地域地質研究報告

Transcription

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2 5 1 Index of the Geological Map of Japan 1 50,000

3 * ** *** 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

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5 Abstract F iii

6 K-Ar _ Fig.1 Summary of the geology of the Ishigakijima-Tohokubu District 72 iv

7 km km km 1.1 1

8 m 300m 238.9m m m m m 246.9m 2

9 1.3 1km 254.8m m 85m cm 3

10 Foster Ujiie and Nishimura 1992 Nishimura

11 2.1 5

12 2.2 6

13 Foster km 1982 Foster 1965 Tumuru-saki 1975 Tumuru 1983 Formation Tomuru Formation Foster km 3.1 Shibata et al km K-Ar 3.2 Rb-Sr 178Ma 202Ma 1983 Nishimura 1998 K-Ar Ma Yoshii 1935 Foster 1965 Hashimoto Ishizuka and Imaizumi I IV m 50m 7 3.3

14 m 10m cm 1m 2,500m 8

15 Tp Tb 500m 9

16 Tb Ts 500m 3.6 mm 100m 10cm 1m mm cm 3cm 10

17 3.7 Tp Tg 500m m cm 10 cm 3.7 1,870m

18 cm 10cm S0 10cm S1 - - S1 cm S1 S km S 2 S F 1 isoclinal closed S 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 Fl 12

19

20 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

21 m 3.14 F 1 S m WNW-ESE NW-SE 500m NE-SW NW-SE WNW-ESE WNW ESE NW-SE NE-SW 15

22 3.15 Tp Tb NE-SW 1.2km F1 F m S0 WNW-ESE S1 WNW-ESE NW-SE WNW ESE 1 - GSJ R a NW-SE F1 F1 - GSJ R b

23 3.16 Tp Tb R 17

24 3.1 Tp - GSJ R c - GSJ R a - - GSJ R b mm GST R c Z b=y 18

25 3.17 Tp

26 3.18 Tp a - b - c - qtz= ms= chl = grt= ap= GST R d b=y I - - II GST R e f Ishizuka and Imaizumi 1988 II b=y I 1983 III IV I II III IV 1983 IV

27 3.2 Tb 21

28 3.19 Tb

29 3.20 Tb a - b - - c d - - e - - f e qtz= ep= chl= Ca-Am= Na-Am= cal= arg= 23

30 Shibata et al Nishimura 1998 Shibata et al K-Ar Rb-Sr Ma 202Ma IV Ujiie and Nishimura 1992 Nishimura 1998 I IV K Fe2O3/ FeO Fe203 MgO/ MgO FeO Fe2 -Ar Ma O Ma

31 4 and Saito Foster 1965 Miyara Formation Nosoko Formation Shiraki and Matsumoto Ma K-Ar 1982 K -Ar a 1899b 4 2 Ml Ms Hanzawa 1935 Foster et al 1960 Foster km 1km km 1 km 1976 Foster Tiba 2km 25

32 P m m 70m 20 m m 46 34Ma 90m Nt Nb Nl Nr Foster Hanzawa 1935 Foster km Foster m 26

33 4.2 27

34 km 40m 28

35 4.5 3km m 450m 500m 4 Foster N20 32 W S A B 4.6 C N80 30 W S D m 29

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37 4.6 A B C D B C D m 200m N42 W 4.10 N 40 W45 N 450m 4.8 N64 84 E N N63 3 W N22 12 E 20m N79 84 E 18 S m Taenidium isp Phycosiphon incertam Fischer-Ooster N58 W28 N 200m 1858 N64 84 E N

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39 33 4.9

40 1982 N E22 N 4.1 N85 E38 S N77 E65 S 4.15 N68 W45 S N28 W20 S 10cm 4.6 GSJ R mm

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42 N E N N33 E EW cm 1.5m N 67 E 68 N 50cm N 9 W 14 S 25cm N65 68 W

43 4.16 GSJ R

44 N W S 4.20 N W N E Miki et al

45 4.19 N 27 E 42 N N 67 E 15 S 15m m 1.5km 40m 4.23 N 28 W 80 N 10cm m

46

47 4.21 K2O Nb 0.5 1mm Ba Zr mm mm GSJ R SiO 2 =55.42 wt 4.27 A B GSJ R C D 0.5 1mm 41

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49 mm 0.5 1mm 0.3mm 0.3 1mm mm mm GSJ R SiO 2 =56.18wt 4.27 E F C D 0.3 mm mm mm mm 0.05mm GSJ R SiO 2=55.98 wt 4.28 A B 43 GSJ R SiO 2 =59.24wt 4.28

