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1.
Sr90 Radiotracer diffusion studies have been carried out on crystals of orthoclase and microcline using an ion implantation method. The activation energies are consistent with calculations based on mineral age data. 相似文献
2.
Development of microporosity,diffusion channels and deuteric coarsening in perthitic alkali feldspars 总被引:8,自引:1,他引:8
Richard H. Worden F. David L. Walker Ian Parsons William L. Brown 《Contributions to Mineralogy and Petrology》1990,104(5):507-515
Turbidity is an almost universal feature of alkali feldspars in plutonic rocks and has been investigated by us in alkali feldspars from the Klokken syenite using SEM and TEM. It is caused by the presence of myriads of tubular micro-inclusions, either fluid-filled micropores or sites of previous fluid inclusions, and is associated with coarsening of microperthite and development of sub-grains. Micropores are abundant in coarsened areas, in which porosities may reach 4.5%, but are almost absent from uncoarsened, pristine braind-microperthite areas. The coarsening is patchy, and involves a scale increase of up to 103 without change in the composition of the phases, low albite and low microcline, or in the bulk composition of the crystal. It occurs abruptly along an irregular front within individual crystals, which retain their original shapes. The coherent braid microperthite gives way across the front to an irregular semi-coherent film perthite over a few m and then to a highly coarsened irregular patch perthite containing numerous small sub-grains on scales of a few hundred nm, in both phases. The coarsening and micropore formation occured at a T400°–450° C and it is inferred to have been driven by the release of coherent strain energy, low-angle grain-boundary migration being favoured by a fluid. The patchy nature of the coarsening and the absence of a relationship with initial grain boundaries suggest that the fluid was of local origin, possibly arising in part through exsolution of water from the feldspar. The sub-grain texture and microporosity modify profoundly the permeability of the rock, and greatly enhance the subsequent reactivity of the feldspars. 相似文献
3.
Dagma Derdau Robert Freer Kate Wright 《Contributions to Mineralogy and Petrology》1998,133(1-2):199-204
Oxygen exchange experiments have been performed between single crystals of sanidine feldspar and oxygen gas enriched in 18O, at temperatures in the range 869–1053 °C, total pressure 1 atmosphere, for times up to 28 days. Oxygen isotope diffusion
profiles in a direction perpendicular to (001) were determined with an ion microprobe. The experimental data obey a single
Arrhenius relationship of the form D = 8.4 × 10−11 exp. (−245 ± 15 kJ mol−1/RT) m2s−1. The results indicate that oxygen diffusion in anhydrous sanidine feldspar is marginally slower than oxygen diffusion in
anhydrous anorthite. Comparison with published atomistic simulation studies suggests that oxygen transport in feldspar is
by an interstitial mechanism.
Received: 17 October 1997 / Accepted: 6 July 1998 相似文献
4.
William P. Leeman 《Geochimica et cosmochimica acta》1979,43(1):171-175
Pb contents were determined by isotope dilution in separated glass, sanidine, and plagioclase from 18 rocks ranging in composition from basalt to rhyolite. These data indicate that Pb is partitioned into silicate melt relative to plagioclase, but is equally distributed between melt and sanidine. Plagioclase/glass distribution coefficients increase from 0.1 to 0.7 in going from basalt to rhyolite. This relationship suggests that the distribution coefficient is dependent upon bulk composition, temperature, or both. Sanidine/glass distribution coefficients are close to unity in rocks ranging in composition from quartz latite to rhyolite. The variation in Pb contents in a natural magma series from Craters of the Moon National Monument, Idaho, indicates that minerals (olivine, plagioclase, magnetite, apatite and clinopyroxene) fractionated from these magmas all have very low crystal/liquid distribution coefficients for Pb. 相似文献
5.
Chemical-optical and X-ray analysis of some perthite groups, from cristalline rock massifs, came into evidence that in perthites with the same order degree of Si/Al distribution, the observed variations of 2VX are strictly related to the Na content in the potassic phase; i.e. 2VX decreases when Ab mixed in the K-phase increases.This fact suggests that for any Si/Al, distribution, not in equilibrium, exists a certain range of non equilibrium mixing between Or and Ab. 相似文献
6.
