Paleomagnetic and tectonic constraints on the Late Cretaceous to early Tertiary northward translation of the Baja California peninsula

Abstract

Cretaceous paleomagnetic data for the Baja California Peninsula (northwestern Mexico; southwestern California, U.S.A.) consistently indicate northward translation ( _͌ 8° in latitude or ~900 Km) and clockwise rotation ( _͌ 20°) of the region relative to ancestral North America prior to opening of the Gulf of California in late Miocene time. Paleomagnetic and rock magnetic studies in Upper Cretaceous rocks younger than the Cretaceous Normal Polarity Superchron (Aptian to Santonian) confirm the age of the Cretaceous magnetization, and paleomagnetic data for early to middle Miocene lava flows indicate that peninsular California was near its pre-Gulf position against coastal Sonora during much of Miocene time. Estimates of potential coastwise displacement of crustal fragments along the western margin of North America by oblique subduction and arc-parallel strike-slip faulting for all of Paleogene time, based on modern analogs and plate reconstruction models of Farallon and Farallon + Kula plate motion ( _͌ 1000-2000 Km), are roughly equivalent to the northward displacement of peninsular California indicated by the Cretaceous paleomagnetic data ( _͌ 900 Km). However, current paleomagnetic and geologic studies indicate that the pre-Miocene displacement of peninsula California may have been completed by early Eocene time. The available paleomagnetic and paleontologic data constrain northward movement to have occurred between Chron 32r and Chron 23r, or between  _͌ 70 Ma and  _͌52 Ma. Coastwise transport of 900 Km during this time interval is most easily explained within the context of our model by arc-parallel strike-slip faulting related to oblique subduction of the Kula plate, although transport could also have occurred within the limits of relative motion of the Farallon plate depending on the trend of the North American margin and efficiency of the mechanism of transport.