Publication Summary
Issue ID: P2015-01-07
Title: Fieldwork in the Sylvester allochthon, Cassiar Mountains, British Columbia: Investigations of the Rapid River tectonite and the Slide Mountain terrane
Author(s): Ryan, J., Nelson, J.L., van Staal, C.
Series Name: Paper
Publication Year: 2015
Larger Work Citation: in Geological Fieldwork 2014, B.C. Ministry of Energy and Mines, Paper 2015-01
NTS Map Sheet(s): 104I,J,O,P
Place Keyword(s): British Columbia, Northwestern British Columbia, Cassiar Mountains
Lat/Long (NSWE): 60, 58, -130.5, -128
Theme Keyword(s): Sylvester allochthon, Slide Mountain Terrane, Rapid River tectonite, Devonian, ophiolites
Back-arc extension during Devonian-Mississippian eastward subduction beneath the western flank of ancestral North America led to separation of Yukon-Tanana terrane from Laurentia, and opening of the Slide Mountain marginal ocean basin. Rocks exposed in imbricated thrust sheets of the Sylvester allochthon record the opening and closing of this marginal basin. At the highest structural level in the allochthon, the Rapid River tectonite is interpreted as a remnant of Yukon-Tanana basement. Pre-Late Devonian deformation in the Rapid River tectonite may represent collision of an exotic arc terrane with the outer peri-Laurentian margin that was the precursor to east-dipping subduction. Preliminary observations indicate that at least part of the Rapid River tectonite has a protolith of mafic mylonite and marble, possibly representing parts of a primitive arc.