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Orogen‐parallel extension in the North Cascades Crystalline Core, Washington
Author(s) -
Brown E. H.,
Talbot J. L.
Publication year - 1989
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc008i006p01105
Subject(s) - geology , plutonism , lineation , metamorphism , pluton , metamorphic core complex , shear zone , metamorphic rock , seismology , shear (geology) , core (optical fiber) , mylonite , geochemistry , petrology , paleontology , extensional definition , tectonics , materials science , composite material
Metamorphic stretching lineations throughout the Crystalline Core of the North Cascades, Washington, show a strong preferred orientation in a horizontal NW‐SE direction. Foliations strike NW and dip steeply. Preliminary observations of shear sense features indicate noncoaxial right‐lateral motion. We interpret these observations to indicate that the Crystalline Core was a broad, right‐lateral shear zone. The ages of the fabrics, as recorded by metamorphic minerals and syntectonic plutons, range from pre 85‐Ma in the south to post 45‐Ma in the north; thus the shear regime was active during an extended interval of metamorphism and plutonism in the orogen. A similar kinematic pattern is suspected for at least part of the Coast Plutonic Complex, British Columbia, which lies on strike with the Crystalline Core to the northwest.