Laboratory growth of sector zoned clinopyroxenes in the system CaMgSi2O6-CaTiAl2O6 |
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| Authors: | A Kouchi Y Sugawara K Kashima I Sunagawa |
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| Institution: | (1) Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Aoba, 980 Sendai, Japan;(2) Present address: Institute of Low Temperature Science, Hokkaido University, 060 Sapporo, Japan |
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| Abstract: | Sector zoning has been experimentally reproduced in CaMgSi2O6-CaTiAl2O6 clinopyroxene crystals by isothermal crystallization using seed crystals. Element partitioning in different growth sectors and between the core and rim portions in single crystals was analysed in relation to growth rate R and degree of supercooling  T. The TiO2 and Al2O3 contents increase with increase in R and T, but when they are compared between different sectors in a single crystal grown at the same T, they correlate negatively with R. The order of faces in respect of contents of TiO2 and Al2O3 is (100)>(110) (010)(111) at T= 13° C and 18° C but changes to (110)>(100)>(010)>(111) at T= 25° C. The growth mechanism is concluded to be controlled by interface kinetics at T= 13–25° C for all these faces, while at T=45° C this relation holds for (100) and (010) faces, but not for (110) and (111), based on the growth rate versus supercooling relation and surface microtopographic observations. The interface kinetics play the essential role in the formation of sector zoning, when the layer growth mechanism takes place. |
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