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TitleKinematics and timing of shear zone deformation in the western Coast Belt: evidence for mid-Cretaceous orogen-parallel extension
AuthorAngen, J J; van Staal, C R; Lin, S; Nelson, J L; Mahoney, J B; Davis, D W; McClelland, W C
SourceJournal of Structural Geology vol. 68, pt. B, 2014 p. 273-299,
Alt SeriesEarth Sciences Sector, Contribution Series 20140128
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS103G/15; 103G/16; 103J/01; 103J/02
AreaPorcher Island
Lat/Long WENS-130.6000 -129.8333 54.1000 53.8000
Subjectsgeochronology; structural geology; structural features; structural interpretations; lineations; foliation; shear zones; uranium lead dates; deformation; orogenesis; tectonic setting; radiometric dating; Cordillera; Coast Belt; Cretaceous; Devonian; Silurian; Ordovician; Jurassic
Illustrationsgeological sketch maps; photographs
ProgramWestern Cordillera Project Management, GEM2: Geo-mapping for Energy and Minerals
AbstractNorthwest-striking sinistral shear zones characterize mid-Cretaceous deformation in the western Coast Belt south of Prince Rupert in north coastal British Columbia. Structurally focused mapping and geochronology have revealed a component of lateral extension to this deformation. General flow characteristics of the shear zones are identified by comparison of fabric patterns to published models for fabric development in shear zones. U--Pb ages from synkinematic dykes constrain motion on northwest-striking sinistral transpressional shear zones, including the Useless, Barrett and Salt Lagoon shear zones, to ca. 104--96 Ma, and dextral transpression on the north-striking Telegraph Passage shear zone to ca. 97 Ma. The geometry, kinematics, and coeval nature of these shear zones suggest that they formed in part as a ductile conjugate set. The orientation of these conjugate sets indicates ENE--WSW (orogen perpendicular) shortening and NNW--ESE (orogen parallel) extension. The conjugate shear zones merge together into the Grenville Channel shear zone, a sinistral transpressional shear zone with high strike-parallel stretch indicating the same strain field. This local strain regime is consistent with large-scale mid-Cretaceous tectonic escape as proposed for the northern Cordillera at that time, expressed in coeval sinistral faulting in the Coast Belt and dextral faulting in the northern Omineca belt.
Summary(Plain Language Summary, not published)
Detailed structural studies of shear zones formed as a result of major faulting along terrane boundaries revealed that the core of the cordilleran mountain belt in western Canada was escaping to the northwest at about 100 million years ago with respect to North america and the outboard terranes. This escape was accomodated by dextral (right hand direction) faulting in the Omineca Belt (central BC) and sinistral (left hand direction)faulting n the Coast Belt along present day BC coast small scale conjugate sets of faults show that this pattern of faulting was scale independent.