cider 2008 composition of the earth stan hart woods hole oceanographic institution
TRANSCRIPT
![Page 1: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/1.jpg)
CIDER 2008
Composition of the Earth
Stan HartWoods Hole Oceanographic Institution
![Page 2: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/2.jpg)
Courtesy of NASA/JPL-Caltech
4.56 Billion Years AgoLet’s begin at the beginning^
7
![Page 3: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/3.jpg)
How do we determine the composition of the Earth??
Best Way: - grind up the Earth.- take a representative sample.- analyze in the lab for
everything.
Or we can take a desperate guess (sometimes
called the chondrite model).
The problem:- direct sampling to only ~15 km.- eruptive “entrainment” sampling to 200 km,
and possibly to 500 km.- mantle plume advection from the base of the
mantle (2900 km). If plumes exist.- no bona fide samples yet from the core.
![Page 4: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/4.jpg)
The Solar Connection:
Palme and Jones 2005
Chondrites ~ Solar Nebula, to within± 20%
Why do we think meteorites have anythingto do with the Earth?
![Page 5: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/5.jpg)
The Solar Connection:
C1 Chondrites ~ Solar Nebula, to within the uncertaintiesof the solar spectroscopic measurements.
Allegre, Hart and Shimizu, 2008
![Page 6: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/6.jpg)
The Chondritic Earth model
All classes of Chondrites have the same Sm/Nd ratio (±1%!) - maybe the Earth is also the same?
(note: Sm/Nd weight ratio is directly proportional to 147Sm/144Nd)
± 1%
![Page 7: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/7.jpg)
Hutchinson, 2004
Chondrites have variable Ca/Si and Al/Si but all classes of chondrites have the same Ca/Al ratio -
Maybe the Earth also has the same Ca/Al?
The Chondritic Earth model
![Page 8: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/8.jpg)
Hutchinson, 2004
Why is Ca/Si and Al/Si variable betweenchondrite classes?
Because Si has a lower condensation temperature than Ca and Al. Then what is the Earth’s Ca/Si and Al/Si?
The Chondritic Earth model
Condensation temperatures of the elements, °K:
Al - 1655°Ca - 1520°Mg - 1340°Fe - 1335°Si - 1310°
![Page 9: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/9.jpg)
Albarede 2003
Upper mantle
peridotites
The first “fuzzy” step -The chondritic Earth model
Chondr
ites
Peridotites represent residues of partial melting.
Chondrites represent differing condensation temperatures.
Intersection defines the composition of the primitive upper mantle (PUM) and suggests Earth had a higher condensation temperature than chondrites.
QED - we know the relative Al, Mg and Si contents of the Earth.
![Page 10: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/10.jpg)
The more the data, the fuzzier it gets!
Mg/Si
Al/
Si
0.81.01.21.4
Canil 2008 Line is Canil’s best fit to the off-craton xenoliths.
Blue pentagon is PUM from McDonough and Sun 1995.
Green star is PUM from Hart and Zindler 1986 (aka HaZi).
(PUM = primitive upper mantle)
![Page 11: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/11.jpg)
Chondrite model can also be used for trace elements:
Hart and Zindler 1986
Like Sm/Nd, Sm/Ca appears constant in chondrites (excepting some “cooked” carbonaceous chondrites).
Ignore the open squares (metasomatized upper mantle peridotites).
Tic marks on melting curve are % increments of melt removal.
partial melting trend
![Page 12: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/12.jpg)
McDonough, 2005
Refractory ElementCondensation Temps
Re - 1820°KW - 1790Zr - 1740Th - 1660REE -1660 - 1490 (Yb)Al - 1655U - 1610Ti - 1580Ca - 1520
Semi-refractory
Mg - 1340Fe - 1335Si - 1310
800°1000°1200°1400°1600°
Estimated Earth Composition relative to C1 chondrites
Good match for Refractory Elements (Tcond. >1500°K)
![Page 13: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/13.jpg)
Abyssal Peridotites = Simple Residues of DMM Melting
Linearized relationshipbetween two elements, A & B,
in a residue of fractional
melting:
Where slope, R €
ln CsA
( ) = R ln CsB
( ) + lnCoA
CoB
( )R
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟
€
R =DB (1−DA )
DA (1−DB )
-9
-8
-7
-6
-5
-4
-3
-2
-1
-9 -8 -7 -6 -5 -4 -3 -2 -1 0
ln(Sm)
ln(Eu)
Primitive Upper Mantle (PUM)McDonough & Sun (1995)
Depletion By Fractional Melting
Workman and Hart, 2005
![Page 14: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/14.jpg)
PUM PUM
Some other trace element trends in abyssal peridotites:
We know the composition of DMM is somewhere on the regression between PUM and the least depleted abyssal peridotite - but where?
