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Title:The Midcontinent exposed: Precambrian basement topography, and fault-and-fold zones, within the cratonic platform of the United States
Author(s):Domrois, Stefanie
Advisor(s):Marshak, Stephen
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Precambrian topography
fault-and-fold zones
cratonic platform of the United States
Abstract:The Midcontinent region of the United States is part of the cratonic platform of the North American craton. This region is underlain by Precambrian basement formed dominantly during Proterozoic accretionary orogenies. It was modified by Proterozoic anorogenic felsic magmatism and was cracked by several episodes of rifting. Subsequently, when North America was part of a supercontinent, the region underwent extensive Late Precambrian erosion and exhumation. Marine transgressions during the Phanerozoic buried the region with sequences Phanerozoic sedimentary strata. The continent-wide contact between Precambrian crystalline rock and the overlying cover of Phanerozoic strata is known as the "Great Unconformity." Though the cratonic platform has been relatively stable, tectonically, for over a billion years, it has been affected by epeirogenic movements that produced regional-scale basins, domes and arches. Also, faults within the region have been reactivated, displacing crustal blocks and warping overlying strata into monoclinal folds—these faults may be relicts of Proterozoic rifting. How can this Phanerozoic tectonism be represented visually in a way that can provide a basis for interpreting new lithospheric features being revealed by EarthScope's USArray seismic network? In the Appalachian and Cordilleran orogens, ground-surface topography provides insight into the character and distribution of tectonic activity, because topography is structurally controlled. This is not the case in the Midcontinent, a region of broad plains where surface topography does not reflect the structure beneath. Fortunately, the Great Unconformity makes an excellent marker horizon for mapping intracratonic structures. In order to create an intuitive visual image of the basement topography and of fault-and-fold distribution in the cratonic platform of the United States, I constructed two maps of the region using ArcGIS software. My study area extends from the Wasatch front on the west to the Appalachian front on the east, and from the Ouachita front and Gulf coastal plain on the south to the southern edge of the Canadian Shield on the north. The first map portrays the top of the Precambrian basement surface in shaded relief, and the second map portrays the distribution of major faults and folds within the region. Production of the maps required compiling and digitizing a variety of data, which was imported into ArcGIS and processed to produce a 3-D surface. The shaded-relief map provides new insight into the crustal architecture of the cratonic platform, by visually emphasizing that the region consists of distinct provinces: the Midcontinent Sector (a broad area of low relief, locally broken by steep faults); the Rocky Mountain Sector (with structural relief of up to 10 km, and relatively short distances between uplifts), the Colorado Plateau Sector (a moderate-relief area containing fault-bounded crustal blocks), and the Bordering Basins Sector (deep rift basins, linked at crustal bridges, and locally amplified by flexural loading). Overlaying the fault map and a map of earthquake epicenters over the shaded relief map emphasizes that seismicity is concentrated in the bordering basins, particularly where steep gradients in basement topography coincide with major faults.
Issue Date:2013-08-22
Rights Information:Copyright 2013 Stefanie Domrois
Date Available in IDEALS:2013-08-22
Date Deposited:2013-08

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