Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 20
Presentation Time: 1:30 PM-4:15 PM


STODDARD, Edward F.1, FUEMMELER, Stephen2, BECHTEL, Randy3, CLARK, Timothy W.4 and SPRINKLE II, D. Parker1, (1)N.C. Geological Survey, 1620 Mail Service Center, Raleigh, NC 27699-1620, (2)Appalachian Landslide Consultants, Asheville, NC 28778, (3)N. C. Geological Survey, 1612 Mail Service Center, Raleigh, NC 27699-1612, (4)3041 Granville Dr, Raleigh, NC 27609,

This mapping, partially funded through the USGS under the Cooperative Geological Mapping Act, STATEMAP and EDMAP elements, covers four 7.5-minute quadrangles in the northeastern Piedmont of North Carolina. The map area includes rocks of the Spring Hope terrane in the east (SHt), representing suprastructural elements of a Neoproterozoic volcanic arc, and the infrastructural Raleigh terrane in the northwest (Rt). In the map area, the Macon fault separates these two terranes. In addition, about half the area is underlain by late Paleozoic granitoid rocks of the composite Rolesville batholith. Rocks of the SHt increase in metamorphic grade from greenschist facies in the east to amphibolite in the center. Thermal metamorphism associated with the granitoid bodies is manifested in a sizable hornfels facies aureole. SHt felsic volcanics include fine-grained metadacite hornfels and phyllitic crystal and crystal-lithic tuff. Mafic volcanics range from epidote-actinolite greenstone to coarse amphibolite, and include abundant amygdaloidal metabasalt. Greenschist-grade metasedimentary rocks in the SHt are predominantly metagraywacke and metasiltstone, with minor metamudstone and rare metaconglomerate. At higher metamorphic grade, SHt rocks include fine two-mica semischist, locally with garnet, and coarse porphyroblastic staurolite-garnet schist. Rt rocks in the area are dominated by mica schists with local sillimanite. Granitoid orthogneiss is also present, displaying mylonitic fabric in the Macon shear zone. The map includes four named plutons containing six mapped granitoid facies. There are also several small unnamed plutons and areas of profuse pegmatite. Reentrants and enclave trains of country rocks separate granite plutons and lobes (cf. Speer, 1994). Early motion on the Macon fault is inferred to be reverse or thrust, with infrastructural Rt over SHt; later motion is dextral. In the northeastern portion of the area, rocks of the SHt have primary layering and foliation that is very gently dipping, defining several late open map-scale folds, probably parasitic to the regional Spring Hope synclinorium (F3 of Farrar, 1985). Some evidence suggests the existence of an earlier regional isoclinal fold (i.e. F2 of Farrar, 1985), but graded bedding in metagraywacke is upright where observed.