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Cr-rich spinel and garnet in two peridotite xenoliths from the Frank Smith mine South Africa: Significance of Al and Cr distribution between spinel and garnet

  • R. A. Exley (a1), J. V. Smith (a1) and R. L. Hervig (a1)

Abstract

Peridotite xenoliths 73–106 and 73–109 have coarse textures. All minerals in 73–106 are very Ti-rich, and include olivine (Fo 87.6), orthopyroxene (En 90.0), garnet (core TiO2 0.8, Cr2O3 7; rim 1.4, 4 wt. %), spinel (TiO2 5, Cr2O3 38), clinopyroxene (A12O3 1–8) secondary mica (TiO2 6, Cr2O3 2.5 near garnet 0.5 away from garnet), and serpentine (FeO 5–12) enclosing perovskite-rimmed ilmenite and minute apatites. All minerals in peridotite 73–109 are Ti-poor, and include olivine (Fo 92.6), orthopyroxene (En 93.6), garnet (Cr2O3 3.1–3.8), spinel (55), ureyitic diopside, primary mica (TiO2 0.06, Cr2O3 1.0, BaO 0.5, Cl 0.04), and serpentine (FeO 2–23). Various thermometers indicate ∼ 1350K (73–106) and 1100K (73–109). The low Al2O3 in the orthopyroxenes gives 39–47 kb for 73–109 from the Wood-Banno barometer. In 73–106, the spinel lies in secondary mica next to the garnet rim, whereas the spinel of 73–109 occurs in grains enclosed by garnet. The former assemblage indicates diffusion-dependent disequilibrium, whereas the latter is attributed to simultaneous growth of spinel and garnet, perhaps consequent upon exsolution from orthopyroxene. Complex behaviour was found for the Cr/Al distribution in published analyses of garnet and spinel. The 73–109 pair lies near the Thaba Putsoa trend, and the 73–106 assemblages are displaced towards the kelyphite region in which garnet and spinel have similar Cr/Al. Spinel and garnet may coexist over a 30 kb pressure interval ranging from ∼ 16 kb for low bulk Cr to ∼ 40 kb for high Cr.

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References

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Aoki, K., and Prinz, M. (1974) Contrib. Mineral. Petrol. 46, 249-56.
Basu, A. R., and MacGregor, I. D. (1975) Geochim. Cosmochim. Acta, 39, 937-45.
Boyd, F. R. (1973) Ibid. 37, 2533-46.
Boyd, F. R. and Nixon, P. H. (1978) Ibid. 42, 1367-82.
Carswell, D. A., Clarke, D. B., and Mitchell, R. H. (1979) In The Mantle Sample: Inclusions in Kimberlites and other Volcanics (F. R., Boyd and H. O. A., Meyer, eds.), Washington; Am. Geophys. Union, 127-44.
Danchin, R. V. (1979) Ibid. 104-26.
Dawson, J. B., and Stephens, W. E. (1975) J. Geol. 83, 589-607.
Dawson, J. B., Smith, J. V., and Delaney, J. S. (1978) Nature, 273, 741-3.
Delaney, J. S., Smith, J. V., Dawson, J. B., and Nixon, P. H. (1979) Contrib. Mineral. Petrol. 71, 157-69.
Delaney, J. S., Smith, J. V., Carswell, D. A., and Dawson, J. B. (1980) Geochim. Cosmochim. Acta, 44, 857-72.
Ferguson, J., Ellis, D. J., and England, R. N. (1977) Geology 5, 278-80.
Haggerty, S. E. (1973). In Lesotho Kimberlites (H. Nixon, P., ed.), Maseru, Lesotho National Development Corporation, 149-58.
Haggerty, S. E. (1975) Phys. Chem. Earth, 9, 295-307.
Harte, B., and Gurney, J. J. (1975) Carnegie Inst. Washinffton Yearb. 74, 528-36.
Hervig, R. L., and Smith, J. V. (1980) J. Geol. 88, 337-42.
Hervig, R. L., and Smith, J. V. (1981) Eos, Trans. Am. Geophys. Union, 62, 1055.
Irving, A. J. (1974) J. Petrol. 15, 1-40.
Jenkins, D. M., and Newton, R. C. (1979) Contrib. Mineral. Petrol. 68, 407-19.
Lock, N. P., and Dawson, J. B. (1980). Trans. R. Soc. Edinburgh: Earth Sci. 71, 47-53.
MacGregor, I. D. (1970) Phys. Earth Planet. Inter. 3, 372-7.
MacGregor, I. D. (1979) In The Mantle Sample: Inclusions in Kimberlites and other Volcanics (R. Boyd, F. and Meyer, H. O. A., eds.), Washington, Am. Geophys. Union, 156-72.
Mitchell, R. H., Carswell, D. A., and Clarke, D. B. (1980) Contrib. Mineral. Petrol. 72, 205-17.
Nixon, P. H., and Boyd, F. R. (1973) In Lesotho Kimberlites (H. Nixon, P., ed.), Maseru, Lesotho National Development Corporation, 48-56.
Nixon, P. H., and Boyd, F. R. (1979) In The Mantle Sample: Inclusions in Kimberlites and other Volcanics (R. Boyd, F. and Meyer, H. O. A., eds.), Washington, Am. Geophys. Union, 400-23.
Nixon, P. H., Chapman, N. A., and Gurney, J. J. (1978). Contrib. Mineral. Petrol. 65, 341-6.
O'Hara, M. H., Richardson, S. W., and Wilson, G. (1971) Ibid. 32, 48-68.
O'Neill, H. St.C. (1981) Ibid. 77, 185-94.
O'Neill, H. St.C. and Wood, B. J. (1979) Ibid. 70, 59-70.
Pasteris, J. D. (1981) Geology, 9, 356-9.
Reid, A. M., and Dawson, J. B. (1972) Lithos, 5, 115- 24.
Reid, A. M., Donaldson, C. H., Brown, R. W., Ridley, W. I., and Dawson, J. B. (1975) Phys. Chem. Earth, 9, 525-43.
Shervais, J. W., Wilshire, H. G., and Schwarzman, E. C. (1973) Earth Planet Sci. Lett. 19, 120-30.
Smith, J. V., and Dawson, J. B. (1975) Phys. Chem. Earth, 9, 309-22.
Sobolev, N. V. (1977) Deep-seated inclusions in kimberlites and the problem of the composition of the upper mantle. Trans. by D. A. Brown and F. R. Boyd. Washington, Am. Geophys. Union.
Stephens, W. E., and Dawson, J. B. (1977) J. Geol. 85, 433-49.
Wells, P. (1977) Contrib. Mineral. Petrol. 62, 129-34.
Wood, B. J. (1977) Second Kimberlite Conference Extended Abstracts, unpaged.
Wood, B. J. and Banno, S. (1973) Contrib. Mineral. Petrol. 42, 109-24.

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