GEOLOGICAL ARCHITECTURE OF NORTH AMERICA

The new Geologic Map of North America reveals the grand architecture of the continent enhanced by the surrounding seafloor geology that displays the plate tectonic framework. The continent's Precambrian foundation,dimpled by younger basins,is well exposed in the Canadian Shield, on Greenland and in uplifts piercing the Phanerozoic cover of western and central U.S.A. It includes an aggregate of Archean microcontinents assembled by 2.5 Ga. The Superior microcontinent, for example, formed within 30 Ma by southward accretion of belts of greenstone, metasediments, gneiss and granitoids to collide with the Minnesota foreland by 2.68 Ga. In the Early Proterozoic, the microcontinents were welded by collisional orogens to form the craton, Laurentia. The sinuous 2.0 - 1.8 Ga orogens, which extend from SW U.S.A. to Greenland, reflect the indentation of the orogens by colliding microcontinents. From 1.19 to 0.99 Ga a collision between Laurentia and another continent to the southeast formed the Grenville orogen. This event was coeval with the development of the Midcontinent Rift and related mafic volcanism in the Lake Superior region. For the first time a plethora of dike swarms is shown.

The continental core is ringed by mountainous Phanerozoic orogens: Appalachian-Ouachita, Cordilleran, Innuitian and in Greenland the Caledonian, all of which feature continent-directed fold-thrust belts within their passive margin and clastic-wedge assemblages. Accreted terranes, arc and back-arc volcanism, granitoid batholiths and long transcurrent faults lie farther outboard. The central plains are underlain by Paleozoic cratonic cover and Phanerozoic clastic wedges shed from the orogens.

The passive Atlantic margin is recognized by its extensive continental shelf and associated overlapping Cenozoic and Cretaceous strata of the Coastal Plain. Salt laden equivalents in the Gulf of Mexico contain numerous growth faults and salt diapirs. The young rifted margins around Greenland, however, are sites of Tertiary volcanism. By contrast, the active Pacific margin lacks continental shelves but instead comprises three convergent-subdduction zones with associated chains of active volcanoes on land - Aleutian, Cascades and Middle America - separated by the Queen Charlotte and San Andreas dextral transform faults.