552．3（521．8）

肛1意亙a潰｝＆sie Roeks i箪 亡畳直e 趣】aしs意e瓢 P＆置意 o£ 意恥e C恥期gok朋猛one，」脚蹴畏

βy

SAcHIo IGI撒＆KIIKuo ABE果鞭

亘聡旗o題眠e髄o〕嬢

In the eastern part of the chugoku zone，Japa，n，ma・ny ultraba・sic rock masses with various dimensions are intruded．into Paleozoic formations and their metamor－ phosed equivalents。AIthough thesc rocks were summarized in a paper by“the Research Group of Peridotite Intrusion” （1967）， they have not been describcd in detai1。Generally they occur as the r＆ther large masses in the non－metamorphic or slightly metamorphic te∬ains，and乱s rather small masses in the higher grade metamorphic in Tari district；and they are remarkably’serpentinized，and have a little or no relicts of original minerals such as olivine and pyroxene．The purposc of this study is，then，to discuss whether t五ere are differences between these ultra－ basic rocks，based chiefly on their chemical characteristics，or not． This study has been d！one as one of the investigation subjects by “the Research Group of Peridotite Intrusion’，．The expense of this study w＆s partly defrayed by the uMP（UpPer M＆ntle Project）of the sciencc council of Japan・

A磁簸OW亘e誼9職e旙S The authors wish to express their thanks to members of the Research Group of Peridotite Intrusion，who influenced them with kind．suggestions．Thanks are also due to Dr。M．HAYAsHI，Assistant Professor of Kyushu University，for glving his unpublishcd data and，his kind ad，vices，and to Dr』K。TAK：AH：AsHI for analyses of minor clements by means of JA（）o：Ebert3．4m stigmatic grating spectrograph・ Any acknowledgment would bc incomplete without expressing deep gratitud。e to Miss・ Yukiko ONoDERA for 五er help in copying figures and manuscript of this paper・

Geo且09五e Set能箪9我聡雌Pe眈ogra豆》塩y

Distribution of the ultrabasic rocks in thc eastem p乱rt of the Chugoku zone， ‘‘Inn．er Zone of Southwest Japan7’，is s：hown in Figure1。The representative ultエa－ basic rock masses in the region are those from Sekinomiya，Wakasa，：Katsuyama， Atetsu and Tari districts，as given in Eigure1，and most of them penetrate the non－metamorphosed or slightly metamorphosed Paleozoic sediments，formed by the Sangun regional metamorp五ism、However，t五e ultrabasic rocks in t五e nort五em

勢 Read before the74th An職ual Meeting（1967）of the Geological Society ofJapanatNagoyaCity． 鞭 Geology Department 欄 Geochemistry＆Techn圭cal Service Department

39一（39） 地質調査所月報（第20巻第1号）

07「077’0バ》1 熱2轟離熱

麗舳ε1副 ○〃1”三7ノ

論如70η，ゐ03θゴ07 η0〃一〃7θごσ耀0η功（乳5θ（ガ 圏 危どθozoど08θゴ諭θ傭

1 3θたどηo吻α4ど5！7どoオ

2陥えσ5αゴど3オr∠oオ 二爺 3 καオε解磁ゴど5配σど 一租～磯

4． ！4まθ言5μ ゴどεま7Zo彦 嘉 ’ 0 10 20 30 40km 57セ7εゴ‘8孟7・‘o孟

Fig． 1 Distribution of ultrabasic rocks in the eastern part of the Chugoku zone．

牛叢撫、、、

，講縷簑蒙欝熱

聯 窪糞譲驚藥響

， 懸穐1一」一㎞ □oび・盤、 匿雛雛、灘匿…坤轍 麗騒賂鵜ど臨．，，，ク題題緬繍 ！／励 1

匿iiiヨ隔・脇麗どoη匡…盈朧灘駕轟竃難髭疹瀦蹴

匿唾陵繍，輪駿慧瞭・

Fig 2 Geological map of Tari district，Tottori prefecture， after Tottori－ken（1966）and IGI（unpublishcd），

