Illite “Crystallinity” Revisited

Abstract

Abstract--The Kfibler Index (KI) is defined as the full width at half-maximum height (FWHM) of the 10-,~ X-ray diffraction peak of illite-smectite interstratified (I-S) clay minerals. The only parameters controlling the Ktibler Index are assumed to be the mean number of layers (N) in the coherent scattering domains (CSD), the variance of the distribution of the number of layers of the CSD, the mean percentage of smectite layers in I-S (%S), and the probability of layer stacking (Reichweite).The Kiibler-Index measurements on air-dried (KIAD) and ethylene-glycolated (KIEG) samples were compared to N and %S using the NEWMOD computer program to simulate X-ray diffraction patterns.Charts of KIAD versus KIEG corrected for instrumental broadening were made and isolines were mapped for constant N and %S. Isolines allow a direct and rapid determination of N and %S from KI measurements.The method allows quantification of the metamorphic anchizone limits by considering mean thickness of fundamental particles in MacEwan crystallites. The transition from diagenesis to the anchizone and from the anchizone to the epizone of low-grade metamorphism corresponds to thicknesses of 20-and 70-layer fundamental particles, respectively.

Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States

“…Tectonic thickening of the miogeocline during Paleozoic-Cretaceous thrusting would increase peak temperatures in structurally lower thrust sheets. Jaboyedoff et al 2001). Illite is a phyllosilicate consisting of "packets" of 1-nm-thick sheets, which in turn are made up of tetrahedal and octahedral aluminosilicate layers separated by interlayer potassium cations (e.g., Moore and Reynolds 1997).…”

“…During prograde metamorphism, I/S containing significant interlayered smectite is progressively converted to more illite-rich compositions (e.g., Hower and Mowatt 1966;Hower et al 1976;Moore and Reynolds 1997). Expandable layers (i.e., smectite) will broaden the 1-nm XRD peak, leading to larger values of IC (e.g., Eberl and Velde 1989;Jaboyedoff et al 2001;and see fig. 3 in Jaboyedoff and Thé lin 1996 for a summary of clay mineral transformations and XRD transitions during low-grade metamorphism).…”

Influência da pressão e temperatura na cristalinidade da illita em sequências Proterozoicas: Norte do Distrito Federal e Goiás, Brasil

“…As transformações da esmectita para illita e desta para muscovita, condicionadas pelo aumento de temperatura e pressão, começaram a ser mais detalhadamente estudadas a partir da década de 1960, com o intuito de definir a zona diagenética e a anquizona (Kübler 1968;Dunoyer de Segonzac 1969;Hower et al 1976;Boles & Franks 1979;Singer & Müller 1983;Hillier 1989;Velde & Vasseur 1992;Leoni et al 1996;Wang et al 1996;Dudek & Srodon 2003;Srodon et al 2009), bem como o limite do metamorfismo de baixo grau (Kisch 1983;Frey 1987;Jahren & Aagard 1992;Árkai et al 1996;Warr & Nieto 1998;Jaboyedoff et al 2001;Lee & Lee 2001;Abad et al 2003;Kamp 2008), inclusive quando há influência de esforço tectônico (Hoffman & Hower 1979;Eslinger & Sellars 1981;Piqué 1982;Akande & Erdtmann 1998;Poyatos et al 2001).…”

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

“…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(Kübler , 1968Dunoyer de Segonzac et al 1968, Jaboyedoff et al 2001). 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.…”

“…However, it is well known that KI is influenced by many parameters (Frey 1987) and must not be overinterpreted (e.g. Guggenheim et al 2002;Jaboyedoff et al 2001;Battaglia et al 2004). These metapelites are intruded by many contemporaneous rhyolite and dolerite intrusions; the effect of these intrusions on KI is not established in the literature.…”