Abstract
The carbonatite at Magnet Cove, Arkansas, USA contains a great variety and abundance of magmatic and hydrothermal inclusions that provide an informative, though fragmentary, record of the original carbonatite melt and of late hydrothermal solutions which permeated the complex in postmagmatic time. These inclusions were studied by optical and scanning electron microscopy.
Primary magmatic inclusions in monticellite indicate that the original carbonatite melt contained approximately 49.7 wt% CaO, 16.7% CO2, 15.7% SiO2, 11.4% H2O, 4.4% FeO+Fe2O3, 1.1% P2O5 and 1.0% MgO. The melt was richer in SiO2 and iron oxides than the carbonatite as now exposed; this is attributed to crystal settling and relative enrichment of calcite at shallower levels. The density of the carbonatite melt as revealed by the magmatic inclusions was approximately 2.2–2.3 g/cc. Such a light melt should separate rapidly from any denser parent material and could be driven forcibly into overlying crustal rocks by buoyant forces alone. Fluid inclusions in apatite suggest that a separate (immiscible) phase composed of supercritical CO2 fluid of low density coexisted with the carbonatite magma, but the inclusion record in this mineral is inconclusive with respect to the nature of any other coexisting fluids. Maximum total pressure during CO2 entrapment was about 450 bars, suggesting depths of 1.5 km or less for apatite crystallization and supporting earlier proposals of a shallow, subvolcanic setting for the complex.
Numerous secondary inclusions in the Magnet Cove calcite contain an intriguing variety of daughter minerals including some 19 alkali, alkaline earth and rare earth carbonates, sulfates and chlorides few of which are known as macroscopic phases in the complex. The exotic fluids from which the daughter minerals formed are inferred to have cooled and diluted through time by progressive mixing with local groundwaters. These fluids may be responsible for certain late veins and elemental enrichments associated with the complex.
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References
Anderson, C.A.: Electron probe analysis of thin layers and small particles with emphasis on light element determinations in the electron microprobe (T.D. McKinley et al., ed.). New York: John Wiley and Sons 1966
Currie, K.L., Ferguson, John: A study of fenitization around the alkalic carbonatite complex at Callander Bay, Ontario, Canada. Can. J. Earth Sci. 8, 498–517 (1971)
Eckermann, H. von: The alkaline district of Alnö Island. Sveriges Geol. Undersok Ser. Ca. 36 (1948)
Erickson, R.L., Blade, L.V.: Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas. U.S.Geol. Soc. Profess. Papers 425, p. 94 (1963)
Franz, G.W., Wyllie, P.G.: Experimental studies in the system CaO-MgO-SiO2-CO2-H2O in Ultramafic and related rocks (P.J. Wyllie, ed), pp. 323–326. New York: John Wiley and Sons, 1967
Franz, G.W., Wyllie, P.J.: Melting relationships in the system CaO-MgO-SiO2-H2O at 1kb pressure. Geochim. Cosmochimi. Acta 30, 9–22 (1966)
Fryklund, V.C., Harner, R.S., Kaiser, E.P.: Niobium (columbium) and titanium at Magnet Cove and Potash Sulphur Springs, Arkansas. U.S. Geol. Soc. Surv. Bull. 1015-B, 23–56 (1954)
Gold, D.P.: Average chemical composition of carbonatites. Econ. Geol. 58, 988–991 (1963)
Henrich, E.Wm.: The geology of carbonatites, p. 555. Chicago: Rand McNally and Co. 1966
Howard, J.M.: Transition element geochemistry and petrography of the Potash Sulfur Springs intrusive complex, Garland County, Arkansas. Unpublished M.S. Thesis, Univ. of Arkansas, 118 (1974)
