LITHOSPHERIC BLOCKS AND RIFTING IN CENTRAL NORTH AMERICA: STRUCTURE, TECTONICS, AND GLOBAL ANALOGS

Central North America consists of a complex collage of tectonic blocks whose assembly began at ~2GA. This process involved suturing of blocks such as the Wyoming craton and the Medicine Hat block to the ancient terranes to the north. By the end of the Precambrian, the North American craton (Laurentia) had formed. However, rifting long its margins began in the Early Paleozoic, and at least one block along Laurentia's southern margin rifted away and is interpreted to be presently located in Argentina. This Early Paleozoic rifting did create a sinuous margin extending from the southeastern U.S. across Texas into northern Mexico that is clearly defined by a linear gravity high and a few integrated deep seismic/gravity profiles across this margin. The bends in this margin are associated with failed rift zones (aulacogens) that extend into the interior of Laurentia and form triple junctions. By the end of the Paleozoic, continental assembly via the Appalachian-Ouachita orogeny added new terrains to the eastern and southern margins of Laurentia and the assembly of the supercontinent Pangea was complete. This orogenic activity produced a variety of deformation in the triple junctions. The tectonic inversion in the Southern Oklahoma Aulacogen is a globally significant example of this type of tectonism. Then, Mesozoic rifting opened the Atlantic and Gulf of Mexico with large crustal blocks such as Yucatan being detached. Within the craton, several major episodes of rifting occurred within the interior and around the margins of Laurentia. The ~1.1 Ga Mid-Continent rift system that is dramatically expressed in gravity and magnetic maps represents a failed attempt to break Laurentia apart. This rift has two arms that managed to cut across the older NE-trending terrain boundaries, and, to some extent, wrap around a crustal block similar to the Tanzanian craton, which is bounded by two the arms of the East African rift. Other distinct crustal blocks in Laurentia include the Wyoming craton, the Colorado Plateau, and Medicine Hat block in western Laurentia. Other tectonic blocks surely exist to the east but are covered by Phanerozoic sediments and heavily intruded by Proterozoic magmatism.