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1.
D. Gournis A. E. Mantaka-Marketou M. A. Karakassides D. Petridis 《Physics and Chemistry of Minerals》2001,28(4):285-290
The interaction of γ-rays with smectites induces paramagnetic defects in the structure of these clay minerals. The EPR spectra
of three different smectites detect the creation of structural defects and trapping of organic free radicals in the clay structure
upon irradiation. The defects are assigned to positive holes or trapped electrons stabilised by existing local charge imbalances
in the mineral lattice. The organic radicals are derived from organic compounds present as impurities in the crystal lattice
of the clay minerals. In addition, γ-rays cause migration of small interlayer cations (such as Li+) into the layers, as clearly evidenced by EPR and FT-IR reflectance spectroscopies.
Received: 20 April 2000 / Accepted: 2 December 2000 相似文献
2.
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
3.
M. R. Krbetschek J. Götze G. Irmer U. Rieser T. Trautmann 《Mineralogy and Petrology》2002,76(3-4):167-177
Summary ?Feldspar specimens covering the whole Or–Ab–An ternary have been investigated by cathodoluminescence (CL), photoluminescence
(PL), radioluminescence (RL) and radiophosphorescence (RP) spectrometry. A red luminescence emission, which is commonly explained
by Fe3+ lattice defects, is a characteristic feature of all the spectra. Different shifts of the peak-wavelength between ∼680–750 nm
(1.82–1.65 eV) were observed with varying feldspar composition. Despite the dependence of the peak position on the Ca/Na ratio,
initially described for CL in the 1970s, there is also a shift induced by changing NaK composition. The observed effects can
be explained by known relations that the peak position of the red luminescence emission in feldspars can be affected both
by the structural state of the feldspar and the site occupancy of the trivalent iron. In the case of alkali feldspars another
factor may influence the peak-shift. The incorporation of the larger potassium ion causes non-linear variations of the cell
dimensions and therefore Fe–O bond distance. The behaviour of the red peak-shift dependent on the feldspar composition is
not equal for all types of luminescence investigated. This is most likely caused by the different luminescence excitation
mechanism.
Received December 3, 2001; revised version accepted March 25, 2002 相似文献
4.
The infrared spectrum of CaAl2Si2O7 · H2O-lawsonite, has been characterized to pressures of 20 GPa at 300 K. Our results constrain the response to compression of
the silicate tetrahedra, hydroxyl units, and water molecules in this material. The asymmetric and symmetric stretching and
bending vibrations of the Si2O7 groups (at zero pressure frequencies between 600 and 1000 cm−1) increase in frequency with pressure at rates between 3.6 and 5.9 cm−1/GPa. All silicate modes appear to shift continuously with pressure to 20 GPa, although the lowest frequency stretching vibration
becomes unresolvable above 18 GPa, and a splitting of the main bending vibration is observed near this pressure. The O-H stretches
of the hydroxyl units exhibit a discontinuity in their mode shifts at ∼8–9 GPa, which we interpret to be produced by a pressure-induced
change in hydrogen bonding. The stretching and bending vibrations of the water molecule are relatively unaffected by compression
to 20 GPa, thus demonstrating that the structural cavities in which water molecules reside are relatively rigid. Significant
changes in the amplitude of the O-H stretches of the hydroxyl and water units are observed at this pressure as well; nevertheless,
our results demonstrate that the dominant structural units in lawsonite persist metastably at 300 K with only modest structural
modifications well beyond the known stability field of this phase.
Received: 10 July 1998 / Revised, accepted: 23 October 1998 相似文献
5.
