Abstract
Based on the measurements of refractive index, specific gravity, unit cell parameter, and mineral chemistry and infrared absorption spectrum analyses of pyropes in kimberlites from China, systematic studies of the physical properties and compositional variations of pyropes of different colors and diverse paragenetic types, within and between kimberlite provinces have been undertaken. The origin of pyropes in the kimberlites and the depth of their formation have been discussed.
Pyropes of the purple series are different from those of the orange series in physical and chemical properties, for example, pyropes of the purple series are higher in a0, RI, SG, Cr2O3, MgO, Cr/(Cr+ Al), Mg/(Mg+ Fe), and Mg/(Mg+ Ca), and lower in A12O3, Fe2O3 + FeO than those of the orange series. The classification of garnets in kimberlites from China by the Dawson and Stephens’ method (1975) has been undertaken and clearly demonstrates that pyropes of diamond-rich kimberlites contain much more groups than those of diamond-poor, especially diamond-free kimberlites. The higher in a0, RI, SG, Cr2C3, Cr/(Cr + Al), knorringite and Cr-component the pyropes are, the richer in diamond the kimberlites will be. The infrared absorption spectrum patterns of pyropes change with their chemical composition regularly, as reflected in the shape and position of infrared absorption peaks. Two absorption bands at 862–901 cm-1 will grade into degeneration from splitting and the absorption band positions of pyropes shift toward lower frequency with increasing Cr2O3 content and Cr/ (Cr+ Al) ratio of pyropes. LREE contents of orange pyrope megacrysts are similar to those of purple pyrope macrocrysts, but the former is higher in HREE than the latter, showing their different chondrite-normalized patterns. The formation pressures of pyropes calculated by Crcomponent, Ca-component, knorringite molecules of pyropes show that some pyropes of the purple series in diamondiferous kimberlites fall into the diamond stability field, but all pyropes of diamond-free kimberlites lie outside the diamond stability field. The megacrysts were formed through early crystallization of kimberlites magma at high pressure condition, the majority of the purple pyrope macrocrysts have been derived from disaggregated xenoliths, but the minority of them appear to be fragments of the discrete megacryst pyropes, or phenocrysts.
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References
Boyd, F.R. and J.B. Dawson, 1972, Kimberlite garnets and pyroxene-ilment intergrowths: Carnegie Inst. Washington Yearbook., v. 71, p. 373–378.
Boyd, F.R. and J.J. Gumrney, 1982, Low calcium garment: keys to craton structure and diamond crystallization: Carnegie Inst. Washington Yearbook., v. 81, p. 261–267.
Boynton, W.V., 1984, Cosmochemistry of the rare-earth element: meteorite studies: Dev. Geochem., v. 2, p. 63–114.
Dawson, J.B., 1967, Geochemistry and origin of kimberiite, in Wyllie, P. J., ed., Ultramafic and related rocks: New York, John Wiley and Sons, p. 262–278.
Dawson, J.B., 1980, Kimberlites and their xenoliths: New York, Springer-Verlang, p. 65–187.
Dawson, J.B. and W.E. Stephens, 1975, Statistical analysis of garnets from kimberlites and associated xenoliths: J. Geol. v. 83, p. 589–607.
Dong Zhenxin, 1981, Pyropes from kimberlites and other rocks in China: Acta Mineralogica Sinica, no. 4, p. 19–229 (in Chinese with English abstract).
Dong Zhenxin, 1992, dinopyroxenes in kimberlites of China: Acta Geological Sinica, v. 5, p. 259–270.
Dang Zhenxin, 1996, Pyropes in basalts and their comparison with those in kimberlites: Acta Geoscientia Sinica (Special Issue, dedicated to the 30th International Geological Congress), p. 134–140.
Dong Zhenxin, Zhou Jianxing, Lu Qi, and Peng Zhizhong, 1984, Yimengite, K (Cr, Ti, Fe, Mg)12O19—a new mineral: Chinese Science Bulletin (KexueTongbao), v. 29, n. 7, p. 920–923.
Eggler, D.H., M.E. Mc Callum, and C.B. Smith, 1979, Megacryst assemblages in kimberlite from northern Colorado and southern Wyoming: petrology, geothermometry, barometry and a real distribution, in Boyd, F. R., H. O. A. Meyer, eds., The mantle sample: inclusions in kimberlites and other volcanics: AGU, Washington, p. 213–226.
Farmer, V.C., 1975, The infrared spectra of minerals: Mineral. Sco. Monog., London, v.4.
Garanin, V.K. et al., 1984, Ilmenites in kimberlites: Nauka, Moscow, p. 100–105 (in Russian).
Green, D.H. and A.E. Ringwood, 1967, The stability field of aluminous pyroxene peridotite and garnet peridotite and their relevance in upper mantle structure: Earth Planet. Sci. Lett., v. 3, p. 151 -160.
