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Hi All, I am thinking about the issue of transient ductile deformation in orogenic belts, and was wondering if some of you might have recent information on the duration of deformation ģeventsē during orogenesis. If one considers, for argument, a plate convergence rate of 10 cm/year, and assumes, again just for argument, that the strain is taken up homogeneously over a plate-boundary-perpendicular length of 100 km, that results in a (conventional) strain rate of 3.17x10-14 if I did my back-of-the-envelope math correctly. That means that a stretch of 0.5 (moderate-strain crenulation cleavage for example) would take about 500,000 years to accumulate. Of course, this is silly because strain does not accumulate homogeneously, strain is taken up over much longer line lengths in most orogens, etc... Does anyone out there know of good constraints on the time it takes to form a crenulation cleavage or other moderate-strain foliation in a mica schist? I have not been keeping up with the Ar/Ar work on foliated rocks. Cheers - Scott ************************************************************************* Scott E. Johnson Department of Earth Sciences 5790 Bryand Global Sciences Center University of Maine Orono, ME 04469-5790 USA email: [log in to unmask] phone: (207) 581-2142 Fax: (207) 581 2202 http://www.geology.um.maine.edu/user/scott_johnson/HM.html *************************************************************************