earth models and primordial heat

Earth models and primordial heat... and geonu emission from deep mantle piles

Ondřej ŠrámekUniversity of Maryland

Collaborators: Bill McDonough & Vedran Lekić (Univ. Maryland) Edwin Kite (Caltech) Steve Dye (Hawaii Pacific Univ.) Shijie Zhong (Univ. Colorado at Boulder)

presented at Neutrino Geoscience 2013, Takayama (Japan), 21–23 March 2013

Present-day dynamics

Quantify major energy terms

Earth’s bulk composition

Spatial distribution of radioactivity

Geoneutrino constraints

Present-day Earth

U Th K

???

?

??

Building blocks

Solar nebula

Planetary formation

Early differentiation processesFirst few 100 MyCore formationMagma ocean

Ongoing dynamic evolutionChemical fractionation vs. homogenizationCrust formationSubductionMantle, core dynamics

Solar System formation Present-day Earthtime

Planetary formationSolar nebula composition

Big Bang (H, He, Li) + stellar (higher Z) nucleosynthesis

Compositional gradients, heterogeneity in the cooling solar nebula?

Condensation temperature, volatilityU & Th refractory, K moderately volatile

Planetary formationLast stage of planetary formation.Outcome of 4 simulations – planet position, radius, composition in terms of original heliocentric distance of material.

Chambers, EPSL 2011

Some memory of compositional gradient in the nebula

color = original radial location of material





Dust & gas to grains to planetesimalsPlanetesimals to planetary embryos ~1 MyLast stage ~100 My

Giant impactsPlanet radial migration

The “Grand Tack Scenario” Walsh et al. 2011

Jupiter formed at ~3.5 AU

Spiraled inward to ~1.5 AU (present-day Mars orbit) due to gas drag

Then migrated outward to current location at 5.2 AU

Saturn experienced a similar sequence

• Can explain the small size of Mars

• Consistent with the existence of asteroidal belt

• May have rid the inner Solar System of volatiles

Inward-then-outward migration of Jupiter, Saturn





Dust & gas to grains to planetesimalsPlanetesimals to planetary embryos ~1 MyLast stage ~100 My

Giant impactsPlanet radial migration

Hot beginningGravitational energy released upon accretion, differentiation

Extensive melting, magma ocean(s)Incompatibility, solid vs. melt partitioning

U, Th, K incompatible, enter the melt

Gravitational energy

of accretion – forming a homogeneous body

dispersed in space planet

Earth:ΔTacr = GM2/R / (MCP)

~ 5 × 104 K

Eacr = GM2/R

Eg = 4⇡

RZ

0

g(r)⇢(r)r3dr

undifferentiated differentiated

of differentiation – forming the core

ΔTdiff ~ 2000 K

petrological constraint based on inference of melting temperature of primitive mantle melts

Abbott et al. JGR 1994

inferred cooling rate of 50 ± 25 K/Gy

translates into 8 ± 4 TW mantle heat output due to cooling

Loosing primordial heat – Mantle cooling rate

Giant impacts, Moon formation, magma oceanFrom Hf–W chronology (Kleine et al. GCA 2009):Core formation at ~30–100 My after beginning of Solar SystemMoon formation

Deep magma ocean (metal–silicate equilibration at >400 km depth; Wood et al. Nature 2006)Siderophile elements go in the coreLithophile elements go in the silicate phase: negligible in U, Th, K in the core

Core formationmajor chemical

differentiation event

Makes sense to talk about “Silicate Earth”

Composition of Silicate Earth (BSE)U Th K

• “Geochemical” estimate

• “Cosmochemical” estimate

• “Geodynamical” estimate

Composition of CI chondrites matches solar photospheric abundances in refractory lithophile, siderophile, and volatile elements.

Wood Phys.Today 2011

Best representative of primordial nebular material

Most primitive, highest volatile abundance of chondrites

Geochemical BSE estimate(s)

Ratios of Refractory Lithophile Element abundances constrained by CI chondrites

Absolute RLE abundances and non-refractory element abundances inferred from available mantle & crustal rock samples

Uses petrological models on peridotite xenoliths, massif peridotites, primitive melts

McDonough & Sun (1995) ... 20 ± 4 ppb UAllègre (1995) ... 21 ppb UHart & Zindler (1986) ... 20.8 ppb UPalme & O’Neill (2003) ... 22 ± 3 ppb U

