Abstract

Early Proterozoic rocks in northern New Mexico can be used to document 100-170 km of right-lateral slip along a network of north-striking Laramide (Late Cretaceous-early Tertiary) faults that formed the precursor of the Rio Grande rift. Piercing lines are defined by the intersection of a subborizontal 4 kbar isobaric surface with steeply dipping stratigraphic markers and regional structures. Restoration of slip provides new insight into the nature of Proterozoic orogenic and crustal province boundaries. The Yavapai crustal province (1.75-1.72 Ga juvenile volcanogenic rocks) is imbricated with overlying Hondo Group sedimentary cover in an originally east-trending ductile thrust belt that formed near the southern margin of the Yavapai province. A series of offset magnetic anomalies (Jemez lineament) is interpreted to mark the thrust-buried boundary between older (Yavapai province) and younger (Mazatzal province) crust. Our microplate tectonic model suggests that Laramide strike-slip movement (New Mexico) was kinematically linked with coeval extensional collapse (Arizona) and foreland shortening (Wyoming) during decoupling and northward movement of the rigid Colorado Plateau relative to the undeformed midcontinent. Crustal-scale strike-slip faults in New Mexico were reactivated during later Tertiary extension and continue to localize high heat flow in the Rio Grande rift and northward into Colorado.

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