Page 1
551.23550.36(521.12)550.85
Geo且ogie朗S軸盛yo£M&ts眺aw&Geo騰e懸&豆Area,.
No窟theas奮」蹄罎
By
Hisayoshi NAKAMuRA甚 & Kiyoshi SuMI菅菅
亘聡亡rodl胆et亘0聡
Along the Backbone:Ranges of Northeast Japan,there are some
volcanic regions consisting of Quatemary volc翫noes.Among them,Hachi-
mant&i National Park is one of the famous volcani cregions in Japan
and it occupies the area extending over1000km2along the boundary of
Iwate and,Akita prefectures.In this region,twelve fum.arolic and hotspring
areas are distributed.
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■ 工wa七e ぜoガ Pref.
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、
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Koma
Morioka
Fig。1 Index map showing the location of Matsukawa area
The M:atsukawa geothermal area is located in the southeastem comer
of Hachimantai volcanic region and on the northeastern foot of Mt,
Iwate,an active volcano.It is about50km far from M:oriok&and it takes
one and a.ha.1f hour by caL (Fig。1)
Formerly,Matsukawa w&s a,small re自ort area,but fifteen years ago,
drilling was made by village office to get thermal water for bathing。
It is interesting to say that geothermal steam was emitted from the bore
holes of150-300m,in depth though geothermal manifestation is so poor that
there are no館maroles exclusive of a few hotsprings with temperature
of40-800C.This is the beginning of geothermal exploration in this area
*Water Resources&Engineering Geology Department**Geology Department
58一(132)
Page 2
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Fig・2 Geological map of Matsukawa and its surroundi且g area
暑岩石標本採取地(標本番写)
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Page 3
地質調査所月報(第18巻第2号)
and since1958,the regular exploration has been made under the cooP-
emtion of Geological survey of Japan乱nd Azuma Ka.ko co,,:Ltd..After
geological survey,geophysical prospecting a皿d test drilling were carried
out,four prod』uctivo wells have been drilled by the Company under the
乱id of the Research Development of(】orpomtion of Japan,since1963・
The depths of No.1-No.4wells&re945,1080,12003nd1500m respectively。
Among them,No。1,No.2乱nd No。3wells have succeeded.to get geother-
mal steam of150tons per hour in total discharge.Japan/s first geother-
mal power plant was put in operation on October8th,1966・Its capacity,
1imited to 9500 kilowatts at the outset,is to be increased to 15,000
kilowatts by next Apri1。
The writers have carried out geological survey and core investigations
in this aroa since1957. In this paper,the results of studies on subsurface
structure,rock alterεしtion and geothermal condition of this are乱 are
describe(1briefly on the basis of the data mainly obtained by drilling・
1.G・eology
The geological map of southeastem p3rt of the Hachimantai volcanic
region includ.ing Matsukawa area is shown in Fig.2・
The most part of this region is covered,by Q,uatemary volcanic
rocks.h the Matsukawa area,Matsukawa andesite,Marumori somma,
1ava乱nd.its debris a.re exposed,(NAKAMuRへand.SuMI,1961),As topogra・
phical feature,caldera a.nd central cone can be seen,but it is not sure
th就the cald.era was formed,by which way,depression or eズPlosion.
Thr ough this area,Matsukawa river runs away from south-west to
north-e批st and it has two tributaries,Akagawa and,Sumikawa.rivers.
The north side of the M:atsukawa river is relatively gentle in topogra.
phic relie£while upper str6ams of these rivors make steep gorges in
M:批tsukawa andesite.
The basement rocks of this area are composed of Tertiary welded
tuff and marine se(liments distributed on Takinoue geothermal area,
about8km far£rom M:atsukawa to southwestem direction,and along
the Kit&nomata river located on the north side of Matsukawa area.
