Abstract
The anhydrous solidus of a natural clinopyroxene-ilmenite intergrowth from the kimberlite pipe at Monastery was found to be 1300° C at 20 kb increasing to 1470 ° C at 47 kb. The slope of the solidus is 6 ° C/kb, with a constant melting interval of approximately 140 ° C. Clinopyroxene was the liquidus phase in all but one case, and the ilmenite-out curve coincided with the beginning of melting. Controlled cooling experiments resulted in liquidus clinopyroxene crystals surrounded by intergrowths of clinopyroxene and ilmenite. The experimental and natural intergrowths are texturally, crystallographically and chemically similar. These results support the view that the natural clinopyroxene-ilmenite intergrowths found in kimberlites are a product of eutectic crystallisation in the upper mantle. Compositional similarities between the liquidus clinopyroxene and discrete clinopyroxene nodules from kimberlite suggest that the latter are possibly related to the clinopyroxene-ilmenite intergrowths by fractional crystallisation. Differences between the temperatures of equilibration obtained for clinopyroxenes from the natural intergrowths, and the beginning of melting on the clinopyroxene-ilmenite join, may be the result of hydrous melting in the former case, or as a consequence of the natural intergrowths existing as mantle veins or pegmatites at the ambient temperature prior to their incorporation in the kimberlite.
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References
Akella, J.: Friction measurements in solid-media, high pressure apparatus. Carnegie Inst. Wash. Yearbook 73, 606–609 (1974)
Akella, J., Boyd, F.R.: Partitioning of Ti and Al between pyroxenes, garnets and oxides. Carnegie Inst. Wash. Yearbook 71, 378–384 (1972)
Boyd, F.R., England, J.L.: Apparatus for phase-equilibrium measurements at pressures up to 50 kb and temperatures up to 1750 ° C. J. Geophys. Res. 65, 741–748 (1960)
Boyd, F.R., Nixon, P.H.: Origin of the ilmenite-silicate nodules in kimberlites from Lesotho and South Africa. In: Lesotho kimberlites, P.H. Nixon, ed. pp. 254–268. Maseru: Lesotho National Development Corp., 1973
Dawson, J.B., Reid, A.M.: A pyroxene-ilmenite intergrowth from the Monastery Mine, South Africa. Contrib. Mineral. Petrol. 26, 296–301 (1970)
Gurney, J.J., Fesq, H.W., Kable, E.J.D.: Clinopyroxene-ilmenite intergrowths from kimberlite; A re-appraisal. In: Lesotho kimberlites, P.H. Nixon ed., pp. 238–253. Maseru: Lesotho National Development Corp. 1973
Harger, H.S.: The diamond pipes and fissures of South Africa. Trans. Geol. Soc. S. Africa, 8, 110–134 (1906)
MacGregor, I.D.: An hypothesis for the origin of kimberlite. In: Mineralogy and petrology of the upper mantle, sulphides, mineralogy and geochemistry of non-marine evaporites, B.A. Morgan, ed., pp. 51–62, Min. Soc. Am. Spec. Papers 3 (1970)
MacGregor, I.D., Wittkop, R.W.: Diopside-ilmenite xenoliths from the Monastery Mine, Orange Free State, South Africa. Abstracts with Programs for 1970, 2, Geol. Soc. Am. (1970)
Mitchell, R.H., Carswell, D.A., Brunfelt, A.O.: Mineralogy and rare earth geochemistry of an ilmenite-clinopyroxene xenolith from the Monastery Mine. In: Lesotho kimberlites, P.H. Nixon, ed., 224–229. Maseru: Lesotho National Development Corp. 1973
McAllister, R.H., Meyer, O.A., Brookins, D.G. “Pyroxene”-ilmenite xenoliths from the Stockdale Pipe, Kansas: Chemistry, crystallography and origin. In: Physics and chemistry of the earth, Vol.9, L.H. Ahrens, J.B. Dawson, A.R. Duncan, A.J. Erlank, eds., pp. 287–293. Oxford-New York-Toronto-Sydney-Paris-Braunschweig: Pergamon Press 1975
Ringwood, A.E., Lovering, J.E.: Significance of pyroxene-ilmenite intergrowths among kimberlite xenoliths. Earth Planet. Sci. Lett. 19, 371–375 (1970)
Williams, A.F.: The genesis of the diamond, 2 vols. London: E. Benn 1932
Wyatt, B.A., McAllister, R.H., Boyd, F.R., Ohashi, Y.: An experimentally produced clinopyroxene-ilmenite intergrowth. Carnegie Inst. Wash. Yearbook 74, 536–539 (1975)
Yund, R.A., McAllister, R.H.: Kinetics and mechanisms of exsolution. Chem. Geol. 6, 5–30 (1970)
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Wyatt, B.A. The melting and crystallisation behaviour of a natural clinopyroxene-ilmenite intergrowth. Contr. Mineral. and Petrol. 61, 1–9 (1977). https://doi.org/10.1007/BF00375941
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DOI: https://doi.org/10.1007/BF00375941