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和寒・比布地域に産する中新世高マグネシア安山岩類の化学組成とマグマ混合

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(1)Title. 和寒・比布地域に産する中新世高マグネシア安山岩類の化学組成とマグ マ混合. Author(s). 和田, 恵治; 小田, 幸子; 山中, 千佳. Citation. 北海道教育大学紀要. 第二部. B, 生物学,地学,農学編, 43(1): 35-45. Issue Date. 1992-07. URL. http://s-ir.sap.hokkyodai.ac.jp/dspace/handle/123456789/6484. Rights. Hokkaido University of Education.

(2) . 北海道教育大学紀要 (第2部B) 第43巻 第1号 Jouma lof Hokkaido Universi ty ofEducat i ion DB) Vo l 43 t on(Sec . ,No.I. 平成 4年7月 ly 1992 Ju ,. 至遁iocene h igh-登壇g andesites and re1ated rock from. ‐ ‐ the VVassalnu ぞiPPu district northern 閥okkaido j 1: , , aPa1 Chemical characteristics and magma mixing r. * ** Ke i i Wrada j ,Sachiko oda and Chika Yamanaka. Ear i thSc i do Uni i ence Laborato i ty ofEduca t ver s ly, Hokka on ikawa at Asah ,Asahikawa070 ,Japan. Abstract. ハ4iocene vo1Canic rocksf rom the ▽▽assaエnu ido i ‐Pippu district,northern H0kka tof s ,cons basa l i t i h5 3 o t 2 te S 6 8 c andesite and and t i 0 t ; w {器i h db l % o d t i K t a w n e ong o e me 皿 r n- rock ‐ 2 ‐ , , l Th i K 0 h series l ey are ower n 2 t an Quatemary vo canic rocks f , rom Taisetsu, Tomuraushi , i d h t i i h and Tokachi j t t d P f i i t t t u s o M o n u s e e i s r c t e a c co tesshow low Feo本/ c e a n os andes , . M 客)rat ios( 0-1 1 5 lass i f i * )and arec ianandes i i edintohi ‐ma t es crocksi n si02vs . gh ≦ p l ‐ ‐ Feo / MgC }diagrams. Thesechemicalfeatures suggestthatthe W assamu‐pippu Miocene volcanic rocks notf i ionl ldertectonic cond ike Quaterna ormed ul t ion .γ subduct. ‐ Thebasa l i i t tehasPhenocrystsof。 l ivi candes l i l lamountsof neandc ths noPyroxene wi ・ 幻 ー a ・ i l i h tassemblage ofandesitesiscomposed ofplagioclase pagocase m cr。p enocrysts. Phenocrys. , 1 i onhopyroxene 1 ivi nopyroXene hornb1 ende o ne andFe thorwi -Tioxideswi thoutqua【zand ,c. , , , biot i te dence 。f magrna m・xing such asreversezoning of rographi ce▽i - Theserocksshow pet trographi lcharacteristicsindi phenocrysts candchemi ca ian ‐ The pe catethatthehigh-magnes i i t andes crocksf i i rom the▽▽assamu t -PiPpud imi s r ctwereproducedby mlxlngofpr i l t t vebasa ivine and c mlagpna containing D4g‐ l inopyroxene phen。crysts and hornblende daci rich 。l te. magpna ssuggeststhattectonicstressi idd1 i nthe1aten iona la . 1 1owing ‐ Thi e ルー ocene wastens i i t the pri t 1 1 l ve mーag i ly ascend t r t roughthe crust. ゴ ロ na o eas. lntroduct ion An int imate relat ionship between subduct ion processes and arc mag i sm has been コmat demonstrated by m鋼l k i wo r Q e r s t i t n t K ua ema tems( ml 1959 S i y 1960 ly ec oncs s. o y ; ug m皿↑a ; , , Di cki nson and Hathe〕”on,1967 R t f f ) t f K A J d e c 鷹 i i e c n t f e e t l o s i o - a e e e rm n a n v g o o o c a n c , ‐- fno賃heastern Hokka rocks o idoindi l catethatlate midd l i i e公4i ocenevo buted cani t crocki sd r s. *Pre sentaddr ima e l ミ 渇; Urakawa pr ーγ schoo **Pr esentaddres t s; Yube sujuni orhi ghschoo. (35).

