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Title Petro-chemical Study on the Lavas from Volcano Rishiri, Hokkaido, Japan

Author(s) Katsui, Yoshio

Citation Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy, 8(3), 245-258

Issue Date 1953-03

Doc URL http://hdl.handle.net/2115/35868

Type bulletin (article)

File Information 8(3)_245-258.pdf

Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP

PErleciRO.CHEMXCAL SrWUDY ON "WHE LAVAS FROM

VOLCANO RXSk3IXRX, HOKKAXDO, JAPAN

By

Yoshio KATsul (With 5 [Irables and 8 Figuifes)

Contribution from the Department of Geology and Mineralogy,

Faeulty of Scien'ee, Hokkaido Univeysity. No. 484

CONTENTS Introduction ･･････L･･････`･+･････L･･-･･････+･i･iL･-･････････････i････････････････i･･ 245

Geological summary of Volcano Rishiri Li････････････････tit･･･s-･･･････ 246

Chemical eompositions of the lavas £rom Volcano Rishiri ･E}････L･ 24S Consideration on the chemical eompositions ･･････+･･･-･･L･･Li････=･･L･ 252

SUMMarY･=･4････Li･････････+･･･････i･-････-･･･････t･････4=･+･･････--･･･.･････}i･.･t.･･ 257

References eited ･･････････L･}t･････-････････-･･:･･･=･････}･･-･････ti･･････････････ 25S

IRtroduction

Rishiri island is an extiiict volcano situated in the north-easterik

part o£ the Japan Sea, to the west of Wakkanai city in northern Hok- ･kaido (Fig, 1). It forms a beautifu} c'onical vo!cano (1718 meters above

sea level)with many younger parasitie cones on its flanks.

Up to present, no geological investigation on this volcano has been

made excepe by ABE(') and a few others. AiiE investigated the geology

in detail and published a geological map and 3 chemieal analyses o£the lavas. Prior to his investigation, a few geological items on this

voleano had been published: Voleano Rishiri had been said to be aruined

strato-cone built up chiefiy of pyrexene-andesite ;(2)C3> and the problem

to what voleanic zone this voleano must be related had been diseussedby $eveyal geologists.(2)('`>C5)Cfi) It was advoeated by K6zu and WATtiNABE(")

from t･he petrographical point of view that this volcano belongs to the

Nasu zone, and even now this view is aceepted, We must, howevey,note the tectonic stand-point ef AKAGi(6) ehat the noythern payt of the

Nasu zone shouid be regarded as independent of its main part; thatis, as the Rishiri zone.

The writer carried out field work on this vo}cano duri"g several

weel<s o£ the lase two summers followed by laboratory worl<, including

ehemical analysis of 7 lavas,

The lavas from tliis voleano vary fyom olivine-augite-basalt to hyper-

sthene-andesite, ranging £rom 49,26% to 66,41% in si!iea contents, andare charaeter2zed by a paucity of hornblende and quartz, A generalcharacteyistic of their chemieal compositions is their comparative yiclt-

ness in alkalies, especially in soda, and a]so Iewness in al-cclk o£ NiGGn'svalue, contyary to the general characteristic of the Nasu zone whieh

was yecently notieed by IsiimAwA.(7)

In this paper, the writer describes the geology of this voicanobriefiy, and then the ehemical compositions of the lavas, eonsidering

their chemical compositions in re£erence to the general characteristicof the Nasu zone and to that ef Oshima-6shima which be}ongs to theCh6I<ai (or Kanpfi) voieanie zone along the inner are of Japanese isiands,

In pub}ishing this paper, the writer wishes to express his cordinalthan}<s to I?ro.f. [r. IsE{mAwA for va}uable instruct'ions receivedt through-

out this study, and to the menbers of the Department of Geology and

]N4{iiieralogy, Hekkaido Univeysity, for many adviees duying the work.

The writer is also indebted to IYIr. A. ABE for the geological map and

its explanations in this paper. Thanks are likewise due for a grantfyom the Scientifie Research Fund of the Department of Edueationwhich was used for this study.

Geological Summary of Volcaxxo Rishiri

The general geologicai map of Volcane Rishiri shown in Figure 1was prepared by ABiil, slightly modified by the wrtter, [I]he geo}ogical

history of this voleano ean be inctueed from this map and its explana-

tions (Table I).

