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1.
B. N. Filyushkin M. A. Sokolovskiy N. G. Kozhelupova I. M. Vagina 《Doklady Earth Sciences》2011,439(1):986-989
In the northeastern portion of the Atlantic Ocean, at depths of 500–1500 m, there are regular intrathermocline eddies that
are characterized by high temperature and salinity. As these eddies interact with the ambient medium, they can transmit a
dynamic signal to the ocean surface. These eddies are clearly identifiable on altimetric maps showing variations in the ocean’s
surface level obtained by satellites. Such observations allow recording not only the complex interaction pattern of surface
cyclonic and anticyclonic eddies, but also the processes of merging and separation of intrathermocline eddies. 相似文献
2.
Movement of seasonal eddies in the Bay of Bengal (BOB) and its relation with cyclonic heat potential (CHP) and cyclogenesis
points have been investigated in this study using 6 years (2002–2007) of global ocean monthly analysis datasets based on the
Simple Ocean Data Assimilation (SODA) package (SODA v2.0.4) of Carton et al. (2005) and Indian Meteorological Department cyclogenesis points. The region dominated by anticyclonic eddies with CHP greater than
70 × 107 J/m2 as well as good correlations (>0.9) with sea surface height (SSH) and 26°C isothermal depth (D
26) can be a potential region of cyclogenesis. The region dominated by cyclonic eddies with CHP greater than 50 × 107 J/m2 and good correlation (>0.9) with both SSH and D
26 can serve as a potential region of high-level depression. Potential cyclogenesis regions are the southern BOB (5°N–12°N)
for the post-monsoon season and the head of BOB (north of 15°N) during southwest monsoon. Seven potential regions are identified
for the eddy formation for different seasons, which are consistent with the cyclogenesis points. The CHP distributions alone
are able to explain the cyclone tracks for the pre-monsoon and post-monsoon seasons but not for the monsoon season. 相似文献
3.
Savita B. Morwal S. G. Nagar V. S. N. Murty P. Seetaramayya 《Journal of Earth System Science》2006,115(5):587-599
During the period 12–16 June 1996 a tropical cyclonic storm formed over the southwest Bay of Bengal and moved in a north-northeasterly
direction. The thermodynamic characteristics of this system are investigated by utilizing the surface and upper air observations
collected onboardORV Sagar Kanya over the Bay of Bengal region. The response of the cyclonic storm is clearly evident from the ship observations when the
ship was within the distance of 600–800 km from the cyclonic storm. This study explores why (i) the whole atmosphere from
surface to 500 hPa had become warm and moist during the cyclonic storm period as compared to before and after the formation
of this system and (ii) the lower layer of the atmosphere had become stable during the formative stage of the cyclonic storm. 相似文献
4.
Mesoscale eddies are active and energetic in the South China Sea (SCS), and play an important role in regulating the multi-scale circulation and mass transportation in the region, especially for those long-lived strong eddies. Using AVISO altimeter data and outermost closed contour sea level anomaly method, this study identified and tracked mesoscale eddies in the northern SCS during 2011-2018, and focused on the temporal and spatial characteristics of mesoscale eddies in recent years. Similarly to previous results in this region, statistical results show that about 8.6 anticyclonic eddies and 4.5 cyclonic eddies (lifetime > 28 days) were born per year. Among them, about 1/3 of the total number are strong eddies (lifetime > 45 days), showing relatively strong dynamic characteristics, such as strong Eddy Kinetic Energy (EKE) and highly nonlinear feature. Statistics also show significant seasonal variability in mesoscale eddies’ birth places, trajectories and distribution of frequency of occurrence. Specifically, anticyclonic eddies mainly form at the north part of Luzon Strait between autumn and winter, and then move southwestward along isobaths. During this period, the largest value of the frequency of occurrence is over 30%. In summer, most of them form in the west off Luzon Island, and then move westward paralleling to latitude lines. In contrast, cyclonic mainly form in the west off Luzon Strait, and then move westward in winter and spring. During this period, the largest value is about 26%. In addition, observation finds that the strong mesoscale eddy pair could generate off the southwest of Taiwan Island. Analysis of the Kuroshio SCS Index (KSI) implies that loop current caused by Kuroshio intrusion is the most important mechanism for the formation of eddy pair. 相似文献
5.