(3) . ika Yamanaka Ke i i Wada j ,Sachiko odaand Ch. 36. i lcan ly N‐S westem al i ld eastem vo c zones 甑′atanabe and Yamaguchi n general , 1988; ionof f NE SW d i t i f l f f i d i rec i ‐ Wra erent rom ) tanabe et al rect on o vo an czones s sdi . Thi . ,1991 f ferencesi i l insinthe Kur cenViro止 nthetectoni catesdi Quatemary volcanic cha earc ,andindi ly Quat t l i f i t tt - ti l dd sthus mpor an o car y no on e Miocene andthe Quatemary n mi menti , l ls logi tudi i led pet i sregion have not esi n thi i ro ca t also 弾1 sm. Data erna1 ocene mag コ ロ ロat 「 y bu i ig in ofN1 beenreponed however. Thustheor ocene volcanic rock has been unclear. i i t crock lnthi s paper we present petrography and majorelement data on Mioceneandes ,. tofthe i ア i ′assanqu-Pi tinthe western zone s40 km no【hwes t s areai f r c s rom the下 ppu di ‐ Thi i f h l i l l t h i d n a r s o cal h i e chemi i o Quatema set su‐Tokac vo can c c an 1γ Ta , an so a ows a comp l lyt i i t tes cate ion o ndi f Miocene andesites al calresu si t ・dthe Quatema composi ly andes . Ana i i t i tes; The vvas s hi c rock i ld -Pippu andes i f f i sa工nu gh‐ chen l ca erence between these andes , i ian andes i i cani crock‐ onthe ‐Tokachivol t set su I 1es candhaslower K20 contentthan Ta mag ike lyproducedby a mlxlng tl lcharacteristics,these andesites Were mos bas i ca sofpet rographi 1ude d i i d d h h b 1 t can therefore conc 1 i w i b i t e 節 ロ i a a n f t ma orn en e ac c g コm , o pr tve asa c mag コma w iona lst / l ressthanthe iocenevol thatlate middl cani sm mayhavetakenplaceunder moretens eD i f ionsys t tem ofthe Paci c plate. presentsubduc. Nayo【O basiQ 0 o 。 . 夢 8 W - ・ - .・ . . ‐′- ・ . ・ ‐ . . ◆ ‐ ・ 、 - ‐ .. r ▼ Er . , . ◆ ・ ・ ‐ . ‐ .◆ . . a ロ ロ ′ s s u a 、. ニ ず孝慧ミ. . O. 5如. ig F .l. i tr f i i si 口lpl ‐Pippudi s ct imu edgeolo淳c mapofthe÷Wassa ‐ NUぱnbers ,nonhem Hokkaido l denotesa i ty and sa ]mp1 enu omber ] □ n eloca ‐. (36).

(4) . D 僅i △なg andes i l te ocesehi - sandre i atedrockf ro 1 1 ntheVVas t t samu gh ‐Pi s r c PPudi. 37. Sam i p酔 desc嘘p韻。n Fig ion ofthe andesites ana lyzedi tudy n the present s ‐l shows thelocat . The volcanic 8 l l ) wereco rocksi n Wrassamu(Nos - lnmockyremnant ectedf rom hu soflavassurroundedby ‐1 P1ei stocene to Holocenesedimentsi nthesouth Nayoro basin‐. Theselavas belong to Bi fuka. Format ion wh i i buted alongthe wes i tem andeas tem bordersofthebas ta chi sdi st r n(Matsushi. i et al ) t goup escan bedividedintothree andesite groups: thef rs yzedsampl . ‐ Theanal ,1977 4 l l;thesecond (Nos )i 為四卯伽棚 hi ‐ s referred to a s“蹴餌細粥“ ”%庇s撫 子’sampledfrom 財Z ‐1 ” “ ” 〆 i 亙 粥 ≠ 5 7 dt h h i d N 8 (Nos d e 豆 { They t )a α “ 賜 gs e‐ s 簾鍵粥“ 2 云g 皿’ e r ( o ; an 餌鄭伽“ α7 .‐ ‐ )as ivine and hornb1ende phenocr are p1agioc1ase-phyric and contain both o1 「 ysts -. Biot i te phe‐. i 1. tes nocrysts are presenti ・nu ande n VVassa s ‐工 and‐1 The Bi fuka Formation i ta et al s overlain by otobeyama lava (Matsushi ) whi ch ‐ , 1977 ) extendstothe Pippuarea(Suzuki ‐ T wosamplescorrespondingtothe otobeyamnalava ,1957 ‘P幼少”α lyzed i i )i t wereana sreferredtoas‘ 7 2dgs紡げ’ ‐ ende contai ningporphyr c ‐9 ,one(No ,hombl ” ” 1 Zだ ( )as 猛蓉硲 廟‐2 thwes tofPippu rocks Q初Szb餌錫Zた α7 2ばB S sampl ednor .10 ,andtheother(No inopyroxene phenoc1γsts l ivi town ) th o neand cl ‐ ,a massive compact rock wi K‐Ar age of Mikasayama andesite,corresponding tosample No‐1,is ll‐I Ma(Goto 1992 ,. i 3 Ma(訳/atanabeand Yamaguch i ) n prep ) s9 . ‐ ‐ ,andthatofotobeyamalavai ,1988. Anal l 亘es口舵s y誠にa M【a luorescence s l ips jor element analyses were performed bythe X‐ray f rometer(Phi pect P帆‐ 1404 machine i ing the ana l i l method of Tsuchi l ) of Hokkaido Uni ty vers ca yt ya et a . ,us i 1989 tsthebulk rock compositions ofthesamples‐ ) ( s ‐ Tablell Table1 sa l mnp e No .. Ma lememt compositions of volcanic rocksf jore rom Vrassamu -Pi ppu. 1. 