5 1 19 6 NG-51-12 18-1 15
5 1 Index of the Geological Map of Japan 1 50,000
* ** *** 14 * 11-12 13-14 ** 12 13-14 *** Keywords geological map 1 50,000 Ryukyu Island Arc Yaeyama Islands Ishigaki Island Hirakubo Peninsula Kabira Peninsula Permian Triassic Early Jurassic Eocene Pleistocene Holocene Yaeyama Metamorphic Rocks Tomuru Formation Miyara Group Miyaragawa Formation Nosoko Formation Ryukyu Group Nagura Formation Ohama Formation Dune deposits Beach sand deposits Beach rock Alluvium Rhyolite Nosokoishizaki Andesite Oonosaki Andesite Nosokozaki Andesite High P/T type metamorphism
ii 1 1 1 1 2 1 2 3 1 3 3 2 4 3 7 3 1 7 3 2 7 3 3 11 3 4 12 3 4 1 12 3 4 2 14 3 5 16 3 5 1 16 3 5 2 18 3 6 20 4 25 4 1 25 4 2 25 4 3 26 4 3 1 29 4 3 2 34 4 3 3 39 4 3 4 43 5 49 5 1 49 5 2 49 5 3 51 5 4 53 5 5 55 5 6 55 6 58 6 1 58 6 2 58 6 3 59 7 63 7 1 63 7 2 63 7 3 63 7 4 63 7 5 63 7 6 64 8 65 8 1 65 8 2 65
9 66 9 1 66 9 2 66 9 2 1 66 9 2 2 67 69 Abstract 71 1.1 1.2 1.3 2.1 2.2 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 1 2 3 5 6 8 8 9 9 10 10 11 11 12 3.10 13 3.11 14 3.12 14 3.13 15 3.14 F 1 15 3.15 16 3.16 17 3.17 19 3.18 20 3.19 22 3.20 23 3.21 24 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 26 27 28 28 29 31 32 32 33 4.10 34 4.11 34 iii
4.12 35 4.13 35 4.14 36 4.15 36 4.16 37 4.17 37 4.18 38 4.19 39 4.20 40 4.21 41 4.22 42 4.23 42 4.24 43 4.25 45 4.26 45 4.27 46 4.28 47 4.29 47 4.30 48 4.31 48 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.1 6.2 6.3 6.4 6.5 6.6 7.1 9.1 51 52 52 53 54 54 55 56 56 59 60 60 61 61 62 63 68 3.1 3.2 4.1 4.2 5.1 5.2 9.1 9.2 18 21 30 44 50 K-Ar 50 67 68 _ Fig.1 Summary of the geology of the Ishigakijima-Tohokubu District 72 iv
1 24 28-24 38 18km 124 6-124 21 24 28 19.7-24 38 19.7 124 6 01.4-124 21 01 4km 4 1.1 1982 1.2 1km 1.1 1
1.2 0.8 336.0m 300m 238.9m 1 1 74 100m 1.2 100m 26 200m 5.2 300m 246.9m 2
1.3 1km 254.8m - - 100m 85m 1 2-1 3 1 3 50cm 3
2 1982 2.1 2.2 1975 1989 Foster 1965 1976 1989 Ujiie and Nishimura 1992 Nishimura 1998 1983 1976 1982 1982 4
2.1 5
2.2 6
3 4 3 1 1975 1977 1978 1983 1983 5 1975 Foster 1965 1.25km 1982 Foster 1965 Tumuru-saki 1975 Tumuru 1983 Formation 5 1 1989 1982 Tomuru Formation Foster 1965 - - 4 - - 1977 1km 3.1 Shibata et al 1968 1972 1.5km K-Ar 3.2 Rb-Sr 178Ma 202Ma 1983 Nishimura 1998 K-Ar 230-160Ma Yoshii 1935 Foster 1965 Hashimoto 3 2 1974 1977 Ishizuka and Imaizumi 1988 1983 I IV m 50m 7 3.3
3.1 3.2 m 10m 10 3.4 3.5 50cm 1m 2,500m 8
3.3 3.4 Tp Tb 500m 9
3.5 3.6 Tb Ts 500m 3.6 mm 100m 10cm 1m mm cm 3cm 10
3.7 Tp Tg 500m 3.8 200m cm 10 cm 3.7 1,870m 3.8 3 3 3.3 11
3.9 3.9 cm 10cm S0 10cm - - - - S1 - - S1 cm S1 S0 3.12 2km S 2 S 1 15 30 3.13 F 1 isoclinal closed S 1 3.14 S1 F l F2 F l open mm cm F 3 100m cm km open gentle F l F 2 F 3 FLl FL2 FL3 Sl 3 4 3.10 3.11 Fl 12
