Paleomagnetic Studies in Southwestern U.S.: The J1 Cusp

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For ages older than mid-Mesozoic, apparent polar wander (APW) paths of the major continents become the most important single source of information about lithospheric plate motions. The validity of these APW paths and the degree to which they can be interpreted in terms of path geotectonic motions is ultimately dependent upon the quality of he paleomagnetic poles on which they are based. Recent studies have indicated that the Mesozoic North American APW path can be well modeled by paleomagnetic Euler pole (PEP) analysis in which the APW path is viewed as sequence of small circle tracks separated by corners or "cusps" in the path. The "J1 cusp" occurs in the Late Triassic to Early Jurassic and is related to changing North American plate motion associated with the breakup of Pangea. However, because of inadequacies in the paleomagnetic pole data base, the J1 cusp is certainly not as clearly defined as it could be with acquisition of high-quality paleomagnetic data. Recent results from the Moenave Formation clearly demonstrate that careful paleomagnetic studies can produce very well defined poles from the Late Triassic-Early Jurassic strata of northeastern Arizona. Further paleomagnetic studies of the Chinle, Kayenta, and to her formations will be performed in this project in order to more clearly define the pattern of North American APW during this critical time interval. Results will (1) greatly improve knowledge of Late Triassic and Early Jurassic APW for North American and (2) provide a major test for applicability of PEP models, with attendant global geodynamic implications.