The North American continental crust was created by accretion of crustal provinces during the Archean and Proterozoic (everything older than 800 million years old). Work done by Bennett and DePaulo (1987) determined a crustal province, Mojavia, that was different from any of the provinces in North America. Geochemical work on the element Neodymium found in the Precambrian metamorphic rocks were used to determine the formation age of the Mojavia crust. Workers found that the Mojavia crust (2.2-2.6 billion years old) was much older than the neighboring crustal provinces, Yavapai and Mazatzal (1.7-1.8 billion years old). Obviously Mojavia came from a different continet, but what continent?
Also, the Precambrian and Paleozoic rocks (1.4 billion years old to 500 years old) that were deposited in ancient basins were showing evidence of a different continent. These formations of sedimentary rocks also contained rift sediments (dikes, basalts, landslide deposits). North America (or Laurentia as it is termed in the Precambrian) was probably attached to another continent in the Precambrian, and the two rifted apart in the Paleozoic! Furthermore, mineral and element analysis of the sedimentary rocks could not find the source for these sediments--the source must be from another continent!
Well, what was this mysterious continent? Other work on Precambrian geology have determined that all the continents were attached in one supercontinent, Rodinia, during the Precambrian. Several models for the configuration of Rodinia theorize on what continent was attached to Laurentia. The SWEAT (southwestern US and east Antarctica) model proposed by Moores (1991) suggests that Antarctica was attached to western Laurentia (pictured below, from Moores, 1991). Then the source for Mojavia would be the Miller range in the Transantarctic moutains in Antarctica. The sedimentary source for the Paleozoic sedimentary basins would be Antarctica also.
Another model (pictured below, from Karlstrom et al., 2001) proposed for Rodinia is the AUSWUS model (Australia and western United States). This was proposed by Karlstrom et al., (1999) and would suggest that Australia is the source for Mojavia and for the Paleozoic sediments.
Other models have also been suggested for what was attached to western Laurentia. Various workers believe Siberia, south China, or Tasmania was attached to western Laurentia. Which model is correct? Unfortunately there is not enough reliable data to determine the best model. Each model proposes new tests and studies to help determine which model fits. More data needs to be collected from Antactica, Australia, Siberia, south China, and Tasmania to match with the data from Laurentia.
interested in learning more? start on Mojavia, and then work your way through the site!