SPECTRAL MAPPING OF MUSCOVITES IN LOW-GRADE METAMORPHIC ROCKS IN THE BLACK HILLS, SD

Previous studies have shown a correlation between the wavelength of the Al-OH absorption band in white micas and increasing degrees of metamorphism as measured by the appearance of metamorphic index minerals, metamorphic isograds and metamorphic zones.

This study collected spectral data from across the lower grade metamorphic zones of the Black Hills, SD, and was combined with previous work done by A. Leahy and E. Duke into a geodatabase of 716 spectra. The spectra were analyzed to determine Al-OH wavelengths in order to investigate the spatial variance of the data. An Inverse Distance Weighted interpolation map was then created to better visualize the trends in the wavelengths.

As a result, the variance in metamorphism suggested by the Al-OH wavelengths follows the general trend of the previous metamorphic isograd map of the Black Hills. However, there are trends in the spectral data that suggest a possible northern extension of the staurolite isograd and a possible chlorite zone in the current biotite zone. These trends were not previously known and will be investigated in the future.