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Bouguer gravity anomaly and isostatic residual gravity maps of the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada

Miscellaneous Field Studies Map 1877-D

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Abstract

These gravity maps are part of a folio of maps of the Tonopah 1 degree by 2 degrees quadrangle, Nevada, prepared under the Conterminous United States Mineral Assessment Program. Each product of the folio is designated by a different letter symbol, starting with A, in the MF-1877 folio. The quadrangle encompasses an area of about 19,500 km2  in the west central part of Nevada.

The set of gravity data consists of 4,185 observation points. Plouff (1990b) described data sources, base stations, reduction and compilation methods, and the accuracy of the data. Principal facts for the gravity data are listed in tables and are in digital format on a magnetic diskette. That report incorporates and partly supersedes principal facts published by Healey and others (1980), Saltus and others (1981), and Boland others (1983).

A 4-minute band of gravity data obtained from Plouff (1982) and Saltus (1988b) for the area surrounding the Tonopah quadrangle provided sufficient data coverage to contour Bouguer gravity anomalies to the edges of the Tonopah quadrangle (sheet 1). This map supersedes the gravity map published by Healey and others (1981). Values of observed gravity were tied to the International Gravity Standardization Network of 1971 (Morelli, 1974). Theoretical gravity at sea level was determined by using the Geodetic Reference System, 1967 formula (International Association of Geodesy, 1971, p. 60). The standard free-air formula (Swick, 1942, p.65) and a standard reduction density of 2.67 g/cm3 were used. Corrections for the Earth's curvature and terrain were calculated to a standard distance of 166.7 km. These parameters were selected so that the Bouguer gravity anomaly map merges with previously published gravity maps (Plouff, 1987; and Saltus, 1988a).

A residual isostatic gravity map (sheet 2) was prepared so that the regional effect of isostatic compensation present on the Bouguer gravity anomaly map (sheet 1) would be minimized. Isostatic corrections based on the Airy-Heiskanen system (Heiskanen and Vening Meinesz, 1958, p. 135-137) were estimated by using 3-minute topographic digitization and applying the method of Jachens and Roberts (1981). Parameters selected for the isostatic model were 25 km for the normal crustal thickness at sea level, 2.67 g/cm3 for the density of the crust, and 0.4 g/cm3 for the contrast in density between the crust and the upper mantle. These parameters were selected so that the isostatic residual gravity map would be consistent with isostatic residual gravity maps of the adjacent Walker Lake quadrangle (Plouff, 1987) and the state of Nevada (Saltus, 1988c).

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Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Bouguer gravity anomaly and isostatic residual gravity maps of the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada
Series title:
Miscellaneous Field Studies Map
Series number:
1877
Chapter:
D
Year Published:
1992
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Description:
2 Plates: 35.05 x 43.72 inches and 29.19 x 23.35 inches
Country:
United States
State:
Nevada
Scale:
250000
Online Only (Y/N):
N
Additional Online Files (Y/N):
N