic metal enrichments ranged from 0.9–4.7. Anthropogenic excess metal loadings
averaged over 1996 ranged from 6–306 and 25–1302 μg cm−2 year−1 between sites for Cu and Zn, respectively. Based on Fe-normalized trace metal signatures, Susquehanna River sediment does
not significantly contribute to upper Bush River. Organic matter was found to dilute total metal concentrations, whereas past
studies suggested organics enhance labile metal content. Analysis of metal input pathways shows that marsh metals are primarily
imported from nearby subtidal accumulations of historic watershed material by tidal flushing.
Received: 29 April 1999 / Accepted: 7 December 1999 相似文献
18.
S. Maaløe 《Mineralogy and Petrology》2005,85(3-4):163-204
Summary The investigated mantle section of the Leka ophiolite complex extends 1.4 km from and 1.1 km along the exposed Moho. The foliated
peridotite contains numerous tabular and elongated dunite bodies, orthopyroxenite dikes, websterite veins, and dikes. The
foliation of the peridotite is inclined by about 45° to the Moho. The dunite bodies and the dikes cut the foliation at low
angles. The dunite bodies vary in width from 0.1 to 50 m and in length from 10 m to more than 1 km. Wider dunite bodies are
commonly surrounded by 0 to 1.0 m wide margins of dunitized peridotite. Websterite veins may be present outside these margins.
Apart from sporadic chromite layers the dunite is very homogenous. The dunite bodies are considered to have formed by deposition
of olivine along the walls of dikes originally containing tholeiitic melt. The tholeiitic melt at first heated the peridotitic
sidewalls so that they became partially molten and dunitized. The ascending magma then eroded the sidewalls and removed olivine
as xenocrysts. When the ascent rate decreased, the temperature of the sidewalls decreased, so that olivine (Fo89–92) began to crystallize along the dike walls. There is also evidence for percolative melt migration along foliation planes,
however, the largest proportion of the melts intruded along dikes.
The websterite dikes are mostly 1 to 4 cm wide and 3 to 20 m long and dispersed with mutual distances of 20–50 m. The websterite
veins and dikes probably originated from melts that were generated along the heated sidewalls of the dunite bodies. The 0.02
to 10 m wide orthopyroxenite dikes have exceptionally high MgO contents for their SiO2 contents; about 36 wt.% MgO and 50 wt.% SiO2. They may have formed as segregates from a SiO2-rich magma, although the parent magma does not appear to have been boninitic. The parent magma may instead have formed by
second stage partial melting of depleted lherzolite. 相似文献
19.
A detailed study based on textural observations combined with microanalysis [back scattered electron imaging (BSE) and electron
microprobe analysis (EMPA)] and microstructural data transmission electron microscopy (TEM) has been made of K-feldspar micro-veins
along quartz–plagioclase phase and plagioclase–plagioclase grain boundaries in granulite facies, orthopyroxene–garnet-bearing
gneiss's (700–825 °C, 6–8 kbar) from the Val Strona di Omegna, Ivrea–Verbano Zone, northern Italy. The K-feldspar micro-veins
are commonly associated with quartz and plagioclase and are not found in quartz absent regions of the thin section. This association
appears to represent a localised reaction texture resulting from a common high grade dehydration reaction, namely: amphibole + quartz
= orthopyroxene + clinopyroxene + plagioclase + K-feldspar + H2O, which occurred during the granulite facies metamorphism of these rocks. There are a number of lines of evidence for this.
These include abundant Ti-rich biotite, which was apparently stable during granulite facies metamorphism, and total lack of
amphibole, which apparently was not. Disorder between Al and Si in the K-feldspar indicates crystallisation at temperatures
>500 °C. Myrmekite and albitic rim intergrowths in the K-feldspar along the K-feldspar–plagioclase interface could only have
formed at temperatures >500–600 °C. Symplectic intergrowths of albite and Ca-rich plagioclase between these albitic rim intergrowths
and plagioclase suggest a high temperature grain boundary reaction, which most likely occurred at the start of decompression
in conjunction with a fluid phase. Relatively high dislocation densities (>2 × 109 to 3 × 109/cm2) in the K-feldspar suggest plastic deformation at temperatures >500 °C. We propose that this plastic deformation is linked
with the extensional tectonic environment present during the mafic underplating event responsible for the granulite facies
metamorphism in these rocks. Lastly, apparently active garnet grain rims associated with side inclusions of K-feldspar and
quartz and an exterior K-feldspar micro-vein indicate equilibrium temperatures within 20–30 °C of the peak metamorphic temperatures
estimated for the sample (770 °C). Contact between these K-feldspar micro-veins and Fe-Mg silicate minerals, such as garnet,
orthopyroxene, clinopyroxene or biotite along the interface, is observed to be very clean with no signs of melt textures or
alteration to sheet silicates. This lends support to the idea that these micro-veins did not originate from a melt and, if
fluid induced, that the water activity of these fluids must have been relatively low. All of these lines of evidence point
to a high grade origin for the K-feldspar micro-veins and support the hypothesis that they formed during the granulite facies
metamorphism of the metabasite layers in an extensional tectonic environment as the consequence of localised dehydration reactions
involving the breakdown of amphibole in the presence of quartz to orthopyroxene, clinopyroxene, plagioclase, K-feldspar and
H2O. It is proposed that the dehydration of the metabasite layers to an orthopyroxene–garnet-bearing gneiss over a 4-km traverse
in the upper Val Strona during granulite facies metamorphism was a metasomatic event initiated by the presence of a high-grade,
low H2O activity fluid (most likely a NaCl–KCl supercritical brine), related to the magmatic underplating event responsible for
the Mafic Formation; and that this dehydration event did not involve partial melting.
Received: 15 February 2000 / Accepted: 26 June 2000 相似文献
20.
Summary Interfaces between geomaterials may be critical for the long term confinement of the engineered barriers of nuclear waste
disposals, particularly if there is water flow. Hydromechanical compression tests have been performed on rock-bentonite interfaces
representing the contact between a host rock (toarcian argillite) and an engineered barrier within a nuclear waste repository.
The results show that there is no major influence of the bentonite fraction or the nature of the additive as long as the additive
is inert (sand or crushed rock): all the interfaces are closed for low values of normal stress (about 4 MPa). On the other
hand, the hydromechanical behaviour of the interfaces changes when a high fraction of cement is used. Moreover, it has been
shown that bentonite is very sensitive to hydraulic erosion, producing flow channels within the interface zone. A numerical
study confirms the importance of erosion for the hydromechanical behaviour of the interface.
Authors’ address: Olivier Buzzi, Laboratoire Sols, Solides, Structures, Université Joseph Fourier, BP 53, 38041 Grenoble,
Cedex 9, France 相似文献