THE BUMPY ROAD FROM RODINIA TO PANGEA

Supercontinents have formed through geologic time, and may be the ultimate mechanism for continent formation and growth of continental crust. The Grenville orogeny formed supercontinent Rodinia and breakup left attached fragments that grew several continents. Rodinia formed 1.2-1.0 Ga, and began to break up in eastern Laurentia (LR, present coordinates) by 950 Ma, producing a rifted margin that evolved into a carbonate platform by the Ordovician. It broke up on all sides of LR by 750 Ma, opening Iapetus ocean in eastern LR by 565 Ma. The platform was short-lived, and destruction of its outer margin began ~495 Ma with subduction (SD) and growth of island arcs. These arcs collided diachronously with LR (495-445 Ma, Taconic orogeny) shedding debris into foredeeps on the platform, deforming (DF) and metamorphosing (MM) rifted margin sediments, intruding plutons (PL), and obducting arcs and ophiolites along the LR margin, with nearly coeval orogenies in Britain, Iberia, and Scandinavia. Collision of peri-Gondwanan terranes (PGT) with LR began in the N during the Early to Mid-Devonian (DV) and rotated into zippered (ZP) collision southward during the Late DV to early Mississippian (MS) (380-355 Ma) closing the Rheic ocean, and producing the Acadian-Neoacadian orogeny (420-355 Ma). Diachronous clastic wedges, DF, PL, and upper amphibolite (AM) facies MM record this event as LR components were SD beneath the PGT. Assembly of Pangea occurred via E- and W-dipping SD, N-to-S rotational-transpressional (ZP) LR-Gondwana collision, and formation of the Appalachian (AP)-Variscan orogen from the late MS through the Early Permian (325-260 Ma). This event produced large dextral faults throughout followed by continentward-directed megathrust sheets in the S that produced diachronous wedges and the classic AP foreland fold-thrust belt in front of it; AM facies MM; and PL along the southern margin. Florida block may have collided last with the LR margin forming an E-W suture along the southern margin, truncating earlier Alleghanian faults, and producing a sinistral northward escaping block in the collision zone, currently beneath the southern Coastal Plain. AP history contrasts with that in many orogens, with three major accretionary-collisional events producing the assembled chain. This built the bumpy road from Rodinia to Pangea.