THE RIFTED EDGE OF THE GRENVILLE OROGEN OF SOUTHERN LAURENTIA: POTENTIAL PIERCING POINTS FOR AMAZONIA

Palinspastic maps of terranes of the Grenville orogen are portrayed on the magnetic anomaly map of North America for the Elzevirian orogeny; the Shawinigan, Ottawan, and Rigolet phases of the Grenvillian orogeny; and post-Grenvillian magmatism during failed rifting (760-600 Ma) prior to successful Iapetan rifting at 565 Ma. Accreted terranes had unique histories prior to amalgamation and share common tectonic events afterwards. The Elzevirian suture, partially preserved beneath the Appalachians, separates the Reading Prong terrane from Laurentia (i.e., Adirondacks and composite-arc terrane and Canadian Grenville province). The Shawinigan suture, partially preserved in the Llano area, separated the now-fragmented and allochthonous Amazonian blocks of the outboard Blue Ridge and Sauratown Mountains terranes from the Reading Prong terrane in the Appalachian region. Within Laurentia, the Mars Hill terrane, containing a pre-Grenvillian inlier, is the only fragment of Amazonia believed to have been accreted during the main Ottawan phase. The outboard Ottawan suture may have served as locus of Iapetan rifting along much of Laurentia. The Rigolet phase (ca. 1020-1000 Ma) is characterized by widespread “Basin and Range” type extension (NW-SE) associated with inferred sinistral movement on the NY-AL lineament, mobilization of core-complexes (Adirondack Highlands), and AMCG magmatism along the outboard flank of the extensional region. Subsequently, the Appalachian region is characterized by NW-SE extension during passage of a possible hotspot along a NE-track (760-600 Ma) across the Blue Ridge and other terranes, prior to successful Iapetan rifting (565 Ma). The palinspastic rifted margin of southern Laurentia crosses many of these terranes and sutures as well as the possible region of Rigolet extension and the possible hotspot track, thus providing many potential piercing points within the Grenville orogen for comparison with terranes of Amazonia or elsewhere.