Welded t㎡foverlain by M:atsukawaandesite wasfou皿datthedepthof160m
when drilling w&s made by the village ofHce in the Matsukawa area。
¢ θ
麹… 縦3σご5hご… 螺舞製瓢!\下恥 縦一尼 5論… }二…夏’ レ」 ・::i::…誌 1
一一一・ 曜
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A
Fig.3 Geological section of the Matsukawa geothermal area
60一(134)
Page 4
Geological Study of Matsukawa Geothermal Area,Northeast Japan(H.Nakamura&K。Sumi)
Fig.3shows the profile through Takinoue,Matsukawa and,the upper
stream of Kitanomata rivers.Geological structure of Takinouo area has
a complicated anticlinal structure with steep faults.As to geothermal
m.anifestation,fumaroles and hotsprings issue along anticlinal axes developed
in Tertiary sediments.In the Matsukawa翫rea,the structuTe of the
basement rocks shows a.1so a皿ticlinal or domo st瓢cture as explainod
Iaゼer.
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凸
Fig.4 Index map showing the locations of亡est bore holes and
productive wells
Fig。4 is the index m.ap showing Iocations of test bore holes εmd
productive wells。MR-1,M:R-2,M:R-3and MR-4a,re productive wells
and other symbols a皿d numbers show the positions of test bore holes・
The distances of each亘rod.uctive well are150-300m。
According to the core investigation of each productive we11,the
stratigraphic pro£ile of the Matsuka.w&a.rea is shown in Fig.5,in which
the bound.ary between Tertiary marine sediments and welded t㎡f is
61一(135)
Page 5
地質調査所月報(第18巻第2号)
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1:
3:
5:
7:
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lMafic tuff breccia
Siliceous shale
Sedimentary tuffAccidental tuff breccia
2468:
Andesite welded tuff and lava 10
Yamatsuda formation
Rhyolite volcanic breccia
Black shaleConglomerateDacite welded tuff
Andesite lava
62一(136)
Page 6
Geological Study of Matsukawa Geothermal Area,Northeast Japan(H.Nakamura&K.Sumi)
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圃 一 一
Fig.6 Stratigraphic sequence at the Matsukawa geothermal area
arranged on the same leve1. From this data, stratigraphic sequence
can be mεしde (Fig.6).
In this8equence, Matsukawa andesite of150m thick is regarded as a
cap rock because of low alter乱tion a.nd、10w temperature as known by
drilling(ANDo and WATANABE,1957).The welded tu£f formation is
divided into nine members by lithological d.i£ferences and most of them
have horizontal welding planes which can be seen in core samples.
Compared with the Takinoue area,the thickness of marine sediments
named Yama仁suda form.ation is extremely thin in this area and below
this formation,so.called green tuff formation i弩found.
2。 S肥bs盟置£aee S亡虻朋et盟re
It is difficuユt to know the subsurfa,ce structure of Matsukawa area
by geological survey on the sur£ace,because this area is almost covered
by Q,uatemary volcanic rocks.Eowever,some informations of the
・63一(137)
Page 7
地質調査所月報(第18巻第2号)
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器≦ρ!
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。警織難奪 夕 8
ト 8 応 ぞ
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の
0 500m
Fig.7 Structural contour颯ap of the Mlatsukawa geothermal area
Numbers show the height of the base of welded tuff
formation with the unit above sea leve1.
