| Summary: | Paleogeographic models have proposed that the Arequipa Terrane, in southern Peru, and the Dashwoods Terrane, in western Newfoundland, rifted apart ~550 Million years ago during the opening of the Iapetus Ocean, linking their parent cratons, Amazonia and Laurentia, in the supercontinent Rodinia. Investigation of the tectonic history of these two terranes tests paleogeographic reconstructions through geological mapping, stratigraphy, chemostratigraphy, U-Pb geochronology, and paleontology. Investigation of Dashwoods was first carried out by constraining large-scale orogen-parallel displacement in western Newfoundland, which has been proposed to explain an apparent absence of Grenville (~1250–950 Ma) magmatism. Numerous Grenville ages are presented from crustal blocks previously interpreted as far-travelled, suggesting that significant displacement did not occur. The age and tectonic affinity of the adjacent Dashwoods Terrane, was tested with an investigation of its metasedimentary rocks, previously correlated with late Ediacaran to Early Ordovician Laurentian rift-drift deposits. U-Pb dates constrain the age of deposition from Middle Ordovician to Early Silurian. Thus, metasedimentary rocks previously correlated with rifting of eastern Laurentia are identified as younger forearc deposits, and imply that Dashwoods may not be peri-Laurentian. The Marcona Group in southwestern Peru records Cryogenian to Cambrian environmental and tectonic evolution on the Arequipa Terrane. Basal strata were deposited in a 717–635 Ma rift basin with a 635-630 Ma rift-drift transition manifested across a southwest-facing hinge zone. A late Ediacaran to early Cambrian carbonate platform is drowned by >2 km of early Cambrian ichnofossil-bearing volcaniclastic turbidites deposited and deformed during the Pampean Orogeny, and correlated with the Puncoviscana Formation in northwestern Argentina. In the Altiplano of southern Peru, a newly identified late Cambrian fossil assemblage and unconformity are recognized, and in combination with 540–510 Ma detrital zircon, are interpreted to represent the opening and closing of a late Cambrian backarc that formed after collision of the Arequipa Terrane with the southwestern Amazonian margin. This suggests that the Arequipa Terrane underwent a complete Wilson Cycle prior to the opening of the Iapetus Ocean and that paleogeographic models of Rodinia and the timing of its fragmentation may need to be re-evaluated. Earth and Planetary Sciences
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