Structure of the Lithosphere in a Young Subduction Zone: Results from Reflection and Refraction Studies
- Muawia Barazangi and
- Larry Brown
Published Online: 15 MAR 2013
Copyright 1986 by the American Geophysical Union.
Reflection Seismology: The Continental Crust
How to Cite
Clowes, R. M., Spence, G. D., Ellis, R. M. and Waldron, D. A. (1986) Structure of the Lithosphere in a Young Subduction Zone: Results from Reflection and Refraction Studies, in Reflection Seismology: The Continental Crust (eds M. Barazangi and L. Brown), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD014p0313
- Published Online: 15 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875905143
Online ISBN: 9781118670118
- Seismic reflection method—Congresses
Vancouver Island, on the west coast of Canada, is believed to have formed through the process of accretionary tectonics and represents a dispersed block of the Wrangellia terrane. Presently, the oceanic Juan de Fuca plate is subducting beneath the continental plate, A series of refraction and reflection experiments has been carried out to provide better delineation of lithospheric structure in this complex zone of convergence. An offshore-onshore refraction profile has enabled development of a lithospheric model from the deep ocean to near the volcanic arc. Seaward of the continental slope, the plate which includes a 9 km thick crust dips ∼1° landward; below the slope the angle of dip increases to ∼3°; and below the continental shelf it increases substantially to ∼15°. At depths of 30 to 40 km below the shelf, a landward-dipping upper mantle boundary has been inferred from wide-angle reflection phases, and is interpreted as the base of the subducting oceanic lithosphere. In the overlying continental crust a large block of high velocity (∼7.7 km/s) material is embedded and may represent a detached remnant of subducted slab. A test multichannel explosion profile shows reflections to two-way traveltimes of 11 s; four reflectors correspond closely to boundaries in the refraction model. A 1984 follow-up Vibroseis program has produced high quality data, which, combined with the refraction data, illustrate the complementary nature of the two data sets.