The Moho of North America: A brief review focused on recent studies

Recent national programs in Canada (Lithoprobe) and the U.S. (EarthScope) are providing vast quantities of data and many new scientific insights concerning crustal and lithospheric mantle structure and evolution. More modest but significant results are also being produced in and about Mexico. This paper primarily focuses on results published since 2005 and presents an updated Moho map of North America. This overview of crustal structure does reveal a number of interesting observations. For example, two buried distinct crustal blocks have been discovered in the past 20 years. One was caught in a Precambrian suture zone in Canada, and the other is buried under the Gulf Coast region and is still of unknown origin. The Precambrian assembly of the continent has been documented by the mapping of numerous suture zones, and shallow portions of subducted slabs have been preserved in several cases. Not surprisingly, the internal structure of these suture zones is complex and highly variable. Isostatic adjustment has been shown to be a complex process involving the lithospheric mantle not just crustal structure variations. Specifically, the correlation of crustal thickness with elevation is only approximate at best. Several crustal blocks that have been stable over very long periods of time possess unusually thick crust whose lower portion is usually fast (Vp > 7.0 km/s). Rifting has been shown to affect the crust in a variety of ways ranging from the massive magmatic modification that produced the Mid-continent rift system to the broad region of extension in the Basin and Range province. Crustal structure along the active modern western margin of North America is highly complex as would be expected as a result of transitions between subduction and transform faulting and variations in volcanism and intraplate magmatism. We clearly still have a lot to learn about the structure and evolution of this continent.