An examination of the cataclastic fabrics and structures of parts of Nisutlin, Anvil and Simpson allochthons, central Yukon: test of the arc-continent collision model

Abstract

Collision of an arc complex against the Yukon part of the North American craton during the Mesozoic resulted in northeastward transport of arc rocks onto the craton. The arc rocks comprise three distinguishable tectonostratigraphic assemblages called: Nisutlin Allochthon, quartz muscovite and chlorite schist derived from sedimentary and intermediate volcanic protoliths; Anvil Allochthon, amphibolite, gabbro, ultramafic rocks and sepentinite; and Simpson Allochthon, granitic and granodioritic rocks and schist derived from them. Deformation, recovery and recrystallization structures show that parts of the allochthons are blastomylonite, formed at temperatures of 350–700°C and at depths between 15 and 40 km. The stacking order of the allochthons is inconsistent and complex, and locally, the cataclastic rocks are overthrust by autochthonous strata. The allochthons are truncated by late steep faults that have mainly strike-slip displacement, and may be contemporaneous with Tintina Fault. The proposed tectonic history of the region is supported by detailed results of the study.