NEAR INFRARED SPECTRA OF ILLITE AND MUSCOVITE IN VERY LOW-GRADE METAMORPHIC ROCKS OF THE BELT SUPERGROUP, MONTANA AND IDAHO

摘要

The Mesoproterozoic Belt Supergroup extends across western Montana and northern Idaho into eastern Washington, and the stratigraphically equivalent Purcell Supergroup covers parts of southwestern Alberta and southeastern British Columbia. The thickness of Belt sediments increases from near zero in central Montana to over 16 km in western Montana and northern Idaho.