Petrology and origin of Precambrian metamorphic rocks in the eastern Ruby Mountains southwestern Montana

Precambrian schists and gneisses are exposed in much of the Ruby Mountains of southwestern Montana. The major rock types include abundant quartz-feldspar gneiss hornblende gneiss amphibolite quartzitic gneiss and marble. Minor rock types important in the study area include anthophyllite gneiss hornblende-pyroxene-plagioclase gneiss quartz-hypersthene-garnet granulite iron-formation and hornblende-hypersthene granulite. These rocks form a concordant series folded into a broad open antiform-synform pair in the study area. This volume is a revised edition containing the complete original text plus the addition of a number of appendices. These include all maps data tables field notes and petrographic descriptions. I have included a new structural analysis treating the area as a single domain with all 342 strike and dip measurements and a structure cross-section cartoon and a suggested pre-metamorphic sedimentary section. These appendices allow the reader to assess the evaluation from original descriptions.