Abstract
Eclogite inclusions from kimberlitic diatremes on the Colorado Plateau contain intricately zoned garnet and pyroxene and unusual textures. Detailed electron microprobe traverses for a clinopyroxene-garnet-phengite-lawsonite-rutile assemblage show garnet zoning from Alm69Gr21Py10 (core) to Alm61Gr13Py26 (rim) and pyroxene zoning from Jd50 (core) through Jd77 to Jd55 (rim). Pyroxene cores are Cr-rich in another rock. Sharp compositional discontinuities and zoning reversals are preserved in garnet and pyroxene. Oscillatory zoning occurs in both phases on a 10–20 μm scale, with variations of up to 6% Py in garnet and 15% Jd in pyroxene. Phengite is unzoned and contains 74% celadonite endmember.
Skeletal, pyroxene-filled garnet crystals are common in some rocks, and garnets in other rocks clearly began growth as shell-like crystals. Some rocks contain domains of coarse, prismatic pyroxene with very fine-grained, interstitial magnesium silicates. The texture appears to have resulted from crystallization in the presence of a fluid phase, and water pressure is inferred to have equalled total pressure during crystallization. Eclogite formation at high water pressure may reflect subcrustal crystallization.
An analysis of error propagation shows that ferrous iron calculations from electron probe data are not meaningful for these jadeitic pyroxenes, and temperature differences between core and rim crystallization cannot be documented. The garnet textures and oscillatory zoning are unusual for metamorphic rocks, and they suggest disequilibrium crystallization after overstepping of reaction boundaries. All data fit a model of eclogite formation during cooling and metasomatism of basaltic dikes intruded into a cool upper mantle, but the results here do not preclude other origins, such as subduction zone metamorphism.
Similar content being viewed by others
References
Albee, A.L., Ray, L.: Correction factors for electron probe microanalysis of silicates, oxides, carbonates, phosphates, and sulfates. Anal. Chem. 42, 1408–1414 (1970)
Bearth, P.: Zur Entstehung alpinotyper Eklogite. Schweiz. Mineral. Petrogr. Mitt. 45, 179–188 (1965)
Bottinga, Y., Kudo, A., Weill, D.: Some observations on oscillatory zoning and crystallization of magmatic plagioclase. Am. Mineral. 51, 792–806 (1966)
Bryhni, I., Griffin, W.L.: Zoning in eclogite garnets from Nordfjord, west Norway: Contrib. Mineral. Petrol. 32, 112–125 (1971)
Chapman, D., Pollack, H.N.: Regional geotherms and lithospheric thickness. Geology 5, 265–268 (1977)
Church, W.R.: Eclogites. In: Basalts: The Poldervaart Treatise on Rocks of Basaltic Composition (H.H. Hess and Arie Poldervaart, eds.), Vol. 2, pp. 755–798. New York, London, Sydney: Interscience Publishers 1968
Coleman, R.G., Lee, D.E., Beatty, L.B., Brannock, W.W.: Eclogites and eclogites: their differences and similarities. Geol. Soc. Am. Bull. 76, 483–508 (1965)
Dudley, P.P.: Electron microprobe analyses of garnet in glaucophane schists and associated eclogites. Am. Mineral. 54, 1139–1150 (1969)
Ernst, W.G.: Significance of phengitic micas from low-grade schists. Am. Mineral. 48, 1357–1373 (1963)
Ernst, W.G., Seki, Y., Onuki, H., Gilbert, M.C.: Comparative Study of Low-Grade Metamorphism in the California Coast Ranges and the Outer Metamorphic Belt of Japan. Geol. Soc. Am. Mem. 124, 276 p. (1970)
Essene, E.J., Fyfe, W.S.: Omphacite in Californian metamorphic rocks. Contrib. Mineral. Petrol. 15, 1–23 (1967)
Essene, E., Ware, N.G.: The low temperature xenolith origin of eclogites in diatremes. Geol. Soc. Am. Abstr. 2, 547–548 (1970)
Fisher, G.W.: Rate laws in metamorphism. Geochim. Cosmochim. Acta 42, 1035–1050 (1978)
Griffin, W.L., Raheim, A.: Convergent metamorphism of eclogites and dolerites, Kristiansund area, Norway. Lithos 6, 21–40 (1973)
Helmstaedt, H., Anderson, O.L., Gavasci, A.T.: Petrofabric studies of eclogite, spinel-websterite, and spinel-lherzolite xenoliths from kimberlite-bearing breccia pipes in southeastern Utah and northeastern Arizona. J. Geophys. Res. 77, 4350–4365 (1972)
Helmstaedt, H., Doig, R.: Eclogite nodules from kimberlite pipes of the Colorado Plateau — samples of subducted Francican-type oceanic lithosphere. Phys. Chem. Earth 9, 95–111 (1975)
