Research: Rock Fabrics
Magnetic fabrics in very low strain (<5%) sandstone
Rocks in the sub-metamorphic portions of regions like the Hudson Valley fold-thrust belt usually develop only slight penetrative strains, which generally only partially overprint preexisting, primary (depositional) fabrics. The resulting composite (strain/primary) fabrics present a problem when using traditional strain analysis (e.g., normalized Fry and Rf/phi) to resolve regional tectonic histories.
Indeed, the projections of the long axis of Fry strain ellipses measured in sandstone samples collected in the Hudson Valley near Rosendale do not cluster in a direction parallel to the structural grain defined by the trends of cleavage, folds, and faults. However, the projections of the long axes of anisotropy of magnetic susceptibility (AMS) ellipsoids measured in the same rocks cluster closely to the structural grain (Fig. 2). This observation implies that in very low-strain sandstone, AMS analysis provides a more sensitive indicator of tectonic fabric than does normalized Fry analysis.
In collaboration with:
Eric Ferré, Southern Illinois University
Paul Wetmore, University of South Florida
Helge Alsleben, Texas Christian University
Geoffrey Pignotta, University of Wisconsin, Eau Claire
Scott Paterson, University of Southern California
Michael J. Harrison, Tennessee Technical University
Stephen Marshak, University of Illinois