Modifying the normalized fry method for aggregates of nonelliptical grains
Abstract
A modification of the normalized Fry method is developed to avoid the problems associated with approximating nonelliptical grains by bestfit ellipses. This modified method is a more general approach for constructing a normalized Fry plot and determining the orientation and axial ratio of the fabric ellipse. Grains can be approximated by any shape as long as the center and area of each grain can be determined. Irregular polygons work particularly well since they can be used to approximate both elliptical and nonelliptical grains. Once the center and area of each grain in an aggregate is calculated, existing methods can be used to construct a normalized Fry plot. Determining the fabric ellipse, however, requires a new approach. A circular grid is used to find points on the ring of maximum point density along a series of radial vectors. The leastsquares bestfit ellipse calculated through these points gives an initial estimate of the fabric ellipse. An iterative approach is taken, using the fabric estimate to calculate a plane strain irrotational inverse deformation matrix which, in turn, is used to unstrain grain centers. The newly determined centroids are used to calculate a new fabric ellipse. This process is repeated until the axial ratio of the remaining fabric ellipse is 1.00. The fabric ellipses for each stage are combined to calculate the total fabric ellipse. Tests of this method using computer generated data sets of elliptical and nonelliptical grains show a strong correlation of measured fabric with known artificially imposed fabric.
 Publication:

Journal of Structural Geology
 Pub Date:
 April 1994
 DOI:
 10.1016/01918141(94)900930
 Bibcode:
 1994JSG....16..493M