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

在中生代中期以后，主要大陆的视极移路径成为岩石圈板块运动最重要的单一信息来源。这些APW路径的有效性以及它们在路径大地构造运动方面的解释程度最终取决于它们所依据的古磁极的质量。近年来的研究表明，古磁欧拉极（PEP）分析可以很好地模拟北美洲中生代APW路径，将APW路径视为路径上由角或“尖”分隔的小圆形路径序列。“J1尖峰”发生在晚三叠世至早侏罗世，与泛大陆分裂引起的北美板块运动变化有关。然而，由于古磁极数据库的不足，J1尖点的定义肯定不像获取高质量的古磁极数据那样清晰。最近来自莫纳韦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晚三叠世-早侏罗世地层中得到非常明确的两极。本项目将对Chinle， Kayenta及其地层进行进一步的古地磁研究，以便更清楚地确定这一关键时期北美APW的模式。结果将(1)大大提高对北美晚三叠世和早侏罗世APW的认识；(2)为PEP模型的适用性提供了重要的检验，并具有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.