Detrital zircon constraints on terrane ages and affinities and timing of orogenic events in the San Juan Islands and North Cascades, Washington

Edwin H. Brown, George E Gehrels

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Detrital zircon geochronology of this report pertains to Cretaceous orogeny in northwest Washington, an event that involved blueschist metamorphism and emplacement of nappes in the San Juan Islands - northwest Cascades thrust system and continental arc magmatism and associated Barrovian metamorphism in the neighboring Coast Plutonic Complex. Structurally low in the thrust system, quartzose gneiss of the Yellow Aster Complex yields an entirely Precambrian suite of detrital zircons, with an age pattern that is similar to that of Ordovician miogeoclinal rocks and the outboard Yukon-Tanana, Yreka, and Shoo Fly terranes elsewhere in the Cordillera. Midway in the nappe pile of the northwest Cascades, sandstone in the Bell Pass Mélange has a zircon age population of 110 Ma, an age that together with the spectrum of exotic materials associated with the sandstone suggests the mélange was a major zone of dislocation during mid-Cretaceous nappe emplacement. At a high level in the thrust system are nappes of the Fidalgo Complex, Lummi Formation, Constitution Formation, and Easton Metamorphic Suite, all with a prominent age peak in the range of 148-155 Ma. These units appear to be mutually related, represent inter-arc marginal basins, and are correlative with terranes in the western Klamath Mountains. The Nooksack Formation, foorwall to nappes in the Cascades, has a zircon population at 114 Ma, providing a maximum age of nappe emplacement. The Tonga Formation of the Coast Plutonic Complex bears zircons that indicate a depositional age of <125 Ma, thus yielding a maximum age for the beginning of Barrovian metamorphism and continental arc plutonism in this region.

Original languageEnglish (US)
Pages (from-to)1375-1396
Number of pages22
JournalCanadian Journal of Earth Sciences
Volume44
Issue number10
DOIs
StatePublished - Oct 2007

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terrane
nappe
zircon
continental arc
emplacement
metamorphism
thrust
sandstone
Cretaceous
blueschist
marginal basin
plutonism
coast
cordillera
dislocation
geochronology
orogeny
gneiss
magmatism
Ordovician

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

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title = "Detrital zircon constraints on terrane ages and affinities and timing of orogenic events in the San Juan Islands and North Cascades, Washington",
abstract = "Detrital zircon geochronology of this report pertains to Cretaceous orogeny in northwest Washington, an event that involved blueschist metamorphism and emplacement of nappes in the San Juan Islands - northwest Cascades thrust system and continental arc magmatism and associated Barrovian metamorphism in the neighboring Coast Plutonic Complex. Structurally low in the thrust system, quartzose gneiss of the Yellow Aster Complex yields an entirely Precambrian suite of detrital zircons, with an age pattern that is similar to that of Ordovician miogeoclinal rocks and the outboard Yukon-Tanana, Yreka, and Shoo Fly terranes elsewhere in the Cordillera. Midway in the nappe pile of the northwest Cascades, sandstone in the Bell Pass M{\'e}lange has a zircon age population of 110 Ma, an age that together with the spectrum of exotic materials associated with the sandstone suggests the m{\'e}lange was a major zone of dislocation during mid-Cretaceous nappe emplacement. At a high level in the thrust system are nappes of the Fidalgo Complex, Lummi Formation, Constitution Formation, and Easton Metamorphic Suite, all with a prominent age peak in the range of 148-155 Ma. These units appear to be mutually related, represent inter-arc marginal basins, and are correlative with terranes in the western Klamath Mountains. The Nooksack Formation, foorwall to nappes in the Cascades, has a zircon population at 114 Ma, providing a maximum age of nappe emplacement. The Tonga Formation of the Coast Plutonic Complex bears zircons that indicate a depositional age of <125 Ma, thus yielding a maximum age for the beginning of Barrovian metamorphism and continental arc plutonism in this region.",
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