The Piney Branch Complex consists of subequal parts of highly altered peridotite, pyroxenite, and gabbro and crops out over an area of slightly more than 9km2 in Fairfax County, Va. The lack of discernible order to the distribution of these rock types within the Piney Branch Complex suggests it is a melange resulting from the deformation of a layered complex that contained repetitive cycles of ultramafic and mafic layers. Severely metamorphosed relict cumulate textures can be seen in some specimens of both serpentinite and metagabbro. Small dikes and sheets of plagiogranite occur throughout the complex. The Piney Branch closely resembles the ophiolite material that crops out in southeastern Pennsylvania and Maryland, in the kind, and relative abundance of rock types and in the chemical composition of the rocks, and it represents a continuation of the pattern of southwesterly increasing regional metamorphism of ophiolite material in the central Appalachians. Other bodies of ophiolitic material within the central Appalachians, although at different tectonic levels, also evidence of multiple movement. These bodies and the Piney Branch are believed to be fragments of a large dismembered 'Central Appalachian ophiolite' which records part of the complicated tectonic history of the eastern continental margin of N America.-Authors
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The Piney Branch Complex - a metamorphosed fragment of the central Appalachian ophiolite in northern Virginia.