Deep seismic structure and plate tectonic evolution of the Canadian Appalachians

Abstract

Three seismically defined lower crustal blocks (LCBs) have been recognized to underlie the familiar tectonic‐stratigraphic zones of the Canadian Appalachians. Tectonic development of the orogen is inferred to have been strongly influenced by collision of the two outboard LCBs (Central and Avalon LCBs) against the sharply irregular North American craton (Grenville LCB), as evidenced by an abrupt offset in the trend of the orogen localized at this irregular edge. The LCBs are restored to a precollisional configuration by (1) removing Carboniferous strike‐slip motion on major faults linking through the Magdalen pull‐apart basin; and (2) removing Devonian(?) offset along a hypothesized fault through the present‐day Strait of Canso (Canso fault) to realign the Central and Avalon LCBs, presumed to have been continuous prior to accretion to North America. The restoration leads to (1) a qualitative explanation for deep seismic reflection observations across the Magdalen basin which suggest that portions of the underlying crust do not correspond to any of the three principal LCBs; and (2) a plate tectonic model for the orogen which suggests the backarc basin separating the Taconian (Ordovician) arc from the eastern margin of the early Paleozoic Iapetus ocean was at least as wide (>450 km) as the offset in the irregular Grenville LCB, inherited from rifting of Iapetus. The present‐day Southwest Newfoundland Transform Margin may be a segment of the Canso fault reactivated during Mesozoic opening of the Atlantic ocean.

Provenance of tectonic history of the Gander Zone in the Caledonian/Appalachian Orogen: Implications for the origin and assembly of Avalon

“…The clastic rocks of the Gander Zone are thus autochthonous to parautochthonous with respect to their basement. The seismically defined lower crustal block underneath the Gander Zone (Marillier et al, 1989;Stockmal et al, 1990) thus probably represents its original basement. Quinlan et al (1992) recently argued on the basis of continuity of seismic reflectors that the lower crustal block is similar to the basement of the Hermitage Flexure (Bras d'Or-Brookville belt) in southwestern Newfoundland (Fig.…”

Whole-rock Ar-Ar dating for low-grade metavolcanics within the Dabie orogen and its geological significance

“…We consider that all these metavolcanic, as well as metagranite at Bixiling, the Luzhenguang igneous complex in the northern part of the Dabie orogen and the Wulian complex in the northwestern part of the Sulu orogen were not brought to mantle depths during the Triassic continental subduction. These rocks were scraped off from the subducted continental crust, similar to flake tectonics or tectonic wedge [7,28,[31][32][33][34][35][36][37] . It witnesses crustal detachment between the basement and cover units during the continental collision [37] .…”

Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians

“…1; Blackwood and Kennedy, 1975;Dallmeyer et al, 1981;Holdsworth, 1994) and is correlated at depth with a geophysically-defined crustal-scale structure that offsets the Moho (Keen et al, 1986;Marillier et al, 1989;Stockmal et al, 1990). Sinistral shear is recorded in a ~20 km wide NE-striking zone of ductile shear that parallels the Dover Fault, the Wing Pond shear zone ( Fig.…”