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51.
The redox state of sillimanite zone (650700°C, 56kbar) metasediments of the Barrovian type area, Scotland, wasinvestigated using estimates of metamorphic oxygen fugacity(fO2), sulfur fugacity (fS2), and fluid chemistry based on newdeterminations of mineral and rock compositions from 33 samples.A total of 94% of the samples lack graphite, contain both ilmenitehematitesolid solutions (RHOMOX) and magnetite, and had metamorphicfO2 about 2 log10 units above the quartzfayalitemagnetite(QFM) buffer. The regional variation in metamorphic fO2 forthese rocks was minimal, about ±0·3 log10 units,reflecting either a protolith that was homogeneous with respectto redox state, or an initially variable protolith whose redoxstate was homogenized by metamorphic fluidrock interaction.RHOMOX inclusions in garnet porphyroblasts that become richerin ilmenite from the interior to the edge of the host porphyroblastsuggest that at least some syn-metamorphic reduction of rockoccurred. Significant variations in bulk-rock oxidation ratio(OR) that are probably inherited from sedimentary protolithsare found from one layer to the next; OR ranges mostly between 相似文献
52.
Reflectivities of uniform and broken layered clouds 总被引:2,自引:0,他引:2
53.
EUGSTER H. P.; ALBEE A. L.; BENCE A. E.; THOMPSON J. B. JR.; WALDBAUM D. R. 《Journal of Petrology》1972,13(1):147-179
The chemical compositions of synthetic paragonite-muscovitepairs were obtained by electron probe microanalysis of run productsprepared hydrothermally at 300, 400, 500, and 600 ?C and 2.07kbar. The microcrystalline run products were dispersed on polishedberyllium rods, and Na, K, and Si were determined simultaneously.Compositions were determined from K/Si and Na/Si ratios referredto standards. Tentative excess thermodynamic mixing properties of paragonite-muscovitecrystalline solutions, based on the two-phase composition dataand on X-ray diffraction data, are represented by the followingthird-order Margules formulation:
which leads to a critical temperature of 833 ?C and a criticalcomposition of 39.0 mole per cent Mu at 2.07 kbar (the criticalphase is probably metastable with respect to alkali feldsparand corundum). These results are quantitatively in agreementwith Iiyama's (1964) ion-exchange data. From relationships amongthe quantities (arctanh s)/s, In r2, and 1/T we obtain criticalconditions which are in good agreement with the above (Tc =829 ?C, N2c = 0.396). The critical curve obtained from the aboveMargules parameters is given by: Tc(?C) = 768.8 + 31.00P(kbar). The above results are complicated by polymorphism and by possiblelack of complete equilibrium between the two-mica synthesisproducts and possible substitution of hydronium for alkalies.We emphasize, therefore, that the phase diagrams and derivedmixing properties should be applied with caution to naturalmuscovite- and paragonite-bearing assemblages. 相似文献
54.
The Petrology of Grospydite Xenoliths from the Zagadochnaya Kimberlite Pipe in Yakutia 总被引:2,自引:1,他引:2
The xenoliths of garnetclinopyroxenedisthene rocks(grospydites and associated kyanite eclogites) from the Zagadochnayakimberlite pipe in Yakutia have been studied in detail. Contraryto previous data, the presence of a continuous range in thepyrope-grossular series of garnets is shown on the basis ofnumerous X-ray data and 17 chemical analyses of garnets. Thisconclusion is confirmed by the study of separate grains withkyanite intergrowths from the kimberlite heavy fraction, whichare present in the kimberlite as the result of destruction ofgrospydite xenoliths, and possible, of garnet-kyanite rocksalso. A close connection of the calcium content in the garnetwith the sodium content in the coexisting clinopyroxes is alsoshown. An increase in the chemical potential of sodium resultsin the stability of the pryoxene-kyanite assemblage insteadof a garnet of intermediate composition (50 percent of grossular).The interval of the miscibility gap between calcium-rich andcalcium-poor garnets is increased in this way. The data of chemicalanalyses of 14 pyroxenes from the xenoliths indicate that theydiffer in the high aluminium and sodium content from other pyroxenesof eclogite-facies rocks. Chromium-rich bands with a high chromiumcontent in coexisting garnet, pyroxene, and kyantic have beenoccasionally found in the xenoliths. A study has been made ofthe chrome-kyanite with 12.86 per Cr202. The presence of chromium-richminerals in the grospydite xenoliths confrms their connectionwith ultrabasic rocks. 相似文献
55.