subsurface structure have been gotten by drilling as follows:
According to stratigraphic pro£ile in each wel1,the d.epth to the top
of Tertiary marine sedimonts is different between the north side and
south sid.e of M:atsukawa river.From this d飢a,,the structural contour
map can be made as shown in Figs。7and8、In these figures,numbers
show the height of the baβe of weld.ed tuff formation with the unit
above sea leve1. If the bed(iing Planes of the basem£nt rocks are nearly
horizont乱l as seen in core s&mples of welded tnff£ormation,this means
血at there may be a fault zone parε軌11el to the structural contour lines,
namely along the M:atsukawa riveL Besides Ithis fault zone,there
must be another break line formed.by the compound,of two di伍erent
stresses and,drawn by connecting each cross point of contour lines.Since
磁e present developed area is not only limite(1 to small extent but deep
bore holes㎝e a few,it is not sure what kind of fault is predominant in
this area。But,it may be ass甲ned that the structural movement of this
area would be related to the activity of M:arumori volcano from the
viewpoin.t of geological situation ofsubsur£ace structure presented。in Fig。8。
亘亘亘。 Roe藍 A旦te買a窟童o盟
In spite of weak geothermal manifestation ofthis area,a large altered
rock area is{iistributed.along the M:atsuk乱wa river with the direction
from north-east to south-west as shown in Eig.g。
Formerly,the writers tried to classify the altered,rocks into four
subzones by macroscopic features(NAK:AM:uRAand SuM:1,1961),but,in
t五is paper,they are classif1ed into six subzones by the characteristics
of mineral assemblage(SuMI,1966).As seen in T乱ble’1,the altered rocks
64一(138)
Page 8
GeologicalStudyofMatsukawaGeothe「maIA「?a・No「theastJapan(H・Nakamu「a&K・sumi)
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Fig・8 Subsurface structure in the Matsukawa geothermal area
65一(139)
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Page 9
地質調査所月報(第18巻第2号)
癖濃灘
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Fig.9 Distribution map of altered rocks in the Matsukawa geothermal area
Wこweaklyalteredzone M:MontmorillonitezoneK:Kaoline zone A:Alunite zoneP:Pyrophyllite zone1:Bore hole 2:Hotspr ing
66一(140)
Page 10
Geological study of Matsukawa Geothermal Area,Northeast Japan(H.Nakamura&K.sumi)
Table l Mineral assemblages in each altered zone
Zone1
]工
Saponite
Montmorillonite
Sericite
Kaolin
Alunite
Pyrophyllite
Andalusite
Diaspore
Zunyite
Chlorite
quartz
α唄Cristobalite
“Leucoxene,,
Rutile
Pyrite
Calcite
Sulfur
Weaklyaltered。zone
Dark greencolored zone
Montmoril-10nite zone
Kaolin zone Alunite zone
Argillized zone
Silicifie(1zone
SiIica・
stone
zone
Pyrophyllite
zone
1=Kl.SUMI(1966),II:H.NAKAMuRA&K.SuMI(1961)
of this area are composed of weakly altered zone,montmorillonite zone,
kaoline zone,alunite zone and pyrophyllite zone。The n,ew subd、ivision
was made by using some kinds of clay minerals as index;by set血g the
boundaエy between montmorillonite and kaoline with disappearance of
montmorillonite,and that between k&01ine and alunite with disappearance
of kaoline. PyroP五yllite zone is characterized by containing diaspore,
anhydrite and zmyite in addition to pyrophyllite,and this zone overlaps
one above another and t五erefore,the boundary between t五is zone and
others is not clear.According to the data of temperature measureme耳t
in bore holes,the temperature near surface of this are&is not so high as
pyrophyllite can be formed.Accordingly,it is assumed tllat pyrophyllite
zone would not be the same product乱s other subzone,but that of early
stage of geothermal activity。
Figs。9乱nd.10show the cross section of altered.zone made by core
investiga.tions of test bore holes我nd prod』uctive wells.In the limit to
t五e depth of600m,zonaI arrangement of alunite,kaoline and montmori1-
10nite zone is also fomd from inner to outer in vertical plane.
In Fig.g,the alunite zone exposed along the upper strcam of Ak&gawa
river is regard.ed as the shallowest prod』uct formed by fumarolic action
when geothermal activity was stronger。If the sur£ace of the present
developed area kept the same altitude as the above-mentioned area at
67一(141)
Page 11
Table2 Chemical composition of hotsprings Fe2+acidity
Name
1.
2.
3.