Volcano Rishiyi is a strato-cone formed by a eentral eruption on

the base o£ a low hill cemposed of Pliocene sediments and igneeusrocl<s, with many parasitie cones on its flanks, The summit of the main

body laas suffered £rom intense erosion, while the skirts are coveredby voleanie de'tritus and fan deposits. No indication of voleanie activity

is shown in this voleano at present.

The erater of the main body has vanished from sight by erosion,

bgt it can be estimated that the erater inas situated on the south o£the present summit, judging from the dips aiicl eourses of lava fiows

and from the orientations of radial dykes. Most of the parasitie eones

show their oxiginal form with more er Iess eompiete craters, in eontrast

Petro-Chemieal Stud y on the Lav'as 'fttom Volcano Rishivi, Hokkaido, Japan 247

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,Figure ･ 1. Geological map of Volcano(Slightly modified. by the

legend refer to Table I.>

Rishiri by A. ABE, l934.

wviter. Numbeys of the

24S Y. Katsui

[EliABI]E

Erosion produets

Produets from tl)e'parasitie cyaters of

/Volcano Rishiri

i (ffolocene>

･Produets from the

main erater ofVolcano Risbiri

(PIeistoeene ?

to Holocene)

Basement rocks (Plioebne)

Numbers £rom 1 to l7 exeept numbers ll and following the eruption

lava fiow (j2) may be

The stars (") indicate

to that of the maincones arrange on thethere is none on theare coneentrated on It ean be supposed

body from south to

Chemical Compositions of the Lavas

from Voicano Rishiri

Among the produets fxom.Volcano Rishiri, the 4nalysed, lavas are

9 in sort as shown''in [Vables I and'II, The Iavas £yom this voleanoaye divisible petrographyeally into 3 types: olivine-azigite-basalt (SiO.･

--- 49,26-53.29%), augite-hypeysthene-andesite (SiO,,==rr58.44-63.48%) and

I, Explanation of the Geologieal Map.

{ 17. Voleanie detritus and fan deposit.

I6. Explosion produets.

15. Cinders and Iava flows (olivine-augite-basalt).

,l4t Oniwaki ]ava flow (olivine-a.ugite-basalt)'ki. ･

j.3` Ishiyama dome lava (hypersthene-andesite)'k9.

12. Tanetonnai lava fiow (augite-hypersthene-andesite). .

(ii' l:teddeigl.tegSektecS). (Olivine-auglte-basaltbe'2, aygite-hyperFthene-

' ' le. Motodomavi lava fiow (olivine-augite-basalt)":'5. '･

9. Kutsugata lava fiow (olivlne-augite-basait)'"6.

' 8. Notsuka lava fiow (olivine-augite-basalt)"i"3. '

' ' .7. 3rd ejeeta, Iava fiows and agglomerates (augite-hypersthene-{ ' .'andesite)x7. / tt 6, 2nd ejeeta, Iava fiows and agglomerates (oiivine-augite-

basa}t)K4. . ' 5. Ist ejecta, Iava fiows and aggtemerates (augite-hypevsthene-

' aitdesite)'8. ･ . .< 4.' Early ejeeta, agg}omerates (augite-hypersthene-andesite).-

3. Dykes (hornblende-augite-hypersthene-andesite)

2. Tufraeeous mudstone in whieh Mact?"a sp., 7lellina sp.,

Gastropoda, Tbleostei and Diato"z oeeur.

I. Lava fiow and agglomerate (augite-hypersthene-andesite).

show the geolo.crieai sueeession in Rishiri island oldey to younger, 1

12:11 stands for the radial dykes which ineruded duying and/

of the main voleano; and the date of the extrusion of Tanetonnai

eonternporapeous to tha£ of Zshiyama dome lava.the numbers ef ehemiacl analysis Witl} reference to Table II.

volcano, It is very interesting that the parasitic

north and south fiatnks of the main voleano, while

west and east, Added to this, the radial dykes the south and north sides of the summit. i that the tectonic line crosses through the main

north,

Petro-Cbemica} Study on the Lavas £yom Voleano Rishiri, Hokkaido, Japan 249

TAisT,E II, Chemical compositions of the lavas from Volcano Rishiri.

wv%Si02 ･

' T[]iO,,

Al,O,

,Feti03 .

