[M-ZZ48] Geology and culture

[MZZ48-06] Historical distribution of granitic stone materials from Setouchi area in the San-in and Hokuriku regions, Southwest Japan

*Tohru Sakiyama¹ (1.Institute of Geo History, Japan Geochronology Network)

Keywords:granite, stone material, history, magnetic susceptibility

Many ancient quarries for granites are remained in islands and coastal area of the Seto Inland Sea. 14^th to 19^th century stone materials of the granites from these quarries are widely distributed in coastal area of the Sea of Japan. Identification of quarry area of the granites is one of the important issues in Japanese historical study. I reveal distribution of such granitic stone materials in San-in and Hokuriku region and discuss transition of quarried areas.

Granitic rocks of the stone materials are divided following five types resulted by magnetic susceptibility and description.
Type A (Rokko Mountains): Medium-grained biotite granite with pinkish K-feldspar interstitially, with or without hornblende. Magnetic susceptibility ranges from 1X10^-3 to 3X10^-3 SI.
Type B (Onomichi): Medium-grained hornblende biotite granite with white colored porphyritic K-feldspar. Magnetic susceptibility ranges from 1X10^-3 to 3X10^-3 SI.
Type C (Kitagishima, Yoshima or Oshima): Medium-grained biotite granite to hornblende biotite granite. Magnetic susceptibility ranges from 0.1X10^-3 to 1X10^-3 SI.
Type D (Shodoshima or Naoshima): Coarse-grained biotite granite. Magnetic susceptibility ranges from 0.04X10^-3 to 0.07X10^-3 SI.
Type E (San-in or Hokuriku area): Various granitic rocks occurred in local area. Most of them have very high magnetic susceptibility (from 5X10^-3 to 11X10^-3 SI), except low magnetic granites from Mihama area (from 0.03X10^-3 to 0.05X10^-3 SI).
Relation between age and rocks forming stone materials in San-in to Hokuriku region indicate following history. In medieval time (14^th to 16^th century), type A granites which have been occurred in Rokko mountains area mainly distributed to San-in area. Circulation of other granites from Setouchi area began in early 17^th century and become maximum in 19^th century. On the other hand, proportion of type A granites decreased from 17^th to 19^th century.