Miocene paleomagnetism and tectonic setting of the Baja California Peninsula, Mexico

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Abstract
A paleomagnetic pole calculated from 64 virtual geomagnetic poles for Miocene volcanic rocks of the Baja California Peninsula (86.1°N, 142.6°E, α95= 3.9°) is similar to a reference pole for the North American craton (87.4°N, 129.7°E, α95= 3.0°), consistent with the Baja Peninsula having been adjacent to the Mexican mainland in its pre‐Gulf of California position from at least early Miocene time to the Pliocene opening of the Gulf. This result is in agreement with marine geophysical and geologic evidence from the Gulf of California and Baja Peninsula and does not support a long‐period nondipole geomagnetic field in the region during Miocene time, or 10° of northward transport of the peninsula since then, inferred from smaller data sets (included in this work) by previous workers. This study also indicates that a pre‐Gulf of California northward translation (9° of latitude) and clockwise rotation (24°) of the Baja Peninsula with respect to North America, determined from paleomagnetic studies of Cretaceous rocks within peninsular California occurred prior to Miocene time. Paleomagnetic results from Late Cretaceous to early Tertiary basement rocks in western Sinaloa, Mexico are similar to those results from Cretaceous rocks of the Baja Peninsula, supporting the early Tertiary northward translation of the peninsula between 45 and 34 Ma and suggesting that the tectonic boundary separating peninsular California from North America at that time was east of the present‐day Gulf of California.