THE MOHO OF NORTH AMERICA: A REVIEW

New insights about the crustal structure of North America have been obtained by combining earlier results with those of programs such as Lithoprobe in Canada and EarthScope in the U.S. The mapping of numerous suture zones and shallow portions of subducted slabs that have been preserved document the assembly of the continent. The internal structure of these suture zones has been shown to be as complex as would be expected. Cratonal crustal blocks generally have unusually thick crust whose lower portion is usually fast (Vp>7.0 km/s), which appears to have contributed to their stability. The crust has been affected by rifting in several ways ranging from the massive magmatic modification that accompanied the formation of the Mid-continent rift system to the broad region of extension in the Basin and Range province. The modern western margin of North America is associated with highly complex crustal structure as would be expected as a result of subduction, transform faulting, and magmatism. Moho depths often do not correlate well elevation indicating that isostatic adjustment is a complex process involving the lithospheric mantle not just crustal structure variations. However in most cases Precambrian and Paleozoic orogenic belts generally still have crustal features that date back to their formation. A Moho map has been constructed to show these relationships.