On the use of regional joint sets as trajectories of paleostress fields during the development of the Appalachian plateau, New York.

To compare the orientation and development of jointing with the orientation and magnitude of finite strain recorded in the Upper Devonian rocks of the Appalachian plateau, New York, we mapped systematic joint sets on an area of 20,000 km². In this area, Wedel(1932) mapped folds with limb dips of less than a degree and axes that change strike by 30^o from 090^o in the east to 060^o in the west. We observed two different cross-strike joint sets that maintain their approximate cross-strike position from east to west. Yet, in detail the angle between the sets is 18^o plus/minus 2^o in the east and 30^o plus/minus 4^o in the west. In many outcrops one joint set parallels the direction of maximum compressive strain (episilon_f) as recorded by deformed fossils, whereas the other joint set never parallels episilon_f. Rare calcite-filled joints are oriented parallel to the direction of episilon_f. In addition, the calcite-filled joints both cut and are cut by solution cleavage. These observations suggest that the joint set paralleling episilon_f formed during the deformation event represented by the deformed fossils. The joint set that does not parallel episilon_f somehow reflects a deformational event other than that producing fossil distortion, as suggested by strain relaxation experiments. -Authors Lamont- Doherty Geological Observatory of Columbia Univ., Palisades, New York 10964.