3.10 13
3.11 3.12 Tp Tb S 0 S 1 NE-SW WNW-ESE ENE-WSW m 3.15 S1 ENE-WSW S1 ENE-WSW S0 S1 ENE-WSW NE-SW 500m S 0 S1 14
3.13 400m 3.14 F 1 S 2 300 m WNW-ESE NW-SE 500m NE-SW NW-SE WNW-ESE WNW ESE NW-SE NE-SW 15
3.15 Tp Tb NE-SW 1.2km F1 F1 3.16 239 m 3.1 3.17 S0 WNW-ESE S1 WNW-ESE NW-SE WNW ESE 1 - GSJ R77865 3.18 a NW-SE F1 F1 - GSJ R77875 3.18 b 3 5 16
3.16 Tp Tb R 17
3.1 Tp - GSJ R77861 3.18 c - GSJ R77824 3.20 a - - GSJ R77791 3.20 b 3.2 3.19 - - mm GST R77816 3.20 c Z b=y 18
3.17 Tp 3.1 19
3.18 Tp a - b - c - qtz= ms= chl = grt= ap= 1983 4 3.21 - - GST R77802 3.20 d 1983 3.21 b=y I - - II GST R77850 3.20 e f Ishizuka and Imaizumi 1988 II b=y I 1983 III IV 20 3 6 20 I II III IV 1983 IV
3.2 Tb 21
3.19 Tb 3.2 22
3.20 Tb a - b - - c - - - d - - e - - f e qtz= ep= chl= Ca-Am= Na-Am= cal= arg= 23
3.21 1983 Shibata et al 1968 1972 Nishimura 1998 Shibata et al 1968 1972 K-Ar Rb-Sr 1983 1 178Ma 202Ma IV 3.21 1983 Ujiie and Nishimura 1992 Nishimura 1998 I IV K Fe2O3/ FeO Fe203 MgO/ MgO FeO Fe2 -Ar 129-144 Ma O3 1967 230-160Ma 3.21 1971 24
4 and Saito 1974 4 1 1964 1932 Foster 1965 Miyara Formation Nosoko Formation 1982 1964 1932 Shiraki and Matsumoto 1988 1989 73Ma K-Ar 1982 K -Ar 1982 1982 1885 1897 1899a 1899b 4 2 Ml Ms Hanzawa 1935 Foster et al 1960 Foster 1965 1982 0.5 1976 1982 1.5km 1km 1982 1.5km 1 km 1976 Foster 1965 4.1 Tiba 2km 25
4.1 1976 1982 P 29 4.5 1985 80m 4 2 10m 70m 20 m 1976 1982 1976 1982 4.1 1998 45m 46 34Ma 90m 2000 4 3 Nt Nb Nl Nr 4 3 4.4 Foster 1965 10 20 1885 Hanzawa 1935 Foster 30 40 1965 2 3 km Foster 1965 4m 26
4.2 27
4.3 4.4 1.5km 40m 28
4.5 3km 1976 1982 1985 450m 450m 500m 4 Foster 1965 1976 1982 - - 390 1982 N20 32 W 14 28 S 4 4.7 6 A B 4.6 C N80 30 W 18 25 S D 6 4.8 200m 29
4.1 1982 30
4.6 A B C D B C D 4.9 170m 200m N42 W 4.10 N 40 W45 N 450m 4.8 N64 84 E 32 73 N - 4.9 4.12 N63 3 W 40 56 N22 12 E 20m 18 48 4.13 N79 84 E 18 S 4.14 4.11 200m Taenidium isp Phycosiphon incertam Fischer-Ooster N58 W28 N 200m 1858 N64 84 E 32 62 N 1982-1982 31
4.7 4.8 32
33 4.9
1982 N 40 54 E22 N 4.1 N85 E38 S N77 E65 S 4.15 N68 W45 S N28 W20 S 10cm 4.6 GSJ R77880 4.16 0.05mm 4.17 4.10-4.11 34
4.12 4.13 35
4.14 4.15 - N 23 55 E 10 20 N N33 E EW 4.13 10 40 4.18 10 cm 1.5m N 67 E 68 N 50cm N 9 W 14 S 25cm N65 68 W 13 54 36
4.16 GSJ R 77880 4.17 37
4.18 4.7 - N 16 43 W 18 24 S 4.20 N 25 43 W N 63 83 E 12 35 39 52 Miki et al 1990 4.19 4.21 38
4.19 N 27 E 42 N N 67 E 15 S 15m 4.9-12 30 4.22 1m 1.5km 40m 4.23 N 28 W 80 N 10cm 4.2 4.25 10m 4.26 4.24 39
40 4.20
4.21 K2O Nb 0.5 1mm Ba Zr 0.3 0.5mm 0.05 0.2 mm GSJ R 77879 SiO 2 =55.42 wt 4.27 A B GSJ R77881 4.27 C D 0.5 1mm 41
4.22 4.23 42
