Southern continuation of the Coast shear zone and Paleocene strain partitioning in British Columbia-Southeast Alaska

M. E. Rusmore, George E Gehrels, G. J. Woodsworth

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

This paper documents the newly recognized southern continuation of the early Tertiary Coast shear zone, extending its known length by ~350 km to more than 1200 km. Three sites along the shear zone in British Columbia, Douglas Channel, Bella Coola, and Machmell River, have similar histories during the period ca. 65-55 Ma. The shear zone is 2-11 km thick and is defined by well-developed mylonite zones that strike northwest and dip steeply northeast. Motion on the shear zone was predominantly reverse, with the northeast side up. Synkinematic plutons are common in the shear zone. Lower plate rocks, high-grade gneiss derived from an ancient continental margin assemblage, show little evidence of the extensive deformation and plutonism in the shear zone. North of Bella Coola, high-grade gneiss forms the upper plate, but to the south weakly metamorphosed rocks of Stikinia compose the upper plate. Geochronologic data show that the shear zone was active between ca. 60 and 55 Ma at Douglas Channel, ca. 62 and 56 Ma at Bella Coola, and after 66 and before 56 Ma near the Machmell River. These features match those of the Coast shear zone in southeast Alaska and adjacent British Columbia. Together the shear zones formed a continental-scale reverse ductile fault in Paleocene time. Plate reconstructions show an oblique component to the dominantly dextral transcurrent Paleocene margin. Partitioning of this motion across the continental margin produced a regional system of strike-slip faults and contraction on the Coast shear zone.

Original languageEnglish (US)
Pages (from-to)961-975
Number of pages15
JournalBulletin of the Geological Society of America
Volume113
Issue number8
DOIs
StatePublished - Aug 2001
Externally publishedYes

Fingerprint

strain partitioning
Paleocene
shear zone
coast
gneiss
continental margin
mylonite
plutonism
strike-slip fault
river
rock
contraction
pluton
partitioning

Keywords

  • British Columbia
  • Plutons
  • Shear zones
  • Tectonics
  • Thrust faults

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

Southern continuation of the Coast shear zone and Paleocene strain partitioning in British Columbia-Southeast Alaska. / Rusmore, M. E.; Gehrels, George E; Woodsworth, G. J.

In: Bulletin of the Geological Society of America, Vol. 113, No. 8, 08.2001, p. 961-975.

Research output: Contribution to journalArticle

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