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GEOREF RECORD

Dramatic effects of stress on metamorphic reactions

John Wheeler
Dramatic effects of stress on metamorphic reactions
Geology (Boulder) (June 2014) 42 (8): 647-650

Abstract

Thermodynamic calculations predict mineralogy from temperature and pressure and vice versa. Such calculations assume that stress is isotropic despite the fact that differential stresses prevail in Earth, resulting from large-scale tectonics and/or differences between fluid and rock pressures in porous rocks. New calculations show that differential stress can have significant effects on thresholds for metamorphic reactions, depending on the grain-scale reaction pathways. A differential stress may, depending on the reaction pathway, have an effect equivalent to a pressure difference on the order of (assemblage volume)/(reaction volume change) X (differential stress). The multiplying factor is typically 10 or more. For example, the onset of a garnet + clinopyroxene breakdown reaction may be offset, up or down, by the equivalent of 500 MPa in pressure for a 50 MPa differential stress. The effect is equivalent to a temperature difference on the order of (assemblage volume)/(reaction entropy change) X (differential stress). For example, the onset of muscovite + quartz breakdown may be offset, up or down, by the equivalent of 130 degrees C for a 50 MPa differential stress. Much of Earth is under differential stress, so the new calculations invite a reappraisal of metamorphic mineralogy and microstructure, indicating that new insights into stresses and fluid pressures on Earth can be gained.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 42
Serial Issue: 8
Title: Dramatic effects of stress on metamorphic reactions
Author(s): Wheeler, John
Affiliation: University of Liverpool, Department of Earth, Ocean and Ecological Sciences, Liverpool, United Kingdom
Pages: 647-650
Published: 20140609
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 15
Accession Number: 2014-048992
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2014241
Illustration Description: illus.
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201427
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