G. S. Dvoryaninov A. A. Kubryakov A. A. Sizov S. V. Stanichny N. B. Shapiro 《Doklady Earth Sciences》2016,466(1):100-104
On the basis of altimetry data, the dynamics of the interaction between the subtropical anticyclonic (SA) and subpolar cyclonic (SC) gyres of the North Atlantic is considered. It is shown that the westerlies in the lower troposphere represented by the North Atlantic Oscillation (NAO) index are the main factor responsible for the dynamics of the gyres, which controls the inflow of warm Atlantic water into the Polar basin. 相似文献
6.
Pablo Huq 《Estuaries and Coasts》2009,32(4):709-719
This investigation examines the influence of the Kelvin number (K) and fractional depth (h/D) on bulge formation from buoyant outflows from an estuary or strait perpendicular to the coastline. Here K = W/R is the ratio of the width (W) at the mouth of the estuary to the deformation radius (R), and h and D are the buoyant layer and ambient ocean depths, respectively. Measurements of velocity and lateral shear (≈ relative vorticity
ζ) at the baymouth are reported for experiments on a flat-bottomed rotating turntable. The form of the velocity profile across
the mouth depends on the value of K. The buoyant outflow flows across the entire width of the estuary for narrow estuaries (i.e., K ≤ 1). In contrast, for wide estuaries (K > 2), dense oceanic water inflows on the left and the buoyant waters outflow on the right (looking seaward). Velocity profiles
of the inflowing oceanic waters are laterally uniform with velocities (V/C ≈ −0.4), whereas velocity profiles of the outflowing buoyant waters are laterally sheared with peak velocities of V/C ≈ 1.0 at the right hand exit. The flow pathways when bulges form comprises an anticyclonic turn offshore of the mouth and
a downshelf propagating coastal current. Anticyclonic bulges form for surface-advected outflows h/D < 0.25. Anticyclonic bulges do not form for sufficiently large magnitudes of non-dimensional relative vorticity ζ/f (>0.4), and an additional flow pathway is that buoyant waters recirculate back cyclonically into the estuary at the left-hand
(upshelf) side of the estuary. The offshore extent of buoyant waters associated with this cyclonic recirculation can be as
large as 7R. 相似文献
7.
SAVITA PATWARDHAN ASHWINI KULKARNI K KRISHNA KUMAR 《Journal of Earth System Science》2012,121(1):203-210
A state-of-the-art regional climate modelling system, known as PRECIS (Providing REgional Climates for Impacts Studies) developed
by the Hadley Centre for Climate Prediction and Research, UK is applied over the Indian domain to investigate the impact of
global warming on the cyclonic disturbances such as depressions and storms. The PRECIS simulations at 50 × 50 km horizontal
resolution are made for two time slices, present (1961–1990) and the future (2071–2100), for two socioeconomic scenarios A2
and B2. The model simulations under the scenarios of increasing greenhouse gas concentrations and sulphate aerosols are analysed
to study the likely changes in the frequency, intensity and the tracks of cyclonic disturbances forming over north Indian
Ocean (Bay of Bengal and Arabian Sea) and the Indian landmass during monsoon season. The model overestimates the frequency
of cyclonic disturbances over the Indian subcontinent in baseline simulations (1961–1990). The change is evaluated towards
the end of present century (2071–2100) with respect to the baseline climate. The present study indicates that the storm tracks
simulated by the model are southwards as compared to the observed tracks during the monsoon season, especially for the two
main monsoon months, viz., July and August. The analysis suggests that the frequency of cyclonic disturbances forming over
north Indian Ocean is likely to reduce by 9% towards the end of the present century in response to the global warming. However,
the intensity of cyclonic disturbances is likely to increase by about 11% compared to the present. 相似文献
8.
