Nd isotopic constraints on the magmatic history of the Goochland terrane, easternmost Grenvillian crust in the southern Appalachians
Published:January 01, 2004
Brent E. Owens, Scott D. Samson, 2004. "Nd isotopic constraints on the magmatic history of the Goochland terrane, easternmost Grenvillian crust in the southern Appalachians", Proterozoic Tectonic Evolution of the Grenville Orogen in North America, Richard P. Tollo, James McLelland, Louise Corriveau, Mervin J. Bartholomew
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Nd isotopic compositions for ten samples from the State Farm Gneiss (ca. 1046–1023 Ma), the Montpelier Anorthosite (1045 Ma), and several Neoproterozoic Atype granitoids (ca. 600 Ma) in the Mesoproterozoic Goochland terrane range in initial εNd from −0.4 to +1.3. The A-type granitoids reflect Neoproterozoic rifting of the Goochland terrane, and their isotopic compositions are consistent with a substantial contribution from the State Farm Gneiss, or equivalent crust at depth, in their petrogenesis. Protoliths of the State Farm Gneiss and Montpelier Anorthosite were emplaced at approximately the same time, and their Nd isotopic compositions are the same. Based on our results and age, bulk compositional, and isotopic similarities between the State Farm Gneiss and Mesoproterozoic rocks (Pedlar River and Archer Mountain suites) in the Blue Ridge Province, we suggest that the gneiss and anorthosite represent a coeval anorthosite-charnockite suite. The unusually potassic Montpelier Anorthosite is also isotopically similar to, and the same age as, the alkalic Roseland Anorthosite in the Blue Ridge Province. Depleted mantle model-ages for the State Farm Gneiss and Montpelier Anorthosite range from 1.38 to 1.43 Ga. These ages are similar to those of many other Grenvillian crustal blocks (e.g., Adirondacks, Blue Ridge, Llano uplift) along the eastern and southern margins of Laurentia, which show a strong peak from 1.3 to 1.5 Ga. Petrological, geochronological, and geochemical data obtained thus far from the Goochland terrane are consistent with the view that it represents a fragment of Laurentia.