40一（40） Utrabas三c Rocks圭n the Eastem Part of the Chugoku Zone，Japan（IGI＆ABE） part of Tari district occur as small masses in albite－spotted schists and．phyllitic rocks l on the other hand，those in the southem part as large masses in non－meta－ morphosed。Paleozoic sediments。The geologic map of this district is given in Figurc2． According to：Research Group of Perid、otite Intrusion（1967），the main types of the ultrabasic rocks in the Sangun metamorp五ic belt，thc metamorphic parts of the Chugoku zone， arc五arzburgite and dunite． In this region described 五ere， t：b．e rocks have nearly completely altered．into serpentinite with chromitic spineL However，judging from roughly estimated modal compositions of the relict－minerals such as olivine，orthopyroxene and clinopyroxene，the rock species of the original peridotite are likewise dunite and harzburgite，being accompanied by a small amount of pyroxenite，1herzolit6＆nd wehrlite in some cases．The associ＆ted dikes are gabbro and microdiorite。 The ultrabasic rocks occurring as small masses in the northem part of Tari district have wholly been serpentinized，without any relicts of the origi臓1peridotite， excluding chτomian spinels，and are not associated with any gabbroic rocks．

The Sekinomiya mass，the largest in．the Chugoku zone，is in．trud，ed into the Sangun metamorphic rocks of glaucophanitic facies derived。from the Paleozoic sediments（1：KEBE and IGI，unpublished），and is covered by Tertiary volcanics and sediments。The mass is mainly composed of serpentinized dunite and harzburgite， in which chromite deposits are sporadically found． Several masses of Wakasa ultrabasic rocks occur separately in the metamo卜 p組c rocks of epidlote amphibolite facies and are covered by Tcrtiary volcanics （MIYAKAwA，19611Tottori－ken，19661YAMADA，SAK：AMoTo and UEMuRA，unpub－ 1ished）．In a certain mass，monomineralic vein of altered clinopyroxene，optical properties of which are not able to be determined，with2～5cm in width，is found・ Some of serpe・ntinites have been altered into colourless amphiboIe－bearing rocks formed probably by thermal effect of intrusion of granitic rocks not・yet exposed around the serpentinite masses。 In Katsuyama district，the serpentinite m乱sses with medium sizes，derived mainly from dmite and harzburgite，are isolated each other and are intruded into the low grade metamoro1オc rocks（MITsuNo and OMoRI，1963）・Serpentinite from Hokubo－cho contains not only olivine and orthopyroxene but also clinopyroxene as relict－minerals of original peridotite，pres㎜ably I五erzoIite，and is accompanied with altered clinopyroxenite l that is exceptional in the Ghugoku zone。 The serpentinitc masses in Atetsu district penetrate the non－metamorphosed Paleozoic sediments，and are injected by dikes of gabbroic rocks。The original peridotites are also probably dunite and harzburgite， In Tari district，as mentioned above，there are two types of the serpentinite masses，namely small one in the northem part and large onc in the southem part。

41一（41） Table1 Mineral associations of serpentinitcs analyzed chemically，from the eastem Chugoku zone． Numbers，1－11correspond to specimen numbers in Table2．

Ortho－ Clino－ Serpentine Other （secondary） Other rock－facies No。 Locallty 01ivine（Fo％） Spine1 minera1 minerals and associated rocks py「oxene py「oxene i ！ （Chromite） Chlorite HalzbUlgite （92） P，B，V Talc－c＆rbonate rock 撚 1 X X Brown （m．s．） （magnetite） Tremolite－bealing serpentinite SEKINOMIYA 1 （Chromite） Chlorite 8器離／dike・・are § 2 Dunite X （92） （？） P，V（B） （Magnetite） 妻 Brown Carbonate，talc 難 Dunite Harzburgite （91） （X） Yellowish brown V，P，B 3 X （m，s．） Chlorite Clinopyroxenite vein WAKASA 醤 襲 （Homfelsof） Tremolitic amphipole 臨 ！ 4 （86） （？） ？ ？ G艦lendegabbr．｝dike？ Peridotite X （Magnetite）Chlorite 劃 セ 蹴 Chlorite （Harzburgite） Lherzolite （90） Brown Carbonate Dunite 潔 l 5 KATSUYAMA X X X Yellowish brown P，B，V 鳶 （Magnetite） Clinopyroxcnite 面 l龍 i 難 Dunite （95） Yel． brown P，V T＆1c X （black－rim） （m。S．＆d） （Magnetite） N“ 6 黙 ） ATETSU （Magnctite） 8 Harzburgite （92） （X） Ye1．brown P，V，B Bl熱盤o／d三ke 7 X （black－r血） （m．s．） Carbonate 瞭