Tetsutaro Takikawa Goh Onitsuka Ken-ichi Fukudome Jong-Hwan Yoon Akihiko Morimoto Masatoshi Moku Atsushi Watanabe 《Estuaries and Coasts》2011,34(4):775-784
Horizontal, vertical and temporal distribution of a cyclonic (counterclockwise) eddy, where biological productivity is high,
downstream of the Tsushima Islands in the eastern channel of the Tsushima Straits in November 2007 was revealed using conductivity–temperature–depth
and acoustic Doppler current profiler data. The eddy had a horizontal scale of approximately 40–60 km, and the accompanying
baroclinic current was more than 15 cm s−1 at the edge of the eddy. The island-induced cyclonic eddy moved east-northeastward at about 10 km day−1 (∼10 cm s−1) along the Tsushima Warm Current and was intensified by the barotropic instability in the current shear. The cyclonic eddy
with high surface chlorophyll a concentrations intensified in the vicinity of the Tsushima Islands and was advected by the Tsushima Warm Current towards
the southwestern Japan Sea. 相似文献
9.
Andrey A. Gurenko Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》1998,131(1):95-110
Major elements, S, F, Cl concentrations and relative proportions of S6+ to total S were analyzed with electron microprobe in sideromelane glass shards from Pleistocene volcaniclastic sediments
drilled during ODP Leg 157. Glasses are moderately to strongly evolved and represent a spectrum from alkali basalt, basanite
and nephelinite through hawaiite, mugearite and tephrite to phonolitic tephrite. Measured S6+/ΣS (0.03–0.98) and calculated Fe2+/Fe3+ (2.5–5.8) ratios in the melt yield preeruptive redox conditions ranging from NNO−1.4 to NNO+2.1. The morphology of the glass
shards, variations of S and Cl concentrations (0.010–0.127 wt% S, 0.018–0.129 wt% Cl), calculated preeruptive temperatures
(1030–1200 °C) and oxygen fugacities suggest that glasses deposited even within the same ash layers have diverse origin and
may have resulted from both submarine and subaerial eruptions. Most vesicle-free glasses are characterized by high concentrations
of S and represent undegassed or slightly degassed submarine lavas, whereas vesiculated glasses with low concentrations of
S and Cl are strongly degassed and can be ascribed to the eruptions in shallow water or on land. Sideromelane glass shards
at Sites 953 are thought to have resulted from submarine eruptions northeast of Gran Canaria, glasses at Site 954 represent
mostly volcaniclastic material of shallow water submarine and subaerial eruptions on Gran Canaria and Tenerife, and glasses
deposited at Site 956 resulted from submarine or explosive eruptions on Tenerife.
Received: 8 April 1997 / Accepted: 27 October 1997 相似文献
10.
An early Palaeozoic supra-subduction lithosphere in the Variscides: new evidence from the Maures massif 总被引:1,自引:0,他引:1
Jean-Philippe Bellot Christine Laverne Georges Bronner 《International Journal of Earth Sciences》2010,99(3):473-504
Petrographic and geochemical studies of peridotites and melagabbros from the Maures massif (SE France) provide new constraints
on the Early Palaeozoic evolution of the continental lithosphere in Western Europe. Peridotites occur as lenses along a unit
rooted in the main Variscan suture zone. They are dominantly spinel peridotites and minor garnet–spinel peridotites. Spinel
peridotites represent both residual mantle and ultramafic cumulates. Mantle-related dunites and harzburgites display high
temperature textures, with olivine (Mg#0.90), orthopyroxene (Mg#0.90) and spinel (TiO2 < 0.2%; Cr#0.64–0.83) compositions typical of fore-arc upper mantle. Ultramafic cumulates are dunite adcumulates, harzburgite heteradcumulates
and mesocumulates, melagabbro heteradcumulates and amphibole peridotites, with olivine (Mg#0.85–0.89), orthopyroxene (Mg#0.86–0.89) and Cr-spinel (TiO2 = 0.5–3.3%; Cr#0.7–0.98) compositions typical of ultramafic cumulates. Cr-spinel compositions of both spinel peridotite types suggest their genesis
in a supra-subduction zone lithosphere. Core to rim zoning in spinel is related to the incomplete influence of regional metamorphism
and serpentinisation. The covariation of major and minor elements with Al2O3 for cumulates is consistent with igneous processes involving crystal accumulation. Both mantle and cumulate dunites and harzburgites
