Calibrations of modal space for metamorphism of mafic schist

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doi: 10.2138/am.2005.1717
Authors:Thompson, Alan Bruce; Laird, Jo
Author Affiliations:Primary:
ETH, Department of Earth Sciences, Zurich, Switzerland
University of Texas at Austin, United States
University of New Hampshire, United States
Volume Title:Ernstfest festschrift; mineralogy and petrology of high P/T terranes, P-T-ometry, and experimental phase relations
Volume Authors:Sorensen, Sorena S., prefacer; Carlson, William
Source:American Mineralogist, 90(5-6), p.843-856; 2003 annual GSA meeting, Seattle, WA, Nov. 2-5, 2003, prefaced by Sorena S. Sorensen and William Carlson. Publisher: Mineralogical Society of America, Washington, DC, United States. ISSN: 0003-004X
Publication Date:2005
Note:In English. Includes appendices. 41 refs.; illus., incl. 4 tables
Summary:Three independent net-transfer reactions determine compositional and modal changes for green-schist-, blueschist-, and amphibolite-facies metamorphism of mafic rocks, as different paths are followed though pressure, temperature, and aH2O space. For natural terrains, only one aH2O-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.
Sections:Experimental mineralogy
Subsections:Metamorphism: regional, dynamic
Subjects:Amphibolite facies; Blueschist facies; Dehydration; Experimental studies; Facies; Ferric iron; Ferrous iron; Greenschist facies; Iron; Mafic composition; Metals; Metamorphic rocks; Metamorphism; P-T conditions; Phase equilibria; Schists; Theoretical studies; Thermodynamic properties; CFMASH system; CMASH system
Abstract Numbers:05M/2300
Record ID:2005044715
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, copyright, Mineralogical Society of America, Reference includes data from GeoScienceWorld, Alexandria, VA, United States
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