Geology and tectonics of the Ryukyu Islands

Tectonophysics, 125 (1986) 193-207 Elsevier Science Publishers

GEOLOGY

KOSHIRO

193

B.V.. Amsterdam

AND TECTONICS

- Printed

in The

Netherlands

OF THE RYUKYU ISLANDS

KIZAKI

Department of Marine Scienizes, University of the Ryukyus, Okinawa 903-01 (Japan) (Revised

version

received June 10, 1985; accepted

September

17, 1985)

ABSTRACT Kizaki,

K., 1985. Geology

and tectonics

X. Le Pichon (Editors),

of the Ryukyu

Geodynamics

Islands.

In: J. Angelier,

of the Eurasian-Philippine

R. Blanchet,

C.S. Ho and

Tectonophysics,

Sea Plate Boundary.

125: 193-207. The Ryukyu central

Islands

and south

Belt of southwest characterized sediments. established

composed

geological

Ryukyu

and

and geologically represents

of Mesozoic-Eocene

metamorphic

contrasts

transgression

volcanics

between

covered

into three island

the geological

sedimentary

rocks, Eocene

structural

before the late Miocene

sequences,

whereas

and limestone,

north-central

groups:

continuation

and

north,

of the Outer south Ryukyu

is

and lower Miocene south

the whole area. The Ryukyu

Ryukyus

are

Islands have been

since then.

The successive Okinawa

Japan,

morphologically

North-central

by high-pressure The

conspicuous

are divided

Ryukyus.

Trough

southeastward

developments since the Miocene,

shift of the basins

of the Goto-Tunghai-Senkaku and of the grabens in relation

basins

since

the Paleogene,

near the Island group since the Pliocene,

to the activity

in the granite

diapir

of the signify a

zones accompanied

by

volcanism.

INTRODUCTION

The Ryukyu

Islands,

an island

arc between

Kyushu

and Taiwan,

stretch for 1200

km, being composed of small island groups.From the Pacific side to the continental margin of China, the Ryukyu Trench, a row of islands, an active volcanic belt and the Okinawa Trough strike parallel. The islands are divided morphologically as well as geologically into three groups: north Ryukyu (Osumi Islands), central Ryukyu (Amami-Oshima and Okinawa Islands), and south Ryukyu (Miyako and Yaeyama Islands). The islands are separated by the Tokara Channel and Miyako Depression, both of which are identified by the left-lateral strike-slip faults detailed by the submarine geological works by Anma (1976) and UjiiC (1983). It is significant that the pre-Miocene sediments of north-central Ryukyu are regarded as the extension of those of the southwest Japanese Islands, whereas the pre-Miocene geology of south Ryukyu is somewhat similar to that of Taiwan.

0040-1951/86/$03.50

0 1986 Elsevier Science Publishers

B.V

194

An outline

of the geology of the Ryukyu

considers

the structural

framework

GEOLOGY

OF THE ISLANDS (Table 1)

Islands

is presented

first; the paper then

of the islands.

Yaeyama metamorphic rocks The oldest rocks of the Islands the

Yaeyama

metamorphic

may be represented

rocks

of

south

by the Tomuru

Ryukyu,

which

are

Formation

of

composed

of

greenschist, blueschist, siliceous schist, pelitic schist, metagabbro of the glaucophane schist facies and also pillow lavas and hyaloclastic rocks in less metamorphosed areas.

The metamorphic

throughout

PALEOZOIC ? Tomuru

c

Tomuru

the Yaeyama

Islands

Formation

is shown

to be distributed

but also in the area of the Miyako

GROUP F (Greenschist,

Submarine

Blueschist)

Equivalents

128’

Fig. 1. Distribution of the Paleozoic? group.

136

Islands

not only because

195 TABLE 1

Standard geologic columnof theRyukyu Islands

N.

Ryukyu

c.

Ryukyu

s.

Ryukyu

Taiwan

Uruma Movement Zuaternary UenakaF.(Gravel) FqukyuG.(Is,Gravel) qrukyuG.(Ls,Gravel) Taz&t 1.6

!-

Shimajiri G.

