enl・ ech.elonl faults・ al:ong=. the! medi'anτectoni.c line...

Journal of Geosciences, Osaka City University Vol. 17, Art. 5, p. 99-116. March, 1974

Enl・ ech.elonl Faults・ al:ong=. the! Medi'anτectoni.c Line i1n Sbobudani-H'ir;rono: District, Wakayama Prefecture,

Southwest japan*

Takao MIYATA, Wataru MAEJIMA, Shin-ichi MAENO,

Y oshitsugu 0HIRA and Kazuhisa ONISHI

I. Introduction

The northwestern Kii is tectonically divided into the area of the Izumi group (inner

side) and that of the Sambagawa metamorphic rocks (outer side) by the Median tectonic

line, which runs through the southern foot of the Izumi Range. Generally, the Sambagawa

metamorphic rocks along this line are covered extensively with the Shobudani formation

(Pliocene), so that there are not many places where the above圃 mentionedMedian tectonic

line can be directly observed. The investigated area is the Shobudani”Hirono district

through the northern Koyaguchi-cho, Wakayama prefecture (Fig. 1-A). In the northern

Koyaguchi-cho, however, the Sambagawa metamorphic rocks are widely distributed

(IWAHASHI, 1963). The Median tectonic line, as observed in this district, has hitherto been

regarded as the boundary fault between the Izumi group (north) and the Sambagawa meta-

morphic rocks plus the Shobudani formation (south). Through our investigation, however,

it is clar泊ednow that this line should be understood as a complicated fault system (Fig.

3) which was formed mainly through the two stages of development as will be seen later.

The Median tectonic line at the first stage has hitherto been considered to be a normal

fault. In this paper, however, we discussed a differe11t movement picture against it. The

purpose of this paper is to clarify the status of the Median tectonic line as a fa ult system

and especially to discuss about the nature of en echelon faults.

In Shobudani, the Median tectonic line was described by KAWADA (1939) for the first

time. Two types of faults are observed here. Generally speaking, one is the boundary

fault between the Sambagawa metamorphic rocks and the Izumi group (Pl. 1, Fig. 3),

the other is tbe contact between the Sambagawa metamorphic rocks and the Shobudani

formation. The latter is well-known as a product of the so-called Shobudani phase by

KOBAYASHI (1941). Since then, geology of a part of this area was reported by HIRAYAMA

et al. (1959), IWAHASHI (1963) and OKUDA (1969).

:n・. Geologic Setting

Outline of Geology

The present area along the Median tectonic line is composed mainly of the Sambagawa

metamorphic rocks, the Izumi group (Late Cretaceous), acidic-andesitic dykes and the

Shobudani formation (Pliocene) as shown in Fig. 1・B. In addition, terrace and fan depo輔

sits are present but they are not dealt with in the present paper.

* Contribution from Department of Geosciences, No. 273.

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En echelon Faults along the Median Tectonic Line 101

A) San1bagawa metamorphic rocks

These rocks are distributed in the following four areas. The first is at Yamada and

is composed of green schist, black schist and quartz schist. The distribution is very small

here, i.e. about 450×150 m. The serpentinite is intruded locally into these rocks oblique to

the schistosity plane of the crystalline schist (N70°E, 80°N). The seoond is an area between

the northern Katsuragi-cho and the northern Koyaguchi-cho and is composed chiefly of

green schist (partly massive) and black schist. These rocks are bounded, on the 11orth,

by the Median tectonic line and, on the south, are covered unconf ormably with the Shobu-

dani formation. These rocks are generally strongly crushed at some places. The thrid

and the fourth areas are at Higashi圃 Kashiwaraand at Hirono, respectively. They consist

mainly of sheared black schist.

B) Izumi group

This group is composed mainly of sandstone, conglomerate and mudstone, subordinate

amount of acidic tuff in addition to normal-fine alternation of sandstone and mudstone.

