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Eldridge (and others). Have a look at: Bell, T.H., and Welch, P.W., 2002. Prolonged Acadian Orogenesis: Revelations from foliation intersection axis (FIA) controlled monazite dating of foliations in porphyroblasts and matrix. Am. J. Sci., 302, 549-581. Although the authors have not dated 'shear zones' sensu stricto, it does provide an interesting concept for constraining the age of foliation development. Hope this is helpful, Nick Timms ______________________________ Dr. Nick Timms Dept. of Applied Geology Curtin University of Technology GPO Box U1987 Perth, WA 6845 [ph] +61 (0)8 9266 4372 [mobile] +61 (0)424 010726 [fax] +61 (0)8 9266 3153 ______________________________ -----Original Message----- From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of Eric Essene Sent: Thursday, February 03, 2005 6:18 AM To: [log in to unmask] Subject: Re: dating shear zone deformation Rob, If there are any sulfides and the rocks are old, Re/Os may give some constraints. Otherwise, not much would be possible from chronology. Maybe rock magnetism could be useful. eric On Feb 2, 2005, at 2:05 PM, Robert Twiss wrote: While this topic of dating shear zone deformation is on people's minds, I'd like to ask if anyone knows of any way of dating serpentine slickenfibers in shear zones. The Coast Range of California and the Sierra Nevada have many serpentinized ultramafic rocks in which shear zones have developed. The shear zones characteristically have abundant serpentine slickenfibers that have grown on shear fractures. The fibers are presumably mixed with fine-grained magnetite, because they carry a magnetic signature. Being able to date the shearing would go a long way toward helping sort out the deformation history of these rocks, but I don't know if it is even possible. Rob Twiss _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ Robert J. Twiss, Prof. Emeritus email: [log in to unmask] Geology Department telephone: (530) 752-0179 University of California at Davis FAX: (530) 752-0951 One Shields Ave. website: www.geology.ucdavis.edu/ Davis, CA 95616-8605, USA faculty/twiss.html _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/