ShimajiriG. (Silt,SS,Tuff)

Pliocene !! 5.3 i, 5 ! Miocene 23.7

) 3

p

t

Oligocene 36.6__ " i T= r

;

Y z

KuMge G. (SS,Shale)

m V" Kayo F.(SS,Slate) v v v(Lava,Pycl)v (wan0F.) !!iyara F.(L.s,SS) /

57.8

Paleocene

i

66.41 Cretaceous 14‘

‘C

Jurassic

"Shimant SuPergroup" (Slate,SS,Greenstine)

I

? YonamineF. (Phy,Chertl ?

Fusaki

F.

(Phy.Ls.cherU

l-------E

NanaoM.

26

t Triassic 2L5

NakijinF. Chert,J.s)olistoMotobuF. liths &s,chert, Greenstone)-

Permian 266 arbniferous 360

TtxnuruF. ? ?

196

Tertiary ---. ^_.-_

Cretaceous _-._-.__ ..______ I 1

_

1 T&-lx-

Jurassic

Juii

~Taiwad

Sanbagawa

Sangun

j%q

Radiometric ’

I-2’ K-Ar B Blotlte

[ __: Rb-Sr

C

Chlorite

Ii

ages(Ma)

mineral

Hornblende

$3 M

Fig. 2. Frequency

diagram of the radiometric

Japan and Taiwan

(Nishim~r~.

the glaucophane

White

Rb-Sr mica

isochron W

Whole

rock

ages of the high-pressure-type

metamorphics

III southwest

1983).

schist-bearing

conglomerate

occurs in the basal part of the Shimajiri

Group of Pliocene age in the Islands (Fig. 1). The radiometric ages of the metamorphism have been dated as Jurassic: 159-175 Ma by the K-Ar method (Shibata et al., 1968: Nishimura et al., 1983) and 195 Ma by the Rb-Sr method (Shibata et al., 1972). According to the frequency diagram of the radiometric ages of the high-pressure metamorphic rocks from southwest Japan and Taiwan (Nishimura, 19X3), the age of the Yaeyama metamorphic rocks is to be correlated with the older episode of the Nagasaki metamorphic rocks and with the younger episode of the Sangun metamorphic rocks in the Inner Belt of southwest Japan (Fig. 2). It is therefore suggested that the Yaeyama metamorphic rocks could be attributed to the high-pressure metamorphic rocks of the Inner Belt of southwest Japan and also the original rocks could be Triassic to Paleozoic, similar to other

197

high-pressure metamorphic rocks in southwest Japan and Taiwan (Yen, T.P., 1971). Structural analysis has revealed two main deformation phases; the first phase folding, with a NW-SE axis, is principal and associated with a high pressure metamorphism having preferred mineral lineation parallel to the fold axis, and the second phase, of close to open minor folds with E-W axis, superimposes on the first phase folding to result in dome and basin structures in some places (Fujii and Kizaki, 1983). The Fusaki Formation of the Yaeyama metamorphic rocks, composed of phyllite, sandstone, chert and conglomerate without greenstone, has been regarded as a lower grade chlorite-sericite phyllite of the metamorphics of the same age. However, the Formation, together with the Eocene Nosoko Formation, is over thrust by the Tomuru Formation and it is not deformed by the NW-SE trending folds of the first phase but only by the E-W trending, open and gentie folds of the second phase. A chert bed of the Formation produces radioralia older than lower Cretaceous (K. Iwata, pers. commun, 1984). So, the Fusaki Formation may have been deposited between the Jurassic and lower Cretaceous, after the metamorphism of the Tomuru Formation. The Fusaki Formation is distributed in the southern part of Ishigaki Island and to the north of Miyako Island where 38 Ma phyliite (K-Ar method) has been obtained from a bored core (Aiba and Sekiya, 1979). However, such an Eocene metamorphism is not known in north-central Ryukyu and further north, so that the rock probably belongs to the Fusaki Formation. Me.~ozoic and Pa[eogene ~~~rn~~to~uFergro~p

