Emplacement and Cooling History of a Pluton With Evident Laminated Structure Constrained by Field Anatomy of the Kinpusan Pluton, Central Japan

There are limited examples of incremental emplacement models of pluton that can be demonstrated through field observations. Comprehensive field investigations identified the existence of magmatic structures of alternating layers of multiple magmatic enclave-rich and enclave-free granite sheets in the Kinpusan pluton in central Japan, which geologically constrains the geometry and duration of the intrusion time interval of the incremental magmatic unit. Most layer boundaries are inferred by the presence or absence of enclaves, and the microstructure of the granites comprising the different layers is hardly distinguishable. However, several outcrops that show clear subhorizontal structures due to grain size contrast in the host granite exist. The emplacement history consists of repetitive downward accretion of 20–200 m thick subhorizontal magma sheets with relatively high magma flux, and is a good candidate for comparison with thermal models used by many researchers in recent years. The observed grain size, aplite, and miarolitic cavities show a tendency to increase in the lower center of the body, indicating a longer period of high-temperature preservation than the pluton margin. Spatial patterns at this map scale were consistent with the predictions of the intrusion thermal model and the results of the zircon U–Pb dating together with a zircon saturation modeling, supporting the validity of the modeling.