Adsorption, desorption and oxidation of arsenic affected by clay minerals and aging process 总被引:20,自引:0,他引:20
Adsorption/desorption and oxidation/reduction of arsenic at clay surfaces are very important to the natural attenuation of
arsenic in the subsurface environment. Although numerous studies have concluded that iron oxides have high affinities for
the adsorption of As(V), very little experimental work has addressed the arsenic attenuation capacities of different clay
minerals and aging process affecting the transformation of arsenic. The abundance of clay minerals in a variety of geochemical
environments and their influence on adsorption of contaminants suggests a need for more experimental work to characterize
the adsorption desorption, and oxidation of arsenic on clay minerals. In this investigation three types of clay mineral were
studied: the 1 : 1 layer clays [halloysite (IN), sedimentary M-kaolinite, and weathered EPK-kaolinite]; the 2 : 1 layer clays
[illite (MT) and illite/montmorillonite (MT)]; the 2 :>: 1 layer clay [chlorite (CA)]. The halloysite and the chlorite had
much greater As(V) adsorption (25–35 folds) than the other clay minerals. The clay minerals had lower As(III) adsorption than
As(V) adsorption, and the adsorption was affected by pH. Desorption of arsenic from the clay minerals was significantly influenced
by the aging process. The quantities of extractable As(III) and As(V) decreased with increasing aging time. The results demonstrated
that oxidation of As(III) to As(V) occurred on the clay surfaces, whereas reduction of As(V) to As(III) was not found in any
of the clay minerals studied. The oxidation of As(III) was affected by the types of clay and aging time.
Received: 22 March 1999 · Accepted: 15 April 1999 相似文献
6.
Summary Fe-Ti-P-rich rocks (FTP) are unusual with respect to their mineralogy and bulk composition. Varieties of these rocks are mostly
related to Proterozoic massif-type anorthosites and to a lesser extent to the upper parts of mafic-ultramafic intracratonic
layered complexes and other igneous rock suites. We present results on the geology, mineralogy and geochemistry of a new occurrence
of FTP, associated with mafic rocks in the northwestern part of Iran. The Qareaghaj mafic-ultramafic intrusion (QMUI) is a
small igneous body situated between Palaeozoic sedimentary rocks and a Precambrian low grade metamorphic complex. The QMUI
is composed mainly of non-mineralized mafic and apatite- and Fe-Ti oxide-rich ultramafic rocks. The mafic rocks, mainly coarse-grained
gabbro, microgabbro and amphibolite, have a simple mineral assemblage (plagioclase + clinopyroxene + ilmenite) and based on
field observations, mineralogy and chemical composition are comagmatic. The ultramafic rocks with high proportion of olivine
(∼40–66 vol.%), apatite (∼0.1–16 vol.%), ilmenite (∼11–19 vol.%) and magnetite (∼2–13 vol.%), have unusual bulk compositions
(e.g., SiO2 ∼ 21–30 wt.%, total iron expressed as Fe2O3
tot ∼ 26–42 wt.%, TiO2 ∼ 5–11 wt.%, MgO ∼ 9–20 wt.%, P2O5 up to 5.1 wt.%, Cr ∼ 40–160 ppm, Ni ∼ 7–73 ppm). The FTP forms numerous sill-like layers, ranging in thickness from ∼5 cm
to few meters. These rocks, totally enclosed in mafic rocks with sharp and concordant contacts, show a magmatic lamination
and follow the general NW–SE trend of QMUI. The apatite-rich ultramafic rocks makes up 90–95% of the total ultramafic outcrops
and contain Mg-poor olivine (Mg# ∼ 40–58) and low-Mg spinel (Mg# ∼ 30–44) in contrast to apatite-poor ones (∼60–63 and ∼43–46,
respectively). Field relationships, mineral compositions and geochemical data suggested that the FTP are not related to the
mafic host rocks. On the contrary, they intruded latter into the gabbros during plastic, high temperature deformation in local
shear zones. Fractional crystallization of P-rich ferrobasaltic parental magma at depth, probably in an open magmatic system,
not far from the QMUI magma chamber, is considered as responsible for the formation of the evolved FTP in QMUI. 相似文献
7.
Controls of surface erosion on the evolution of the Alps: constraints from the stratigraphies of the adjacent foreland basins 总被引:5,自引:0,他引:5
F. Schlunegger 《International Journal of Earth Sciences》1999,88(2):285-304
The combined information about the stratigraphies from the foreland basins surrounding the Swiss Alps, exhumation mechanisms
and the structural evolution of the Alpine orogenic wedge allow an evaluation of the controls of erosion rates on large-scale
Alpine tectonic evolution. Volumetric data from the Molasse Basin and fining-upward trends in the Gonfolite Lombarda indicate
that at ∼20 Ma, average erosion rates in the Alps decreased by >50%. It appears that at that time, erosion rates decreased
more rapidly than crustal uplift rates. As a result, surface uplift occurred. Because of surface uplift, the drainage pattern
of the Alpine hinterland evolved from an across-strike to the present-day along-strike orientation. Furthermore, the decrease
of average erosion rates at ∼20 Ma coincides with initiation of a phase of thrusting in the Jura Mountains and the Southern
Alpine nappes at ∼50 km distance from the pre-20-Ma thrust front. Coupled erosion-mechanical models of orogens suggest that
although rates of crustal convergence decreased between the Oligocene and the present, the reduction of average erosion rates
at ∼20 Ma was high enough to have significantly influenced initiation of the state of growth of the Swiss Alps at that time.
