Volcanoes on the Rim

55 Million Years of Volcanism in the Pacific NW

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Mt. St. Helens, 1980

Major Events of the Cenozoic

65

55

45

35

25

15

0

5

Age (Myrs)

Straight CreekTransform Fault

WesternCascade Arc

Challis Arc

High Cascade Arc

Columbia River Basalts

Formation ofOlympic Rocks

Accretion ofOlympic Rocks

MajorSedimentaryBasins

Volcanism Tectonics Olympics Sedimentary Events

Ice Ages

Volcanic Episodes

65

55

45

35

25

15

0

5

Age (Myrs)

WesternCascade Arc(37-15 Myrs)

Challis Arc(55-42 Myrs)

High Cascade Arc(5-0 Myrs)

Columbia River Basalts(17-6 Myrs,Most 17-14 Myrs)

Yellowstone Hot Spot(14-0 Myrs)

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Challis Arc

Challis Arc

G-2

Late Cretaceous/Early Tertiary Batholiths

Mark the plate boundary

Note the embayment

Plates During Challis Time

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Formation of Challis Arc

Kula Plate

Farallon Plate

NorthAmerican

Plate

Challis Arc

Straight Creek (Strike-Slip) Fault

Post Challis Arc

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Arc now runsnorth-south

Cascade Arc

Cas

cade

Arc

Challis Arc

G-2

West &High Cascades

G-1

West Cascade Arc(37-15 Myrs)

High Cascade Arc(5-0 Myrs)

Why did it shift eastward?

G-1

Change in dip of plate?

100 km Depth

Steep Subduction Shallow Subduction

Consistent with younger age of Juan de Fuca Plate

West Cascades in Washington

G-2

Include volcanic rocks and intrusions

North vs. South

Young Basement Rocks (Terranes)

North Cascades South Cascades

WestCascadeVolcanics

WestCascadeBatholiths

North vs. South

More uplift to the north Erosion

North vs. South

Young Basement Rocks (Terranes)

North Cascades South Cascades

High Cascades

West Cascade VolcanicsWest Cascade Batholiths

Some Landmarks…

North Cascades South Cascades

Mt. Rainier

TatooshBatholith

Mt. Baker SnoqualmieBatholith

ChilliwackBatholith Glacier Peak

West Cascade Rocks in WA

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Fifes PeakFormation

OhanapecoshFormation

Stevens RidgeFormation

•Basaltic andesite•Andesite•Rhyolite•Tuff•Conglomerate (lahars)•Greywacke

West Cascade Rocks in WA

Granodiorite BatholithsQuickTime™ and a

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Erosion ofthe West

Cascade Arc

Produces major sedimentary

formations to the east and west

G-3

West ofthe ArcMid-Eocene

D-3

SeattleTukwila Formation

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West ofthe Arc

Late-Eocene & Oligocene

D-4

SeattleBlakeley Formation

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D-5

West ofthe Arc

Miocene

Seattle

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East of the ArcJohn Day Fossil Beds National Monument

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Painted Hills (Pete Yamagata)

John Day National

Monument, Oregon

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Rhino skull

G-3

Clarno Formation (54-37 Myrs)

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1. "Rhinoceros" - Hyrachyus

2. Creodont - Patriofelis

3. Small browsing "horse” - Orohippus

4. Crocodile - Pristichampsus

5. Brontothere - Telmatherium

6. Magnolia - Magnolia

7. Black walnut - Juglans

8. Palm - Sabalites9. Horsetail -

Equisetum10. Chestnut -

Castanea11. Fig - Ficoxylon12. "Grape" - Vitis13. Cycad - Dioon14. Sycamore -

Platanusycamore Platanus

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John Day Formation (39-18 Myrs)

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1. Sabre-toothed "tiger" - Pogonodon

2. Oreodont - Eporeodon

3. Three-toed "horse" - Miohippus

4. Tortoise - Stylemys

5. Mouse-deer - Hypertragulus

6. "Dog" - Mesocyon7. Oreodont -

Promerycocherus8. "Rhinoceros" -

Diceratherium9. Chestnut oak -

Quercus10. Hawthoren -

Crataegus11. Fern - Polypodium12. Hackberry -

Celtis13. "Maple" - Acertis14. "Maple" - Acer

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Mascall Formation (15-12 Myrs)

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1. Early mastodon - Zygolophodon

2. Rhinoceros - Teleoceros

3. Giraffe-deer - Dromomeryx

4. Mountain beaver - Mylagaulus

5. Dog - Telmatherium

6. Camel - Miolabis7. Pony-sized horse

- Merychippus8. Swamp cypress -

Taxodium9. Ginkgo - Ginkgo10. Sassafras -

Sassafras11. Serviceberry -

Amelanchier12. Cattail - Typhaer13. Cattail - Typha

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Rattlesnake Formation (8-6 Myrs)

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1. Short-faced bear -Indarctos

2. Single-toed horse - Pliohippus

3. Peccary - Prosthennops

4. Dog - Canis5. Hyena-like dog -

Osteoborus6. Elephant -

Tetralophodon7. Elm - Ulmus8. Sycamore -

Platanus9. Willow - Salix

Meanwhile to the East…