SOUTHERN LAURENTIA IN RODINIA: COLLABORATIVE COMPILATION OF A TECTONIC MAP FOR IGCP 440

Numerous reconstructions of the Proterozoic supercontinent of Rodinia have been proposed, but there little agreement exists on firm piercing points, between any two continental blocks, for any time between 1700 and 500 Ma. Continued efforts at resolution of this issue can be considered an international challenge to merge geologic and refined paleomagnetic data to: 1) understand the pre-Pangeans configurations of continents, and 2) understand secular changes in Earth?s tectonic regimes. The IGCP 440 compilation of 1:10 M maps of all the Rodinia components offers a chance for discussion of the best portrayal of tectonic elements for different cratons, then an evaluation of the best piercing points between cratons.

Laurentia is proposed to have been at the core of Rodinia because it is rimmed by Neoproterozoic rifted margins. The length of these rifted margins is comparable to the combined length of rifted margins for rifted Pangea, hence many Rodinia continents must have nestled against Laurentia prior to 750 Ma. Laurentia also offers one of the most complete geologic, geophysical and isotopic data sets of any continent and hence provides a template to test piercing points. Compilation of pre-Neoproterozoic tectonic belts in southern Laurentia is aided by extensive geochronology and isotopic crustal model ages and aeromagnetic data that show structural trends in the sub-Phanerozoic basement. We attempt to show all pre-750 Ma tectonic elements that may be useful for reconstructions. Rifted margins, because they are thinned and modified during extension are invariably overprinted by younger orogens, hence the importance of the isotopic data combined with geologic studies (e.g. for the Mojave province and pre-Appalachian rifted margin). Also, the map will attempt to palinspastically restore post- Neoproterozoic displacements using structural and geophysical data. Detrital zircon and monazite studies, including ?fingerprinting? of zoning patterns using monazite, locally provides information about provenance outside Laurentia. Dike patterns and compositions and paleomagnetism offer potential to identify piercing points that formed from mantle magmatic events whose scale transcends that of cratons. The integrated understanding of the geologic history of a craton ultimately will provide the best confidence in linking once-adjacent blocks.