Generally, it forms a homoclinal structure, which has strikes of N60-70°E and dips SE at

40-80°, but in the neighbourhood of the Median tectonic line the structure of the Izumi

group becomes much complicated.

C) Dykes

Nt1merous small圃 scaledykes are found along the Median tectonic line and within the

Sambagawa metamorphic rocks in the neighbourhood. The age of intrt1sion of dykes is

regarded as the Middle Miocene time (ICHIKAWA and MIYATA, 1973) in terms of a cor-

relation with the 01mogo acidic rocks in the western ,Shikoku (HORIKOSHI, 1964) and the

Takamiyama acidic rocks in the Central Kii (UMEDA et al., 1968).

D) Shobudani formation

It consists of gravel, sand and clay beds. The gravels are mainly represented by sand帽

stone and mudstone of the Izumi group, acidic rocks and the Sambagawa metamorphic

rocks. The stratigraphy o,f this formation will be reported fully by the Shobt1dani Research Group.

Median Tec,tonic Line

According to MINATO et al. (1965), IKEBE and ICHIKAWA (1967) and ICHIKAWA et al.

(1970), the Median tectonic line of the Kinki district has a long and complex history, so

that the present state is an integration of various kinds of movements at different times.

Concerning this area, the activity of this line is conveniently divided into the following

stages;

(1) post-Cretaceous～pre-Middle Miocene (or pre・MiddleEocene) time,

(2) post-Pliocene～Recent time.

Activities prior to (1) are present (cf. ICHIKAWA and MIYATA, 1973), but is not discussed

here, because of lack of positive evidence in the present area. Likewise, movements be帽

tween (1) and (2) are not dealt with in this paper. Movements in this interval are ascer-

tained in Shikoku (cf. SUYARI et al., 1973) and may have taken place also in the present

area, but the positive record is not found at present here. Stage (2), as used here, may

embrace n1ore than one substage of different nature, but its subdivision is not the main

thema of this paper. The activity of the first stage is regarded as essential. The Sambagawa

metamorphic rocks and rocks of the Izumi group along this line are strongly and widely

sheared, and the shear zones are covered unconformably with the Shobudani formation,

、

102 T. MIYATA, W. MAEJIMA, S. MAENO, Y. OHIRA and K. ONISHI

After that, the younger activity of the second stage took place, which is represented by

thrust, cutting the Shobudani f 014mation.

111 this area, the so-called Median tectonic line, as phenomenal boundary fault, is a

combined lineament of high-and low圃 angleshear zones of various nature (x -x1 in Fig. 3).

III. Features of en echelon Faults

Analysis of the Median Tectonic Line as a Fault System

The Median tectonic line in this area is a mixed fault system of the two stages, which

corresponds to the “Median tectonic line fault system”by OK.ADA (1970). The fault system

is composed of high圃 andlow-angle shear zones (Fig. 2). These zones are recorded in

the Izumi group, the Sambagawa metamorphic rocks and the Shobudani formation. The

present state of the shear zones is classified into several kinds of type according to the struc-

ture and the stage of activity.

1) A high-angle shear zone which runs between the Izumi group and the Sambagawa

metamorphic rocks: The width and e仔ectof shearing are great. At present, the Izumi

group overrides on the Sambagawa metamorphic rocks through faults dipping toward the

north at many outcrops. Now, we represent this type as notation H~（l ・ 2), where H, i, s and (1・2)mean the high-angle shear zone, the Izumi group, the Sambagawa metamorphic rocks and the time of activity ranging from stage (1) to (2), respectively, and superscript

and subscript indicate hanging wall and footwall, respectively. When the dip of fault

plane is vertical, we use the notation fiis(l・2). As mentioned already, it is beyond doubt

that the primary stage at which the Izumi group and the Sambagawa metamorphic rocks

are brought into fault contact is the stage (1). Accordingly, the relationship at the stage

(1) can be shown under notation H~（l). When the early stage of dip of fault plane is d江－

ficult to interpret, the notation Hsi(l) may be applied. The analogous notation is used .

in this paper. The major high-angle shear zone H!(l・2)branches into the Izumi group or

the Sambagawa metamorphic rocks off from the gross t~end o,f the Median tectonic line as

shown in Fig. 3. In this kind of branches notations are H~（l ・ 2) and H~（l ・ 2), respectively.