A transmission electron microscope study of intracrystalline boundaries between two perthites of markedly different composition in composite crystals, one a tenary mesoperthite (Or26Ab52An22, initially a homogeneous potassian monalbite) the other a more potassic cryptoperthite (Or61Ab33An6, initially a homogeneous sodian sanidine), shows that the two perthites are in nearly parallel intergrowth. Most boundaries examined were of (hkO) type; (010) boundaries are straight, whereas other (hkO) boundaries are curved or stepped. Exsolution occurred first in the potassian monalbite (mesoperthite) and was unaffected by the boundary. Subsequent exsolution in the sodian sanidine (cryptoperthite) was affected by the boundary, but for up to only a few micrometers. Exsolution occurred by heterogeneous nucleation and growth of oligoclase on and from the intracrystalline boundary. At almost the same time the rest of the volume of sanidine exsolved by spinodal decomposition. 1–2 μm from the boundary in the intervening K-rich matrix of the sodian sanidine, further exsolution occurred by homogeneous nucleation. Time — temperature — transition curves for continuous cooling have been devised to account for the unusual complexity of the exsolution texture. Except in such exceptional circumstances as the example studied, the initial exsolution in high-temperature alkali feldspars of intermediate composition, unlike other minerals, probably does not occur by nucleation, but only by spinodal decomposition. 相似文献
7.
Oxygen diffusion in albite has been determined by the integrating (bulk 18O) method between 750° and 450° C, for a P H2O of 2 kb. The original material has a low dislocation density (<106 cm?2), and its lattice diffusion coefficient (D 1), given below, agrees well with previous determinations. A sample was deformed at high temperature and pressure to produce a uniform dislocation density of 5 × 109 cm?2. The diffusion coefficient (D a) for this deformed material, given below, is about 0.5 and 0.7 orders of magnitude larger than D 1 at 700° and 450° C, respectively. This enhancement is believed due to faster diffusion along the cores of dislocations. Assuming a dislocation core radius of 4 Å, the calculated pipe diffusion coefficient (D p), given below, is about 5 orders of magnitude larger than D 1. These results suggest that volume diffusion at metamorphic conditions may be only slightly enhanced by the presence of dislocations. $$\begin{gathered} D_1 = 9.8 \pm 6.9 \times 10^{ - 6} (cm^2 /\sec ) \hfill \\ {\text{ }} \cdot \exp [ - 33.4 \pm 0.6(kcal/mole)/RT] \hfill \\ \end{gathered} $$ $$\begin{gathered} D_a = 7.6 \pm 4.0 \times 10^{ - 6} (cm^2 /\sec ) \hfill \\ {\text{ }} \cdot \exp [ - 30.9 \pm 1.1(kcal/mole)/RT] \hfill \\ \end{gathered} $$ $$\begin{gathered} D_p \approx 1.2 \times 10^{ - 1} (cm^2 /\sec ) \hfill \\ {\text{ }} \cdot \exp [ - 29.8(kcal/mole)/RT]. \hfill \\ \end{gathered} $$ 相似文献
8.
Summary Feldspar phenocrysts in alkali rhyolite from Oki-Dogo island in the Sea of Japan show mantled textures with cores of anorthoclase and rims of sanidine. These feldspars were examined by electron microscopy, X-ray diffraction and X-ray microanalysis. Anorthoclase first crystallized, then was partially resorbed, and finally sanidine overgrew on the anorthoclase. Saw-tooth or comb-like interfaces between the cores and rims were likely formed at the magmatic stage of resorption and overgrowth. Optically perthitic intergrowths appear in thin sections cutting saw-tooth or comb-like interfaces of the mantled feldspars. The sanidine preserves primary cryptoperthitic textures of a periodicity smaller than 10 nm, which are considered to have been produced by subsolidus exsolution after the resorption event ended. The anorthoclase has no exsolution texture under an electron microscope.
With 6 Figures 相似文献
Feldspatkristalle in Alkali-Rhyolith von der Insel Oki-Dogo, Japan
Zusammenfassung Feldspatkristalle in Alkali-Rhyolith von der Oki-Dogo Insel im Japanischen Meer zeigen ummantelte Texturen mit Kernen von Anorthoklas und Rändern von Sanidin. Diese Feldspate wurden mit Elektronenmikroskopie, Röntgendiffraktion und Mikrosondenanalyse untersucht. Anorthoklas kristallisierte zuerst, wurde dann teilweise resorbiert und schließlich wuchs Sanidin über den Anorthoklas. Sägezahn- und Kamm-ähnliche Grenzen zwischen Kernen und Rändern wurden wahrscheinlich wahrend des magmatischen Stadiums von Resorption und Überwachsung gebildet. Unter dem Mikroskop erkennt man, daß perthitische Verwachsungen durch Sägezahn- oder Kamm-artige Grenzen der ummantelten Feldspäte hinwegsetzen. Der Sanidin erhellt primäre kryptoperthitische Texturen mit einer Periodizität von > 10 nm, die als Produkte einer Subsolidus-Entmischung nach der Resorption interpretiert werden. Anorthoklas läßt unter dem Elektronenmikroskop keine Entmischungstexturen erkennen.
With 6 Figures 相似文献
9.
