Linking orogenesis across a supercontinent; the Grenvillian and Sveconorwegian margins on Rodinia

Abstract

The Sveconorwegian orogeny in SW Baltica comprised a series of geographically and tectonically discrete events between 1140 and 920Ma. Thrusting and high-grade metamorphism at 1140–1080Ma in central parts of the orogen were followed by arc magmatism and ultra-high-temperature metamorphism at 1060–920Ma in the westernmost part of the orogen. In the eastern part of the orogen, crustal thickening and high-pressure metamorphism took place at 1050 in one terrane and at 980Ma in another. These discrete tectonothermal events are incompatible with an evolution resulting from collision with another major, continental landmass, and better explained as accretion and re-amalgamation of fragmented and attenuated crustal blocks of the SW Baltica margin behind an evolving continental-margin arc. In contrast, the coeval, along-strike Grenvillian orogeny is typically ascribed to long-lived collision with Amazonia. Here we argue that coeval, but tectonically different events in the Sveconorwegian and Grenville orogens may be linked through the behavior of the Amazonia plate. Subduction of Amazonian oceanic crust, and consequent slab pull, beneath the Sveconorwegian may have driven long-lived collision in the Grenville. Conversely, the development of a major orogenic plateau in the Grenville may have slowed convergence, thereby affecting the rate of oceanic subduction and thus orogenic evolution in the Sveconorwegian. Convergence ceased in the Grenville at ca. 980Ma, in contrast to the Sveconorwegian where convergence continued until ca. 920Ma, and must have been accommodated elsewhere along the Grenville–Amazonia segment of the margin, for example in the Goiás Magmatic Arc which had been established along the eastern Amazonian margin by 930Ma. Our model shows how contrasting but coeval orogenic behavior can be linked through geodynamic coupling along and across tectonic plates.