For example, the type H~（l ・ 2) is typically recognized through northern Koyaguchi-cho

(Loc. 5) along the fat1lt S-2 in Fig. 1. At Loc. 5, outcrops of the strongly sheared black

schist and the disturbed sandstone (Izumi group) about 100-150 m in width are observable.

Unfortunately, boun1dary oon,tact of them is not directly observed at present. The sand圃

stone has a strike of N66°E and a dip of 56°N. The similar kind of outcrop is recognized

at northern part of Hirono. Trace of the fault S-2 is almost linear on the map. On the

other hand, the type H~（l ・ 2) is typically recognized along S-1 and S-3 (Loc. 3), which run

through Sagadani and northern part of・ Yamada, respectively. At Loc. 3 the extensively

sheared Izumi group about 100 min width is observed (Pl. I, Fig. 1). S-3 beoomes to be

represented by the type H~（l ・ 2) toward the west.

2) A low-angle shear zone between the Izumi group and the Sambagawa metamorphic rocks: Two types are recognized in it. One is the situation in which the Sambagawa

metamorphic rocks overrides on the sheared Izumi group. In this case, it is cipherized

as L~（l ・ 2), where L means the low-angle shear zone. For example, it is seen at Yamada

(Tl in Fig. 1) (Loc. 2: Pl. I, Fig. 2), Hashimoto city. The green and black schists are

here distributed in three ridges of NNW-SSE trend. On the north, they are bounded

from the Izumi group by a fault, which dips Nat 35°. On the south and east, the sheared

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En echelon Faults along the M

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106 T. MIYATA, W. MAETIMA, S. MAENO, Y. OmRA and K. ONISHI

Izumi group is again outcropped. Thus the mass of the crystalline schists here can be

regarded as being situated above the Izumi group. This situation was newly discovered

in this district througl1 our investigation. Also, according to NAGAI (1970, 1973), there is

this type in the western Shikoku (Kaminada thrust). The other is a type in which the

Izumi group overrides, in turn, on the sheared Sambagawa metamorphic rocks. It is

cipherized as L~（l ・ 2). An example is observed in the northeast of Tahara (T2 in Fig. 1).

The fault (Loe. 4: Pl. I, Fig. 4) has strike of N40°W and dips NE at 36° as shown in Fig. 2-D.

3) A small-scale high-angle shear zone which is formed by the movement along the

Median tectonic line at a later age: This is divided as follows. One is a fault between

the sheared Izumi group and the Shobudani formation, cipherized as H~（2), where p and (2)

mean the Shobudani formation and the younger stage of activity (post-Pliocene～Recent),

respectively. The effect of shearing in the Shobu.d,ani formation is, in general, very small

and beyond cQmparison with that in the Izumi group. The Shobudani formation covers

frequently the already sheared Izumi group with unconfor1nity (P1. I, Fig. 6). This type

is rather rare泊 thepresent area but is observed in the western Izumi Range (MIYATA,

1972a; ICHIKAWA and MIYATA, 1973). The other is a fault which is developed within the

Izumi group behind the type L~（2), cipherized as H~（2).. The example is at Loe. 6 in Fig.

