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^(39)Ar-^(40)Ar Dating: The Importance of K-Feldspars on Multi-Mineral Data of Polyorogenic Areas

Albarede, F. and Feraud, G. and Kaneoka, I. and Allegre, C. J. (1978) ^(39)Ar-^(40)Ar Dating: The Importance of K-Feldspars on Multi-Mineral Data of Polyorogenic Areas. Journal of Geology, 86 (5). pp. 581-598. ISSN 0022-1376. https://resolver.caltech.edu/CaltechAUTHORS:20180522-143240814

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Abstract

A comparative ^(39)Ar-^(40)Ar study of two hercynian crystalline segments in southern France is presented in this work. The first area, the Montagne Noire, has been left undisturbed since ca. 300 m.y. while the second, the Eastern Pyrénées, has been severely overprinted by alpine metamorphism about 95 m.y. ago. In the Montagne Noire, all the analyzed minerals (micas and low-temperature K-feldspars) have preserved hercynian age plateaux whereas in the Eastern Pyrénées, hercynian minerals (micas, amphiboles, plagioclases, and low-temperature K-feldspars) have been outgassed to a variable extent. Low-temperature K-feldspars are shown to be a sensitive indicator of tenuous thermomechanical disturbance, even for samples whose biotite is apparently undisturbed. This is considered to result from lowering of the effective grain size of the perthitic crystals by the tectonic event and not from an abnormally high diffusion coefficient for argon. An evaluation of this grain size is proposed which uses the recoil effect of ^(39)Ar production in the neutron irradiation. We conclude that discordant mica ages may be interpreted as cooling ages only after the associated K-feldspars have been shown to have suffered a slight disturbance or none.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1086/649726DOIArticle
http://www.jstor.org/stable/30060681JSTORArticle
ORCID:
AuthorORCID
Albarede, F.0000-0003-1994-1428
Alternate Title:39Ar-40Ar Dating: The Importance of K-Feldspars on Multi-Mineral Data of Polyorogenic Areas
Additional Information:© 1978 University of Chicago Press. Manuscript received September 30, 1977; revised February 24, 1978. We are indebted to J. Hamet, H. Maluski, A. Michard-Vitrac, A. Stettler, and G. Turner for fruitful discussions. S. Wilhelm made X-ray determinations of analyzed K-feldspars. We gratefully acknowledge the help of H. Jaffrezyck and J. L. Joron for sample irradiation. M. Girard, A. Lecomte, and M. Vassenaix gave competent assistance for the technical part of this work. Thanks are due to M. Semet for English editing of the present text. Dr. H. P. Taylor, Jr., granted the use of facilities for preparation of the manuscript
Issue or Number:5
Record Number:CaltechAUTHORS:20180522-143240814
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180522-143240814
Official Citation:F. Albarede, G. Feraud, I. Kaneoka, and C. J. Allegre, "39Ar-40Ar Dating: The Importance of K-Feldspars on Multi-Mineral Data of Polyorogenic Areas," The Journal of Geology 86, no. 5 (Sep., 1978): 581-598. https://doi.org/10.1086/649726
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86557
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:24 May 2018 16:42
Last Modified:03 Oct 2019 19:45

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