Results in ~20 TW radiogenic power in BSE

Cosmochemical BSE estimate

Isotopic similarity between Earth rocks and enstatite chondrides

Similarity in oxidation state

Build the Earth from E-chondrite material

Javoy et al. EPSL 2010 ... 12 ppb U

Gives ~11 TW radiogenic power in BSE

Also “collisional erosion” model (O’Neill & Palme 2008)

Earth formed with “geochemical” abundances (22 ppm U in BSE)

Differentiated early crust (enriched in U, Th, K)

This crust was lost during a giant impact collision → 10 ppm U in BSE

Fri AM: Claude Jaupart

Geodynamical BSE estimate

Based on energetics of mantle convection

Parameterized convection models:

heat loss = radiogenic heating + secular cooling

Classical scaling between Qs (Nusselt number) and vigor of convection (Rayleigh number)

Need a large proportion of radiogenic heating to account for mantle heat flow, otherwise “thermal catastrophe” in the Archean

Requires mantle Urey ≥ 0.6 (geochemical = 0.3, cosmochemical = 0.1)

Therefore needs higher abundance of U, Th, K

Radiogenic heating ≥ 30 TW in BSE

Qs(t) = Hrad(t)� CdT (t)

dt

Nu / Ra(T )1/3

Thu PM: John Crowley

• “Geochemical” estimate– Ratios of RLE abundances constrained by C1 chondrites– Absolute abundances inferred from Earth rock samples– McDonough & Sun (1995), Allègre (1995), Hart & Zindler (1986), Palme & O’Neill (2003), Arevalo et al. (2009)

• “Cosmochemical” estimate– Isotopic similarity between Earth rocks and E-chondrides– Build the Earth from E-chondrite material– Javoy et al. (2010)– also “collisional erosion” models (O’Neill & Palme 2008)

20±4

11±2

33±3

BSE Mantle

3±2

12±4

25±3• “Geodynamical” estimate

– Based on a classical parameterized convection model– Requires a high mantle Urey ratio, i.e., high U, Th, K

TW radiogenic power

?

Composition of Silicate Earth (BSE)U Th K

BSE = Mantle + CrustOceanic: 0.22 ± 0.03 TWContinental: 7.8 ± 0.9 TWCRUST2.0

thickness Tomorrow: New crustal model by Yu Huang et al.CC = 6.8 (+1.4/-1.1) TW

How is radioactivity distributed in the mantle?

?Educated hypothesis → Geoneutrino flux prediction →

Testing with geoneutrino measurement

Mantle geoneutrino emission

Uniform mantle

�(r) =n⌫�hP i

4⇡

Z

⌦

A(r0)⇢(r0)

|r� r0|2 dr0

Flux Φ at position r from a given radionuclide distributed with abundance A in volume Ω

Mantle geoneutrino U+Th signal prediction

Cosmochemical Geochemical Geodynamical

"UNIF" mantle

0

5

10

15

20

25

TN

U

4.1 ± 1.2Salters & Stracke (2004)

Workman & Hart (2005) 2.8 ± 0.4

7.5 ± 1.5

MORB-source mantle abundance estimates

Arevalo & McDonough (2010)

TW if occupying entire mantle

Shallow mantle composition

Require enriched material in the mantle

Geochemical

CosmochemicalBulk mantle (=BSE−Crust)

Geodynamical

3.3 ± 2.012 ± 425 ± 3

TW

?Mid-Oceanic Ridge Basalt composition

→source rock abundances

in shallow mantle

Uniform mantle Enriched layer (10% of mantle)

Spherically symmetric U & Th distribution in the mantle



N/A


"UNIF" mantle

"EL" with A&McD DM

"EL" with S&S DM

"EL" with W&H DM

0

5

10

15

20

25

TN

U

Mantle geoneutrino U+Th signal predictionUniform mantle Enriched layer (10% of mantle)

Measurements

Combined analysis of detection at KamLAND and Borexino (Bellini et al. arXiv:1303.2571)

Spherically symmetrical U & Th distribution in the mantle


N/A


"UNIF" mantle

"EL" with A&McD DM

"EL" with S&S DM

"EL" with W&H DM

0

5

10

15

20

25

TN

U

+ new KamLAND data ??

Bull et al. EPSL 2009

Seismic shear wave speed anomalyTomographic model S20RTS (Ritsema et al.)