1. The shear zone within the Izumi group has about 20 m wide here.

4) A low-angle shear zone between the sheared Izumi group (or the sheared Sambagawa

metamorphic rocks) (north) and the Shobudani formation (south) This is commonly

recognized in this area ( f in Fig. 1 ). The example is at Loe. 7 (Pl. I, Fig. 5) in Fig. 1. Here,

the width of the shear zone is about 50 cm. Effect of shearing in the Shobudani forma-

tion is very small. This type is cipherized as L~（2). It is regarded as a superficial overthru-

sting (cf. WELLMANN, 1955; SuooATE, 1963). It is possibly a product of gravitational

spreading or gravitational sliding which was caused by the younger uplift movements of the

Izumi group side.

The fault system in this area is characterized by a combination of the above-mentioned

types as shown in Fig. 3. High-angle shear zone group, which is represented by faults

S-1～S-5 (Fig. 1 ), is arranged en echelon.

Structure of Deep-Seated Shear Zone

When we discuss about the movements along the Median tectonic line before the

Miocene time, it must be taken into account that the present state of the shear zone struc-

ture observed on the surfa~e outcrop is not necessarily identical with the original one,

because it is superposed by post-Pliocene movements (cf. Fig. 4).

However, the high圃 angleshear zone of the Izumi group, co:vered unconf ormably with

the Shobudani formation, can be regarded to remain considerably the original state of the

fault at the stage (1). The term“deep岨 seatedshear zone”is applied to this kind of shear

zone. The dip of the sheared Izumi group is 50°N to vertical. This is observed also in

the western Izumi Range (MIYATA, 1972a; ICHIKAWA and MIYATA, 1973) (cf. Fig. 4・IIB).

It is not easy to observe directly the deep-seated shear zone on the surface at many places.

Although the types H~（l ・ 2) and H~（l ・ 2) are products of multiple activations, the extensive

shear zone structure associated with them can be regarded to manifest the gross trend of

the deep-seated shear zone at the stage (1), i,n view of t~e above圃 mentionedunconform1ity.

Their .traces are linear on the map.


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Fig. 4. Schematic diagrrun showing activity of the Median tectonic line in this area (without scales). IA: End of sedimentation of the Izumi group (Latest Cretaceous). The Izumi

group is inferred to have been distributed also in a part of the area south of MTL (ICHIKAWA et al., 1970). This is modified after ICHIKAWA (1970).

IB, IB': period prior to the sedimentation of the Kuma group. Inferred types H~（l) and L~（l) were formed. The illustrated domain corresponds to the rectangular area in IA.

IIA: period of the sedimentation of the Shobudani formation. This formation covered unconformably the Izumi group and the Sambagawa metamorphic rocks.

IIB, IIB': present state of MTL of types Hi(2) and L~（2). Type H~（2) is recognized behind the type L~（2).

p: Shobudani formation, i: Izumi group, s: San1bagawa metamorphic rocks, r: Ryoke complex (including the Sennan acidic rocks), mr: rocks of “Missing-Ryoke segment” s.z.: shear zone, vc: vertical component (The horizontal component is omitted.), EO-MTL: Eo-Median tectonic line

108 t. MIYATA, W. MAEnMA, $. MAENO, Y. OmRA and K. 0NISH1

The deep-seated shear zones of the Izumi group are characterized as follows; 1) the

width of the shear zone, proper, in which fault breccia and fault gouge are well developed,

attains to lOOm., 2) the dip is very steep, 3) they are arranged en echelon, namely, they are

en echelon fa叫ts,and 4) stage of essential construction is regarded as (1) as schematically

illustrated in Fig. 4-IB and IB'. The amount of shearing in stage (2) is regarded as not so

important, as mentioned already.

The type L]i(2) is often observed at many places in this area. As shown in Fig. 4-

IIB', however, the type Hf(2) is developed within the Izumi group behind the type L~（2).

