Cathodoluminescence Petrography of Microstructural Fabrics in Deformed Limestones: ABSTRACT

Abstract

Cathodoluminescence petrography has been shown to be a valuable tool for analyzing strain microfabrics in deformed rocks. This study shows that cathodoluminescence petrography is useful for illustrating the details of the varied and heterogeneous nature of deformation mechanisms involved in the formation of deformation twins in calcite crystals. The advantage of viewing grains and syntaxial calcite cements in some deformed skeletal limestones is that finely banded luminescent growth zones in the cements commonly act as very sensitive displacement markers. The detailed structure associated with deformation bands can be observed, and the sense of displacement clearly determined. Deformation microfabrics apparent from displacement of the luminescent growth zones in calcite cements commonly are coincident with deformation twin lamellae that are visible in transmitted light. Cathodoluminescence petrography shows that modes of deformation associated with the twin lamellae vary between ductile deformation (formation of chevron-like microfolds in the luminescent zones) to offset of luminescent zones along discrete slip surfaces, to combinations of both mechanisms. Additionally, apparent ductile kink geometries in deformation twins observed in transmitted light are shown to result from twin development in microfracture-filling cements, when samples are viewed under cathodoluminescence. this study further illustrates the usefulness of cathodoluminescence petrography for studies ofmore » microstructural fabrics in deformed limestones.« less