2. 3. 4. 5. 6. 7. 8. 9. 1o. si02. 56 61 ‐. 58 09 .. 58 51 .. 45 62 .. 62 30 ‐. 20 60 .. 58 48 .. 59 96 ‐. 60 98 .. Ti02. 83 0 ‐ 43 15 ‐. 0 77 . 30 15 .. 0 81 . 15 53 .. 0 65 . 16 01 .. 0 78 ‐ 16 76 ‐. 0 74 . 15 70 .. 0 73 . 15 73 ‐. 0 68 ‐ 17 34 ‐. 0 78 . 16 09 .. 20 53 . 0 8 .0 15 09 .. 7 90 ‐ 0 14 ‐. 7 32 . 013. 66 7 ‐ 0 13 .. 87 5 . 0 13 .. 6 28 ‐ 0 07 ‐. 6 74 ‐ 13 0 .. 37 7 ‐ 0 13 ‐. 99 6 . 0 12 .. 6 24 . 0 12 .. 8 85 . 0 15 .. CaO. 7 28 ‐ 7 76 ‐. 5 97 . 7 38 .. 5 15 . 7 51 ‐. 3 48 . 75 5 .. 2 03 ‐ 5 32 ‐. 4 41 . 7 12 .. 5 02 ‐ 7 61 ‐. 3 32 . 6 18 ‐. 3 59 . 5 52 ‐. 8 86 ‐ 9 69 .. Na 20 K20. 3 05 . 1 19 .. 3 19 . 1 40 .. 3 20 ‐ 36 1 ‐. 3 74 ‐ 82 1 .. 3 85 ‐ 1 79 ‐. 3 40 . 1 49 .. 3 22 ‐ L32. 3 71 . 1 42 ‐. 3 58 ‐ 1 66 ‐. 2 77 . 0 89 ‐. P205. 15 0 . 100 34 ‐. 0 15 ‐ 99 70 ‐. 0 15 ‐ 100 01 ‐. 0 15 . 100 05 ‐. 0 16 . 99 34 ‐. 0 13 . 06 100 ‐. 0 12 ‐ 99 73 .. 0 13 ‐ 99 8 ‐5. Fe。*/M8 98 ‘ ) ○ ・. LIO. 1 34 ・. . 52 -. 2 79 -. L38. 1 32 -. 1 90 ‐. A1 203 本 Fe 203 Mno Mgo. total. (37). 0 17 0 13 ‐ ‐ 98 3 7 1 0 0 4 ‐ ‐3 1 56 0 90 ‐ ‐.

(5) . 38. ika Yamanaka Ke i iWr j ada ,Sachiko 。daand ch. ☆日 g 2 1 湖如昭次 倒 閣胎(勾扇獅霞 B鯖擬-. di 0 秒後 l p m“ “4 m -灯 o M. . . 55・. 60 s iQ2. 65 wt%. in F i i Eお oflow-K, medimr n-K, and h ‐K are g gh ‐2 K20 Versus Si02 dia≦享mm‐ The boLmdaIγ 1 f T T h i d T i takenf k h i G l K t i l 1 9 8 dt h 0 1 ( ) ー n r l a seSu are rom eaverage 2 0 o ac , o u aus ,aー ,an 食om lshi l 1990 ) zakieta .( ‐. oto tudy variesf rom 53 The si02 content ofthe volcanic rocks anal nthe presents yzedi ‐ l i i l s c andesites are the e 62 8 wt%, most ntermediate to f ng thati ndi cat y above 58 wt .%,i . i ions F h i 2 t i dommantrock typei nthi sregion- The K20 vs . )s owsthecompos .Sio2dagam ( g l( 1981 ion i l ium-K ser t f 1ass i i ) esofGi ed asthe med of Wassam法Pippu volcanicrockC . lnaddi , hi h are Quatema i h T T i d t w c a s e s the average K20 contents in Tokachi a s a n u omu r u l y , , , l l lus i do t rom dataof ng orderofK201 eve s n descendi ratedi volcanoesi n centraI Hokka ,f ,arei l lofthe wrassa iageam,the K201 s l l 1990 cani crocksi Inu ‐Pippuvo eve ) shi zakiet a , lnthe d ‐( lylowerthanthatofthe Quatemaly volcanicrocks. marked 8 i i i te )havehigh8 i l te(No )and 汎rassamu andes Higash ‐1 (No t candes -Takasu basa ‐ ‐1 .10 * i 2 8 o 9 t k M [ t f 0 0 T b l F / e 次元-% and 3 Wt g ra o ranges rom . o ., -% Mgo contents- he uk roc le No i l i b ds T k h B H i h i t h te and samp a l l b l l 9 t t c a n a a ‐ a a s u s a w o e s n r e o e e g g y ‐l of the ‐‐ * l l 0 I M [ 0 i i Mikasaya i t Fe0 / g rato のeow ‐) i te are characterzed bythe rloWes u ゴ ロa ande s . * b l i i t igh- t b d T o i h we i 0 F o d n e en h h S /M Fi o a 3i c om o s n a r t o u e a am v p y g gr . g 2 s ‐ e ‐ s e 1989 i lkal ) lじa inerockser i i ianandes rom Sato( t stakenf es(CA)i crock(HMA)andca mag1 es ‐ i lじa lka l ine andes P D Q i tesf lI i iona Thi ine represents a compos t tofca rom Quate111ary strato‐ sl i f i lass lcanoes(Sato 98 9 ‐Pi edinto H MA,dueto ) rom Wrassamu ppuarec vo . Most andesitesf ,1 * f廿 l d i o i thelow Feo /Mg ratoso e 細l estes ‐ i l l fal t l i i i ln and mos te(No The Wrassai tfe ) of Wrassa e ‐1 te i ゴ ロu andes = nu ande ‐ s c andes s ‐7 ions o l fca l ine rock series. he composi t ‐alka undert c. Petrography l i i l lyana lyzedsamp tthe Fi rSi02 esaga ns tassemblageofchemi ca g ‐4showsthephenoclys l i i d l i i k Th H i h i T n r X n ・ i d i f c o o e e phe - py e basatc a l l este rom content gas - a asu carres o vne an ‐. (38).