of the north and central Ryukyus

The Shimanto Supergroup of the north and central Ryukyus is the continuation of the Outer Belt of the southwest Japanese Islands. The rocks consist mainly of an alternation of flysch-type sandstone and slate with basaltic greenstones of Upper Cretaceous-Eocene age and are metamo~hosed generally up to the greenschist facies, though locally metamo~~sm grades up to the epidote amphibolite facies which might have been affected by granite emplacements (Hashimoto, 1978). The structure of the Shimanto belt is characterized by a significant monoclinal structure, dipping to the NW and showing an intense overturned fold with southeast vergence. The age of the metamorphism and deformationis thought to be post-Eocene but pre-late Miocene Takachiho Movement because the deformed Supergroup is covered unconformably by the Shimajiri group of the late Miocene to early Quaternary age. The Butsuzo Tectonic Line, B long thrust fault which can be traced from southwest Japan to the Ryukyu Islands, brings older, late Paleozoic to Triassic rocks of the Chichibu belt southeastwards over the S~rn~to belt. However, it is now evident that the Chichibu belt of the islands is characterized by an olistostrome composed of allochthonous blocks of Carboniferous, Permian .and Triassic limestone, chert, greenstone and mudstone in a Middle Cretaceous to Upper Jurassic

19x

MESOZOIC

GROUP

v”y”yEocene

(mcludmg

Nosoko

Paleogene)

0

Vokamcs 3

-FIX&

Formaton Olistoslrome

- ~-fSubmarrne

of SRyukyu

Formatox

m

N and

Fig. 3.

Dtstribution

sedimentary sheets

Shimanto Osozawa

Up Jurassoc - M Cretaceou!

matrix.

The olistoliths

hundred

in size (Fujita, Supergroup

128”

126”

of the Mesozoic (including

of several

centimeters

I ‘l

C Ryukyu

Equvaients

1L

+

meters,

Paleogene)

group

are giant and

1983). Similar

of Amami-Oshima

small

B-L: Butsuzo Tectonic

bodies blocks

olistoliths Island

IWJ”

of several and

Line.

kilometers,

pebbles

are also reported

in the Cretaceous

platy

of meters

to

within

the

formations

by

et al. (1983) (Fig. 3).

Eocene formations

of south Ryuk,vu

The Miyara and Nosoko Formations of Eocene age occur only in the Yaeyama Islands of south Ryukyu, in addition to the Eocene formation of the Shimanto Supergroup of north-central Ryukyu. The Miyara Formation, composed of limestones and sandstones, contains various foraminifera such as Nummulites, Discocyclina, Pellatispira. Some of these fossils are also found in the tuffs and tuffaceous sandstones of the Nosoko Formation which is composed of pyroclastic rocks and andesite lavas.

199

The Miyara Formation represents a littoral facies whereas the Eocene flysch sediments occur in the Shimanto Supergroup, and further deformation and metamorphism are not recognized in the Miyara and Nosoko Formations but do clearly in the Supergroup of north-central Ryukyu. The paleomagnetic investigation of the Nosoko Formation revealed that a clockwise rotation of 40 degrees took place after the deposition of the Formation, probably in the Oligocene (Sasajima, 1977). The Eocene volcanism was only developed in south Ryukyu whereas the Miocene “Green Tuff Volcanic? are distributed throughout north-central Ryukyu from Kyushu; nevertheless the rock facies are quite similar to each other. However, the pyroxene andesites of south Ryukyu indicate a lower alkali-lime index (58.3) than the Miocene andesites (61.8) of north-central Ryukyu (Matsumoto, 1964) (Figs. 3 and 4). Neogene Group

