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Mineral and isotope features related to the resetting of Rb-Sr whole-rock isotope systems during low-grade metamorphism

J. A. Evans
Mineral and isotope features related to the resetting of Rb-Sr whole-rock isotope systems during low-grade metamorphism (in Low-grade metamorphism of mafic rocks, Peter Schiffman (editor) and Howard W. Day (editor))
Special Paper - Geological Society of America (1995) 296: 157-169

Abstract

The interaction between rocks and water during low-grade metamorphism leads to the growth of a predominantly hydrated secondary mineral assemblage and results in the elevation of whole-rock oxygen isotope values. Rb-Sr whole-rock isotope systems are also disturbed during low-grade metamorphism and give reset metamorphic ages. The process of isotope disturbance during low-grade metamorphism is examined by comparing the behavior of the oxygen isotope systems in rocks of similar composition that have undergone differing levels of metamorphic recrystallization. Two intrusions from the Ordovician volcanic province of North Wales represent metamorphically undisturbed systems. They give low oxygen isotope whole-rock values of delta (super 18) O (sub SMOW) (standard mean ocean water) = 7.3 per mil + or - 0.3 per mil, their Rb-Sr whole-rock systems are undisturbed and they show minimal metamorphic recrystallization. By comparison, other Ordovician igneous rocks have elevated oxygen isotope values enriched between 1 per mil and 7 per mil over undisturbed rocks and give metamorphic Rb-Sr whole-rock regression ages. Interaction with water is shown to be the main influence on the resetting of Rb-Sr systems during low-grade metamorphism. The metamorphic pressure-temperature conditions are not a controlling factor.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 296
Title: Mineral and isotope features related to the resetting of Rb-Sr whole-rock isotope systems during low-grade metamorphism
Title: Low-grade metamorphism of mafic rocks
Author(s): Evans, J. A.
Author(s): Schiffman, Petereditor
Author(s): Day, Howard W.editor
Affiliation: NERC Isotope Geosciences Laboratory, Keyworth, United Kingdom
Affiliation: University of California at Davis, Department of Geology, Davis, CA, United States
Pages: 157-169
Published: 1995
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 0-8137-2296-9
References: 27
Accession Number: 1995-032505
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch map
N51°30'00" - N53°30'00", W05°15'00" - W02°40'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 199512
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