4. Field trip: This Saturday VOLUNTARY Meet here (to carpool?) and then drive to Bridger to rendezvous with Dr. Zwick at 9 AM. Bring lunch and something to drink. Expect to return in the afternoon

5. The Aleutian Island Chain

6. Seismic activity in the Aleutian Islands

7. Melting of upper mantle and oceanic crust often creates mafic to ultramafic rocks.

8. Basalts (Ophiolites) Marine sediments (cherts, limestones, red clays) Turbidites, clays, silts, sands Granites and Rhyolite Lavas and pyroclastics Rock/sediment type Tectonic setting MaficFelsic

9. Igneous Activity and Plate Tectonics 1 Mafic igneous rocks are commonly formed at divergent boundaries –Increased heat flow and decreased overburden pressure produce mafic magmas from partial melting of the asthenosphere Igneous activity occurs primarily at or near tectonic plate boundaries

10. Composition of the Ocean Crust Seismic surveys suggest oceanic crust is ~7 km thick and comprised of three layers –First layer is marine sediment of various composition and thickness (extensively sampled) –Second layer is pillow basalt overlying basaltic dikes (extensively sampled) –Third layer is thought to be composed of sill-like gabbro intrusions (not directly sampled) Ophiolites are rock sequences in mountain chains on land that are thought to represent slivers of ocean crust and uppermost mantle –Composed of layers 1-3 overlying ultramafic rock

12. Sampled ocean crust Ophiolite Why would we find similar rocks in western Montana/Idaho?

13. Intermediate (chemically) igneous rocks are commonly formed at convergent boundaries Partial melting of basaltic oceanic crust produces intermediate magmas Igneous Activity and Plate Tectonics 2

14. Felsic igneous rocks are commonly formed adjacent to convergent boundaries –Hot rising magma causes partial melting of the granitic continental crust Igneous Activity and Plate Tectonics 3

15. Intraplate volcanism Rising mantle plumes can produce localized hotspots and volcanoes when they produce magmas that rise through oceanic or continental crust. Hawaii is an example Composition?

16. Diamonds ascend to the Earth's surface in rare molten rock, or magma, that originates at great depths. Carrying diamonds and other samples from Earth's mantle, this magma rises and erupts in small but violent volcanoes. Just beneath such volcanoes is a carrot-shaped "pipe" filled with volcanic rock, mantle fragments, and some embedded diamonds. The rock is called kimberlite after the city of Kimberley, South Africa, Ants, erosion and Namibian diamonds

18. > 2.5 Ga 1.6 to 2.5 Ga

20. Namibia

21. The Orange river has delivered diamonds to the Namibian coast for millions of years