Reconnaissance geologic mapping of a portion of the rain‐forest‐covered Guiana Shield, Northwestern Brazil, using SIR-B and digital aeromagnetic data

Geophysics ◽  
1994 ◽  
Vol 59 (5) ◽  
pp. 733-743 ◽  
Author(s):  
Fernando Pellon de Miranda ◽  
Anne E. McCafferty ◽  
James V. Taranik
Keyword(s):  
Integrated Analysis ◽  
Guiana Shield ◽  
Aeromagnetic Data ◽  
Geologic Mapping ◽  
Worst Case ◽  
Geomorphic Features ◽  
Geologic Map ◽  
Digital Manipulation ◽  
Spaceborne Radar ◽  
Shaded Relief

This paper documents the result of an integrated analysis of spaceborne radar (SIR-B) and digital aeromagnetic data carried out in the heavily forested Guiana Shield. The objective of the research is to interpret the geophysical data base to its limit to produce a reconnaissance geologic map as an aid to ground work planning in a worst‐case setting. Linear geomorphic features were identified based on the interpretation of the SIR-B image. Digital manipulation of aeromagnetic data allowed the development of a color‐shaded relief map of reduced‐to‐pole magnetic anomalies, a terrace‐magnetization map, and a map showing the location of maximum values of the horizontal component of the pseudogravity gradient (magnetization boundary lines). The resultant end product was a reconnaissance geologic map where broad terrane categories were delineated and geologic faults with both topographic and magnetic expression were defined. The availability of global spaceborne radar coverage in the 1990s and the large number of existing digital aeromagnetic surveys in northwestern Brazil indicate that this approach can be potentially useful for reconnaissance geologic mapping elsewhere in the Guiana Shield.

THE NATIONAL GEOLOGIC MAP DATABASE -- A RESOURCE FOR GEOLOGIC MAPPING

2016 ◽  
Author(s):  
David R. Soller ◽  
◽  
Nancy R. Stamm ◽  
Robert C. Wardwell ◽  
Christopher P. Garrity
Keyword(s):  
Geologic Mapping ◽  
Geologic Map

Geologic Map of the Park Reservoir Quadrangle, Sheridan County, Wyoming

2020 ◽  
Vol 57 (4) ◽  
pp. 375-388
Author(s):  
Ryan Bessen ◽  
Jennifer Gifford ◽  
Zack Ledbetter ◽  
Sean McGuire ◽  
Kyle True ◽  
...  
Keyword(s):  
Structural Features ◽  
Geologic Mapping ◽  
Rock Types ◽  
Basement Rocks ◽  
Geologic Maps ◽  
Geologic Map ◽  
Tear Fault ◽  
Mapping Techniques ◽  
Wyoming Province ◽  
Bighorn Mountains

This project involved the construction of a detailed geologic map of the Park Reservoir, Wyoming 7.5-Minute Quadrangle (Scale 1:24,000). The Quadrangle occurs entirely in the Bighorn National Forest, which is a popular recreation site for thousands of people each year. This research advances the scientific understanding of the geology of the Bighorn Mountains and the Archean geology of the Wyoming Province. Traditional geologic mapping techniques were used in concert with isotopic age determinations. Our goal was to further subdivide the various phases of the 2.8–3.0 Ga Archean rocks based on their rock types, age, and structural features. This research supports the broader efforts of the Wyoming State Geological Survey to complete 1:24,000 scale geologic maps of the state. The northern part of the Bighorn Mountains is composed of the Bighorn batholith, a composite complex of intrusive bodies that were emplaced between 2.96–2.87 Ga. Our mapping of the Park Reservoir Quadrangle has revealed the presence of five different Archean quartzofeldspathic units, two sets of amphibolite and diabase dikes, a small occurrence of the Cambrian Flathead Sandstone, two Quaternary tills, and Quaternary alluvium. The Archean rock units range in age from ca. 2.96–2.75 Ga, the oldest of which are the most ancient rocks yet reported in the Bighorn batholith. All the Archean rocks have subtle but apparent planar fabric elements, which are variable in orientation and are interpreted to represent magmatic flow during emplacement. The Granite Ridge tear fault, which is the northern boundary of the Piney Creek thrust block, is mapped into the Archean core as a mylonite zone. This relationship indicates that the bounding faults of the Piney Creek thrust block were controlled by weak zones within the Precambrian basement rocks.

scholarly journals An experimental aeromagnetic survey in the Volturno valley area (South-Eastern Latium)

