The Growth of Western North America Exotic Terranes Photo of Mt Shuksan by Patti Bleifuss

How do you “grow’ a continent? 1.Sedimentation (along the continental shelf) 2.Subduction (plutons, volcanoes) 3.Collision (accretion of terranes)

How do you “grow’ a continent? 1.Sedimentation (along the continental shelf) 2.Subduction (plutons, volcanoes) 3.Collision (accretion of terranes)

How do you “grow’ a continent? 1.Sedimentation (along the continental shelf) 2.Subduction (plutons, volcanoes) 3.Collision (accretion of terranes) Fast

New Land Accreted to the West of the “706 Line” 706 Line

Terrane Basic Definition: Fault bounded package of rocks with a similar geologic origin. Terranes form somewhere else and then become accreted to the continent. Exotic Terrane: Traveled a great distance befor becoming accreted to the continent. Superterrane Two or more terranes the have “amalgamated” with one another before accreting to the continent.

Types of terranes 1.Microcontinents 2.Island Arcs 3.Hot Spot Islands & Seamounts 4.Ridges (Divergent Zones) Rock Types: Felsic Volcanic & Plutonic Metamorphic Conglomerate, Sandstone, Coal Example: Madagascar

Types of terranes 1.Microcontinents 2.Island Arcs 3.Hot Spot Islands & Seamounts 4.Ridges (Divergent Zones) Rock Types: Intermediate/Felsic Volcanics Greywacke (eroded volcanoes) Graded Beds Limestone Example: Aluetian Islands

Types of terranes 1.Microcontinents 2.Island Arcs 3.Hot Spot Islands & Seamounts 4.Ridges (Divergent Zones) Rock Types: Basalt Limestone Sandstone, Siltstone, Shale Example: Hawaiian Islands Basalt Limestone

Types of terranes 1.Microcontinents 2.Island Arcs 3.Hot Spot Islands & Seamounts 4.Ridges (Divergent Zones) Rock Types: Example: Juan de Fuca Ridge

Ocean Crust = Ophiollite 10 km Serpentinite (From hydrothermal metamorphism) Gabbro Basalts (with pillow structures) Shale, Chert (or limestone if shallow water) B-1

Types of terranes 1.Microcontinents 2.Island Arcs 3.Hot Spot Islands & Seamounts 4.Ridges (Divergent Zones) Rock Types: Shale, Chert, Limestone Basalt (Pillows) Gabbro Serpentinite Example: Juan de Fuca Ridge

How do we know where terranes came from? 1.Rock Types 2.Microfossils 3.Sediment Provenance 4.Paleomagnetics a)Inclination b)Declination Tillite Limestone

How do we know where terranes came from? 1.Rock Types 2.Microfossils 3.Sediment Provenance 4.Paleomagnetics a)Inclination b)Declination Foraminifera Pollen

Sediment Provenance 100 Myrs Ago Terrane A Transform Boundary River Sediment

Sediment Provenance Today Terrane A Match Sediment to Source

Paleomagnetics: Earth’s Magnetic Field Inclination: Dip of magnetic field relative to Earth’s surface

Paleomagnetics: Inclination Inclination: Dip of magnetic field relative to Earth’s surface 0° 30° 45°90° Inclination = Latitude

Paleomagnetics: Declination Declination: The angle between magnetic north and true north at a particular location.

Location of North Pole Terrane? No - Magnetic declination is consistent All rocks are the same age Magnetic Declination

Location of North Pole Terrane? Yes - Magnetic declination is not consistant All rocks are the same age Magnetic Declination

Location of North Pole Terrane? Yes - Magnetic declination is not consistant All rocks are the same age Location of terrane formation Magnetic Declination

Paleomagnetic Record Preserved in Rocks

How do we know when terranes accreted (docked)? Terrane ATerrane B Rock Age 220 Myrs Rock Age 160 Myrs

How do we know when terranes accreted (docked)? Terrane ATerrane B Rock Age 220 Myrs Rock Age 160 Myrs Accretion Accretion Age = Less than 160 Myrs ago

How do we know when terranes accreted (docked)? Terrane ATerrane B Rock Age 220 Myrs Rock Age 160 Myrs Accretion Age = Between 160 and 110 Myrs ago “Stitching Pluton” - Age = 110 Myrs

How do we know when terranes accreted (docked)? Terrane ATerrane B Rock Age 220 Myrs Rock Age 160 Myrs Accretion Age = between 160 and 125 Myrs ago 110 Myrs Overlap Sequence - Age = 125 Myrs

