Improving the geological interpretation of magnetic and gravity satellite anomalies

Quantitative analysis of the geologic component of observed satellite magnetic and gravity fields requires accurate isolation of the geologic component of the observations, theoretically sound and viable inversion techniques, and integration of collateral, constraining geologic and geophysical data. A number of significant contributions were made which make quantitative analysis more accurate. These include procedures for: screening and processing orbital data for lithospheric signals based on signal repeatability and wavelength analysis; producing accurate gridded anomaly values at constant elevations from the orbital data by three-dimensional least squares collocation; increasing the stability of equivalent point source inversion and criteria for the selection of the optimum damping parameter; enhancing inversion techniques through an iterative procedure based on the superposition theorem of potential fields; and modeling efficiently regional-scale lithospheric sources of satellite magnetic anomalies. In addition, these techniques were utilized to investigate regional anomaly sources of North and South America and India and to provide constraints to continental reconstruction. Since the inception of this research study, eleven papers were presented with associated published abstracts, three theses were completed, four papers were published or accepted for publication, and an additional manuscript was submitted for publication

New standards for reducing gravity data: The North American gravity database

The North American gravity database as well as databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revising procedures for calculating gravity anomalies, taking into account our enhanced computational power, improved terrain databases and datums, and increased interest in more accurately defining long-wavelength anomaly components. Users of the databases may note minor differences between previous and revised database values as a result of these procedures. Generally, the differences do not impact the interpretation of local anomalies but do improve regional anomaly studies. The most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conventionally used geoid or sea level. Principal facts of gravity observations and anomalies based on both revised and previous procedures together with germane metadata will be available on an interactive Web-based data system as well as from national agencies and data centers. The use of the revised procedures is encouraged for gravity data reduction because of the widespread use of the global positioning system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with North American and national databases. Anomalies based on the revised standards should be preceded by the adjective “ellipsoidal” to differentiate anomalies calculated using heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid

Midcontinent Rift System in Northeastern Kansas

One of the major tectonic features of North America is the 1,100-Ma Midcontinent Rift System (MCR). This paleorift now lies largely buried under the thick Phanerozoic cover of the North American Craton; therefore, its trend, extent, and structural nature is detected only by geophysical means and the occasional deep drill hole. The rift was first reported in Kansas by Woollard (1943) as a result of his transcontinental gravity profile and was later to be known as the Midcontinent Gravity High. Subsequent aeromagnetic investigations showed a correlative magnetic anomaly and the feature was renamed the Midcontinent Geophysical Anomaly (MGA). The MGA is recognized as extending from Lake Superior to Kansas (Van Schmus and Hinze, 1985) and southerly into Oklahoma (Yarger, 1981). It is delineated by a positive central high and flanking minima on both gravity and magnetic maps. The rocks associated with the MGA crop out only in the Lake Superior Basin and comprise the classical association of bimodal volcanic, plutonic, and clastic sedimentary units of the "Keweenawan" suite (Morey and Green, 1982; Van Schmus and Hinze, 1985). It is primarily this association of a large volume of mafic and clastic rocks occurring along a long segmented belt which transects the regional pre-existing geologic pattern over most of its length that leads to the interpretation of the MGA and related segments as a rift (Hinze and Braile, 1988). Growing interest in the Midcontinent Rift System over the past several years, fostered in part by the potential of this Keweenawan rift as a frontier hydrocarbon province, has led to an increased number of deeply penetrating seismic-reflection profiles over the structure. Two studies by the Consortium for Continental Reflection Profiling (COCORP) across the MCR in Kansas and Michigan (Brown et al., 1982; Brown et al., 1983; Serpa et al., 1984), and more recently, seismic lines acquired in Lake Superior as part of the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) image a deep asymmetric central graben with prominent reflectors extending to depths of 30 km (18.6 mi) in places (Behrendt et al., 1988; Cannon et al., 1989). In addition, the seismic lines show that normal faulting played a prominent role in rift development before later compression changed them into high-angle reverse faults. In 1984-85, Texaco, U.S.A. drilled a hole in northern Kansas (Berendsen et al., 1988) to test the petroleum potential of the "clastic rock assemblage of the MCR. Texaco's interest was spurred in part by the results of the seismic-reflection investigation of the MCR conducted in northern Kansas by COCORP. These drill-hole data have added valuable constraints to understanding the structural style and tectonic evolution of the MCR in northeastern Kansas