Griffin, W.L., CG. Ryan, J.J. Gurney, N.V. Sobolev, and T.T. Win, 1994, Chromite macrocrysts in kimberlites and lamproites: geochemistry and origin, in H.O.A. Meyer and O.H. Leonardos, eds., Kimberlites, related rocks and xenoliths: CPRM Spec. Publ. 1A/93, p. 366–377.
Griffin, W.L., F. Kaminsky, S.Y. O’Reilly, C.G. Ryan, and N.V. Sobolev, 1995, Mapping the Siberian lithosphere with garnets and spinels (Extended Abstracts): 6th International Conference, Novosibirsk, p. 194–195.
Gurney, J.J., W.R.O. Jakob, and J.B. Dawson, 1979, Megacrysts from the Monastery kimberiite pipe, South Africa, in Boyd, F.R., H.O. A. Meyer, eds., The mande sample: inclusions in kimberlites and other volcanics: AGU, Washington, p. 227–243.
Huang Wenhui et al, 1992, Kimberlites and diamonds in Huabei platform: Beijing, Geological Publishing House, p. 89–112 (in Chinese).
Jago, B.C. and R. H. Mitchell, 1985, Mineralogy and petrology of the Ham kimberlite, Somerset Island, N. W. T., Canada: Can. Mineral, v. 23, p. 428–436.
Malinovsky, I. Yu. and A. M. Doroshev, 1977, Evaluation ofP-T conditions of diamond formation with reference to chrome-bearing garnet stability: Second International Kimberlite Conference, Biship’s Lodge, Santa Fe, New Mexico, Extended Abstracts (unpaged).
Meyer, H.O.A., 1987, Inclusions in diamonds, in Nixon, P. H., ed, Mantle xenoliths: New York, John Wiley and Sons, 501–523.
Mitchell, R.H., 1978, Mineralogy of the Elwin Bay kimberlite, Somerset Island, N.W.T., Canada: Am. Mineral, v. 63, p. 47–57.
Mitchell, R.H., 1986, Kimberlites: mineralogy, geochemistry and petrology: New York, Plenum Press, p. 137–152.
Nixon, P. H. and F. R. Boyd, 1979, Garnet-bearing lherzolites and discrete nodule suites from the Malaita alnoite, Solomon, Islands, S. W. Pacific, and their bearing on oceanic mantle composition and geothem, in Boyd, F. R., H. O.A. Meyer, eds., The mantle sample: inclusions in kimberlites and other volcanics: AGU, Washington, p. 400–423.
Rickwood, P.C., 1968, On recastion analyses of garnet into end member molecules: Contrib. Mineral. Petrol., v. 18, p. 175–198.
Ringwood, A.E., S.E. Kesson, W. Hibberson, and N. Ware, 1992, Origin of kimberlites and related magmas: Earth Planet. Sci. Lett., v. 113, p. 521–538.
Sobolev, N. V., 1977, Deep-seated inclusions in kimberlites and the problem of the composition of the upper mantle: American Geopysical Union, Washington, D.C. 279p.
Sobolev, V.N., L.A. Taylor, G.A. Snyder, N.V. Sobolev, N.P. Pokhilenko, and A.D. Kharkir, 1995, A unique metasomatised peridotite xenolith from the Mir kimberlites, Siberian platform, Extended Abstracts: 6th International Conference, Novosibirsk, p.555–560.
Sobolev, N.V., N.P. Pokhilenko, and V.P. Afans’ev, 1993, Kimberlite pyrope and chromite morphology and chemistry as indicators of diamond grade in Yakutian and Arkhangelsk provinces: Proc. of the GAC-MAC Symposium, Canada, Edmonton, p. 63–69.
Sobolev, N.V., Yu.G. Lavren’yev, N.P. Pokhilenko, and L.V. Usova, 1973, Chrome-rich garnets from the kimberlites of Yakutia and their paragenesis: Contr. Mineral, Petrol., v. 40, p. 39–52.
Taylor, L.A., J.W. Shervais, and R.H. Hunter, 1983, Major and trace element geochemistry of garnets and ilmentes from eastern U.S. A. kimberlites: Geol. Soc. Amer. Ann. Mtg. Indianapolis (abstracts), p. 198–199.
Zhang Andi et al., 1991, Indicator minerals for diamonds and the data base, Beijing, Beijing Science Technique House, p. 46–123 (in Chinese with English abstract).
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This research project was supported by the Geological Museum of China, the Chinese Academy of Geological Sciences, and the National Natural Science Foundation of China (No. 49472094).
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Zhenxin, D. Mineralogical studies of pyropes in kimberlites from China. Chin. J. Geochem. 17, 29–43 (1998). https://doi.org/10.1007/BF02834620
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DOI: https://doi.org/10.1007/BF02834620