[M-ZZ52] Geology and culture

[MZZ52-P02] Provenance of the granitic gravestones in the great graveyard of the feudal lords (Yamauchi Daimyo) evaluated by multiple non-destructive rock analyses

*Wataru Tanikawa¹, Yoshichika Mochizuki², Tokuyama Hidekazu², Syota Takagi³, Yuhji Yamamoto², Yohei Hamada¹, Atsushi Wanatabe³ (1.Japan Agency for Marine-Earth Science and Technology, Kochi Instutute for Core Sample Research, 2.Kochi University, 3.Kochi Castle Museum of History)

Keywords:Magnetic susceptibility, Provenance, Granite, gravestone, graveyard of feudal load

There are magnificent graveyards for feudal lords built during the Edo period all over Japan, and the huge gravestones in the graveyards, which are several meters high, reflect the politics and culture of the time. The place of origin and transportation process of the stones used for the gravestones also provide clues to the culture of the time, but there are few documents that describe the origin of the stones in many gravestones. Several gravestones in the graveyard of the feudal lords of the Yamauchi family in Kochi Prefecture are made of granite, but the origin of the granite has remained debated. In this study, we conducted multiple non-destructive rock analyses on the gravestones of the feudal lords of the Tosa-Yamauchi family; magnetic susceptibility measurement, grain size analysis of colored minerals, and color measurement of potassium feldspar. The characteristics obtained by non-destructive analyses were compared with those of granite obtained from Kochi Prefecture and Sanyo granite in the Seto Inland Sea to estimate the origin of the gravestones. The magnetic susceptibility of the tombstones showed 0.3~0.4×10^-3 SI and followed a Gaussian distribution. The grain size of colored minerals in the granite follows a log-normal distribution, and the areal fraction and grain size of colored minerals are characterized to be larger than those in other granites. The similar characteristics of magnetic susceptibility and grain size were observed in the granite produced in Otsuki-cho, southwestern Kochi Prefecture. For the Sanyo granite, only Shiraishijima granite matched the two characteristics, but the potassium feldspar in the Shiraishijima granite showed a stronger reddish color compared to the tombstones. The results indicate that the granite of the Yamauchi family tombstones is most likely derived from the granite produced in Otsuki-cho. The stone structures in Kochi Prefecture built in the Middle Ages before the Edo period were said to be derived from Sanyo granite. The results of this study provide important insights into whether the distribution route of stone materials in Kochi Prefecture changed before the Edo period, and if so, what triggered the change. Or the origin of medieval stone structures being derived from Sanyo granite should be reevaluated.