have U-shaped REE patterns and extremely low trace element contents, similar to peridotites from modern fore-arc peridotites
(South Atlantic) and from ophiolites related to supra-subduction zones (Semail, Cyclops, Pindos, Troodos). Melagabbros also
have U-shaped REE patterns similar to xenoliths from the Philippine island arc, but also similar to intrusive ultramafic cumulates
from the Semail nappe of Oman related to a proto-subduction setting. A wehrlite has a REE pattern similar to that of amphibole
peridotites reflecting metasomatism of clinopyroxene-bearing peridotites due to subduction-related fluids. The Maures spinel
peridotites and melagabbros are therefore interpreted as the lowermost parts of a crustal sequence and minor residual mantle
of lithosphere generated in a supra-subduction zone during Early Palaeozoic time. Garnet–spinel peridotites are chemically
close to melagabbros, but have recorded high pressure metamorphism before their retrogression similar to spinel peridotites
into amphibolites to greenschists facies metamorphism. They indicate burial to mantle depths of the margin of the supra-subduction
lithosphere during the Early Palaeozoic continental subduction. Both peridotite types were exhumed during the Upper Palaeozoic
continental collision. Comparable observations from other Variscan-related peridotites, in particular of the Speik complex
of the Autroalpine basement, and a common age for the subduction stage allow extension of these regional conclusions to a
broad area sharing the Cambrian suture zone, extending from the Ossa-Morena to the Bohemian massif. 相似文献
11.
Shimaraev M. N. Troitskaya E. S. Blinov V. V. Ivanov V. G. Gnatovskii R. Yu. 《Doklady Earth Sciences》2012,442(2):272-276
Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature
stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and
alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous
to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10−2−6.5 × 10−2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling
in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800
m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation
of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar
with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at
that. 相似文献
12.
The summer monsoon rainfall over Orissa, a state on the eastern coast of India, is more significantly related than Indian
summer monsoon rainfall (ISMR) to the cyclonic disturbances developing over the Bay of Bengal. Orissa experiences floods and
droughts very often due to variation in the characteristics of these disturbances. Hence, an attempt was made to find out
the inter-annual variability in the rainfall over Orissa and the frequencies of different categories of cyclonic disturbances
affecting Orissa during monsoon season (June–September). For this purpose, different statistical characteristics, such as
mean, coefficient of variation, trends and periodicities in the rainfall and the frequencies of different categories of cyclonic
disturbances affecting Orissa, were analysed from 100 years (1901–2000) of data. The basic objective of the study was to find
out the contribution of inter-annual variability in the frequency of cyclonic disturbances to the inter-annual variability
of monsoon rainfall over Orissa.
The relationship between summer monsoon rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa shows
temporal variation. The correlation between them has significantly decreased since the 1950s. The variation in their relationship
is mainly due to the variation in the frequency of cyclonic disturbances affecting Orissa. The variability of both rainfall
and total cyclonic disturbances has been above normal since the 1960s, leading to more floods and droughts over Orissa during
recent years. The inter-annual variability of seasonal rainfall over Orissa and the frequency of cyclonic disturbances affecting
Orissa during monsoon season show a quasi-biennial oscillation period of 2–2.8 years. There is least impact of El Nino southern
oscillation (ENSO) on inter-annual variability of both the seasonal rainfall over Orissa and the frequencies of monsoon depressions/total
cyclonic disturbances affecting Orissa. 相似文献
13.