Alkali feldspar cleavage fragments from the Klokken layered syenite, South Greenland, were heated to 700°C at 0.1 GPa in 99% H2
18O for 75 h. These samples were then polished and imaged by ion microprobe for 18O. The feldspars were known to contain areas of pristine, braid micro-perthite which were not turbid and areas of deuteric patch perthite which were turbid. Turbidity is related to the presence of micropores in the feldspars. On imaging the grain, it was found that the 18O had penetrated into the parts of the grain which were microporous and not into the pristine areas. Micropores are therefore responsible for rendering the feldspars permeable as well as porous. The implications of micropermeable feldspars in several areas of geology are discussed. 相似文献
10.
George D. Guthrie Jr. David R. Veblen 《Contributions to Mineralogy and Petrology》1991,108(3):298-304
Partially turbid alkali feldspars from hydrothermally altered Tertiary granites on the Isle of Skye (the Red Hills granites)
were studied using light microscopy, scanning and transmission electron microscopies, and energy-dispersive X-ray spectroscopy.
Limpid cores and turbid rims of individual crystals were compared to determine the causes of the turbidity. The limpid cores
were cryptoperthitic, with lamellar widths of 0.1–0.3 μm. In contrast, the turbid rims contained K-rich and Narich areas coarsened
to >0.5 μm. Turbid regions contained abundant inclusions, whereas limpid regions did not. Two generations of turbidity were
recognized. Feldspars from the Beinn an Dubhaich granite, a granite with near-normal values for 18O/16O possessed limpid cores surrounded by turbid rims that cast a reddish-brown hue in transmitted light. When viewed in darkfield
light microscopy, the regions with the reddish-brown turbidity were blue. This is consistent with the hypothesis that the
cloudy appearance of these turbid regions arises from the scattering of light by micrometerto submicrometer-sized inhomogeneities
in refractive index caused by fluid-filled cavities. Feldspars from the Loch Ainort granite, a granite with low values for
18O/16O possessed limpid and reddish-brown-turbid cores surrounded by turbid rims that cast a blackish hue in transmitted light.
Ion thinning of the turbid areas produced an abundance of small holes (≤1–2 μm) apparently the remains of fluid inclusions.
Transmission electron microscopy revealed that some holes from regions of reddish-brown turbidity contained non-feldspar material,
including halite and metal-rich phases of various compositions. In contrast, blackish turbid regions contained cavities filled
with alteration products, such as kaolinite. Hence, the feldspars from granites on the Isle of Skye apparently record interactions
with at least two fluids: a saline fluid (possibly a late-stage magmatic fluid) and a meteoric fluid. 相似文献
11.
Strontium and samarium diffusion in diopside 总被引:1,自引:0,他引:1
Mark Sneeringer Stanley R. Hart Nobumichi Shimizu 《Geochimica et cosmochimica acta》1984,48(8):1589-1608
The volume chemical diffusion of trace amounts of Sr in diopside has been measured as a function of temperature (1100–1300°C), pressure (1 bar–20 kbar), crystallographic direction, and composition. Three experimental/analytical techniques were employed: radiotracer and sectioning; stable tracer and ion microprobe; and Rutherford back-scattering spectroscopy. Comparison of the three yielded excellent agreement. Both natural and synthetic single crystal samples were used with results in the natural diopside giving diffusivities approximately two orders of magnitude greater than those in the man-made crystals. Samarium diffusion in the synthetic crystals was also examined with the ion probe technique with results similar to Sr.Arrhenius relations for diffusion (D = D0exp[?ΔHa/RT]) were calculated for different pressures and analytical techniques, and activation volumes (gDVa) were derived from the equation D = D' exp[?PΔVa/ RT]. Values of ΔVa were negative for Sr diffusion. An empirical relation describing the temperature and pressure dependence of D for Sr in the c direction of the synthetic samples is: D(P, T) = 1200 (cm2/sec) exp[?122 (Kcal/mol)/RT (°K)]exp[?P (bar)/(2.94T ? 4640)R]. The expression for DSr in the natural samples (c direction) at one atmosphere is: D(0, T) = 54 (cm2/sec) exp[?97 (Kcal/mol)/RT (°K)]. A single compensation trend for all the data was evident for all values of D0 and ΔHa in the synthetic crystals.A number of models of geologic processes were investigated in light of the present data. Closure temperatures (Tc) were calculated for examples of mineral-mineral age-dating and trace element geothermometry. High values of Tc indicate that pyroxenes record emplacement events and are generally not disturbed unless a fluid enters the system. Isotopic equilibration times were examined for lower crustal xenoliths and the mantle source region for MORB using the formula of Hofmann and Hart (1978). Equilibration was shown to be too fast for production of isotopic anomalies in MORB via disequilibrium melting. Also. reasonable residence times at lower crustal temperatures were shown to produce the mineralogical-scale isotopic homogeneity observed in a crustal xenolith from Kilbourne Hole, New Mexico. 相似文献
12.
