CONSTRAINING HIGH TEMPERATURE DEFORMATION AND METAMORPHISM IN THE SOUTHERN WET MOUNTAINS, COLORADO, USA: NEW P-T-T RESULTS FROM HIGH GRADE METAMORPHIC BASEMENT AND IMPLICATIONS FOR THE PICURIS OROGENY

The Wet Mountains of Colorado are underlain by exhumed Proterozoic metamorphic rock that lies north of the recently identified Picuris orogen in northern New Mexico. The Picuris orogen is presently inferred to have formed in response to a Mesoproterozoic (ca. 1.49-1.40 Ga) contractional and transpressional event along an evolving convergent margin that resulted in the Pinware-Baraboo-Picuris orogen. This study focused on the record of high temperature deformation, metamorphism, and plutonism in the southern Wet Mountains interpreted as a consequence of Mesoproterozoic tectonism related to the southwestern segment of this orogen. The rocks experienced upper-amphibolite to granulite facies metamorphism and multiple episodes of penetrative deformation attributed to NW-SE sub-horizontal contraction. From north to south along a transect of the Wet Mountains, the presence of migmatites increases. While previous studies have worked to constrain the pressures and temperatures experienced in the northern to central Wet Mountains, these conditions have not been assessed for the southern Wet Mountains. Research for this project addressed two major questions: 1) the timing and conditions of Mesoproterozoic deformation events, and 2) the pressure and temperature conditions of the southern Wet Mountains. U-Pb zircon dating via laser ablation ICP-MS of several granitic orthogneisses yielded ~1.44 – 1.41 Ga crystallization ages and a metasedimentary rock intruded by granite hosted detrital zircons as old as 1.77 Ga. Phase equilibria modeling via Perple_X for a Grt + Sil + Crd + Bt + Kfs + Pl + Qtz migmatite yielded inferred peak conditions of > 0.6 GPa and > 700^oC. These results are consistent with contraction and burial to > 20-km-depths during deformation and metamorphism related to the Picuris orogeny. This work supports the hypothesis that the southern Wet Mountains preserve a middle crustal record of penetrative ductile deformation that was contemporaneous with syn-magmatic partial melting of Paleoproterozoic metasedimentary host rocks.