Plate tectonics, volcanism and the lithosphere in British Columbia

Abstract

THE most important feature of the present tectonic situation off the west coast of Canada is the ridge–trench–fault type triple junction between the Juan de Fuca, Pacific and American lithospheric plates near the continental margin, at approximately 51°N (Fig. 1). The half spreading rate for the Juan de Fuca Ridge, based on the magnetic lineation pattern, is 2.9 cm yr⁻¹, and the calculated rate of motion along the Queen Charlotte transform fault between the American and Pacific Plates is 6 cm yr⁻¹ (ref. 1). The main part of the Juan de Fuca Ridge is probably spreading parallel to the north–east trending Blanco fracture zone which marks the southern edge of the plate at approximately 43.5°N. The vector diagram for the relative motion of the three plates during the late Cainozoic suggests that the Juan de Fuca Plate is being thrust obliquely below the American Plate at 2.5 cm yr⁻¹ in a direction of N 35° E (ref. 1).