Remagnetization of Cretaceous forearc strata on Santa Margarita and Magdalena Islands, Baja California sur: Implications for northward transport along the California margin

Paleomagnetic data for two sections of Cretaceous forearc strata with diffe rent structural attitudes an Santa Margarita and Magdalena Islands in Baja California Sur, Mexico, indicate that these rocks have been remagnetized, p robably during the late Cenozoic. The in situ paleomagnetic directions, how ever, are similar to data from other Cretaceous racks on peninsular Califor nia with unexpectedly shallow inclinations and easterly declinations. These data have been interpreted as indicating either northward tectonic transpo rt (10 degrees-15 degrees of latitude) and clockwise rotation (>20 degrees) or compaction shallowing of magnetic inclinations in sedimentary rocks com bined with southwestward tilting of plutonic racks. The available paleomagn etic data for Cretaceous forearc strata in southern and Baja California can be divided into three groups: (1) sections with normal-polarity magnetizat ions that fail fold tests and are remagnetized, (2) sections with normal-po larity magnetizations with no or inconclusive fold tests that may or may no t be remagnetized, and (3) sections with both normal- and reversed-polarity intervals where pervasive remagnetization has not occurred. Other rocks of the Mesozoic Great Valley Group, Coast Range ophiolite, and Franciscan Com plex in California also have secondary magnetizations with directions simil ar to younger geomagnetic field directions. Although these widespread remag netizations could have variable local causes, we propose regional burial an d uplift, related to changes in subduction parameters, as a possible explan ation. Two episodes of remagnetization are apparent: one in the Late Cretac eous and a second in the late Cenozoic. On the other hand, the unremagnetiz ed and apparently reliable data from sedimentary and plutonic rocks on the Baja Peninsula consistently indicate northward translation (14 degrees+/-3 degrees) and clockwise rotation (29 degrees+/-8 degrees) with respect to No rth America since the Late Cretaceous.