4.24 0.5 1mm 0.5 1mm 0.3mm 0.3 1mm - 0.05 0.3mm 0.05 0.2mm GSJ R 77883 SiO 2 =56.18wt 4.27 E F C D 0.3 mm 0.1 2 0.2 3mm mm - 0.05 0.2mm 0.05mm GSJ R 77902 SiO 2=55.98 wt 4.28 A B 43 GSJ R 77906 SiO 2 =59.24wt 4.28
4.2 GSJ R Fe 20 3 100 JSX-60 S7 44
4.25 4.26 GSJ R 77880 GSJ R 77881 GSJ R 45
4.27 A B GSJ R 77879 A B C D GSJ R 77881 C D E F GSJ R 77883 E F 1992 N26 GSJ SiO R 77900 2 =75.05wt 4.31 78 W 20 38 4.29 SiO2 75 77wt 0.05 0.1mm 4.25 4.30 46
4.28 A B GSJ R 77902 A B C D GSJ R 77906 C D 4.29 47
4.30 4.31 GSJ R 77900 48
5 5 1 1987 Foster 1965 1976 1987 1982 1982 1987 5.1 20m N 50 E 50 N 3.5km 1982 N 70 80 E 55 64 N 47.5 3.0Ma FT 1982 44.1 1.8Ma FT 47.5 3.0Ma 43.5 1.8Ma FT 1982 1987 Miki et al 1990 1991 N 9 W 14 S 25cm 10Ma 19 2 1 12m 9.6 0.8Ma K-Ar 13.1 1.1Ma K-Ar 1991 Miki et al 1990 N 45 E 75 N 1.8m 1991 K-Ar N 70 E 20 S 5.1 5.2 EW 68 S 5 2 5m SiO2 76 86 wt 5.1 SiO2 49 5.1 N 5 W
5.1 GSJ R Fe 2O 3 100 JSX-60 S 7 5.2 K-Ar GSJ R 77908 SiO 2 85.51wt 5.2 76 78 wt SiO2 Al2O3 Nb 2 5mm 50
5.1 0.05 0.1mm 4.23 4m 10m 5.3 5 3 N 45 E 2m 5.3 N 30 E 20 W 51
5.2 GSJ R 77908 5.3 52
SiO2 74wt K-Ar 27.7 0.7Ma 5.2 TiO2 Fe2O3* Na2O Zn Zr 5.5 GSJ R 77900 SiO 2 =73.97wt 5.4 N 6 68 W 18 27 S 0.5mm N 35 E 46 N 0.05 0.2mm K-Ar 28.1 0.7Ma 5.2 0.1mm 0.05 0.1mm SiO2 57 58 wt 0.2mm 5.1 TiO2 Fe203* Al2O3 CaO 5 4 GSJ R 77882 SiO 2=57.36wt 5.6 A B 0.2mm K-Ar 0.3mm N47 E84 N 0.05 0.3mm 5.4 GSJ R77898 53
5.5 5.6 A B GSJ R 77882 C D GSJ R 77888 54
GSJ SiO 2 =57.73 R 77888 wt 5.6 C D mm cm 0.05 0.3mm 0.05mm 5 6 5.7 5 5 2.59Ma 2km 10m 1991 mm m 2 17m m m 5.8 8 10 15cm 5km NE-SW K-Ar 3.13 0.17Ma mm 10 mm 5.2 cm m 5.7 55
5.8 A B C D 17m 5.9 GSJ R 77893 4 5.1 SiO2 58 59 wt GSJ R 77893 SiO 2 58.80 K2O Ba Rb Sr wt 5.9 56
- 0.05 0.2mm 0.5 1mm 0.5 1mm 0.3 1mm 57
6 20 30m 40m 19 6 1 1985 1885 Foster Yoshiwara 1901 1965 Bunera Clay Member Raised Coral Reef Yabe and Hanzawa 1925 Raised Coral Reef 1930 1932 1932 Hanzawa 1935 Foster 1965 500m Ryukyu Limestone Nagura Gravel Sakishima Group 6.1 1976 1982 1985 Foster 1965 Foster 1965 Nagura Gravel Ryukyu Limestone 6 2 g 1976 1982 Foster 1965 Nagura Gravel 1976 1982 1965 Foster 1965 1976 1982 1976 1982 Martini 1971 NN 20 NN 21 1980 Emiliania huxleyi Koba et al 1985 5m 10m ESR 173 20 190 30 15 192 31 21 200 32 22 222 34 25 ka 5 10m 40m 58
6.1 500m 6 3 ls 6.2 1976 1976 Foster 6.3 1965 Ryukyu Limestone 0.7km 6.5 0 60m 80 60m 60m - 20m 40m 10 40m 500m 60m 20m 20m 59 6.4 1m
6.2 6.3 500m 60
6.4 6.5 20m 40 50m 0 5m 61
6.6 6.6 4.5 4.21 1976 1982 62
7 7 1 7 3 d 1.5km 2km m 10m 10m 7 2 a 2 1,300 100 B.P. 1985 7 4 s 1985 N 5 7.1 63
7 5 50cm 7.1 7 6 r 64
8 8 1 Foster 1965 8 2 1991 30m C Foster 1965 1976 1982 1976 1982 250m Foster 1965 100m 65