FeOMltO

MgOcao

Na20

K,O･ P20ii.

H,･O(+)

H,O(-)

Total

l

49:26

l.25

17.71

2.67

7.l2

.057.91

]o.ot

3.0S

.56

,19

.36

.17

2I

'49.5S

1.41.

I6.8S

4.I9

5.97

.25 5.29

10.75

'3.85

.8S

.os

.61

.24

3

IOO.34 I 99.9S

49.6e

l,40

l6,e6

4.05

7.IO

, .21I 6,12

IO,S6

2.76

.86

.l7 .54

.m99.85

4I,50.69

1.28

l6,59

4.06

5.01

.107.34

IO.OO

3.49

l,03

,14 .43'

.IS

leO.32

50.78

L09

l5.55

3.90

7.02

.l2

7.06

9.82

3.75

-.59

.07

.30

.20

100.20

6

53.29

IS.14

3.63

5.12

6.o2

9.83

3.48

IJ7

99.6S

7

58.44

l7.12

2.36

4,3i

2.70

7124

3.62

1-.13

96.92

s

63.4S

.56. 'l. 689

2S2 2.77

.10 2.54 6'.21

4.04

.97

.14

.20 .05 '

IOO.77

9.,

66,41

･.55

l6.20

1.98

2,93

.09

i.55

3.46

5.14

1.74

.17

.25

.05

100.52

(1) Oniwaki lava (Olivine-augite-basalt), southern shore of Oniwaki.

(2> Dyke (Olivine-augite-basalt earrying a few biotites and museovltes), R6sokuiwa neay

the top of Vol.eano Rishiri.

(3) Notsuka iava (Olivine-augite-basak eavrying a few biotites), Sainol<awara, noeth of

the summit of Voldano Rishiri. (4) Lava of 2nd e.jeeta (Olivine-augite-basalt), eastern side of the top of Voleano Rishiri.

(5) Motodoynari iava (O}ivine-augite-basalt), nor'thern eoast o£ Rishiri' island.

(6) Kutsugata ]ava (Olivine-augite-basalt), shore o£ Kutsugata,

(7) Lava o/ff 5'rd ejecta (Augite-hyperstbene-andesite), summit o£ Volcano Rishiri. (S) Lava of lst ejeeta (Aug-ite-hyperstbene-andesite), eastern rid.cre ef Voleano Rishiri.

(9) Ishiyama dome lava (Hypersthene-andesite), Ishiyama, west of Oniwaki.

Nos. (6) and (7) analyzed by A, AB]r.,(i) and other 7 by tbe wyiter.

hypersthene-andesite (SiO,,=66,41%). These mineral assemblages arerather simple. Basalts usually show i'ntersertal texture with oy without

a little brown glass, and eonsist main}y of plagioelase (Alt72-An40 inphenoeryst, Ati70-An28 in groundmass), augite (+2V r.560-440 in pheno-

eryst, +2V =5eO-420 in groundmass) and olivine (-2V ==9eQ-820 in pheno-

eryst, -2V =7-900-740 in groundmass), sometimes carrying s}ight amountof biotite and museovite as interstitial mineyals, but no silica mineral

in any speeimens. Auglte-hypersthene-andesites are strongly poyphy-ritie in texture usually with glass, and eomposed mainly of plagioclase

(An60--An38 in phenoeryst, An43-An33 in groundmass), hypersthene(-2V=:720--690 in phenocryst, --2V:=-700 in groundmass, both with week

pleoehyoism) and augite (+2V i=-510-430 in phenocryst.', laeking in ground-

mass), usually with cristobalite and tridymite in g:oundmass. Hypers-thene-andesite, oecuttring only at Ishiyama, shows porphyritic and hya-

loplitie iR texture usually with glass, axxd eonsists chiefiy of plagioelase

(An39-Aii26 in phenoeryst) and hypersthene (-2V:-=T640-600 in pheno-

cryst). Both minexals are met with in groundmass, usua}ly witheristobalite.

In short, interstitial minerals estimated as products of later crystal-

}ization are characterized by a paueity of silica minerals and $ometimes

by the presence of mica with regard to basalts; on the other hand, by

the free silica with regard to andesites. Plagioelase met wieh in these

lavas is rather low in An content and usua}ly surrounded by Rarrow

rims of more sodic plagioclase. Chemical compositions of the lavas from Veleano Rishiri are pre-

sented on a varlation diagyam (Fig. 2). I£ one is justified in usingthe eurves as dyawn ilt the figure, the alkali-lime index is about 64.