1998 ◽  
Vol 41 (3) ◽  
Author(s):  
M. Chiappini ◽  
F. Ferraccioli ◽  
V. Bosi ◽  
E. Bozzo ◽  
G. Caneva ◽  
...  
Keyword(s):  
Structural Features ◽  
Tectonic Activity ◽  
Aeromagnetic Survey ◽  
Magnetic Image ◽  
Geologic Map ◽  
Anomaly Map ◽  
Area North ◽  
Valley Area ◽  
Shaded Relief ◽  
Extensional Setting

A helicopter-borne experimental aeromagnetic survey, covering an area of 200 km2, was performed in the Volturno valley area north of the Roccamonfina volcano and south of Venafro in November 1994. Although severe logistical, instrumental and meteorological conditions significantly reduced the planned coverage, the processed magnetic image still shows a remarkable improvement in the description of the geological and structural features of the area in comparison with previous regional aeromagnetic data. A multi-directional shaded relief anomaly map displays two moderately positive NW magnetic bands associated with lavas, pyroclastics and dykes of the Roccamonfina volcanic district together with N-S, NNE-SSW and NE-SW lineations. A comparative magnetic-geologic map allows correlation with known Pleistocene faults and reveals the existence, especially in the area between Sesto Campano and Presenzano, of a larger presence of high susceptibility dykes than seen in the outcrop, which is dominated by non-magnetic carbonatic rocks. We interpret the curvilinear and intricate pattern of magnetic lineaments as suggestive of an extensional setting along the main NW structures with previous strike slip components and of tectonic activity along a N-S fabric; the latter has no superficial evidence and has also been used for magma upwelling. Overall, this local scale investigation shows both the utility and the need for further efforts in high resolution aeromagnetics in Italy both for geological and environmental purposes similar to those successfully carried out in many other countries throughout the world.

Practical considerations in the use of edge detectors for geologic mapping using magnetic data

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. J1-J8 ◽  
Author(s):  
Mark Pilkington ◽  
Victoria Tschirhart
Keyword(s):  
Magnetic Field ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Recent Effort ◽  
Aeromagnetic Data ◽  
Geologic Mapping ◽  
Magnetization Direction ◽  
Model Studies ◽  
Edge Detectors

Locating the edges of magnetized sources provides a fundamental tool in the geologic interpretation of magnetic field data. Much recent effort has been expended on developing improvements to existing edge-detection methods, resulting in purported increases in accuracy and continuity along edges, reduction of noise effects, and limiting the influences of variable depth to source, magnetization direction, and source dip. These endeavors are valuable and provide interpreters with a wider range of tools to carry out geologic interpretations of aeromagnetic data. Nevertheless, survey parameters such as flight height and line spacing impose limits on the quality of edge locations that can be achieved. Using model studies, we quantify the effects that source size, depth, and interference between sources have on calculated edge locations. Based on the known behavior of established edge detectors, we found that many of the newer approaches offer limited advantages over older methods. Consequently, we studied an example of field mapping of geologic contacts in the Canadian Shield, supported by aeromagnetic data, using calculation of a standard edge detector: the horizontal gradient magnitude of the total magnetic field or TF-hgm. Calculated edge locations estimated from this method appear sufficiently accurate and continuous to provide a solid basis on which the mapping campaign was based and executed successfully.

scholarly journals Supplemental material: Guides to understanding the aeromagnetic expression of faults in sedimentary basins: Lessons learned from the central Rio Grande rift, New Mexico

2007 ◽  
Author(s):  
V.J.S. Grauch ◽  
Mark R. Hudson
Keyword(s):  
Rio Grande ◽  
Sedimentary Basins ◽  
Lessons Learned ◽  
Rio Grande Rift ◽  
Aeromagnetic Data ◽  
File Size ◽  
Aeromagnetic Survey ◽  
Map Projection ◽  
Map Scale ◽  
Shaded Relief

Geosphere, December 2007, v. 3, p. 596-623, doi: 10.1130/GES00128.1. Plate 1 - Color shaded-relief image of reduced-to-pole (RTP) aeromagnetic data for the central Rio Grande rift, compiled from Sweeney et al. (2002) and Bankey et al. (2006). The colors primarily reflect the broad variations in the data, whereas the illumination (from the west) emphasizes detailed variations, especially linear features associated with faults. Selected geographic, geologic, and interpretative features are labeled. Map projection is NAD27, UTM zone 13, in units of meters. Inset shows locations and names of aeromagnetic survey areas. Map scale 1:250,000. File size is 9.2 MB.

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