Encyclopedia of Geochemistry

Living Edition
| Editors: William M. White

Siderophile Elements

  • James M. D. DayEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-39193-9_234-1

Keywords

Carbon Capture Solar Nebula Carbonaceous Chondrite Core Formation Planetary Body 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Definition

Siderophile elements preferentially partition into metal phases during cosmochemical and geochemical processes. The siderophile elements include the highly siderophile elements (HSE; Re, Os, Ir, Ru, Pt, Rh, Au, Pd), which are characterized by low-pressure metal–silicate distribution coefficients of more than 104; the moderately siderophile elements (MSE; including Mo, W, Fe, Co, Ni, P, Cu, Ga, Ge, As, Ag, Sb, Sn, Tl, Bi), with low-pressure metal–silicate partition coefficients that are typically more than 10, but less than 104; and the slightly siderophile elements (SSE; Mn, Cr, and V) (Table 1). The SSE, along with the highly chalcophile elements (HCE: S, Se, Te, Pb), and elements that otherwise exhibit atmophile, lithophile, or chalcophile affinity, can become siderophiles at specific temperatures (T), pressures (P), compositions (x), or oxygen fugacity (fO2). An example of this phenomenon is the composition of Earth’s core which, from seismological constraints, requires an alloy of FeNi metal and light elements. The nature of the light alloying element(s) remains uncertain, with Si, O, S, H, and C all considered as potential candidates, implying potential siderophile behavior of these elements at high pressures and temperatures.
Table 1

Behaviors and abundances in CI chondrites and the bulk silicate Earth (BSE) for the HSE and MSE

Element

  

Atomic number

Cosmochemical behavior

50 % Tc (K)

Units

CI-chondrite

BSE abundance

BSE/CI

Examples of radioactive isotope systems

Phosphorus

P

MSE

15

Moderately volatile

1229

μg g−1

1080

90

0.083

 

Sulfur

S

HCE

16

High volatile chalcophile

664

μg g−1

54,000

250

0.005

 

Vanadium

V

SSE

23

Refractory

1429

μg g−1

56

82

1.464

 

Chromium

Cr

SSE

24

Transitional

1296

μg g−1

2650

2625

0.991

 

Manganese

Mn

SSE

25

Moderately volatile

1158

μg g−1

1920

1045

0.544

 

Iron

Fe

MSE

26

Transitional

1334

%

18.1

6.26

0.35

60Fe-60Ni (t1/2 = 4.7 Ma)

Cobalt

Co

MSE

27

Transitional

1352

μg g−1

500

105

0.210

 

Nickel

Ni

MSE

28

Transitional

1353

μg g−1

10,500

1960

0.187

 

Copper

Cu

MSE

29

Moderately volatile

1037

μg g−1

120

30

0.250

 

Gallium

Ga

MSE

31

Moderately volatile

968

μg g−1

9.2

4.0

0.435

 

Germanium

Ge

MSE

32

Moderately volatile

883

μg g−1

31

1.1

0.035

 

Arsenic

As

MSE

33

Moderately volatile

1065

μg g−1

1.85

0.05

0.027

 

Selenium

Se

HCE/MSE

34

High volatile chalcophile

697

μg g−1

19.7

0.075

0.004

 

Molybdenum

Mo

MSE

42

Refractory

1590

μg g−1

900

50

0.056

 

Ruthenium

Ru

HSE

44

Refractory

1551

ng g−1

631

7.0

0.011

 

Rhodium

Rh

HSE

45

Refractory

1392

ng g−1

130

1.2

0.0092

 

Palladium

Pd

HSE

46

Transitional

1324

ng g−1

563

7.1

0.013

107Pd-107Ag (t1/2 = 6.5 Ma)

Silver

Ag

MSE

47

Moderately volatile

996

ng g−1

200

8.0

0.040

 

Tin

Sn

MSE

50

Highly volatile

704

ng g−1

1650

130

0.079

 

Antinomy

Sb

MSE

51

Moderately volatile

979

ng g−1

140

5.5

0.039

 

Tellurium

Te

HCE/MSE

52

High volatile chalcophile

709

ng g−1

2330

12

0.005

 

Tungsten

W

MSE

74

Refractory

1789

ng g−1

93

13

0.140

182Hf-182W (t1/2 = 8.9 Ma)

Rhenium

Re

HSE

75

Refractory

1821

ng g−1

37.3

0.35

0.0094

187Re-187Os (t1/2 = 42Ga)

Osmium

Os

HSE

76

Refractory

1812

ng g−1

450

3.9

0.0087

 

Iridium

Ir

HSE

77

Refractory

1603

ng g−1

424

3.5

0.0083

 

Platinum

Pt

HSE

78

Refractory

1408

ng g−1

864

7.6

0.0088

190Pt-186Os (t1/2 = ~460Ga)

Gold

Au

HSE

79

Moderately volatile

1060

ng g−1

149

1.7

0.011

 

Thallium

Tl

MSE

81

Highly volatile

532

ng g−1

140

3.5

0.0250

 

Lead

Pb

MSE

82

High volatile chalcophile

727

ng g−1

2470

150

0.061

U-Th-Pb dating

Bismuth

Bi

MSE

83

Highly volatile

746

ng g−1

110

2.5

0.023

 

50 % Tc = Equilibrium condensation temperatures for a solar system composition gas presented as the 50 % trace element concentration

CI-chondrite carbonaceous Ivuna (type 1) chondrite, BSE bulk-Silicate Earth, taken as being the primitive mantle composition (after McDonough and Sun 1995; Lodders 2003).