9 9 1 Foster 1965 1995 1900 Foster 1965 1975 Foster 1965 9 2 Foster 1965 1985 1935 9.1 Foster 1965 1625 1985 Foster 1965 1.8km 0.245 0.0085 1771 3.7km 1771 8 4 24 0.003 0.0027 1900 1,135 Foster 1965 8,439 9.2 1968 Neuschel 1952 Foster 1965 10 20m 9.1 Foster 1968 1965 1983 1.5km 1 10 40m Foster 1965 66
9.1 1985 2 1975 1924 10 31 1927 3 3 10 8 1982 1968 1927 1981 67
9.2 1968 1980 7 29 9.1 68
1932 195p vol 7 p 339-346 1897 vol 5 1987 p 1-12 vol 82 p 370-381 Foster H L 1965 Geology of Ishigaki-shima Ryukyu Retto U S Geol Surv Prof Paper 339-A 119p Foster H L Stensland C H May H G Fosberg F R and Alvis R L J 1960 Military geology of Ishigaki -shima Ryukyu-Retto I II Intell Div Eng HQ USAP with USGS 323p 1983 1975 no 22 p 15-26 vol 8 p 50 56 1885 1977 vol 7 no 5 p 3-46 1932 p 283-288 vol 8 no 2 p 39-51 1968 462 Hanzawa S 1935 Topography and geology of the Ryukyu Islands Sci Rep Tohoku Imp Univ 2nd Ser geol vol 17 p 1-61 Hashimoto M 1974 Rebeckite-aegirine-quartz schist of Ishigaki-shima Mem Natn Sci Mus Tokyo no 7 p 19-24 1935 1 vol 47 p 255-256 Ishizuka H and Imaizumi M 1988 Metamorphic aragonite from the Yaeyama metamorphic rocks on Ishigaki vol 6 -jima southwest Ryukyu Islands Jour Geol Soc p 1-3 Japan vol 94 no 9 p 719-722 Miki M Matsuda T and Otofuji Y 1990 Opening 1989 mode of the Okinawa Trough paleomagnetic evidence from the South Ryukyu Arc Tectonophys vol no.33 p 259-275 175 p 335-347 1981 1991 Vol 6 p 41-47 vol 3 p 212-216 1982 Vol 6 p 49-58 1983 no 84 p 1-22 vol 89 p 471-474 1998 1991 105 437p 1980 vol 18 no 4 p 189-208 Koba M Ikeya M Miki T and Nakata T 1985 ESR ages Japan Ikeya M and Miki T eds ESR dating and dosimetry Ionics p 93-104 1985 1967 p 148-152 1899a 1 vol 6 p 283-289 1899b 2 vol 6 p 307-310 1975 119p 1985 278 p p Martini E 1971 Standard Tertiary and Quaternary calcareous nannoplankton zonation Proc II Planktonic Conf Rome p 739-785 1964 vol 2 p 57-73 1971 49-55 1982 p 61 Neuschel S K 1952 The Kamiyama manganese mine Ishigaki-shima Ryukyu-retto Intelligence Div Office of the Engineer Gen Headquarters U S Army Far East Command memo rept 4p Nishimura Y 1998 Geotectonic subdivision and areal extent of the Sangun belt Inner Zone of Southwest 69
Japan Jour Metamorphic Geol vol 16 p 129-140 1983 no 1 p 21-33 K-Ar no 22 p 27-37 1985 vol 28 p 569-574 46p Tiba T and Saito Y 1974 A note on the volcanic rocks 1975 5 4 of Iriomote-jima Ryukyu Islands Mem Natn Sci 1 1,128p 1995 1 Ujiie H and Nishimura Y 1992 Transect of the central 1 and southern Ryukyu Island Arcs In 29 th IGC Field 424p 2000 vol 5 p 337-361 Yabe H and Hanzawa S 1925 A geological problem 107 p 247 1927 vol and Taiwan A consideration based on the fossil 10 p 1-42 Shibata K Konishi K and Nozawa T 1968 K-Ar age of muscovite from crystalline schist of the northern Rep Tohoku Imp Univ 2nd Ser geol vol 7 p 29 