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

对于中生代以上的年龄，主要大陆的视极移轨迹(APW)成为关于岩石圈板块运动的最重要的单一信息来源。这些APW路径的有效性以及它们在多大程度上可以用路径大地构造运动来解释，最终取决于它们所依据的古地磁极的质量。最近的研究表明，中生代北美APW路径可以用古地磁Euler极点(PEP)分析很好地模拟，在PEP分析中，APW路径被视为由路径中的角点或尖点隔开的一系列小圆形轨迹。“J1尖点”出现在晚三叠世至早侏罗世，与与盘古裂解有关的北美板块运动的变化有关。然而，由于古地磁磁极数据库的不足，J1尖点的定义肯定不像获取高质量古地磁数据时那样清楚。最近来自Moenave组的结果清楚地表明，仔细的古地磁研究可以从亚利桑那州东北部的晚三叠世-早侏罗世地层中产生非常明确的两极。该项目将对钦勒、卡扬塔和她的地层进行进一步的古地磁研究，以便更清楚地确定北美APW在这一关键时间间隔内的模式。这些结果将(1)极大地提高对北美晚三叠世和早侏罗世APW的认识；(2)为PEP模型的适用性提供一个重大测试，并伴随着全球地球动力学意义。

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.