The Yaeyama Group, distributed in the Yaeyama Islands of south Ryukyu is composed mainly of sandstone with intercalations of coal seams, mudstone, conglomerate and limestone. Coal seams, cross laminae and trace fossils indicate littoral environments of sedimentation. The age of the Group has been assigned to Lower Miocene, based on paleontological data (Takahashi and Matsumoto, 1964; Nakagawa et al., 1982). The Group is correlated with the Lower Miocene formation of Taiwan, Senkaku Islands, off the Miyako Islands and northern Kyushu. Heavy minerals occur in the Group such as zircon, tourmaline and garnet, often associated with rutile, staurolite and monazite which have probably been supplied from granite and gneiss. However, none of the islands in the vicinity of the Ryukyus, including Taiwan, displays such granite and gneiss. The source area could be related to the submerged “East China Oldland” (Liew and Lin, 1974), if not to the southeast coastal area of mainland China. The Yaeyama Group is structurally slightly tilted and faulted. This a less deformed structure of the Eocene formations and the Neogene Group in south Ryukyu implies a stable environment since early Miocene, although severe deformation due to the Takachiho Movement affected the Shimanto Supergroup in north-central Ryukyu (Fig. 4). The Shimajiri Group, composed mainly of siltstone interbedded by sandstone and tuff, ranges from the Upper Miocene to the Lower Pleistocene (LeRoy, 1964; Natori et al., 1972; UjiiC and Oki, 1974). It is distributed in the fore-arc area on land and offshore (Fig. 4). The deposition of the Shimajiri Group throughout the Ryukyu Islands, does not start before the late Miocene. The Shimajiri basin is the first evidence of a basin common to north and south Ryukyus. Before the Miocene, the Mesozoic and Eocene Shimanto Supergroup was deposited only in north-central Ryukyu whereas the Miyara-Nosoko formations and Yaeyama Group were deposited only in south

200

NEOGENE

Stimajiri

:z

y??;sh’”

G

Thickness

Fig. 4. Distribution

Ryukyu

GROUP

m

Group

Cmtour(>XD3m)

of the Neogene

in a separate

basin.

group.

After Alba and Sekiya (1979), modified

It is thus evident

that south Ryukyu

by the author.

and north-central

Ryukyu had a different geological and tectonic history before the deposition of the Shimajiri Group. The thickness of the Shimajiri Group tends to decrease westwards and the deepest basin (more than 5000 m) is located on the outer side of the Ryukyu Ridge. The deep elongated Neogene basins are seen along the inner side of the islands and also along the Tunghai continental slope (Fig. 4). The Shimajiri Group is also not much deformed except for minor undulations parallel to the elongation of the island arc, tilting and faulting. Quaternary

Ryukyu Group

The Ryukyu Group of the Middle Pleistocene, composed mainly of limestone associated with sand and gravels, is distributed throughout the islands south of the

QUATERNARY

GROUP

=

Rykyu

g

Submarine

Grwp(Ls

m

Volcanc

with

Grad

Eqwaients

Front

-2c

Fig. 5. Distribution of the Ryukyu Group. After M. Kimura.

Tokara Channel. It is less than 100 m thick and is characterized by coral reef and its associated sediments (Fig. 5). The Group is not deformed but is faulted. Limestone formations are distributed 200 m above sea level in such islands as Kikai-jima and Okinawa-jima, similar limestone formations are found on the sea bed as deep as 1000 m. The vertical distribution of the Ryukyu Group, particularly of the limestone beds, implies block movements accommodated by step faultings. This event is called the “Uruma Movement” of the late Quaternary (Okinawa Quaternary Research Group, 1976). TECTONIC

FRAMEWORK

Fukien-Ryeongnam

OF THE RYUKYU

ISLANDS AND THEIR ENVIRONS (Fig. 6)

Belt

Wageman et al. (1970) first explained the significance of the Fukien-Ryeongnam Belt. The Fukien region of southeast coastal China is occupied by terrestrial deposits

PHILIPPINE

Fig. 6. Tectonic

framework

Line, KWMS - Kyushu

around

Western

SEA

+

MesomiC (Pakecqw)

x

hlmcene

the Ryukyu

Marginal

Granite

Granite

Islands.

M-L-Median

Line.

B-L

-Butsuzo

Tectonic

Shear.

associated with various voluminous volcanic materials, such as welded tuff, pyroclastics and lavas in the collapsed basins or grabens of NE-SW trend in late Mesozoic time. In addition, Jurassic granites in the Kanton-Fukien zone and Cretaceous granites in the coastal area are emplaced within the region (Jahn et al., 1976). The southern region of the Korea Peninsula is characterized by acid volcanic activity and intrusion of Cretaceous granites, and its southern part is occupied by Paleogene granites. Therefore, the Fukien-Ryeongnam Belt was an active belt of acid volcanism and granite intrusion, mainly in the Cretaceous, when identical igneous activity is recognized in the Inner Belt of the southwest Japanese Islands (Fig. 6). Goto Belt

