The Accotink Schist, Lake Barcroft Metasandstone, and Popes Head Formation— Keys to an understanding of the tectonic evolution of the northern Virginia Piedmont

Abstract

The Accotink Schist, Lake Barcroft Metasandstone, and Popes Head Formation Keys to an understanding of the tectonic evolution of the northern Virginia Piedmont.

Geologic map of the Washington West 30’ × 60’ quadrangle, Maryland, Virginia, and Washington D.C.

“…Individual beds of meta-arenite are as much as 2 m (7 ft) thick, but much of the rock appears to be the result of sedimentary amalgamation. The meta-arenite was interpreted by Drake and Lyttle (1981) to be a sequence of turbidites. The unit grades down into the Accotink Schist; the contact is placed where the schist constitutes more than 50 percent of the rock sequence.…”

“…Old Mill Branch Metasiltstone Member (Drake and Lyttle, 1981)-Light-greenish-gray, thin-to medium-bedded, medium-to very fine grained, very mature, micaceous metasiltstone. The metasiltstone beds are 2 to 24 cm (0.8 to 9.4 in.)…”

“…Station Hills Phyllite Member (Drake and Lyttle, 1981)-Light-greenish-gray, dusky-yellowish-weathering phyllite and lesser very fine grained metasiltstone and chlorite-rich mafic metatuff. Beds are 2 to 12 cm (0.8 to 4.7 in.)…”

Terranes and overlap sequences in the Central and Southern Appalachians, an expanded explanation for part of the Circum-Atlantic terrane map

“…REFERENCES-Crowley (1976); Drake (1985aDrake ( , 1985bDrake ( , 1986Drake ( ,1987; Drake and Lyttle (1981); Drake and Morgan (1981); Hill (1987); Horton and others (1989a); Mose and Nagel (1982); Pavlides (1989) NA2h: SMITH RIVER TERRANE TERRANE BOUNDARIES~The Smith River terrane, as defined by Horton and others (1989a), lies in a fault-bounded synform within the Jefferson terrane just northwest of the Sauratown terrane. The Smith River terrane is bounded by the Ridgeway thrust fault, and locally by the younger Bowens Creek fault (Espenshade and others, 1975;Conley, 1988).…”

“…EVIDENCE FOR TERRANE IDENTITY AND TIME OF AMALGAMATION»In northern Virginia the thrust stack was assembled and the composite terrane was amalgamated prior to the deposition of the overlapping Popes Head Formation (Drake and Lyttle, 1981; illustrated in Figure 1). The thrust stack was amalgamated and the overlap sequence was deposited prior to the emplacement of the Early Ordovician (or Late Cambrian?)…”