Shallow marine sediments of the Buyat-Ratototok district of North Sulawesi, Indonesia, are affected by submarine disposal
of industrial gold mine tailings and small-scale gold mining using mercury amalgamation. Industrial mine tailings contained
590–660 ppm arsenic, 490–580 ppm antimony, and 0.8–5.8 ppm mercury. Electron microprobe survey found both colloidal iron–arsenic-phases
without sulphur and arsenian pyrite in tailings and sites to which tailings had dispersed, but only arsenopyrite in sediments
affected by artisanal mining. Antimony in tailings was present as antimony oxides, colloidal iron–antimony phases, colloidal
iron–antimony phases, and stibnite in sediments affected by both types of mining. A sequential extraction found that 2% of
arsenic held in tailings and tailings-contaminated sediments was exchangeable, 20–30% was labile, including weakly adsorbed,
carbonate- and arsenate bound, 20–30% was metastable, probably incorporated into iron or manganese oxyhydroxides, or strongly
adsorbed to silicate minerals, and 40–48% was relatively insoluble, probably incorporated into sulphides or silicates. Arsenic
in sediments affected by artisanal gold mining was 75–95% relatively insoluble. Antimony in all sediments was >90% relatively
insoluble. Relative solubility patterns of most other metals did not differ between industrial tailings-affected, artisanal-mining
affected areas, and fluvial sediments. Results suggest that submarine tailings disposal is not suitable for refractory Carlin-like
gold deposits because ore processing converts arsenic to forms unstable in anoxic marine sediments.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
14.
Martin Wipf Ulrich Anton Glasmacher Daniel Fritz Stockli Axel Emmerich Thilo Bechstädt Heinrich Baur 《International Journal of Earth Sciences》2010,99(3):675-686
Miocene Intrusives and Lower Cretaceous siliciclastic sedimentary rocks from the Basal Complex in western-Fuerteventura were
analyzed with low-temperature thermochronometric methods such as fission-track, and (U–Th–Sm)/He dating, in order to reveal
the evolution of the island’s exhumation history. The obtained thermochronometric data yields a very slow rate of cooling
in the order of 1.5–3°C/Myr from ~50 to 20 Ma for the Early Cretaceous siliciclastic rocks. These sedimentary units have never
been heated significantly above 240°C after deposition and still record the submarine onset of the island’s formation in the
Eocene. Intrusive bodies associated with the early Miocene magmatic activity of the central volcanic complex of the island
show rapid initial cooling rates of 50–70°C/Myr from ~20 to 14 Ma. Contemporaneous with the intrusions the cooling rate of
the Cretaceous sedimentary units increased to 25–35°C/Myr and it is inferred that this increase is associated with enhanced
uplift and erosion of the Central Volcanic Complex. After ~14 Ma rates slowed down to 3–6°C/Myr. Palaeosols overlying the
sedimentary units are themselves covered by Pliocene basalt flows and reveal that the sedimentary rocks reached the surface
before ~5 Ma. The thermochronometric data obtained in this study for central Fuerteventura is difficult to reconcile with
the cooling history derived from previously obtained fission-track and K–Ar data from the north-western part of the island.
This inconsistency is likely to indicate that the exhumation history of Fuerteventura is more complex and regionally subdivided
than previously believed. 相似文献
15.
The Paleoproterozoic Ruttan Cu–Zn volcanogenic massive-sulfide (VMS) deposit is a large, relatively low grade, bimodal-siliciclastic
type deposit in the Rusty Lake volcanic belt of northern Manitoba. The deposit contained over 82.8 million tonnes of massive
sulfide, of which 55.7 million tonnes were mined from 1973 to 2002. The deposit consists of a series of moderately to steeply
dipping, south-facing lenses that extend along strike at the surface for 1.1 km and to a depth of 1.0 km. These lenses occur
within a steeply dipping, bimodal volcanic, volcaniclastic and siliciclastic sequence. In the immediate mine area, transitional
calc-alkalic to high-silica (tholeiitic), felsic, and intermediate volcanic/volcaniclastic rocks of the Mine Sequence are
host to, and intercalated with, the massive-sulfide lenses. Transitional tholeiitic to calc-alkalic basalt and andesite are
present in the footwall sequence, approximately 500 m down-section from the ore horizon. The overlying rocks are predominantly
fine-grained volcaniclastics and siliciclastics, but include polyfragmental agglomerate that contains mafic bombs and scoriaceous
felsic fragments. Syn-depositional felsic and mafic dikes, sills, and apophyses are ubiquitous throughout the Mine Sequence,
