Abstract
Single whole crystals of calcic augite from M. Etna, Sicily, which display both sector and oscillatory zoning, have been serially sectioned and the form of the sectors mapped out. The principal intersectorial chemical variation is shown to be that of Ti and Al by as much as 39% (cation %) change in each, and the least variation, that of Ca (showing a 0.77 to 3.20% change). For each of three isochronous surfaces the ratio of Ti∶Al is shown to be individually constant no matter what the sector and this is thought to indicate near equilibrium conditions at the crystal/liquid interface. In addition to sector zoning these crystals display two types of concentric banding, having dimensions of about 0.25 mm, 20 μm. The 20 μm banding is shown to be both optically and chemically oscillated. Relative diffusion rates of cationic species in the melt, and growth rates of crystal faces are thought to play an important role in the formation of the oscillations, and the sector zoning.
Similar content being viewed by others
References
Bottinga, Y., Kudo, A., Weill, D.: Some observations on oscillatory zoning and crystallisation of magmatic plagioclase. Am. Mineralogist 51, 792–806 (1966)
Bowland, J. N., MacLaren, A. C., Hobbs, B. E.: Dislocations associated with optical features in naturally deformed olivines. Contr. Mineral. and Petrol. 30, 53–63 (1971)
Boyd, F. R., Smith, D.: Compositional zoning in pyroxenes from lunar rock 12021, Oceanus Procellarum. J. Petrol. 12, 439–464 (1971)
Hollister, L. S., Gancarz, A. J.: Compositional sector zoning in clinopyroxenes from the Narce area Italy. Am. Mineralogist 56, 959–979 (1971)
Hollister, L. S., Trzcienski, W. E., Jr., Hargreaves, R. B., Kulik, G. G.: Petrogenetic significance of pyroxenes in two Apollo 12 samples. Proc. Second Lunar Sci. Conf. 1, 529–557 (1971)
Lofgren, G.: Temperature induced zoning in synthetic plagioclase feldspar, in Proceedings of NATO Conference on Feldspars. Manchester: University of Manchester Press 1973
Nakamura, Y.: Origin of sector zoning of igneous clinopyroxenes. Am. Mineralogist 58, 986–990 (1973)
Smith, A. L., Carmichael, I. S. E.: Quaternary trachybasalts from S. E. California. Am. Mineralogist 54, 909–923 (1969)
Strong, D. F.: Formation of the hourglass structure in augite. Mineral. Mag. 37, 472–479 (1969)
Washington, H. S., Merwin, H. E.: A note on augites from Vesuvius and Etna. Am. J. Sci. l, 20–30 (1921)
Weill, D. F., Grieve, R. A., McCallum, I. S., Bottinga, Y.: Mineralogy—Petrology of the lunar samples. Microprobe studies on samples 12021 and 12022. Proc. Second Lunar Sci. Conf. 1, 413–430 (1971)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Downes, M.J. Sector and oscillatory zoning in calcic augites from M. Etna, Sicily. Contr. Mineral. and Petrol. 47, 187–196 (1974). https://doi.org/10.1007/BF00371538
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00371538