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.
Suggested Citation
Horton, J., Daniels, D.L., 1999, Application of aerial gamma-ray spectrometric and magnetic surveys in geologic mapping: a case study in southern Virginia and northern North Carolina, chap. of Geology of the Fall Zone Region along to North Carolina-Virginia State Line: guidebook for the 1999 meeting of the Carolina Geological Society, p. 29-36.
Study Area
| 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 |
| Country | United States |
| State | North Carolina;Virginia |