TERRANE ACCRETION AND TRANSPRESSION IN THE CENTRAL APPALACHIAN PIEDMONT: AN EXAMPLE FROM THE ENIGMATIC GOOCHLAND TERRANE

The central Appalachian Piedmont includes terranes with both Laurentian and peri-Gondwanan affinities. The Goochland Terrane has long been recognized as a distinctive, but enigmatic sequence of igneous and metamorphic rocks in eastern Virginia Piedmont. Researchers have debated the provenance of the Goochland Terrane for more than four decades. Mesoproterozoic granitoid gneiss, meta-anorthosite, and Neoproterozoic A-type granitic plutons are exposed in a series of elongate NE-SW trending domes. The domes are framed by an aerially extensive cover sequence that includes heterogeneous gneissic units with discontinuous layers of amphibolite and pegmatitic gneiss. The contact between the gneissic domes and cover sequence has traditionally been interpreted as either unconformable or intrusive.

New U/Pb (zircon, rutile, and apatite) geochronology from both the domes and overlying cover sequence indicates that Mesoproterozoic rocks in the Goochland domes were not in contact with cover sequence gneisses until after 400 Ma. We propose that high-grade cover sequence rocks are peri-Gondwanan, and were emplaced over a Proterozoic basement sequence during the Acadian orogeny, likely in the northern Appalachians. The Goochland domes are tectonic windows, bound by a cryptic and previously unrecognized suture. Domes formed post-accretion during the Alleghanian orogeny as transpressional deformation translated the Goochland Terrane hundreds of kilometers southwest along the Appalachian margin. The Goochland Terrane was rapidly exhumed in the Triassic at the onset of pre-Atlantic rifting.