including the ore lenses, indicating continued, near-vent magmatism, and volcanism during ore formation. Fabrics in altered
hostrocks have consistent, down-plunge stretching lineations to the SSE that suggest the deposit has been elongated by a factor
of ~1.2–1.5; otherwise, the deposit is remarkably undeformed. Syn- and post-depositional faults in the mine area have relatively
minor displacements up to tens of meters. Proximal (within 200 m) footwall rocks exhibit moderate to strong chloritization,
characterized by the upper greenschist to lower amphibolite facies assemblages that include cordierite–almandine–andalusite–sillimanite–biotite ± staurolite ± anthophyllite ± talc,
and local silicification. The proximal hanging wall rocks are characterized by sericite ± gahnite alteration, which is restricted
to within approximately 75 m of the uppermost lenses. Additional gangue minerals are anhydrite and carbonate minerals (siderite,
dolomite, ankerite, and calcite), as well as chlorite, sericite, biotite, talc, and quartz. Carbonate (excluding siderite),
potassium feldspar, silicification and epidotization are common distal alteration zones in the footwall to the Mine Sequence
several kilometers to the northeast. There are three principal groups of massive sulfide lenses; the East lenses, the West
lenses, and the Western Anomaly lenses to the far west. In general, Cu is relatively enriched at the stratigraphic base and
in the center of the deposit, whereas Zn is enriched upsection and at the outer margins. Some of the Zn-rich ore exhibits
primary mineralogical layering. Parts of the West and Western Anomaly lenses show two layers with Cu-rich bases and Zn-rich
tops. The massive sulfide is typically 10–40-m thick; one area along the margin of the main lenses is over 130-m thick and
may represent deposition adjacent to a syn-depositional fault. The main sulfide phases are pyrite, pyrrhotite, chalcopyrite,
sphalerite, and galena, with tetrahedrite as the most abundant trace phase. Gahnite is ubiquitous in the chlorite-rich assemblages
adjacent to the ore lenses. The average base, precious and trace metal contents estimated from Cu and Zn concentrates, and
from millhead grades and recoveries. Metals easily transported as chloride and bisulfide complexes in hydrothermal fluids
including: Pb, Ag, In, Cu, Cd, Au, and Zn are enriched by 1.5–2.5 orders of magnitude in comparison to the bulk continental
crust. Other elements such as Sn, Mo, and As are at near-crustal concentrations, whereas Mn, Ga, and Co are significantly
depleted in comparison to the crust. Calculated metal concentrations in the average hydrothermal fluid based on the average
metal contents are comparable to, or higher than those measured at sediment covered ridge hydrothermal systems, which precipitate
much of their metal budget in the subsurface. Average rare earth element contents for the sulfide are light rare earth element
enriched (LaN/YbN=22) and range from 0.45 to 0.02x chondritic values, with a moderate negative Eu anomaly (Eu*=0.51). Metal and trace element
contents in the Ruttan exhalite horizon, and in proximal (within 1–2 km) exhalites along strike from the 0.6 million tonne
Dar-2 Cu–Zn deposit 12 km south of Ruttan, have positive Eu anomalies, whereas negative Eu anomalies are present at distance.
The positive Eu anomalies reflect high temperature paleoseafloor hydrothermal venting and precipitation of Eu2+-enriched clays and possibly carbonates, and indicate proximity to base-metal deposits. Silver and lead are also enriched
in the exhalites near the deposits, whereas Mn is enriched at ~1–3 km along strike, but not consistently.
Editorial handling: B. Gemmel
An erratum to this article is available at . 相似文献
16.
The Oramiriukwa River is within the sandy coastal plain strata of the Benin formation (Miocene–Recent). The base flow is very
high ranging from 79.13–98.56%, which is caused by the excellent hydraulic interconnection between the river and the adjacent
unconfined aquifer. Recharge rates are high, estimated to range from 1.8×1012–2.5×1012 m3/year. Coastal sands are medium-to-coarse grained, moderately-to-poorly sorted, angular to subangular, with lenses of clay
and clayey fine-grained sands. The coastal sands and clay lenses form aquifer and aquitard systems, which are unconfined to
semi-confined. Groundwater recharge potential is high. Runoff from precipitation is low. Groundwater and surface water are
fairly acidic; pH ranges from 5.5–6.1 (groundwater) and 5.8–6.5 (surface water), and hardness is generally low. Chemical analysis
and percentage sodium show that groundwater and surface water are somewhat potable after some pH modification of the surface
water. The waters are good for agricultural use, especially for irrigation and poultry water supply. However, pollution from
landfill leachate is serious.
