Reconnaissance geology and U-Pb geochronology of the west flank of the Coast Mountains between Bella Coola and Prince Rupert, coastal British Columbia

Abstract

Metamorphic pendants within and west of the Coast Mountains between Bella Coola and Prince Rupert British Columbia belong to three northwest-trending belts of metasedimentary and metavolcanic rocks. These belts separate Mesozoic and older strata of the Stikine terrane on the northeast from Wrangellia terrane strata on the southwest. The northeastern belt, herein referred to as the Burke Channel assemblage, consists primarily of interlayered quartzite, marble, metapelite, and metavolcanic rocks that are interpreted to have accumulated along a continental margin with one or more phases of arc-type(?) volcanism. Similarities in protoliths and detrital zircon ages indicate that this assemblage correlates with components of the Yukon-Tanana, Nisling, and/or Stikine terranes of northern British Columbia, Yukon, and eastern Alaska. The southwestern belt, referred to as the Banks Island assemblage, consists mainly of quartzite, marble, and metapelite that may also have accumulated in a continental margin setting. The tectonic affinity of these rocks is uncertain. Separating these assemblages is a belt of metasedimentary and metavolcanic rocks of the Alexander terrane and possibly the Gravina belt. Structures bounding the three sets of pendants are not well known, but are interpreted to include: (1) an early Tertiary reverse fault (part of the Coast shear zone) that juxtaposes Stikine strata westward over the Burke Channel assemblage in the Bella Coola area; (2) a mid-Cretaceous thrust fault that juxtaposes the Burke Channel assemblage over Alexander and possibly Gravina strata; and (3) the sinistral Kitkatla fault, which separates the Banks Island assemblage from the Alexander terrane.