Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter March 28, 2015

Calibrations of modal space for metamorphism of mafic schist

  • Alan Bruce Thompson EMAIL logo and Jo Laird
From the journal American Mineralogist


Three independent net-transfer reactions determine compositional and modal changes for greenschist-, blueschist-, and amphibolite-facies metamorphism of mafic rocks, as different paths are followed though pressure, temperature, and aHO space. For natural terrains, only one aHO.dependent reaction is chosen, whereas to interpret experimental studies, where H2O is in excess, there is an advantage to choosing two dehydration reactions. Published experimental studies on the greenschist to amphibolite transition and thermodynamic calculation in simple systems and with pseudosections, show that reactions involving Al2Mg-1Si-1 in amphibole and chlorite predominate, that FeMg-1 exchange and Al2Mg-1Si-1 are strongly coupled, and that all reactions and, in particular, the stability of chlorite are affected by Fe3+/Fetotal. Modal spaces for mafic schist are constructed for different sets of independent reactions, and permit correlation of mineral mode with directions of change of pressure and temperature. These can be used to deduce field gradients in these variables in natural terrains, when only modal change data are available and when compositional and thermodynamic data are limited.

Received: 2005-2-19
Accepted: 2004-5-21
Published Online: 2015-3-28
Published in Print: 2005-5-1

© 2015 by Walter de Gruyter Berlin/Boston

Downloaded on 6.6.2023 from
Scroll to top button