4.
UpPer stream of Akagawa river
UpPer stream of Sumikawa river
KyounsoHotel
Shofuso HoteI
Temp.
(。C)
31.6
44.4
44.6
78.5
pH
3.9
5.8
3.2
3。1
C1一
1.0
1.5
3.0
3.0
SO42一
229.6
306.2
94.6
315.2
acid-
ity
(meglJ)
3.64
9.52
5.06
3.95
HS-HCO3
14.9
62.7
44.6
5.0
0.0
198.3
0.0
0.0
Na+
20.8
70.3
14.0
40.0
K+
10.0
17.6
7.3
9.6
A13+
5.3
2.1
5.3
11.5
Fe2+
0.7
1.4
0.7
8.6
Ca2+
48.2
76.9
8.2
31.8
Mg2+
8.7
24.2
2.1
8.2
NH4+ HBO2 H:2Sio3 T.S.M。
unit:
1.5 2.2 36.4
2.0 19.9 49.4
2.f 11.1 29.9
2.5 13.3 88.4
mg/J Analyst::K.MAEDA
413
734
250
670
Table3 Ghemical composition of steam,its condensed water and drainage water from productive wells
鵠 1
倉合)
Name
Steam from MR-1
Steam from MR-2
Date
Aug.15,
Aug.15,
1964
1964
vapour gas (vol.%)
99.80
99.78
0.20
0.22
Component of gases(vo1.%)
H2
13.7
14.1
CO2
82.1
81.8
SO2
tr.
tr.
02 R.
0.0 4,.2
0.0 4.1
Analyst :K.MAEDA
Name
1.
2.
3.
4.
5,
6。
7。
8.
Condensed water of MR-1
〃
Drainage water of MR-1
Condensed water of MR-2
Drainage water of MR-2
Condensed water of MR-2
Condensed water of MR。一3
Drainage water of MR-3
Date
Jan.25,1964
Aug.15,1964
Aug.15,1964
Aug.15,1964
Aug.15,1964
Feb, 2,1965
Feb. 2,1965
Feb. 2,1965
PH
4.6
4.5
4.9
5.3
6.9
5.9
4.0
5.0
RPH
4.7
4。6
4.9
5。3
6.9
5、9
4.2
5.0
Cl一
3。9
6.7
12。4
1.7
5.3
0.5
0.5
8.8
SO42-HCO3
3。3
13.2
1779.9
2.8
114.8
2.1
72.0
1343.3
1.5
6.1
36.6
9.1
45.8
0.0
18.3
Na+
0.8
2.2
263.5
0.7
57.0
5.6
40.4
204.8
K+
0.3
1.2
143.5
0.2
4.0
3.0
16.2
84.2
Ca2+
0.1
0.6
22.9
0.4
5.6
0。40
3.42
28.79
Mg2+
0.1
2.2
8.7
0.4
1.3
0.24
0.44
2.62
Fe2+
0.45
4.30
507.7
0.004
0.11
0.04
18.61
389.5
A13+ CO2
0.38
0.35
28.6
0.18
4.2
0.1
0.1
12.8
15.4
73.7
81.4
50.1
83。0
H2S HBO2H2SiO3
11.9
49.8
tr。
60.7
tr.
101.0
14.9
tr。
0。1
0.1
248.2
1.2
43.4
2.0
4.8
65.3
2.3
6.5
825.5
1.7
594.1
2.6
34,7
773.5
T,S.M.
