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Challis West Cascade Arc

VIEWS: 1 PAGES: 29

  • pg 1
									Volcanoes on
  the Rim

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 55 Million Years
 of Volcanism in
 the Pacific NW



                                          Mt. St. Helens, 1980
       Major Events of the Cenozoic
             Volcanism          Tectonics             Olympics       Sedimentary Events
  65

  55

                Challis Arc         Straight Creek
  45                                Transform Fault       Formation of       Major
                                                          Olympic Rocks      Sedimentary
  35                                                                         Basins
                Western
                Cascade Arc
  25

  15
                  Columbia River Basalts
                                                            Accretion of
   5                                                        Olympic Rocks
                 High Cascade Arc
                                                                             Ice Ages
   0

Age (Myrs)
 Volcanic Episodes
  65

  55
             Challis Arc
  45         (55-42 Myrs)
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  35
             Western
             Cascade Arc
  25
             (37-15 Myrs)

  15                            Columbia River Basalts
                                (17-6 Myrs,
                                Most 17-14 Myrs)
   5
             High Cascade Arc   Yellowstone Hot Spot
             (5-0 Myrs)         (14-0 Myrs)
   0

Age (Myrs)
                            G-2


Challis Arc


              Challis Arc
       Late
Cretaceous/Early
Tertiary Batholiths

  Mark the plate boundary



   Note the embayment
 Plates During Challis Time



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                   Formation of
                    Challis Arc
   Straight Creek (Strike-Slip) Fault

                                        Challis Arc


Kula Plate
                                                        North
                                                      American
                                                         Plate



Farallon Plate
                             Post Challis Arc


                                         Arc now runs
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                              G-2


Cascade Arc



  Cascade Arc   Challis Arc
                       G-1



    West &
High Cascades

    West Cascade Arc
    (37-15 Myrs)

    High Cascade Arc
    (5-0 Myrs)
                                                    G-1


  Why did it shift
   eastward?
         Change in dip of plate?

    Steep Subduction         Shallow Subduction




              100 km Depth




Consistent with younger age of Juan de Fuca Plate
                         G-2



   West
Cascades in
Washington

Include volcanic rocks
    and intrusions
              North vs. South
   North Cascades                 South Cascades




                                    West
       West                         Cascade
       Cascade                      Volcanics
       Batholiths



Young Basement Rocks (Terranes)
               North vs. South




More uplift to the north         Erosion
              North vs. South
   North Cascades                    South Cascades

     West Cascade Batholiths
                                  West Cascade Volcanics
                                                           High Cascades




Young Basement Rocks (Terranes)
             Some Landmarks…
       North Cascades                   South Cascades

Chilliwack   Mt. Baker            Snoqualmie
Batholith          Glacier Peak    Batholith   Tatoosh
                                               Batholith   Mt. Rainier
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                                                                         West Cascade
                                                            Fifes Peak   Rocks in WA
                                                            Formation

                                                                            •Basaltic andesite
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                                                                            •Andesite
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                                                                            •Rhyolite
                                                                            •Tuff
                                                            Stevens Ridge
                                                            Formation       •Conglomerate (lahars)
                                                                            •Greywacke

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                                                            Ohanapecosh
                                                            Formation
                                       West Cascade
                                       Rocks in WA
                                       Granodiorite Batholiths
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                                                     QuickTime™ and a
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                         G-3

 Erosion of
 the West
Cascade Arc
   Produces major
    sedimentary
formations to the east
      and west
                                                   D-3
                 West of
                 the Arc
                  Mid-Eocene



          Tukwila Formation
Seattle




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                                                            D-4
               West of
               the Arc
               Late-Eocene &
                 Oligocene


          Blakeley Formation
Seattle




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                                                D-5
          West of
          the Arc
            Miocene




Seattle




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        East of the Arc
John Day Fossil Beds National Monument




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                                       Painted Hills (Pete Yamagata)
                                                    G-3

        John Day
         National
        Monument,
         Oregon


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Rhino skull
Clarno Formation (54-37 Myrs)

                                          1.    "Rhinoceros" - Hyrachyus
                                          2.    Creodont - Patriofelis
                                          3.    Small browsing "horse” -
                                                Orohippus
                                          4.    Crocodile - Pristichampsus
                                          5.    Brontothere -
           QuickTime™ an d a                    Telmatherium
           QuickTime™ an d a
  TIFF (Uncompressed) decompressor        6.    Magnolia - Magnolia
     are need ed to see decompressor
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     are need ed to see this p icture .   7.    Black walnut - Juglans
                                          8.    Palm - Sabalites
                                          9.    Horsetail - Equisetum
                                          10.   Chestnut - Castanea
                                          11.   Fig - Ficoxylon
                                          12.   "Grape" - Vitis
                                          13.   Cycad - Dioon
                                          14.   Sycamore -
                                                Platanusycamore Platanus
John Day Formation (39-18 Myrs)
                                           1.    Sabre-toothed "tiger" -
                                                 Pogonodon
                                           2.    Oreodont - Eporeodon
                                           3.    Three-toed "horse" -
                                                 Miohippus
                                           4.    Tortoise - Stylemys
                                           5.    Mouse-deer -
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                                                 Hypertragulus
   TIFF (Uncompressed) decompressor
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   TIFF (Uncompressed)this p icture .      7.    Oreodont -
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                                                 Promerycocherus
                                           8.    "Rhinoceros" -
                                                 Diceratherium
                                           9.    Chestnut oak - Quercus
                                           10.   Hawthoren - Crataegus
                                           11.   Fern - Polypodium
                                           12.   Hackberry - Celtis
                                           13.   "Maple" - Acertis
                                           14.   "Maple" - Acer
Mascall Formation (15-12 Myrs)
                                          1.    Early mastodon -
                                                Zygolophodon
                                          2.    Rhinoceros - Teleoceros
                                          3.    Giraffe-deer -
                                                Dromomeryx
                                          4.    Mountain beaver -
                                                Mylagaulus
                                          5.    Dog - Telmatherium
           QuickTime™ an d a
           QuickTime™ an d a              6.    Camel - Miolabis
  TIFF (Uncompressed) decompressor
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     are need ed to see this p icture .   7.    Pony-sized horse -
                                                Merychippus
                                          8.    Swamp cypress -
                                                Taxodium
                                          9.    Ginkgo - Ginkgo
                                          10.   Sassafras - Sassafras
                                          11.   Serviceberry -
                                                Amelanchier
                                          12.   Cattail - Typhaer
                                          13.   Cattail - Typha
Rattlesnake Formation (8-6 Myrs)

                                           1.   Short-faced bear -
                                                Indarctos
                                           2.   Single-toed horse -
                                                Pliohippus
                                           3.   Peccary - Prosthennops
            QuickTime™ an d a              4.   Dog - Canis
   TIFF (Uncompressed) decompressor        5.   Hyena-like dog -
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                                                Osteoborus
                                           6.   Elephant -
                                                Tetralophodon
                                           7.   Elm - Ulmus
                                           8.   Sycamore - Platanus
                                           9.   Willow - Salix
Meanwhile to the East…

								
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