Geophysical aspects of the craton: U.S.
The midcontinent province between the Appalachian-Ouachita orogen and the Rocky Mountains is that portion of the United States craton which has been relatively stable tectonically for roughly the past billion years. Diastrophism has been restricted largely to broad, slow, vertical movements and highly attenuated, passive response to orogenic activity, which has occurred at plate margins around the North American craton. Thus, except for very localized structures associated with rare anoro-genic intrusions and meteorite impacts, the Phanerozoic sedimentary rocks are only disturbed by minor faulting and gentle warping. As a result, regional geophysical investigations of the midcontinent have primarily focused on the study of the more laterally variable physical properties of the crystalline rocks of the basement and deeper portions of the crust. However, a great number of detailed geophysical investigations have been conducted over cratonic basins in the search for structural and stratigraphic variations within the Phanerozoic sedimentary rocks. With a few notable exceptions, these surveys, largely seismic reflection and gravity, have been conducted to locate hydrocarbon accumulations and consequently are represented by proprietary data. Thus, although geophysical studies, particularly those employing modern, common-depth-point, seismic-reflection techniques, have great utility in mapping the minor structural and stratigraphic variations that occur within the Phanerozoic sedimentary rocks of the midcontinent, our principal source of information regarding the subsurface nature of these rocks is drillhole data. In contrast, our knowledge of the basement igneous and metamorphic rocks of the craton is based on regional geophysical studies working in concert with the irregularly distributed basement
Figures & Tables
Sedimentary Cover—North American Craton
The “sedimentary cover” refers to the stratified rocks of youngest Proterozoic and Phanerozoic age that rest upon the largely crystalline basement rocks of the continental interior. The early chapters of the volume present data and interpretations of the geophysics of the craton and summarize, with sequential maps, the tectonic evolution of the craton. The main body of the text and accompanying plates and figures present the stratigraphy, structural history, and economic geology of specific sedimentary basins (e.g., Appalachian basin) and regions (e.g., Rocky Mountains). The volume concludes with a summary chapter in which the currently popular theories of cratonal tectonics are discussed and the unresolved questions are identified.