Relationship of Granitic Weathering Regolith and Dike identified through Micromorphology

This study aims to understand how dykes affect the weathering of granitic regolith based on micromorphological observations. The physical structure and fractures are not significantly different between the upper and lower weathering mantles. The most notable micromorphologic feature in the weathering mantles is the physical and chemical weathering of biotite. Biotite is a mineral with a unique structure called a bundle of cleavage, and its shape and character may change as weathering progresses. In the early stages of weathering, widely spaced cleavage joints develop. When narrower cleavage joints develop between wide cleavage joints, the physical weathering of biotite further progresses. Chemical weathering associated with cleavage induced water causes the color of biotite to change gradually from blackish brown to lighter brown. Migration of iron in the weathering materials during the chemical weathering process is observed along the edges(outer boundary) of quartz or potassium feldspar when the amount of weathering materials is limited. However iron is accumulated substantially enough to fill the pores of the microjoints within these minerals when the supply of weathering mantles is highly increased. It is also observed that chemical weathering is more intensively progressed above the dikes than below them.