HR: 09:15h
AN: V41A-06    [PDF]
TI: Tectonic evolution of the Notre Dame magmatic arc, Newfoundland Appalachians
AU: * van Staal, C
EM: cvanstaa@nrcan.gc.ca
AF: Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E* Canada
AB: Notre Dame continental arc magmatism in Newfoundland had an overall lifespan of c. 60 Ma (489-429 Ma). Extensive age dating suggests that arc construction took place in 3 distinct stages, separated by gaps of magmatic quiescence (arc shut-off). The first phase of quiescence (c. 480-468 Ma) corresponds to the start of Taconic collision between the initially west-facing Notre Dame arc and Laurentia. The second phase of magmatic quiescence (455-445 Ma) corresponds to collision between the now east-facing Notre Dame arc and the west-facing, peri-Gondwanan Victoria arc built on a piece of Ganderian crust. Resurgence of arc magmatism followed stepping- back of the west-dipping subduction zone into the oceanic marginal basin that separated the Victoria arc from the Gander margin. A gradual transition (431-429 Ma) from arc-like to mainly juvenile, bimodal within plate-like magmatism coincides with suturing of the Notre Dame arc with the Gander margin along the Dog Bay line and probably reflects break off of the west-dipping Ganderian slab. Preservation of an unconformable and unmetamorphosed Silurian cover, consisting of red beds and bimodal volcanic rocks, over large tracts of the Notre Dame arc indicates that the arc was extinct and stabilized by the Late Silurian (c. 425 Ma) and did not experience any significant overprint during the Early Devonian Acadian orogeny, the effects of which were mainly localized further to the east due to accretion of Avalonia to Laurentia. The second, Mid-Ordovician phase of arc magmatism (c. 469-456 Ma) appears most voluminous and was mainly characterized by K-poor, calc-alkaline quartz diorite to tonalite and, to a lesser extent granodiorite, plutons. These calc-alkaline plutons intruded during deformation and significant thickening of the Notre Dame arc, presumably as a result of ongoing shortening following initial collision with Laurentia and an arc-polarity reversal. Such a tectonic scenario is consistent with the high metamorphic grade of the supracrustal rocks they intruded and high La/Yb content of most tonalites, which suggests melting of garnet-amphibolite near the base of an over thickened arc. The first evidence of emergence of the Notre Dame arc following its thickening is provided by unconformably overlying, late Caradoc (c. 453 Ma) subaerial ignimbrite and conglomerate. Parts of the Notre Dame arc show very rapid exhumation of its middle to lower crust at c. 430 Ma, following shortening during the Early Silurian. Exhumation was presumably triggered by slab breakoff during final suturing between Ganderia and Laurentia.
DE: 8102 Continental contractional orogenic belts
DE: 8110 Continental tectonics--general (0905)
DE: 8157 Plate motions--past (3040)
DE: 9350 North America
DE: 9614 Paleozoic
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting