Robert S. Hildebrand

Dept. of Earth & Planetary Sciences, University of California, Davis, California 95616-8605, USA

ABSTRACT

Paleomagnetic results indicate that much of the North American Cordillera migrated more than 1000 km northward during the 80–58 Ma Laramide event, yet geologists cannot find either the faults along which such movement might have taken place or readily identifiable piercing points to document offset. Here, I suggest that the sinistral Texas Lineament, which extends west-northwest from the Gulf of Mexico to the Cordilleran fold-thrust belt southwest of Las Vegas, and the sinistral Lewis & Clark transverse zone, located about 1300 kilometers to the north, and extending from southern Vancouver Island east-southeast to the thrust belt in the Helena salient, can be restored to one through-going zone to provide a piercing point that constrains meridional migration. I interpret the zone as the result of plate interactions on a left-stepping transform margin formed along the southern margin of North America during Jurassic opening of the Atlantic Ocean. The structure was dismembered and partly transported northward along faults in and/or adjacent to the Cordilleran fold-thrust belt. The proposed restoration also reunites two conspicuous bands of Late Cretaceous–Paleocene slab-failure plutons and porphyry copper deposits into a single zone extending continuously along western North America. This reconstruction obviates the need for Laramide flat slab subduction.

Manuscript received 24 June 2015; accepted 17 July 2015.

doi: 10.1130/GSATG255A.1