FRACTURE-CONTROLLED LINEAMENT DOMAINS OF THE APPALACHIANS: GEOLOGIC CORRELATIONS AND REPRODUCIBILITY TESTS

Regional-scale topographic lineament swarms are among the least understood of all fracture-related features. This reproducibility experiment identifies ~40 overprinted lineament domains along the entire Appalachians. It is based on topographic lineaments digitized by two observers (DUW, LWG) on radar-like 1:1,000,000 mosaics assembled from 1:250,000 plastic relief maps, side-lighted with 6 azimuths from 0 to 150°. Repeat observations on all six mosaics for added reproducibility testing produced a total of ~25,000 lineaments. In theory, any real lineament could appear 24 times at the same location on a composite plot but an illusionary shadow-lineament would be diluted to only 6 appearances. Rose diagrams were calculated for all lines within 60 km of 294 half-degree lat-long points using Salvini’s Margarita program. Domains with typical quasi-elliptical shapes and 300-500 km extent were identified by correlation of single azimuthal petals among adjacent roses; petals fade but do not change strike at domain edges.

One set of domains expands strike-parallel Piedmont orientations NW through the Plateau as overprinted boundaries of salients and recesses. Other sets show no readily apparent geologic correlations. A similar study of Italy (GSA Bull., 1985) correlated most domains with extensile tectonic environments conducive to joint development. Outcrop examples in other regions show such lineaments as minor normal faults or zones of intense development of joint sets with multiple orientations. Both studies include extensile collapse of regional thrust sheets but that of the U.S. Mesozoic is less regional. Transient asthenospheric-warpings are a possible origin mechanism for some of these domains.

Machine identification of lineaments is advancing but seems not yet able to out-perform the trained human eye. This data set is freely available for reproducibility tests, application to practical problems, or search for tectonic origin(s)of these enigmatic features.