Low-Temperature Chlorite Geothermometry and Related Recent Analytical Advances: A Review

Abstract

Chlorite, a 2:1:1 phyllosilicate, has all the required attributes to form the basis of a geothermometer: this mineral is ubiquitous in metamorphic, diagenetic, and hydrothermal systems with a broad field of stability and a chemical composition partly dependent on temperature (T) and pressure (P) conditions. These properties led to the development of a multitude of chlorite thermometers, ranging from those based on empirical calibrations (linking T to AlIV content) to thermodynamic or semi-empirical models (linking T to chlorite + quartz + water equilibrium constant). This present study provides an overview of these geothermometers proposed in the literature for low-temperature chlorite (T < 350 °C), specifying the advantages and limitations of each method. Recent analytical developments that allow for circumventing or responding to certain criticisms regarding the low-temperature application of thermometers are also presented. The emphasis is on micrometric and nanometric analysis, highlighting chemical intracrystalline zoning—which can be considered as evidence of a succession of local equilibria justifying a thermometric approach—and mapping ferric iron content. New perspectives in terms of analysis (e.g. Mn redox in Mn-chlorite) and geothermometer (molecular solid-solution model, oxychlorite end-member) are also addressed.

Influence of Deformation and Fluids on Ti Exchange in Natural Quartz

“…We applied chlorite thermometry (Bourdelle, 2021) to obtain independent information on the deformation temperature to complement the Ti‐in‐quartz estimates. This method has been shown to be particularly efficient for determining deformation temperature in the greenschist facies (Calzolari et al., 2018; Cantarero et al., 2014; Lacroix et al., 2012; Mizera et al., 2020; Zihlmann et al., 2018).…”

Metamorphic peak estimates of the Marguareis Unit (Briançonnais Domain): New constrains for the tectonic evolution of the south‐western Alps

“…This has been progressively improved (Bourdelle & Cathelineau, 2015; Lanari et al, 2014) following the pioneering calibrations of Cathelineau and Nieva (1985) and Cathelineau (1988) and successfully applied in low‐grade metamorphic and/or hydrothermal systems (e.g. Beauchamps et al, 2021; Bourdelle, 2021; Favier et al, 2021; Vérati et al, 2018).…”

Formation of a Composite Albian–Eocene Orogenic Wedge in the Inner Western Carpathians: P–T Estimates and 40Ar/39Ar Geochronology from Structural Units

“…Determining the P-T condition in low-grade metamorphic rocks (up to "epizone" T < 350 • C) is challenging because of the lack of indexing minerals and other factors (e.g., Bourdelle, 2021). This has mostly been achieved in the past decades by several calibrations of chlorite thermometers and phengite barometers (e.g., [70][71][72]108]).…”

“…This has mostly been achieved in the past decades by several calibrations of chlorite thermometers and phengite barometers (e.g., [70][71][72]108]). LT-LP chlorite thermometry, however, is still open to debate [109][110][111]. Two main approaches are still used today.…”