The interval between 1.78 and 1.63 Ga was one of major crustal growth and assembly in southwestern Laurentia. The prevailing view is that the culminating event for this tectonism was the ca. 1.654-1.633 Ga Mazatzal orogeny. We present evidence for a continuum of deformation, magmatism, metamorphism, and new mineral growth from 1.65 to 1.58 Ga from southern Wyoming to Sonora, Mexico. We suggest that the Mazatzal orogeny may have extended in time to ca. 1580 Ma and in space to the Cheyenne belt, southern Wyoming. If our interpretation for an extended Mazatzal orogeny is correct, the duration of the orogeny may have been ~70 m.y., similar to many orogenies in Earth's history. The ca. 1.6 Ga tectonism appears to represent a shift in tectonic style from that typically associated with the Yavapai (ca. 1.70 Ga) and "classic" Mazatzal (1.65 Ga) orogenies to widespread intracontinental deformation. If correct, a corollary to our interpretation is that newly accreted Paleoproterozoic crust stabilized rapidly and facilitated stress transfer far inboard of any active plate margin.
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