AMALGAMATION AND BREAKUP OF EASTERN RODINIA, PART I: THE SOUTHERN APPALACHIANS

Recently published isotopic data highlight the exotic nature of basement in the southern Appalachians. These basement complexes are distinct from equivalent age material located inboard of the Appalachian crystalline core and Paleozoic deformation front; Appalachian basement is isotopically more mature (Sm-Nd; e.g., Carrigan et al., 2003) and has elevated ²⁰⁷Pb/²⁰⁶Pb whole-rock values (e.g., Loewy et al., 2003). The boundary between these isotopic domains resides in the subsurface of the eastern U.S. somewhere between the easternmost basement samples of 1.4 Ga Granite-Rhyolite province and the basement massifs of the southern Appalachian crystalline core. The boundary must also lie to the southeast of Grenville aged material in the Adirondacks and Llano Uplift; the NY-AL lineament is the northwesternmost suture candidate. Amalgamation of the Rodinian supercontinent during the Grenville orogenic event(s) in the southern Appalachians therefore involves the suturing of non-Laurentian material (likely Amazonia) to Laurentia whereas to the north Baltica was sutured to the Laurentian margin. Sedimentary cover unconformably deposited across the Grenvillian suture of the central and southern Appalachians in the Late Neoproterozoic during Rodinian breakup was largely, if not entirely, sourced from the sutured material in this part of eastern Rodinia. A local provenance of the cover is supported by detrital zircon ages, whole-rock Sm-Nd, and Pb isotopic data and does not require an extensive drainage system covering most of Laurentia during the Late Proterozoic. Subsequent Paleozoic deformation and suturing (of pan-African material) events have variably obscured these relationships. This more detailed understanding of the earliest tectonic history along the Laurentian margin permits further refinement of Paleozoic and younger events which inherit components of Rodinia's amalgamation and breakup.