This value i$ lower than that o£ Japanese volcanic roei<s (65,5) calculated

by YAMADA,<S) though it is more ealcic than the indices fer seme pro-vinces in Circum Pacific region (Medicine ial<e highiand: 60,5,(") Crat<e,,Y

Lake: 61.5,(iO) Mount Shasta: 63.7,<iO) Katmai: 63,8,"i) Lassen Peak: 63･9)･

2

o10S..

e At,O,

' Caoo e oim-

i5

ee

,

5 N..o+x,oe

Opte.

ee NaO o

e8 1F

10 eKaO

8 Zevb"ne[oTH:O,NeaOiX20tUozOurvl ceol

･st

oo

oo

rotatFeOll5

Mo ll'

o olotu

:-L'

Io Ztre 1.tneter rte2,HgO,TetelPe20sandA120s O.va

50 5S 60 (64) 65 l

Si02

Figure Z. Variation diagram for the Iavas from Volcano Rishiri.

The average values of six analyses of basalts and two altalyses of

augite-hypersthene-andesites from Rishiri are shown in Table III, adding

one analysis of hypersthene-andesite. For comparison, avexage values

Petro-Chemica} Study on the Lavas frorn Voleano Rishiri, Kokkaido, Japan 251

of Japanese basait, andesite and rhyolite-andesite ealeulated by YA"fADA(i2)

and DAT,y's average vaiuesCiS) of basalt, andesite and dacite in Europe

and America are arranged respectively in the same table.

TABi.E III, Average ehemical compositions of volcanie rocks,

Wt %

Si02

Ti02

Al,O,

Fe203

FeO

MnOMgO'Cao

Na20

K,OP20s

H20

1

50.53

l.2S

16.99

3.57

6.22

.156.46

10.21

3.40

.S4

.ll

.63

Totalil IOO,3g

2

50.9

.418.3

4.5

6.6

.14.7

IO.3

2.1

.6

.11.4

100.0

3

eg.o6

1.36

15.70

5.38

6.37

.31

6.17

8.95

3.ll

1.52

.45

1.62

100.00

4

60.96

.56

17.00

2.59

3.54

.IO

2.61

6.73

3.83

1.05

.14

.25

99.36

5

59.8

.217.6

3.7

3.8

.1

2.7

6.9

2.7

1.4

.2

l.2

6

59.59

.77

17.31

3.33

3.]3

.IS

2.75

5.SO

3.5S

2.04

.26

1.26

IOO.3 l lOO.OO

7

66.41

.55

16.20

1.98

2.93

.09

1.55

3.46

5.14

1.74

.17

.30

8

E

64.6

'.3

16.3

2.6

3.1

.1l.6

5.3

2.9

l.7

.21.3

loo.s2 l loo.o

9

65.68

.57

16.25

2.38

l.90

.06

1.41

3.46

3.97

2.67

J51.50

IOO.OO

(1) Average of6basalts from Volcano Rishivi. ,' (2) Average of 29 basalts <less than 55% in siliea content) in Japan, (YA}fim,s)(iL').

(3) Average of 198 basalts in Europe, Ameriea･ etc,, (D.sr,y)(i3).

(4) Average of 2 augite-hypersthene-andesites frorn Volcano Rishitti.

(5) Average of 57 andesites in Japan (YA}fADA)(iz).

(6) Average of 87 andesites in Europe, Arnerlca etc,, (DAr.y)(i:`>.

(7) Hypersthene-andesite frorn Volcano Rishiri.

(S) Average o£ 40 rhyolite-andesite rocks <60-70% in siliea content) in Japan (Y.sbfAD,x)(i'!).

(9) Average of 90 dacites in Europe, America ete., (DALy)(i3).

From Table III, the ehemical eomposition of this voleano is eharac-

terized by riehness in Na2e and poorness in Fe203. K20 and CaO arecontained to nearly the same degree as in Japanese effusive roel<s,Compared with those of the world, ehe former is lower, while the latter

rather high. The quantity of Ti02 is nearly the same as that of the

world, bu't larger than that o£ Japan.

