Piney Branch Complex

Piney Branch Complex (Drake and Morgan, 1981). Heterogeneous assemblage of metamorphosed peridotite, pyroxenite, and gabbro; dominant rock-types include serpentinite, soapstone, and actinolite schist. The unit contains dikes and sheets of plagiogranite. Secondary unit decription from USGS Geologic Names lexicon (ref. VA004): It is a tectonic melange resulting from the deformation of a layered complex that contained repetitive cycles of ultramafic and mafic rocks that are now metamorphosed to serpentinite, soapstone, actinolite schist, and metagabbro, and intruded by dikes and sheet of plagiogranite. It has a discontinuous underlying border of precursory ophiolitic melange, the Yorkshire Formation. The allochthon consisting of the Piney Branch and Yorkshire was thrust upon the Peters Creek Schist, and with it form a composite allochthon that was emplaced on the Sykesville Formation perhaps by gravity sliding. It unconformably underlies the Popes Head Formation. Movement of the Piney Branch began in the Late Proterozoic after the metamorphism of the Peters Creek, and ended during the Taconic Orogeny. Age is Late Proterozoic and (or) Early Cambrian.
State Virginia
Name Piney Branch Complex
Geologic age Proterozoic Z-Cambrian
Lithologic constituents
Major
Metamorphic > Metaigneous > Serpentinite
Metamorphic > Schist
Minor
Igneous > Plutonic > Graniticplagiogranite
Comments Western Piedmont (Northern)
References

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.

USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/

https://ngmdb.usgs.gov/Geolex/search

NGMDB product
Counties Fairfax - Prince William - Fairfax