How do we know when terranes accreted (docked)? Terrane ATerrane B Rock Age 220 Myrs Rock Age 180 Myrs Accretion Age = about 140 Myrs ago Regional Metamorphism - Age = 140 Myrs

How do we know when terranes accreted (docked)? Terrane ATerrane B Rock Age 220 Myrs Rock Age 160 Myrs 110 Myrs Based on age of: 1.Terrane rocks 2.Stiching plutons 3.Overlap sequences 4.Regional metamorphism

Back to the Pacific Northwest…

Major Terranes of WA Covered with younger volcanic and sedimentary rocks Okanogan Highlands Methow Basin North Cascades & San Juan Islands Insular Superterrane Intermontaine Superterrane Kootnay Arc Olympic & Coasgt Mtn Terranes B-2

Edge of North America Myrs B-3 Belt & old basement rock Continental Shelf Sedimentary Rocks B-4 Ocean Sandstone, Shale, Limestone

Edge of North America About 200 Myrs B-3 Belt & old basement rock Ocean B-4 Continental Shelf Sedimentary Rocks New Subduction Zone Forms

Edge of North America About 200 Myrs B-3 Ocean B-4 North American Plate Farallon Plate

Kootnay Arc B-4 Shelf Sediments: Sandstone, Shale, Limestone Metamorphosed to: Quartzite, Slate, Marble

Northeast Washington Metaline Limestone Fm Maitlen Phyllite Fm Addy Quartzite Fm

Pangea Permian (270 Myrs ago) B-2

Breakup of Pangea Jurassic (starting about 200 Myrs ago) B-2

Meanwhile, the Farallon Plate was carrying a large superterrane… B-3 Ocean North American Plate Farallon Plate Intermontain Superterrane

Intermontaine Superterrane Accretes About Myrs B-5 Ocean Subduciton Zone Relocates after accretion

Intermontaine Accretion B-5 Intermontain Superterrane 200 Myrs 150 Myrs

Intermontain Superterrane Amalgamated in Triassic B-6 Terranes 1.Stikinia 2.Cache Creek 3.Quesnellia 4.Slide Mtn

Quesnellia Terrane B-6 Rocks: Volcanic (int.) Greywacke (few limestones) Terrane Type: Island Arc Age: Devonian to Triassic Came from: ???

Cache Creek Terrane B-6 Rocks: Chert/Shale Limestone Basalt/Gabbro Ultramafic Rock Fossils: Tethyian Forams Terrane Type: Ridge/Ocean Crust Age: Mississippian To Triassic Came from: ???

Cache Creek Terrane Chert Tethyian Forams (Fusulinids) in Limestone

Tethys Sea Between Africa/India and Asia B-2

Cache Creek Terrane B-6 Rocks: Chert/Shale Limestone Basalt/Gabbro Ultramafic Rock Fossils: Tethyian Forams Terrane Type: Ridge/Ocean Crust Age: Mississippian To Triassic Came from: Tethys Sea

Stikinia & Slide Mtn Terranes B-6

Intermontaine Ages Stikinia Cache Creek Quesnellia Slide Mountain Kootnay Arc Intermontaine Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Tertiary Precambrian Kootnay Arc Accreted Intermontaine Superterrane Amalgamated Intermontaine Superterrane Accreted

After Accretion - New Volcanic Arc Forms About 150 Myrs B-5 Ocean Subduciton Zone Sediment washes off highlands

Major Terranes of WA Covered with younger volcanic and sedimentary rocks Okanogan Highlands Methow Basin North Cascades & San Juan Islands Insular Superterrane Intermontaine Superterrane Kootnay Arc Olympic & Coasgt Mtn Terranes B-1

Methow Basin B-5

Methow Basin Formation Virginian Ridge Fm Harts Pass Fm Panther Creek Fm Description Chert-pebble conglomerate Western source Arkose Eastern source Greywacke, shale Eastern source Interpretation Eroding volcanoes (arc to the east) Eroding batholiths (arc to the east) Eroding ocean crust (new terrane arriving to the west) Coarser - Basin filling up

Methow Basin - Age Formation Virginian Ridge Fm Harts Pass Fm Panther Creek Fm Intermontaine Superterrane below Myrs Basalt flows above - 89 Myrs Methow Age - Between 150 and 89 Myrs (New terrane to the west must be arriving at the end of that time)

Arrival of the Insular Terrane and the North Cascades… C-3