Air photo interpretation along with limited field work is the basis of a compilation map of Tertiary structures in the Upper Paleozoic through Mesozoic platform cover strata of Nordenskiold Land. Permian Kapp Starostin Formation strata form a continuous marker horizon delineating both a large NE-verging fold complex, which involves the basement (Hecla Hoek sequence) through basal Tertiary strata, and somewhat smaller scale folds, some of which may have formed in association with detachments and thrusts within the platform cover sequence. The map pattern is both a function of local structural plunge and changes in fold geometry along strike. Regional considerations suggest that subsurface basement-involved thrusts exist. In S Nordenskiold Land, to the E of folded Kapp Starostin Formation strata, a 3.5 km wide zone of folding and thrusting in Triassic and Jurassic strata above a subhorizontal decollement is inferred to occur. Further E is the W limb of the central Tertiary basin syncline. 相似文献
56.
Graciano P. Yumul JR Carla B. Dimalanta Rodolfo A. Tamayo JR Jenny Anne L. Barretto 《Island Arc》2000,9(4):627-637
Abstract The Palawan microcontinental block collided with the Philippine Mobile Belt in the Central Philippine region resulting in the counterclockwise rotation of Mindoro– Marinduque and clockwise rotation of Panay. The collision also brought about the clockwise rotation of north-east Negros, Cebu, north-west Masbate and Bohol (collectively called the Western Visayan block), resulting into their present-day northeast–southwest trend. This suggests a far more dramatic role of the collision than was previously recognized. Furthermore, the south-east Sulu Sea sub-basin is inferred to have also undergone collision-related clockwise rotation which can account for the observed east-west trending magnetic lineations in the basin. Aside from explaining the contrasting morphological trends of the different islands in Central Philippines, the rotation can also explain, albeit in a different way, how the belts of sedimentary basins, ophiolites and arcs in Panay and Negros can extend to Northern Luzon. Published paleomagnetic data suggest that the collision-related rotation commenced during the early to middle Miocene and had ceased by the late Miocene. 相似文献
57.
腾格里沙漠面积广阔 ,区内分布着数十个盐湖 ,盐湖面积大的为十余平方千米 ,小的仅为 0 .0 18km2 。盐湖卤水主要为湖表卤水 ,其矿化度较高 ,大部分盐湖卤水含盐量已达饱和 ,因而进入了自析盐阶段。盐湖卤水化学成分以 Na+ 、K+ 、Cl-、SO4 2 -、HCO3 -、CO3 2 -为主 ,占卤水总含盐量的 99% ,卤水中还有 B2 O3 、L i、I、Br等微量元素。盐湖盐类沉积有碳酸盐类、硫酸盐类和氯化物型盐类、主要盐类矿物为芒硝、钾芒硝、天然碱、泡碱、碳钾钠矾、石盐等。盐湖粘土矿物组合以蒙脱石的普遍存在为特征 ,含有少量的伊利石和水云母。 相似文献
58.
59.
WILLIAM R. GORDON JR NADER M. SOUBRA 《International journal of geographical information science》2013,27(4):267-278
Abstract Practitioners and academics from many fields of study are currently facing numerous issues involving the diffusion of technologies from geographical information systems within their respective professions. This paper has two aims. The first is to report the partial results of a postal survey of selected municipal planning departments in the U.S.A. In measuring trends related to the adoption of computer and geographical information system technologies, the survey focuses on the availability of trained geographical information system and computer literate staff and on alternative means of training existing staff, as well as on the adequacy of collegiate education. The presentation of survey results is used to establish a framework for the principal discussion of this paper. The second part examines the relationship between planning and education in geographical information systems. Parallels within other disciplines and professions are derived. Curricula and training considerations within academic programmes and professional practice are suggested. 相似文献
60.
ABSTRACT Long term changes in streamflow following forest cutting are presented for three experimental basins at Coweeta Hydrologic Laboratory, North Carolina, USA. Previous analyses have shown that, following forest cutting, streamflow increases and then declines with the logarithm of time as the forest regrows. Recent data indicate that the streamflow decline following cutting is related to vegetation regrowth, but the relationship is not a consistent function of simple stand measurements. The mixed hardwood forest of one basin was clearcut twice in the past 40 years. During the second regrowth period, streamflow increases after the first year were about one-half the increases at the same points in time after the first treatment. Concurrent with the second cutting, two other basins were cut whose mid-elevations are 400 m higher. The increases for the upper basins were similar, even though basal area was reduced by only 65% on one. Both streamflow increases were less than for either cutting on the lower basin. Variability of flow increases for the three concurrent treatments is similar and appears partly related to precipitation. 相似文献