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Volcanoes on the Rim

Volcanoes on the Rim. 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 Transform Fault. 45. Formation of Olympic Rocks. Major Sedimentary

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Volcanoes on the Rim

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  1. Volcanoes on the Rim 55 Million Years of Volcanism in the Pacific NW Mt. St. Helens, 1980

  2. Major Events of the Cenozoic Volcanism Tectonics Olympics Sedimentary Events 65 55 Challis Arc Straight Creek Transform Fault 45 Formation of Olympic Rocks Major Sedimentary Basins 35 Western Cascade Arc 25 15 Columbia River Basalts Accretion of Olympic Rocks 5 High Cascade Arc Ice Ages 0 Age (Myrs)

  3. Volcanic Episodes 65 55 Challis Arc (55-42 Myrs) 45 35 Western Cascade Arc (37-15 Myrs) 25 Columbia River Basalts (17-6 Myrs, Most 17-14 Myrs) 15 5 Yellowstone Hot Spot (14-0 Myrs) High Cascade Arc (5-0 Myrs) 0 Age (Myrs)

  4. Challis Arc G-2 Challis Arc

  5. Late Cretaceous/Early Tertiary Batholiths Mark the plate boundary Note the embayment

  6. Plates During Challis Time

  7. Kula Plate North American Plate Farallon Plate Formation of Challis Arc Straight Creek (Strike-Slip) Fault Challis Arc

  8. Post Challis Arc Arc now runs north-south

  9. Cascade Arc G-2 Challis Arc Cascade Arc

  10. West &High Cascades G-1 West Cascade Arc (37-15 Myrs) High Cascade Arc (5-0 Myrs)

  11. Why did it shift eastward? G-1 Shallow Subduction Steep Subduction 100 km Depth Change in dip of plate? Consistent with younger age of Juan de Fuca Plate

  12. West Cascades in Washington G-2 Include volcanic rocks and intrusions

  13. West Cascade Volcanics West Cascade Batholiths North vs. South North Cascades South Cascades Young Basement Rocks (Terranes)

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

  15. North vs. South North Cascades South Cascades West Cascade Batholiths West Cascade Volcanics High Cascades Young Basement Rocks (Terranes)

  16. Some Landmarks… North Cascades South Cascades Mt. Baker Snoqualmie Batholith Chilliwack Batholith Glacier Peak Tatoosh Batholith Mt. Rainier

  17. West Cascade Rocks in WA Fifes Peak Formation • Basaltic andesite • Andesite • Rhyolite • Tuff • Conglomerate (lahars) • Greywacke Stevens Ridge Formation Ohanapecosh Formation

  18. West Cascade Rocks in WA Granodiorite Batholiths

  19. G-3 Erosion ofthe West Cascade Arc Produces major sedimentary formations to the east and west

  20. West ofthe ArcMid-Eocene D-3 Tukwila Formation Seattle

  21. West ofthe ArcLate-Eocene & Oligocene D-4 Blakeley Formation Seattle

  22. West ofthe ArcMiocene D-5 Seattle

  23. East of the ArcJohn Day Fossil Beds National Monument Painted Hills (Pete Yamagata)

  24. G-3 John Day National Monument, Oregon Rhino skull

  25. Clarno Formation (54-37 Myrs) "Rhinoceros" - Hyrachyus Creodont - Patriofelis Small browsing "horse” - Orohippus Crocodile - Pristichampsus Brontothere - Telmatherium Magnolia - Magnolia Black walnut - Juglans Palm - Sabalites Horsetail - Equisetum Chestnut - Castanea Fig - Ficoxylon "Grape" - Vitis Cycad - Dioon Sycamore - Platanusycamore Platanus

  26. John Day Formation (39-18 Myrs) Sabre-toothed "tiger" - Pogonodon Oreodont - Eporeodon Three-toed "horse" - Miohippus Tortoise - Stylemys Mouse-deer - Hypertragulus "Dog" - Mesocyon Oreodont - Promerycocherus "Rhinoceros" - Diceratherium Chestnut oak - Quercus Hawthoren - Crataegus Fern - Polypodium Hackberry - Celtis "Maple" - Acertis "Maple" - Acer

  27. Mascall Formation (15-12 Myrs) Early mastodon - Zygolophodon Rhinoceros - Teleoceros Giraffe-deer - Dromomeryx Mountain beaver - Mylagaulus Dog - Telmatherium Camel - Miolabis Pony-sized horse - Merychippus Swamp cypress - Taxodium Ginkgo - Ginkgo Sassafras - Sassafras Serviceberry - Amelanchier Cattail - Typhaer Cattail - Typha

  28. Rattlesnake Formation (8-6 Myrs) Short-faced bear -Indarctos Single-toed horse - Pliohippus Peccary - Prosthennops Dog - Canis Hyena-like dog - Osteoborus Elephant - Tetralophodon Elm - Ulmus Sycamore - Platanus Willow - Salix

  29. Meanwhile to the East…

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