Journal ArticleDOI
Sector and oscillatory zoning in calcic augites from M. Etna, Sicily
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In this article, 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 and 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 of Ca (showing a 0.77 to 3.20% change).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.read more
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References
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Journal Article
Some observations on oscillatory zoning and crystallization of magmatic plagioclase
Y. Bottinga,A. Kudo,D. Weill +2 more
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Origin of sector-zoning of igneous clinopyroxenes
Yasuo Nakamura,Yasuo Nakamura +1 more
TL;DR: In this article, several types of sector-zoning are interpreted, based on the concept of protosites, and the geometry of each protosite on each growth surface differs from that of the corresponding true structural site in variable degree.
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Dislocations associated with optical features in naturally-deformed olivine
TL;DR: In this paper, the dislocations are arranged in arrays forming low-angle sub-boundaries which have been identified with features observed in the optical microscope, and a comparison of this dislocation substructure with that observed in olivine and in metals, experimentally deformed under various conditions, suggests that the deformation in nature has occurred by creep.
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