A review of Proterozoic to Early Paleozoic lithotectonic terranes in ...

atlantic geology . volume 47 . 2011 234
that in the Exploits backarc basin of central Newfoundland
(MacLachlan and Dunning 1998; van Staal et al. 2003, 2009;
Valverde-Vaqeuro et al. 2006a; Zagorevski et al. 2007).
The Popelogan terrane was accreted to the Laurentian margin
in the Late Ordovician (Katian). This late Taconic event effectively
closed the main tract of the Iapetus Ocean between
Laurentia and Gondwana. As a result of this closure, the trench
jumped outboard of the Iapetus margin, and the direction of
subduction flipped to the northwest beneath Laurentia. The
subsequent subduction of the oceanic crust of the Elmtree terrane
led to closure of the ensimatic part of the Tetagouche backarc
by the Early Silurian (late Llandoverian). This early Salinic
event is marked by the unconformity between late Llandoverian
conglomerate of the Chaleurs Group and underlying
ophiolitic rocks of the Fournier Group. Shallow slab subduction
during this stage generated arc-related, mafic volcanic
rocks interbedded with Lower Silurian conglomerate near the
base of the Chaleurs Group. In the later stages of subduction,
the leading edge of the more buoyant, ensialic part of the Tetagouche
backarc basin of the Miramichi terrane entered the
northwesterly directed subduction zone and was exhumed by
the Middle Silurian. Following the exhumation, Upper Silurian
(Ludlovian) conglomerate was deposited along the northern
margin of the Miramichi terrane.
The closure of the Tetagouche backarc basin during the Salinic
orogeny united the peri-Gondwanan terranes of Ganderia
with composite Laurentia by the early Late Silurian. Later
within-plate volcanism in the Matapédia Basin during the later
Silurian and Early Devonian is attributed either to transcurrent
fault movement or to the break-off of the Salinic subducting
slab. The Acadian orogeny began with the latest Silurian to
earliest Devonian collision of Avalonia with Laurentia during
contraction and closure of the Acadian Seaway. Subduction of
Avalonia beneath Laurentia led to the progressive migration
of the deformation front from the southeast to the northwest
resulting in inversion of the Matapédia Basin by the late Early
to early Middle Devonian and termination of the Acadian orogeny
in the northeastern Appalachians.
ACKNOWLEDGEMENTS
Malcolm McLeod and Sandra Barr provided valuable discussions
about field relationships, and together with Reg Wilson
offered comments on an early draft of the paper. Terry Leonard
and Erin Smith prepared the figures. Insightful suggestions by
journal reviewers Jim Hibbard and Doug Reusch for improving
the manuscript are greatly appreciated.
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