Observations on the effect of proximity to rhyolitic intrusions on Kübler index

Sorcha Diskin,Stephanus Coetzee

doi:10.2478/v10002-010-0006-z

Abstract

Observations on the effect of proximity to rhyolitic intrusions on Kübler index

Highlights

In the last four decades, the Kübler Index (KI) has commonly been used as an empirical measure of the changes in the width of illite basal X-ray diffraction (XRD) reflections
The KI is commonly considered to be primarily a function of illite crystallite thickness normal to (001), and this hypothesis has been confirmed by combined transmission electron microscope (TEM) and XRD studies (e.g. Merriman et al 1990)
The intensity ratio (Ir) of the illites was calculated in each case to assess the proportion of illitic material present (Środoń 1984) and generally was found to equal 1, indicating that no expanding clays were present

Summary

Introduction

In the last four decades, the Kübler Index (KI) has commonly been used as an empirical measure of the changes in the width of illite basal X-ray diffraction (XRD) reflections. The KI is the full width at half maximum height (FWHM) of the illite 10 Å X-ray diffraction peak, measured on the < 2 m size fraction of an air-dried clay specimen using CuK radiation (Kübler 1967, 1968; Dunoyer de Segonzac et al 1968, Jaboyedoff et al 2001). Measurements of illite “crystallinity” (IC) are widely used as an indicator of incipient metamorphism and are interpreted from the KI. Numerous authors (including Kisch 1987; Frey 1987) have shown how IC increases (i.e. by an increase of crystal ordering and in the size of individual crystallites) as metamorphic grade increases. Due to the relative simplicity of the KI technique it continues to be widely applied to regional surveys of sub-greenschist facies metamorphism in pelitic rocks (e.g. Liu 2003; Crouzet et al 2007; Kim et al 2007; Ruiz Cruz 2008)

Methods

Results

Discussion

Conclusion