NORTHERN ANCESTRY FOR THE GOOCHLAND TERRANE AS A DISPLACED FRAGMENT OF LAURENTIA

The ancestral position of the Goochland terrane during Grenvillian orogenesis is obscured by its present location as an isolated block of Mesoproterozoic crust in the Virginia Piedmont. Previous interpretations range from an origin as a parautochthonous block to displaced Laurentian crust to an exotic terrane. Possible correlation with the Grenvillian Virginia Blue Ridge is based on general similarities in age, lithology, and Pb isotopic compositions. Nevertheless, the presence of a dextral strike-slip bounding fault and differences in stratigraphic sequences suggest large-scale translation prior to Paleozoic re-accretion. New ages and geochemical data for felsic rocks associated with Neoproterozoic rifting in the Goochland terrane, Blue Ridge, Reading prong, and Manhattan prong suggest that the former was closely linked to the Reading and Manhattan prongs prior to breakup of Rodinia. Ages of extension-related A-type granitoids and volcanics within the North Carolina (760-740 Ma) and Virginia (735-680 Ma) Blue Ridge suggest physical separation from the Goochland terrane (630-588 Ma), Reading Prong (602 Ma), and Manhattan Prong (563 Ma). Correlation between the Goochland terrane and Grenvillian rocks to the north is further supported by compositional similarities between A-type granitoids in the former and felsite dikes in the Reading prong and granitic gneisses in the Manhattan prong. Pre-Iapetan placement of the Goochland terrane to a position that was proximal to the Reading Prong and along strike of the northeastern Blue Ridge, accounts for its unique stratigraphy with affinities to the Blue Ridge (unique anorthosites) and Manhattan prong (abundant amphibolites), and circa 600 Ma A-type granitoids. Thus, as Madagascar was translated out of Africa, the Goochland terrane was probably rifted from proximity to the Reading and Manhattan prongs and dextrally translated nearly 500 km prior to re-accretion. Other internal Grenvillian massifs of the Appalachians may have experienced similar histories.