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Isotopic Dating of Strain Fringe Increments: Duration and Rates of Deformation in Shear Zones
Wolfgang Müller,1*
Domingo Aerden,2
Alex N. Halliday1
The time scales over which deformation in the Earth's crust
remains localized in shear zones are poorly known, as are theassociated strain rates. We have determined the longevity andrates of
deformation using rubidium-strontium (Rb-Sr) microsamplingdating of
increments of fibrous strain fringes from a Pyreneanshear zone. The
fibers grew quasi-continuously through a protracteddeformation history
between 87 and 50 million years ago, overa period comparable to that
of an orogeny. During a short intervalbetween 66 and 62 million years,
a rise in strain rate from 1.1× 1015 to 7.7 × 1015 seconds1 occurred. This
acceleration correlates with an abrupt changein fiber-growth direction
and a stress-field inversion from gravitationalcollapse to renewed
horizontal crustal shortening.
1 Institut für Isotopengeologie und
Mineralische Rohstoffe, Department Erdwissenschaften, Sonneggstrasse 5, ETH Zürich, CH-8092 Zürich, Switzerland.
2 Departamento de Geodinamica, Universidad de
Granada, E-18071 Granada, Spain.
*
To whom correspondence should be addressed. E-mail:
wolfgang.mueller{at}erdw.ethz.ch
Fast strain rates during pluton emplacement: Magmatically folded leucocratic dikes in aureoles of the Mount Stuart Batholith, Washington, and the Tuolumne Intrusive Suite, California.
15 to 7.7 × 10