(6) . . latedrockf i △”g andes tesandre igh Dd i i i ro - ] m the VVas t t sa 】 mu oceseh -Pi s r c ppu d. 1. 0. 2. 0. 39. 3. O. Feo*岱1 go F i i02versus Feo*/Mgo diaー#aIn. Thebow1dariesbetween H MA al g‐3 S ・dCA,andbetween CA and TH arebased on Sato(1989)al d Mi h i 1 9 7 4 ly.Symnbol ive l ) yas ro( sareas ,respect in Fig ‐2 .. ★〉 1 0●5 1 0 ・1 ‐ 5 0〈 - 1 ‐0 o L%). .c超e. 10. !. 237. 86. 9 45. o. ★. 撒 . 炊. ★ 炊. o. 仰. o oo. o 0. .‐ 0. o 質ぴ瑠璃ene. o. . ●・ . ”. Z Z 比e ne 質ザ【. -. . . ・・ . ”. . ・o. .. ・幻. 節. . ・.. 0. 0. ‐ 0. - -0. 60. w I L%. 刀e. ‘釧キ メ e. -. ーe. -. 力皮. -. . . - ◆ 00 - -. . - -・. . 55 Si0 2. F i odeandphenoclystaミ鵜emblagesinthe÷Wrassamu‐Pippuvolcmnicrocks g ‐4 M[ .Nmmbersare sa ] n nple nu u 〔 nber . l 鑓nounts of p nocrysts Wi th smーal lagioc lase microphenocysts, and the andesites have phe- f plagioclase, ol ivine cl inopyroxene onhopyroxene honlblende and Fe nocrysts o ‐Tioxides , , , , , th or wi故outbiot i te and qua賞z. The fo wi l lowi i ng i it ion wi s a br ef pet ro淳「 aphi th c descr. p. focus on t heobserved d i l ibr iwm texture・ sequi. ( 1 ) 猛省餌 脳‐7 7 i z αた硲“ る餌αZ ) c α”吻 露β(No .10. (39).

(7) . iにa Yamanaka d Ch iko 0daa Ke i iWr I l i ada ,Sacね. 40. F i g‐5. d lcaldcrocks col s Photomi imu‐Pippuvo croglaphsoftheVVassa ‐aandc; crossed ni ,b, , l d . m b 。 2 S n e d l h l x e l i i z n e c o o pyr -po arze e l コd f;plane gt .a;reversey o ‐ cae ar ‐ mm ,a l ) rkab t wi th strongly resorbed core(mostly darked pa貧)(No y phenocrys ‐10 ,b;rema. h (No ) l th reversezoned ove i immed wi rgroWt nop resorbed c ー江oxene phenocrystr .1 ,c; dark zone th resorbed co ) t wi )(No ly zoned orthopyroxene phenocrys re( reverse .6 ,d; 1 b i d i i F T i t wi 1 iぬopyroxene phenocrys 1y zoned c thcore,contan ng e ‐ ox es reverse ,a rupty ’ i ) l l l l i ne( ar row)(No )markedbyBeck sl r s near o es chzmgedi e( nto M舎r ch mant yco ‐7 ,e; ion d db t l i h t i i l i r e a c f i i h h t s ss n r o u n e i u n e n c 立ag v e o t f c n a n o y n s o - [ y n c u s o n ma c w c P e 〕 = D so lus i ion whi f ch i cinc t sof maf ) fhomblende,padtly opaci zed(No rimso .5 ,andf; ragment lase phenocrys ins plagioc t s conta .. tharesorbedcoredi t Sp1ayst rong1 C1 i ねopyroxenephenoc!ys y markedZoningtoward a s Wi i i t ioofthereSorbedc。recompos oni shigherthan 5 )rat i Mgr ) ‐a chrml(Fig ‐ The Mg/(Mg十Fe . i i i i l ibi h t th maf c o ) 8 煙ナ ada and Goto,1992in prep. ,and so these p enocrys s are n equ r 皿 w .. ma柳a ‐ 4 ) ‐ ( 2 ) 溺餌爾粥” αれば偽 物-ヱ (肌流餌qyα粥αリ(Nos .1 C1 ino‐. and. o【hopyroxene. phenocrysts. com mon1y. show. reverse. Zoning. Some. i ー ne ‐ t節 t ts di l g into abundant f i rongly resorbed core sePara sP1ay a s s noPyroxene Phenocロゾ c l l i ly cooress c noP b) i ~ l ー打oxene th Mg t ch overgrowth (Fig M r ed wi .5 . Near grains and man ,. (40).