Received: 8 June 1998 / Accepted: 30 October 1998 相似文献
8.
Synthesis of feldspar bicrystals by direct bonding 总被引:1,自引:0,他引:1
We have produced synthetic feldspar bicrystals using a direct bonding technique. A gem-quality orthoclase crystal from Itrongay,
Madagascar, was used for the bonding experiments. Microprobe analysis shows only minor concentrations of iron and sodium.
Orthoclase single crystal plates oriented parallel (0 0 1) were cut and chemomechanically polished with silica slurry. From
interferometry, final roughness of the square crystal plates was about 0.34 nm. Specimens were wet-chemically cleaned using
deionised water. The bonding procedure produced an orthoclase bicrystal with an optically straight grain boundary-oriented
parallel (0 0 1), which was investigated by HREM. Along the interface no amorphous layer was observed between lattice fringes
of both crystals. We suggest that the bicrystals formed by initial hydrogen bonding and subsequent water loss and polymerisation
of silanol and aluminol groups at elevated temperatures.
Received: 19 February 2001 / Accepted: 16 May 2001 相似文献
9.
Twenty nine samples of silica sinter, ranging in age from modern to Miocene, record temporal changes in both mineralogy and
texture. When first deposited, sinters consist largely of noncrystalline spheres (<1–8 μm diameter) of opal-A exhibiting varying
degrees of close-packing. Particle densities range from 1.5 to 2.1 g cm−3, total water 4–10 wt%, and porosities 35–60%. Changes over ∼10,000 years following deposition are slight although the spheres
may be invested by an additional film of secondary silica. For the next 10,000 to ∼50,000 years, the silica incrementally
crystallises to become poorly crystalline opal-CT and/or opal-C; spherical particles of thin-bladed crystals (lepispheres)
replace opal-A particles and coalesce in microbotryoidal aggregates (∼10–30 μm diameter). Amygdaloidal fibrous clusters occur
with lepispheres. As silica lattice ordering becomes enhanced, total water content drops to <7 wt%, particle density increases
to ∼2.3 g cm−3, and porosity reduces to <30%. The change from opal-A to opal-C takes place over a briefer periods (∼50 years) in silica
sinters that contain other materials (e.g. calcite, sulfur, alunite, plant remains). Sinters older than ∼50,000 years have
recrystallised to microcrystalline quartz. With the onset of quartz crystallisation at ∼20,000 years, total water is <0.2 wt%,
particle density approximates quartz (2.65 g cm−3), and porosity is <4%. The progressive changes in silica species and texture yield ageing profiles for sinters that may serve
as guides to the paleohydrology of geothermal systems and/or epithermal ore deposits in areas where surface thermal activity
has declined or ceased.
Received: 18 November 1998 / Accepted: 6 July 1999 相似文献
10.
Raman spectra of a single-crystal fragment of hydrous γ-Mg2SiO4, synthesized in a multianvil press, have been measured in a diamond-anvil cell with helium as pressure-transmitting medium
to 56.5 GPa at room temperature. All five characteristic spinel Raman modes shift continuously up to the highest pressure,
showing no evidence for a major change in the crystal structure despite compression well beyond the stability field of ringwoodite
in terms of pressure. At pressures above ∼30 GPa a new mode on the low-frequency site of the two silicate-stretching modes
is clearly identifiable, indicating a modification in the spinel structure which is reversible on pressure release. The frequency
of the new mode (802 cm−1 extrapolated to 1 bar) suggests the presence of Si–O–Si linkages and/or a partial increase in the coordination of Si. Direct
determination of the subtle structural change causing the new Raman mode would require high-pressure, single-crystal synchrotron
X-ray diffraction experiments. The Raman modes of hydrous and anhydrous Mg-end-member ringwoodite are nearly identical up
to 20 GPa, suggesting that protonation has only minor effect on the lattice dynamics over the entire pressure stability range
for ringwoodite in the mantle.
