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141.
Late-stage hydrous fluids, which evolved during the cooling of the Cadillac Mountain granite, Maine, USA, produced narrow veins that transect the pluton. The vein margins contain microstructures transitional between granite and the vein centre. They preserve the vestige shapes of original Na-rich alkali feldspar crystals that have been pseudomorphed by cordierite+quartz+K-rich alkali feldspar. Closer to the centres of the veins, the minerals change from an outer zone with cordierite, hercynitic–galaxite spinel, minor corundum, K-feldspar and plagioclase to an inner zone with remnant cordierite, hercynitic gahnite, strongly zoned almandine–spessartine garnet, chlorite and quartz. Three allochemical reactions are inferred to have occurred with the influx of hydrous fluids during the replacement process. Reaction (1) is Na-rich alkali feldspar+iron ions in solution=Fe-cordierite+quartz+K-feldspar+sodium ions in solution. Reactions (2) and (3) occurred during desilication. Reaction (2) is Fe-cordierite=hercynite+silica in solution, and reaction (3) is Fe-cordierite+water=corundum+iron hydroxide in solution+silicic acid in solution. Two independent techniques, experimental silica-solubility data and spinel–cordierite thermobarometry, constrain the conditions of vein formation to c. 1.0 kbar and both methods indicate that the progressive mineral reactions occurred during cooling of the hydrous fluids from c. 775° to 400–340 °C. This cooling trend is consistent with the petrographic evidence, which demonstrates that reactions occurred before desilication, during desilication, and then diminished with a final phase of resilication. Although the veins are minor features of the Cadillac Mountain granite, they provide insight into the conditions that prevailed during cooling of the pluton, and similar features may be important for constraining the cooling history of shallow-level plutonic complexes elsewhere. 相似文献
142.
RUAN Xiaohong SONG Gaopeng ZHANG Yichun LI Yingxia 《中国海洋大学学报(英文版)》2007,6(2):196-198
A convenient and effective procedure was developed for the conversion of alcohol to olefin by tosylation and subsequent β-elimination promoted by silica gel in this study. Treatment of the alcohols with p-toluenesulfonyl chloride in pyridine at 0℃ affords tosylates which undergo β-elimination with silica gel in dichloromethane or chloroform at room temperature, yielding olefinswith high productivity. 相似文献
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The species of Epithemia ocellata (Ehr.) Kuetz. from Northeastern China were observed by scanning electron microscopy (SEM). The studies on silica valve formation in different stages were made. At the early stage, a Y-shaped raphe sternum was found. Areolae were made from virgae and vimines. In immature valves, the canal formation before the raphe fissure is visible. The raphe system, virgae and vimines (areolae) might be the early siliceous elements of the valve during morphogenesis. The formations of virgae and vimines are similar to that of Gephyria media W. Arnott. Rows of silica papillae formed gradually on the face of the valve. After the areolae were covered with silica and form rows of papillae, the outer valve surface could become mature. Details of the internal costae were observed in mature valves. 相似文献
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