A Thermochronologic Transect of Basement Rocks across Central Sonora, Mexico: Implications for Laramide Tectonics and Cenozoic Extension
Most plutonic basement across Sonora was emplaced during the Late Cretaceous to early Tertiary and represent igneous activity during Laramide time (ca. 8050 Ma). Following emplacement, most plutons experienced rapid post-magmatic cooling at high temperatures (700-450 °C) followed by protracted cooling (<20 °C/m.y.) throughout the PaleoceneEocene and even into the early Oligocene. The lack of significant thermal events during this time may reflect a period of extended tectonic quiescence across Sonora and suggest that significant Laramide deformation is largely absent in this region. This conclusion is supported by the broad concordance of Late Cretaceous/early Tertiary sediments with Oligo-Miocene deposits in many parts of Sonora, including Santa Rosa in eastern Sonora and the Suaqui Grande and Sierra Mazatan regions of central Sonora.
Metamorphic core complexes in Sonora represent the only exposed basement that remained hotter than 300 °C until the Oligo-Miocene. Sonoran core complexes all experienced rapid footwall cooling related to tectonic exhumation that began during the late Oligocene (ca. 25 Ma) and continued until the early-middle Miocene (ca. 15 Ma). This major phase of extension began and mainly occurred during subduction and cannot be linked to post-12 Ma transtensive Pacific-North American plate motions. Total estimated slip at Sonoran core complexes was 625 km and occurred at average rates of 17 mm/yr based on these data.