According to the concept of gravitational spreading, it is considered that the type L~（2)

joins with the type H~（2) under the deep ground and cl1anges from the low-angle shear

zone near the surf ace to the high-angle shear zone as shown in Fig. 4圃 IIB'(OKUDA’1969;

OKADA’1970’1973; SUYARI, 1972; MA1 has formed by a very young activity along the Median tectonic line in the Late Quaternary,

and that it is characterized by the right-lateral component (KANEKO, 1966; OKADA, 1968,

1970, 1973; OKUDA, 1969; HUZITA, 1969; HUZITA et al., 1973; MATSUDA, 1973.) Although

the type H~（2) refers to a young fault with a narrow shear zone, its surface trace is generally

continuous with that of type H~（l ・ 2) (cf. S-2 in Fig. 3). Therefore the trace of H~（2) is

also useful in reconstructi1ng the distribution of the deep-seated sheaF z;one.

Fig. 1 shows that en echelon fa叫ts(S・1～S・5)in the Izumi group branch off from the

gross trend of the Median tectonic line. This line has a regional trend of N80-70°E in

the western Kii1. The acute angle between this trend and the en echelon faults is 10-20°

(cf. Fig. 3・A).

IV. Comparison with Model Experiments and Earthquake Faults

、

The formation of en e,chelon faults in the Izumi group is assumed to be closely re1ated

with the movement along the Median tectonic line. When the pre-existing Median tectonic

line (prior to the sedimentation of the Izumi group) as shown in Fig. 5 moved beneath

the cover, oomposed of the Izumi group, at the stage (1), what sort of fault system is ex-

pected to have occurred in the cover?

Some results of model experiments an1d pattern of eatrhquake faults are cited in the

following for the sake of comparison. The experimental approach for en echelon faults

had been opened by H. CLoos (1928) and W. RIEDEL (1929). Subsequently, similar

stt1dies have been reported by E. CLOOS (1955) and TANNER (1962). Recently, MORGENSTERN 、

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TL

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Fig. 5. Comparison of relation between the Median tectonic line and the Izumi group, at the beginning of the stage (1), with model experi-ment. The symbols are the same as those of Fig. 4.

Etz ~chelon Faults along the Median Tectonic Line

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109

et al. (1967) and 'fcHAL1ENKO (1968) made further experiments and discussed about the

shear zone structures ii1 clay samples, produced along the shear planes, as shown in

Fig. 6, i.e. the Riedel shear (R) at about ¢/2 to the direction of movement, the conjugate

Riedel shear (R') at 90° -¢/2, the thrust shear (P) at -¢/2 and the principal displacement

shear (D) in the direction of movement, are formed, where φ（the peak angle of shearing

resistance) is 24°. The Riedel shears are arranged en echlon, while the conjugate Riedel

shears are poorly formed. Development of the Riedel shears is further discussed and

recognized by COULSON (1971) and WILCOX (1973).

The earthquake (April 9, 1968: M. 6.5), which took place near the Borrego Mountain,

California, formed a notable fault pattern (ALLEN et al., 1968; SHARP et al., 1972). The

earthquake was accompanied w此ha right-lateral displacement along the Coyote Greek fa ult

and the maximum displacement observed was about 38 cm. Some of the associated faults,

which were formed in the Quaternary deposits in the Solton trough, are comparable with

t11e Riedel shears. Also, the Riedel shears are recognized in the Dasht圃eBayaz earthquake

fa ult, which occurred in east輔 centralIran at August 31, 1968 (TcHALENKO et al., 1970;

TcHALENKO, 1970). According to them, under the simple shear condition, the Riedel

shears are formed on all scales.

As a result of comparison of our pattern with that of some model experiments and

earthquake faults, it can be considered that the en echelon high-angle faults formed in the

Izumi group are essentially similar to the Riedel shears. They indicate a left”handed

patter11. The movement along the Median tectoneic line at the stage (1) is essentially left-

lateral (MIYATA et al., 1973). Considering vertical component, it was associated with the

relative t1plift of the Sambagawa belt. Near the surface, the superficial overthrusting,

represented by the type L~（l), was formed locally from south to north.

