Active Source Seismic Studies

A critical part of this project will be to produce robust models for the present crustal structure beneath the batholith. This data is critical for constraining, subsurface lithology, structural interpretations and gravity models. Because fjords cross the CPC, we can resolve present-day deep crustal features using offshore-onshore seismic techniques. By utilizing both P- and S-waves, we can provide constraints on both the structure and composition of the crust and sub-Moho lithospheric mantle. By analyzing the strength, sharpness, and fine layering of the Moho from its reflectivity, we can establish the presence of present-day melts possibly related to underplating. By determining seismic anisotropy, we can put constraints on the presence of significant metasedimentary residuals within the lower crust and preferred mineral orientation within the uppermost mantle. By constraining the depth extents and shapes of the plutons from variations in P- and S-wave velocities and seismic reflections within the upper and middle crust, we can estimate their volumes and establish the crustal mass balance.

Determination of Vp, Vp/Vs, and anisotropy will constrain lithologic types and distinguish granite, diorite, gabbro-pyroxene, granulite-restite and dunite-eclogite fromeach other (Christensen and Mooney, 1995; Morozov et al, in press) (Figure 10). We will also work to correlate these features with the volume, age, and chemistry of plutons that occur at the surface, and whether they correlate with areas where substantial extension and exhumation occurred. The combined dataset will allow us to determine how compositional variations within the crust and uppermost mantle correlate with crustal scale faults and shear zones exposed at the surface. The WARRP and MCS data will provide critical constraints on the teleseismic and gravity models.

The active seismic results will provide the critical constraints needed in order to subtract the crustal signature from the velocity and gravity signatures of the mantle. Lateral variations in crustal velocity and thickness will be accurately subtracted from the teleseismic models to better constrain upper mantle velocity. Crustal density models, constrained by the WARRP velocity models, must be stripped from the gravity data to determine if a mass excess indicative of an ultramafic root is present beneath the batholith (Figure 13).