Pluton Emplacement During East-West Stretching at the Northern Termination of a Gneiss Dome in the Central Gneiss Complex, British Columbia
Davidson, C (1), Chardon, D (2), Hollister, L S (2),EM: davidson@beloit.edu
(1) Dept. of Geology, Beloit College Beloit, WI 53511 United States, (2) Dept. of Geosciences, Princeton University Princeton, NJ 08544 United States
Abstract:
Kinematic indicators in igneous and mylonitic supracrustal rocks at the northern termination of a gneiss dome in the Central Gneiss Complex (Chardon and Andronicos, 1997) at the latitude of Portland Inlet (55 degrees N) record a progressive change from top to the south shearing along N-S mineral and stretching lineations to top to the West and top to the East shearing along near horizontal East-West lineations. Kilometer-scale isoclinal recumbent folds with W-SW fold axes are associated with the top to the west shearing. The great axis of the dome strikes 320 degrees with shallow to moderate north dipping foliation (30 degrees average) at the northern termination. The dome projects north into the ACCRETE seismic profile where a crustal-scale dome structure is imaged.
Syn-plutonic sills ranging from a few centimeters thick to kilometer-scale plutons display dramatic deformation gradients, and contain magmatic, submagmatic and solid-state fabrics. In addition, these fabrics are cut by younger dikes and sills that contain magmatic and solid-state fabrics concordant to the fabrics in the plutonic and supracrustal rocks. The deformation gradients and cross-cutting relationships suggest that pluton and sill emplacement was synchronous with East West stretching along the northern margin of the gneiss dome. Extant U-Pb zircon dates suggest that the Central Gneiss Complex was intruded by synkinematic plutons and experienced high temperature deformation from at least 78 Ma to $\sim$53 Ma.
Reference:
Chardon, D., and Andronicos, C.L. (1997) The Central Gneiss Complex: an asymmetrical extensional gneiss dome bounded by the Coast shear zone. GSA Abstracts with Programs, v. 29, no. 6.
