Comparison of Fry strain ellipse and AMS ellipsoid trends to tectonic fabric trends in very low-strain sandstone of the Appalachian fold-thrust belt

K. C. Burmeister, M. J. Harrison, S. Marshak, E. C. Ferré, R. A. Bannister, K. P. Kodama

Research output: Contribution to journalArticlepeer-review

Abstract

In moderately to highly strained sandstones, both the long axis of the bedding-parallel finite-strain ellipse, as calculated by the normalized Fry method, and the projection of the long axis of the AMS ellipsoid on the plane of bedding, align well with local "structural grain" (trends of cleavage, folds, and faults). This relationship implies that results of both 2D Fry and AMS analyses represent the local layer-parallel tectonic strain component. Do both methods provide comparable results for very low-strain sandstone (e.g., <5%)? To address this question, Fry and AMS analyses were conducted in very low-strain sandstone from two localities in the Appalachian foreland fold-thrust belt: near Rosendale in New York and the Lackawanna synclinorium of Pennsylvania. We compared the map projections of both bedding-parallel Fry ellipses and AMS ellipsoids to the local structural grain. In both study areas, projections of the long axis of Fry strain ellipses do not cluster in a direction parallel to structural grain, whereas the projection of the long axes of AMS ellipsoids do cluster closely to structural grain. This observation implies that in very low-strain sandstone, AMS analysis provides a more sensitive "quick" indicator of tectonic fabric than does normalized Fry analysis.

Original languageEnglish (US)
Pages (from-to)1028-1038
Number of pages11
JournalJournal of Structural Geology
Volume31
Issue number9
DOIs
StatePublished - Sep 2009

Keywords

  • AMS
  • Anisotropy of magnetic susceptibility
  • Appalachian fold-thrust belt
  • Fry strain analysis
  • Hudson Valley fold-thrust belt
  • Lackawanna synclinorium
  • Rosendale
  • Tectonic fabrics

ASJC Scopus subject areas

  • Geology

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