Ishigaki-shima Ryukyu Islands Bull Geol Surv -56 Japan vol 19 p 529-533 1930 Wanless R K p 83-126 1972 2 3 Yoshii 1935 On some glaucophane-rocks from Ryukyu Rb-Sr vol 23 p 505-510 archipelago Sci Rept Tohoku Imp Univ II vol 1991 16 p 225-248 Mg K-Ar 1900 vol 12 no vol 86 p 323-328 141 p 557-558 Shiraki K and Matsumoto Y 1988 The pyroxene crystallization trend of a magnesian andesite from Iriomote-jima Ryukyu Islands a boninite analogue Jour Geol Soc Japan vol 94 p 387-390 1989 p 53-58 1976 1977 Mus vol 7 p 25-30 Trip Guide Book ed Geological Survey of Japan concerning the raised coral-reefs of the Riukiu Islands foraminifera faunas contained in the raised coral-reef fomation and the youngest deposits underlying it Sci Yoshiwara S 1901 Notes on the raised coral reefs in the islands of the Riukiu Curve Jour Coll Sci Imp Univ Tokyo vol SVI art 1 p 1-14 1978 no 3 p 11-17 70
QUADRANGLE SERIES, 1 : 50,000 Miyakojima (19) No. 6 _ Geology of the Ishigakijima-Tohokubu District By Yoshiyuki KANEKO *, Yoshinobu KAWANO ** and Naotomo KANEKO *** (Written in 2002) (ABSTRACT) Ishigaki Island, Yaeyama Islands, an island in the southern Ryukyu Arc Islands, is about 440 km southwest of Okinawa Island and 240 km east of Taiwan. The Ishigaki Tohokubu district, which is a quadrangle of lat. 24 28-24 38 N and long. 124 6-124 21 E (lat. 24 28 19.7-24 38 19.7 N and 124 6 01.4-124 21 01.4 E referred to the International Terrestrial Reference Frame, ITRF), is located in the northern part of Ishigaki Island. YAEYAMA METAMORPHIC ROCKS (TOMURU FORMATION) Tomuru Formation (Yaeyama Metamorphic Rocks) occurs widely from Ishigaki to Iriomote Islands in the Yaeyama _ -shoto. The Tomuru Formation includes alkali amphibole, lawsonite and aragonite, and belongs to the high-p/t type of metamorphism in the Late-Triassic to Middle-Jurassic (Fig. 1). In this area, the Tomuru Formation is divided into the Hirakubo and Ibaruma units, that is widely distributed in the Hirakubo Peninsula. The northern part of the Hirakubo unit forms a synform with a NE-SW trend, and the central part of this unit forms an antiform with an ENE-WSW trend. On the other hand, the Ibaruma unit forms an antiform with a NW-SE trend in the central part of this unit. Total thickness of the Hirakubo unit is more than 2,500 m, and that of the Ibaruma unit is more than 1,870 m. They are composed mainly psammitic, pelitic and basic schists, and minor amounts of siliceous and graphite schist. The basic schist derived from basic volcanic rocks, often preserves pillow lava, pillow breccia, hyaloclastite structure. TERTIARY The Eocene Miyara Group unconformably overlies the Tomuru Formation (Fig. 1). The group comprises the Miyaragawa and Nosoko Formations. The former is