The Goto Belt proposed by Kagami et al. (1971), represents a part of the Taiwan-Sinji Folded Zone described by Wageman et al. (1970). The uplifted belt is

203

composed of Paleogene to early Miocene sediments associated with welded tuff and granitic rocks of Miocene age, of which the igneous rocks are observed in the Goto and Danjo Islands, and is mostly covered by Pliocene sediments equivalent to the Shimajiri Group, Late Miocene granitoids are also found in the Senkaku Islands. Therefore, this belt is generally called the Goto-Senkaku Belt. The Belt was uplifted in the Middle Miocene and in some parts in to Pliocene time. Thick sediments had been deposited in the Goto, Tunghai and Senkaku basins between the F&en-Ryeongnam and Goto-Senkaku Belts since the Paleogene without the Middle Miocene sediments (Aiba and Sekiya, 1979) (Fig. 6).

Okinawa Trough The deposition in the Okinawa Trough started in the late Miocene after a period during which the Okinawa Trough would have been an uplifted land area, namely the Central Uplifted Zone described by Nash (1979). Then, the subsidence and fragmentation of the Zone proceeded in the late Miocene associated with the tectono-magmatic activity and the transgression by which the Shimajiri Group began to be deposited throughout the Ryukyus. The Shimajiri basin was one of the largest sedimentary fore-arc basins in the Japanese Islands in late Miocene to early Pleistocene. The basement of the Okinawa Trough is not yet clearly known but fragments of Cretaceous granites have been obtained by dredging and coring (Nash, 1979; Kimura, 1983). Exotic pebbles of altered volcanic rocks and granite, probably of Miocene, and schistose metabasite of the grarmlite facies were obtained from the dacitic tuff breccia of early Pliocene in Aguni-jima of central Ryukyu. The schistose metabasite may have been derived from the basement (Kato, 1983). Dredged rocks from the Onodera Seamount in the southern part of the Okinawa Trough are altered granitic and volcanic rocks, probably derived from the Nosoko Formation, and sedimentary rocks similar to those of the Fusaki Formation. Therefore, the basement of the southern part of the Okinawa Trough may be made of the same rocks as those of the outcrops of the Yaeyama Islands of south Ryukyu. Before the late Miocene the northern and central parts of the Okinawa Trough were the uplifted land area constructed by Cretaceous granite and older country rocks. The geological situation therefore seems to have been similar to that of the Inner Belt of the southwest Japanese Islands. Since the late Miocene, the Central Uplifted Zone started to collapse and fragment. However the depression does not seem to be deep because of thin deposition and the absence of the Shimajiri Group in some areas. The downward depression and extension of the area culminated in the Pleistocene, and the graben was then formed by normal step faulting (Kimura, 1983). A sequence of doing-~fting-d~fting in the formation of the Okinawa Trough was stressed by Lee et al. (1980).

204

Ryukyu Islands (Ryukyu Ridge)

The Ryukyu

Islands

are intruded

Outer Belt of the southwest an exceptional of central

occurrence

Islands,

of Paleogene

granitoids

the same as the

though there is some discussion

granites

in Amami-Oshima

grabens

to Pleistocene

which

have thick

sediments

age (Fig. 4) were developed

close to the innerside

Western Marginal

depression

of central

and the frag-

Shear

The marginal area of western Kyushu represents a peculiar situation geological as well as a structural point of view. The Nagasaki metamorphic high pressure-low tectonic situation.

from a rocks of

temperature type, have long been controversial because of their The structure of the metamorphic rocks is revealed to be a

superimposed fold system and is characterized by a thrust fault of NE-SW with southeast vergence. Such movement rotated the axis of the sedimentary of late Cretaceous Himenoura Group in the western anticlockwise: from a ENE-WSW to a NE-SW situation for the Ryukyu (T. Matsumoto, 1976). The Shimanto north,

about

and Tokunoshima

of 2000 to 3000 m of late

Ryukyu. The grabens represent the Pliocene-Quaternary mentation of the land area (Aiba and Sekiya, op.cit.) Kyushu

just

Ryukyu.