(8) . Mi d豊 i latedrockf tesandr ocesehi ‐Mg a I ~ ノ r l s i gh e i rom the▽ t t as sa j □ Qu -Pi s r c ppu d. 41. icr。phenocrystsShow sectorzoning and of nl ten occurintheaggregateparts M taf i l ionS ci nc us . i th ol inopー打oxene phenocrysts are present i i wi vine and M gr ch cl f l i d i N n esc an este ( o ) ‐4 .. 0【hopyroxene hol nbl ende -Tioxides coexistin g.o] lmmps エ ー erophyric c .ase , t ,and Fe ‐ P1agioc ly thick tabular or rounded for phenocrySts are usual th dusty zoneS and large ones ・n wi , ional lyi l occas d h h b l d ncu e orn en e p enocrySt.. ( 3 ) 賜餌s 7 ) α粥“ ”“叱s錦参互 (Nos - ‐5 C1 ino‐and or t … hopyroxene phenocrystS usua l l y Show abrupt reverse zoning from the core inc lud ing Fe l i l l ‐TioxideS d i l lthe clear mantle and rim (Fig 5 a o c a t s e a n a s s g ,p g c and d , ) ‐‐ . Some cl inopyroxene phenocrysts are near ly color less showing ハ4g- i h i i r t c c om n o s o , and p , normal zoning‐ orthopyroxene phenocrySts wi th resorbed cores are Sunounded b t ck y hi . i c nopyroxene overgrowth‐ C1 inopyroXene microphenoc!ysts Show sector or nonnal i zon ng, and often occurinthe aggregatePar t i lus ionSwi s l ivi cinc th o ledb ts mant nePhenoc ‐ M[af lys. y. hi lende reaction r at ck homb l lm are presentin mos i tfe i te(No s lyzed(Fig c andes )ana ) ‐ e .7 ‐5 .. lnthefe I i S c andesite,hornblende phenocrystscom momy show dusty coreSfringed wi th aclear. thin mantle, wh le the n・ icrophenocrySts have clear surfaces P1a ioclase h i g p enoc・ysts are . ly Strongly zoned and occasional most ly di splay conoded f or ns and dus ty zoneS l l l , ‐ Sma fAAr amounts o i ch phenoc〃st are di screte or presentin gabbro icpart ) s(No 6. ‐ ‐. { 4 ) 溺硲sα粥” α7 2〆偽 物‐班 (No ) ‐8. EuhedraltoSubhedra IP 1agioc lasePhenoclystsareabundantand most ly 立 l ludeblack glass c inclusions Suggest i hatthey areder ngt ivedf i rom maf 1 9 9 1 c magma(新′ada , ) ‐ They constitute , f maf ic inc lus ions (Fig phenocrysts o 5 P h ly Show reverse requent ‐ ‐リー yroxene P enocrystS f zoning and are 。bs o立l erVedin g1 erophyric c1mmpstoge ther wi th Fe . deS phenoc. -Tioxi r ysts ‐ ◎. 乃 か” αれ〆g 7 7 s物 「 α如 卿 焔ッ鰯彫の (No ) .9. Someonhopyroxene andresorbed clinopyroxene phenocrystssh w clearl o yreversezoning‐ There are gl。merophyric clu刀nps of normal inopyroxenes Aqg- -zoned cl inopyroxene rich c. ‐ phenoc.ysts are Strong1y zoned and some imes contain Spine1 t ly co1or l ino‐ and e器s c1 ‐ Near r t h i h o opyroxene m crop enocrysts Show sector and nonna1 zoning M【oSt ofthe la ioc p g 1ase ・ microphenocrystsshow euhed lto Subhedra lform ra. .. lmportance of 皿agma m 無i ngin andesite genesis The etro. a hicob. i rv t. b i. ibl. se a onS may e tposs etosunnmar p gr p izeevidenceoflnag 〕 = na ml xlng for the wr assam止Pi i l i br i } di ppu volcanic rocks 1 Sequ u コ n n phenocryst assemblages such as ivine phenocryStz狂ld hol coe×i fol stenceo i 1lblende quartz orbiot te phenocr st ( 2)coe×it ,. y ;. s ence. r lal of norl ‐ and revese‐zoned phenocrySts euhedral and anhedra l phenocrysts, and clear and , dusty coreS 3 ) reverse zoning of phenocrySts 4) resorpt i on texture of phenocrysts 5 ) ion products Such as augi react te overgrowth on orthopyroxene phenocr St au i im on y , gte r h t u a r z t n dh blender q im on ol p e ocrys,an i l ・ l o vinephenocrys t; and( 6 ) maf i cinclusions‐. Thi i l i br i sdi sequ tassemblageandtexturei umnphenocrys sbesti ixingof nterpretedbythe口l f f two di erent mag国nas( 1 9 7 9 l h e ) i t d k h n h m t e x e r c .g-Sakuyama o s t - , , ese p enocwss can be di dedintotwogroups eachofwhi vi h h l i br i c S owsequi lageofpre‐mlxlng taSse um phenocryS rnb ,. (41).

