THE ROLE OF THE PICURIS OROGEN IN THE TECTONIC CONFIGURATION OF MESOPROTEROZOIC NORTH AMERICA (Invited Presentation)

The Picuris orogeny is a newly recognized event in the Mesoproterozoic tectonic record of the western US. We have identified this ca. 1.46-1.35 Ga orogenic event by examining the timing and geographic extent of deposition, magmatism, metamorphism, and deformation in western North America, and by analyzing the connections between these orogenic processes.

North America is known for extensive Mesoproterozoic igneous activity, including the emplacement of voluminous, chemically diverse plutons that are presently exposed in the western US. Recent investigations of the spatial and temporal distribution of zircon U-Pb crystallization ages show that Mesoproterozoic igneous rocks may have been emplaced along and inboard of a continent-scale convergent margin. In this tectonic model, the Picuris orogen of western North America makes up one segment of an extensive system of arcs and backarcs. This convergent and collisional margin system stretched from southwest to northeast North America (present coordinates), and produced the Southern (SGR) and Eastern Granite Rhyolite (EGR) provinces of central North America, and the Pinware orogen of eastern North America.

The rock record illustrates that greenschist to near granulite facies regional metamorphism and deformation are associated with the Picuris orogen. Lutetium-hafnium garnet age data from New Mexico and Colorado vary systematically along a broadly north-south transect, with statistically significant age breaks across regionally extensive shear zones. Paleo- and Mesoproterozoic Lu-Hf garnet ages are preserved in rocks from southern Colorado, and mark the northern margin of the Picuris orogen. Schist and gneiss samples from the Manzano Mountains, New Mexico and the Wet Mountains, Colorado, yield Lu-Hf garnet ages that are ~35 M.y. older than adjacent Mesoproterozoic plutons, which demonstrates that crustal temperatures were already elevated regionally, prior to pluton emplacement.

The Proterozoic western US is fertile ground for continued investigations into continental growth and modification. Our understanding of the tectonic configuration of North America in the Mesoproterozoic is still evolving.