An investigation of the role of coupled boron-hydroxyl substitution in mantle olivine

Adam J.R. Kent* and George R. Rossman

Division of Geological and Planetary Sciences, Mail Code 170-25,

California Institute of Technology, Pasadena, CA, 91125, U.S.A

*current address: Department of Geosciences
Oregon State University
Corvallis, OR 97731, U.S.A.

American Mineralogist 87, 1432-1436

The Mineralogical Society of America
1015 18th St NW Ste 601, Washington, DC 20036-5274 USA


We report secondary ion mass spectrometry (SIMS) measurements of boron and lithium and Fourier-transform infrared spectroscopy (FTIR) measurements of water contents in a suite of ten mantle-derived olivine crystals. Water measurements are based on re-analysis and/or re-processing of data previously reported in the literature. Our data allows us to assess the role of substitutions between these elements in olivine. In particular it provides a means to test the role of the coupled substitution B(F,OH)Si-1O-1 in controlling the boron and water contents of mantle olivines.

Analyzed olivines have lithium, boron and water (present as structurally bound hydroxyl) contents of 0.9 - 7.8 and 0.01 - 67, and 0.8 - 61 ppm-weight. An olivine from Kingiti, Tanzania, possibly derived from metasomatized mantle peridotite, is clearly anomalous having substantially higher boron and lithium contents (65, 7.8 ppm). The remaining olivines have boron and lithium contents that are below 3 and 1 ppm. Our data show that, although boron and water contents vary substantially in natural olivine, their cation proportions per formula unit are not strongly correlated. Importantly, the incorporation of boron and water in olivine by the B(F,OH)Si-1O-1 substitution does not appear to be a universal feature of mantle olivine, although it may be significant in those with the highest boron contents. Lithium contents of olivines are also only weakly correlated with boron and water.

Our data also support suggestions that olivine may be a potential reservoir of hydrogen, lithium and boron in the lithospheric and upper asthenospheric mantle, and thus olivine may play a key role in the geochemical cycling of these elements within the mantle, and between the mantle and crust.

Table 1 Summary, H, Li and B contents of Olivines

Number Locality H (ppm wt.) Li (ppm wt.) B (ppm wt.)
3 Norway 2.6 1.2 0.30
9 Monastery Mine, South Africa 6.8 0.9 0.15
34 Kimberely, South Africa 16.5*, 3.2# 2.3 0.06
17 Kingiti, Tanzania 1.8 7.8 65
21 Hebei Province, China 0.7 0.8 0.02
15 Mt. Vesuvius, Italy 5.3 2.7 0.28
11 Emali, Kenya 3.8 0.9 0.01
19 Nosy Mitsio, Madagascar 0.8 1.5 0.03
14 Toowoomba, Australia 0.09 1.1 0.03
sample number from (Miller et al., 1987)   *including molecular water; # without