Publication Date:
2015-08-22
Description:
The chlorites are good indicators of rock history because their wide compositional variations are sensitive to the formation conditions, like pressure ( P ), temperature ( T ), redox state, fluid composition. Accordingly, many geothermometers based on their composition, either empirically or thermodynamically, have been proposed during the last 30 years, especially in low-temperature contexts ( T 〈 350°C). This paper presents a graphical tool that considerably facilitates the use of two of the most recent chlorite thermometers for low- and very-low- T chlorites. The temperature–composition relationships for low- T chlorites are represented in T –R 2+ –Si diagrams, allowing chlorite compositions to be predicted as a function of temperature or, conversely, temperature to be estimated from compositional fields of natural chlorites. This graphical projection is based on a comparison of the parameters (ideal chlorite compositions and calculated T ) predicted by geothermometers with analyses of natural chlorites for which independent T estimates are available over a range of geological environments. The new T –R 2+ –Si diagram provides a practical tool for thermometric purposes in the applicability range of the considered models, in particular for diagenesis and low-grade metamorphism.
Print ISSN:
0935-1221
Electronic ISSN:
1617-4011
Topics:
Geosciences
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