Development of joints in the Sandankyo Area, Hiroshima Prefecture, Southwest Japan Yasuyuki Hirayama*, Takaya Hayashi**, Shinichi Nakai**, Atsuo Tsushima*** and Yukimasa Oho* * Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Japan ** Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Japan *** Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan Abstract Joints are markedly developed in the acidic welded tuff of the Sandankyo Area, Hiroshima Prefecture, Southwest Japan. Six sets of joint are distinguished in this area, namely N-S set, NE- SW set, NNE-SSW set, NW-SE set, NNW-SSE set, and horizontal set. It is considered that NE- SW, NNE-SSW, NW-SE, and NNW-SSE sets of joint were formed by the simple shear due to NE-SW strike-slip faulting with right-lateral shear sense. Detailed microscopy shows that N-S and NE-SW sets of joint contain narrow quartz vein with newly recrystallized muscovite, and cut by the other sets. This suggests that, preceding the NE-SW faulting, WNW-ESE extention accompanied with granite porphyry intrusion formed N-S and NE-SW sets of joint. ( 1000 m) (400-600 m) ( 100 m) ( 1972), 19591959, 1985
N 48 78 12 64 79 70 86 34 18 79 Mochinoki fault 23 74 Misumi Index map Sandankyo area Hiroshima 76 5 86 66 82 81 83 88 Yokogawa fault 79 87 88 Mochinok i 14 84 85 81 79 88 79 10 Yokogawa river 34 36 88 71 14 60 81 86 76 70 65 74 66 86 60 72 60 83 76 16 132 11 77 68 88 15 Yoshigahara 8 86 74 75 82 84 76 76 74 22 78 62 54 85 60 78 18 56 78 86 70 76 84 6 Shiwagi river 70 70 62 Kurofuchi 50 82 82 78 Shiwagi Rhyolitic pyroclastic rocks Granite porphyry Strike and dip of major joints Fault 85 10 86 4 84 52 72 Granite 14 78 1km Itagatani fault 1965192000 20052006 1965 1983 1989 1997
Fig. 1 1995 1985 1985 1995 1-5 mm0.2-1 mm 10-30μm1995 NE-SW 1959Fig. 1 1959 19851986 1997 K-Ar 1997 12 N NE-S W,ENE-WS W set s N-S set NE-SW set N ENE-WSW set NW-SE,NN W-SS E set s Horizontal N-S set NW-SE set Horizonta l se t NNW- SSE set 5% 4% 3% 2% 1% 1989 1983 10 km
(Figs. 1, 2, 3) Fig. 3 Fig. 3 N-SNE- SWENE-WSWNW-SENNW-SSE Fig. 2 m 10 m cm1 m 20 cm cmfig. 4 N20 W N20 E 60 NS 70 E 10 cm m cm Fig. 4N-S 1 km Fig. 3N50 E 85 SE 10 cm cm N60 E N E N70 E SE 10cm N50 W 85 NE 1 km 10 cm N30 W N30 W 70 SW NNW-SSE 30 cm1 m 20 cm 1 mcm Type-1 Type-2 Type-3 Type-1
広島県三段峡地域における節理の形成過程 2 1 27 Horizonta l set N-S set N-S set 50c m 3 NE-S W set 10c m 50c m 4 5 NNW-SS E set Horizonta l set 50c m NW-SE set NE-S W set 50c m Fig. 4. Joints in the welded acidic tuff of the Sandankyo Area. Fig. 4.1: N-S set of joint, striking N11 W and dipping to 78 E. Space between the two original fracture surfaces of joints is 2 to 10 cm. Fig. 4.2: N-S and horizontal sets of joint. N-S set strikes N3 W and dips 74 E, and horizontal set strikes N3 E and dips 8 E. Fig. 4.3: NE-SW set of joint, striking N45 E and dipping 78 S. Fig. 4.4: NNW-SSE set of joint, striking N43 W, dipping 82 S. Dashed line shows joint, striking N23 E and dipping 72 E (N-S set?). Fig. 4.5: NE-SW, NWSE and horizontal sets of joint. NE-SW set strikes N47 E and dips 81 S. NW-SE set strikes N61 W and dips 84 N. Horizontal set strikes N30 E and dips 12 N.