Talc H：arzburglte 遽 （Dunite） （X） Ye1．blown P，V Lherzolite 8 （m．s．） （black－rim） （Magnet1te） Clinopyloxenite 一 越ロ TARI（1） Amphibole－bearing peridotite ChlOlite Amphibole rock ） Red－brown P，V （Magnetite） Dun呈te X，C（？）（96） 9 （black－r血） （m，s．） （Anthophy11itic 鰹’灘bb「O／dik・ amphibole）

10 Yel．brown Chlorite （black－rim） V，P TARI（五） （Peri（玉otite） Carbonate 11 Red＿brown （Magnetite） （black－r三m） P，V

X： Illustrates existence only P： Prismatic （m．s。）： Mesh structure C： Cleavable olivine B： Bastitic d： Decussate structure Fo％： De亡ermined by X－ray powder method（after Yoder＆Sahama，1957） ▽： Vein ultrabasic Rocks in the Eastem Part of the Chugoku zoneシJapan（IGI＆ABE）

The masses in the southem part are composed．of serpentinites derived from dunite and harzburgite，rarely from pyroxenite，judging from their relict minerals。 Some of the masses，however，are of anthophyllite－or tremolitic colourless amphi－ bole－bearing serpentinite altered by the thermal effects of the late Mesozoic granitic intrusions． （）hromite deposits are also foun（i in the large masses and are now wor：ked at the we11－known chrome－mines of Japan，such as the Hirose and Wakamatsu mines． 丁五e mineral association and petrography of the representative ultrabasic rocks analyzed chemically are summarized in Table1．

Pe意買oe丑良e職is亡ry

Eleven specimens of the serpentinized ultrabasic rocks are selected from the representative masses mentioned above，for chemical analysis。 The results are shown in Table2．C＆1culated MgO：FeO十Fe203×0．9 ratios varying from3．9to6．9are also given in it・Two specimens of Nos・4and 5are of amphibole－be乱ring metamorp五〇sed peridotite and of serpentinized lherzo一

Table 2 Chemical compositions of serpentinites from the eastem Chugoku zone． Analyst：：Kikuo ABE

1 2 3 4 5 6 7 8 9 10 11

Sio2 39．59 33．88 37．80 44．31 39．21 37．56 39．32 35．65 35．62 39．22 41．45 Tio2 0．06 0，07 0．05 0．09 0．10 0．05 0．05 0．05 0．05 0．07 0．07 1．11 A1203 0．43 1．64 1．62 1．34 0．81 1．00 1．26 0．83 1．13 1．55 5．53 Fe203 3．36 4．73 8．49 6．24 5．14 4．43 7．31 6．68 7．53 4．92 FeO 2．81 1．60 1．81 5．53 3．02 1．77 1．58 1．07 1．02 1．62 3．21 MnO 0．10 0．30 0．21 0．11 O．22 0．19 0．18 0．11 0．12 0．14 0．09 MgO 38．15 38．57 33．49 40．21 35．71 39．75 38．51 38。32 41．93 35．15 36。02 CaO 0。74 5．69 0．04 0．49 3．30 0．04 0．04 0．02 0．02 0。03 0．06 Na20 0．13 0．12 0。21 0．46 0．30 0．20 0．28 0．06 0．01 0．05 0．02 K20 0．03 0．01 0．01 0．02 0．02 0．01 0．02 0．05 0．04 0．04 0．05 P205 0．01 0．01 0。01 0。01 0。01 0．01 0．01 0．01 10．39 13．19 11．93 4．49 H20（十） 8．99 12．59 12．95 13．41 11．38 11．54 11．44 0．85 0．90 0．93 0．23 H20（一） 0．74 0．92 0．90 1．63 1．78 2．41 0．62 0．39 0．33 0．28 Cr203 0．15 0．36 0．33 0．29 0．61 0．19 0．95 0．50 C 0．02 ＜0．01 ＜0．01 0．01 く0．01 ＜0．01 ＜0．01 CO2 0．88 0．43 0．31 0．01 0．41 0．48 0．32