Received: 7 December 2001 / Accepted: 16 April 2002 相似文献
11.
Genesis of diamonds in the lower mantle 总被引:3,自引:0,他引:3
Lin-gun Liu 《Contributions to Mineralogy and Petrology》1999,134(2-3):170-173
The “forbidden” assemblage (ferropericlase + enstatite) as inclusions in diamonds has been taken as evidence to imply that
these inclusions and their host diamonds formed initially in the lower mantle. Magnesite is probably the only stable carbonate
at depths greater than ∼220 km. Like dehydration reactions, the reaction boundary for the decarbonation of magnesite has a
positive dT/dP slope at lower pressures, which becomes negative at higher pressures, if no other phase intervenes. This reaction boundary
probably intersects the geotherm between ∼900 and ∼1100 km, below which magnesite decomposes into an assemblage periclase + diamond + oxygen.
Thus, ferropericlase is the most likely inclusion in diamond formed in the lower mantle. The high frequency of sole occurrence
of ferropericlase in diamonds from Sao Luiz, Brazil seems to substantiate the present speculation.
Received: 8 June 1998 / Accepted: 28 September 1998 相似文献
12.
Summary Investigations of natural and synthetic quartz specimens by cathodoluminescence (CL) microscopy and spectroscopy, electron
paramagnetic resonance (EPR) and trace-element analysis showed that various luminescence colours and emission bands can be
ascribed to different intrinsic and extrinsic defects.
The perceived visible luminescence colours in quartz depend on the relative intensities of the dominant emission bands between
380 and 700 nm. Some of the CL emissions of quartz from the UV to the yellow spectral region (175 nm, 290 nm, 340 nm, 420 nm,
450 nm, 580 nm) can be related to intrinsic lattice defects. Extrinsic defects such as the alkali (or hydrogen)-compensated
[AlO4/M+] centre have been suggested as being responsible for the transient emission band at 380–390 nm and the short-lived blue-green
CL centered around 500 nm. CL emissions between 620 and 650 nm in the red spectral region are attributed to the nonbridging
oxygen hole centre (NBOHC) with several precursors.
The weak but highly variable CL colours and emission spectra of quartz can be related to genetic conditions of quartz formation.
Hence, both luminescence microscopy and spectroscopy can be used widely in various applications in geosciences and techniques.
One of the most important fields of application of quartz CL is the ability to reveal internal structures, growth zoning and
lattice defects in quartz crystals not discernible by means of other analytical techniques. Other fields of investigations
are the modal analysis of rocks, the provenance evaluation of clastic sediments, diagenetic studies, the reconstruction of
alteration processes and fluid flow, the detection of radiation damage or investigations of ultra-pure quartz and silica glass
in technical applications.
Zusammenfassung
Ursachen, spektrale Charakteristika und praktische Anwendungen der Kathodolumineszenz (KL) von Quarz – eine Revision
Untersuchungen von natürlichen und synthetischen Quarzproben mittels Kathodolumineszenz (KL) Mikroskopie und -spektroskopie,
Elektron Paramagnetischer Resonanz (EPR) und Spurenelementanalysen zeigen verschiedene Lumineszenzfarben und Emissionsbanden,
die unterschiedlichen intrinsischen und extrinsischen Defekten zugeordnet werden k?nnen.
Die sichtbaren Lumineszenzfarben von Quarz werden durch unterschiedliche Intensit?tsverh?ltnisse der dominierenden Emissionsbanden
zwischen 380 und 700 nm verursacht. Einige der KL Emissionen vom UV bis zum gelben Spektralbereich (175 nm, 290 nm, 340 nm,
420 nm, 450 nm, 580 nm) stehen im Zusammenhang mit intrinsischen Defekten. Die kurzlebigen Lumineszenzemissionen bei 380–390 nm
sowie 500 nm werden mit kompensierten [AlO4/M+]-Zentren in Verbindung gebracht. Die KL-Emissionen im roten Spektralbereich bei 620 bis 650 nm haben ihre Ursache im “nonbridging
oxygen hole centre” (NBOHC) mit verschiedenen Vorl?uferzentren.
