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Three-dimensional isograds from the Lukmanier Pass, Switzerland, and their tectonic significance

Published online by Cambridge University Press:  01 May 2009

J. S. Fox
J. S. Fox
Affiliation:
Geology DivisionSaskatchewan Research CouncilSaskatoonCanada
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Summary

Four mineralogical zones, corresponding to the following ‘maximum’ metapelitic assemblages

zone 1: chloritoid-chlorite-kyanite

zone 2: staurolite-chloritoid-chlorite-kyanite

zone 3: biotite-staurolite-chloritoid-chlorite-kyanite

zone 4: biotite-staurolite-garnet-chlorite-kyanite

have been mapped in the Ultrahelvetic rocks of the Lukmanier area in Switzerland. Petrographic study suggests that, despite the ubiquity of ‘disequilibrium’, the zone boundaries accord with the simple univariant equilibria

chloritoid+kyanite = staurolite+chlorite+quartz+H2O

chloritoid+chlorite+muscovite = staurolite+biotite+quartz+H2O

and chloritoid+muscovite+quartz = staurolite+garnet+biotite+H26

Using structural contours, minimum isogradic dips of 35° north have been obtained.

The Lukmanier parageneses require the Lepontine phase of Alpine metamorphism to have had a geotherma! gradient distinct from both Alpine blueschists and the Bergell contact metamorphites. The high minimum value for isograd and isotherm orientation here points to a convective heat source for the Lepontine event.

Type
Articles
Information
Geological Magazine , Volume 112 , Issue 6 , November 1975 , pp. 547 - 564
Copyright
Copyright © Cambridge University Press 1975

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