Midcontinent Rift System in Northeastern Kansas

One of the major tectonic features of North America is the 1,100-Ma Midcontinent Rift System (MCR). This paleorift now lies largely buried under the thick Phanerozoic cover of the North American Craton; therefore, its trend, extent, and structural nature is detected only by geophysical means and the occasional deep drill hole. The rift was first reported in Kansas by Woollard (1943) as a result of his transcontinental gravity profile and was later to be known as the Midcontinent Gravity High. Subsequent aeromagnetic investigations showed a correlative magnetic anomaly and the feature was renamed the Midcontinent Geophysical Anomaly (MGA). The MGA is recognized as extending from Lake Superior to Kansas (Van Schmus and Hinze, 1985) and southerly into Oklahoma (Yarger, 1981). It is delineated by a positive central high and flanking minima on both gravity and magnetic maps. The rocks associated with the MGA crop out only in the Lake Superior Basin and comprise the classical association of bimodal volcanic, plutonic, and clastic sedimentary units of the "Keweenawan" suite (Morey and Green, 1982; Van Schmus and Hinze, 1985). It is primarily this association of a large volume of mafic and clastic rocks occurring along a long segmented belt which transects the regional pre-existing geologic pattern over most of its length that leads to the interpretation of the MGA and related segments as a rift (Hinze and Braile, 1988). Growing interest in the Midcontinent Rift System over the past several years, fostered in part by the potential of this Keweenawan rift as a frontier hydrocarbon province, has led to an increased number of deeply penetrating seismic-reflection profiles over the structure. Two studies by the Consortium for Continental Reflection Profiling (COCORP) across the MCR in Kansas and Michigan (Brown et al., 1982; Brown et al., 1983; Serpa et al., 1984), and more recently, seismic lines acquired in Lake Superior as part of the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) image a deep asymmetric central graben with prominent reflectors extending to depths of 30 km (18.6 mi) in places (Behrendt et al., 1988; Cannon et al., 1989). In addition, the seismic lines show that normal faulting played a prominent role in rift development before later compression changed them into high-angle reverse faults. In 1984-85, Texaco, U.S.A. drilled a hole in northern Kansas (Berendsen et al., 1988) to test the petroleum potential of the "clastic rock assemblage of the MCR. Texaco's interest was spurred in part by the results of the seismic-reflection investigation of the MCR conducted in northern Kansas by COCORP. These drill-hole data have added valuable constraints to understanding the structural style and tectonic evolution of the MCR in northeastern Kansas

Gravity and magnetic exploration: principles, practices, and applications

This combination of textbook and reference manual provides a comprehensive account of gravity and magnetic methods for exploring the subsurface using surface, marine, airborne, and satellite measurements. It describes key current topics and techniques, physical properties of rocks and other earth materials, and digital data analysis methods used to process and interpret anomalies for subsurface information. Each chapter starts with an overview and concludes by listing key concepts to consolidate new learning. An accompanying website presents problem sets and interactive computer-based exercises, providing hands-on experience of processing, modeling and interpreting data. A comprehensive online suite of full-color case histories illustrates the practical utility of modern gravity and magnetic surveys. This is an ideal text for advanced undergraduate and graduate courses, and a reference for research academics and professional geophysicists. It is a valuable resource for all those interested in petroleum, engineering, mineral, environmental, geological and archeological exploration of the lithosphere.This combined textbook and reference manual introduces key topics and techniques in gravity and magnetic exploration, with practical online resources

Gravity and aeromagnetic anomaly maps of the southern peninsula of Michigan /

2 folded maps in pocket.Updates and replaces Hinze's previous report published in 1963.Includes bibliography (p.13-14).Mode of access: Internet.Maps removed from pocket of MHC copy and cataloged separately