Paleomagnetic and 40Ar/39Ar evidence for remagnetization of Mesozoic oceanic rocks on the Vizcaino Peninsula, Baja California Sur, Mexico

Previously published paleomagnetic data for Upper Jurassic pillow lavas of the Vizcaino Peninsula indicate that they were deposited near a paleolatitude of 14°N or S. Whether or not this result implies northward transport with respect to the continental interior has been controversial due to the lack of reliable Jurassic reference poles for the North American plate. Available paleomagnetic data for nearby Upper Triassic pillow basalts and overlying pelagic sediments at Punta San Hipólito, however, fail a fold test indicating that these rocks were remagnetized post-folding. Indistinguishable in-situ paleomagnetic directions and perturbed ⁴⁰Ar/³⁹Ar age spectra for the Triassic and Jurassic pillow lavas are consistent with resetting of their magnetic and isotopic systems in the middle Cretaceous, probably during burial by the overlap Valle Formation (>10 km thick). Resetting apparently occurred post-deformation so the paleolatitude of remagnetization is unknown. High-coercivity directions from a few samples of the Triassic rocks might represent an older magnetization acquired during deposition at paleolatitudes near 6°N or S.