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1.
Hiroshi Nagasawa 《Contributions to Mineralogy and Petrology》1973,39(4):301-308
Rare-earth, Sr and Ba abundances were determined for three basalts, one mugearite, one trachyandesite and five trachytes from Dogo, Oki Islands, Japan and Ca-rich clinopyroxene and feldspar phenocryst samples separated from them. It is concluded that rareearth, Sr and Ba abundance patters for basalts and three trachytes could be explained by crystallization differentiation of olivine basalt magma, while those for other samples suggest more complicated process of magma production. Calculated Eu2+ to total Eu ratios in the magmas showed a increasing trend with differentiation. It is found that Yb and Lu partition coefficients were larger than those of lighter rare earths for clinopyroxenes in trachytes suggesting preferential substitution of the heavy rare-earth ions for Mg-site in the clinopyroxenes. 相似文献
2.
Dr. S. Nakano 《Mineralogy and Petrology》1992,46(2):123-135
Summary The cooling history of the feldspars of a hypersthene-augite trachyte lava of Oki-Dogo island, Japan was investigated by optical microscope, electron microscope and X-ray microanalyzer. Anti-Rpakivi mantled feldspars in the alkaline volcanic rocks consist of anhedral plagioclase cores and subhedral to euhedral sanidine mantles. The interfaces between the cores and mantles are wavy, saw-tooth-like, or comb-like under the optical microscope, suggesting sanidine overgrowth after plagioclase was partially resorbed. Perthitic lenses or lamellae of plagioclase are also observed in the sanidine near the interfaces. After the formation of such mantled feldspars at the magmatic stage, perthitic lamellae were produced in sanidine due to subsolidus exsolution. Periodicity of the perthitic lamellae is below 10 nm.[/ab]
Zusammenfassung Die Abkühlungs-Geschichte von Feldspäten einer Hypersthen-Augit-Trachyt-Lava von der Insel Oki-Dogo, Japan, wurde mikroskopisch, elektronenmikroskopisch und mit der Mikrosonde untersucht. Anti-Rapakivi-Feldspate in den Alkali-Vulkaniten bestehen aus anidiomorphen Plagioklas-Kernen and idiomorphen Sanidin-Rändern. Die Grenzen zwischen Kernen and Randern erscheinen unter dem Mikroskop gewellt, sägezahnartig oder kammartig. Dies deutet darauf hin, daß Überwachsung mit Sanidin nach teilweiser Resorption von Plagioklas stattgefunden hat. Perthitische Linsen oder Lamellen von Plagioklas im Sanidin wurden im Grenzbereich der beiden Feldspäte beobachtet. Perthit-Lamellen im Sanidin entstanden durch Subsolidus-Entmischung nachdem die Feldspäte wahrend der magmatischen Phase gebildet worden waren. Die Periodizität der Perthit-Lamellen liegt unter 10 nm.相似文献
3.
Robert J. Stull 《Lithos》1978,11(3):243-249
Mantled feldspars that formed by resorption, development of skeletal plagioclase crystals, and filling with alkali feldspar are common in the Golden Horn batholith, Washington. Subhedral plagioclase mantles have weak normal zoning from An17 to An10. Plagioclase zoning and twinning are crosscut by resorption channels. Resorption cavities and channels are coated with albite (An10). Anhedral, perthitic orthoclase within the plagioclase is optically continuous with orthoclase in channels and on the mantle exterior.This texture resulted from resorption of calcic cores of plagioclase as pressure decreased when water-undersaturated granite magma intruded to a shallow crustal level. At shallow level, only alkali feldspar and quartz crystallized and were available to fill the skeletal plagioclase. 相似文献
4.
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
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.
D. R. Waldbaum 《Contributions to Mineralogy and Petrology》1967,17(1):71-77
Recent hydrofluoric acid solution calorimetric data are used to derive standard enthalpies and Gibbs free energies of formation of low-albite, high-albite, NaAlSi3O8 glass, microcline, sanidine, and KAlSi3O8 glass. The data are presented as high-temperature functions from 298.15 to 1400° K. 相似文献
7.
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
8.
The Miocene Kitami rhyolite, consisting of orthopyroxene and plagioclase-phyric lavas and dikes, occurs on the back-arc side of the Kuril arc with coeval basalts and Fe-rich andesites. Temperatures estimated from orthopyroxene–ilmenite pairs exceed 900°C. Although the whole rock compositions of the Kitami rhyolite correspond to S-type granites (i.e., high K, Al, large ion lithophile elements, and low Ca and Sr), Sr–Nd isotope compositions are remarkably primitive, and similar to those of the coeval basalts and andesites. They are distinct from those of lower crustal metamorphic rocks exposed in the area. Comparison of chondrite-normalized rare earth element (REE) patterns between the rhyolite and the basalts and andesites show that the rhyolite is more light REE enriched, but has similar heavy REE contents than the basalts. All rhyolites show negative Eu anomalies. The geochemical data suggest that did not formed by simple dehydration melting of basaltic rocks or fractional crystallization of basaltic magmas. The features of slab-derived fluids expected from recent high pressure experimental studies indicates that mantle wedge is partly metasomatized with “rhyolitic” materials from subducted slabs; it is more likely that very low degree partial melting of the metasomatized mantle wedge formed the rhyolite magma. 相似文献
9.