Die unterschiedlichen KL-Farben und Emissionsspektren von Quarz k?nnen oft bestimmten genetischen Bildungsbedingungen zugeordnet
werden und erm?glichen deshalb vielf?ltige Anwendungen in den Geowissenschaften und in der Technik. Eine der gravierendsten
Einsatzm?glichkeiten ist die Sichtbarmachung von Internstrukturen, Wachstumszonierungen und Defekten im Quarz, die mit anderen
Analysenmethoden nicht oder nur schwer nachweisbar sind. Weitere wesentliche Untersuchungsschwerpunkte sind die Modalanalyse
von Gesteinen, die Eduktanalyse klastischer Sedimente, Diageneseuntersuchungen, die Rekonstruktion von Alterationsprozessen
und Fluidmigrationen, der Nachweis von Strahlungssch?den oder die Untersuchung von ultrareinem Quarz und Silikaglas für technische
Anwendungen.
Received March 29, 2000 Accepted October 27, 2000 相似文献
13.
The Géant Dormant gold mine is a sulfide-rich quartz vein gold deposit hosted by a volcano-sedimentary sequence and an associated
felsic endogenous dome and dikes. The auriferous quartz-sulfide veins were preceded by two synvolcanic gold-bearing mineralizing
events: early sulfidic seafloor-related and later disseminated pyrite in the felsic dome. This deposit differs from classical
Archean auriferous quartz vein deposits by the low carbonate and high sulfide contents of the veins and by their formation
prior to ductile penetrative deformation. The δ18O values of quartz associated with seafloor-related auriferous sulfides average 11.9 ± 0.6‰ (n = 3). The seafloor hydrothermal fluids had a δ18O value of 3.2‰ calculated at 250 °C. The oxygen isotope composition of quartz and chlorite from veins average 12.5 ± 0.3‰
(n = 20) and 5.9 ± 1.1‰ (n = 4) respectively. Assuming oxygen isotope equilibrium between quartz and chlorite, the veins formed at a temperature of
∼275 °C, which is consistent with the calculated temperature of 269 ± 10 °C from chlorite chemistry. The gold-bearing fluids
had a δ18O value of 4.7‰ calculated at 275 °C. The δ34S values of sulfides from the three gold events range from 0.6 to 2.8‰ (n = 32) and are close to magmatic values. Sulfur isotope geothermometry constrains the sulfide precipitation in the gold-bearing
veins at a temperature of ∼350 °C. The similarity of the isotope data, the calculated δ18O of the mineralizing fluids and the likely seawater fluid source suggest that the three mineralizing events are genetically
related to a volcanogenic hydrothermal system. The high value of the auriferous fluids (δ18O = 4.7‰) is attributed to a significant magmatic fluid contribution to the evolved seawater-dominated convective hydrothermal
system. The two-stage filling of veins at increasing temperature from quartz-chlorite (275 °C) to sulfides (350 °C) may reflect
the progressive maturation of volcanogenic hydrothermal systems. These results, together with field and geochemical data,
suggest that formation of gold-rich volcanogenic systems require specific conditions that comprise a magmatic fluid contribution
and gold from arc-related felsic rocks, coeval with the mineralizing events. This study shows that some auriferous quartz-vein
orebodies in Archean terranes are formed in volcanogenic rather than mesothermal systems.
Received: 12 December 1998 / Accepted: 5 July 1999 相似文献
14.
F. Farges 《Physics and Chemistry of Minerals》2001,28(9):619-629
Fe–K edge XAFS spectra (pre-edge, XANES and EXAFS) were collected for eight grandidierites from Madagascar and Zimbabwe,
as well as for Fe(II) and Fe(III) model compounds (staurolite, siderite, enstatite, berlinite, yoderite, acmite, and andradite).
The pre-edge spectra for these samples are consistent with dominantly 5-coordinated ferrous iron. The analysis of the XANES
and EXAFS spectra confirms that Fe(II) substitutes for Mg(II) in grandidierite, with a slight expansion of the local structure
around Mg by ∼2%. In addition, ferric iron was also detected in some samples [5–10 mol% of the total Fe or 500–1100 ppm Fe(III)].