Helmstaedt, H., Schulze, D.J.: Type A-Type C eclogite transition in a xenolith from the Moses Rock diatreme-further evidence for the presence of metamorphosed ophiolites beneath the Colorado Plateau. In: Extended Abstracts. Sec. International Kimb. Conf. (1977)
Kirkpatrick, R.J.: Crystal growth from the melt: a review. Am. Mineral. 60, 798–814 (1975)
Krogh, E.J., Raheim, A.: Temperature and pressure dependence of Fe-Mg partitioning between garnet and phengite, with particular reference to eclogites. Contrib. Mineral. Petrol. 66, 75–80 (1978)
Lofgren, G.: An experimental study of plagioclase crystal morphology: Isothermal crystallization. Am. J. Sci. 274, 243–273 (1974)
McGetchm, T.R.: The Moses Rock dike: geology, petrology and mode of emplacement of kimberlite-bearing breccia dike, San Juan County, Utah. Doctorate dissertation, Calif. Inst. Tech., 405 p. (1968)
McGetchm, T.R., Silver, L.T.: A crustal-upper mantle model for the Colorado Plateau based on observations of crystalline rock fragments in the Moses Rock dike. J. Geophys. Res. 77, 7022–7037 (1972)
McGetchin, T.R., Ullrich, G.W.: Xenoliths in maars and diatremes with interferences for the moon, Mars, and Venus. J. Geophys. Res. 78, 1833–1853 (1973)
Murad, E.: Zoned birefringent garnets from Thera Island, Santorini Group (Aegean Sea). Mineral. Mag. 40, 715–719 (1976)
Newton, R.C., Fyfe, W.S.: High pressure metamorphism. In: The Evolution of the Crystalline Rocks (D.K. Bailey and R. MacDonald, eds.), pp. 101–186. London-New York-San Francisco: Academic Press 1976
Newton, R.C., Kennedy, G.C.: Some equilibrium reactions in the join CaAlSi2O8-H2O. J. Geophys. Res. 68, 2967–2976 (1963)
Nitsch, K.H.: Das P-T-Xco2-Stabilitätsfeld von Lawsonit. Contrib. Mineral. Petrol. 34, 116–134 (1972)
Nitsch, K.H.: Neue Erkenntnisse zur Stabilität von Lawsonit. Fortschr. Mineral. 51, Beiheft 1, 34–36 (1974)
O'Hara, M.J., Mercy, E.L.P.: Eclogite, peridotite, and pyrope from the Navajo country, Arizona and New Mexico. Am. Mineral. 51, 336–352 (1966)
Raheim, A., Green, D.H.: Experimental determination of the temperature and pressure dependence of the Fe-Mg partition coefficient for coexisting garnet and clinopyroxene. Contrib. Mineral. Petrol. 48, 179–203 (1974)
Raheim, A., Green, D.H.: P, T paths of natural eclogites during metamorphism — a record of subduction. Lithos 8, 317–328 (1975)
Ryburn, R.J., Raheim, A., Green, D.H.: Determination of the P, T paths of natural eclogites during metamorphism — record of subduction. Lithos 9, 161–164 (1976)
Shewmon, P.G.: Transformations in Metals, 394 p. New York: McGraw-Hill 1969
Sibley, D.F., Vogel, T.A., Walker, B.M., Byerly, G.: The origin of oscillatory zoning in plagioclase: a diffusion and growth controlled model. Am. J. Sci. 276, 275–284 (1976)
Smith, D.: Hydrous minerals and carbonates in peridotite inclusions from the Green Knobs and Buell Park kimberlitic diatremes on the Colorado Plateau. Proc. Sec. International Kimb. Conf. (in press)
Smith, D., Levy, S.: Petrology of the Green Knobs diatreme and implications for the upper mantle below the Colorado Plateau. Earth Planet. Sci. Lett. 29, 107–125 (1976)
Thompson, A.B., Tracy, R.J., Lyttle, P.T., Thompson, J.B. Jr.: Prograde reaction histories deduced from compositional zonation and mineral inclusions in garnet from the Gassetts schist, Vermont. Am. J. Sci. 277, 1152–1167 (1977)
Velde, B.: Phengite micas: synthesis, stability and natural occurrence. Am. J. Sci. 263, 886–913 (1965)
Velde, B.: Si4+ content of natural phengites. Contrib. Mineral. Petrol. 14, 250–258 (1967)
Watson, K.D.: Kimberlite pipes of northeastern Arizona. In: Ultramafic and Related Rocks (P.J. Wyllie, ed.), pp. 261–269. New York: Wiley and Sons 1967
Watson, K.D., Morton, D.M.: Eclogite inclusions in kimberlite pipes at Garnet Ridge, northeastern Arizona. Am. Mineral. 54, 267–285 (1969)
Yoder, H.S. Jr., Chinner, G.A.: Almandite-pyrope-water system at 10,000 bars. Carnegie Inst. Washington Yearbook 59, 81–84 (1960)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Smith, D., Zientek, M. Mineral chemistry and zoning in eclogite inclusions from Colorado Plateau diatremes. Contr. Mineral. and Petrol. 69, 119–131 (1979). https://doi.org/10.1007/BF00371855
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00371855