The cathodoluminescence (CL) of a variety of alkali feldspars from South Greenland has been examined in an attempt to understand
the causes of the CL and its petrological significance. Analytical methods have included CL spectroscopy, secondary ion mass
spectrometry (SIMS) and electron paramagnetic resonance (EPR) to correlate the presence of certain CL emissions to the presence
of certain trace element and point defects. Where possible, blue and red luminescent fractions of the same rock samples have
been separated and analysed separately. Blue CL appears to relate to the presence of electron holes on bridging oxygens, particularly
on the Al-O-Al bridge, as determined from EPR studies. No correlation with other proposed activators for blue CL such as Eu2+, Ga3+ or Ti4+ was observed. Some blue luminescent feldspars also have an emission in the infra-red (IR), invisible during normal visible
CL petrography. The red and IR CL emissions correspond to features in EPR spectra attributed to Fe3+ and support previous suggestions that Fe3+ is related to this emission. However, our studies indicate that the visible red CL relates specifically to Fe3+ on the T1 site, whereas the equivalent CL from disordered feldspars lies in the IR. The difference between red and IR CL
emissions therefore relates to the state of Fe3+ order across the tetrahedral sites. These data allow more meaningful interpretations of CL as a petrographic tool in alkali
feldspar-bearing rocks.
Received: 5 March 1998 / Accepted: 23 November 1998 相似文献
10.
Christos Evangelakakis Herbert Kroll Gerhard Voll Hans-Rudolf Wenk Hu Meisheng Jürgen Köpcke 《Contributions to Mineralogy and Petrology》1993,114(4):519-532
In the alkali feldspars of the amphibolite- and granulite-facies rocks of Sri Lanka, a late-stage, final exsolution event is observed which produced film lamellae and fine-scale spindles. These were investigated by optical, microprobe, single-crystal, transmission electron microscopy and atomic resolution microscopy techniques. The lamellae and spindles exsolved below the coherent solvus at temperatures as low as 300 to 350° C. Precession photographs and ARM micrographs show that the intergrowth is perfectly coherent. In sections (010) the rhombic section of the Pericline twins corresponds to analbite or high albite. The albite lamellae and spindles nucleated and grew at low temperatures in a metastable disordered structural state within a tweed-orthoclase matrix and became periodically twinned analbite or high albite, which subsequently developed only a slight increase in Al, Si order. The relationship between twin periodicity and lamellar width, predicted for coherent intergrowths by Willaime and Gandais (1972), is obeyed. In Or-rich grains, in which coherent exsolution is the only exsolution event, the film lamellae tend to be restricted to the rim, the fine-scale spindles to the centre of the grains. The films nucleated heterogeneously at grain boundaries and grew towards the grain centres. Fine-scale spindles probably nucleated homogeneously in the interior part of grains. Heterogeneous nucleation and coherent growth are not mutually exclusive. 相似文献
11.
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
12.
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
13.
《Applied Geochemistry》1995,10(1):111-113
Positive identification of the origin of fine-grained quartz in highly weathered soils is not proven by routine microscopic examination. The oxygen isotope composition (δ18O vs SMOW) of quartz was determined in the albic horizon of three soils developed on the Cretaceous Nohhi rhyolite from Kiso, central Japan. Differences in the isotopic composition of quartz as a function of particle size were observed and attributed to the degree of hydrothermal alteration. One soil sample developed nearby hornblende porphyrite intrusion showed systematic increases in the δ18O values with increasing particle size, from +3.6‰ (1–10 μm) to +9.5‰ (500–2000 μm). Such a trend is indicative of the higher contribution of secondary quartz precipitated from hydrothermal meteoric fluids in fine size fractions in contrast to primary magmatic quartz in coarse size fractions. Hydrothermal activity was inferred for another soil where no lateral intrusion is mapped. The variation in the oxygen isotopic composition of quartz in different particle sizes precludes both eolian and authigenic origins for the soils. The stable isotope technology provides the only rationale for positive identification of the origin of fine-grained quartz in soils. 相似文献
14.
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
15.
Ken-ichiro Aoki 《Contributions to Mineralogy and Petrology》1970,25(4):284-288
Andesine megacrysts up to 3 cm in size occur sporadically in certain alkali basalts and allied mafic rocks in southwestern Japan. They are sometimes accompanied by megacrysts of mafic minerals and ultramafic and mafic inclusions. Nine andesines have been chemically analysed.From the petrography and chemistry and the results of high pressure experimental work, it is suggested that andesine megacrysts crystallized from alkali basalt magma under dry conditions at a depth of about 30 to 60 km. 相似文献
16.
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
17.
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 |