Some narrow Pliocene

Japanese

by Miocene

is bent

arc formation

Supergroup anticlockwise

might have started

in south Kyushu by nearly

coastal trend.

area of central Thus, a new

trend basins Kyushu tectonic

in the Late Cretaceous.

has a general NE-SW

80” at the Shibi-San

trend and dips

of the southwestern

coastal area of Kyushu, which was named the Hokusatsu Bend by Hashimoto (1961) (Fig. 6). The Supergroup of western Kyushu has a more or less dome-basin structure and is faulted. The principal directions of the faults are NE-SW and NW-SE, these occurred successively so that the structure is characterized by a “Twilled Structure” of the signifying a superimposed structure (Kizaki, 1979). The older structure NE-SW direction has been modified by the newer NW-SE direction to form the twilled structure in Oligocene to middle Miocene time. The Hokusatsu Bend, representing

an oroclinal

deformation

of the Shimanto

belt at southwestern

Kyushu.

was completed by this time. A broad shear zone, recognized as superimposed deformations along the western coastal area of Kyushu, has been called the Kyushu Western Marginal Shear (Kizaki, 1979). The Kyushu Western Marginal Shear was activated

in the Oligocene

to Middle

Miocene when the Ryukyu Islands, including the Okinawa Trough area (Central Uplifted Zone), rotated anticlockwise and made the islands more relatively southeastward. This is shown by the Cretaceous granites collected from the floor of the north and central parts of the Trough which may have been the parallel continuation of the Inner Belt of southwest Japan. The bend of the pre-Miocene formations, by

205

clockwise

rotation

at the northeastern

fore, the relative and Taiwan BACK-ARC

southeastward

tip of Taiwan,

shift of the Ryukyu

is also of significance. Islands

to the Japanese

ThereIslands

seems to be clarified. BASINS

AND DIAPIRISM

Sedimentation in the Goto, Tunghai and Senkaku basins has been shown to have commenced in the Paleogene and continued to the early Miocene, by the Paleogene marine

mollusca

which were dredged

of the middle Miocene the activation Zone

(the Okinawa

Western

Trough

Marginal

area), together

the Takachiho

The Central

the zones of igneous

Uplifted

with the Proto-Ryukyu

activity

Zone subsequently

Trough in association

Movement

Shear by which the Central

Both sides of the land area (the Goto-Senkaku

Ridge, then became the Okinawa

and Emery, 1961). The unconformity

within the basins could correlate

of the Kyushu

southeastwards.

of (Niino

Islands,

to

Uplifted shifted

Belt and the Ryukyu

in the late Miocene.

collapsed

and was fragmented

with the uplift of the Goto-Senkaku

to form

Belt and the

Ryukyu Ridge so that the Goto-Tunghai-Senkaku basins shifted northwestwards, thus becoming localized basins, whereas both sides close to the Goto-Senkaku Belt and the Ryukyu Ridge, were depressed from the late Miocene to form narrow, elongated, deep basins such as the Shimajiri basin in the Ryukyu Islands. Small but elongated grabens were successively developed within the Ryukyu Islands area since the Pliocene. The central rifting in the Okinawa Trough has also been active since the beginning of the Quaternary (Kimura, 1983). Thus, the successive eastwards is recognized

subsidence and depression of the basins as a complex back arc basin.

The Fukien-Ryeongnam zone and is associated

The island

south-

Belt represents a part of the Pan-Pacific granite diapir with volcanism, mainly during the Cretaceous, on the

continental margin. Similarly the Goto-Senkaku to granite diapir zones accompanied by volcanic at the outer margins

and troughs

of the Central

arc volcanism

Uplifted

of the present

Belt and the Ryukyu Ridge belong activity of middle to late Miocene

Zone

Islands

and the proto-Ryukyu

continues

of Miocene granites and associated volcanism could subsidence and depression of the continental crust.

to Recent. have

been

Islands.

The diapirism related

to the

REFERENCES

Aiba, J. and Sekiya, E., 1979. Distribution the Nansei-Shoto Anma,

(Ryukyu

K., 1976. Geological

Geologists,

* In Japanese

Naka,

Islands). structure

1: 163-175.