21.5
44.0
3843
15.0
853
21.9
173
3015
Free S
14.6
6.2
3.9
unit mg/」
Page 12
Geological study of Matsukawa Geothermal Area,Northeast Japan(H.Nakamura&K.sumi)
Altitude
900mBR1
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Fig.10 Geologic section through C_D lines
W,M,K,A&P→see Fig.9
that time,the eroded surface of older topography can be restore(1 as
shown in Fig.g,Based,on such an idea,the altered,rocks exposed.around.
the developed area would.not be the shallowest prod.ucts,but the inner
part300m below from the older surface。 It is another reason why
pyrophyllite is found at the present surface and is considered as the
product of e乱rly stage of geothermal activity in this area,
In Fig,10,the shape of altered rocks翫long vertica1、plane shows
sym江猟)trical apPearance in the extent of300m in depth. This means
that selective alteration was made in the upper part of weld.ed tuff
formation con呂isting of altemation of tuff and lava flow. On the
contrary,theselectivealterationisnotseeninMats曲aw&andesite.This is due to the lithological character of compact Matsukawa and,esite.
It rem&ins unsolvable that,in the d,eeper part,what sort of shape of
zonal arrangement would be seen,but,there may be a possibility to
consider that kaoline zone would spread in welded tuff formation below
300m because it has numerous cracks as seen三n core samples.
69一(143)
Page 13
地質調査所月報(第18巻第2号)
From these facts,it can be said that the occurrences of pyroP}1yllite
zon.e,&nd alun,ite from the depth of600m have an import&nt role to know
the unique condition of hydrothermal system in this area and th飢
Matsukaw乱is another type of geothermal fields which have not seen in
other fields such as Wairakei(STEINER,1953),Salton Se乱(WHITE批nd
MuFFLER,1964) and Steamboat Hotspring (SIGvALDAsoN and WHITE,1961,
1962).
4. C恥em亘ea且Com藍》osi意亘o盟o£Ho重s璽》ri壼gs&n岨D眼Li聾題ge
Wa継壷伽Bo置e Holes
Toconsiderthe£ormationofalteredrocksinthis area,it isimportant to know,the chemicaユcom喰osition of hotsprings乱nd drainage
water from bore holes.
Table2shows the chem直cal composition of hotsprings in this are&・
They are all acidic a,nd characterized by a little high content of
sulph&tes.
Table3shows the chem直cal composition ofsteam,its condensed water
and drainage water f士om productive wells.These samples were obtained
in a period of six months after emission,but,at present,the steam of
prod.uctive wells has become super-heated.and.has no drainage w乱ter.It
is not clear why su、ch a change has occurred,however,it c乱n be assumed
that the chemical composition of drainage water would、present the
original property of hot water reserved in basement rocks of this area・
As seen in Table3,the chemical compositions of MR-1and MR・一3
are different from that of MR-2;the former is acidic and.characterized,
by high content of sulph&tes,while the latter is interm ed,i&te and,
sulphates content is rather Iow.This fact suggests that hydrothermal
water reserved、in the M:atsukawa area is originally acidic o:n.e,and,
altered rocks with alunite and kaoline zones have been formed under
the acidic cond.ition with temperature of about300QG in the depth of
1000m as known by temperature measurement in bore holes,
5.Geo撫er贈a且Co躍漏o賦o£M:蕊s聰]k&w&Aπe&
As mentioned飢the beginning of this report,there are twelve
fumarolic and hotspring areas in the H&chimεmtai volcanic region.It is
one of important an.d,interesting ProbIems that as heat source which
volcano or vOlca,nism.has a relation to geothermal manifestations in
this region。On this question,there are few evidences to clarify the
rel飢ion between volcanism and,geothermal activity in each area。As to
Matsukawa are&,however,the only clue is the distribution of altered
rocks after extrusion of Matsukawa andesite.Judging from the distribu-
tion of volcanoes formed乱fter the extrusion of M:atsukawa and.esite,it
70一(144)
Page 14
Geological Study of Matsukawa Geothermal Area,Northeast Japan(且.Nakamura&K.Sumi)
is assumed that the volcanic activity of Mitsuishi and Marumori volca-
noes might be associated wit五geot五ermal activities in the T3kinoue
and M:atsukawa areas.At the same time,the altered zone along M批tsu-
kawa river is included in乱zone connecting two volcanoes mentioned
above,which is considered as structural zone d.eveloped in basement
rocks.
