The role of the Picuris orogeny in the tectonic evolution of Proterozoic North America
North America is a continent that has grown over time by horizontal attachment of material onto its margins. Studying the process of continental growth in the geologic past gives insight into fundamental components of plate tectonics, and sheds light onto processes at work at modern plate boundaries, in which mid- and lower-crustal rocks are generally hidden from view. This study focuses on the growth of North America during the Proterozoic. Researchers have debated the role of three orogenies in shaping the southwestern margin of North America: the ∼1.80-1.60 Ga Yavapai and Mazatzal orogenies, and the newly recognized ∼1.40 Ga Picuris orogeny. We address this question at local, regional, and continental scales using a variety of methods, including geochronology, structural analysis, and metamorphic petrology. Here we show that portions of New Mexico did not undergo high temperature metamorphism until the Picuris orogeny, and that much of the regional deformation documented in these locations accompanied metamorphism during a single progressive tectonic event that featured thrusting and heterogeneous crustal thickening. Proterozoic rocks in Colorado underwent multiple pulses of high temperature metamorphism during the Yavapai, Mazatzal, and Picuris orogenies, and a tectonic boundary separates the poly-metamorphosed rocks of southern Colorado from the progressively metamorphosed rocks of northern New Mexico. The ∼1.48-1.35 Picuris orogen that spans northern New Mexico and southern Colorado is part of a continent-scale system that links the Picuris orogen to the ∼1.51-1.45 Ga Pinware orogen of eastern North America. These two orogens are the product of a convergent southern margin with a north-dipping subduction zone, which had variably developed continental arcs, backarcs, and zones of transpression; it may have had an orogenic plateau, and convergence may have been accommodated by collision in addition to subduction.
Andronicos, Purdue University.
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