Chemical composition o£ hypersthene-andesite £rom Rishiri resembl6sclosely that of DAT,y's dacite, though different in all<alies. In chemical

eomposition, this lava is comprised in hypersthene-daeite. However this

roek is named hypersthene-andesite here, on account of its earrying

25fu' Y. Ka･tsui' Consideration on Chemical Comp'osition

Norm- and N!ggli:values ealculated from Table II are represented in

Tabie IV, and shown in Figures 3-8. In eomparison wkh voleanic rocks

from the Nasu and Ch6kai voleanic zones whieh are elosely rel'ated to

Volcano Rishiri £roirn geogyaphieai distyibution, those of Voleano Tarumai

TABi,E IV. Norm- and Niggll-values eaieulated £yom Tabie II.

Norms

QOr

AbAnWoEnFs

ApMtIl

1

py,%(

ii}t% i

]

l

ii

IOr. i

AbAnWoEnFs

- 5.5

3.3

25.6

33,3

6.7 '

22,2

8.9

.3

3.7

2.3

5.3

41s8

52.9 '17,9

5S.7

23.4

2

l

- 3.6

4,9

32.5

26.1

11.0

l3.4

5.7

.3

6,O

2.7

7.8

51.2

4!.O 26.s

44.5

19.0

3

.o

5.0

23.0

28.9

le.1

l5.3

7,S

.35,S

2.6

8.9

40.4

5e.7

o.o.4

46.0

23.6

4I 5

l

- 2.1

5.5

29.4.

27.e

9.e

IS.3

3,8

.3

5.S.

2.4

8.8

47.5

43V 2S.9

58:S

12.3

I

l･

l

l

i

i

- 3.l

3.3 '32.0

2)3.S

le.3

17.7

8.1

.3

5.6

2.1.

5.5' 54.t

4e.4

2S.5

49.0

33,5

6

1

iIl/

1.6

6.7

29.3

30.6.

7.7

12.6

6.3

5.3

10.0

44.0

46.0

2S.7

47.4

23.8

7 sill

9

ll

i

i1I/

!

i'

i/

I･

I-

12,8

6.7

30.4

27.2

3.6

685.9

3.5

10,3

47.2

42.5

21.9

41.6 '

36.3

i

l

ii

ll

1I

/

;

l9.S

5.5

34.0

25.3

2,O

6.4

2.0

.34.2

1.1

S.5

52,4

39.1

19,2

61.6

19.2

LI

I

i'

E

19.0

10.5

43s5

l5.S

O.2

･ 2.0

3.0

.3

3.0

1.0

l5.0

62,3

22.7

2,8

54.9

42.3

Nigglis

'si

ag fO'IZ .

c alk'

k

77Z9 al-alic

a.th/al-alic

c-(ag-alk)

' ti

p ql

l･

1lI

l,1ii

I08.0

22.9

46.4･

2Po.4

7.3

.ll .62 15.6

.47 7.S

2.0

,13

- 21.2

118.6

23.6 '

38.6

27.6

IO.2

J3 .49

13.4

.76 l4.2

2.6 .14･- 22.･.2

l17.1

22.4

42,9 27. 'i

7.6

:16

.50

l4,S

.51

12.3

2.5 .14- I[.3.3

119.e

23.0

42.6

25.1

9.3

.l5

.61 13.7

,6S 11.4

2.3 .14- IS.2

117.8

2i.3

44.S

24.5

9.4

.09

.54

1!.9

.79

12.6

I.9

.13

19.S

133- .5

26.7

36.4

26.5

10.4

.17

s52

l6.3

.64

10.2

S.1 -2-

IS5.5

32.0

3e.i

24.6

13.3

.17

.43 IS:7

.71

5.9

32.3 -{-

225.2

33,9

2S,O

22.6

15.5

J3 .46

18.4

.S4

4.2

1.4

.2e

63.2 -y

259.2

37.2

24.5

14,6

23.7

.18

.37

!3,5

l.75

1.1･

1.6

.2364.tt

Numbers of eaeh eolumn with referenee to Table II.

Petxo-Chernieal Stndy on the Lavas fyom Voleano Rishiri, Hokkaido, Japan 253

[I]'ABI,E V. Chemical compositions and Norm- & Niggli-values

of the iavas £rom Volcano Oshima-6shima.

