LOCATION: The outcrops are located on S-42-210, 0.7 mile south of the intersection with S-42-33. (Fig. 16, Cross Anchor quadrangle)
DESCRIPTION: These road cuts and boulders in the adjacent woods show the Buffalo gabbro and the associated felsic rocks mapped on its south margin, and the contact between these two rock types (Medlin, 1966; Medlin and others, 1972). The gabbro here is medium to coarse-grained and black in color. In fact, the mafic rocks of the Buffalo gabbro grade in no apparently systematic way from gabbro to norite (Medlin and others, 1972). Medlin and others (1972) report modal percentages of olivine from 0-20.9% (norites) and 0-23% (gabbros); orthopyroxene from 12-42.2% (norites) and 0.6-21.9% (gabbros); and clinopyroxene from 7.2-36.3% (norites) and 7.8-58% (gabbros). Medlin and others (1972) report 8 olivine, 3 orthopyroxene, and 6 clinopyroxene mineral analyses: olivines range from Fo68-Fo80.6; orthopyroxenes from En75-En78; and, clinopyroxenes from Wo41.5-En44.5 to Wo44En41.
The felsic rocks are bluish-grey with bluish potassium feldspar phenocrysts. Medlin (1966) terms these rocks "biotite quartz monzonite," and Willis (1984) calls them "syenodiorite." Two modal analyses (Medlin and others, 1972) plotted on the 1976 IUGS classification scheme (Streckeisen, 1976) yield points in the quartz monzonite (QAP -> 14-43-43) and quartz syenite (9-62-29) fields Medlin and others (1972) did not think that there was a necessarily a petrogenetic or magmatic relation between the felsic and mafic rocks, but without explicitly establishing the relation, Willis (1984) and Dennis (1991) did.
Several leucocratic dikes may be observed in the weathered residuum in the gully. Medlin and others (1972) note that the aplite to pegmatite veins and dikes cut across both gabbro and felsic rocks.
Medlin and others (1972) compare the Buffalo gabbro with mineralogic data from the other known post-metamorphic gabbros. They stress the differences between Buffalo and Mt. Carmel and Concord. Medlin and others (1972) note that Concord and Mt. Carmel show alkaline affinities, and the Buffalo gabbro either calc-alkalic or tholeiitic affinities.
Based on gross chemical similarities between the post-metamorphic gabbros, their linear arrangement just southeast of the central Piedmont suture, the ca. 400 Ma age of the array, strongly positive [[epsilon]]Nd (ca. +4) for the array, the association of an alkalic group of granites (Salisbury-Southmont group) of the same age with low initial Sr ratios (.7023-.7046) in the same structural position as the gabbros, as well as the pattern of mineral ages in the Inner Piedmont (younging to the east towards the central Piedmont suture), the problem of apparently coeval metamorphism in the Inner Piedmont and Carolina terrane with "cold" rocks in the hanging wall, Dennis (1991) offered the hypothesis that the central Piedmont suture formed (or was reactivated) as a Siluro-Devonian normal fault following crustal thickening accompanying the accretion of Carolina to Laurentia. Data to test this hypothesis, including U-Pb ages of monazite and construction of P-T-t curves are being collected.