Early Paleozoic metamorphism at two crustal levels and a tectonic model for the Pennsylvania-Delaware Piedmont

Alleghanian orogenic-float on the Martic thrust during dextal transpression, central Appalachian Piedmont

“…A generally accepted model for the Martic thrust involves northwest directed displacement (movement perpendicular to the general grain of the orogen) that emplaced the Piedmont siliciclastic metamorphic rocks on top of the Cambrian metacarbonates in a northwesterly direction (i.e. Freedman et al, 1964;Wise, 1970;Crawford and Crawford, 1980;Muller and Chapin, 1984;Wagner and Srogi, 1987).…”

“…In the Piedmont, a complex system of anastomosing ductile shear zones occurs between more rigid blocks of Precambrian crystalline basement, specifically various massifs of Grenville (ca. 1000-1250 Ma) rock (Crawford and Heorsch, 1984;Wagner and Srogi, 1987). The primary evidence for transpression is the presence of broad, open domes cored by basement blocks, that are located between and are contemporaneous with transcurrent shear zones.…”

Hydrogeology and water quality of the West Valley Creek Basin, Chester County, Pennsylvania

“…The contact between the noncarbonate rocks that underlie the South Valley Hills and the carbonate rocks of Chester Valley has been mapped as a thrust fault that is part of a regional fault structure called the Martic Line (Bascom and Stose, 1938). South of the Martic Line, the structures of rocks in the Glenarm Terrain were caused by complex deformation that was accompanied by metamorphism (Crawford and Crawford, 1980;Wagner and Srogi, 1987). The regional structures and the thrust contact between the noncarbonate rocks to the south of Chester Valley trends east-northeast.…”

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

“…REFERENCES-Brown (1937);Farrar (1984Farrar ( ,1985a; others (1978,1982); Horton and others (1989a);Poland and others (1979); Rankin and others (1989); Hatcher (1982, 1983) NA41: WILMINGTON TERRANE TERRANE BOUNDARIES-The Wilmington terrane of Horton and others (1989a) appears to be thrust over the James Run Formation of the Chopawamsic terrane on the southwest. Some geologists (Wagner and Srogi, 1987) think that it is thrust over the "Wissahickon Formation" elsewhere along its western contact, but all planar elements in both units dip to the west suggesting that the "Wissahickon" is above the Wilmington. Available mapping (Ward, 1959) suggests that the small area of "Wissahickon" northeast of the Wilmington terrane dips to the east away from the Wilmington, and thereby that the Wilmington lies beneath a thrust sheet, probably of the Potomac terrane.…”

“…REFERENCES-Brown and Van der Voo (1983); Grauert and Wagner (1975); Poland and Muessig (1978); Horton and others (1989a); Rao and Van der Voo (1980); Wagner and Srogi (1987); Ward (1959) NA42: SUSSEX TERRANE TERRANE BOUNDARIES-The Sussex terrane (Fig. 1), as named by Horton and others (1989a), lies entirely beneath sediments of the Atlantic Coastal Plain in Virginia and Maryland.…”