99．89 100．05 99．52 Tota1 99．90 99．97 99．85 99．88 99．56 99．67 99．88 100．00 Mgo 5．68 3．92 5．40 4．33 4．13 6．21 6．91 5。00 5。96 4．18 4．71 FeO十Fe203×0．9

1．Sekino鳳iya－cho，Yabu－gun，Hyogo Prefecture（U67－8） 9．Nichinan℃ho，Hino－gun，Tottori Prefecture 2。 Sekinom．iya”cho，Yabu『gun，Hyogo Prefecture（U57－3） （Hiro－12） 3．Wakasa－cho，Yazu・gun．Tottori Prefecture（UC－37） 10．Nichinan－cho，Hino－gun，Tottori Prefecture 4．Wakasa－cho，Yazu－gun，Tottori Prefecture（UC－35） （T60－168）…In phyllite 5． Hokubo℃ho，Jobo－gun，Okayama Prefecture（Y63－114） 11．Nichinan－cho．Hino－gun，Tottori Prefecture 6．N王imi－cho，Atetsu－gun，Okayama Prefecture（U66－9） （T60－100〉一 In spotte（i schist 7．Shingo－cho，A電etsu－gun，Okayama Prefecture（U66－2） 8，Nichinan－cho，Hino・gun，Tottori Prefecture（T60・69）

43一（43）

・陶唱P罷 地質調査所月報（第20巻第1号）

Table 3 Minor elements（ppm）in serpentinites from Tari districtbymeansofJACoEbert3．4mstigmatic grating spectrograph （second order）． Numbers，8－11 correspond to those in Table2，

Analyst：Kiyoshi Takahashi

No． 8 9 10 11 B 35 50 60 20 Ba ＜25 く25 く25 く25 Co 45 60 70 65 Cr 1200 4000 6000 3500 Cu 30 40 90 100 Ga 8 12 12 18 Mn 900 800 1工00 700 Ni 800 1800 2300 2500 Sc 35 50 60 45 Sr ＜25 ＜25 ＜25 ＜25 V ＜10 15 ＜10 20

1ite respectively，and both of these rocks have different miner＆10gical characteris－ tics from other rocks．Two specimens of last numbers，10and11，are of wholly serpentinized rocks with small dimensions from t：he northem part of Tari district， and they were added for comparison with the rocks of large masses， Chemical a皿alyser of minor eloments of ultrabasic rocks only from Tari district are performed by means of JAGo Ebert3．4m stigmatic grating spectro－ graph（Second order），and the results are shown in Table3．

0

0 o 10．0 o O O o O Q o σ 皇 』 7，0 2 ∂ £ o E 5．0

Φ Wし ＼

ゆ ≦

1 2 3 4 5 6 7 8 9 10 11

SPECl人へEN NUん～BER

Fig． 3 Diagram showing Mg：ΣFe ratios（molecular ratio）シrecalculated from chemical analyses of serpentinites（after HEss，1938）．Specimen numbers

correspond to those in Table2．

44一（44） Ultrabasic Rocks in the East¢m Part of the Chugoku Zone，Japan（IGI＆ABE）

Recalculated Mg：ΣFe（molecular ratio）are shown in Figure3．They are all over7．0． This f＆ct indicates that these ultrabasic rocks belong to the alpine types（ultramafic magma series）after HEss（1938）． The relations between MgO：total FeO ratio（wt。％）and various oxides are shown in Figure4．Values of most oxides，excepting those of MgO，decrease or are kept constant with increasing of MgO＝total FeO r＆tio。The tendency w1虹ch values of some oxides are kept constant，does not precisely correspond with anyone of rock－series，such as lherzolite，wehrlite，etc。，of the mafic and ultra－ mafic nodules in basaltic rocks of Hawaii，given by KuNo（1968）。It may be of the reason that the ultrabasic rocks described in this paper belong to series of harzburgite and d，unite type（R．esearch Group of Peridotite Intrusion，1967），not yetf・undinthesenodules・

