Skip to main content
U.S. flag

An official website of the United States government

Steady rotation of the Cascade arc

September 1, 2013

Displacement of the Miocene Cascade volcanic arc (northwestern North America) from the active arc is in the same sense and at nearly the same rate as the present clockwise block motions calculated from GPS velocities in a North American reference frame. Migration of the ancestral arc over the past 16 m.y. can be explained by clockwise rotation of upper-plate blocks at 1.0°/m.y. over a linear melting source moving westward 1–4.5 km/m.y. due to slab rollback. Block motion and slab rollback are in opposite directions in the northern arc, but both are westerly in the southern extensional arc, where rollback may be enhanced by proximity to the edge of the Juan de Fuca slab. Similarities between post–16 Ma arc migration, paleomagnetic rotation, and modern GPS block motions indicate that the secular block motions from decadal GPS can be used to calculate long-term strain rates and earthquake hazards. Northwest-directed Basin and Range extension of 140 km is predicted behind the southern arc since 16 Ma, and 70 km of shortening is predicted in the northern arc. The GPS rotation poles overlie a high-velocity slab of the Siletzia terrane dangling into the mantle beneath Idaho (United States), which may provide an anchor for the rotations.

Citation Information

Publication Year 2013
Title Steady rotation of the Cascade arc
DOI 10.1130/G34514.1
Authors Ray E. Wells, Robert McCaffrey
Publication Type Article
Publication Subtype Journal Article
Series Title Geology
Series Number
Index ID 70117449
Record Source USGS Publications Warehouse
USGS Organization Geology, Minerals, Energy and Geophysics Science Center