Large-scale mid-Cretaceous sinistral transpression within the outboard terranes of the Coast Plutonic Complex, British Columbia
Chardon, D (1), Andronicos, C L (1), Hollister, L S (1),
(1) Department of Geosciences, Princeton University Princeton, NJ 08544 United States
Abstract:
A compilation of fabric data, published isotopic ages and new structural observations allows the identification and characterization of the regional shear zone pattern of the western Coast Plutonic Complex between 52 and 56 N. The magmatic arc was affected by subvertical, orogen-parallel, crustal-scale shear zones of mid-Cretaceous age. These shear zones mainly reflect sinistral transpression and were sequentially active from ~110 to 87 Ma, from west to east, during the intrusion of voluminous batholiths. Sinistral shearing was roughly coeval with the development of the thrust belts flanking the Coast Plutonic Complex (between ~101 to ~85 Ma), suggesting plate-scale transpression was a first order process in the construction of the Coast Mountains orogen. These shear zones separate panels with distinct plutonic and coolinghistories suggesting the sinistral displacements between crustal blocks were large (greater than tens to hundreds of km).This transpressive shear system likely reflects the Jurassic to EarlyLate Cretaceous migration of outboard Cordilleran terranes to the south suggested by paleomagnetic evidence and plate reconstruction models. This example from the Coast orogen shows how transpression is partitionned between thermally weakened magmatic arc and outwardly vergent fold-and-thrust belts.
