DOES THE RHEOLOGY OF NATURALLY DEFORMED ROCKS DEPEND ON FINITE STRAIN?
Within each field area, we conducted three-dimensional strain analysis at numerous outcrops recording progressively higher bulk finite strain. The finite strain recorded by the different clast types relative to that of the matrix demonstrates the competence contrast among the rock types. However, the observed clast strength relationships are not constant; at outcrops recording higher bulk strain, clast strength relationships are different from those observed at lower bulk strain. This indicates that the strengths of some clast types change as bulk finite strain increases. These results can be explained two ways: (1) clast rheology is strain dependent, or (2) clast and/or matrix rheology is described by a flow law with a power law exponent n ≠ 1.
Further analysis will focus on using microstructural characteristics of these rocks to distinguish between these two possible causes of clast strength evolution. The presence or absence of particular microstructures may allow us to place absolute constraints on the rheologies of different clast types. Quantitative studies of the rheological evolution of rocks have important implications for geodynamic modeling and our understanding of deformation of complex natural systems at all scales.