5σ

● ＿一●一一一一 0 40 ，，o－6－ ●

Σ 〆Q》 o’● 50 30 ● 0 40 、、隔o ● ● 0 『一『一甲一●一●』一一一｝ 10、0 ￥ ● ● ● ＼ の ＼● ● ●＼ 30 o ＼ ＼ 8，0 Q ● 、．0 、 ● 、o 、 ● 0 0，5 O o㌔・一．。一．一．。、．一．・・一一・一 L 6、O ● 、、● Σ W

1，0 1，0 4，0 o 0 0．5 ♂o・5 『曽一一一一〇隔一鴫 ●● －●遭一＿●． 一●一 一一●動0＿〇一●辱． 一●，＿＿＿●一一 3 o ●

、 6．0

2，0 1．o 俵 、、一Ω＿＿o ● と0，5 ● ●『『も＼＿＿ ● 9 怯 ＿一＿一●一一『一一『一一一一一ro－r一一一占 o ● 、、 O● O ● 0 1．0 、、 ● 丑 o ● 、、 0 3．0 2 3 4 5 6 7 ＜ ● ） Mgo lwr・） FeO量Fe2％O＝9

2 3 晶。 5 6 7 8 FeQ昭e2。3κ・．g岡 2 3 4 5 6 7

Fig． 4 Variation diagram representing the relations between MgO／total FeO ratio and various ox1（ies． Open circles indicatc serpentinites in the spotted schist and phyllite from the northern part of Tari district l solid circles，from other districts。

100

0 6 ／ o ノ た ノノ ら8一”一9ずノ’9 ＾ go 訳 ，ノ’ 2 石 0 E≡ 4 £ 一 80 0 2 3 4 5 6 7 8 猷gO （w†，1 FeOfFe203xO・9

Fig． 5 Re1批tion between MgO／total FeO ratio and forsterite molecular proportion． Numbers for open circles，1－9，correspond to those in Tables l and2。

45一（45）

｝ご柚瓢葡駅｝郷『黒q岬“畑・R岬騰’マ 地質調査所月報（第20巻第1号） Figure5represents the relations between MgO3・total FeO ratio and Fo－ molecular proportion of olivine，determined by X－ray powder method after ’YoDER and SAHAMA（1957），from olivine relict－bearing serpentinites，as aユready given in Table 1．Of these olivines determined here，the “cleavable olivines” （KuRoDA and SHIMoDA，1967）are not contained， It is very difficult to interpret the meaning of the interrelation between variations of the minor elements plotted against MgO：total FeO ratio，as shown inFigure6．

5000 へ

1，000

500

100 づ、 50 、翠

10

5

10 11き

2 3 4 5 6 7 蒲圃 Fig．6 Relation between MgO／total FeO ratio and minor elements． Specimen numbers，8－11correspond to those in Table3．

MgO」2（FeO十Fe203）一5C＆O diagram，as given in“UItrabasic rocks in Japan7，（1967），is shown in Figure7． Excepting special cases of Nos・4and5，the points calcu1乱ted from Table2，are plotted inthesamefieldsof“Sangun－Maizuru”， as given in the paper （Figure3）．

・Co簾面伽聡ofSe蹄e鵡直聾ite鯉膿夢恥ee恥e虚

A triangu1乱r diagram representing the relations between enstatite，talc，ser－ pentine and olivine in the system MgO－SiO2－H20is shown in Figure8． Ultrabasic rocks an乱1yscs from this re癖on，recalculated to molecular percent，are plotted on the diagram．Most of the points plotted are conccntrated around the site of the ideal serpentine，excepting special case of No・4．We cannot see the difference， in this diagram， between serpentines of large masses in slightly or non－metamorphosed rocks and those of small magses in the higher grademetamor－ phic rocks・

46一（46） ultrabasic Rocks in the Eastem Part of the Chugoku zone，Japan（IGI＆ABE）

2（FeO穿Fe203）

猷喚BU－SANBAG舗1。 ／ 〆一一一一一一プ鵠 〆 ！／！ ！！ 89 ‘ ！1 o ， Oo馬6〉 9 5 ぐ i2夕7 4 ／ SANGUN一猷AIZURU

5GqO 猷gO

Fig． 7 MgO－2（FeO十Fe203）一5CaO diagram on serpentinites，after Research Group of Peridotite Intrusion（1967）．Specimen numbers for plotted points，1－11 correspond to those in Table2．

