Petrology and Geochemistry of the Silver Plume-Age Plutons of the Southern and Central Wet Mountains, Colorado.

The 1.43 billion-year-old Silver Plume-age intrusive complex of the central and southern Wet Mountains, Colorado, is subdivided into six units. In inferred order of intrusion, these include: the San Isabel batholith, the granite of Cliff Creek, the granite of Williams Creek, the granite of Bear Creek, the Wixson Divide pluton, and the granite of the Mount Tyndall quadrangle. All rocks are metaluminus to mildly peraluminus, calc-alkaline, and modally range from melanocratic biotite-hornblende-rich granite to leucocratic alaskite. The biotite-rich granites are non-eutectic and crystallized at a temperature of 710(DEGREES)C to 850(DEGREES)C. The leucocratic granites are eutectic and crystallized between 650(DEGREES)C and 700(DEGREES)C. The depth of emplacement is mesozone to catazone, representing an emplacement depth less than 17 kilometers, with a load pressure of less than 4600 bars. The rocks have undergone pre-, syn-, and post-emplacement crystallization followed by late stage recrystallization, mylonization, and potassium metasomatism. Field, modal, and chemical characteristics of the Silver Plume granites, are not clearly indicative of any single model of granite formation. The granites closely resemble I-type or S-type granites. However, the plutons appear to have an anoroginic origin. This seemingly paradoxical situation may suggest that the magma produced during the anorogenic Silver Plume Disturbance-Thermal Event inherited much of its oroginic character from the melting of rocks generated during an earlier event