、

110 T. MIYATA, W. MAEnMA, S. MAENO, Y. OHIRA and K. ONisHt

V. Summary and C0ncJu,sion

1)-Stage of activity of tl1e Median tectonic line, recognized in this area, is conveniently

divided into (1) post-Cretaceous～pre-Middle Miocene (or pre・MiddleEocene) and (2)

post-Pliocene～Rece11t times. The former refers to the stage when the Izumi group was

in essence strongly sheared, while the latter is the stage when the Shobudani formation

was dislocated. Tl1is line is a complicated fault system, which was constructed at least

through the two stages mentioned above. It is ・composed of the high-and low-angle

shear zones.

2)-The present state of tl1ese zones is characterized by the types H;(l・2),Hf(l・2),H:(l・2),L~（l ・ 2), L;(l・2),L~（2) and H~（2), where H, L, i, s, p, (1・2)and (2) mean high-and

low-angle shear zones, the Izumi group, the Sambagawa metamorphic rocks, the Shobudani

formation, time of activity covering stage (1) to (2) and the stage (2) of activity, respectively,

and superscript and subscript indicate hanging wall and f ootwall, respectively. The mode

of the distribution of faults witl1 respect to these types is sho,wn in Fig. 3.

3)-The type L~（2) forms often a complex curve. The type H~（2) is developed within the

Izumi group behin・d the type L;(2). According to the concept of gravitational spreading,

the type L~（2) is considered to join with the type Hf(2) under the ground and to change

into the high-angle type.

4)-The development of the Median tectonic line in this area is shown schematically in

Fig. 4. The term deep-seated shear zone is applied to the shear zone beneath the cover of

the Shobudani formation. The deep-seated shear zone of the Izumi group is characterized

as follows: 1) the width of the shear zone is large, 2) the dip is nearly vertical, 3) it is

arranged en echelon, and 4) it is regarded as being essentially formed in the stage (1). The

shear zone structure of the types H~（l ・ 2) and Hf(l・2)is very similar to that of deep-seated

shear zone and is regarded to reflect the distribution of the latter. Their trace is almost

linear on the 1nap. They form a set of en echelon faults which branch counterclockwise

at an angle of 10-20° to the general trend of the Median tectonic line.

5)-The en echelon faults were compared with some results of model experiments and

earthquake faults. It corresponds to the Riedel shear (RIEDEL, 1929; TcHALENKO, 1968).

Judging from the en echelon pattern, it is concluded that the movement along the Median

tectonic line at the stage (1) had the more prominent left-lateral component than the vertical

one (uplift of the Sambagawa belt) (M町ATAet al., 1973). At this time, the superficial

overthrusting of the type L~（l) was formed locally near the ground from soutl1 to north.

This movement picture ,coincides with that of MIYATA (1'972a, 1972b) and ICHIKAWA and

MIYATA (1973), which is induced from the en echelon folds (or drag folds by Moony and

HILL歩 1956)of the Izumi group along this line at the same stage.

VI. Acknowledgements

We wish to express our sincere appreciation to Prof. K. ICHIKAWA of Department of

Geosciences, Osaka City University, who gave us instructive suggestions and guidance

throughout this investigation and critically read the manuscript. We are also indebted

to Dr. I. HARA of Hiroshima University and Drs. S. HAYASHIDA and K. SHIONO of our

Department for valuable suggesti1011s on the Riedel shear and earth・qt1ake fault. Several

discussions with Profs. N. IKEBE, K. HuzITA and Drs. K. ISHII, M. YOSHIDA, A. YAO and


other members of the same Department and Prof. T. lwAHASHI of Wakayama University

are also gratefully acknowledged. Special thanlcs are due to the Shobuda11i Research

Gro・up that allowed us to use a part of its unpublished data.

References

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preliminary report. Bull. Seis. Soc. Am., 58, p. 1183-1186.