(9) . ika Yamanaka o d Ch Ke iWr i j ada ,Sachiko daan. 42. l i ng i s c mag e コ コ ロasbefore mlxl candf Table2 Deduced phenoc1γst assemblages of maf st assemblage 1 3 ′ phenoc i int he maf c ma gma. muにed rocks. st a s semblage 3 ′ phenoc1 l i in u 1 mma s c mag efe. i te l wrassa ュ コ Quandes. ) (NO .1 ,4 3 2 (No . ,). 。L CPX 01 ,Cpx. PL Hb,op Cp Mt ) ,(QZ P1 ,Bt ,Qz , Hb,opx, Mt. 1 des i wrassannu al te ‐1 .. ) (No ‐5 ,6 ) (No .7. Cp 01 ,(0px) ,P1 C 01 , px. ) (No ‐8 ) (No ,9. P1 ,(Cpx) ,(opx) ,01 Cp 0I P1 ,. C Hb M ,(Qz ) P1 ,0px, px, , t M B t Q o t P1 H b z x p , , , , , Hb, Mt P1 ,op Cp. ‐Wr i te ‐皿 1 〔 nu a I 1des a ≦渇a. i te pippu 鑓ldes. P1 ,op. Cp. Hb,N 1 t. ) e2 ma抑Qa(Tabl ‐ i i te hasclinoP肌ro×ene PhenoclystsshoWing reverse zoning. l t T k i ldes Higash c ar - a asu basa idered to have i inoP班 o×enes have a Mg ‐ r ch cores,they are cons Si nce the reverse‐zoned cl th i c mag コ p nas wi i s suggests thatthere was mlxlng of maf l l i ta c mag zedin maf コma crys . Thi i i he andes t c rocks n na mixing in t lar compositions and phenocn′st assemblages‐ M ag〕 imi s i lage der i ved r assemb nto the ly by g l ng the Phenoc1γstsi i layed more c 1 ouPi ear 「 sp wo山d be d b l i na s cend‐mem er magn rom fe i ‐ f ‐member mag コmaandf cend rom maf i tes nthe wassamuandes i cend-member mag粗ai Thema jorphenociystassemblageofmaf P d i i m d W r u ‐ an おte j ゴ ロu an { l ppi n the assa l i e thati l i li nop l and ‐1 vine and c so i汀oxene , whi h h t w r e F r e e l 2 t e T b r r mo e e ) ( r l u d i a e l n lase wi th oi ne an c nopyroxe e vi i , , tei s plagioc andes h d i t t fthe an es es; e l i ff □ na o cend‐member magコ e s f f locryst assemblage o di erencesin the phel i b ii b l d h i hi li n e d 1 l l ・ l e i tes Wrassa ‐ an ‐ src n o inuandes fe l i ,andconta ns otte nthe÷ cassemblagei s i te consists mainly of i te ‐皿 and Pi ppu andes l n the W’assamu andes tz e thati and quar , whi bl catethat l lamount ende l l l long wi thsma sofho i t . Theseindi s cphenoc lys P班o×enesas maf ,a i tes ‐ samuandes f ferencesintheki i ndsof mixingend‐member mag閃nasofW「as there arelarge d i te -m,and Pi 1,the 汎ァassa imu a l ldes ppu andesite‐ 1,1 rend of the ng t n‐ An average mixi l Fi ‐Si02 diagra g 203 and Mgo vs .6 shows an A1 fer f ightdi l thoughthere ares ththi am,al dl sdiagr tes li Wrassa ndi cated wi ‐l a si 1 1 jnu andesi i A1 0 i th d i encesi nthecompositionsoftheend‐member ma弾じnas. A trendtowar s ncreasng 2 3 w f i lobsel▽ations; ma cend - t i thpe ca aphi tent wi rogr i s increasesi nei scons ngl n Si02inthe mixi l i t r e a f l i n a h n a s b n e c o g o h t lase p enoc1γs s utt e esc lagi oc member magma does not contain p i ‐member i I Si02 content of maf c end fthe hypothet t ca lase phenocrys lagioc s amotmt of p . l 2 o;1 1~ 1 t M h w i ‐member magpna as g .% and ixed as50 wt cend sf ma卸dai ‐%,thenthe maf. imated Mg / t i ne ng l 5 wt 5~9 rom extraPolation ofthe mixi Feo*=8 . The es , ‐%,inferred f , W ft h e assamu i 7 suggests thatthe maf c end‐member magpna o )ratio of about o. (Mg十Fe i i l te h d i t i l i b i t r e t ma n e w p dot . The li q = na equ rae i tes s closest to pr鍵la 1γ mag ‐l and‐1 andes te l i i l ta z ng phase n the early crys ioc lase agai t clinoPyroxene i f plag ns , despi suppression o l re r s u e s i ow 日 中 i o r f h t a p ve magカロ fect a hydrous nature o t e Pr lka l i ne m L ag suba コ ヒ ロa , may rel i l inopyroxene sof l i ionofo l l i Vineandc ta iona代erhighpressurecrys zat l l i . ○nthebas ta zat crys. (42 ).

