PETROGENETIC HISTORY OF ROCKS OF THE SOUTHERN WET MOUNTAINS, COLORADO

The 1.4 Ga belt of granitic plutons which extends through Greenland and Labrador to the southern United States has been the focus of numerous studies, in which these rocks have been referred to as either “anorogenic”, or emplaced in a dynamic tectonic setting. The Proterozoic gneisses exposed throughout the Wet Mountains of central Colorado are host to several large 1.4 Ga plutons which preserve syn- to post-tectonic fabrics. Investigations of these plutons in relation to the surrounding country rock can thus aid in understanding the processes at depth ca.1.4 Ga in North America. Here we present petrologic interpretations of rocks in the southern Wet Mountains, including samples within and adjacent to the 1.37 Ga San Isabel pluton. We use mineral assemblages and pseudosection calculations to constrain the pressure-temperature conditions of metamorphism within the migmatite gneiss country rocks and within the body of the pluton. We consider the petrogenetic significance of partial melt within the country rocks to further constrain the conditions of metamorphism. This study complements the ongoing effort to provide a tectonic model that unifies the petrologic and geochemical data for the ca. 1.4 Ga tectonic event. The results also have implications for processes occurring at depth within modern orogenic belts.