Defining the Boundaries of Defining the Boundaries of the Volcanic Field about the Volcanic Field about

Yucca Mountain, Nevada: Yucca Mountain, Nevada: Implications for Volcanic Implications for Volcanic

Hazard StudiesHazard Studies

Eugene SmithEugene Smith

Deborah KeenanDeborah KeenanUNLV and Geoscience ConsultantsUNLV and Geoscience Consultants

V31E-03

TMBM

PCF

SB

LW

QCF

Amargosa Desert

Jackass Flats

CraterFlat

YuccaFlat

Yucca Mountain

Studies of volcanism are Studies of volcanism are importantimportant

because basaltic activity hasbecause basaltic activity has

occurred in the Yucca Mountainoccurred in the Yucca Mountain

area since 11.2 Ma and eightarea since 11.2 Ma and eight

Quaternary alkali basalt Quaternary alkali basalt volcanoesvolcanoes

ranging in age from 1 Ma to 80 ranging in age from 1 Ma to 80 kaka

occur within 50 km of theoccur within 50 km of the

proposed repositoryproposed repository

Base map from F. Perry (LANL)

TMBM

PCF

SB

LW

QCF

Timber Mountain Caldera Complex

Amargosa Desert

Jackass Flats

CraterFlat

YuccaFlat

AMRV

Crater Flat zone

Amargosa Trough

Base map from F. Perry (LANL)

From presentation by Richard Carlson (PVHA-U)

A shrinking fieldMore or lesscentered on the Timber Mountaincaldera

Based on the AmargosaValley Isotope Province(AVIP) of Yogodzinskiand Smith (1995)

Lunar Crater

Reveille Range

Yucca Mountain

Death Valley

Death Valley-Pancake Range Belt (Vaniman et al. 1982).

Crater Flat-Lunar Crater Volcanic Field

From Smith et al. (2002) and Smith and Keenan (2005)

Lunar Cratervolcanic field

Reveille Range

Buckboard Mesa

Sleeping Butte and Thirsty Mesa

CraterFlat Yucca Mountain

0 30Km

N

Index Map

38° N

37° N

117° W 116° W 115° W

9.5-6.5 Ma

6.5-5.5 Ma

5.5-4.5 Ma

4.5-3.5 Ma

3.5-2.5 Ma

2.5-1.5 Ma

1.5-0.5 Ma

0.5-0.02 Ma

0 30Km

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

0 30Km

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

0 30Km

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

0

2

4

6

8

10

12

0123456789101112131415

AgeN

um

ber

of

Eve

nts

Lunar Crater-Reveille

Crater Flat

Number of Volcanic Events vs. Age

0.5 m.y. bins

Magnetic Anomalies in the Crater Flat-Amargosa Desert Area

From O’Leary et al. (2002)

Age of buried volcanoesUnknown

If many are 3.5 Ma thenhigher recurrence rates in the past 6 Ma

Because volcanism is episodic, another peakof activity with higherrecurrence rates is possible in the future.

SouthwesternUtah

Coso-Big Pine

Crater Flat

Reveille

Lunar Crater

0

2

4

6

8

10

12

0123456789101112131415

AgeN

um

ber

of

Eve

nts

Lunar Crater-Reveille

Crater Flat

SW Utah

Adding data from southwestern Utah

0

2

4

6

8

10

12

0123456789101112131415

AgeN

um

ber

of

Eve

nts

Lunar Crater-Reveille

Crater Flat

Coso

Coso-Lone Pine Volcanic Field

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

From Wang et al. (2002)

Thickening of lithosphereduring Paleozoic and Mesozoic tectonic events along the western boundary of the craton,and thinning of lithospherebeneath the Sierra Nevadamay have resulted in the formation of a mantle keel.

Asthenosphere

Lithospheric Mantle

Crust

Partial Melting

Mantle Eddy

Edge Effect Melting

Next Area of Hot Mantle

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 

87Sr/86Sr

nd

Lunar Crater

Reveille Range

Yucca Mountain area

-20

-15

-10

-5

0

5

10

0.702 0.704 0.706 0.708 0.71

What is the explanation for the different isotopic What is the explanation for the different isotopic and trace element characteristics between Lunar and trace element characteristics between Lunar Crater and Crater Flat?Crater and Crater Flat?

ModelModel

Crust

LM

Asthenosphere

LCLC

Lunar Crater type magma produced by melting of asthenospheric mantle

1% melting of harzburgite 4.6 ppm Nd, 143Nd/144Nd=0.511514, Nd=-20

LC + 8% LM melt

Crater Flat type magma

0.5116

0.5118

0.512

0.5122

0.5124

0.5126

0.5128

0.513

50 70 90 110 130 150 170 190 210

Nd (ppm)

143/1

44

Nd

143 N

d/14

4 Nd

Lunar Crater

8%

Crater Flat

Is there an oldLithospheric mantle(early Proterozoic or lateArchean) in the southernGreat Basin?

Lee et al. (2001) in NatureIndicate that old LMexists in Great Basin.Re-Os model ages of 1.8 to 3.4 Ga.

Main PointsMain Points

Consider Crater Consider Crater Flat-Lunar Crater Flat-Lunar Crater belt when doing belt when doing hazard hazard assessment.assessment.

Main PointsMain Points

Magma generation Magma generation controlled by controlled by interaction of interaction of lithosphere and lithosphere and mantle.mantle.

Partial melting of Partial melting of asthenosphere to asthenosphere to produce basalt produce basalt magma.magma.

Main PointsMain Points

Geochemistry of basalt in Yucca Mountain Geochemistry of basalt in Yucca Mountain area may be explained by contamination area may be explained by contamination with old (Archean) mafic lithospheric with old (Archean) mafic lithospheric mantle.mantle.

Crust

LM

AsthenosphereLC

LC

Main PointsMain Points

Volcanism is episodic Volcanism is episodic and future peaks of and future peaks of activity are possible activity are possible within the within the compliance period compliance period especially if the new especially if the new EPA standard is used EPA standard is used (1 Ma).(1 Ma).

Recurrence rates of Recurrence rates of 11-15 events/m.y. 11-15 events/m.y. possible.possible.

0

2

4

6

8

10

12

0123456789101112131415

Age

Nu

mb

er o

f E

ven

tsLunar Crater-Reveille

Crater Flat