Electronic Publication 相似文献
17.
The Kristineberg massive sulfide deposit is hosted by metamorphosed volcanic and subvolcanic rocks of the Palaeoproterozoic
Skellefte Group. The deposit consists of: (1) two main massive sulfide horizons, the A-ores and B-ores, which dip steeply
southwards and are separated by 100–150 m; and (2) the Einarsson Zone, a complex interval of Cu–Au-rich ‘stockwork‘ sulfides
and small massive sulfide lenses in altered and deformed rocks near the 1,000 m level. The Einarsson Zone occurs some 20–100 m
south of the B-ores. There are no definite younging indicators in the mine sequence. In many areas of the mine, the original
host rocks are impossible to identify petrographically due to the abundance of secondary minerals such as quartz, chlorite,
muscovite, cordierite, andalusite, phlogopite, pyrite and talc, combined with variably schistose fabrics. Application of immobile-element
methods to 600 recent whole-rock chemical analyses has, however, allowed the original rock types to be identified and correlated.
Rhyolite X lies immediately north of the A-ore, while andesitic to dacitic to rhyodacitic rocks make up the 100–150 m interval
between the A-ore and B-ore, and massive rhyolite A lies immediately south of the B-ore. The felsic rocks are mostly of calc-alkaline
affinity, excluding rhyolite X, which is transitional. The mine porphyry, which lies north of the A-ore and forms the marginal
phase of the synvolcanic Viterliden Intrusive Complex, is compositionally similar to dacite and rhyodacite. Mass changes calculated
for all rock types indicate that most of the volcanic rocks in the mine area are strongly depleted in Na and Ca, and have
gained variable amounts of Mg and Fe, whereas Si changes range from negative to positive. Gains in Fe and changes in Si are
largest within 5–10 m of the massive sulfide lenses. Cordierite-bearing schists of andesitic to felsic compositions that lie
between massive sulfide lenses A and B are not as altered. The Einarsson Zone commonly shows large gains in Fe and Mg, while
Si shows large gains to large losses. Immobile-element ratios indicate that very different secondary assemblages in the mine,
e.g. andalusite–quartz–muscovite and cordierite–chlorite–talc, can be produced from the same precursor volcanic unit, e.g.,
rhyolite. Conversely, the same secondary mineral assemblage can be produced from different rocks, e.g. weakly altered andesite
and strongly altered rhyolite. The common presence of cordierite + andalusite in the mine area, without anthophyllite, is
unusual in the alteration systems of volcanic-hosted massive sulfide deposits, and is proposed to have formed by the metamorphic
reaction of the synvolcanic alteration minerals kaolinite and chlorite to produce cordierite. Where kaolinite was in excess
of chlorite, andalusite was also formed. We propose that highly acidic alteration fluids locally produced high-Al minerals
such as kaolinite that either overprinted, or occurred in place of, a more typical sericite–chlorite–quartz alteration assemblage
that otherwise formed near the massive sulfide lenses. Application of lithogeochemical methods to the altered, deformed and
metamorphosed Kristineberg rocks has identified specific volcanic contacts with massive sulfide potential, and quantified
the effects of synvolcanic hydrothermal alteration. Such an approach can increase the effectiveness of mineral exploration
in metamorphosed terrains. 相似文献
18.
Flat-bottomed depression 50–150 m in diameter and 60–80 cm deep occur in the floor of Norton Sound, Bering Sea. These large
erosional bedforms and associated current ripples are found in areas where sediment grain size is 0.063–0.044 mm (4–4.5 φ),
speeds of bottom currents are greatest (20–30 cm/s mean speeds under nonstorm conditions, 70 cm/s during typical storms),
circulation of water is constricted by major topographic shoals (kilometers in scale), and small-scale topographic disruptions,
such as ice gouges, occur locally on slopes of shoals. These local obstructions on shoals appear to disrupt currents, causing
separation of flow and generating eddies that produce large-scale scour. Offshore artificial structures also may disrupt bottom
currents in these same areas and have the potential to generate turbulence and induce extensive scour in the area of disrupted
flow. The size and character of natural scour depressions in areas of ice gouging suggest that large-scale regions of scour
may develop from enlargement of local scour sites around pilings, platforms, or pipelines. Consequently, loss of substrate
support for pipelines and gravity structures is possible during frequent autumn storms. 相似文献
19.
