REVISED DISTRIBUTION OF GRENVILLIAN TERRANES OF THE APPALACHIANS

Since the Mars Hill and Blue Ridge terranes were first distinguished from terranes which form the Adirondacks/New England and the Grenville Province of Canada (Bartholomew and Lewis, 1988, 1992), many Grenvillian rocks within the Appalachians have been examined in much more detail by many researchers. This research suggests that the eastern boundary of the Central Metasedimentary Belt (CMB) continues southwestward at least into TN. Gradual southward convergence of this boundary toward the Grenville Front suggests that either the CMB or the Central Gneiss Belt is probably truncated southward from Canada. This research also continues to suggest that the Mars Hill terrane was an older exotic terrane (1.2-1.8 Ga) accreted to the eastern or southern margin of Laurentia. As originally conceived, the Blue Ridge terrane was interpreted to be a belt of dominantly igneous rocks (<1.2 Ga) intruded by younger plutons during the major culminating event(s) of Grenville orogenic cycle. The ongoing research suggests that this Blue Ridge terrane should be restricted to the Blue Ridge of central and northern Virginia and its palinspastic northeastward continuation – the Goochland terrane (now in eastern Virginia). The Blue Ridge terrane consists of younger plutons (~1050-1080 Ma) of Ottawan age (or younger) that were emplaced into igneous rocks of ~1100-1160 Ma. Because the igneous rocks of Blue Ridge of SW-VA, NC, and TN (French Broad massif) do not appear to contain plutons of Ottawan age (or younger), this belt should be regarded as different from the Blue Ridge terrane to the NE. Thus, models for tectonic development of the French Broad massif may be tectonically more similar either to that of the Llano uplift or to that of the Adirondacks than to that of the Blue Ridge terrane.