Late Neoproterozoic to Early Cambrian geologic, geochronologic, and paleoma
gnetic data from along the Iapetus margin of Laurentia may be reconciled,wi
thin a multistage rift history that involved an initial separation of Laure
ntia from the west Gondwana cratons ca. 570 Ma, followed by rifting of a fu
rther block or blocks from Laurentia ca 540-535 Ma into an already open Iap
etus Ocean to establish the main passive-margin sequence in the Appalachian
s. Paleomagnetic data suggest that Laurentia rifted from Amazonia-Rio de la
Plata cratons and began its northward movement ca. 570 Ma to produce a wid
e Iapetus Ocean by 550 Ma. Geologic data from the Newfoundland segment of t
he Laurentian margin provide evidence for a rift-drift transition ca. 540-5
35 Ma, as constrained by the youngest rift-related magmatism at 550.5 (+3)/
(-2) Ma (U/Pb zircon) for the Skinner Cove Formation and 555 (+3)/(-5) Ma f
or the Lady Slipper pluton, and a late Early Cambrian age of ca, 525-520 Ma
for the oldest drift-related sedimentation. Rifting between the Laurentia
and the west Gondwana cratons was probably distributed among multiple rift
systems that fostered the production of a number of terranes (such as the A
rgentine Precordillera, Oaxacan) as well as the Iapetus Ocean. Development
of Laurentian-derived Iapetan terranes during the final breakout of Laurent
ia from Rodinia may have been facilitated by preexisting 760-700 Ma rift we
aknesses and apparently rapidly changing plate vectors during latest Neopro
terozoic time.