Depletions of siderophile elements in mantles have placed constraints on the conditions on core segregation and differentiation in bodies such as Earth, Earth's Moon, Mars, and asteroid 4 Vesta. Among the siderophile elements there are a sub-set that are also volatile (volatile siderophile elements or VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd), and thus can help to constrain the origin of volatile elements in these bodies, and in particular the Earth and Moon. One of the fundamental observations of the geochemistry of the Moon is the overall depletion of volatile elements relative to the Earth, but a satisfactory explanation has remained elusive. Hypotheses for Earth include addition during accretion and core formation and mobilized into the metallic core, multiple stage origin, or addition after the core formed. Any explanation for volatile elements in the Earth's mantle must also be linked to an explanation of these elements in the lunar mantle. New metal-silicate partitioning data will be applied to the origin of volatile elements in both the Earth and Moon, and will evaluate theories for exogenous versus endogenous origin of volatile elements

Danielson, L.

Nickodem, K.

Pando, K.

Righter, K.

NASA Technical Reports Server

CORE-MANTLE PARTITIONING OF VOLATILE ELEMENTS AND THE ORIGIN OF VOLATILE 
ELEMENTS IN EARTH AND MOON.  K. Righter
1
, K. Pando
2
, L. Danielson
2, 
K. Nickodem
3
,  
1
Mailcode KT, 
NASA Johnson Space Center, 2101 NASA Pkwy., Houston, TX 77058 (kevin.righter-1@nasa.gov); 
2
Jacobs JETS, 
NASA Johnson Space Center, 2101 NASA Pkwy., Houston, TX 77058; 
3
Dept. Geography, Syracuse University, 144 
Eggers Hall, Syracuse, NY 13244-1020. 
 
Introduction: Depletions of siderophile elements 
in mantles have placed constraints on the conditions on 
core segregation and differentiation in bodies such as 
Earth, Earth’s Moon, Mars, and asteroid 4 Vesta (e.g., 
[1]).   Among the siderophile elements there are a sub-
set that are also volatile (volatile siderophile elements 
or VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd), and 
thus can help to constrain the origin of volatile ele-
ments in these bodies, and in particular the Earth and 
Moon.  One of the fundamental observations of the 
geochemistry of the Moon is the overall depletion of 
volatile elements relative to the Earth [2-4], but a satis-
factory explanation has remained elusive.  Hypotheses 
for Earth include addition during accretion and core 
formation and mobilized into the metallic core (e.g., 
[1]), multiple stage origin [5], or addition after the core 
formed (e.g., [6-8]). Any explanation for volatile ele-
ments in the Earth’s mantle must also be linked to an 
explanation of these elements in the lunar mantle [9].  
New metal-silicate partitioning data will be applied to 
the origin of volatile elements in both the Earth and 
Moon, and will evaluate theories for exogenous versus 
endogenous origin of volatile elements.   
 
Concentrations of VSE in Earth and Moon mantles: 
Terrestrial primitive upper mantle (PUM) values of 
VSE can be estimated from measurements made on 
mantle peridotite and basalts, and by looking at trends 
with refractory lithophile elements (RLE) that have a 
similar degree of incompatibility during mantle melting 
(e.g., Ge-Si, In-Yb, As-Ce, and Sb-Pr; [1,10,11]).  For 
Moon we do not have samples of the mantle, but we 
can reconstruct lunar mantle values (PLM) by looking 
at concentrations in lunar basalts and comparing these 
to the melting trends derived from the terrestrial man-
tle.  This approach has been explained in more detail 
by [1] and [12] for some of the refractory siderophile 
elements such as Mo, W, Ni and Co.  For the volatile 
chalcophile elements, magmatic volatility and sulfide 
retention during melting must be considered as well.  
The resulting trends of VSE and RLE element pairs 
can be used to estimate the terrestrial and lunar mantle 
concentrations (Fig. 1).   
 
Regressions: An approach for predicting metal-silicate 
partition coefficients as a function of pressure, temper-
ature, oxygen fugacity, and metal and silicate composi-
tions, has been to derive regression coefficients a to h 
 
Fig. 1: Sn-Sm correlation diagram illustrating trends 
for Earth and Moon, and the calculated lunar mantle 
Sn content (open circle). Peridotite, terrestrial basalt, 
lunar basalt and chondrite data is compiled from [24].   
 
from published metal-silicate experiments: 
 ln D(met/sil) = alnfO2 + b/T + cP/T + d ln(1-Xs) + 
e ln(1-Xc) + f ln(1-XSi) + g (nbo/t) + h 
Regressions for As, Cu, Sb, Ge, Ga, Zn, Sn, and In 
were carried out using available experimental results 
that cover a range of intensive parameters (from refer-
ences compiled in [24]).   
 
