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[1] New geologic data from the Central Gneiss Complex along Douglas Channel help delineate the burial and exhumation of the Late Cretaceous to Eocene Coast Mountains magmatic arc. Arc plutonism was on going between ~90 and 60 Ma, replaced by formation of dikes to 52 Ma. Supracrustal rocks were buried to midcrustal levels by 90 Ma, and garnet and kyanite grew from ~90 through 70 Ma. Subsequent exhumation was nearly isothermal and took place in two stages. The first occurred from ~70 to 59 Ma as the arc contracted obliquely and sillimanite replaced kyanite. Exhumation was slow (~0.5 mm/yr), probably accomplished by erosion aided by coaxial crustal thinning. Exhumation rates about doubled in the second stage of exhumation, after 59 Ma and before ~52 Ma. Penetrative deformation ended prior to intrusion of the Quottoon pluton at 59 Ma and ~6.5 kbar. Production of cordierite rims on garnet at 4.5 kbar and ~700[degrees]C signaled the end of near-isothermal decompression prior to 52 Ma. Rapid cooling (100[degrees]C/106 years) of the Central Gneiss Complex followed cordierite growth; temperatures dropped to ~250[degrees] by ~48 Ma. The increase in exhumation rate and the subsequent rapid cooling are attributed to excision of >6 km of crust on a detachment system on the northeastern side of the Central Gneiss Complex. Comparison to other parts of the Coast Mountains arc, the Sierra Nevada, and Fiordland, New Zealand, shows that the amount and tempo of exhumation vary greatly within and between arcs, suggesting that the processes accommodating exhumation vary significantly. doi: 10.1029/2004TC001750.

Examination of the history of deformation, plutonism and metamorphism reveals the evolution of the eastern Waddington thrust belt as an early Late Cretaceous northeast verging thrust belt. Mid-Cretaceous Coast plutonic arc is involved in the contraction and has provided heat for metamorphism. Radiometric, thermochronologic and structural data suggest that the thrust belt was active at 87 Ma and the occurrence of peak of postkinematic metamorphism between 82 and 84 Ma. Structured data reveal the involvement of synmagmatic contraction in the development of the arc.

Early Late Cretaceous east-vergent thrusts deform much of the eastern margin of the Coast Plutonic Complex in western British Columbia. Similarities in timing and style suggest that the faults represent a system of backthrusts to a west-vergent thrust belt on the west side of the complex. This geometry and the rarity of mid-Cretaceous strike-slip faults indicate that the Coast Plutonic Complex was a strongly contractional orogen in mid-Cretaceous time.

This paper documents the newly recognized southern continuation of the early Tertiary Coast shear zone, extending its known length by ~350 km to more than 1200 km. Three sites along the shear zone in British Columbia, Douglas Channel, Bella Coola, and Machmell River, have similar histories during the period ca. 65-55 Ma. The shear zone is 2-11 km thick and is defined by well-developed mylonite zones that strike northwest and dip steeply northeast. Motion on the shear zone was predominantly reverse, with the northeast side up. Synkinematic plutons are common in the shear zone. Lower plate rocks, high-grade gneiss derived from an ancient continental margin assemblage, show little evidence of the extensive deformation and plutonism in the shear zone. North of Bella Coola, high-grade gneiss forms the upper plate, but to the south weakly metamorphosed rocks of Stikinia compose the upper plate, Geochronologic data show that the shear zone was active between ca. 60 and 55 Ma at Douglas Channel, ca. 62 and 56 Ma at Bella Coola, and after 66 and before 56 Ma near the Machmell River. These features match those of the Coast shear zone in southeast Alaska and adjacent British Columbia. Together the shear zones formed a continental-scale reverse ductile fault in Paleocene time. Plate reconstructions show an oblique component to the dominantly dextral transcurrent Paleocene margin. Partitioning of this motion across the continental margin produced a regional system of strike-slip faults and contraction on the Coast shear zone. Keywords: British Columbia, plutons, shear zones, tectonics, thrust faults.