Very low grade metamorphism of the Taveyanne formation of western Switzerland (original) (raw)

Abstract

The andesitic early Oligocene Taveyanne metagreywacke of the Helvetic nappes of western Switzerland shows an increase of metamorphic grade from zeolite facies through lower greenschist facies. Electron microprobe analysis, fluid inclusion thermometry, stable isotope analysis, coal rank, illite and chlorite crystallinity and thermodynamic calculations were carried out to determine metamorphic conditions. Evaluation of all techniques used in this study suggest that only combinations of different parameters yield reliable information to constrain very low-grade metamorphic conditions. Electron microprobe analyses are presented for actinolite, chlorite, epidote, phengite, laumontite, prehnite, pumpellyite, and titanite. With increasing metamorphic grade, chlorite is enriched in tetrahedral Al, pumpellyite becomes poorer in Fetot and more homogeneous in chemical composition, and titanite tends to incorporate Ti at the expense of Al and Fe3+. Metamorphic _P_-T conditions were determined by a combination of fluid inclusion microthermobarometry, stable isotope thermometry on quartz-calcite veins, chlorite “geothermometry” and thermodynamic calculations. Peak temperatures range from 210–250 °C for zeolite facies to 270–300 °C for prehnite-pumpellyite facies to 300–360 °C for pumpellyite-actinolite facies. An evaluation of 289 chlorite analyses indicates that the tetrahedral Al content is negatively correlated with the saponite component. Temperatures derived from chlorite “geothermometry” match maximum temperature conditions mentioned above. Illite crystallinity data for shales and slates intercalated with the Taveyanne metagreywacke indicate that the diagenetic zone correlates with the zeolite facies, the upper anchizone with the prehnite-pumpellyite facies, and the lower epizone with the pumpellyite-actinolite facies. A comparison of coal rank and illite crystallinity data (_n_=12,_r_=0.91) yielded R max values of 2.9 and 5.5% for the lower and upper boundary of the anchizone, respectively.

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Authors and Affiliations

  1. Mineralogisch-Petrographisches Institut, University of Basel, Bernoullistrasse 30, CH-4056 Basel, Switzerland Fax: +4161 267 2881 e-mail: schmidtd@ubaclu.unibas.ch, , , , , , CH
    David Schmidt, Susanne T. Schmidt, Joseph Mullis, Rafael Ferreiro Mählmann & Martin Frey

Authors

  1. David Schmidt
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  2. Susanne T. Schmidt
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  3. Joseph Mullis
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  4. Rafael Ferreiro Mählmann
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  5. Martin Frey
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Received: 2 August 1996 / Accepted: 16 July 1997

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Schmidt, D., Schmidt, S., Mullis, J. et al. Very low grade metamorphism of the Taveyanne formation of western Switzerland.Contrib Mineral Petrol 129, 385–403 (1997). https://doi.org/10.1007/s004100050344

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