Seismic evidence for craton chiseling and displacement of lithospheric mantle by the Tintina fault in the northern Canadian Cordillera

Abstract

The northern Canadian Cordillera (NCC) of northwestern Canada is segmented by several margin-parallel, right-lateral, strike-slip faults that accumulated several hundred kilometers of displacement between the Late Cretaceous and the Eocene. The depth extent of these faults, notably the Tintina fault (TF), has important implications for the tectonic assemblage and evolution of NCC lithospheric mantle, but geophysical models and geochemical data remain inconclusive. Using a recent three-dimensional P-wave seismic velocity model, we resolved a series of sharp (~10 km) P-wave velocity contrasts (~4%) at uppermost mantle depths beneath the surface trace of the TF. Seismic anisotropy data that represent upper-mantle fabrics revealed similar changes in the orientation and magnitude of anisotropy in the vicinity of the TF. These data suggest that the TF is a lithospheric-scale shear zone. After restoration of 430 km of right-lateral displacement along the TF, fast P-wave anomalies align with the outline of the North American craton margin. We propose the fast anomaly structure currently located in eastern Alaska represents a fragment of the Mackenzie craton that was chiseled and displaced to the northwest by the TF between the Late Cretaceous and the Eocene. A second cratonic fragment currently located in the southern NCC may be associated with the Cassiar terrane at upper-mantle depth. These observations provide the first evidence that large lithospheric-scale shear zones cut through refractory mantle and produce major lateral displacement of cratonic mantle material within cordilleras worldwide.

Surface‐Wave Tomography of the Northern Canadian Cordillera Using Earthquake Rayleigh Wave Group Velocities

“…However, the observed low-velocity region in our surface-wave model does not extend throughout the entire NCVP and, therefore, can only partially explain the volcanism occurring at the northern end of the NCVP. Finally, we note that restoring ≈400 km of dextral displacement along the Tintina fault (Estève et al, 2020a) provides continuity of the low-velocity region across it.…”

“…Teleseismic shear-wave splitting data from SKS phases show a large-scale coherent northeast-southwest fast-axis alignment in the Canadian Shield, interpreted as fossilized fabric within the North American lithospheric mantle, and/or sublithospheric mantle flow subparallel to the present-day absolute motion of North America (Courtier et al, 2010;Snyder & Bruneton, 2007). A similar alignment is observed across northern Yukon, suggesting that the fabrics have a common origin throughout the two regions (Estève et al, 2020a). Across the NCC, the northeast-southwest fabric is overprinted by a northwest-southeast fast-axis orientation near the Tintina and Denali faults, suggesting long-term lithospheric-scale shearing along these faults (Audet et al, 2016;Rasendra et al, 2014).…”

“…Recently, Estève et al. (2020a) showed seismic evidence that the Tintina fault chiseled and displaced a lithospheric‐scale fragment of the Mackenzie craton toward the northwest in Alaska between the Late Cretaceous and the Eocene. We propose that such a mechanism would have resulted in a subvertical craton edge in northern Yukon and is consistent with our tomographic images.…”

Large-scale, crustal-block vertical extrusion between the Hines Creek and Denali faults coeval with slip localization on the Denali fault since ca. 45 Ma, Hayes Range, Alaska, USA

“…The "float" or detachment model was proposed for active tectonic regions in the Yukon territory and Alaska (Mazzotti and Hyndman, 2002) in part based on geophysical evidence that the Moho appears to be relatively flat in the northern Canadian Cordillera. However, more dense seismic arrays deployed in the past 10 years indicate that some of the major active and inactive high-angle faults in Alaska and Yukon have offsets of the Moho directly below them (Brennan et al, 2011;Allam et al, 2017;Miller et al, 2018;Estève et al, 2020). We and others interpret the alignment of the surface trace of these faults and Moho offsets at depth to indicate that the surface expression of these faults corresponds with the geophysical expression at depth, and these faults are lithospheric in scale.…”

Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

“…Such inferences are supported by a variety of geophysical data sets, all of which indicate a fundamental change in the properties of the lower crust and upper mantle across the eastern Denali fault (Allam et al., 2017; Audet et al., 2016; Berg et al., 2020; Miller et al., 2018; O'Driscoll & Miller, 2015; Rasendra et al., 2014; Saltus & Hudson, 2007). The sum of geophysical and geological data from the Denali fault, together with thermochronological and geophysical data sets from other regions of the Cordillera (Enkelmann et al., 2019; Estève et al., 2020), challenge the hypothesis of an active Cordillera‐wide weak lower crustal décollement (e.g., Hyndman et al., 2005).…”