A Discussion on natural strain and geological structure - Experimental evaluation of the deformation path concept

Abstract
Study of natural finite strain states in several oolitic limestones indicates that, unlike most rocks, many limestones have undergone deformation by a process of approximately plane strain. Accordingly, specimens of oolitic limestone were deformed experimentally in plane strain at confining pressures of 100 and 200 MPa, at temperatures of 25, 100, and 200 degrees C, and to total strains from 20 to 50% by increments of 10 and 5%. From subsequent strain analysis, utilizing thin sections of the deformed specimens, we find that the greatest strain heterogeneity exists, as is to be expected, for conditions under which the rock has low ductility, i.e. low confining pressure and low temperature. Increased pressure and temperature promotes a change in microscopic mechanism from cataclasis to intracrystalline gliding. The degree of strain heterogeneity is significantly decreased at higher confining pressure; it is affected to a lesser degree by higher temperature. From our results, it appears that the degree of strain heterogeneity remains sufficient within the deformational mode fields of uniform flow and ductile faulting to justify utilization of the deformation path concept.

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