Lithospheric structure across the craton-Cordilleran transition of northeastern British Columbia

J. K. Welford, R. M. Clowes, R. M. Ellis, G. D. Spence, I. Asudeh, Z. Hajnal

Research output: Contribution to journalArticle

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Abstract

The lithospheric structure of the transition from the craton to the Cordillera in northeastern British Columbia is interpreted from inversion of seismic refraction - wide-angle reflection data along a 460-km profile, and from 3-d (3-dimensional) inversion and 2.5-d forward modelling of Bouguer gravity data. The seismic profile extends westward from the sediment-covered edge of cratonic North America across the Foreland and Omineca morphogeological belts to the eastern boundary of accreted terranes, beyond the Tintina Fault. Across the ancient cratonic margin, the resultant models reveal a westward-thickening package of low upper crustal velocities (6.2 km/s and less) and low densities to almost 20 km depth below the Western Canada Sedimentary Basin, overlying a west-facing ramp of higher velocities and densities in the middle and lower crust. These features are inferred to represent passive-margin sediments deposited on the ancient rifted margin during the mid-to-late Proterozoic and early Paleozoic. A wedge-shaped high-velocity (7.3 km/s) crustal layer at the base of the crust beneath the edge of cratonic North America is interpreted to be the result of magmatic underplating during rifting. In the Cordilleran Foreland Belt, high velocities (6.4 km/s) in the upper 5 km of the crust indicate rocks upthrust from the middle crust. A narrow trench of low velocities in the near-surface, which is imaged ∼20 km to the west of the inferred location of the Tintina Fault, is interpreted to represent the actual location of the fault or a major splay. From east to west, the Moho decreases in depth from ∼40 km to ∼34 km below the rifted margin of ancestral North America, then defines a small root at ∼38 km depth below the high topography and upper crustal velocities of the eastern Foreland Belt, and gradually shallows to ∼34 km beneath the Omineca belt. An enigmatic laterally heterogeneous upper mantle has anomalously high velocities (up to 8.3 km/s) beneath the Foreland Belt, flanked by regions of low velocities (7.7-7.8 km/s). Results indicate that the location of the Cordilleran deformation front west of the ramped cratonic margin directly affected the tectonic evolution of the region.

Original languageEnglish
Pages (from-to)1169-1189
Number of pages21
JournalCanadian Journal of Earth Sciences
Volume38
Issue number8
DOIs
Publication statusPublished - 2001

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lithospheric structure
craton
crust
underplating
forward modeling
seismic refraction
passive margin
Moho
cordillera
tectonic evolution
sedimentary basin
sediment
lower crust
rifting
trench
upper mantle
terrane
Proterozoic
Paleozoic
topography

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

Lithospheric structure across the craton-Cordilleran transition of northeastern British Columbia. / Welford, J. K.; Clowes, R. M.; Ellis, R. M.; Spence, G. D.; Asudeh, I.; Hajnal, Z.

In: Canadian Journal of Earth Sciences, Vol. 38, No. 8, 2001, p. 1169-1189.

Research output: Contribution to journalArticle

Welford, J. K. ; Clowes, R. M. ; Ellis, R. M. ; Spence, G. D. ; Asudeh, I. ; Hajnal, Z. / Lithospheric structure across the craton-Cordilleran transition of northeastern British Columbia. In: Canadian Journal of Earth Sciences. 2001 ; Vol. 38, No. 8. pp. 1169-1189.
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