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Crystal structures by G. Harsch and R. Schmidt (1986)

Yardley, B. W. D.

Copenhagen : International Union of Crystallography (IUCr)

Acta crystallographica 42 (1986), S. 296-296

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ISSN: 1600-5740

Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1107/S0108768186098191

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Digitale Medien

Origin and history of hydrothermal fluids of the Reykjanes and Krafla geothermal fields, Iceland (1986)

Sveinbjornsdottir, A. E. ; Coleman, M. L. ; Yardley, B. W. D.

Springer

Contributions to mineralogy and petrology 94 (1986), S. 99-109

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ISSN: 1432-0967

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie

Notizen: Abstract The Reykjanes and Krafla geothermal fields are both examples of active high temperature systems and show similar assemblages of alteration minerals, but the fluid at Reykjanes is dominantly sea water whereas that at Krafla is meteoric. Oxygen isotope analyses of surface rock and of drill chip samples from different depths are presented, together with results for the Krafla fluid, which is close to local precipitation (δ 18 O = −11.9‰, δD= −86.8‰). Calcite in both systems is apparently in equilibrium with the present deep fluid at the present field temperature, except for the upper 250 m at Reykjanes where the fluid may be more meteoric than at depth. Feldspar gives similar results. Quartz separates at Reykjanes are anomalously lighter than coexisting feldspar and give exceptionally high quartz-fluid temperatures. It is suggested that quartz originally grew when the fluid was more nearly meteoric (? glacial period) and has not re-equilibrated. Bulk-rock 18 O depletion supports this interpretation of the history of the Reykjanes system. Quartz in the Krafla system is mostly in equilibrium at the present field conditions but anomalies occur near the boundary between the upper and lower parts of the system, suggesting that this is not entirely stable. A high fluid:rock ratio (10–100 minimum) is indicated for the Krafla field.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00371231

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Digitale Medien

Retrogression of staurolite schists and the sources of infiltrating fluids during metamorphism (1985)

Yardley, B. W. D. ; Baltatzis, E.

Springer

Contributions to mineralogy and petrology 89 (1985), S. 59-68

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ISSN: 1432-0967

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie

Notizen: Abstract Staurolite-kyanite schists from the Dalradian of Scotland and Ireland show two types of retrograde alteration. In the Irish examples staurolite and kyanite are replaced by muscovite and paragonite, often with margarite and sometimes chloritoid. Plagioclase in these samples may be albitized. In contrast one Scottish sample shows replacement of both staurolite and plagioclase by muscovite. Retrogression resulted from infiltration of fluid, but while in some samples the large number of retrograde phases internally buffered the fluid composition and cation metasomatism cannot be proven, in others the fluid composition was externally controlled and there was cation metasomatism indicating more extensive infiltration. It is demonstrated by the use of activity diagrams showing the relationships between Al-silicate, white mica and alkali feldspar that wholesale alteration to muscovite was most likely caused by fluids moving down-temperature from a granitic or arkosic source. In contrast, if growth of retrograde albite is actually accompanied by Na-metasomatism then the infiltrating fluids are likely to have been moving up-temperature through pelitic lithologies. Large fluid: rock ratios of around 10∶1 are needed to achieve significant alkali metasomatism except in extreme situations of large temperature changes and highly concentrated fluids.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01177591

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