A REVISED LOOK AT LAURENTIA'S PROTEROZOIC APPARENT POLAR WANDER PATH: IMPLICATIONS FOR PALEOGEOGRAPHY AND THE RODINIA SUPERCONTINENT

New paleomagnetic data from Proterozoic sedimentary sequences from southwest U.S. allow for a revised look at Laurentia's Proterozoic apparent polar wander path (APWP). At present Laurentia's Meso- and Neoproterozoic APWP is composed of two major sections: (1) the Logan loop, or Keweenawan sequence (1100 - 1000 Ma), which is the most well defined APWP of any craton for the entire Proterozoic, and (2) the younger Grenville and post-Grenville section (1000 - 750 Ma), which is poorly constrained and has generated considerable debate in the past few decades. The latter section of the path is of particular importance because it corresponds temporally with the life-cycle of the proposed Rodinia supercontinent.

In general, researchers agree that the Grenville section of Laurentia's APWP loops down through the SW Pacific quadrant; however, the geometry and age progression of the path is as yet undetermined. These uncertainties arise from the highly metamorphic nature of Grenville Province rocks and the large degree of uncertainty in the age of individual paleomagnetic results. The temporal ambiguity of poles from the Grenville has produced two opposing hypotheses regarding the younging direction and geometry of Laurentia's APWP: (1) a clockwise loop and (2) a counterclockwise loop. These conflicting APWP geometries have major implications and consequences for the way in which paleomagnetic-based reconstructions for Rodinia are created. In particular, if one attempts to match APWP geometries between cratonic blocks for the purpose of paleo-reconstructions, it is imperative that the geometry of the paths be constrained for the reconstruction to be valid.

New paleomagnetic data from the southwest U.S. combined with recent reinterpretation of some Grenville Province results (Warnock et al., 2000) suggest that Laurentia's APWP has a counterclockwise loop that starts at the Logan loop at ~1150 Ma at ~40° N and 180° E, crosses the equator at ~160° E, travels down to ~40° S, were the path then loops back up along ~180° E eventually crossing the end of the Logan Loop at ~740 Ma. It should be noted however, that there is still a paucity of paleomagnetic data for the 950 to 750 time interval, and consequently, caution is still warranted when comparing Laurentia's APWP with other cratons for the purpose of paleogeographic reconstruction.