Workman and Hart, 2005
![Page 15: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/15.jpg)
We work backward from the average 143Nd/144Nd of melts from thedepleted upper mantle (=0.51317).
Given the Sm/Nd of PUM, we canmodel the evolution of a continuouslydepleting reservoir that ends at thispresent day 143Nd/144Nd of N-MORB.
From this model, we can estimate thepresent day Sm/Nd of DMM (=0.411).
The intersection of this line with the abyssal peridotite trend defines theSm and Nd concentration of DMM.
Workman and Hart, 2005
![Page 16: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/16.jpg)
Composing Trace Element Composition of DMM
Abyssal Peridotite Constraints
0.01
0.10
1.00
Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
PUM Normalized Concentrations
Workman and Hart, 2005
![Page 17: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/17.jpg)
Composing Trace Element Composition of DMM
Parent/Daughter Constraints
0.01
0.10
1.00
Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
PUM Normalized Concentrations
Workman and Hart, 2005
![Page 18: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/18.jpg)
Hofmann 2005
Negative slope means numeratorelement is more compatible thandenominator element.
i.e mineral/melt partition coefficient Di
is larger
Horizontal slope means both elementshave the same partition coefficient.
“Canonical” Ratios
DNb > DTh
DNb < DLa
DNb ~ DU
![Page 19: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/19.jpg)
Some trace elements don’t fractionate from each other!So ratio in melt equals ratio in residue
“Canonical” ratios
Spreading Center LavasPETDB Database
![Page 20: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/20.jpg)
Composing Trace Element Composition of DMM
Cannonical Ratios Constraints
0.01
0.10
1.00
Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
PUM Normalized Concentrations
Workman and Hart, 2005
![Page 21: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/21.jpg)
Composing Trace Element Composition of DMM
Connecting the Dots…
0.01
0.10
1.00
Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
PUM Normalized Concentrations
Workman and Hart, 2005
![Page 22: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/22.jpg)
MORB Generation from model DMM
Workman and Hart, 2005
![Page 23: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/23.jpg)
0.01
0.10
1.00
10.00
100.00
Rb Ba Th U K Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
Sum
DMM
Cont. Crust
Crust-Mantle Mass Balance - I
How much DMM does it take to balance JUST Continental Crust?
CC mass = 0.6% of BSE
Bulk Continental Crust from Rudnick and Fountain (1995)
DMM mass = 33% of BSE
Sum of DMM + CC
PUM normalized
concentrations
![Page 24: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/24.jpg)
Crust-Mantle Mass Balance - II
Bulk Continental Crust from Rudnick and Fountain (1995)
0.01
0.10
1.00
10.00
100.00
Rb Ba Th U K Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
Sum
DMM
Cont. Crust
N-MORB
0.6% CC
Adding Oceanic Crust into the BalanceMost element fit to within 8%
43 ± 3% DMM
2 ± 0.3% MORB
Sum of MORB + DMM + CC
PUM normalized
concentrations
![Page 25: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/25.jpg)
Table 3. Modal abundances and major element composition of DMM.