(10) . i l tesandre Miocesehi i i atedrockf t rom the was t ‐Mg andes s加ー止Pi s r c gh ppu d wt%. 亙7. ・ 、‐ ‐‐ ‐△-. A』 03 2. ☆ / ;/ /. :. 〆. 且5. : 7. 43. ◎ {◎. ☆ ⑪. \ \ \ \ \ 十 も. 5ー. 。. \ 、‐ \ ☆ △-~. 5⑪ F ig‐6. 55. $⑪. s 宜鱒. 5 選. A1 id l i i n 口 ne represents mlxlng of VVassa l n nu 203 and n4go versus Si02 diagra ‐ Sol i 1. Brokenl ineshowsposs ibl tes ingtheVVassa i andes ‐l and‐1 e mixingpass te J o nuandes ‐ 1 1 1 ‐. lkChemi l i ldbedac i thePet t te s e ro 1 1dbu s cend‐member ma鱒ma wou 1γthef 1享aPhya . Thus ,the high ian andesitesof「wassamu andesites-1 andl l wo l 頭dhaVebeenProducedby mixing ‐ma es ミ ロ 1 i i 1 i t tandthe hornb1 t vebasa ende dac e mag ofpr節Q コ ヒ nas . The maf i i ln i lase te ‐ = i c end‐member ・nag・na of ▽Vassamu andes s expected to be plag oc ‐ h l T h f 1 l f t b b i h i i l t k e aPpearence o Pagocase p enoc13′s s pro a ytoo p ace a an P 】建 c ma c ma ‐ r鱒ma ion resul ingfrom aconcentrat l izat ion of A1 t advancedstage ofclystal 203inthe magmnacaused , inop1 by c i l ion ofo l ivi he composition of maf i tal zat neand cl cend ‐member nroxene lys ‐ Thust l l iz i lase wou ld be represented by higher A1 ta magma c ng plagioc lys 203 and lower Mgo l lustratest hehypothet i l mixingt 1 1 contents t maybe ca rendof Wassaエロu andesite‐1 ‐ Fig‐6i . l. i lved basal l i i ld t or basa t te ma印[ nfe l.ed that mixing between evo c andesite and dac nas wou have producedthecal lka l ine wrassa i te i 亡 nu ande -a s -m‐ c. Tecto難に mode 量⑪fthe Wr assa l mu‐F却pu vo亘canic rocks Two sa刀Qples(Nos i i i t )ofthe wrassamu te ‐Pippuandes crocksarehigh‐Mg andes ‐1 andlo M o>6 6 d S i 0 k >5 3 fs h i k i 1 9 8 1 F h f t % h ( g ) to t eseroc scan ra ( wt 2 , w‐ an .%)o ‐ Wt ermore , mos lass i ied into the h be c f igh‐Mg andesite f i ld of sato ( 1989 ) (Fi ) e g‐3 ‐ These andesites are l l f f tes such as sanuk i d and associated rocks, toi rographi ca erentf rom high‐D江g andesi pet y di i l me l l ing ofhydrous mant idot i t tesbeneath a someof whi ch werefonnedby d rectpania eper forearcregi ) e sumi on( ‐g ‐Tat ‐ ,1982 The di f f h i i l d tes ぐwPA t ta t eren pero ap c e s of W「assamu‐Pippu andesi ) and Setouchi 圭 挙 「. (43).

(11) . ra Ke i i iWr ika Ya j ada ama α 1 anak i ,Sachiko odaand Ch. 44. bedbysato( SA)descr idandes i 1982 i te( to )are sanuki. 1 lasephenocws )ubiqui tousplagioc t si n. w「 PA but pauci ty in SA;( 2 )the presence of Mg‐ri ch clinopyroxene phenoc1γsts without bronz i W r PA b i hb i 3 )presenceof Fe te phenoc13′stsi t t tei o c c u 1 ロe n c e ‐Ti n u w ronz n SA; and( ▽PA but a genera1 absencein sA・ oxide phenocrySts m▽ ‐ h d i Thi igh‐ D4gandes d i コ hesanuki teoft toi sev ences owsthattheVVPA doesnotrepresenth i i ived fom primary andes i te mlaglma at fore‐arc tectonics. As ment series w比 chi s der oned l ionof訳rPA- Thustheac i▽i i t t above xl ng playsa prominentro ntheformat ゴ ロ na ml ei esof , mag も中i l i / l i t and dac te magmas are essential to characterize the D i t ve basa pre‐mlxlng pr 。cene ‐ i V mag ln atV s assannu ‐Pippu コ ヒ ロat ‐ ln contrasttot hefore-arcregi iary hi i コ heback- t teshavebeenfoundint on gh心4gandes ,Ter. longthelapそm sea; Notopeninsu laandi lands IHonshu(Hosh ina t arcreg ona si s ra ,cent ,1984; H Sato d o k h ii l d o i h k k k d Y h i 9 1 9 8 9 i d d 1 8 9 t t ) ) us r san ,sou wes os a o a o ( amura an ‐ Sato , ,an , i. 1989 ( ) has suggested that the high‐Mg. i tes f andes rom Noto were produced by mlxlng of b Th ion o i i i l d h d i i fthese andesites i i bl e format s poss pr m tve asat an ap yrc acte maglnas‐ y. latedto opening oftheJapan Seai 989 re n middl ) e Miocene(okamuraand Yoshida ,1 ‐ There igh-ハ4g andes i l tes wi thlarge aj i tandrhyo tei are h コ nounts ofbas al nno【hwest Kyushu ,formed dwingthetectonics ofr i貴i 1 9 8 9 Th i M h h d f i h b k t t ) ng(Sato ‐ n r e s e a e s e s o m ‐ e ac arcshow g g . , featu i f f D ロ i larin or igin to the VVassa touchisanuki t。