Sim3483.pdf - Geologic Map of the South Boston 30’ × 60’ Quadrangle ...

Geologic Map of the South Boston 30' ? 60' Quadrangle, Virginia and North Carolina

By J. Wright Horton, Jr., John D. Peper, William C. Burton, Robert E. Weems, and Paul E. Sacks

Pamphlet to accompany

Scientific Investigations Map 3483

Supersedes USGS Open-File Report 93?244

U.S. Department of the Interior U.S. Geological Survey

U.S. Geological Survey, Reston, Virginia: 2022 Supersedes USGS Open-File Report 93?244

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Suggested citation: Horton, J.W., Jr., Peper, J.D., Burton, W.C., Weems, R.E., and Sacks, P.E., 2022, Geologic map of the South Boston 30' ? 60' quadrangle, Virginia and North Carolina: U.S. Geological Survey Scientific Investigations Map 3483, 1 sheet, scale 1:100,000, 46-p. pamphlet, . [Supersedes USGS Open-File Report 93?244.] Associated data for this publication: Horton, J.W., Jr., Peper, J.D., Burton, W.C., Weems, R.E., Sacks, P.E., and Crider, E.A., Jr., 2022, Database for the geologic map of the South Boston 30 ? 60 quadrangle, Virginia and North Carolina: U.S. Geological Survey data release, .

ISSN 2329-132X (online)

Cover. The layered gneiss of South Boston (Zclg; see Description of Map Units) is an informally named unit within the Neoproterozoic Country Line complex on the western flank of the Carolina terrane. This exposure at the South Boston quarry, Halifax, Virginia (Salem Stone Corporation), shows interlayered hornblende gneiss (right side) and less abundant felsic gneiss (left side) with a hammer (30 centimeters in length) for scale. Photograph by J. Wright Horton, Jr., U.S. Geological Survey.

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Acknowledgments

This geologic map and report benefitted from reviews by geologists Mark Carter and Stephen Schindler (U.S. Geological Survey) and comments by Matt Heller (Virginia Division of Geology and Mineral Resources), Philip Bradley (North Carolina Geological Survey), and David Blake (University of North Carolina at Wilmington). Blake also provided helpful insights and information including geologic maps of nearby areas to the south in North Carolina. This geologic map also benefitted from discussions and field trips over the years with John Aleinikoff, Rick Berquist, David Blake, Philip Bradley, Robert Butler, Mark Carter, Robert Druhan, Stewart Farrar, James Hibbard, Michael Kunk, John Marr, Arthur Nelson, Brent Owens, Edward Stoddard, and others. We thank Allen Crider for digital cartography and geodatabase work, Linda Masonic for digital cartographic production, and Zachary Younger for editorial review that significantly improved the map and report.

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Contents

Abstract............................................................................................................................................................1 Introduction.....................................................................................................................................................1 Geologic Setting and Previous Work...........................................................................................................3 Raleigh Terrane...............................................................................................................................................4

Layered and Stratified Rocks...............................................................................................................4 Intrusive Rocks.......................................................................................................................................5 Carolina Slate Belt of Carolina Terrane.......................................................................................................5 Layered and Stratified Rocks...............................................................................................................5 Intrusive Rocks.......................................................................................................................................6 Western Flank of Carolina Terrane..............................................................................................................7 Layered and Stratified Rocks...............................................................................................................7 Intrusive Rocks.......................................................................................................................................7 Milton Terrane.................................................................................................................................................7 Layered and Stratified Rocks...............................................................................................................7 Intrusive Rocks.......................................................................................................................................8 Late Paleozoic Intrusive Rocks....................................................................................................................8 Mesozoic Rift-Related Rocks........................................................................................................................8 Scottsburg, Randolph, and Roanoke Creek Basins.........................................................................8 Dikes........................................................................................................................................................9 Unconsolidated Surficial Deposits..............................................................................................................9 Regolith...........................................................................................................................................................10 Structure........................................................................................................................................................11 Structure of the Raleigh Terrane.......................................................................................................11 Structure of the Carolina Terrane.....................................................................................................11 Structure of the Milton Terrane.........................................................................................................12 Lake Gordon and Nutbush Creek Mylonite Zones.........................................................................12 Hyco and Clover Shear Zones...........................................................................................................12 Mesozoic Faults...................................................................................................................................13 Metamorphism..............................................................................................................................................13 Tectonics........................................................................................................................................................14 Mineral Resources.......................................................................................................................................14 Water Resources..........................................................................................................................................15 Description of Map Units.............................................................................................................................16 Regolith..................................................................................................................................................16 Unconsolidated Surficial Deposits...................................................................................................16 Mesozoic Rift-Related Rocks.............................................................................................................17

Dikes.............................................................................................................................................17 Scottsburg, Randolph, and Roanoke Creek Basins..............................................................18 Miscellaneous Veins...........................................................................................................................18 Miscellaneous Fault Rocks................................................................................................................19 Late Paleozoic Intrusive Rocks.........................................................................................................19

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Raleigh Terrane....................................................................................................................................21 Intrusive Rocks............................................................................................................................21 Layered and Stratified Rocks....................................................................................................22

Carolina Slate Belt of Carolina Terrane............................................................................................24 Intrusive Rocks............................................................................................................................24 Layered and Stratified Rocks....................................................................................................27

Western Flank of Carolina Terrane...................................................................................................32 Intrusive Rocks............................................................................................................................32 Layered and Stratified Rocks....................................................................................................32

Milton Terrane......................................................................................................................................33 Intrusive Rocks............................................................................................................................33 Layered and Stratified Rocks....................................................................................................34

References Cited..........................................................................................................................................36

Figure

1. Index map of the South Boston 30' ? 60' quadrangle, Virginia and North Carolina, showing sources of geologic data as well as areas of mapping and compilation responsibility..................................................................................................................................2

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Conversion Factors

International System of Units to U.S. customary units

Multiply

millimeter (mm) centimeter (cm) meter (m) meter (m) kilometer (km)

square kilometer (km2) square kilometer (km2)

By Length 0.03937 0.3937 3.281 1.094 0.6214 Area 247.1 0.3861

To obtain

inch (in.) inch (in.) foot (ft) yard (yd) mile (mi)

acre square mile (mi2)

Abbreviations

An Ar CAMP IUGS LA-ICP-MS Ma Nd Pb Rb Sr TIMS U

anorthite argon central Atlantic magmatic province International Union of Geological Sciences laser ablation inductively coupled plasma mass spectrometry mega-annum (million years ago) neodymium lead rubidium strontium thermal ionization mass spectrometry uranium

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