Crustal formation at depth during continental collision

Abstract

The rapid (1-2 mm/yr) and substantial (over 10 km) Tertiary exhumation of the Coast Crystalline Complex near Prince Rupert, British Columbia led to the exposure of rocks formed at crustal depths of 15-20 km and greater. Abundant sills, mostly tonalite in composition, delivered a thermal pulse which locally raised tempeatures to the low-pressure granulite facies within the intruded section. The thermal pulse and exhumation are recorded by the metamorphic mineral assemblages and textures, and by isotopic cooling ages. During uplift, strain was concentrated in the ductile shear zones. If the section had not been exhumed, seismic reflection profiling would show shallow dipping reflectors in the deep crust due to the contrast in density and fabric of the layers. -from Authors