Journal of Petrology, Volume 40, Issue 1: January 1999.

Petrology of High-Pressure Metapelites from the Adula Nappe (Central Alps, Switzerland)

CHRISTIAN MEYRE¹, CHRISTIAN DE CAPITANI¹, THOMAS ZACK² AND MARTIN FREY¹

¹MINERALOGISCH-PETROGRAPHISCHES INSTITUT DER UNIVERSITÄT BASEL, BERNOULLISTRASSE 30, CH-4056 BASEL, SWITZERLAND
²MINERALOGISCH-PETROGRAPHISCHES INSTITUT UNIVERSITÄT GÖTTINGEN, GOLDSCHMIDTSTRASSE 1, D-37077 GÖTTINGEN, GERMANY

High-pressure metamorphism in the Penninic Adula nappe (Central Alps, Switzerland) reached eclogite facies conditions. Besides abundant mafic eclogite lenses, very few metapelitic rocks also preserved high-pressure relics, even though most of the felsic lithologies were retrogressed during a later amphibolite facies overprint. Calculations of equilibrium phase diagrams of whiteschist and sodic whiteschist assemblages reveal conditions of P>20 kbar at T ~650°C. Common metapelitic assemblages (garnet + phengite + kyanite + quartz ± paragonite) are stable over a wide range in pressure and temperature. Calculations of the peak pressure conditions in the investigated metapelite samples are in good agreement with analogue calculations of eclogite samples. These results combined with structural investigations support a single P-T loop for this area with a Tertiary high-pressure event (Late Eocene) that affected the entire Adula nappe.

Keywords: Adula nappe;Central Alps;equilibrium phase diagram;geothermobarometry;high-pressure metapelite

Pages 199-213

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