Application to Earth: Recent modeling indicates 
moderately siderophile element depletions in Earth’s 
primitive upper mantle can be explained by metal-
silicate equilibrium between metallic and silicate liquid 
at high PT conditions during Earth’s accretion (~40 
GPa, ~3400 K; e.g., [1,13]).  Using the regression de-
rived for the volatile siderophile elements above, we 
can examine the evolution of the composition of the 
Earth’s PUM during accretion scenarios with constant 
fO2 (IW-1.5), increasing fO2 (IW -4 to IW-2.4), or de-
creasing fO2 (IW-2 to IW-3.8) (e.g., [14-16]).  Calcula-
tions have been carried out along the PT conditions of 
the liquidus for peridotite [17].  Many elements can be 
fit in each of the scenarios.  However, the calculations 
assuming a constant fO2 result in the most matches to 
the Earth’s PUM concentrations (e.g., Sn in Fig. 2), 
and suggest that the VSE can be explained by a rather 
simple scenario of continuous accretion leading to a 
high PT metal-silicate scenario that establishes the si-
derophile element content of Earth’s PUM near the end 
of accretion.  This scenario does not require multiple 
stages of accretion (reduced or oxidized; low pressure 
https://ntrs.nasa.gov/search.jsp?R=20140007370 2019-08-29T13:45:08+00:00Z
then high pressure; e.g., [5]), nor does it require late 
stage addition of chondritic materials (e.g., [7,18]. 
 
Fig. 2: Evolution of Earth’s PUM Sn during accretion 
for 3 fO2 scenarios; constant (solid circles), decreasing 
(triangles) and increasing (open circles) (see text).  
Horizontal bands represent terrestrial PUM [10].   
 
Application to Moon: The giant impact scenario is the 
generally accepted model for the origin of the Moon, 
but there is no consensus on whether the Moon formed 
from material that was part of the proto-Earth or from 
the impactor (or a mixture of these two).  We consider 
two scenarios: In Scenario A, the Moon may have 
formed from material from the impactor involved in the 
Moon-forming impact (e.g., [19]), and in which a pre-
impact volatile depletion could have been caused by 
impact erosion, or by impact of a planetesimal that 
contains a predominance of volatile element depleted 
materials that perhaps accreted rapidly in the early so-
lar system. In scenario A, the VSE depletions would 
have been inherited from both the impactor and the 
later Moon-forming impact process.  In Scenario B, the 
Moon may have formed from material from the proto-
Earth or the primitive upper mantle (e.g., [20-22]).  
Therefore the bulk composition of the Moon would be 
modeled as that of the primitive upper mantle [9] and 
VSE depletions would have been inherited from both 
the Earth’s mantle and the later Moon-forming impact 
process. 
In either of these scenarios, the Moon would have 
accreted from a circum-terrestrial disk, and then differ-
entiated into a small core and molten mantle.  Core 
formation models for the Moon can explain a broad 
range of siderophile elements including the refractory 
(Ni, Co, Mo, W) and slightly (Mn, V, Cr) siderophile 
elements where metal-silicate equilibrium is at P = 5 
GPa, T = 2500 K, and relative fO2 = IW-2 ([9,23]).  
Modelling that includes either a small amount of S or 
C, or no light element at all, results in a good match to 
the lunar mantle concentrations of most VSE (Fig. 3). 
However, calculated concentrations of In, Sn, and Zn 
(all with Tc < 750 K) are all still too high after core 
formation, and must therefore require an additional 
process to explain the depletions in the lunar mantle. 
We discuss possible processes including magmatic 
degassing, evaporation, condensation, and vapor-liquid 
fractionation in the lunar disk.  
 
Fig. 3: Lunar mantle VSE deduced from lunar basalt 
data, calculated for a bulk Moon depleted in volatile 
elements by a factor of 4 (solid circles), and by a fac-
tor of 10 (open circles) compared to the Earth. Invert-
ed triangles show concentrations after segregation of a 
small core in equilibrium with mantle. The order of 
presentation of volatile siderophile elements is in order 
of 50% condensation temperature, with As the highest 
and In the lowest.   
 