Properties of the Siderophile Elements

The siderophile elements have both long-lived and short-lived radioactive isotope decay schemes and important novel stable isotope systems (e.g., Fe isotopes) embedded within them (Table 1). Of the radiogenic isotope systems, 182W is the decay product of the extinct radionuclide 182Hf and can be used to date core formation due to Hf partitioning into silicate portions of planets, relative to W, which partitions preferentially into metallic cores. The 187Re-187Os is a long-lived isotope chronometer and has found wide application, from geochronology to studies of mantle isotopic heterogeneity or the record of continental weathering from seawater 187Os/188Os composition (Shirey and Walker 1998; Harvey and Day 2016).

During condensation of elements at the formation of the solar nebula, siderophile elements sequestered in refractory metallic alloys, or into iron sulfides, depending on volatility, leading to some fractionation of the siderophile elements. Early differentiation of Earth led to siderophile elements being extracted into a metallic iron core and corresponding depletion of these elements in Earth’s silicate mantle and crust. Application of low-pressure metal–silicate partition coefficients shows that the predicted abundances of some siderophile elements, especially the HSE, are higher than expected from metal–silicate partitioning in the bulk silicate Earth. The overabundance of siderophile elements in Earth’s mantle has been attributed to “late accretion” of materials with generally chondritic bulk composition after core formation ceased, to account for the generally flat, chondrite-relative abundances of the HSE (Figure 1).
Figure 1

Abundances of elements in the bulk silicate Earth (BSE) with slightly (SSE), moderately (MSE), and highly siderophile element (HSE) behavior and with strongly chalcophile element (SCE) behavior, double-normalized to the composition of CI chondrites and to Fe content. Volatile (defined as those elements for which 50 % TC < 1250 K), transitional, and refractory (50 % TC > 1360) behaviors are shown. Abundances of the siderophile elements in the BSE are higher than expected from 1 atmosphere metal–silicate partition coefficients (1 Bar KD met/sil; those with downward arrows = > 104). Higher abundances of these elements, most especially of the HSE, which are in broadly chondritic relative proportions, have been interpreted to reflect late accretion of chondritic material to Earth, after core formation was complete.

Experimental partitioning studies have found that some siderophile elements have decreasing metal–silicate partitioning coefficients at high pressures. Thus, the possibility of high pressure core-mantle equilibration to account for the siderophile element – and specifically HSE – abundances in the bulk silicate Earth cannot be ruled out, but we have to account for both the abundances of these elements and the long-term ratios of Re/Os and Pt/Os that are within 5–10 % of chondritic values deduced from 187Os/188Os and 186Os/188Os in terrestrial mantle rocks (e.g., Day et al. 2016). Asteroidal parent bodies, which underwent metal–silicate partitioning at low pressures, also show enrichments of siderophile elements in broadly chondritic proportions, indicating that late accretion was ubiquitous to planetary bodies. Late accretion is a natural consequence of planetary growth, whereby the end of core formation and metal–silicate partitioning enables buildup of siderophile elements in planetary mantles, in broadly chondritic abundances. For Earth, late accretion of approximately 0.8 % by mass of a carbonaceous chondrite component is required to explain the abundances of the HSE in the mantle. For other planetary bodies, the amount of late accretion is less certain but is likely to be strongly tied to the timing of cessation of core formation and metal–silicate equilibration .

Cross-References

References

  1. Day, J. M. D., Brandon, A. D., and Walker, R. J., 2015. Highly siderophile elements in Earth, Mars, the Moon, and Asteroids. Reviews in Mineralogy and Geochemistry, 81, 78 pp, doi:10.2138/rmg.2014.81.04.Google Scholar
  2. Harvey, J., Day, J. M. D., 2016. Introduction to highly siderophile and strongly chalcophile elements in high temperature geochemistry and cosmochemistry. Reviews in Mineralogy and Geochemistry, 81(1), 3–4.CrossRefGoogle Scholar
  3. Lodders, K., 2003. Solar system abundances and condensation temperatures of the elements. Astrophysical Journal, 591, 1220–1247.CrossRefGoogle Scholar
  4. McDonough, W. F., and Sun, S.-S., 1995. The composition of the Earth. Chemical Geology, 120, 223–253.CrossRefGoogle Scholar
  5. Shirey, S. B., and Walker, R. J., 1998. The Re-Os isotope system in cosmochemistry and high-temperature geochemistry. Annual Review of Earth and Planetary Sciences, 26, 423–500.CrossRefGoogle Scholar

Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  1. 1.Scripps Institution of OceanographyUniversity of California San DiegoLa JollaUSA