*

with English abstract.

and characteristics

of the Neogene

J. Jpn. Assoc. Pet. Technol., of the Tokara

Channel.

sedimentary

44: 97-107.

Geol. Study Ryukyu

basins around

* Isl., Assoc. Okinawan

206

Fujii,

Y. and Kizaki,

Islands. Fujita,

K., 1983. Geology

and structure

Mem. Geol. Sot. Jpn., 22: 15-26.

H., 1983. The “Paleozoic”

of the Yaeyama

metamorphic

rocks.

Ryukyu

Ryukyu

Islands.

*

formation

in the Motobu

peninsula

of Okinawa-jima.

Mem. Geol. Sot. Jpn., 22: 3-13 *. Hashimoto,

I., 1961. Stratigraphy

Kagoshima Hashimoto,

Prefecture.

M.. 1978. Greenstones

Study Ryukyu Jahn, Bor-Ming,

81-87.

significance.

II.. 1971. Marine

Geotogical

Structure.

Problems

Amami

Oshima

and Kerama

Islands,

Geol.

3: 19-22.

geology

around

rocks in southeastern

of the East China

Kyushu.

rocks of central

M., 1983. Formation

Ryukyu

of Okinawa

Proc.

Geol.

Isl., Assoc. Okinawan

K., 1978b. Tectonics

Kizaki,

K., 1979. Kyushu

LeRoy,

L.W., 1964. Smaller

China

and

Sea. in: N. Nasu et al.

Sot.

basin.

Jpn.

Symp.,

Fukuoka.

relationship Geologists,

Y., 1964. Volcanic Islands.

*

Study of the

301.-317.

Earth Sci., 33: 144-151.

of southern

Okinawa.

*

U.S. Geol. Surv..

1980. Okianwa

Trough:

Origin

of a

2: 57-72.

H., Doi, N., Shirao, H., 1983. Outline

M. and Araki,

of the southern

part

of Cenozoic

Yaeyama

and Southwest

Island.

K., 1982. Geology

Tohoku history

development

recent. J. Jpn. Assoc. Pet. Technol.. H., Fukuda,

Islands

Japan.

Geol. Study

1: 1-9. * Rep. Kyushu

Univ. Exp. to the

Univ., 84: l-22.

of the Ryukyu

of Ishigaki

and

Iriomote

Islands,

*

Island, southwestern

Japan.

Mem. Geol.

*

Nash, D.F.. 1979. The Geological M. and fshida,

species in Okinawa

of the Nan-Sei Naka,

formation

*

Rep. Geol. Paleontol.

Sot. Jpn., 22: 67-79.

in the Neogene

17: 23336.

rocks of Iriomote-jima.

Ryukyus,

Islands.

association

Acta Geol. Taiwan..

T.. 1976. Geofogicai

Nakagawa,

arc. In: Geological 26 (Suppl.):

Shear and its significance.

1974. Heavy mineral

Isl., Assoc. Okinawan

Yaeyama

and

3: 1-9. * arc. J. Phys. Earth,

Bibee, L.D.. Lu. R.S. and Hilde, T.W.C..

Ryukyu

Nakagawa,

Mem. Geol. Sot. Jpn., 22: 141-157. of the Ryukyu

from the Late Tertiary

Matsumoto,

Yaeyama

of Kyushu

Mar. Geol.. 35: 219-241.

range, east Taiwan.

Matsumoto,

Naka,

Basement

*

l-58.

Liew, Y.C. and Lin, CC.. of coastal

foraminifera

grabens.

Islands

Marginal

(Editor).

Univ., 2: 33-37.

development

Geologists,

of the Ryukyu

Western

Lee, C.S., Shor, Jr. G.G., back-arc

In: Y. Matsumoto

Trough

on the geological

Kizaki,

Prof. Pap., 454-F:

Ryukyu.

Rep. Dep. Geol. Yamaguchi

Kizaki, K., 1978a. Problems

Niino,

Naka,

area of

*

Collapsed

Natori.

age in the Hokusatsu *

Geol. Sot. Am. Bull., 86: 763-776.

N. and Niino.

Marine

Kate, Y., 1983. Basement Kimura,

Geologists,

of unknown

Univ.. 8: 48-62.

