Fine Structure of the Crust near Yellowknife

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Clee, T. E., Barr, K. G., Berry, M. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1974
• Subjects: General Earth and Planetary Sciences; Northwest Territories; Yellowknife
• Online Access: http://dx.doi.org/10.1139/e74-153; http://www.nrcresearchpress.com/doi/pdf/10.1139/e74-153

A detailed reflection–refraction experiment was conducted near Yellowknife, Northwest Territories, in 1969. Over 3000 seismograms were recorded along two profiles with a geophone separation of 250 m. The high quality, quantity and unexpectedly high frequency content of the data has revealed a crustal structure which correlates well with the local geology and Bouguer gravity. Extensive use has been made of a ray-tracing program which includes an estimate of the amplitudes based on first-order seismic theory.The model includes a belt of greenstones to the east of the Yellowknife Fault, surrounded by granitic rocks. The velocities are, respectively, 6.17 and 6.0 km/s at depths of 1 km and greater, but the granites are overlain by a transition zone with the velocity at the surface being 5.5 km/s. In the granites at a depth of 8–10 km lies a low velocity layer (V p = 5.8 km/s). The bottom of the greenstones corresponds roughly to the bottom of the LVL and both are underlain by a zone in which V p = 6.2–6.4 km/s.The highly complex nature of the Mohorovičić reflection coda suggests that the M transition is characterized by strong lateral variations of velocity over 20 km or less which give rise to sideways reflections and interference patterns at the surface, t 2 , x 2 calculations using some of the M reflections suggest a crustal thickness of about 30 km and an average crustal velocity of 6.22 km/s. Both values are considered low for a stable shield region.