Huang, W.L., Wyllie, P.J.: Eutectic between wollasonite II and calcite contrasted with thermal barrier in MgO-SiO2-CO2 at 30 kilobars, with applications to kimberlite-carbonatite petrogenesis. Earth Planet. Sci. Lett. 24, 305–310 (1974)
Kennedy, G.C., Holser, W.T.: Pressure-volume-temperature and phase relations of water and carbon dioxide. In: Handbook of physical constants (S.P. Clark, Jr., ed.). Geol. Soc. Am. Memoir 97, 371–384 (1966)
Metzger, F.W., Kelly, W.C., Nesbitt, B.E., Essene, E.J.: Scanning electron microscopy of daughter minerals in fluid inclusions. Econ. Geol. 72, pp. 141–152 (1977)
Pecora, W.T.: Carbonatites: A review. Geol. Soc. Am. Bull. 67, 1537–1556 (1956)
Rankin, A.H., Le Bas, M.J.: Liquid immiscibility between silicate and carbonate melts in naturally occurring ijolite magma. Nature 250, 206–209 (1974)
Roedder, E.W.: Liquid CO2 in inclusions in olivine-bearing nodules and phenocrysts from basalts. Am. Mineralogist. 50, 1746–1782 (1965)
Roedder, E.W.: Fluid inclusions as samples of ore fluids. In: Geochemistry of hydrothermal ore deposits (H.L. Barnes, ed.), pp. 515–574. New York: Holt, Rinehart, and Wilson 1967
Roedder, E.W., Coombs, D.S.: Immiscibility in granitic melts indicated by fluid inclusions in ejected granitic blocks from Ascension Island. J. Petrol. 8, 417–451 (1967)
Rucklidge, J.C., Gasparrini, E.: Specifications of a computer program for processing electron microprobe analytical data: EMPADAR VII: Dept. of Geology, Univ. of Toronto, 1969
Schairer, J.F., Osborn, E.F.: The system CaO-MgO-FeO-SiO2: 1, Preliminary data on the join CaSiO3-MgO-FeO. J. Am. Ceram. Soc. 33, 160–167 (1950)
Skinner, B.J.: Thermal expansion. In: Handbook of physical constants (S.P. Clark, Jr., ed.). Geol. Soc. Am. Memoir 97, 75–96 (1966)
Swift, W.H.: The geology of Chishanya, Bihera District, Southern Rhodesia. Trans. Geol. Soc. Edinburgh 15, 346–359 (1952)
Taenouchi, S., Kennedy, G.C.: The solubility of carbon dioxide in NaCl solutions at high temperatures and pressures. Am. J. Sci. 263, 445–454 (1965)
Van Groos, A.F.K., Wyllie, P.J.: Liquid immiscibility in the join NaAlSi3O8-CaAl2Si2O8-Na2CO3-H2O. Am. J. Sci. 273, 465–487 (1973)
Wyllie, P.J.: Melting relationships in the system CaO-MgO-CO2-H2O with petrological applications. J. Petrol. 6, 101–123 (1965)
Wyllie, P.J.: Experimental data bearing on the petrogenetic links between kimberlites and carbonatites. Mineral. Soc. India, IMA Vol., 67–82 (1966)
Wyllie, P.J.: Phase equilibria in the system CaO-CO2-H2O and related systems, with implications for crystal growth of calcite and apatite. J. Am. Ceram. Soc. 50, 43–46 (1967)
Wyllie, P.J., Biggar, G.M.: Fractional crystallization in the “Carbonatite systems” CaO-MgO-CO2-H2O and CaO-CaF2-P2O5-CO2-H2O. Mineral Soc. India, IMA Vol., 92–105 (1966)
Wyllie, P.J., Cox, K.G., Biggar, G.M.: The habit of apatite in synthetic systems and igneous rocks. J. Petrol. 3, 238–243 (1962)
Wyllie, P.J., Haas, J.L., Jr.: The system CaO-SiO2-CO2-H2O. II the petrogenetic model. Geochim. Cosmochim. Acta 30, 525–543 (1966)
Wyllie, P.J., Tuttle, O.F.: The system CaO-CO2-H2O and the origin of carbonatites. J. Petrol. 1, 1–46 (1960a)
Wyllie, P.J., Tuttle, O.F.: Experimental verification for the magmatic origin of carbonatites. Proc. 21st Int. Geol. Congress, Copenhagen 13, 310–318 (1960b)
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Nesbitt, B.E., Kelly, W.C. Magmatic and hydrothermal inclusions in carbonatite of the Magnet Cove Complex, Arkansas. Contr. Mineral. and Petrol. 63, 271–294 (1977). https://doi.org/10.1007/BF00375576
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DOI: https://doi.org/10.1007/BF00375576