North Cascades

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					           North Cascades
• Western Domain
• Metamorphic Core
• Methow Domain
           Western Domain
• Nooksack terrane- volcaniclastic sediments
  deposited in submarine fans (Jurassic to
  Cretaceous age)
• Chilliwack River terrane- Volcanic and
  sedimentary rocks from a volcanic arc-
  slightly metamorphosed- some greenstone
  pillow basalts, phyllites, marbles– strongly
  folded and faulted- Devonian to Triassic
      Western Domain (cont.)
• Bell Pass Melange-(French word for mix)-
  associations of very unusual rocks in the
  same unit (Precambrian to Triassic)
  – Yellow Aster Complex-granulite facies
    metamorphic rocks
  – Twin Sisters Dunite- dunite is a rock composed
    almost entirely of olivine. Interpretation is that
    this is upper mantle rock
 Easton Terrane (formerly called
      Shuksan Greenschist)
• Darrington phyllite- many of the phyllites in
  our collection are from the Darrington
  phyllite. Locally graphitic. Originally deep
  ocean sediments
• Shuksan greenschist- originally oceanic
  basalts. Metamorphosed into greenschists
  and blueschists.
• Jurassic age
    Metamorphic Core Domain
• Chelan Mountains Terrane- contains many
  different units, but a major unit is the
  Cascade River schist- many of our biotite,
  garnet schists are Cascade River schist.
  Originally this terrane was both oceanic and
  arc environments. There are
  metamorphosed plutonic roots to the
  volcanic arc. – Triassic in age
    Metamorphic Core Domain
            (cont.)
• Nason terrane- Metmorphosed submarine arc
  sediments. Mostly schists and gneisses derived
  from the schists. Original sediments deposited in
  Triassic.
• Swakane terrane-If you drive north of Wenatchee
  along the Col. River, this terrane is exposed on
  west side of river. Primarily gneisses derived from
  volcanic or sedimentary arc rocks. Probably
  Precambrian in age.
    Metamorphic Core Domain
            (cont.)
• Little Jack terrane- small terrane north and
  east of Ross Lake. Metamorphosed
  sediments from a submarine fan at the base
  of a volcanic arc. Also contains blocks of
  metamorphosed ultramafics.
Younger gneisses associated with
 the Metamorphic Core Domain
• Skagit Gneiss Complex- gneisses and migmatites
  derived from plutons intruded into the assembled
  terranes of the Meta. Core. Domain. Probably not
  intruded in the present location.
• Othrogneiss- gneiss derived from a granitic
  intrusive rock
• Paragneiss- gneiss derived from sedimentary rocks
           Methow Domain
• Methow terrane- thick sequence of marine
  sediments as old as Jurassic, sediments
  deposited on land (rivers, lakes, etc), and
  some volcanics and associated plutonic
  rocks (Jurassic to Cretaceous)
      Methow Domain (cont.)
• Hozomeen terrane- Crater and Jack
  Mountains on the east side of Ross Lake.
  Composed of deep marine basalts, cherts,
  and associated sediments. Mississippian to
  Triassic in age.
   Metamorphism, Faulting and
           Intrusion
• The terranes of the North Cascades were accreted
  about 90 million years ago (Cretaceous). Many of
  the terranes show metamorphism associated with
  this accretion. The thrust faults in the Western
  Domain formed at this time.
• Strike-slip faulting occurred after the thrust
  faulting, some faults may have been Paleocene,
  others were active through Eocene.
• Intrusion of granitic batholiths throughout the
  Cascades

				
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