FAULT-BOUNDED BLOCKS OF UNCERTAIN AFFINITY ASSOCIATED WITH THE GOOCHLAND-CHOPAWAMSIC TERRANE BOUNDARY, CENTRAL VIRGINIA PIEDMONT

In central Virginia, the boundary between the Goochland terrane, a Mesoproterozoic to middle Paleozoic continental fragment or microcontinent, and the Chopawamsic terrane, an Ordovician volcanic-plutonic arc, is generally understood to be the Spotsylvania high-strain zone. Detailed mapping within that zone, however, has revealed fault-bounded slices of crust that have no obvious affinity to either of the larger terranes. The Pegmatite Belt and Elk Hill Complex were described by Taber (1913), but excluded from mid- to late-20^th century map compilations. Modern mapping shows both to be lithologically distinct fault-bounded blocks. The Pegmatite Belt is composed of strongly deformed grantitic gneiss, pegmatite, and minor amphibolite. The Elk Hill complex is composed of amphibolite and weakly deformed intermediate to felsic volcanic rocks. Unusual mafic to ultramafic rocks, including a thin, elongate belt of metapyroxenite, an extensive metadiorite body, and poorly exposed talc-chlorite schist appear to be entrained along faults or in the high-strain zone. The Ca Ira mélange of Marr (1983) occupies a similar structural position along strike to the southwest. Comparing the lithology, structure, and geometry of each element yields no obvious relationships with adjacent blocks and highlights the need for geochemical and geochronological studies.