'Wt% 1

sio,Ti02'

AI,O,Feg03FeO

MnOMgOcaoNa20

K,OP20,-,

ff20 (+)

H,O(-)

gI/

48.89 l,.e2

ls.eo 2.92

6Al

.2510.6010.91 l.95

l.13

.05 .64 .12

2l

l 3

'

il･I1

49.90

L19f16.05 5.03 5.55

.14 7.03IO.51

2.l5

1.92

.23. .26 .06

ll

11

IIi

55.56 .61l8.28 2.46 5.11

.19 4.05 8.57 2.67

ISO .22 .62 .l3

4

I/

iI

1l･

l

1

Total

Norms Q Or Ab An Wo En Fs. Mt II Apwt%(

f2Vt% t

OrAbAnWoEnFs ,

g

Nigglis

si al .f;nz

c alk ' k 77zg al-alk aliclal-alk

c-(at-alic)

ti pu qz

99.S9

- 4.4 6.7 16S 28.6 IO.7

26.5 8.2 4.2 2,e .o l2.8 32.2 45.0

23.1 59.3.

I7.6

.99.92

-y il.1 IS.3 27.6 9.3

: 17.6 4.4 7.2 2.3 .7 ] l9.5 32.1 48.4

29.7 56.2 14.1

100.27

I･

104,5 18.S 50.5 25.e 5.7

.27 .66 13.1 .43

ll.9 1.6 .o- 18.3

ll6.0 22.0 44.1 26.2 7.7

.36 .55 14.3 .54

11.9 2.0 .3- ]48

+8.3 , IO.6.22.5

32.5 3,5

10.1 6.9 3.5 l.2 .7

16.2 34.3 49.5

17.1 49.2 33- .7

154.6 29.9 34.2 25.5 10.4

.31 .49 19.5 ,53

6.e l.3 .3-F 12.6

61.72 .37 17.71

IJ2 4.33

.IO ' 1.83 5.19 3.21

- 3.28 .20 . .83 .!6

IOO.05

+ 14.1 19.5 27.3 24.2 .3

4.6 ･ 5.7 '1.6

.8 .5

27.4 38.4 44.2

2.8 43.4 43.8

216.6 36.6 25.4 19.5 IS.5

.40 .38 18.1 1.0L)

l.4 1.0 ,2+ 43.0

(1)

(2)

(3)

Sornma lava of Nisbiyama (Augite-olivine-basalt), Yamasedomari.

Central cone lava of Nishiyama (OIivine-augite-basalt), Yakekuzure

Somma lava of Nishiyama (Olivine'& reddish brown hornblende bg.tl}ene-andesite), Aidomavi.

peninsula.

augite:hypers-

(4) Lowev Higashiyama }ava'(Reddish brown hovltblende-augite-hypersthene-andesite),

Aidomari. The writer's analysis was done on the roek speeimens eollected by Mr. M. TAKAyAsv

to whom heartly thanks on here by expressed fop his kiRdly offering the speeimens

for free use.

and other$ belollging to the Nasu zone and of Volcano Oshima-6shima

belonging to the Ch6kai zone were selected, of whieh the former isquoted from Is}iiKAwA's paper,<" and the latter given by the writer

(Table V), . ' ' Norm For convenience; insuMcient silica of undersaturated roeks are repre-

sented as negative Q, Most of the basalts from the Volcanoes Rishiri

and Oshima-6shima are deficient in Q, This fact coincides with their '

laeking silica minerals and earrying a fair amount of olivine in mode,

In andesites, normative Q is ealeulated somewhat high, but lower than

those o£ the average values o£ Japanese andesites. . ' Normative feldspar of Rishiri, as seen in Figure 3, is characterized

by lew values in An and Or. Normative An of augite-hypersthene-andesites (SiO,7:=56.50--60.80%) from Tarumai is higher than those ofbasalts from Rishiri, regard}ess of their silica contents. This relation

is well represented by modal feldspars ; that is plagioclase o£ Taxumailava is very calcic, sometimes including large anorthite crystals in the

dome lava o£ this volcano; on the eontrary, that of Rishiri is very sodicand usually surrounded by a narrow rim of more sodic plagiociase.

