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Multiple deformation episodes at Myra Falls volcanic-hosted massive sulfide camp, central Vancouver Island, British Columbia, Canada

journal contribution
posted on 2023-05-16, 18:55 authored by Jones, S, Ronald BerryRonald Berry, Sinclair, BJ
A detailed deformation history for central Vancouver Island was determined at Myra Falls volcanic-hosted massive sulfide camp with early ductile deformation overprinted by several distinct episodes of brittle deformation. Brittle structures were subdivided into separate groups based on their morphology, geometry, kinematics, and crosscutting relations. The central location of this study provides a link between previous deformation studies in northern and southern Vancouver Island. Late Paleozoic northeast-southwest compression (D 1) produced open upright folds with variably developed north-northwest-striking axial planar cleavage zones (S 1) and subhorizontal stretching lineations (L 1) subparallel to F 1 fold axes. Renewed northeast-southwest compression during the collision of Wrangellia and North America produced a second foliation (S 2) in localized shear zones, slightly oblique to the dominant S 1 foliation. These two events are recorded throughout Vancouver Island wherever the basement is exposed. Mid-Cretaceous northeast-southwest compression during D 3 produced early steep conjugate strike-slip faults (D 3a), overprinted by northeast- and southwest-dipping thrust faults and bedding-parallel shears (D 3b). D 3 structures have been previously recognized in northern Vancouver Island but not as far south as Myra Falls. North-south extension (D 4) produced east, north, and east-southeast-striking normal faults. These faults consistently crosscut earlier D 1-D 3 structures and reactivate steep D 3a faults. Normal faulting is correlated with the development of the Upper Cretaceous Nanaimo Basin, but no faults of this age have previous been reported from onshore studies. The youngest structures at Myra Falls are large northwest-striking, northeast-dipping thrust faults and steep west- to west-northwest-striking sinistral strike-slip faults formed during the D 5 event. These faults are gouge-rich, wavy anastomosing structures, with cleaved wall-rock zones up to several metres wide. The D 5 faults are correlated with Eocene deformation caused by the accretion of the Pacific Rim and Crescent Terranes along the southwestern margin of Vancouver Island. Myra Falls is the northernmost location to have been reported, at which the structures formed as part of the Cowichan fold and thrust belt. © 2006 NRC Canada.

History

Publication title

Canadian Journal of Earth Sciences

Volume

43

Issue

11

Pagination

1711-1732

ISSN

0008-4077

Department/School

School of Natural Sciences

Publisher

National research Council Canada

Place of publication

Ottawa, ON, Canada

Repository Status

  • Restricted

Socio-economic Objectives

Other mineral resources (excl. energy resources) not elsewhere classified

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