Cation site occupancy in chlorites and illites as a function of temperature

Abstract

A B S T RA C T : The relationships between the composition and the crystallization temperature of chlorites and illites have been investigated in different geothermal fields and in particular the Los Azufres system in Mexico, considered to be a natural analogue to experimental laboratories, as the main changes in physical and chemical conditions and mineralogy are related to progressively increasing temperature with depth. Temperature was estimated from combined geothermometric approaches, and especially from fluid inclusion studies on quartz coexisting with clays. The Al(lv) content in the tetrahedral site of chlorites, and the K content and total interlayer occupancy of illites increase with temperature. These chemical changes are mainly related to the marked decrease in the molar fraction of the Si(lv)-rich end-members (kaolinite for chlorites, and pyrophyllite for illites) which become negligible at ~ 300~ Other chemical changes, such as the variation in Fe and Mg contents, are partly influenced by temperature, but are strongly dependent on the geological environment, and consequently on the solution composition. The empirical relationships between chemical variables and temperature were calibrated from 150-300~ but extrapolations at lower and higher temperatures seem possible for chlorites. Such geothermometers provide tools for estimating the crystallization temperature of the clays, and are important for the study of diagenetic, hydrothermal and low-T metamorphic processes.Clay minerals are the most abundant minerals in most of the geological environments submitted to temperatures from 50 ~ to 350~ where estimation of the crystallization temperature of the clay minerals may be difficult. Most of the classical geothermometers cannot be applied, fluid inclusions may be absent, and experimental data are scarce. Nevertheless, such temperature estimations are of critical importance for geological studies related to oil field exploration, as well as for diagenetic and low-T metamorphic processes.

Genesis of Syntectonic Hydrothermal Veins in the Igneous Rock of Teschenite Association (Outer Western Carpathians, Czech Republic): Growth Mechanism and Origin of Fluids

“…The true trapping temperatures and pressures can be specified only if independent temperature and/or pressure estimates are available. Since the aggregates of chlorite enclosed in both granular and fibrous calcite from V2 vein show very high Si values often exceeding the theoretical maximum of 4 apfu, chlorite compositional geothermometers (Cathelineau 1988;Jowett 1991) can not be used for determining the temperature of their formation. However, as an upper possible temperature limit for syntectonic V2 veins can be used the regional burial temperature maximum (ca.…”

Mineral assemblages as a record of the evolutionary history of the Pepper Mts. Shale Formation (the Holy Cross Mts.).

“…(Naglik 2016) Chlorite is one of the most common silicates in variety of geological environments occurring as a product of metamorphism as well as hydrothermal or diagenetic rocks alteration (Jiang et al 1994). The relationship between chlorite chemical composition and physico-chemical conditions of its formation was observed by many authors (Cathelineau & Nieva 1985, Walshe 1986, Kranidiotis & McLean 1987, Cathelineau 1988, Vidal et al 2001, Inoue 2009). A new model published by Bourdelle et al (2013) is applicable for the chlorites formed at the wide range of temperatures (50-350°C) and under pressure lower than 4 kbars.…”

Geochemical and isotopic evidence for Carboniferous rifting: mafic dykes in the central Sanandaj-Sirjan zone (Dorud-Azna, West Iran)

“…P-T estimate for the alkaline dyke assemblage range from 720 ± 30 °C at 5 ± 1.5 kbar. The temperature estimates for the retrograde stage were obtained using the amount of Al iv base in chlorite of Cathelineau (1988). Estimates range from 332 °C to 187 °C in both subalkaline and alkaline dykes, indicating greenschist facies and sub-greenschist facies conditions during metamorphism and alteration.…”