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Models of the Earth: thermal evolution and Geoneutrino studies

Models of the Earth: thermal evolution and Geoneutrino studies. Bill McDonough , Yu Huang and Ondřej Šrámek Geology, U Maryland Steve Dye , Natural Science, Hawaii Pacific U and Physics, U Hawaii Shijie Zhong , Physics, U Colorado Fabio Mantovani , Physics, U Ferrara, Italy.

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Models of the Earth: thermal evolution and Geoneutrino studies

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  1. Models of the Earth: thermal evolution and Geoneutrino studies Bill McDonough, Yu Huang and OndřejŠrámek Geology, U Maryland Steve Dye, Natural Science, Hawaii Pacific U and Physics, U Hawaii ShijieZhong, Physics, U Colorado Fabio Mantovani, Physics, U Ferrara, Italy

  2. Earth Models Update: …just the last 6 months! Campbell and O’Neill (March - 2012, Nature): “Evidence against a chondritic Earth” Murakami et al (May - 2012, Nature): “…the lower mantle is enriched in silicon … consistent with the [CI] chondritic Earth model.” Warren (Nov - 2011, EPSL): “Among known chondrite groups, EH yields a relatively close fit to the stable-isotopic composition of Earth.” Zhang et al (March - 2012, Nature Geoscience): The Ti isotopic composition of the Earth and Moon overlaps that of enstatite chondrites. Fitoussi and Bourdon (March - 2012, Science): “Si isotopes support the conclusion that Earth was not built solely from enstatitechondrites.” - Compositional models differ widely, implying a factor of two difference in the U & Th content of the Earth

  3. Nature & amount of Earth’s thermal power radiogenic heating vs secular cooling - abundance of heat producing elements (K, Th, U) in the Earth - clues to planet formation processes - amount of radiogenic power to drive mantle convection & plate tectonics - is the mantle compositionally layered or have large structures? estimates of BSE from 9TW to 36TW constrains chondritic Earth models estimates of mantle 1TW to 28TW layers, LLSVP, superplume piles Geoneutrino studies

  4. U content of BSE models • Nucelosynthesis: U/Si and Th/Si production probability • Solar photosphere: matches C1 carbonaceous chondrites • Estimate from Chondrites: ~11ppb planet (16 ppb in BSE) • Heat flow: secular cooling vs radiogenic contribution… ? • Modeling composition: which chondrite should we use? • A brief (albeit biased) history of U estimates in BSE: • Urey (56) 16 ppbTurcotte & Schubert (82; 03) 31 ppb • Wasserburg et al (63) 33 ppb Hart & Zindler (86) 20.8 ppb • Ganapathy & Anders (74) 18 ppb McDonough & Sun (95) 20 ppb ± 20% • Ringwood (75) 20 ppbAllegre et al (95) 21 ppb • Jagoutz et al (79) 26 ppb Palme & O’Neill (03) 22 ppb ± 15% • Schubert et al (80) 31 ppbLyubetskaya & Korenaga (05) 17 ppb ± 17% • Davies (80) 12-23 ppbO’Neill & Palme (08) 10 ppb • Wanke (81) 21 ppb Javoy et al (10) 12 ppb

  5. What is the composition of the Earth? and where did this stuff come from? Nebula Meteorite Heterogeneous mixtures of components with different formation temperatures and conditions Planet: mix of metal, silicate, volatiles

  6. “Standard” Planetary Model • Orbital and seismic (if available) constraints • Chondrites, primitive meteorites, are key • So too, the composition of the solar photosphere • Refractory elements (RE) in chondritic proportions • Absolute abundances of RE – model dependent • Mg, Fe, Si & O are non-refractory elements • Chemical gradient in solar system • Non-refractory elements: model dependent • U & Th are RE, whereas K is moderately volatile

  7. Most studied meteorites fell to the Earth ≤0.5 Ma ago

  8. Mg/Si variation in the SS Forsterite -high temperature -early crystallization -high Mg/Si -fewer volatile elements Enstatite -lower temperature -later crystallization -low Mg/Si -more volatile elements

  9. Inner nebular regions of dust to be highly crystallized, Outer region of one star has - equal amounts of pyroxeneand olivine - while the inner regions are dominated by olivine. Boekel et al (2004; Nature) Olivine-rich Ol & Pyx

  10. Olivine-rich Pyrolite-EARTH CO CV CI CM H LL L EL Enstatite-EARTH EH Pyroxene-rich

  11. Earth @ 1 AU Mars @ 2.5 AU Olivine-rich EARTH CO CV CI CM H LL L MARS SS Gradients EL -thermal -compositional -redox EH Pyroxene-rich

  12. Si Fe Mg weight % elements Moles Fe + Si + Mg + O = ~93% Earth’s mass (with Ni, Al and Ca its >98%)

  13. Volatiles (alkali metals) in Chondrites • EnstatiteChondrites • enriched in volatile elements • High 87Sr/86Sr [c.f. Earth] • 40Ar enriched [c.f. Earth] CI and Si Normalized

