CALIBRATION OF CHLORITE COMPOSITION USING MICRO-RAMAN ANALYSIS

Chlorite is a widespread phyllosilicate on Earth, found in a variety of geological environments, including low- to high-grade metamorphic rocks, as well as in many hydrothermal ore deposits. Chlorite forms over a temperature range of 100-550°C, and its chemical composition is dependent on physicochemical conditions at time of formation. Chlorite is, therefore, useful for geothermometry. Based on its chemical composition, chlorites allow for reconstruction of geological thermal history, fluid flow modelling, and determination of the geochemical conditions of the environment.

Here, we determine a calibration for chlorite composition using Raman spectroscopy. Although Raman spectroscopy is primarily a mineralogical technique, chemical composition influences the mineral structure (e.g., by shifting characteristic Raman peaks). We have analyzed a range of chlorite samples representing different geological environments (e.g. hydrothermal, diagenetic, metamorphic) and compositions; chlorite Raman peak shifts are compared to sample chemical composition estimated by electron microprobe analysis.

Preliminary data suggests that chlorites have a unique Raman spectral pattern as a function of their compositions. We distinguish characteristic spectral patterns, peak position, and peak widths associated with chlorite compositions using a peak fitting technique by decomposing each peak into sub-curves. From there, we will extract several empirical rules that will help to quickly identify and characterize chlorite based on in situ Raman spectroscopic measurements. The results of this research is significant for planetary exploration by providing a calibration for future Raman instruments. This chlorite calibration will be useful for studies of the depositional environment on other planets.