Fluid disturbed hornblende K-Ar ages from the Dalradian rocks of Connemara, western Ireland

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doi: 10.1144/gsjgs.148.6.0985
Authors:Miller, W. M.; Fallick, A. E.; Leake, B. E.; Macintyre, R. M.; Jenkin, G. R. T.
Author Affiliations:Primary:
University of Glasgow, Department of Geology and Applied Geology, Glasgow, United Kingdom
Other:
Scottish Universities Research and Reactor Centre, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.148 (Part 6), p.985-992. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1991
Note:In English. 37 refs.; illus. incl. 2 tables, geol. sketch map
Summary:K/Ar age determination and delta D and delta 18O stable isotope measurements on hornblendes from the polymetamorphic Dalradian schists of Connemara show that the hornblende K-Ar systems have been significantly disturbed bylow-T fluid reaction. Correlations between K/Ar ages, delta D values, structural water contents and the occupancy of the structural A sites in the hornblende suggest that excess water as H3O+ occupies vacant A site positions during stable-isotope exchange and displaces Ar causing lowering of the K/Ar ages. This process occurs below the normally accepted closure T for Ar in hornblende and is not detectable by optical or XRD study. It may not be unique to Connemara hornblende and so is of potential importance to geochronology in other metamorphic terrains. [R.A.H.]
Subjects:Absolute age; Amphibole group; Chain silicates; Clinoamphibole; Dalradian; Dates; Fluid phase; Hornblende; Hydrothermal alteration; K/Ar; Metamorphic rocks; Metasomatism; Ordovician; Paleozoic; Schists; Silicates; Connemara; Europe; Galway Ireland; Ireland; Western Europe; Western Ireland
Coordinates:N531500 N534000 W0090000 W0102000
Abstract Numbers:92M/1251
Record ID:1993027668
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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