North Cascades: Coeval partial melting, decompression, extension, and basin formation in a collapsing continental arc

In collaboration with Robert Miller (San Jose State University) and Sam Bowring (MIT) and their graduate students, UMN grad student Stacia Gordon and I are investigating the timing, conditions, and kinematics of flow of high-grade metamorphic rocks and migmatites in the North Cascades core. Our first focus is on rocks on the east side of the North Cascades, in the vicinity of a large strike-slip fault system that was active during the exhumation of the high-grade rocks. In a few places on the east side, the metamorphic rocks exhibit an impressive strain gradient from deep to shallow levels. We are testing the hypothesis that the contact between *flowing* and *non-flowing* crust is represented by low angle structures preserved at the tops of some of the peaks in this area. We need to determine the timing and kinematics of motion, and the relationship of partial melting, decompression, extension, and oblique motion associated with the strike-slip fault. Preliminary results from this and previous work suggests that melting and orogenic collapse in this region were coeval with similar events far to the east in the northern Cordillera (Omineca belt).

North Cascades photo gallery, summer 2006

We acknowledge NSF grant EAR-0510326 for support of this project.