composed of conglomerate, an alternation of sandstone and mudstone and limestone. The latter overlies conformably the Miyaragawa Formation and consists largely of tuff, tuff breccia, andesitic lava and rhyolitic lava. The pyroclastic rocks of the Nosoko Formation are light green, and they resemble the green-tuff of Eocene in the Japan Islands. INTRUSIVE ROCKS Tertiary intrusive rocks intruded into the Tomuru and Nosoko Formations, which are mainly composed of rhyolite, andesite and porphyry. The Eocene rhyorite dikes are recognized around the Oura-yama and Kuura-dake mountains and characterized by phenocrysts of alpha quartz. The andesite dikes are divided into two groups based on their isotopic ages. The older group is distributed in Onozaki and Nosokoishizaki Capes and dated at 27.7 to 28.1 Ma (Fig. 1). Younger andesite dikes intruded into the Nosoko Formation at the Nosokozaki Cape and dated at 3.13 Ma (Fig. 1). The porphyry dikes are recognized around the Kabiraishizaki Cape and intruded into the rhyolite lava of the Nosoko Formation. PLEISTOCENE The Upper Pleistocene Ryukyu Group is horizontal and unconformably overlies the Tomuru, Miyaragawa and Nosoko Formations (Fig. 1). The group comprises the Nagura and Ohama Formations. The former is composed of conglomerate, * Yokohama National University ** Saga University *** Geological Museum 71
Fig. 1 Summary of the geology of the Ishigakijima-Tohokubu District sandstone and mudstone. The latter is composed of coral limestone, bioclastic limestone and sandy to conglomeratic limestone. They are probably interfingering each other. HOLOCENE The Holocene deposits contain alluvium, dune deposits, beach sand deposits and beach rock (Fig. 1). The alluvium distribution is narrow and thin along some rivers. The sand dune deposits form 5 to 10 m high hills above the sea level and are composed of calcareous sand. The beach sand deposits are composed of calcareous sand, organic fragments and gravel and its their origin is the Tomuru and Nosoko Formations. The beach rock is very loose, formed of beach sand and layered. The only reclaimed land is near the port of Ibaruma. 72
1 2 3 4 5 6 7 8 9 2003 5 1 72p 2003 1 5 1 p.1-3 Bibliographic reference _ Kaneko, Y., Kawano, Y. and Kaneko, N. (2003) Geology of the Ishigakijima-Tohokubu District. Quadrangle Series, 1 : 50,000, Geological Survey of Japan, AIST, 72p (in Japanese with English abstract 2p.). Bibliographic reference of each chapter _ Kaneko, Y., Kawano, Y. and Kaneko, N. (2003) Geology of the Ishigakijima-Tohokubu District, Chapter 1, Topography. Quadrangle Series, 1 : 50,000, Geological Survey of Japan, AIST, p. 1-3.
i
Back Cover Photo Looking NNW along the Hirakubo Peninsula at the Nosoko -dake