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MAP A. AEROMAGNETIC MAP

MAP B. BOUGUER GRAVITY MAP

U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

GEOLOGIC INVESTIGATIONS SERIESI–2645–B

Pamphlet accompanies map

AEROMAGNETIC AND GRAVITY MAPS OF THE CENTRAL MARYSVALE VOLCANIC FIELD, SOUTHWESTERN UTAHBy

David L. Campbell, Thomas A. Steven, Charles G. Cunningham, and Peter D. Rowley

1999

Sample locality—Refer to table 1 for description by sample number

Edge of Quaternary unit

Fault—Dotted where inferred; bar and ball on downthrown side

Boundary of major caldera

Gravity station

Edge of Quaternary unit

Fault—Dotted where inferred; bar and ball on downthrown side

Boundary of major caldera

Reduction density 2.4 g/ccGeologic base map modified fromRowley and others (in press)Edited by Diane E. LaneDigital cartography by David L. Campbell andDiane E. LaneManuscript approved for publication April 14, 1999

Geologic base map modified fromRowley and others (in press)

Figure 2. Composite aeromagnetic map of southeastern Nevada and southwestern Utah, showing regional aeromagnetic signatures associated with the Pioche-Marysvale igneous belt. Data from several original surveys were merged to make this map, and where necessary were upward continued to 1,000 ft from original survey elevations, so are different from those on map A. Upward continuation emphasizes broad features at the expense of details. IPCC, Indian Peak Caldera Complex (Rowley and others, 1998); RBIC, Richfield Belt of Intrusions and Calderas (Steven and Morris, 1986); M, Marysvale; P, Pioche; CF, Cove Fort transverse zone; BR, Blue Ribbon transverse zone.

Figure 3. Reduced-to-pole (RTP) aeromagnetic map of southeastern Nevada and southwestern Utah. A mathematical process was used to make aeromagnetic highs and lows fall more directly over their sources. Nevertheless, the low persists north of the study area. Generally, on RTP maps, we expect highs to indicate plutons or thick sequences of volcanic rocks, and lows to reflect reversed-polarity extrusive rocks that have strong remanent magnetization. IPCC, Indian Peak Caldera Complex (Rowley and others, 1998); RBIC, Richfield Belt of Intrusions and Calderas (Steven and Morris, 1986); M, Marysvale; P, Pioche; CF, Cove Fort transverse zone; BR, Blue Ribbon transverse zone.

Figure 4. Topographic map of the central Marysvale volcanic field, Utah, showing selected geographic features. Display is a color-shaded relief image, illuminated from the southeast.

Figure 10. Key to aeromagnetic map of the central Marysvale volcanic field, Utah (map A). Shadows are from a computer-driven “sun” at 60o elevation illuminating the data from the south; such a display emphasizes problems that may have occurred in reducing and compositing the original data. Index letters are keyed to aeromagnetic anomalies that are discussed in the text; lower case, low; upper case, high. Geologic map overlay from figure 6.

Figure 11. Key to Bouguer gravity map of the central Marysvale volcanic field, Utah (map B). Index letters are keyed to gravity anomalies that are discussed in the text; lower case, low; upper case, high. Geologic map overlay from figure 6.

Any use of trade names in this publication is fordescriptive purposes only and does not implyendorsement by the U.S. Geological Survey

For sale by U.S. Geological Survey Information ServicesBox 25286, Federal Center, Denver, CO 80225

This map is also available as a PDF file at http://greenwood.cr.usgs.gov

EXPLANATION

Complete Bouguer gravity field, in milligals—Contour interval 1.25 milligals

EXPLANATION

Magnetic field intensity, in nanoteslas—Contour interval 25 nanoteslas

EXPLANATION

Magnetic field intensity, in nanoteslas—Contour interval 75 nanoteslas

EXPLANATION

Magnetic field intensity, in nanoteslas—Contour interval 75 nanoteslas

EXPLANATION

[See maps A and B for explanation of geologic map symbols]

Complete Bouguer gravity field, in milligals— Contour interval 5 milligals

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EXPLANATION

[See maps A and B for explanation of geologic map symbols]

Elevation, in meters—Contour interval 150 meters

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PAVANT RANGE

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EXPLANATION

[See maps A and B for explanation of geologic map symbols]

Magnetic field intensity, in nanoteslas—Contour interval 100 nanoteslas

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Printed on recycled paper