  14. Earth 142mNd Enstatite chondrites • What does this Nd data mean for the Earth? • Solar S heterogeneous • Chondrites are a guide • Planets ≠ chondrites ? Ordinary chondrites Carbonaceous chondrites Data from: Gannoun et al (2011, PNAS) Carlson et al (Science, 2007) Andreasen& Sharma (Science, 2006) Boyet and Carlson (2005, Science) Jacobsen & Wasserburg (EPSL, 1984)

  15. Enstatitechondrite vs Earth Carbonaceous chondrites diagrams from Warren (2011, EPSL) Carbonaceous chondrites Carbonaceous chondrites

  16. Earth is “like” an EnstatiteChondrite! Mg/Si -- is very different shared isotopic: O, Ti, Ni, Cr, Nd,.. shared origins -- unlikely core composition -- no K, Th, U in core “Chondritic Earth” -- losing meaning… 6) Javoy’smodel – recommend modifications

  17. Th & U K from McDonough & Sun, 1995

  18. U in the Earth: • ~13 ng/g U in the Earth • Metallic sphere (core) • <<<1 ng/g U • Silicate sphere • 20* ng/g U • *Javoy et al (2010) predicts 12 ng/g • *Turcotte & Schubert (2002) 31 ng/g • Continental Crust • 1300 ng/g U • Mantle • ~12 ng/g U “Differentiation” Chromatographic separation Mantle melting & crust formation

  19. vigor of convection Parameterized Convection Models • h = viscosity • = density • g = accel. due gravity • a = thermal exp. coeff. • = thermal diffusivity • d = length scale • T = boundary layer To Thermal evolution of the mantle QRab Q: heat flux, Ra: Rayleigh number, : an amplifer - balance between viscosity and heat dissipation rogan(T1– T0)d3 Ra = hk Ramantle > Racritical mantle convects! At what rate does the Earth dissipate its heat? • Models with b~ 0.3 --- Schubert et al ‘80; Davies ‘80; Turcotte et al ‘01 • Models with b << 0.3 --- Jaupart et al ‘08; Korenaga ‘06; Grigne et al ‘05,’07

  20. Convection Urey Ratio and Mantle Models • Mantle convection models typically assume: mantleUrey ratio: ~0.7 • Geochemical models predict: mantleUrey ratio ~0.3 radioactive heat production Urey ratio = heat loss Factor of 2 discrepancy

  21. Earth’s surface heat flow 46 ± 3 (47 ± 2) Mantle cooling (18 TW) Crust R* (8 ± 1 TW) Core (~9 TW) - (4-15 TW) Mantle R* (12 ± 4 TW) total R* 20 ± 4 *R radiogenic heat (0.4 TW) Tidal dissipation Chemical differentiation after Jaupart et al 2008 Treatise of Geophysics

  22. Plate Tectonics, Convection, Geodynamo Radioactive decay driving the Earth’s engine!

  23. 2011 Detecting Geoneutrinos from the Earth 2005 2010

  24. Terrestrial Antineutrinos 238U 232Th νe+ p+→ n + e+ 1.8 MeV Energy Threshold 1α, 1β 1α, 1β 238U 232Th 40K 234Pa 228Ac 2.3 MeV 2.1 MeV 5α, 2β 4α, 2β 214Bi 212Bi νe νe νe νe 3.3 MeV 2.3 MeV 2α, 3β 1α, 1β 206Pb 40K 40Ca 208Pb Terrestrial antineutrinos from uranium and thorium are detectable 1β 1% 31% 46% 20% Efforts to detect K geonus underway

  25. Geoneutrinos Reactor Background with oscillation Reactor and Earth Signal • KamLAND was designed to measure reactor antineutrinos. • Reactor antineutrinos are the most significant contributor to the total signal. KamLAND

  26. Latest results KamLAND from 2002 to Nov 2009 +4.1 +29 106 9.9 -3.4 -28 Event rates Borexino from May ‘07 to Dec ‘09 under construction

  27. Summary of geoneutrino results Constrainting U & Th in the Earth MODELS Cosmochemical: uses meteorites – Javoy et al (2010); Warren (2011) Geochemical: uses terrestrial rocks – McD & Sun, Palme & O’Neil, Allegre et al Geophysical: parameterized convection – Schubert et al; Davies; Turcotte et al; Anderson

  28. Earth’s geoneutrino flux Interrogating “thermo-mechanical pile” (super-plumes?) in the mantle …

  29. Present and future LS-detectors Borexino, Italy (0.6kt) KamLAND, Japan (1kt) SNO+, Canada (1kt) Europe Hanohano, US ocean-based (10kt) LENA, EU (50kt)

  30. Constructing a 3-D reference model Earth assigning chemical and physical states to Earth voxels

  31. Estimating the geoneutrino flux at SNO+ • Geology • Geophysics seismic x-section

  32. Global to Regional RRM SNO+ Sudbury Canada using only global inputs improving our flux models adding the regional geology

  33. Structures in the mantle

  34. Testing Earth Models

  35. SUMMARY • Earth’s radiogenic (Th & U) power • 20 ± 9 TW* (23 ± 10) • Prediction: models range from • 11 to 28 TW • Future: -SNO+ online early 2013 • …2020…?? • - Hanohano • LENA • Neutrino Tomography… 

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