2. Ancient Northwest The Foundation of a Continent and the Belt Supergroup Logan Pass, Glacier National Park

3. Exposed Rocks of the Precambrian

4. Cordillera A-3 Location in Lecture Handouts

5. Cordillera Part of the North American Mobile Belt Mobile Belt Compared to Craton

6. Anatomy of a Continent Mobile Belt Basement Rock Craton Exposed ancient basement rock Sedimentary rock covering basement rock Continental Shelf

7. How do we study basement rock? Windows (Basement exposed at the surface) Xenoliths/Magma (Carrying pieces of basement to the surface) Drill Cores Samples (Drilling to the basement) Geophysics (“Imaging” the basement)

8. Basement Rock “Windows” in NA A-1 Pacific NW Note: Not many in the west

9. How do we study basement rock? Windows (Basement exposed at the surface) Xenoliths/Magma (Carrying pieces of basement to the surface) Drill Cores Samples (Drilling to the basement) Geophysics (“Imaging” the basement) Mantle Xenolith

10. A-4 Young Basement Old Basement

11. How can we use magma chemistry to tell old/young basement rocks? 1.Rubidium-87 (Rb-87) is radioactive and decays to form Strontium-87 (Sr-87) 2.Rb-87 is common in felsic rocks (continental crust) 3.Young crust - most Rb had not decayed (not much Sr-87) 4.Old crust - lots of Rb has decayed into Sr-87 5.When crust melts - these chemicals end up in magma and magma carries chemical signal to the surface 6.High Sr-87 = old basement below Low Sr-87 = young basement below

12. A-4 Sr87/Sr86 in Plutons > 0.706 (high) < 0.704 (low) “706 Line” > 0.706 (Old Basement Rock) < 0.704 (Young Basement Rock) The Edge of the Old Basement Measure Sr-87 relative to Sr-86

13. How do we study basement rock? Windows (Basement exposed at the surface) Xenoliths/Magma (Carrying pieces of basement to the surface) Drill Cores Samples (Drilling to the basement) Geophysics (“Imaging” the basement)

14. How do we study basement rock? Windows (Basement exposed at the surface) Xenoliths/Magma (Carrying pieces of basement to the surface) Drill Cores Samples (Drilling to the basement) Geophysics (“Imaging” the basement)

15. Seismic Profile

16. Basement Provinces of North America A.K.A. “The United Plates of America” Archean Basement (>2.5 billion years) Proterozoic Basement (2.5-0.5 billion years) Mobile Belts A-2 GF

17. Northwest Basement A-2 GF Wyoming Provenance 2.8-3.5 Gyrs old Includes rocks found in Beartooth Mtns and Grand Teton National Park Hearne Provenance 2.8-3.5 Gyrs old Collision Zone: Great Falls Tectonic Zone (GF) 2.8 Gyrs ago

18. Northwest Basement A-2 GF Collision Zone: Trans-Hudson Belt 1.9-1.8 Gyrs ago Wyoming/Hearne collide with Superior Provenance By 1.8 Gyrs the basement rock of NA was in place