日20

8RUqτE

擬SERPENTINE 9踏“ 5

豊 TAIC

OuVlNE ENSTATLTE Mgo Sio2

Fig． 8 Triangular diagram representing the relation between enstatite，talc， serpentine and olivine in the system MgO－SiO2－H：20 from chemical compositions of serpentinized ultrabasic rocks． Specimen numbers for plotted points，1－12corrrespond to those in Table2．

According to MIYAsHIRo（1966），serpentinite in non－91aucophanitic metamor－ phic terrains tends to be higher in the FeO：Fe203ratio than those in glaucophanitic metamorphic terrains l and the latter in tum tends to be higher in the same ratio than those in non－metamorphic terrains．Figure9is the same diagram as given in MIYAsHIRoys paper，representing the relation of FeO and Fe203contents （wt， ％）of serpentinites from this region．The plotted points are disseminated on the field，drawed．by present authors，which roughly coincid．e with those of rocks from g1乱ucophanitic or non－metamorphic terrains after MIYAsHIRoりaround or under magnetite line，denoting Fe304・

47一（47） 地質調査所月報（第20巻第1号）

譜 10 誇 ！1 ／！ ／！ ！ ぶ 1☆＜／／／漣〆浮 弔 ミ5

◎ 恥 ＼ ／111 × k 養◎身／ピ＼＼ ／・＞〈！．・ 習．ノ ／／＼更．一．ノ ク！／／ 一98 5 10 万θ203砿％

／一、磁〃・・晦磁・加θ伽・7ρ伽α〃4 ㌧一ノη。η一御θ繍。㌍伽α7鰯 ．。．．．．ノ伽一幽・・蜘顧・卯伽・翻・α7θα

Fig．9 Relation between FeO and Fe203contents（wt．％）of serpentinite， after MIYAsHIRo（1966）．Specimen numbers for plotted points， 1－12 correspond to those in Table2．

O

oo ○ O

lO。 20。 500 40。 50。 60・ ＿＿＿一2θ Fig，10 X－ray powder chart of serpcntine mineral of serpentinite（T60－100）in spotted schist from Tari distrlct（2θCuKα）． Peaks marked with open cjrcles fairly consistent with the char＆cteristic （hkl）reflections on antigorite from K6chi city，after Hayashi，s unpub－ lished research（by kindly personal communication）based on Wh三tta－ ker and Zussman（1956＆1958）。

48一（48） Utrabasic Rocks in the Eαstem Part of the Chugoku Zone，」＆pan（IGI＆ABE）

Besi4es，according to CoLEMAN（1966），who studied the New Zealand，ultra－ mafic rocks，X－ray studies of serpentine minerals reve＆1that ortho－and clinochry－ sotile predominate in the highly sheared serpentinites and lizardite is morc common to the massive serpentinites； antigorite is the stable serpentine polymorph in the regionaユ1y metamorphosed，serpentinites within Alpine schist or in restricted．areas of high stress in the Great Ultramafic Belts，HAYAsHI（1968）also states that lizardite serpentinite is formed under the condition of higher oxygen pressure than antigorite serpentinite，namely when：FeO：Fe203ratio is lower，1izardite serpentine cryst乱11izes；when，FeO＝Fe203ratio is higher，a：n．tigorite serpentin，e． Only one specimen of serpentine mineral of serpentinite（T60－100）in spotted schist from Tari district has been prepared for experiment of X－ray diffraction． The X－r＆y diffractogram is shown in Figure10・And the serpentine mineral is identified as a，ntigorite．This fact suggests t五at serpentinite in the spotted。schist might have emp1＆ced during regional metamorphism and．have been formed md．er the condition which oxygen pressure was not so higher．

CO皿el題sion

Most of the serpentinized ultrabasic rocks from the eastem part of the Chugoku zone may originally’be dunite and harzburgite，judging from their relict minerals．However，it is very regrettable that the differences between the small mass in higher grade metamorphosed rocks and the larger one in low grade or non－metamorphosed Paleozoic sediments are not able to be pointcd out，petrologi－ cally or mineralogically，and also petrochemically，because of their strong serpentini－

