Strike‐slip tectonics and development of the Tertiary Queen Charlotte Basin, offshore western Canada: evidence from seismic reflection data

Abstract

Interpretation of seismic reflection data have led to a new model of the development of the Queen Charlotte Basin. New multi‐channel data collected in 1988 and an extensive network of unpublished older single‐ and multi‐channel profiles from industry image a complex network of sub‐basins. Structural styles vary along the axis of the basin from broadly spaced mainly N‐trending sub‐basins in Queen Charlotte Sound, to closely spaced NW‐trending sub‐basins in Hecate Strait, to an E‐W en echelon belt of sub‐basins in Dixon Entrance. Transtensional tectonics dominated in the Miocene and transpression dominated in the Pliocene except in Queen Charlotte Sound. The data we present prove that the origin of the basin is extensional and its most recent deformation is compressive. Evidence for the strike‐slip origin of tectonism includes along‐axis variations in structures, simultaneous extension and compression in adjacent sub‐basins, lack of correlations across faults, and mixed normal and reverse faults within structures. We infer that the Pacific‐North America plate boundary has been west of the Queen Charlotte Islands since the Miocene when relative plate motions have been dominantly strike‐slip. The formation and development of the Queen Charlotte Basin is the result of distributed shear; by which a small percentage of the plate motion has been taken up in a network of faults across the continental margin. As this region of crust deforms it interacts with neighbouring rigid crust resulting in extension dominating in the south of the basin and compression in the north. Continental crust adjacent to some transform plate boundaries can be sheared over a wide region; the network of basins in southwestern California is a good analogue for the Queen Charlotte Basin.

Large‐scale transpressive shear zone patterns and displacements within magmatic arcs: The Coast Plutonic Complex, British Columbia

“…From west to east, they are (1) the PrincipeLaredo fault, (2)the Kitkatla fault, and (3) the Grenville Channel fault (Figure 2). Offshore seismic reflection data [Rohr and Dietrich, 1992] Runkle [1979] from 53 to 54° N, and our own data from 54° to 55° N. Shear zones in southeast Alaska and the Prince Rupert shear zone are partly drawn after Crawford et al [1987], Berg et al [1988]. Crawford and Crawford [1991].…”

Reply to comment by M. E. Beck and B. A. Housen on “Paleomagnetism and geochronology of the Ecstall pluton in the Coast Mountains of British Columbia: Evidence for local deformation rather than large‐scale transport”

“…Within the Queen Charlotte basin, several kilometers of marine strata are preserved within Miocene and Pliocene extensional troughs. Seismic reflection data indicate that strata in the eastern portion of the Queen Charlotte basin generally dip 15°-20°southwestward [Rohr and Dietrich, 1992].…”

Neogene strontium isotope stratigraphy, foraminifer biostratigraphy, and lithostratigraphy from offshore wells, Queen Charlotte Basin, British Columbia, Canada

“…2.2,. The latter resulted from deformation (e.g., seismic line 1 of Rohr and Dietrich 1992) (Fig. 5) during the Early-Middle Miocene, sediment transport and infills between volcanic beds, and (or) overprinting from post-depositional fluid migration through coarsegrained sediments.…”

“…More recently, multidisciplinary work has better assessed petroleum potential, gas seeps, geologic hazards, critical biological conservation areas, and sensitive coastal communities (e.g., Whiticar et al 2003;Ommer 2007;Schuemann and Whiticar 2007;Halliday et al 2008;Lutz and Neis 2008;Barrie et al 2011;Takougang and Calvert 2011;Hannigan and Dietrich 2012). Modeling of basin structures and petroleum potential (e.g., Rohr and Dietrich 1992;Whiticar et al 2003;Schuemann and Whiticar 2007;Schümann et al 2013) was in part dependent on stratigraphy and ages of units obtained from studies in the 1960s-1980s.…”

“…Indications of geologic structure include (i) significant age offsets for thick Lower-Middle Miocene strata in the 21.2,21.1,16.2 Ma and 17.9,17.1,15.8 Ma;Figs. 2.3,[3][4][5], which could be interpreted as reverse faulted units (also shown in Rohr and Dietrich (1992), fig. 5) and (ii) out-of-sequence ages within sandstones interbedded with volcanic units in the lower Osprey D-36 well below 6560 ft (2000 m) (Figs.…”