Sole-Fault Deflection Tectonics and Clockwise Rotation in the Allochthonous Canadian Cordillera

Symons, D T (1)

(1)Earth Sciences University of Windsor Windsor, Ont N9B 3P4 Canada

For a quarter century discordant paleomagnetic poles have been found in Jurassic to Eocene rocks of the accreted terranes in the Canadian Cordillera, and most suggest $\sim$$45\deg$ $\pm$ $25\deg$ of clockwise vertical-axis rotation. Proffered explanations include"ball-bearing" tectonics, horizontal-axis tilts, residual viscous remanence, etc.. Deep crustal seismic reflection surveys show that, like most orogens, sole-fault thrusts dominate Cordilleran tectonics. Palinspastic restorations show that orogen-perpendicular shortening during the Laramide Orogeny reached a few hundred kilometres in places. It is hypothesized that the accreted terranes: 1) had quasi-linear tectonic elements at $\sim$$45\deg$ $\pm$ $25\deg$ to the craton's margin originally; 2) impacted progressively on the margin from south to north; 3) moved inland mainly on sole faults; and, 4) were deflected or progressively rotated as the subhorizontal thrust slices faced increasing resistance at their leading edge, whether verging or subducting, and on their enlarging sole during the Laramide Orogeny. Thus geologicunits/terranes remained as fairly coherent orogen-parallel elements rather than being disarticulated, and their stable remanences were rotated clockwise. Their increasing outboard paleolatitude discordance is attributed mainly to post-Laramide orogen-parallel dextral strike-slip faulting that was focused at terrane boundaries.

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