Quantification of the Textural Variation in Alkaline lgneous Intrusion by Spatial Correlation Function: Murotomisaki Gabbroic Complex

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  • MORISHITA Ritsuo
    Graduate School of Science and Technology, Kumamoto University
  • AKIZUKI Morio
    Department of Earth Sciences, Faculty of Science, Kumamoto University
  • OBATA Masaaki
    Department of Geology and Mineralogy, Faculty of Science, Kyoto University

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  • 空間相関関数による塩基性火成貫入岩体の組織変化の定量的評価について-室戸岬はんれい岩体を例として
  • クウカン ソウカン カンスウ ニ ヨル エンキセイ カセイカンニュウガンタイ

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The texture of igneous rocks from the Murotomisaki gabbroic complex, Shikoku island, were quantitatively studied by means of a digital image analysis coupled with the two point spatial correlation method. The complex has a layered structure and a considerable variation of modal composition and the texture. Seven samples at different stratigraphic positions of the complex were selected for the textural analysis. Two kinds of correlation functions, σ and τ distributions, for olivine, pyroxene and plagioclase were calculated from digital images taken from photomicrographs of each sample. Significant variation of the slope of the τ distribution at zero distances for plagioclase-pyroxene and olivine-pyroxene pairs were observed among the samples. In order to interpret the textural variation in terms of the crystallization history and kinetics, a series of computer simulation based on a simple geometric model was conducted in which two new phases appear in an old phase in different sequences and with different timing. The σ and τ distributions were also calculated for simulated textures. We compared with the simulated textures and observed textures on the Murotomisaki gabbro. As a result, it was inferred that olivine preceded the plagioclase precipitation near the margin of the body while the plagioclase preceded the olivine precipitation in the interior.

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