Geology of the Harpers Ferry Quadrangle, Virginia, Maryland, and West Virginia Prepared in cooperation with the Maryland Geological Survey, the National Park Service, and the 1oudoun County Department of Environmental Resources Cover: Looking vvcsl at Harpers Ferry. West Virginia, from the Loudoun Heights trail on Blue Ridge in Virginia. Photograph taken March 1989 by Scott Southvvorth. Geology of the Harpers Ferry Quadrangle, Virginia, Maryland, and West Virginia By Scott Southworth and David K. Brezinski U.S. GEOLOGICAL SURVEY BULLETIN 2123 Prepared in cooperation with the Maryland Geological Survey, the National Park Service, and the Loudoun County Department of Environmental Resources Structure and stratigraphy of the Middle Proterozoic through Early Cambrian rocks of the complexly deformed Late Paleozoic Blue Ridge-South Mountain anticlinorium UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1996 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY GORDON P. EATON, Director For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center, Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Published in the Eastern Region, Reston, Va. Manuscript approved for publication January 9, 1995. Library of Congress Cataloging in Publication Data Southworth, Scott, 1957- Geology of the Harpers Ferry Quadrangle, Virginia, Maryland, and West Virginia/ by Scott Southworth and David K. Brezinski. p. cm. (U.S. Geological Survey bulletin : 2123) "Prepared in cooperation with the Maryland Geological Survey, the National Park Service, and the Loudoun County Department of Environmental Resources." "Structure and stratigraphy of the Middle Proterozoic through Early Cambrian rocks of the complexly deformed Late Paleozoic Blue Ridge-South Mountain anticlinorium." Includes bibliographical references (p. - ). Supt. of Docs, no.: 119.3:2123 1. Geology West Virginia Harper's Ferry Region. 2. Geology, Stratigraphic. I. Brezinski, David K. II. Maryland Geological Survey. III. Loudoun County (Va.). Dept of Environmental Resources. IV Title. V Series. QE75.B9no. 2123 [QE178] 557.3 s dc 2095-9727 [557.54'99] CIP CONTENTS Abstract........................................................................................................................... 1 Introduction and Geologic Setting.................................................................................. 1 Middle Proterozoic Rocks............................................................................................... 3 Garnet Graphite Gneiss........................................................................................... 3 Hornblende Gneiss.................................................................................................. 4 Garnet Monzogranite .............................................................................................. 4 Biotite Gneiss.......................................................................................................... 5 Late Proterozoic Rocks................................................................................................... 7 Swift Run Formation............................................................................................... 7 Metadiabase Dikes.................................................................................................. 7 Metarhyolite Dikes.................................................................................................. 8 Catoctin Formation ................................................................................................. 10 Paleozoic Rocks.............................................................................................................. 10 Chilhowee Group.................................................................................................... 10 Loudoun Formation ........................................................................................ 10 Phyllite.................................................................................................... 11 Conglomerate.......................................................................................... 12 Weverton Formation........................................................................................ 12 Buzzard Knob Member........................................................................... 13 Maryland Heights Member..................................................................... 13 Owens Creek Member ............................................................................ 13 Harpers Formation.......................................................................................... 13 Antietam Formation........................................................................................ 14 Tomstown Formation.............................................................................................. 14 Bolivar Heights Member................................................................................. 15 Fort Duncan Member...................................................................................... 15 Benevola Member........................................................................................... 15 Jurassic Diabase Dikes.................................................................................................... 15 Metamorphism................................................................................................................ 16 Structural Geology.......................................................................................................... 16 Gneissic Foliation ................................................................................................... 16 Mylonitic and Phyllonitic Foliation........................................................................ 17 Bedding................................................................................................................... 17 Cleavage.................................................................................................................. 17 Middle Proterozoic Rocks............................................................................... 17 Late Proterozoic and Lower Cambrian Rocks ................................................ 17 Late Proterozoic Dikes.................................................................................... 19 Crenulation Cleavage.............................................................................................. 19 Shear Band Cleavage.............................................................................................. 19 Lineations................................................................................................................ 19 Joints ....................................................................................................................... 19 Folds........................................................................................................................ 19 Faults....................................................................................................................... 22 Tectonic History.............................................................................................................. 25 Middle Proterozoic.................................................................................................. 25 Late Proterozoic...................................................................................................... 26 Paleozoic................................................................................................................. 26 in IV CONTENTS Mesozoic................................................................................................................. 29 Cenozoic................................................................................................................. 29 Quaternary Bedrock Landslides...................................................................................... 29 Surficial Geology............................................................................................................ 29 Acknowledgments .......................................................................................................... 29 References Cited............................................................................................................. 30 PLATE [Plate is in pocket] 1. Geologic map of the Harpers Ferry quadrangle, Virginia, Maryland, and West Virginia. FIGURES 1. Index map showing the location of the Harpers Ferry quadrangle and adjacent quadrangles within the Blue Ridge-South Mountain anticlinorium, and type localities of the members of the Weverton and Tomstown Formations.............................................................................................................................................. 2 2. Quartz-alkali feldspar-plagioclase feldspar diagram showing modal compositions of Middle Proterozoic rocks, and normative feldspar plot of Middle Proterozoic rocks in the Harpers Ferry quadrangle......................... 3 3. Index map showing the locations of isotopically dated rock units discussed in text............................................... 6 4. Photograph showing garnet monzogranite and gneissic foliation defining Grenvillian folds................................. 7 5. Photograph showing sericitic quartzite of the Swift