Abstract
Thermally metamorphosed and metasomatised fragments of basement actinolite-chlorite-calcite-quartz schists and quartz-bearing marbles are found as inclusions in Quaternary agglomerates and historic (197 B. C.—1950) dacitic lavas of Santorini volcano, Greece.
Inclusions in agglomerates preserve the structure of parent schists in the alternation of bands rich in diopside or salite with bands rich in plagioclase. By contrast, inclusions in historic dacites are not banded. Most develop a thin zone of hybrid material at the contact with enclosing lava. The assemblage calcic clinopyroxene-wollastonite-plagioclase is commonly developed. The clinopyroxene is a Fe3+-rich salite or ferrosalite. Andradite-rich garnet and sphene are accessory minerals. Most examples carry interstitial siliceous glass of distinctive chemical composition, and several show minor olivine, augite, hypersthene and calcic plagioclase of magmatic origin.
Other inclusions exhibit the assemblage anhydrite-calcic clinopyroxene, the latter mineral ranging widely in Al content. A single example has been observed to develop two distinct assemblages, the first coarsely crystalline melilite-wollastonite-magnetite, the second finely intergrown melilite-wollastonite-andraditic garnet (-xonotlite).
Stability data for hedenbergite and andradite as constituents of skarn assemblages suggest that the clinopyroxene-rich assemblages of inclusions in historic dacites formed at temperatures near to or above 800° C and oxygen fugacity (fO2) considerably greater than that which could be imposed upon the inclusions by dacite magma (T ∼900° C, fO2∼10−13 atm.). Thermal breakdown of original carbonates of the inclusions probably supplied the necessary oxygen.
T-fO2 data for the reaction 4 Magnetite+18 Wollastonite ⇌ 6 Andradite indicate that the assemblage melilite-wollastonite-magnetite of the last inclusion described formed at higher T and/or lower fO2 than the assemblage melilite-wollastonite-garnet. The latter assemblage undoubtedly formed during inclusion of the fragment by dacite magma, while metamorphism by a more basic, high temperature magma may have produced the former. Temperature data for reactions limiting the stability of melilite in the system CaO-Al2O3-SiO2-H2O indicate a minimum temperature of around 800° C for formation of both assemblages.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Boettcher, A. L.: The system CaO-Al2O3-SiO2-H2O at high pressures and temperatures. J. Petrol. 11, 337–380 (1970).
Buddington, A. F., Lindsley, D. H.: Iron-titanium oxide minerals and synthetic equivalents. J. Petrol. 5, 310–357 (1964).
Clark, J. R., Papike, J. J.: Crystal-chemical characterization of omphacites. Amer. Mineralogist 53, 840–868 (1968).
Coughlin, J. P.: Contributions to the data on theoretical metallurgy. XII. Heats and free energies of formation of inorganic oxides. U. S. Bur. Mines, Bull. 542, 80 p. (1954).
Deer, W. A., Howie, R. A., Zussman, J.: Rock forming minerals. Vol. II: Chain silicates. London: Longmans 1963.
Eugster, H. P., Wones, D. R.: Stability relations of the ferruginous biotite, annite. J. Petrol. 3, 82–125 (1962).
Fouqué, F.: Nodules à wollastonite, pyroxene fassäite, grenat melanite des laves de Santorin. Compt. Rend. 80, 631 (1875).
—: Santorin et ses éruptions, 440 p. Paris: Masson et Cie. 1879.
Gustafson, W. I.: Stabilities of andradite and hedenbergite and their relation to skarn equilibria (Abstract). Geol. Soc. Amer., Annual Meetings, Mexico City (1968).
Häkli, T. A., Wright, T. L.: The fractionation of nickel between olivine and augite as a geothermometer. Geochim. Cosmochim. Acta 31, 877–884 (1967).
Holland, H. D.: Some applications of thermochemical data to problems of ore deposits. II: Mineral assemblages and the composition of ore-forming fluids. Econ. Geol. 60, 1101–1166 (1965).
Huckenholz, H. G.: Synthesis and stability of Ti-andradite. Yb. Carnegie Instn. Wash. 67, 139–153 (1968).
Kténas, C.: Les enclaves enallogènes et les laves endomorphisées de Fouqué-Kameni. Compt. Rend. 184, 1012 (1927).
Lacroix, A.: Les enclaves des roches volcaniques, 710 p. Macon: Protat Freres 1893.
—: Sur les transformations endomorphiques de la andesite de Santorin sous l'influence d'enclaves enallogènes calcaires. Compt. Rend. 130, 272 (1900).
—: Sur deux nouveaux groupes d'enclaves des roches eruptives. Bull. Soc. Franc. Mineral. 24, 488–504 (1901).
Nicholls, I. A.: Petrology and geochemistry of the Santorini lavas. Unpubl. Ph. D. thesis, Cambridge Univ. 275 p. (1968).
—: Petrology of Santorini volcano, Cyclades, Greece. J. Petrol. 12, 67–119 (1971).
Ninkovich, D., Heezen, B. C.: Santorini tephra, p. 413–452 in Submarine geology and geophysics, 464 p. London: Butterworths 1965.
Reck, H.: Santorin: der Werdegang eines Inselvulkans und sein Ausbruch 1925–28, 3 vol. Berlin: Dietrich Reimer 1936.
Reverdatto, V. V.: Paragenetic analysis of carbonate rocks of the spurrite-merwinite facies. Geochem. International 1038–1053 (1964).
Walter, L. S.: Experimental studies on Bowen's decarbonation series III: P-T univariant equilibrium of the reaction: Spurrite+monticellite ⇌ merwinite+calcite and analysis of assemblages found at Crestmore, California. Am. J. Sci. 263, 64–77 (1965).
Winkler, H. G. F.: Petrogenesis of metamorphic rocks, 237 p. Berlin-Heidelberg-New York: Springer 1967.
Yoder, H. S., Jr., Tilley, C. E.: Origin of basalt magmas: an experimental study of natural and synthetic rock systems. J. Petrol. 3, 342–532 (1962).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Nicholls, I.A. Calcareous inclusions in lavas and agglomerates of Santorini volcano. Contr. Mineral. and Petrol. 30, 261–276 (1971). https://doi.org/10.1007/BF00404722
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00404722