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

Abstract

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.