11:00 AM - 1:00 PM
[MZZ52-P03] Lithology and magnetic susceptibility of stone stupas (cho-ishi) on the approach to the Koyasan, Wakayama Prefecture.
Keywords:granite, stone material, history, magnetic susceptibility
Many stone stupas are situated along the approach to Koyasan area which has been designated a world heritage. The stone stupas are made of granitic rocks except one sandstone stupa. Lithological features were described, and magnetic susceptibilities were measured on 219 granitic stone stupas situated along 24km trail from Jison-in Temple at the foot of Koyasan to Okuno-in which is holiest zone of Koyasan, and quarrying areas of the stones were discussed. It has been understood that they were originally built at 13th century (1265-1279) and were restored at 18th century (1771-1778) and at 20th century (1912-1913) by the inscription on the stones.
Granitic stones forming the stupas are composed of following 6 type stones.
A: Medium- to fine-grained biotite granite with pinkish alkali-feldspar. Color index: 3 to 4 vol.%. Magnetic susceptibility: 1.2 to 5.4X10-3SI. Fifty-nine stupas are made of these granite and established years of 13th century are inscribed on twenty-one of them. Relation diagram of magnetic susceptibility and color index revealed that stones of type A are similar to so-called “Rokko granites” distributing southern part of Hyogo Prefecture.
B: Coarse-grained porphyritic hornblende biotite granite to granodiorite. Color index: 9 to 17 vol.%. Magnetic susceptibility: 0.16 to 0.28X10-3SI. This type is characterized by large euhedral white K-feldspar and are often strongly foliated by K-feldspar and mafic minerals. Elongated mafic enclaves sometimes present in parallel to the foliation. A hundred stupas are made of this type and established years of 13th century are inscribed on thirty of them. They are low magnetic despite being rich in mafic minerals and they often have foliation. These characteristics indicate that the stones of type B were from Ryoke zone.
C: Coarse-grained to medium-grained equigranular biotite granite with or without hornblende. Color index: 4 to 7 vol.%. Magnetic susceptibility: 0.07 to 0.17 X10-3 SI. Aggregation of fine-grained felsic minerals by deformation and weak foliation are partly observed. Felsite vein frequently intrude into this type granites.Twenty-one stupas are made of this type granites and established years of 13th century are inscribed on eight of them. Most of type C granites are more leucocratic and lower magnetic than the granites of type B. However, some of type C granites show similar rock facies to type B granites and these two type granites are plot on same trend in magnetic susceptibility - color index diagram. Granites of type C may be one rock facies of type B.
D: Coarse-grained biotite granite. Color index: 3 to 7 vol.%. Magnetic susceptibility: 0.04 to 0.18 X10-3 SI. They have leucocratic and homogeneous appearance. Ten stupas are made of this type granites and established years of 13th century are inscribed on all of them.
E: Medium-grained hornblende biotite granodiorite. Magnetic susceptibility: 1.1 X10-3 SI. Only one stupa of this stone was found in the area. There is an inscription of 18th century (1771). Type D and E stones has not been able to identify the specific quarried area, but it is close to the some granites of the Seto inland sea region.
F: Coarse-grained biotite granite with pink K-feldspar. Color index: 8 to 10 vol.%. Magnetic susceptibility: 0.9 to 1.9 X10-3 SI. Established years of 20th century were inscribed on twenty-six stupas within twenty-seven stupas of this type. Stones of type F is assumed to be granite in the Mannari region in Okayama Prefecture from their appearance, and this is supported from the magnetic susceptibility and the color index.
The historical changes of the above-mentioned stone quarried areas are summarized as follows. The stone stupas was built in the early 13th century using the Rokko granite and Ryoke granites. Later, some stupas were restored by granite in the Seto Inland Sea in the 18th century. Furthermore, in the early 20th century, many stupas were restored.
Granitic stones forming the stupas are composed of following 6 type stones.
A: Medium- to fine-grained biotite granite with pinkish alkali-feldspar. Color index: 3 to 4 vol.%. Magnetic susceptibility: 1.2 to 5.4X10-3SI. Fifty-nine stupas are made of these granite and established years of 13th century are inscribed on twenty-one of them. Relation diagram of magnetic susceptibility and color index revealed that stones of type A are similar to so-called “Rokko granites” distributing southern part of Hyogo Prefecture.
B: Coarse-grained porphyritic hornblende biotite granite to granodiorite. Color index: 9 to 17 vol.%. Magnetic susceptibility: 0.16 to 0.28X10-3SI. This type is characterized by large euhedral white K-feldspar and are often strongly foliated by K-feldspar and mafic minerals. Elongated mafic enclaves sometimes present in parallel to the foliation. A hundred stupas are made of this type and established years of 13th century are inscribed on thirty of them. They are low magnetic despite being rich in mafic minerals and they often have foliation. These characteristics indicate that the stones of type B were from Ryoke zone.
C: Coarse-grained to medium-grained equigranular biotite granite with or without hornblende. Color index: 4 to 7 vol.%. Magnetic susceptibility: 0.07 to 0.17 X10-3 SI. Aggregation of fine-grained felsic minerals by deformation and weak foliation are partly observed. Felsite vein frequently intrude into this type granites.Twenty-one stupas are made of this type granites and established years of 13th century are inscribed on eight of them. Most of type C granites are more leucocratic and lower magnetic than the granites of type B. However, some of type C granites show similar rock facies to type B granites and these two type granites are plot on same trend in magnetic susceptibility - color index diagram. Granites of type C may be one rock facies of type B.
D: Coarse-grained biotite granite. Color index: 3 to 7 vol.%. Magnetic susceptibility: 0.04 to 0.18 X10-3 SI. They have leucocratic and homogeneous appearance. Ten stupas are made of this type granites and established years of 13th century are inscribed on all of them.
E: Medium-grained hornblende biotite granodiorite. Magnetic susceptibility: 1.1 X10-3 SI. Only one stupa of this stone was found in the area. There is an inscription of 18th century (1771). Type D and E stones has not been able to identify the specific quarried area, but it is close to the some granites of the Seto inland sea region.
F: Coarse-grained biotite granite with pink K-feldspar. Color index: 8 to 10 vol.%. Magnetic susceptibility: 0.9 to 1.9 X10-3 SI. Established years of 20th century were inscribed on twenty-six stupas within twenty-seven stupas of this type. Stones of type F is assumed to be granite in the Mannari region in Okayama Prefecture from their appearance, and this is supported from the magnetic susceptibility and the color index.
The historical changes of the above-mentioned stone quarried areas are summarized as follows. The stone stupas was built in the early 13th century using the Rokko granite and Ryoke granites. Later, some stupas were restored by granite in the Seto Inland Sea in the 18th century. Furthermore, in the early 20th century, many stupas were restored.