Crustal Velocity Structure across the Transition between the Coast Plutonic Complex and Stikinia - ACCRETE and SNorCLE Transects
Hammer, P T (1), Clowes, R M (1), Ellis, R M (1)
(1) Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
The Coast orogen of British Columbia and SE Alaska contains the suture resulting from the mid-Cretaceous collision between the exotic Insular superterrane (Alexander and Wrangellia terranes) and the previously accreted Intermontane superterrane (Stikinia, Taku and Yukon terranes). This geotectonic environment has been targeted by the ACCRETE and LITHOPROBE Slave-Northern Cordilleran Lithospheric Evolution (SNorCLE) Transects to investigate the growth of continents by magmatic and terrane accretion.
The 1994 ACCRETE seismic refraction/wide-angle reflection (R/WAR) experiment and the 1997 SNorCLE R/WAR Experiment (SNoRE) provide a continuous profile across the transition between the Coast Plutonic Complex (CPC) and the Skeena fold and thrust belt of the Stikinia terrane. Using coastal fjords for access, ACCRETE profiled with a towed 132 {\it l} airgun array. Data were recorded by 40 REFTEK 3-component seismographs deployed along the 180 km-long Portland Canal. 17 additional seismographs were deployed in-line with the shiptrack, extending the profile 105 km northeast from the head of the fjord through the CPC and into Stikinia. Seismic coverage across the transition was significantly improved by the overlapping SNoRE Line 22 dataset. Extending south from the Tintina Fault across the Intermontane terranes and into the CPC, the profile reaches 50 kmdown Portland Canal, providing 150 km of overlap with ACCRETE. Nine explosive shots (1000 - 3000 kg) were detonated along the 600 km profile. Data were recorded by 450 1-component (PRS and SGR) and 3-component (REFTEK) seismographs.
The two R/WAR datasets provide a densely sampled, 2-D profile. Data quality is excellent; numerous reflected and refracted P- and S-phases are identifiable and are observed to large offsets. Structural models of P-velocity, S-velocity and Poisson's ratio describe a well-defined transition from the CPC to Stikinia; upper and average crustal velocities decrase and Moho depth increases. The slower velocities within Stikinia are not restricted to the thin-skinned Skeena fold and thrust belt, but extend to the lower crust.
