Continental rifting models predict a variety of spatiotemporal patterns of rift initiation, fault development, and time scales of rift integration. The Rio Grande rift (southwestern United States) is an example of a rift for which both synchronous opening and propagation models have been proposed and, hence, offer differing predictions for the timing of rift development. Low-temperature thermochronometry data from six vertical transects in the upper Arkansas River valley reveal exhumation histories that delineate the initiation, growth, and linkage of rift-bounding faults. Extension initiates on separate fault segments between ca. 22 and 18 Ma, and spatial patterns in fault initiation and exhumation rate suggest that individual fault segments linked to form a coherent ∼75-km-long fault system by ca. 13 Ma. Our results, combined with data from throughout the northern Rio Grande rift, support a model of synchronous early Miocene rift initiation, with full rift integration occurring no earlier than ca. 10 Ma. Densely spaced sampling transects and slow extension rates in the Rio Grande rift allow us to resolve differences in the timing of fault initiation and rates of exhumation that yield insight into the processes of fault growth and linkage that cannot be easily discerned in rapidly evolving rift systems.

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