Structural and geochronologic relations along the western flank of the coast mountains batholith: Stikine river to Cape Fanshaw, central southeastern Alaska

W. C. McClelland, G. E. Gehrels, S. D. Samson, P. J. Patchett

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

Geologic and U-Pb geochronologic studies in central southeastern Alaska provide constraints on the mid-Cretaceous to mid-Tertiary deformation west of the Coast Mountains batholith. The NE-dipping Sumdum and Fanshaw faults record the W-directed emplacement of the Ruth assemblage (Yukon-Tanana terrane) and Taku terrane over the subjacent Gravina belt and Alexander terrane. Ductile fabrics of the Sumdum-Fanshaw fault system truncate early-formed foliation and thrust faults in Albian and older Gravina belt strata. U-Pb age data from syn- and post-tectonic plutons suggest that deformation was ongoing at 92.9 ± 3.0 Ma but had mostly ceased by 90 Ma. The Sumdum-Fanshaw fault system marks the tectonic boundary between the Alexander-Wrangellia terrane and inboard Yukon-Tanana and Stikine terranes and lies within a thrust belt that extends from southern Alaska to northern Washington. Mid-Cretaceous structures are truncated to the east by NE-dipping ductile fabrics of the Coast shear zone. Sheet-like Paleocene tonalites were emplaced into and deformed within the shear zone. Undeformed mid-Eocene dikes cross-cut the tonalites. Kinematic relations in the Coast shear zone suggest a complex displacement history that includes both east-side-up (reverse) and west-side-up (normal) shear. The shear zone probably accommodated the collapse of overthickened crust developed during mid-Cretaceous shortening.

Original languageEnglish (US)
Pages (from-to)475-489
Number of pages15
JournalJournal of Structural Geology
Volume14
Issue number4
DOIs
StatePublished - Apr 1992
Externally publishedYes

ASJC Scopus subject areas

  • Geology

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