Modal Abundances in DMM (%):
Olivine Opx Cpx Spinel
57 28 13 2
PUMMineral compositions: Primary minus
Olivine Opx Cpx Spinel Bulk DMM PUM a N-MORB b 3% N-MORB
SiO2 40.70 53.36 50.61 44.71 44.90 49.51 44.87Al2O3 6.46 7.87 57.54 3.98 4.44 16.75 4.07
FeO* 10.16 6.27 2.94 12.56 8.18 8.03 8.05 8.05
MnO 0.14 0.12 0.09 0.16 0.13 0.13 0.14 0.13
MgO 48.59 30.55 16.19 19.27 38.73 37.71 9.74 38.68
CaO 0.05 2.18 19.52 3.17 3.54 12.50 3.27Na2O 0.05 0.89 0.13 0.36 2.18 0.30Cr2O3 0.76 1.20 10.23 0.57 0.38 0.07 0.39TiO2 0.16 0.63 0.13 0.20 0.90 0.18
NiO 0.36 0.09 0.06 0.24 0.24 0.25 - -
K2O 0.006 c 0.029 0.065 0.028P2O5 0.019 d 0.021 0.095 0.019
Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00Mg # e 89.5 89.7 90.8 73.2 89.4 89.3 70.6 89.5Cr # f 10.7
CaO/Al2O3 0.34 2.48 0.80 0.80 0.75 0.80
* Total Fe as FeO.a Primitive Upper Mantle (PUM) from McDonough and Sun (1995).b Primary N-MORB from averaged glass compositions in Presnall and Hoover (1987).c Calculated by inverting parental N-MORB at 0.1 wt% K2O for 6% melting and assuming DK = 0.0013.d Calculated by extracting 3% primary N-MORB (shown here) from PUM.e Mg # = molar ratio of Mg/(Mg+Fe2+); Mg # of N-MORB uses 90% total FeO as Fe2+.f Cr # = molar ratio of Cr/(Cr+Al).
Summary of Upper Mantle Composition
- DMM ~ PUM minus -3% melt
- N-MORBs are ~ 6% melts of DMM.
- DMM mineralogy is still a lherzolite.
- DMM physical properties are like PUM.
- Heat production is only 15% of PUM.(2.4 pW/m3)
Workman and Hart, 2005
![Page 26: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/26.jpg)
Physical properties calculated with model of Stixrude and Lithgow-Bertelloni 2005
- produces a huge effect on isotopes, heat production and some trace elements but an insignificant effect on density and shear wave velocity!
Deplete the primitive upper mantle to make a depleted MORB mantle:
![Page 27: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/27.jpg)
So we’re done, right?
![Page 28: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/28.jpg)
Boyet and Carlson 2006
hmmmmmm
142Nd is the daughter of 146Sm, an extinct parent.
142Nd in the accessible Earth is 20 ppm higher than in chondrites.
So is the chondritic model for the Earth wrong?
Maybe!
Only two simple choices: - the earth is not chondritic. - there is a hidden terrestrial low Sm/Nd reservoir we’ve not yet seen.
All consequences are drastic!
![Page 29: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/29.jpg)
Hutchinson 2004
PUM
Terrestrial fractionation line
Oxygen isotope compositions of Earth, Ordinary chondrites (H, L LL),Enstatite chondrites (EH, EL), and Carbonaceous chondrites (C1, CM, etc).
Earth is similar onlyto the EnstatiteChondrites.
![Page 30: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/30.jpg)
Hutchinson 2004
PUM
Terrestrial fractionation line
Oxygen isotope compositions of Earth, Moon, Mars,Iron meteorites and differentiated meteorites
Earth is similar onlyto the Moon, andAubrites (Enstatiteachondrites).
This oxygen “DNA” testsuggests the deep Earthmay be richer in enstatitethan olivine (higherperovskite/periclase ratio).
Seismologists and mineral physicists to the rescue??
I’m done!
![Page 31: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/31.jpg)
Stay tuned -
![Page 32: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/32.jpg)
![Page 33: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/33.jpg)
![Page 34: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/34.jpg)
0.01
0.1
1
10
Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
PUM Normalized Concentrations Average Upper Mantle
Observed Oceanic Crust
Element Concentrations
Normalized to Bulk Silicate Earth
Generation of Oceanic Crust using our Upper Mantle Composition
![Page 35: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/35.jpg)
0.01
0.1
1
10
Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Hf Sm Eu Ti Gd Tb Dy Ho Y Er Yb Lu
PUM Normalized Concentrations DMM
Observed Oceanic Crust
Model Oceanic Crust
Average Upper Mantle
Element Concentrations
Normalized to Bulk Silicate Earth
Generation of Oceanic Crust using our Upper Mantle Composition
![Page 36: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/36.jpg)
![Page 37: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/37.jpg)
![Page 38: CIDER 2008 Composition of the Earth Stan Hart Woods Hole Oceanographic Institution](https://reader030.vdocuments.us/reader030/viewer/2022032802/56649dff5503460f94ae6ea6/html5/thumbnails/38.jpg)
-8
-7
-6
-5
-4
-3
-2
-1
0
1
-7 -6 -5 -4 -3 -2 -1 0
ln(Sm)
ln(Nd)
Sm/Nd = 0.411
PUM
Defining a unique position on the mantle depletion trends
DMM