50 4.2 GSJ R Fe JSX-60 S7 44

51 GSJ R GSJ R GSJ R 45

52 4.27 A B GSJ R A B C D GSJ R C D E F GSJ R E F 1992 N26 GSJ SiO R =75.05wt W SiO wt mm

53 4.28 A B GSJ R A B C D GSJ R C D

54 GSJ R

55 Foster m N 50 E 50 N 3.5km 1982 N E N Ma FT Ma FT Ma Ma FT Miki et al N 9 W 14 S 25cm 10Ma m Ma K-Ar Ma K-Ar 1991 Miki et al 1990 N 45 E 75 N 1.8m 1991 K-Ar N 70 E 20 S EW 68 S 5 2 5m SiO wt 5.1 SiO N 5 W

56 5.1 GSJ R Fe 2O JSX-60 S K-Ar GSJ R SiO wt wt SiO2 Al2O3 Nb 2 5mm 50

57 mm m 10m N 45 E 2m 5.3 N 30 E 20 W 51

58 5.2 GSJ R

59 SiO2 74wt K-Ar Ma 5.2 TiO2 Fe2O3* Na2O Zn Zr 5.5 GSJ R SiO 2 =73.97wt 5.4 N 6 68 W S 0.5mm N 35 E 46 N mm K-Ar Ma mm mm SiO wt 0.2mm 5.1 TiO2 Fe203* Al2O3 CaO 5 4 GSJ R SiO 2=57.36wt 5.6 A B 0.2mm K-Ar 0.3mm N47 E84 N mm 5.4 GSJ R

60 A B GSJ R C D GSJ R

61 GSJ SiO 2 =57.73 R wt 5.6 C D mm cm mm 0.05mm Ma 2km 10m 1991 mm m 2 17m m m cm 5km NE-SW K-Ar Ma mm 10 mm 5.2 cm m

62 5.8 A B C D 17m 5.9 GSJ R SiO wt GSJ R SiO K2O Ba Rb Sr wt

63 mm 0.5 1mm 0.5 1mm 0.3 1mm 57

64 m 40m Foster Yoshiwara Bunera Clay Member Raised Coral Reef Yabe and Hanzawa 1925 Raised Coral Reef Hanzawa 1935 Foster m Ryukyu Limestone Nagura Gravel Sakishima Group Foster 1965 Foster 1965 Nagura Gravel Ryukyu Limestone 6 2 g Foster 1965 Nagura Gravel Foster Martini 1971 NN 20 NN Emiliania huxleyi Koba et al m 10m ESR ka 5 10m 40m 58

65 m 6 3 ls Foster Ryukyu Limestone 0.7km m 80 60m 60m - 20m 40m 10 40m 500m 60m 20m 20m m

66 m 60

67 m 40 50m 0 5m 61

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69 d 1.5km 2km m 10m 10m 7 2 a 2 1, B.P s 1985 N

70 7 5 50cm r 64

71 8 8 1 Foster m C Foster m Foster m 65

72 9 9 1 Foster Foster Foster Foster Foster Foster km km ,135 Foster , Neuschel 1952 Foster m 9.1 Foster km m Foster

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75 p vol 7 p vol p 1-12 vol 82 p 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 no 22 p vol 8 p vol 7 no 5 p p vol 8 no 2 p 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 vol 47 p 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 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 p Vol 6 p vol 3 p Vol 6 p no 84 p 1-22 vol 89 p p 1980 vol 18 no 4 p 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 p a 1 vol 6 p b 2 vol 6 p p p p Martini E 1971 Standard Tertiary and Quaternary calcareous nannoplankton zonation Proc II Planktonic Conf Rome p vol 2 p 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

76 Japan Jour Metamorphic Geol vol 16 p no 1 p K-Ar no 22 p vol 28 p p Tiba T and Saito Y 1974 A note on the volcanic rocks of Iriomote-jima Ryukyu Islands Mem Natn Sci 1 1,128p 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 Yabe H and Hanzawa S 1925 A geological problem 107 p 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 Wanless R K p Yoshii 1935 On some glaucophane-rocks from Ryukyu Rb-Sr vol 23 p archipelago Sci Rept Tohoku Imp Univ II vol p Mg K-Ar 1900 vol 12 no vol 86 p p 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 p Mus vol 7 p 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 no 3 p

77 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 N and long E (lat N and 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

78 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

79 p 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.

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81 Back Cover Photo Looking NNW along the Hirakubo Peninsula at the Nosoko -dake