The granodioritic and gneissic Hercynian basement in Corsica was intruded, in the Triassic, by non-orogenic ring complexes in which the association early rhyolite-hypersolvus granite-granophyre-late subsolvus granite is clearly developed. The association of low albite and maximum microcline in mesoperthites cannot be attributed to Alpine low-grade metamorphism, restricted to fault zones. On a number of lines of evidence, the development of ordered, almost pure K-feldspar in this rapidly cooled complex appears related to an episode of mild reheating attending emplacement of late subsolvus granites, rocks formed from melts enriched, perhaps even saturated in aqueous fluids. 相似文献
13.
Intracrystal microtextures formed by a process of mutual replacement in alkali feldspars record fluid–rock reactions that
have affected large volumes of the Earth’s crust. Regular, ≤1 μm-scale ‘strain-controlled’ perthitic microtextures coarsen,
by up to 103, by a dissolution–reprecipitation process, producing microporous patch or vein perthites on scales >100 μm. We have developed
earlier studies of such reactions in alkali feldspar cm-scale primocrysts in layered syenites from the Klokken intrusion,
South Greenland. We present new hyperspectral CL, SEM images, and laser ICPMS analytical data, and discuss the mechanism of
such replacement reactions. The feldspars grew as homogeneous sodic sanidines which unmixed and ordered by volume diffusion
during cooling into the microcline field at ~450°C, giving regular, fully coherent ‘braid’ cryptoperthite. At ≤450°C the crystals
reacted with a circulating post-magmatic aqueous fluid. The braid perthite behaved as a single reactant ‘phase’ which was
replaced by two product phases, incoherent subgrains of low albite and microcline, with micropores at their boundaries. The
driving force for the reactions was coherency strain energy, which was greater than the surface energy in the subgrain mosaic.
The external euhedral crystal shapes and bulk major element composition of the primocrysts were unchanged but they became
largely pseudomorphs composed of subgrains usually with the ‘pericline’ and ‘adularia’ habits (dominant {110} and subordinate
{010} morphology) characteristic of low T growth. The subgrains have an epitactic relationship with parent braid perthite. Individual subgrains show oscillatory zoning
in CL intensity, mainly at blue wavelengths, which correlates with tetrahedral Ti. Regular zoning is sometimes truncated by
irregular, discordant surfaces suggesting dissolution, followed by resumption of growth giving regular zoning. Zones can be
traced through touching subgrains, of both albite and microcline, for distances up to ~500 μm. At ≤340°C, the microcline subgrains
underwent a third stage of unmixing to give straight lamellar film perthites with periodicities of ~1 μm, which with further
cooling became semicoherent by the development of spaced misfit dislocations. Sub-grain growth occurred in fluid films that
advanced through the elastically strained braid perthite crystals, which dissolved irreversibly. Braid perthite was more soluble
than the strain-free subgrain mosaics which precipitated from the supersaturated solution. Some volumes of braid texture have
sharp surfaces that suggest rapid dissolution along planes with low surface energies. Others have complex, diffuse boundaries
that indicate a phase of coherent lamellar straightening by volume diffusion in response to strain relief close to a slowly
advancing interface. Nucleation of strain-free subgrains was the overall rate-limiting step. To minimise surface energy subgrains
grew with low energy morphologies and coarsened by grain growth, in fluid films whose trace element load (reflected in the
oscillatory zoning) was dictated by the competitive advance of subgrains over a range of a few tens of mm. The cross-cutting
dissolution surfaces suggest influxes of fresh fluid. Removal of feldspar to give 2 vol% porosity would require a feldspar:fluid
ratio of ~1:26 (by wt). The late reversion to strain-controlled exsolution in microcline subgrains is consistent with loss
of fluid above 340°C following depressurization of the intrusion. A second paper (Part II) describes trace element partitioning
between the albite and microcline subgrains, and discusses the potential of trace elements as a low-T geothermometer.
This paper and the Part II are dedicated in memory of J.V. Smith and W.L. Brown, both of whom died in 2007, in acknowledgement
of their unrivalled contributions to the study of the feldspar minerals over more than half a century. 相似文献
14.
A.E. Beswick 《Geochimica et cosmochimica acta》1973,37(2):183-208
K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm2 total pressure.Complete solid solution of RbMg3AlSi3O10(OH)2 in KMg3AlSi3O10(OH)2 exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi3O8 in KAlSi3O8 has been found at all temperatures investigated.Distribution coefficients, expressed as in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined values and their approximate Rb end-member mole fraction () ranges of constancy are summarized as follows: (°C)
(°C)T | ||||
500 | 0–0.2 | 0–0.07 | ||
700 | 0–0.2 | 0–0.1 | ||
800 | 0–0.2 | 0–0.1 |