Based on theoretical calculations of the EXAFS region, Fe(III) appears to be located in the 5-coordinated sites of Mg(II)
or in the most distorted 6-coordinated sites of Al (depending on the sample studied). Special attention is therefore required
when using grandidierite as a model for ferrous iron in C3v geometry, because of the possible presence of an extra contribution related to Fe(III). This additional contribution enhances
significantly the Fe–K pre-edge integrated area [+40% for 1000 ppm Fe(III)]. Therefore, only a few grandidierite samples can
be used as a robust structural model for the study of the Fe(II) coordination in glasses and melts.
Received: 26 June 2000 / Accepted: 19 February 2001 相似文献
15.
Colin M. Graham John W. Valley John M. Eiler Hideki Wada 《Contributions to Mineralogy and Petrology》1998,132(4):371-389
Using a recently developed ion microprobe technique, a detailed oxygen isotope map of calcite grains in a coarse-grained
marble has been constructed, supported by trace element (Mn, Sr, Fe) analysis and cathodoluminescence (CL) imaging, in order
to constrain scales of oxygen isotope equilibrium, timescales and mechanisms of metamorphic fluid infiltration, and fluid
sources and pathways. Results are compared with a previous study of this sample (Wada 1988) carried out using a cryo-microtome
technique and conventional oxygen isotope analysis. The marble, from the high temperature/low pressure Hida metamorphic belt
in north-central Japan, underwent granulite facies followed by amphibolite facies metamorphic events, the latter associated
with regional granite intrusion. The CL imaging indicates two types of calcite, a yellow luminescing (YLC) and a purple luminescing
(PLC) variety. The YLC, which occupies grain boundaries, fractures, replacement patches, and most of the abundant deformation
twin lamellae, post-dates the dominant PLC calcite and maps out fluid pathways. Systematic relationships were established
between oxygen isotope and trace element composition, calcite type and texture, based on 74 18O/16O and 17 trace element analyses with 20–30 μ m spatial resolution. The YLC is enriched in Mn and Fe, and depleted in 18O and Sr compared to PLC, and is much more 18O depleted than is indicated from conventional analyses. Results are interpreted to indicate infiltration of 18O-depleted (metamorphic or magmatic) fluid (initial δ18O = 9‰–10.5‰) along grain boundaries, fractures and deformation twin lamellae, depleting calcite grains in Sr and enriching
them in Mn and Fe. The sample is characterised by gross isotopic and elemental disequilibrium, with important implications
for the application of chromatographic theory to constrain fluid fluxes in metacarbonate rocks.
Areas of PLC unaffected by “short-circuiting” fluid pathways contain oxygen diffusion profiles of ∼10‰/∼200 μm in grain boundary
regions or adjacent to fractures/patches. When correction is made for estimated grain boundary/fracture and profile orientation
in 3D, profiles are indistinguishable within error. Modelling of these profiles gives consistent estimates of Dt (where D is the diffusion coefficient and t is time) of ∼0.8 × 10−8 m2, from which, using experimental data for oxygen diffusion in calcite, timescales of fluid transport along grain boundaries
at amphibolite facies temperatures of ∼103 to ∼104 years are obtained. These short timescales, which are much shorter than plausible durations of metamorphism, imply that
rock permeabilities may be transiently much higher during fluid flow than those calculated from time integrated fluid fluxes
or predicted from laboratory measurements. The preservation of 18O/16O profiles requires either rapid cooling rates (∼100–600 °C/million years), or, more plausibly, loss of grain boundary fluid
such that a dry cooling history followed the transient passage of fluid. The δ18O/trace element correlations are also consistent with volume diffusion-controlled transport in the PLC. Fluid transport and
element exchange occurred by two inter-related mechanisms on short timescales and on different lengthscales – long-distance
flow along cracks, grain boundaries and twin lamellae coupled to ∼200 μm-scale volume diffusion of oxygen.
Received: 8 December 1997 / Accepted: 18 May 1998 相似文献
16.
Osvaldo M. Rabbia Laura B. Hernández David H. French Robert W. King John C. Ayers 《Mineralium Deposita》2009,44(8):849-866
Mineralogical, textural, and chemical analyses (EPMA and PIXE) of hydrothermal rutile in the El Teniente porphyry Cu–Mo deposit
help to better constrain ore formation processes. Rutile formed from igneous Ti-rich phases (sphene, biotite, Ti-magnetite,
and ilmenite) by re-equilibration and/or breakdown under hydrothermal conditions at temperatures ranging between 400°C and
700°C. Most rutile nucleate and grow at the original textural position of its Ti-rich igneous parent mineral phase. The distribution
of Mo content in rutile indicates that low-temperature (∼400–550°C), Mo-poor rutile (5.4 ± 1.1 ppm) is dominantly in the Mo-rich
mafic wallrocks (high-grade ore), while high-temperature (∼550-700°C), Mo-rich rutile (186 ± 20 ppm) is found in the Mo-poor
felsic porphyries (low-grade ore). Rutile from late dacite ring dikes is a notable exception to this distribution pattern.
