*WINNER* Grain-scale strain analysis of rock in middle Tennessee

  • Kathleen Thompson
  • Lori Nabors
  • Michael Harrison


"Rock deformation begins at the grain scale. Grain-scale deformation can be expressed as finite strain—the total strain affecting the rock over time. Finite strain can be quantified by a geospatial technique known as Fry analysis that assesses the geometric arrangement of rock grains with respect to each other. Fry analysis is used to measure the amount of strain and the direction of shortening and extension.
In this study, 8 oriented samples that included Hartselle Formation quartz arenite and Monteagle Limestone grainstone were collected for Fry analysis. Four samples were collected east of Cookeville, TN and 4 samples were collected from Brown Gap quarry 20 kilometers south of Crossville, TN. Polished slabs of the bedding plane were scanned and imported into EllipseFit for Fry analysis.
Six samples yielded shortening directions of east-west to northwest-southeast (azimuth of 257-346 degrees) and one sample showed a shortening direction of 207 degrees (the final sample was too fine grained for the analysis). The strain ratio, a measure of strain magnitude, ranged from 1.1-5.9. The grain-scale deformation was accomplished principally by microfracturing, pressure-solution and calcite- twinning mechanisms. The shortening direction measured in these samples is consistent with the tectonic deformation associated with the Alleghanian orogeny 320-280 million years ago."

Earth Sciences