Canadian Cordilleran displacement: palaeomagnetic results from the Early Jurassic Hazelton Group, Terrane I, British Columbia, Canada

Abstract

SUMMARY The Early Jurassic Telkwa Formation, comprising the base of the Hazelton Group, was sampled at three areas in the central part of the Stikine Terrane, British Columbia. Detailed alternating field and thermal step demagnetization on samples from nine sites from the Red Canyon area and 10 sites from the Zymoetz River area, both of which are in the Bulkley Ranges, and eight sites from the Telkwa Range area isolate stable remanence magnetization components. The components are interpreted to be primary magnetizations because of the presence of two polarities and the much improved agreement of their inclinations after full tilt correction of the sites from the Bulkley Ranges. Within‐locality declinations agree well; between‐locality declinations are discordant. The expected cratonic declination is ˜340° whereas declinations from this study are 265°, 227° and 328° for the Red Canyon, Zymoetz River and Telkwa Range areas respectively. These results are similar to those of Monger & Irving (1980) and we concur that the discordant declinations are the result of differential rotation about vertical axes between sample localities. Our observed mean inclination of 52° is in good agreement with Monger & Irving's (1980) result of 54°. They interpreted this to indicate ˜1300 km of northward displacement since the Early Jurassic and their interpretation was substantiated by several later studies. However, with revisions to the geologic time‐scale and the Early Jurassic reference pole for North America, the Early Jurassic Canadian Cordillera palaeomagnetic data base appears latitudinally concordant. This indicates that Terrane I and southern Wrangellia were in much the same latitudinal position relative to the North American craton as they are now. Tectonic displacement models developed in view of discordant Cretaceous palaeomagnetic data from the Canadian Cordillera must now consider latitudinally concordant Permian to Early Jurassic data and Middle Eocene to Recent data. This tectonic senario appears more reconcilable with the regional tilt hypothesis. However, this hypothesis cannot account for discordant Cretaceous data from bedded volcanic rocks in Terrane I. It is therefore probable that Cretaceous Cordilleran tectonics were characterized by both regional tilting and moderate latitudinal displacement.

Influence of inclination error in sedimentary rocks on the Triassic and Jurassic apparent pole wander path for North America and implications for Cordilleran tectonics

“…APW path based on PEP analysis, and by Irving and Wynne [1990] and Vandall and Palmer [1990] using reference paths based predominantly on sedimentary results, indicate that they were not significant. Since 1990, new evidence from Cretaceous bedded rocks, for which the paleohorizontal can be accurately estimated, has appeared and tilt as a general explanation for the offsets has been extensively criticized [e.g., Ague and Brandon, 1996;Irving et al, 1996;Enkin, 2006].…”

“…The paths from around 250 Ma to 160 Ma (Late Triassic through Middle Jurassic) have critical differences that were substantially responsible for the conflicting estimates of terrane displacement as described in text. example, May and Butler [1986], Irving and Wynne [1990] and Vandall and Palmer [1990] found rotations but no significant latitudinal displacements.…”

“…Results from the Eocene Ootsa Lake volcanics (49.6 Ma; OL in Figure 8) of central British Columbia [ Vandall and Palmer , 1990], the Flores volcanics (50 Ma; FL) of Vancouver Island [ Irving and Brandon , 1990] and the late Neogene basalts of southern British Columbia (SBC) [ Mejia et al , 2002] show no significant offset, indicating that Baja British Columbia was in place relative to the craton by the Eocene.…”

“…For example, when comparisons were first made between the APW path and results from Triassic and Jurassic strata from the Canadian Cordillera, displacements of about 1000 km from the south were found. These results were from the two largest exotic terranes in the Cordillera: Wrangellia on Vancouver Island [ Schwartz et al , 1980; Yole and Irving , 1980] and Stikinia on the British Columbia mainland [ Monger and Irving , 1980; Vandall and Palmer , 1990]. Even larger displacements approaching 3000 km were obtained from Triassic lavas of the Wrangellian terrane in Alaska [ Hillhouse , 1977; Hillhouse and Gromme , 1984].…”

The odyssey of the Cache Creek terrane, Canadian Cordillera: Implications for accretionary orogens, tectonic setting of Panthalassa, the Pacific superwell, and break-up of Pangea

“…Reversed polarity recorded by Permian strata implies a northern hemispheric origin, because during much of the Permian the earth's magnetic field resided in a reversed polarity superchron [30]. Late Triassic and Early Jurassic volcanic rocks yield paleolatitudes, relative to autochthonous North America, that are similar to their current latitude, leading to the suggestion that Stikinia-Quesnellia has been fixed to North America since the Triassic [31]. Stikinia-Quesnellia is, however, characterized by Carnian and Norian sponge reefs that are otherwise unknown outside of tropical Tethyan sequences [28,29], implying that the arc lay within the tropics between 220 and 200 Ma.…”