M. Franceschelli M. Puxeddu G. Cruciani D. Utzeri 《International Journal of Earth Sciences》2007,96(5):795-815
Metabasites with eclogite facies relics occur in northern Sardinia as massive to strongly foliated lenses or boudins embedded
within low- to medium-grade rocks (Anglona) and migmatites (NE Sardinia). U–Pb zircon dating yielded 453 ± 14, 457 ± 2 and
460 ± 5 Ma as the protolith ages; 400 ± 10 and 403 ± 4 Ma have been interpreted as the ages of the HP event and 352 ± 3 and
327 ± 7 Ma as the ages of the main Variscan retrograde events. A pre-eclogite stage is documented by the occurrence of tschermakite,
zoisite relics within garnet porphyroblasts (Punta de li Tulchi) and an edenite–andesine inclusion within a relict kyanite
porphyroblast (Golfo Aranci). Four main metamorphic stages have been distinguished in the eclogite evolution: (1) eclogite
stage, revealed by the occurrence of armoured omphacite relics within garnet porphyroblasts. The Golfo Aranci eclogites also
include kyanite, Mg-rich garnet and pargasite; (2) granulite stage, producing orthopyroxene and clinopyroxene–plagioclase
symplectites replacing omphacite. At Golfo Aranci, the symplectitic rims around relict kyanite consist of sapphirine, anorthite,
corundum and spinel; (3) amphibolite stage, leading to the formation of amphibole–plagioclase kelyphites between garnet porphyroblasts
and pyroxene–plagioclase symplectites and to the growth of cummingtonite on orthopyroxene. Tschermakite to Mg-hornblende,
plagioclase, cummingtonite, ilmenite, titanite and biotite are coexisting phases; (4) greenschist to sub-greenschist stage,
defined by the appearance of actinolite, chlorite, epidote ss, titanite, sericite and prehnite. The following P–T ranges have been estimated for the different stages. Eclogite stage 550–700°C; 1.3–1.7 GPa; granulite stage 650–900°C; 0.8–1.2 GPa,
clustering in the range 1.0–1.2 GPa; amphibolite stage 550–740°C; 0.3–0.7 GPa; greenschist stage 300–400°C; 0.2–0.3 GPa. Comparable
ranges characterise the other Variscan massifs in Europe; eclogite stage: T = 530–800°C; P from 0.7–1.1 to 1.7 ± 0.3 GPa; granulite stage T = 760–870°C and P from 1.1–1.4 to 7.2–9.9 GPa, clustering around 1.0–1.2 GPa. Whole-rock chemistry: Sardinian eclogites are N- to T-MORB;
European ones N- to E-MORB or calc-alkaline. 相似文献
20.
NumericalN-body studies of the dynamical evolution of a cluster of 1000 galaxies were carried out in order to investigate the role of
dark matter in the formation of cD galaxies. Two models explicitly describing the darkmatter as a full-fledged component of
the cluster having its own physical characteristics are constructed. These treat the dark matter as a continuous underlying
substrate and as “grainy” matter. The ratio of the masses of the dark and luminous matter of the cluster is varied in the
range 3–100. The observed logarithmic spectrum dN ∼ dM / M is used as an initial mass spectrum for the galaxies. A comparative numerical analysis of the evolution of the mass spectrum,
the dynamics of mergers of the cluster galaxies, and the evolution of the growth of the central, supermassive cD galaxy suggests
that dynamical friction associated with dark matter accelerates the formation of the cD galaxy via the absorption of galaxies
colliding with it. Taking into account a dark-matter “substrate” removes the formation of multiple mass-accumulation centers,
and makes it easier to form a cD galaxy that accumulates 1–2% of the cluster mass within the Hubble time scale (3–8 billion
years), consistent with observations. 相似文献