平 28 山 恭 之 林 隆 也 中 井 真 一 津 島 淳 生 於 保 幸 正 2 1 Type- 1 Type- 1 0.5mm 1mm 3 4 Type- 2 0.05mm 0.5mm 6 5 Type- 3 Type- 3 Type- 1 1mm Type- 2 0.5mm Fig. 5. Photomicrographs of three types of joint, Type-1, Type-2 and Type-3. Fig. 5.1-5.2: Type-1 joint. Type-1 joints infilled by quartz vein, cutting quartz phenocryst and matrix. Highlight platy minerals, which are muscovite, crystallize along Type-1 joint. Fig. 5.3: subgrains in quartz vein. Fig. 5.4: Type-2 joint, fracturing quartz phenocryst. The boundary part consists of micro-fractures. Fig. 5.4: Type-3 joint defined by empty fissures. Fig. 5.6: Type-1, Tpye-2 and Type-3 joints. Type-1 is intersected by both Type-2 and Type-3. Fig. 5.1-5.4 and Fig. 5.6: Crossed polars, Fig. 5.5: Plane-polarized light. る石英脈の組み合わせとして特徴づけられる Fig. は石英やカリ長石の斑晶 および基質を切って連 5.1-5.3 Type-1の節理は５地点でのみ観察され 続的に発達している 破断面の形態は全体として 南北あるいは北東 南西方向の走向を持ち ほぼ みると直線あるいは緩やかな曲線を示す 石英脈 垂直に傾斜している Fig. 6 このタイプの節理 の幅は0.3-0.6 mm程度で その幅は一つの連続し
N Type 1 Type 2 Type 3 0.2-0.5 mm 20 50 μm Fig. 5.3 Fig. 5.2 mm 10-100 μmtype-1 Type-2 Fig. 5.4 Type-2 Fig. 6 μm 0.3-1 mm 10 μm 100 μm Type-2 Type-1Fig. 5.6 Type-3 Fig. 5.5 Fig. 6 30 μm 0.3 mm Type-1Fig. 5.6Type-3 Type-2 Type-2 Type-3 Type-2 1959
19851986 1959 PTXRR' Nicolas, 19841989Fig. 7(1) NE- SWNNW-SSENW-SEENE-WSW NE-SW XR'R Fig. 7(2)PT PNNE-SSW NE-SWN-S T E-W NE-SWNNW-SSENW-SE ENE-WSW (1) Pattern of second order fractures associated with a dextral fault T R (2) Joint system of Sandankyo area NNE-SSW? X 95-105 45 5-25 NW-SE NNW-SSE N-S P fault R NE-SW ENE-WSW E-W? NE-SW fault N-S Type-1 Fig. 5.2
Type-1 Type-1 Type-1 Fig. 6N-S NE-SW Type-1 Type-2 Type-3 Type-2 Type-3 Type-3 Type-2 Type-3 N-S Type-1Type-2 Type-3 Type-1 Fig. 5.6 Type-1 Type-1 N-SNE-SW Fig. 6 Type-1 N-SNE-SW 1985 N-S Type-1 N-S NE-SW N-S N30 E N60 E N20 W N50 W Fig. 8 N-SNE-SW Fig. 3 Type-1 N-SNE-SW 1983 1989 N
1997 NE-SW NW-SE 1989 NW-SENE-SW N-S 1983 N-S N-S NE-SWNW-SE Kitagawa & Nishido 1994 1997 K-Ar 31- Ma Type-1 N-S NE-SW NE-SWENE-WSWNW-SE NNW-SSE N-SNE-SWENE-WSWNW-SE NNW-SSE 20 cm cm N-SNE-SW cm Type-1 Type-2 Type-3 Type-1N-SNE-SW Type-2 Type-3 Type-1N-SNE-SW Type-2 Type-3 NE-SWENE- WSWNW-SENNW-SSE Type-1 N-S NE-SW NE-SW Type-1 Type-2 Type-3
2000 106 249-263 -------- 2005 6 137-144 1995 102 133-155. 19865 1 1965 71 18-31 1959 17-28 -------- 1959 ( ) 64-83 1985 vol. 39, 372-384 19 86 105-118 Kitagawa, R. and Nishido, H., 1994, Orientation Analysis and Formation Ages of Fractures Filled with Clay Minerals (Clay Veins) in Hiroshima and Shimane Prefectures, Southwest Japan. Jour. Japan Soc. Eng. Geol., Vol. 35, No. 2, 14-22. 1997 K-Ar -, Vol. 38, No. 5, 299-303 2006 47 13-22 Nicolas, A., 1984 ed., Principles of Rock Deformation. D. Reidel Publishing Company, Dordrecht, 208p. 1989 ed., 226p. 1965 14307-316 1972 ---Structure Contour Map ---III525-34 1985 245 253 1985 20 1997 105-119 --------1983 131-153 -------- -------- 1989 15-32