1. Defining the Boundaries of the Volcanic Field about Yucca Mountain, Nevada: Implications for Volcanic Hazard Studies Eugene Smith Deborah Keenan UNLV and Geoscience Consultants V31E-03

2. TM BM PCF SB LW QCF Amargosa Desert Jackass Flats Crater Flat Yucca Flat Yucca Mountain Studies of volcanism are important because basaltic activity has occurred in the Yucca Mountain area since 11.2 Ma and eight Quaternary alkali basalt volcanoes ranging in age from 1 Ma to 80 ka occur within 50 km of the proposed repository Base map from F. Perry (LANL)

3. TM BM PCF SB LW QCF Timber Mountain Caldera Complex Amargosa Desert Jackass Flats Crater Flat Yucca Flat AMRV Crater Flat zone Amargosa Trough Base map from F. Perry (LANL)

4. From presentation by Richard Carlson (PVHA-U) A shrinking field More or less centered on the Timber Mountain caldera Based on the Amargosa Valley Isotope Province (AVIP) of Yogodzinski and Smith (1995)

5. Lunar Crater Reveille Range Yucca Mountain Death Valley Death Valley-Pancake Range Belt (Vaniman et al. 1982).

7. Crater Flat-Lunar Crater Volcanic Field From Smith et al. (2002) and Smith and Keenan (2005)

8. Lunar Crater volcanic field Reveille Range Buckboard Mesa Sleeping Butte and Thirsty Mesa Crater Flat Yucca Mountain 0 30 Km N Index Map 38° N 37° N 117° W 116° W 115° W

9. 9.5-6.5 Ma

10. 6.5-5.5 Ma

11. 5.5-4.5 Ma

12. 4.5-3.5 Ma

13. 3.5-2.5 Ma

14. 2.5-1.5 Ma

15. 1.5-0.5 Ma

16. 0.5-0.02 Ma

17. 0 30 Km N 38° N 37° N 117° W 116° W 115° W 0.5-0.02 Ma 2.5-1.5 Ma 5.5-4.5 Ma 6.5-5.5 Ma 9.5-6.5 Ma 4.5-3.5 Ma 3.5-2.5 Ma 1.5-0.5 Ma

18. 0 30 Km N 38° N 37° N 117° W 116° W 115° W 0.5-0.02 Ma 2.5-1.5 Ma 5.5-4.5 Ma 6.5-5.5 Ma 9.5-6.5 Ma 4.5-3.5 Ma 3.5-2.5 Ma 1.5-0.5 Ma

19. 0 30 Km N 38° N 37° N 117° W 116° W 115° W 0.5-0.02 Ma 2.5-1.5 Ma 5.5-4.5 Ma 6.5-5.5 Ma 9.5-6.5 Ma 4.5-3.5 Ma 3.5-2.5 Ma 1.5-0.5 Ma

20. Number of Volcanic Events vs. Age 0.5 m.y. bins

21. Magnetic Anomalies in the Crater Flat-Amargosa Desert Area From O’Leary et al. (2002) Age of buried volcanoes Unknown If many are 3.5 Ma then higher recurrence rates in the past 6 Ma Because volcanism is episodic, another peak of activity with higher recurrence rates is possible in the future.

22. Southwestern Utah Coso-Big Pine Crater Flat Reveille Lunar Crater

23. Adding data from southwestern Utah

24. Coso-Lone Pine Volcanic Field

25. Melting beneath the Crater Flat–Lunar Crater zone is especially deep. Deep melting requires hot and buoyant mantle with mantle potential temperatures about 200 °C greater than those in the western Great Basin (Wang et al., 2002). From Wang et al. (2002)

26. Thickening of lithosphere during Paleozoic and Mesozoic tectonic events along the western boundary of the craton, and thinning of lithosphere beneath the Sierra Nevada may have resulted in the formation of a mantle keel.

27. Asthenosphere Lithospheric Mantle Crust Partial Melting Mantle Eddy Edge Effect Melting Next Area of Hot Mantle

28. Western US relative P- velocity variations Low velocity zones (red) may be areas of hotter lithosphere or asthenospheric. From presentation by K. Dueker, University of Wyoming

29. 87 Sr/ 86 Sr  nd Lunar Crater Reveille Range Yucca Mountain area -20 -15 -10 -5 0 5 10 0.7020.7040.7060.7080.71 What is the explanation for the different isotopic and trace element characteristics between Lunar Crater and Crater Flat?

30. Model Crust LM Asthenosphere LC Lunar Crater type magma produced by melting of asthenospheric mantle 1% melting of harzburgite 4.6 ppm Nd, 143 Nd/ 144 Nd=0.511514,  Nd =-20 LC + 8% LM melt Crater Flat type magma

31. Nd 143 Nd/ 144 Nd Lunar Crater 8% Crater Flat Is there an old Lithospheric mantle (early Proterozoic or late Archean) in the southern Great Basin? Lee et al. (2001) in Nature Indicate that old LM exists in Great Basin. Re-Os model ages of 1.8 to 3.4 Ga.

32. Main Points Consider Crater Flat- Lunar Crater belt when doing hazard assessment. Consider Crater Flat- Lunar Crater belt when doing hazard assessment.

33. Main Points Magma generation controlled by interaction of lithosphere and mantle. Magma generation controlled by interaction of lithosphere and mantle. Partial melting of asthenosphere to produce basalt magma. Partial melting of asthenosphere to produce basalt magma.

34. Main Points Geochemistry of basalt in Yucca Mountain area may be explained by contamination with old (Archean) mafic lithospheric mantle. Geochemistry of basalt in Yucca Mountain area may be explained by contamination with old (Archean) mafic lithospheric mantle. Crust LM Asthenosphere LC

35. Main Points Volcanism is episodic and future peaks of activity are possible within the compliance period especially if the new EPA standard is used (1 Ma). Volcanism is episodic and future peaks of activity are possible within the compliance period especially if the new EPA standard is used (1 Ma). Recurrence rates of 11-15 events/m.y. possible. Recurrence rates of 11-15 events/m.y. possible.