The time scales over which deformation in the Earth's crust remains localized in shear zones are poorly known, as are the associated strain rates. We have determined the longevity and rates of deformation using rubidium-strontium (Rb-Sr) microsampling dating of increments of fibrous strain fringes from a Pyrenean shear zone. The fibers grew quasi-continuously through a protracted deformation history between 87 and 50 million years ago, over a period comparable to that of an orogeny. During a short interval between 66 and 62 million years, a rise in strain rate from 1.1 × 10-15 to 7.7 × 10-15 seconds-1 occurred. This acceleration correlates with an abrupt change in fiber-growth direction and a stress-field inversion from gravitational collapse to renewed horizontal crustal shortening.
[log in to unmask]">A question: radiometric dating of shear zone fabrics Dear Colleagues:
I am interested in general references on the recent advances in radiometric dating of various minerals in shear zone fabrics. Does anyone know of any such references? I would greatly appreciate any ideas that you might have.
Best regards,
Eldridge--Distinguished Professor of Emeritus of Geology
Vice President, International Union of Geological Sciences
Department of Geology, University of California
One Shields Avenue
Davis, CA 95616
Tel: 530-752-0352
Fax: 530-752-0951
"Civilization exists by geologic consent, subject to change without notice"
"Civilization is an interval between ice ages"
(Will Durant)
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