2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 8
Presentation Time: 8:00 AM-12:00 PM


WYLD, Sandra1, UMHOEFER, Paul J.2 and WRIGHT, James E.1, (1)Geology, Univ of Georgia, Athens, GA 30602, (2)Department of Geology, Northern Arizona Univ, Box 4099, Flagstaff, AZ 86011, swyld@gly.uga.edu

In an accompanying abstract presented in this session, we describe our reconstruction of the Late Cretaceous (~80 Ma) paleogeography of the United States and Canadian Cordillera, based on (i) restoring displacements within the major Late Cretaceous to Cenozoic contractional and extensional belts of the Cordillera, and (ii) restoring displacements along the major Late Cretaceous to Cenozoic dextral strike-slip faults of the northern Cordillera. In this poster, we will present large format maps of the reconstruction, showing more details of local geology, as a forum for discussion and analysis. Several aspects of the reconstruction can be explored. (1) Timing and amount of offset on the major strike-slip faults, possible links between faults, and projections of faults to the south (beneath Cenozoic cover) into Washington and Oregon. Some faults are well characterized in these aspects, while others are less certain. The requirements of kinematic compatability in a regional reconstruction like this highlight the need to obtain more information on these parameters, and pinpoint which regions of the northern Cordillera most crucially need more study. (2) The reconstruction juxtaposes many terranes or provinces that have previously been correlated or likely evolved together, as well as others that have not been correlated but that could have evolved together. The implications of these juxtapositions are intriguing and important to analyze, and will be facilitated by the large format presentation. (3) In the ongoing Baja B.C. controversy, large offsets indicated for northern Cordillera terranes by paleomagnetic data are generally contrasted with geology-based models that essentially involve no offset. Our reconstruction is a more realistic alternative, and provides a new point of comparison with paleomagnetic-based models. It also requires some modifications to the "crucial tests" proposed by Cowan et al. (1987). (4) The reconstruction provides intriguing new insight into older episodes of strike-slip terrane dispersal in the Cordillera. We will highlight features that relate to this topic and offer some speculative interpretations. (5) The maps can also be used to explore implications of the reconstruction for Farallon-Kula-Resurrection plate interactions, and for the origin of the Columbia embayment.