Two large scale seismic speed anomalies – below Africa and below central Pacific

Anti-correlation of shear and sound wavespeeds + sharp velocity gradients suggest a compositional component

Seismic tomography image of present-day mantle

Candidate for an distinct chemical reservoir

“piles” or “LLSVPs” or “superplumes”

Sat AM: Ed Garnero

Origin of deep mantle reservoir

Remnant of dense basal magma ocean at the bottom of the mantle?

Labrosse et al. EPSL 2006

the presumed building-blocks of our planet, thechondritic meteorites.

4. Implications of the non-chondritic 142Nd/144Nd interrestrial rocks

The 142Nd excess in terrestrial rocks compared tochondrites potentially can be explained in one of threeways. 1) The difference reflects imperfect mixing of r-and s-process nuclides in the solar nebula. In this case,

the variation in 142Nd is not due to 146Sm decay butinstead reflects nucleosynthetic anomalies in meteoritescompared to Earth. 2) The Earth has a Sm/Nd ratiohigher than chondritic. 3) The Earth experienced aglobal differentiation while 146Sm was still present thatled to the formation of chemically complimentary re-servoirs within the Earth, one with Sm/Nd higher, andone with Sm/Nd lower, than chondritic.

4.1. Nucleosynthetic anomalies

This suggestion was made in light of the discovery ofisotopic variation in Ba in chondrites [34], and followson recent discoveries of isotope anomalies in Mo, Ru[35] and Os [30] at the whole meteorite scale. For themeteorite analyses reported in Boyet and Carlson [9],Sm isotopic composition also was determined primarilyas a measure of the neutron capture effects on 149Sm dueto cosmic ray exposure, which also can affect 142Nd. Smhas two pure s-process isotopes, 148Sm and 150Sm, and142Nd also is produced purely by the s-process. 150Smalso is produced by neutron addition to 149Sm and hencecannot be used to check for nuclear anomalies in sam-ples, such as meteorites, that have experienced exposureto cosmic rays (Fig. 2). Based on the few calcium–aluminum-rich inclusions in the carbonaceous chondriteAllende where incomplete mixing of s- and r-processnuclides has been clearly demonstrated, a 20 ppm deficitin 142Nd should be accompanied by a roughly 70 ppmdeficit in 148Sm [36].

As shown in Fig. 2, measurements of 148Sm/152Sm inthe meteorites analyzed by Boyet and Carlson [9]overlap within uncertainty with the terrestrial standard.The average 148Sm/152Sm measured for Allende showsa 27±13 ppm excess compared to the terrestrial Smstandard, but ordinary chondrites (2±15 ppm), eucrites(−17±18 ppm), and Isua samples (−12±12 ppm) showno resolvable difference in 148Sm/152Sm. These resultsthus do not support the suggestion that the difference in142Nd/144Nd between meteorites and terrestrial rocksreflects nucleogenic isotope anomalies in meteoritic Nd.Instead, they support the suggestion that this differenceis the result of the decay of now extinct 146Sm.

4.2. A non-chondritic Earth

The Earth's mantle does not have chondritic abun-dances of many elements, for example siderophile andvolatile elements (e.g. [37]). The former group ofelements presumably is sequestered away in Earth'score, while the volatile elements may never have beenpresent in chondritic abundances in the terrestrial

Fig. 1. 142Nd/144Nd in the samples analyzed here, expressed (ε142Nd) asparts in 10,000 deviation from the average measured for the La JollaNd standard, which is approximately 0.2 ε142Nd higher than theaverage measured for chondrites and eucrites [9]. The grey bar showsthe average external precision obtained on repeat analyses of the samesample. Error bars on the individual points show the 2σ deviationobtained for multiple measurements of each sample. Only 5 samplesfrom Isua show deviation outside of analytical uncertainty from the142Nd/144Nd measured for La Jolla Nd.

258 M. Boyet, R.W. Carlson / Earth and Planetary Science Letters 250 (2006) 254–268

Boyet & Carlson EPSL 2006

Early differentiation of primordial mantle?

Next talk: Dapeng Zhao

Fri AM: Sujoy MukhopadhyaySat AM: Matt Jackson

Continuously recycled subducted slabs buried at core–mantle boundary?

Thermochemical piles in deep mantle?

O.Š., McDonough, Kite, Lekić, Dye, Zhong, EPSL 2013

KamiokaGran Sasso

Sudbury

Hawaii

Pyhasalmi

HomestakeBaksan

Mantle geoneutrino signal − thermochemical piles

8.0

8.5

9.0

9.5

10.0

10.5TNU


Can we detect such variation in mantle geonu flux?

