Geology of the Corner Brook-Glover Island region, Newfoundland

The Corner Brook Lake-Glover Island region includes carbonate shelf rocks and parts of the Humber Arm Allochthon (externides of the Humber Zone) as well as slices of variously metamorphosed rift-facies siliciclastic rocks resting on Precambrian basement and intruded by latest Precambrian igneous rocks (internides of the Humber Zone). U-Pb zircon dating suggests that the rift-drift transition, marking opening of the Iapetus Ocean, occurred about 555 Ma. Ophiolitic rocks of the Dunnage Zone, thrust westward over the Humber Zone, are locally intercalated with the siliciclastic rocks. Original emplacement of the Humber Arm Allochthon and ophiolites on Glover Island may have been a mid-Ordovician (Taconic) event. However, most of the deformation is Silurian (as dated by U-Pb zircon, rutile, and monazite, and Ar-Ar ages). Deformation was accompanied by thermal activity which produced P-T conditions as high as 7-9 kilobars at about 650°C in a metamorphic culmination just west of the Humber-Dunnage boundary, and extensive granitoid plutonism in the Dunnage Zone. Following this climactic event, relaxation produced extensional and transtensional faults culminating in development of the Carboniferous Deer Lake Basin, a pull-apart basin along the Cabot Fault system which is filled with little-metamorphosed clastic rocks. Important gold prospects occur along the Humber-Dunnage boundary on Glover Island, zinc prospects occur in carbonates of the Humber Zone, and garnet and staurolite have been examined as industrial minerals in the metamorphic rocks. All the mineralization is Silurian or younger.