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[SCG73-09] Variation of the average aspect ratio of plagioclase in the Atsumi dolerite sills, Northern Japan
Keywords:aspect ratio, cooling rate, Atsumi dolerite
As a result, the following results were obtained for plagioclase from the two sills: (1) The ranges of the average aspect ratios (major axis length / minor axis length) are about 3.8-5.6 and 6.4-9.8 for the Kayaoka sheet and the intrusive body in Hakuzan island, respectively. (2) There is a negative correlation between the average aspect ratios and the calculated crystallization times in the two sills. (3) In the Kayaoka sheet, the average aspect ratio increases from the central part towards the top and bottom but decreases again only in the undermost few meters (Fig.1; S-shaped profile). The features of (2) and (3) are the same as those reported in Holness (2014). However, compared between sills of comparable thickness, average aspect ratios in our study are significantly larger than those in Holness (2014) (for example, the average aspect ratio in the 129-meter-thick Whin sill is about 3.0 - 3.6). The differences in plagioclase aspect ratio are likely to be caused by the influence of magma viscosity on diffusion coefficient.