Presentation by Dr. Collin Brandl
A New Subduction Zone in the Northeast Pacific? Oblique Convergence along the Queen Charlotte Plate Boundary
Abstract:
The formation of new subduction zones is critical for plate tectonics, but uncertainties remain about environments that are favorable for initiation and the evolution of a system from nucleation to self-sustained subduction. Modeling suggests that transform boundaries with a degree of convergence may be one of the most favorable environments, but there are few active locations that can be observationally studied. The transform Queen Charlotte Plate Boundary (QCPB) separates North America from the Pacific plate between the Cascadia and Alaska subduction zones and experiences oblique convergence in its southern segment. A magnitude 7.8 thrust earthquake offshore Haida Gwaii in 2012 and sparse seismological indications of a dipping slab has led many investigators to consider this a young subduction zone, but there is no associated Wadati-Benioff zone or arc volcanism. There has been a lack of direct imaging of the full crustal structure along the plate boundary, so the behavior of the system and the presence of a dipping slab remain uncertain. Using multichannel seismic reflection profiles acquired in 2021, we constrain the southern segment of the plate boundary, including the deep crustal structure of the Queen Charlotte Terrace and the first imaging of the Haida Gwaii plate boundary thrust. These data show that the Queen Charlotte Terrace behaves as a forearc sliver, bounded by the strike-slip Queen Charlotte Fault and the Haida Gwaii thrust. This work suggests that this section of the plate boundary is at an early stage of the subduction initiation process, where the system is evolving towards self-sustained subduction but has not yet reached it. Like the Puysegur trench south of New Zealand, the QCPB is one of few sites of ongoing subduction initiation at a transform plate boundary, albeit at an earlier stage in the process.
Zoom link:
https://columbiauniversity.zoom.us/j/93981266342?pwd=1rs8ibcC5eZ208BbbPaxtOwsN8Biq2.1
