Anatomy of the Cretaceous Hobenzan pluton, SW Japan: Internal structure of a small zoned pluton, and its genesis

The Hobenzan pluton retains a history of granitoid magma evolution in a subvolcanic magma reservoir. The GD formed as a rigid sponge, and melt fraction increases inwards from the walls, forming the HBG mush by fractional crystallization, coupled with small degrees of assimilation of adjacent schists. A more evolved and enriched low-density melt segregated from the mushy cumulate of the HBG by incomplete crystal-melt separation, and moved upwards with the assistance of gas-driven filter pressing, as indicated by the presence of miarolitic cavities, thus forming the BG at the roof of the pluton.