LLSVPs

Assume these piles represent an enriched reservoir. δlnVs isocontours ⇒ shape

Crust + Mantle geoneutrino emission

Longitude = 161 W

Crust Mantle, geodynamical

Mantle, geochemical

Mantle, cosmochemical

Site #1

Site #2

A&McD DMS&S DMW&H DM

Geochemical BSEA&McD DM

0

5

10

15

20

25

30

35

TN

U

−90−60−300306090Latitude in degrees

Site #1

Site #2

Mantle / Total

20

30

40

50

60

70

80%

Crust+mantle geoneutrino signal

15

20

25

30

35

40

45

50

55TNU

Crust + mantle

Longitude = 161 W


Mantle, geochemical


Site #1

Site #2



0

5

10

15

20

25

30

35

TN

U


Site #1

Site #2

Mantle / Total

20

30

40

50

60

70

80%


15

20

25

30

35

40

45

50

55TNU

Mantle contribution to total signal

To constrain mantle Th, U, we need to measure in the ocean.

Hanohano (proposed)

Continental locations: not more than ~25% of geonu signal coming from mantle


Longitude = 161 W


Mantle, geochemical


Site #1

Site #2



0

5

10

15

20

25

30

35

TN

U


Site #1

Site #2

Mantle / Total

20

30

40

50

60

70

80%


15

20

25

30

35

40

45

50

55TNU

Prediction along 161°W meridian

KamiokaGran Sasso

Sudbury

Hawaii

Pyhasalmi

HomestakeBaksan

Mantle geoneutrino signal − thermochemical piles

8.0

8.5

9.0

9.5

10.0

10.5TNU

Spher

ically

sym

met

ric m

antle

TOMO model −

deep mantle

pilesResolvable d

iffere

nce

Geodynamical

Geochemical

Cosmochemical

central value

+/− 1σ

A&McD DM

S&S DM

W&H DM

0

4

8

12

16

20

24

Pre

dic

ted

eve

nt

rate

at

site

#2

in T

NU

0 4 8 12 16 20 24 28 32Predicted event rate at site #1 in TNU

10−kiloton detector

(Hanohano)


live−timein months

un

iform

ma

ntle

no

t re

solv

ab

le

Cosmo−chemical Geochemical Geodynamical

0.5

1

2

5

10

20

De

tect

or

size

in 1

03

2 f

ree

pro

ton

s

0 4 8 12 16 20 24 28 32Mean event rate in TNU

100 101 102 103 104

Proposed two-site measurement in the Pacific

Longitude = 161 W


Mantle, geochemical


Site #1

Site #2



0

5

10

15

20

25

30

35

TN

U


Site #1

Site #2

Mantle / Total

20

30

40

50

60

70

80%


15

20

25

30

35

40

45

50

55TNU

Prediction along 161°W meridian

Longitude = 161 W


Mantle, geochemical


Site #1

Site #2



0

5

10

15

20

25

30

35

TN

U


Site #1

Site #2

Mantle / Total

20

30

40

50

60

70

80%


15

20

25

30

35

40

45

50

55TNU

Mantle contribution to total signal


Spher

ically

sym

met

ric m

antle

TOMO model −

deep mantle

pilesResolvable d

iffere

nce

Geodynamical

Geochemical

Cosmochemical

central value

+/− 1σ

A&McD DM

S&S DM

W&H DM

0

4

8

12

16

20

24

Pre

dic

ted e

vent ra

te a

t si

te #

2 in

TN

U

0 4 8 12 16 20 24 28 32Predicted event rate at site #1 in TNU


(Hanohano)


live−timein months

unifo

rm m

antle

not re

solv

able

Cosmo−chemical Geochemical Geodynamical

0.5

1

2

5

10

20

Dete

ctor

size

in 1

03

2 fre

e p

roto

ns

0 4 8 12 16 20 24 28 32Mean event rate in TNU

100 101 102 103 104

detection uncertainty(crustal, reactor, other bg)

not resolvedresolved!

• Process of planetary formation

• Hot beginning of the Earth

• Early differentiation events– core formation– early fractionation of silicate Earth?

• Three classes of BSE compositional models

• [ Enstatite chondrite model inconsistent with geonu measurements (1σ) ? ]

• Ocean site measurement needed to significantly constrain mantle radioactivity. Multiple-site to resolve lateral variations.

Summary

earth models and primordial heat

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