Normative £eldspar of Oshima-6shima is very high in,Or. This Or 'moleeu}e seems to depend upon modal potash feldspar'in groundmass

as already report.ed by KuNo.`･"4)

Or f

N

@ eO O.o% sege ee,be

O RighSvt lava , @ Tai,uritat lava, @ Oshima-6shtua lavq

Figure 3. Diagram showing Norm feldspav.

Petvo-Chemical Study on the Lavas from Voleano Rishiri, Hokkaido, Japan 255

Normative pyroxene of Rishiyi is rathex high in Wo, except hypers-

thene-andesite which is exCxemely low. Oshima-6shima resembles that

o£ Rishirij whi}e Tarumai is far lower in Wo, and C is sometimescalculated,

Wo Qb Os .6

@ oo

@@ ig ee @ ee ee-M-Mee@MOee@+eeig men ..k Symbols same as in Figure 3'

F{gure 4. Diagram showing Norm pyroxene.

?50

&

200

oo

mo

ua

o

-5V

e bvCasu2bne e Reshtrt e 4) C]shima-ashima

ee e ge zx- - e zX e MZ pi .-/

2}.sc.Y.xVffge"if'NtsptkV

tk.gi-ee--i'ilxtli:gtti-H-,.

eege/

'

.-'!

-

x

6

t--

--

"x- 7-'

tr ---

-

as ,,,iiiiigigt

-7z.7-

teo ne 2an

Figure S.

2ua eoo asp 'H siDiagram showing qx values.

eoo･ doo

256 Y. Katsul'

Niggli

As seen inlower than thatnormative Q.

R'gureof the

5, Niggli-qz

Nasu zone,

of

as

Rishiri and

is expeeted

Oshima-6shimafrom iow vaiues

are of

4e

:ts

30'

ro

to

o

e Nasa lone e .' eRiEhiti ee e .e e @OshimQ-eshimn e e eee ees$ ¢ee ge eeeeeee e te ge Se esagee'ee e eet"-'j`i.i,e

>,.h-r)`i

痴',spa,iK.lil'li'A.iii,iiiil.,,,tliSliiiii'iliiillliiiilS:4i/k.Ei{;:hsstiif}iii

igure 6.

?50 300 S5Vh- siiagram showing al-alic values.

In al-aZic (Fig. 6) also,

he Nasu zoiie Voieanoes-(al-alk) (Fig. 7).

ishiri

nd onndhe

shima-6shima are lowey thanontrary, are rather higher in

20

7o"-o

-i o

'U s s N-"thtshN.

2.&r.}siszsis..X " ts

9s-"li-I:Ii.--til'ili'ill"ii-tt,.-g',ga9}gs/itsl'i;ii;lll...t

e eees. e e

e-A-･

lbhiti 1ijFe

-.-tptt""'di'i7ijPexFii},.sH;gt,vvo3nPe "

X:"rg-]e--fi

Nasufone Rishirf Oshiina-6shima

m-mve...-E.c';~

"n.egs.qee ---.

h -. O .w--vatlotvslone %rA' 4･pe -.---M"'--"-'--'------

--A

--iu.-m-----ttw.t,ft,tt,-eptL,lsieQ-n//.sl'eFe

oo rrmm50 ?OO 250 . 30[7･ -35e -stigure 7. Diagra.m showing c-(al-a･lls) values,

00 tiO

Petro-Chemieal Study on the Lavas from Voleano Rishiri, Hokkaido, Japan 257

･ As £or k-mg ratio (Fig. 8), Ri.shiri shows low va}ue in k, but highvalue in 7ng. Oshima-6shima 2s also hiigh Sn 7ng, bu'v' extrelme}y rieh in

k, in eontxast to the poorness in k of }]lishiri. This relation eoineides

with their mode aiid norms.

tt ･@ oo a6

os

O,49i

oj

a?

o.t

e

e

eO

va

e

l gee ee lL-rm----o-Te--e e LfiLuL-Tm-u-7m- eO e@i "e es lee

e eoet el e ee el ee tegt e ' ee eeol e e l eie e H aee i 'e L----grmm.--1 i Se i .e . e. el i Il l･t ee l' .t ±i e ' ･ L--:----.mn-J--TrmmN---J e ' e'

' - [:Ill,iil'i aO')E6'".htZfeAd,,di,'tt,s,ofc,,kd;t"i,i..po`htS for vofeanib rocks

e desu Zb.ne o Rishirt' @ (Zs'himn-Dshinja

e

o.t ae 'n3 ･･ a4 ' a's. ' -k. ' Figure 8. I])iagran) showinp.' 7i7g-k relation.