The Sb content in rutile from the high-temperature potassic core of the deposit to its low-temperature propylitic fringe remains
relatively constant (35 ± 3 ppm). Temperature and Mo content of the hydrothermal fluids in addition to Mo/Ti ratio, modal
abundance and stability of Ti-rich parental phases are key factors constraining Mo content and provenance in high-temperature
(≥550°C) rutile. The initial Mo content of parent mineral phases is controlled by melt composition and oxygen fugacity as
well as timing and efficiency of fluid–melt separation. Enhanced reduction of SO2-rich fluids and sulfide deposition in the Fe-rich mafic wallrocks influences the low-temperature (≤550°C) rutile chemistry.
The data are consistent with a model of fluid circulation of hot (>550°C), oxidized (ƒO2 ≥ NNO + 1.3), SO2-rich and Mo-bearing fluids, likely exsolved from deeper crystallizing parts of the porphyry system and fluxed through the
upper dacite porphyries and related structures, with metal deposition dominantly in the Fe-rich mafic wallrocks. 相似文献
17.
M. V. Portnyagin L. V. Danyushevsky V. S. Kamenetsky 《Contributions to Mineralogy and Petrology》1997,128(2-3):287-301
We present a detailed mineralogical, petrological and melt inclusion study of unusually fresh, primitive olivine + clinopyroxene
phyric Lower Pillow Lavas (LPL) found near Analiondas village in the northeastern part of the Troodos ophiolite (Cyprus).
Olivine phenocrysts in these primitive LPL show a wide compositional range (Fo82–92) and have higher CaO contents than those from the Upper Pillow Lavas (UPL). Cr-spinel inclusions in olivine are significantly
less Cr-rich (Cr/Cr + Al = 28–67 mol%) compared to those from the UPL (Cr# = 70–80). These features reflect differences in
melt compositions between primitive LPL and the UPL, namely higher CaO and Al2O3 and lower FeO* compared to the UPL at a given MgO. LPL parental melts (in equilibrium with Fo92) had ∼10.5 wt% MgO and crystallization temperatures ∼1210 °C, which are significantly lower than those previously published
for the UPL (14–15 wt% MgO and ∼1300 °C for Fo92). The fractionation path of LPL parental melts is also different from that of the UPL. It is characterized initially by olivine + clinopyroxene
cotectic crystallization joined by plagioclase at ∼9 wt% MgO, whereas UPL parental melts experienced a substantial interval
of olivine-only crystallization. Primitive LPL melts were formed from a mantle source which was more fertile than that of
tholeiites from well-developed intra-oceanic arcs, but broadly similar in its fertility to that of Mid-Ocean Ridge Basalt
(MORB) and Back Arc Basin Basalts (BABB). The higher degrees of melting during formation of the LPL primary melts compared
to average MORB were caused by the presence of subduction-related components (H2O). Our new data on the LPL coupled with existing data for the UPL support the existing idea that the LPL and UPL primary
melts originated from distinct mantle sources, which cannot be related by progressive source depletion. Temperature differences
between these sources (∼150 °C), their position in the mantle (∼10 kbar for the colder LPL source vs 15–18 kbar for the UPL
source), and temporal succession of Troodos volcanism, all cannot be reconciled in the framework of existing models of mantle
wedge processes, thermal structure and evolution, if a single mantle source is invoked. Possible tectonic settings for the
origin of the Troodos ophiolite (forearc regions of intra-oceanic island arc, propagation of backarc spreading into arc lithosphere)
are discussed.
Received: 20 May 1996 / Accepted: 25 March 1997 相似文献
18.