CLoos, E. (1955): Experimental analysis of fracture patterns. Bull. Geo!. Soc. A . .,-z., 66, p. 241-

356.

CLoos, H. (1928): Experiments zur innereri Tektonik. Centralblatt f iir Mineralogie, Geologie

und Paliiontologie, 1928B, p. 609-621. Cou.LSoN, J.H. (1972): Shear strength of flat surfaces i1n roclc. Stability of rock slopes, Am.

Soc. Civil Engineers, p. 77-105. HIRAYAMA, K. & N. KAMBE (1959): Geological inap of Japan, Koyasan sheet, scale 1 :50,000

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western part of Shikoku (in Japanese with English abstruct）.λ!fem. Ehime Univ., Sec. II

(Sci.), 5. p. 7-16. HuzITA, K. (1959): Tectonic development of southwest Japan in the Quaternary period. lour.

Geosci., Osaka City Univ., 12, p. 53-70. HuZITA, K. & S. OKUDA (1973): Neotectonics of Median tectonic line in Kinki and Shikoku,

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of Southwest Japan. Island Arc and Ocean, Tokai Univ. Prress, p. 193-200.

IcmKAWA, K., Y. FunTA & M. SHIMAZU (Edit.) (1970): The geologic development of the

Japanese Island (in Japanese). Tsukiji-Shokan, 232 p. ICHIKAWA, K. & T. MIYATA (1973): Median tectonic line of the Kinki district in the pre-Miocene

time (in Japanese with English abstract）.λ1edian Tectonic Line, Tokai Univ. Press,p. 87-95. IKEBE, N. & K. lcmKAWA (1967): Geologic sketch of the Kinki district, central Japan. lour.

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areas in the Kinki district, central Japan. lour. Geosci., Osaka City Univ., 11, p. 79-146.

IWAHASHI, T. (1963): Geologic map of the Sambagawa belt, north of Koyasan, Ito-gun, Waka-yama prefecture. Pub. Wakayama ,Univ., Liberal Arts Coll.

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、

，


APPENDIX

Shobudani 菖蒲谷 Sagadani l嵯峨谷

Yamada 山田 Hashimoto city 橋本市Tahara 田原 Koyaguchi-cho 高野口町Hirono 広野 Katsuragi-cho 葛城町Hishino 短野 Izumi Range 和泉山脈

，

．

Plate t

．

、

116

E玄planationof Plate I

Fig. 1. Types Hf (1・2)(left: north) and L~（l ・ 2) (right: south) at northern part of Yamada

(Loe. 3 in Textfig. 1), Hashimoto city.

Fig. 2. Type L~（l ・ 2) at Yamada (Loe. 2). The Sambagawa metamorphic rocks are distribut-

ed on the ridge (right: north) and the sheared Izumi group is outcropped in the trough

with pond.

Fig. 3. MTL between the Izumi group and the Sambagawa metamorphic rocks at Shobudani

(Loc. 1), Hashimoto city. The two Focks are strongly and widely sheared. This

belongs to the type Li(l・2).

Fig. 4. Type L~（l ・ 2) at northern part of Tahara (left: NNW) (Loc. 4).

Fig. 5. Type L~（2) at northern part of Hirono, Katsuragi-cho (left: north ) (Loc. 7).

Fig. 6. Unconformity between the sheared Izumi group (lower part) and the Shobudani

formation (upper part). About 800 m of the Miyukitsuji railway-station of the Nankai

line. This locality is at about 1.2 km east of the eastern end of the geologic map shown in Textfig. 1.

i: Izumi group, s: Sambagawa metamorphic rocks, p1: Shobudani formatio民 U:

unconformity, MTL: Median tectonic line

MIYATA et al.: Median tectonic line, Shobudani-Hirono district.

h

e

J

－

M九

M

a

筏省。

．．

1

3

5

Plate 1

2

4

6

enl・ ech.elonl faults・ al:ong=. the! medi'anτectoni.c line...

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