Download - 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
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
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
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
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
Mantle geoneutrino emission
Mantle geoneutrino U+Th signal prediction
N/A
Cosmochemical Geochemical Geodynamical
"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
Mantle geoneutrino emission
N/A
Cosmochemical Geochemical Geodynamical
"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
Mantle geoneutrino U+Th signal prediction
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
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
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
O.Š., McDonough, Kite, Lekić, Dye, Zhong, EPSL 2013
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
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)
1−kiloton detector
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
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
Prediction along 161°W meridian
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
Mantle contribution to total signal
O.Š., McDonough, Kite, Lekić, Dye, Zhong, EPSL 2013
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
10−kiloton detector
(Hanohano)
1−kiloton detector
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