Fast tectonometamorphism and exhumation in the type area of the Barrovian and Buchan zones
- 1Crustal Geodynamics Group, School of Geography and Geosciences, St. Andrews University, St. Andrews, Fife, Scotland KY16 9ST, UK
- 2Institut für Geochemie, Universität Tübingen, Wilhelmstrasse, 56D-72074, Tübingen, Germany
- 3Max-Planck Institut für Chemie Abteilung Geochemie, 55020 Mainz, Germany
Abstract
The beginning of the Grampian episode of tectonometamorphism in Scotland is dated by collision and obduction of the Ballantrae Ophiolite Complex at 478 ± 8 Ma. For the first time we have used zircon and garnet to radiometrically date the peak of the Caledonian Buchan and Barrovian tectonometamorphism in their type areas as contemporaneous at 467 ± 2.5 Ma. Detrital garnet from the neighboring Southern Uplands flysch terrane has the same radiometric age and occurs in 465 ± 2.5 Ma molasse in the Midland Valley. We show that the entire Grampian episode lasted 15 ± 2.5 m.y. and that it took fewer than 7.6 m.y. to expose high-grade rocks following the peak of metamorphism. Those who study Precambrian orogeny should note the brevity of this Scottish tectonometamorphic episode and the speed of exhumation.
Footnotes
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↵GSA Data Repository item 200050, Table 1, Zircon U-Pb Isotope Data, and Table 2, Garnet Sm-Nd Isotope Data, is available on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, editinggeosociety.org, or at www.geosociety.org/pubs/drpint.
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*gjhost-and.ac.uk
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Data Repository item 200050 contains additional material related to this article.
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- Accepted February 16, 2000.
- Received October 21, 1999.
- Revision received February 2, 2000.
- Geological Society of America