' ' ' Summary ' From the above deseription, k is coneluded that the ehemiea} eompo-

sitions oE the lavas from Voleano Rishiri are elosely related to iinodal

inine]ral compositions and charaeterized by their being' rieh in Na,,O,

while eomparatively poor in Sro,, eompaz'ed with those of the Nasuvoleanic zone ineluding Voleano Tair-uma,i. Alkali-lime index of theRishiyi ]ava is estimated aboutt 64, whieh indieates that it is more alkalic

than the index of Japanese voleanie yoel<s.

The ehemical eompositions of 'the iavas from Voleano Oshima-6shi]na

25S Y. Katsui

differ in aikalies from those of Rishiri; that is, the foumer is rieh in

K,O and also high in Or and k, while the lattey is rich in Na.,O apd

low in Oy, AR and k, though they contain nearly the same amount o£total alkalies, Voieano Kanpft at 'Oga peninsula, Ai}<ta prefecture,beionging to the Ch6}<ai volcanie zone, is also high in alkalies (alkali-

lhne index was estimated 60 by [I]ANEDA),(iS) but its K,O<'fieviS) is some-

what highex than that of Rishiyi.

In the iight of the chemieal ehraeters outlined above, it may be

supposed that the voleanie zone te which Vo}eano Rishiri beloRgs isindependent of the Nasu zone, as already suggested by AKAG5G) fromtectonie stand-point. But this suppositiolt must be depe'ndent upon

£urther investigations including petrographical and ehemical studies on

the lavas £rom Volcanoes of Syol<anbetsu in Hokkaido and Kamabusein Saghalien ete., belonging to the Rishiri volcanic zone,

Referenees eited

(i)

(2)

(3)

(4)

(5)

(6)

(7)

(s)

(9)

(IO)

(ll)

(12)

(13>

(14)

(15)

(16)

(l7>

(18)

ABE, A.: Crad. thesis Dept. Geoi. & Mineralogy, HokkaidoUniv. (Manuscript> (l934).

KoT6, B.: Jour. Geol. Soc. Japan (1916).

WATtxNABE, H. & I}ftsizum, M.: Geogr. Rev. Japan, 3, 599 (1927).

To}iupA, S.: Jour. Geol. Soc. Japan, 25, ll2-l33 (191S).

Ke}zu, S. & WAT.NNfsiiE, M. : Proe. Pan-Pacifie Sei. Cong. (Japan), 1, 770-7SO (i926).

" : Jour. Jap. Assoe. Petv. Min. Econ. Geol., l, 25-2S, 7S-S4 (1929>.AKAGi, [E]. : Geol. & Min. Resour. Japan (Geol. Surv. Japan), l93-l99 (l932).

Xs}iiKtswts, T : Jour. Fae. Sci. Hokkaido Univ., Ser. IV, 7, 339-354 (1951).

" : Ibid. 8, 107-135 ･(l952). .Y,K}iAr)tt, S.: [rour. Geol. Soe. Japan, 38, 407 (1931).

ANDERsoN, C. A. : Univ. Calif. Publ. Bull. Dept. Geol. Sei., 25, 401 (lg41).

WiLT.itx}fs, H. : Bull. Geol. Soe. Am, 46, 253-304 (l935).

PEAooeK, M. A.: Jour. Geol., 39, 54-67 (1931).

YA}ftxDxs, S.: Jouv. Geol. Sec. Japan, 3Z 1-5 (lg30).

DjsLy, R. A: Igneous Roeks and Their Origin, l5-17 (l914). ･

KuNo, H.: Jour. Geol. Soe. Japan, 43, 392-393 (1932).

TtsNim.x, S. : Sei. Rept. Fac. Sci. Kyfishfi Univ., Geol., 3, 64-65 (1952).

CHiTtsNi, Y.: Jour. Geogr. [roky6, 37, 672 (1924).

6i-ftxtsHi, R. : Jouv. Geol. Soe. Japan, 38, 2S6 (1931).

IwtxsfsKE, M.: Grad. [l]hesis Dept. Geol. Toky6 Univ. (Manuseript) (l937).