Application of chlorite thermometry to estimation of formation temperature and redox conditions

Abstract

ABSTRACTDiverse applications of chlorite thermometry have been considered for better understanding the formation process in nature. Here, an approach which combined a semi-empirical thermometer (Inoueet al.,2009) with the method of Walshe (1986) was tested to estimate the redox conditions (logfO2) and the formation temperature, using the literature data from Niger, Rouez and St Martin and new data for chlorite which coexists with pink-coloured epidote in the Noboribetsu geothermal field. The logfO2predicted for the former data sets were compatible with those estimated by Vidalet al.(2016), suggesting that the present approach is valid for quantifying the variations in logfO2. The Noboribetsu chlorites have lower Fe/(Fe + Mn + Mg) and greater Fe3+/ΣFe ratios than those observed in adjacent propylite rocks. The peculiar mineral assemblage and chemical composition are attributed to the formation under higherfO2conditions and possibly low Fe concentration in the alteration fluids.