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Application of aerial gamma-ray spectrometric and magnetic surveys in geologic mapping: a case study in southern Virginia and northern North Carolina

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Abstract

Aerial gamma-ray spectrometric and magnetic survey maps are valuable aids for geologic mapping where rocks are poorly exposed in south-central Virginia and northernmost North Carolina. Broad low areas on the potassium and thorium gamma-ray survey maps distinguish the Carolina, Spring Hope, and Roanoke Rapids terranes from more highly radiogenic areas of the Raleigh and Triplet terranes, reflecting differences in the compositions of residual soils. Granitic rocks are delineated most clearly by potassium highs and less clearly by thorium highs. Nearly all the thorium highs other than those related to granites are associated with amphibolite-facies rocks of the Raleigh and Triplet terranes. Contrasting thorium lows within these terranes help to distinguish the individual rock units. In the Carolina and Roanoke Rapids terranes, high-gradient magnetic patterns delineate stratified metavolcanic and metasedimentary units that are not discernible from the gamma-ray surveys. Circular magnetic highs coincide with gabbro plutons, and numerous magnetic lineaments correspond to Jurassic diabase dikes. Magnetically uniform, low-gradient areas coincide with less mafic plutons. A magnetic lineament (high) coincides with the Nutbush Creek fault zone, and other faults are distinguished as boundaries between zones of contrasting geophysical properties. The gamma-ray spectrometric and magnetic survey maps most effectively indicate geologic features in the region if they are employed collectively, and if they are interpreted in concert with simultaneous geologic field investigations.

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Additional Publication Details

Publication type:
Book chapter
Publication Subtype:
Book Chapter
Title:
Application of aerial gamma-ray spectrometric and magnetic surveys in geologic mapping: a case study in southern Virginia and northern North Carolina
Year Published:
1999
Language:
English
Publisher:
Carolina Geological Society
Contributing office(s):
Eastern Geology and Paleoclimate Science Center
Description:
8 p.
Larger Work Type:
Book
Larger Work Subtype:
Other Government Series
Larger Work Title:
Geology of the Fall Zone Region along to North Carolina-Virginia State Line: guidebook for the 1999 meeting of the Carolina Geological Society
First page:
29
Last page:
36
Number of Pages:
8
Country:
United States
State:
North Carolina;Virginia