Abstract

Paleomagnetic data from Cretaceous igneous and sedimentary rocks of the Peninsular Ranges and Continental Borderland of the Baja California Peninsula yield an average pole position of 83°N, 344°E (A95 = 3.4°), suggesting that the peninsula as a whole has moved northward ∼11° and rotated 32° clockwise, with respect to the North American craton, since Cretaceous time. Only a small portion of this movement is due to the Neogene opening of the Gulf of California. Results from stratified rocks giving both positive and negative fold tests are included in the average Cretaceous pole. The rocks that fail fold tests have been deformed and remagnetized by nearby intrusives that are only slightly younger; unconnected directions from these sites closely match corrected directions from sites where the fold tests are positive. Oceanic rocks were also sampled in the Continental Borderland from Upper Triassic and Upper Jurassic tectonostratigraphic terranes which are apparently allochthonous with respect to the western Baja Peninsula and each other. These oceanic rocks show magnetizations indicating low paleolatitudes, although the hemisphere of origin is presently unknown. The Cretaceous rocks of the Baja California Peninsula may have originally formed adjacent to the now-truncated continental margin along the northern Middle America Trench. Northward transport of the peninsula probably occurred by transcurrent faulting associated with oblique subduction of the Farallon plate beneath western North America between Late Cretaceous and late Miocene time.

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