Magnetic fabrics

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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