Z＆tion． The researchon the condition of serpentinite emplacement and．serpentinization， based on oxygen pressure or serpentine polymorph，has not been done enough…

References

GoLEMAN，R．G，（1966）：New Zealand serpentinites and associated metaromatic rocks．1V卿Zθσ伽4G601．S％7∂．B％ll．，n，s．76． HAYAsHI，M，（1968）：Chemical ch＆racteristics of the serpentinites in Shikoku・1吻％・ Pεケ．Eoo鴛o挽づ6σεo乙，voL59，no，2，P．60～72 （in Japanese with Eng－

1ish abstract）． HEss，H．H，（1938）＝A primary peridotite magma・A耀7・力％7・So云，voL35，no・

209，p，321～344。 IGI，S．（unpublished）：1：50，000geological map of“Tari”and its explanatory text・ GeoL Surv・Jap乱n・ IKEBE，N．＆IGI，S。（unpublished）31：50，000geological map of‘‘Muraoka”and its explanatory text・Geo1・surv・Japan・ ：KuNo，H．（1968）：Mafic and ultramafic nodules in basaltic rocks of Hawaii・060」・

Soo．ノ生吻67．，ハ46郷o〃， 115，p，189～234．

49一（49） 地質調査所月報（第20巻第1号） KuRoDA・Y・＆ SHIMoDA，S・（1967）：01ivine with we11－developed，cleavage－its geological and mineralogical meanings， ノo％飢G60」。Soo。ノ初力σ％， vo1．73， nO．8，p、377～388． MITsuNo，C・＆OMoRI7T・（1963）：1＝150，000geological map of Okayama prefec－ ture，and its explanatory text。okayama－ken（in Japanese）． MIYAKAwA，K（1961）3Sangun metamorphic rocks in the Wakasa area，Tottori prefecture・ ノloz6敷 σ601．Soo． ノゆρσ％， voL67， no．793， P．549～560 （in Japanese with English abstract）． MIYAsHIRo，A・（1966）；Som。e aspects of peridDtite and，serpentinite in orogenic belts。 Z ／l G．C・，vo1・37，no。1，P。45～61． Research Group of Peridotite Intrusion（1967）3Ultrabasic rocks in Japan，．ノ∂％γ。 660」・So6・カカσ％，voL73，no．12，P。543～553． Tottori－ken（1966）31：100，000geological map of Tottori prefecture，and its expla－ natory text （in Japanese）． wHITTAKER，E．J．w．＆zussMAN，J。（1956）：The characterization of serpentine minerals by X－ray diffraction．Mi銘。1吻g，voL31，p、107～126． wHITTA：KER，E．」．w．＆zussMAN，J．（1958）：The characterization of serpentine mineτals・ ∠L卿6γ・Mi多z・，voL43，P・917～920． YAMADA，：N・，SAKAMoTo，T．＆UEMuRA，F。（unpublished）：1：50，000geological map of“wakasa”，and its explanatory text．Geo1．surv．Japan． YoDER｝H．S．＆SAHAMA，T。G。（1957）＝Olivine X－ray determinative curve．A耀グ・ 砿i銘67。，vo1。42，P。475～491．

要 旨

中国帯には，大小さまざまな超塩基性岩類が分布している。これらいずれの岩体も蛇紋岩化がいちじ るしいが，わずかな残晶から，大体duniteとh＆rzburgiteを原岩とすることが推定される。ここでは， 大小両岩の相異を検討してみようと試みたが，それは残晶の大部分が変質しているので，岩石の化学組 成のみによった。その結果は，特殊な例をのぞくと両者はほとんど差異がなく，MgO／ΣFeO（ωt％） も，3．9～6．9の範囲内にある。ここでも若干検討はしたが，今後は，FeO／Fe203の関係，蛇紋岩化の 程度あるいはserpentine mineralのpolymorphなどにより，その生成の地質条件を検討してみる必要 がある。 地 名 Atetsu……………・…一…・阿哲 Hokubo・……・……・………北 房 Katsuyama一…・一・……・・勝 山 Nichinan……・…・………一目南 Niimi・・…一…・…・一……新見 Sekinomiya…………・・一…関 宮 Shingo…一…………・……新郷 Tari…………………………多 里 Wakasa・…・………・曜……・・若桜

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