Chen, P.Y. and Yen, T.P.. 1976. Rb-Sr ages of granitic

H., Nasu,

(Editors),

of the group

Arts, Kyushu

from the islands between

Isl., Assoc. Okinawan

their tectonic Kagami,

and structure

Rep. of Liberal

of the North Okinawa

M.. 1972. The late Cenozoic

and Miyazaki.

Trough

area from Neogene

time to

44: 109-119. stratigraphy

J. Jpn. Assoc. Pet. Technol..

Ii. and Emery, K.O.. 1961. Sediments

of shallow portions

by planktonic

fora~niferal

37: 48-53.

of East China Sea and South China Sea.

Geol. Sot. Am. Bull.. 72: 731-762.

Nishimura.

Y., 1983.

peninsula, Yamaguchi Nishimura,

Univ., 2: 20-24.

Y., Matsubara,

metamorphic Okinawa

Nagasaki

In: Y. Matsumoto

Research

with English

Nakamura,

Islands. Group.

14S--162. *

* In Japanese

rocks

Basement

and

K-Ar

of Kyushu

ages

in western

and Collapsed

part

Structure.

of the Nomo Rep. Dep. Geol.

*

Y. and

rocks, Ryukyu

Quaternary

metamorphic (Editor),

abstract

E., 1983. Zonation

and

Mem. Geol. Sot. Jpn., 22: 27-37. 1976. Quaternary

of Okinawa

K-Ar

ages of the Yaeyama

*

and Miyako

Islands.

Earth Sci., 30:

207

Osozowa,

S., Aita,

Y., Nakamori,

Amami-Oshima,

central

transportation Sasajima, Shibata,

K., Konishi,

northern Shibata,

on geologic

S., 1977. Ryukyu

of the basement

construction.

K. and Nozawa, Ryukyu

R.K., Kano,

Takahashi,

K. and Matsumoto, Islands.

Islands.

Shimajiri

UjiiC, H., 1983.

Submarine

development. Wageman,

Naka,

Hilde,

1: 21-33.

west

T.W.E.

and Emery,

*

from crystalline

Islands.

K., 1972. Rr-Sr ages

K.O.,

*

Islands.

Geol. Study

* Islands,

Pleistocene

group of Iriomote-jima,

Ryukyu,

2: 35-46.

planktonic

Islands

in relation

the

*

foraminifera

Mem. Nat. Sci. Mus. Tokyo,

off the Okinawa

*

schist of the

*

Island, the Ryukyu

study of the Yaeyama

Miocene-Lower

the Ryukyu

Mem. Geol. Sot. Jpn., 22: 131-140.

J.M.,

of Ishigaki

of

of gravity

Mar. Sci., 9: 19-26.

T., Igi, S. and Konishi,

Univ. Exp. to the Yaeyama

geology

Japan.

to effect

Bull. Geol. Surv. Jpn., 23: 505-510.

Y., 1964. Palynological

group of Miyako-jima,

H., 1983. Geology

reference

age of muscovite

H., Nozawa,

Islands.

Geologists,

Ujiie, H, and Oki, K., 1974. Uppermost

special

Bull. Geol. Surv. Jpn., 19: 525-533.

H., 1976. Geology

Rep. Kyushu

S. and Nakagawa, with

in southwest

T., 1968. K-Ar

rocks of the Japanese

Isl., Assoc. Okinawan

Yaeyama

Islands,

Mem. Geol. Sot. Jpn., 22: 39-56.

H., Yoshida,

Shirao, G., Doi, N. and Nakagawa, Ryukyu

A., Kanisawa,

of the Ryukyu

arc. Eocene paleomagnetism

Ishigaki-shima,

K., Wanless,

T., Niibe,

part

from the

7: 31-58.

to the Ryukyu

Arc

* 1970. Structural

framework

of East China

Sea and

Sino-American

science

Yellow Sea. Am. Assoc. Pet. Geol. Bull., 54: 1611-1643. Yen,

T.P.,

1971.

cooperation

* In Japanese

Geology

colloquium

with English

of Taiwan-a

review

on Ocean Resources,

abstract.

especially

1, Taipei.

on stratigraphy.