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The Making of a Future Accreted Terrane: Plate Tectonics of the Queen Charlotte Fault System and the Development of the Queen Charlotte Terrace Adjacent to Haida Gwaii

Description: 

The NE-section of the Pacific (PAC) and North America (NAM) plate boundary is generally envisioned as a large-scale transform fault (akin to the San Andreas) extending from north of Vancouver Island to eastern Alaska. However its history and present nature along the translational Queen Charlotte-Fairweather Fault system is less clear - particularly along the Haida Gwaii margin. There the extent of underthrusting of the Pacific plate beneath Haida Gwaii, the role of the Queen Charlotte Terrace (QCT) in the plate kinematics, and the way in which the slight obliquity of relative plate motions (~15°) is accommodated all remain unclear and/or contested. As the PAC - NAM plate motions have changed over the past 20 Ma, the Haida Gwaii section of the Queen Charlotte fault (QCF) has become progressively more transpressive. The result is underthrusting of the Pacific plate beneath western Haida Gwaii, and deformation along the continental margin. Earthquakes along the plate boundary, uplift of the western margin of Haida Gwaii, patterns of plate-interface coupling, and detailed analyses of seismic imagery along the margin allow us to propose an evolving, multi-component 3-D structure to the plate boundary in the vicinity of Haida Gwaii.

This plate boundary evolution has led to the QCT adjacent to Haida Gwaii. Although often linked to the Pacific plate (e.g. it lies outboard of the QCF), the QCT is integral to the partitioning of oblique motion between the PAC and NAM plates. This results in the QCT acting as a terrane that is an independent crustal block with sedimentary structures that differ from the adjacent Pacific plate along an abrupt deformation zone. The QCT shows evidence (through seismicity) of being at most partially coupled along its base to the Pacific plate, and is also kinematically independent (across the QCF) of the adjacent Haida Gwaii. We describe the evolution of this present day plate boundary structure from a simple translational plate boundary (pre-12 Ma), to its current configuration and assess the amounts and timing of underthrusting, uplift, and internal deformation of the QCT terrane.

Session: Structure, Seismicity and Dynamics of the Queen Charlotte-Fairweather Fault System - I

Type: Oral

Date: 5/1/2024

Presentation Time: 05:00 PM (local time)

Presenting Author: Kevin

Student Presenter: No

Invited Presentation: 

Authors