REMAGNETIZATION OF JURASSIC VOLCANIC-ROCKS IN THE SANTA-RITA AND PATAGONIA MOUNTAINS, ARIZONA - IMPLICATIONS FOR NORTH-AMERICAN APPARENT POLAR WANDER

Paleomagnetic poles for the Jurassic Corral Canyon sequence and Glance Conglomerate in southern Arizona have been used to construct apparent polar wander (APW) paths for the North American plate, but they are c ontroversial and conflict with higher-latitude poles from New England. Lower Jurassic dacites and ash flow tuffs of the Mount Wrightson Form ation in the Santa Rita Mountains were initially sampled to provide an additional paleopole for southern Arizona. These rocks, however, have a predominantly reversed-polarity characteristic magnetization (in si tu, I = -47-degrees, D = 154-degrees, alpha95 = 9-degrees) which is st atistically indistinguishable from that for the nearby latest Cretaceo us Elephant Head pluton (I = -48-degrees, D = 165-degrees, alpha95 = 8 -degrees). Although magnetizations of both polarities are observed in the ash flow tuffs, they are mostly carried by hematite, and dual pola rity components are observed within some specimens. Moreover, widespre ad mineralization and a K-Ar age of approximately 67 Ma for altered ro cks of the Mount Wrightson Formation imply that these rocks were subje cted to a prolonged episode (greater than one polarity interval) of lo w-temperature alteration and remagnetization. Middle Jurassic ash flow tuffs of the Corral Canyon sequence in the Patagonia Mountains to the south have a similar geologic setting: They are exposed along strike amid mineralized rocks on the eastern flank of a mountain range cored by Paleocene intrusions. Hematite is also the dominant remanence carri er in most of the Corral Canyon sequence, and its predominantly normal -polarity direction (in situ, I 51-degrees, D = 326-degrees, alpha95 = 9-degrees) is indistinguishable from that for the nearby Patagonia Gr anodiorite (I = 49-degrees, D = 342-degrees, alpha95 = 8-degrees). Roc ks of the Corral Canyon sequence therefore are likely remagnetized as well. Problems also exist with the Glance Conglomerate pole. These roc ks are situated within a caldera structure and have been potassium met asomatized. This potassic alteration could have occurred shortly after emplacement or at a later time, postdeformation. The low-latitude Jur assic APW path for North America and J-2 cusp therefore are not well s upported and may need revision.