Down-plunge viewing: a rapid method for estimating the strain ellipsoid for large clasts in deformed rocks

Abstract

The shape of the strain ellipsoid for an aggregate of clasts with initially isotropic fabric can be estimated from measurements made while viewing the clasts along the plunges of at least two of the axes of strain, even though the outcrop faces are not orthogonally related to any of the strain axes. The accuracy of this estimation depends on the shape of the strain ellipsoid and the obliquity between the strain axes and the outcrop faces.Application of the technique to conglomerates of the Missi Group near Flin Flon, Manitoba and Saskatchewan, suggests that in moderately to highly deformed rocks it can be useful for comparing the strain behaviour of clasts with different competences as well as for determining regional strain variations.