Mylonite, Mylonite Gneiss, and Cataclastic Rocks

Mylonite. Includes protomylonite, mylonite, ultramylonite, and cataclastic rocks. Lithology highly variable, depending on the nature of the parent rock, and on intensive parameters and history of deformation. In most mapped belts of mylonite and cataclastic rock (my), tectonized rocks anastomose around lenses of less-deformed or undeformed rock. In the Blue Ridge, some of these lenses are large enough to show at 1:500,000 scale. In many places mylonitic and cataclastic rocks are gradational into less deformed or undeformed adjacent rocks, and location of contacts between tectonized rocks (my) and adjacent units is approximate or arbitrary. These boundaries are indicated on the map by color-color joins with superimposed shear pattern. Most mapped belts of mylonite represent fault zones with multiple movement histories. In the Blue Ridge, Paleozoic age contractional deformation fabrics are superimposed on Late Precambrian extensional fabrics (Simpson and Kalaghan, 1989; Bailey and Simpson, 1993). Many Piedmont mylonite zones contain dextral-transpressional kinematic indicators that formed during Late Paleozoic collision al tectonics (Bobyarchick and Glover, 1979; Gates and others, 1986). Paleozoic and older faults were reactivated in many places to form extensional faults during the Mesozoic (Bobyarchick and Glover, 1979).
State Virginia
Name Mylonite, Mylonite Gneiss, and Cataclastic Rocks
Geologic age Proterozoic - Paleozoic ?
Lithologic constituents
Metamorphic > Gneiss
Tectonite > Cataclasite
Tectonite > Mylonite

Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.

Virginia Division of Mineral Resources, 2003, Digital Representation of the 1993 Geologic Map of Virginia, Publication 174, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, scale 1:500,000.

NGMDB product
Counties Albemarle - Amelia - Amherst - Appomattox - Bedford - Botetourt - Brunswick - Buckingham - Campbell - Caroline - Charlotte - Chesterfield - Culpeper - Cumberland - Dinwiddie - Fauquier - Goochland - Greene - Halifax - Hanover - Henrico - Henry - Lunenburg - Madison - Mecklenburg - Nelson - Nottoway - Pittsylvania - Powhatan - Prince Edward - Rappahannock - Stafford - Danville