Modifying the Coast

Transform Motion

Our Story So Far…

Animated Cordillera - James Sears

Question stillin debate…

Where did the Insular Terrane

actually accrete to North America?

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Intermontaine ST

Insular ST

N. Cascades

Present Day

WA State

Two Hypotheses

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Intermontaine ST

Insular ST &N. Cascades

Hypothesis Aat 90 Myrs

Hypothesis Bat 90 Myrs

WA State

Baja BCHypothesis

Baja BC85 Myrs

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Baja BC80 Myrs

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Baja BC70 Myrs

Baja BC60 Myrs

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Main Evidence for Baja BCPaleomagnetics of Mt. Stuart Batholith

Mt. Stuart90 Myrs30° inclination

Eocene Volc.Rocks<55 Myrs45° inclination(Modern lat.)

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Other Evidence:Sediment Provenance

Inconclusive - needs more study

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Source A

Source B

What do the overlapping

sedimentary rocks tell us?

Other Evidence:Fossils

What do the fossils tell us?

New study - not yet

published

Supports Baja BC

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Other Evidence:Plate Tectonic Reconstructions

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Supports Baja BC

However - there are problems…

1. No major faults discovered

2. Sedimentary rocks around the batholith are tilted…could it be tilted, too?

The Question Remains Unanswered…

Post-Insular Plate Tectonics

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Graphics by Steve Dutch - U of Wisconsin

D-2

80Myr: Formation of the Kula Plate

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D-2

55 Myrs

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D-2

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40 Myrs

D-2

30 Myrs

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D-2

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20 Myrs

D-2

Present

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D-2

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