Asking the pikas politely…
Southwest of Gunnison, Colorado, within the Wildcat Gulch study area, syenitoid plutons intrude the Proterozoic Dubois Greenstone. Limited work has been done to document their lithologic character, ascertain their origin, or place them within the regional geology of central Colorado. These syenitoid intrusions may be related to the igneous rocks of the ~1700 Ma Routt Plutonic Suite that formed during the Colorado orogeny that included episodes of arc collision and accretion during the Early Proterozoic. Alternatively, these syenitoid intrusions may be related to the rocks of the ~1400 Ma Berthoud Plutonic Suite that formed during the Berthoud orogeny in an episode of crustal thickening and shortening during the Middle Proterozoic. It is also possible that the syenitoid intrusions in the Wildcat Gulch study area are related to the syenite intrusions of the Iron Hill complex (570 Ma) that formed in an extensional continental environment. This study provides a petrological and geochemical characterization and assessment of the informally named Wildcat Gulch syenite to aid the placement of these syenitoid intrusions within the regional geology of Colorado. Through petrologic and geochemical analyses this study finds that the Wildcat Gulch syenite can be classified as quartz syenite and quartz monzonite. Although these rocks vary in terms of their mineralogy, they are geochemically very similar. The geochemical data suggest that the syenitoid varieties may have evolved from a single, possibly basaltic parent magma, through fractional crystallization. Additionally, it is suggested that the Wildcat Gulch syenite intrusions formed between 1390 - 1330 Ma as part of the Berthoud orogeny.
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