References: [1] Righter, K. (2011) EPSL 304, 158–
167. [2] Ringwood, A.E. and Kesson, S. (1977) The 
Moon 16, 425-464. [3] Delano, J.W. and Ringwood, 
A.E. (1978) Moon and the Planets 18, 385-425. [4] 
Wolf, R. and Anders, E. (1980) GCA 44, 2111-2124. 
[5] Mann et al., (2009) GCA 73: 7360–7386. [6] Alba-
rède, F. (2009) Nature, 461, 1227-1233. [7] Ballhaus, 
C., et al. (2013) EPSL 362, 237-245. [8] Yi, W. et al. 
(2000) JGR 105, 18927-18948. [9] Righter, K. (2002) 
Icarus 158, 1-13. [10] Witt-Eickschen, G., et al. (2009) 
GCA 73, 1755-1778. [11] Righter, K., et al. (2009) 
GCA 73, 1487-1504. [12] Drake, M.J. (1980) Rev. 
Geophys. Space Phys. 18, 11-25. [13] Wade, J., et al. 
(2012) GCA 85, 58 – 74. [14] Rubie, D.C., et al. 
(2011) EPSL 301, 31-42. [15] Righter and Ghiorso, 
2012 PNAS 109, 11955-11960. [16] Siebert et al., 
2013 Science 339, 1194-1197. [17] Andrault, D., et al. 
(2011) EPSL 304, 251-259. [18] Rose-Weston, L., et 
al. (2009) GCA 73, 4598-4615. [19] Canup, R.M. 
(2004) Ann. Rev. Astron. Astrophy. 42, 441-475. [20] 
Zhang, J., et al. (2012) Nat. Geosc. 5, 251-255.  [21] 
Cuk, M. and Stewart, S.T. (2012) Science 338, 1047-
1051. [22] Canup, R.M. (2012) Science 338, 1052-
1054. [23] Rai, N. and van Westrenen, W. (2012) 43rd 
LPSC, #1781. [24] Righter, K. et al. (2014) GCA, in 
review. 


Core-Mantle Partitioning of Volatile Elements and the Origin of Volatile Elements in Earth and Moon

Depletions of volatile siderophile elements (VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd) in mantles of Earth and Moon, constrain the origin of volatile elements in these bodies, and the overall depletion of volatile elements in Moon relative to Earth. A satisfactory explanation has remained elusive [1,2]. We examine the depletions of VSE in Earth and Moon and quantify the amount of depletion due to core formation and volatility of potential building blocks. We calculate the composition of the Earth's PUM during continuous accretion scenarios with constant and variable fO2. Results suggest that the VSE can be explained by a rather simple scenario of continuous accretion leading to a high PT metal-silicate equilibrium scenario that establishes the siderophile element content of Earth's PUM near the end of accretion [3]. Core formation models for the Moon explain most VSE, but calculated contents of In, Sn, and Zn (all with Tc < 750 K) are all still too high after core formation, and must therefore require an additional process to explain the depletions in the lunar mantle. We discuss possible processes including magmatic degassing, evaporation, condensation, and vapor-liquid fractionation in the lunar disk

Righter, Kevin

Please ensure that your abstract fits into one column on one 
page and complies with the Instructions to Authors 
available from the Abstract Submission web page. 
CORE-MANTLE PARTITIONING OF VOLATILE 
ELEMENTS AND THE ORIGIN OF VOLATILE 
ELEMENTS IN EARTH AND MOON 
K. RIGHTER1, K. PANDO2, L. DANIELSON2, K. 
NICKODEM3 
1 Mailcode KT, NASA Johnson Space Center, 2101 
NASA Pkwy., Houston, TX 77058 
2Jacobs JETS, NASA Johnson Space Center, 2101 
NASA Pkwy., Houston, TX 77058 
3Dept. Geography, Syracuse University, 144 Eggers 
Hall, Syracuse, NY 13244-1020 
 
Depletions of volatile siderophile elements (VSE; 
Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd) in mantles of 
Earth and Moon, constrain the origin of volatile 
elements in these bodies, and the overall depletion of 
volatile elements in Moon relative to Earth. A 
satisfactory explanation has remained elusive [1,2].  
We examine the depletions of VSE in Earth and Moon 
and quantify the amount of depletion due to core 
formation and volatility of potential building blocks.   
We calculate the composition of the Earth’s PUM 
during continuous accretion scenarios with constant 
and variable fO2.  Results suggest that the VSE can be 
explained by a rather simple scenario of continuous 
accretion leading to a high PT metal-silicate 
equilibrium scenario that establishes the siderophile 
element content of Earth’s PUM near the end of 
accretion [3].  Core formation models for the Moon 
explain most VSE, but calculated contents of In, Sn, 
and Zn (all with Tc < 750 K) are all still too high after 
core formation, and must therefore require an 
additional process to explain the depletions in the lunar 
mantle. We discuss possible processes including 
magmatic degassing, evaporation, condensation, and 
vapor-liquid fractionation in the lunar disk. 
References: [1] Ringwood, A.E. and Kesson, S. (1977) 
The Moon 16, 425-464. [2] Delano, J.W. and 
Ringwood, A.E. (1978) Moon and the Planets 18, 385-
425. [3] Righter, K. (2011) EPSL. 
https://ntrs.nasa.gov/search.jsp?R=20140003556 2019-08-29T14:23:31+00:00Z


Core-Mantle Partitioning of Volatile Elements and the Origin of Volatile Elements in Earth and Moon

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