Both stratiform/stratabound and granite-related models have been used to explain the genesis of W(Mo) deposits in the Okiep
copper district in western Namaqualand, South Africa. Apparently, stratabound mineralization (Fe-rich wolframite with accessory
molybdenite) occurs in foliation-parallel quartz veins in high-grade (∼750 °C, 5–6 kbar) metapelites of the Wolfram Formation,
and less commonly in small bodies of silicified leucogranites and pegmatites. Six Re–Os ages for molybdenites from four deposits
(Nababeep Tungsten Far West, Kliphoog, Narrap, Tweedam) range between 1000 ± 4 and 1026 ± 5 Ma. These molybdenites define
a well-constrained 187Re–187Os isochron with an age of 1019 ± 6 Ma, which is interpreted as the age of W(Mo) mineralization. This age is significantly
younger than Proterozoic protolith ages for supracrustal rocks and the emplacement ages for the main intrusive suites, but
geologic evidence requires overlap with a period of high-grade metamorphism. We suggest that W(Mo) mineralization is genetically
linked to intra-crustal magmatic processes at ∼1020 Ma, thereby precluding the ∼1060 Ma Concordia granite as the source for
mineralizing fluids. A narrow range of positive δ34S compositions (+3.6 to +4.5‰) for eight molybdenites from five W(Mo) mines is consistent with a SO2-rich fluid and a granite-related genetic model. Post-peak metamorphic deformation and metamorphism of W(Mo) ores is most
likely related to the retrograde stage of the Namaquan orogeny, which overlaps emplacement of late-orogenic, evolved granites
and pegmatites, and the formation of W(Mo) deposits in western Namaqualand. Therefore, the effects of retrograde Namaquan
metamorphism extend at least to ∼1020 Ma or, alternatively, these W(Mo) veins were affected by a poorly constrained later
event (e.g. early Pan-African).
Received: 12 September 1999 / Accepted: 20 April 2000 相似文献
19.
A case of new particle formation observed during dissipation stage of a thunderstorm at a tropical station, Pune, India on
3 June 2008 is reported. The flash rate and rainfall intensity increased as high as 110 flashes per 5 minutes and 150 mm hour − 1 respectively during the active stage of thunderstorm, and then gradually decreased during the dissipation stage. The number
concentration of particles in the size range of 10–100 nm sharply increased from 350 particles cm − 3 to ∼8000 particles cm − 3 during the dissipation stage of a thunderstorm and grew to larger diameter subsequently. Observations suggest that the atmospheric
conditions such as (i) reduced background aerosol concentration after heavy rain, (ii) high humidity condition, and (iii)
increased ion concentration during the dissipation stage by corona discharges, favoured generation of new particles by ion-induced
nucleation (IIN). Observations also suggest that generation of unipolar ions by corona discharges may be more favourable for
IIN and subsequent growth of the particles. 相似文献
20.
N. S. Bagdassarov 《Physics and Chemistry of Minerals》1999,26(6):513-520
The present study deals with the small strain torsion deformation of MACOR glass-ceramic samples at high temperatures (450–850 °C)
and over a range of low frequencies (20 Hz–5 mHz). The samples of MACOR ceramic consist of 55 vol% randomly oriented, sheet-like
fluorophlogopite mica crystals (∼100–20 μm in planar size, 1–2 μm in thickness) and 45 vol% of isotropic alumino-borosilicate
glass matrix. Measurements of the complex shear modulus show that the sample does not possess the relaxed shear viscosity
even at temperatures above the glass transition temperature of the glass matrix. The maximum of the imaginary component G
′′() of the shear modulus is ∼0.15 of the unrelaxed value G
∞, the relaxation strength Δ≈0.9. The activation energy of the peak of G
′′() is ∼245 kJ mol−1. Using this value of E
a
, the data obtained at various frequencies and temperatures have been reduced to a master curve using the dimensionless variable
ωτ, where ∼0 exp(−E
a
/RT). The internal friction Q−1(ωτ) is ∝1/()0.35−0.4 in the low-temperature high-frequency range (1); passes through a maximum at ∼1 and trends asymptotically to a value Q−1∼0.25–0.30 at ≪1. The behaviour of Q
−1(ωτ) differs from that of a Caputo body by the presence of the resolved peak which may be attributed to the slow mechanical
relaxation of mica crystals due to rotation as well as flexing and bending modes of crystal deformation.
Received: 26 June 1998 / Revised, accepted: 13 January 1999 相似文献