Interaction between local tectonics and glacial unloading on the Pacific margin of Canada

Variations in Late Quaternary coastal deformation along the Pacific margin of Canada reflect not only differences in glacial history, but also local non-glacial tectonics. A forebulge developed to the north in the Queen Charlotte Basin (QCB) from 13.2 until after 9.7 ka BP resulting in exposure of the currently submerged shelf; whereas similar exposure was not evident to the south in the Georgia Basin. A semi-quantitative effective elastic lithosphere thickness of between 10 and 20 km is estimated for the QCB. We propose that this warm, relatively thin lithosphere combined with tectonic movement influenced crustal displacement, particularly the decoupling of the North American plate along the Queen Charlotte (QC) Fault, which may have allowed the QCB to behave like a hinge in response to glacial unloading. This would explain large magnitude crustal tilting (2.1 m km⁻¹) observed adjacent to the QC Fault. The 50 m of depression observed in the early- and mid-Holocene may imply that the western edge of the North America Plate ‘flexed’ down below present elevation, producing a second wave of response to ice loading and unloading.