At the beginning of geoth,ermaI activity in Matsukawa,the activity
would be so strong that pyrophy且ite was formed under more acidic
condition with higher te:mperature than those at present.During this time,
hyd.rotherm翫1water might be char&cterized by containing free hydro-
chloric&cid from the fact that zunyite is found accompanied with
pyrophyllite zone5
There is no information about when caldera and,central cone of
Mar㎜ori volcano were formゆd, but it m.ay be considere(i that the
subsurface structure aromd M:arumori volcano was formed by the effect
of extrusion of magma as shown in figs。7and8,
Summarizing the historical review of geothermal activity,it is
concluded that hydrotherm乱1water in the Matsukawa area is charac-
terized by sulphuric acid at present,though it might contain£ree hydro.
chloric acid in early stage,and that it is reserved in fissuエes developed
along structural zone,especially in those form£d by crustal movement
relating to the extrusion of Marumori volcano,and in horizontal cracks
d.eveloped in weld、ed tuff formation.It goes without saying that the
fissures cutting through the basem喰nt rocks互ave more important role
than horizontal cracks to produce geothermal steam and, accordingly,
that it is necessary to detect the fault zone around Marumori volc&no
for the purpose of geothermal development of the Matsukawa area in
future.
Re£6買e簸ces
ANDo,T.&WATANABE,:K.(1957):On the Matsukaw批Geothermal District
in Iwate Prefecture.B%ll.G601.S解∂.ノ41勉銘,vol.8,no.10.
NA:KAMuRA,H.&SuMI,K(1961):Geothermal Investigations of Matsu-
kawa Hotspring Area,Iwate Pref.B%ll,G60」.S%7∂.1砂伽,vo1.12,
no.2.
SIGvALDAsoN,G.E&WHITE,D.E、(1961):Hydrotherm飢Alteration of
Rocks in Two Drill Holes at Steamboat Springs,Washoe County,
Nevada,.ノ腕.33Z i%U.S.0601.S%グ∂.Pグげ.P砂07424.P.
SIGvALDAsoN,G.E&WHITE,D。E.(1962):Eydrothermal Alteration in
Drill Holes GS-5翫nd GS-7,Steamboat Springs,Nevad.a.U.S.0召ol.
Sz67z7.P〆6ゾ.んカ67450-P.
STEINER,A.(1953):Hydrothermal Rock Alteration at Wairakei,New
71一(145)
Page 15
地質調査所月報(第18巻第2号)
Zealand.Eoo多z.G60」.,vo1.48,no。1.
SuMI,K(1966):Hydrothermal Rock Alteration of Matsukawa,Geother-
mal Area,Iwate Prefecture.M初伽g GθoJ.,vo1.16,no,79.
WHITE,D。E.&MuFFLER,:L。」.P。(1964):Metamorphism ofLate Ceno-
zoic Sediments to Greenschist Mineral Assemblages,M:anuscript.
松川地熱地域における地質学的研究
中村 久由 角 清愛
要 旨
日本で初めて地熱開発に成功した岩手県松川地域において筆者らがこれまで行なってきた地
質調査,調査井・生産井のコア調査の結果を取り纏め,地下構造,岩石の変質,地熱のあり方
についてその要点を説明した。すなわち,松川地域の地下構造は,背斜状またはドーム状の構
造を示すがこれは丸森火山の活動に関係があるらしい。地熱は松川沿いに走る断層帯に伴う
が,2次的に第三紀熔結凝荻岩の横の割目にも貯えられる。岩石の変質はアルナイト・カオリ
ン・モンモリロナイト帯で特徴づけられ一部パイ・フイライトを含むところがある。これらの
変質作用は酸性の熱水によってもたらされたものであり,現在生産井から噴出する熱水の性質
もこれを裏書きしている。
72一(146)