id i res d r n se erentfrol inu ‐Pippu ,but are sP. hi 卦4g andes l ivi i i imi i t t ty ofpr t magコ c rocks m theact vebasa ロ ロa gh‐ ‐ i i l imi ive mag因na in terms of cws Quate l t t t ta 1nary mag囲at sm i e pr s characterized by l fract ionat ion in mag ion in the crust コma cha力Qbers because of compress ‐. The ascent of. ive andes ヒ Pi i l t te to and southwest Kyushu t magコ rom the prn ヒ ロas ,in No ,Setouchi , and basa ,f hesu・face wi ionat ionwou ldbeper fonnedundertens sou thoutf ioninthel i ゴ ー 「cetot thosphere ract ‐ Thi 1 1 dethe i thoughfoundi ssuggeststhattheformation of▽▽as ‐Pippuvo samu cani crocks ns ,a l i l i blytook p ace by tens ona stressinthe crust. arc at present ss ,po ACknow1 bataforhe lpfu ladvi edge郡 ー ents: ▽▽e aregratefu1to N1 r cei ntheXRF ‐TomoyukiShi V V l lys i i d b d t 取 【 Y h h f i i k G b l t i h dd fK - A t a r t e o e a s n r ana s o e e o o o orunpu s e a ao r age and ・ - os Dr ion ・nuraforreferenceinformat ‐Sat。shioka .. RefefenceS. Di 1967 i i 1 はon, T‐( i t i nson cki ) Andes ty aromld the c volcanism and se smi c , ▽.R‐and Hathe Pac f i i 803 c - ‐ sdgれ”,157 ‐ ,801 Gi l l o i d i l 1 9 8 t d ingerver lag 1 J ( ) r o e n ca n s n e e sa cs g patetectoni . Spr ‐ ,‐ ,390p Neogene volcanic rocksi 日 Hoshina h h N 1 9 8 4 ft h Pen無s司a t n t ( ) th nt r en o em a e o o o p . , , wi * * f i l t h i d i 肌 G Z S 2 t 4 4 5 5 8 r e e r e n c e o ap コ speca の吻‐ ゆ‐ oc ′ rcan es es ‐ ‐入物α”, , ‐ ‐ l i 恒zaki lo 1990 s ) Ge。 sui rol。 ≦評 and pet ≦W of Tommaushi , Y‐ , Nakagawa , M. , and Kat , Y.( l T i T t k h i l i h P vo cano, ase s 1 o ac voc2 U nc c a節. ro lmme and Abst ract s of l99O ミロa 本 Spr i i l ISoci 6 6 ng Meet ng ofthe Vo canologi ca ety ofJapan ,p . Km10 1959 ig in ofCenozo i ) or c pet ld smr rowlding areas ro ap恒c provinces ofJapzm a1 ≦ ; r . , H.(. (44).

(12) . DGoce dg andes i l tesandre i t t ‐D sehi c atedrockf s r rom theVVas s鑓mu ‐Pi gh PPu di. 45. β”仏 拓oにα 7 2メリ 20 ‐76 ‐ ,37 Mat i ta 1977 lanato logi lmap ) Exp sushi ca ly textofthe Geo ,K. ,Terashima ,K‐ ,and osana ,H‐( 水 本 le ・:50000 ”Kenbuch i a G l i .S H k s c a f k i d 3 0 。fJap鑓n e c a oo uwey o 0 a o , , , . , p oka 1989 ian .ase ph ]mw「a, S i ) Hi i te f es c andes ro 1 m gh‐ma鱒] ~ z r -and Yoshida , T.( , plagioc. i1 land okushi do i t Hokkai ian andesites in r s ) “Ma raki ( ed 主犯es - K.Sh . , southwes ’ i Japad, Repoe質 of Grant i - ‐operat n‐Aid for Co t ve Research A of Mi ni s ly of Educat ion S i d C l f N 3 0 t 6 1 2 0 2 7 176 ) u ureo japan( o ‐ ‐ , cencean ‐ ,167 Sakuya 1979 uma, M, ( )Evidenceof magm a mlxlng: petrologicalstudy ofShi rou uma ‐。ike caIG. lka l i i l tevo 208 a neandes cano 7 20Z ‐ s ‐ ヱ ”o化α ‐ G8o物勿粥‐Re ‐ ,ヱapan ‐ ,5 ,179 Sato 1982 ) Geolo≦聾 of Goshikidai and adjacent areas, northeast Shikoku,Japzul: Field , H‐( id and assoc iated volani to occ tぱrence and petro厚raphy ofsanuki crocks ‐ Sd .Rep ‐ , 認おれαzα 2 7 N 1 1 3 7 0 2 Uα ひれ勿. o ‐ . , , ‐, Sato 19 89 ) Studiesin the genetic environmnent ofhigh-ma鱒iesian andesites. Report of , H‐( Grant i f i i i ini i t i l ‐ n‐AidforSc c Research ofW【 ent ture s ryofEducat on ence ,Sc ,and Cu 率 本 木 9 9 ) ofJapan(No p ‐61540593 ‐ Shi 1 981 teand Sanuki te raki ) Bonini 88 ‐ ‐( . ReceれZ P節gz 斯鰭”質 Sd.五ゆα”,6 ,K . ,84 Sugimura 1960 l arrangement of some geophys i l and pet log ) Zona i lf ca ro ca eatures in , A‐( i japan andi E Sd 苫 t び覆 S 2 153 senvrons り .Z αc . ‐ 〆勢力, ec ‐2 1,133‐ . “ ” Swzuki 9 E 1 5 7 l f t t h l i j t l ( ) t f l e x l n 000 x a a o r J o e e o a o c ma o a a n c a p y s e :50 g g p p , ,‐ , , Pippu. * * S Geo logi I f 2 7 ca urvery o japan ‐ , p Tatsu 2 198 i imi l tes i l ) origin of high‐maきりlesian andes t n the Setouchi Vo cani c be , Y.( , h h 1‐Me l i t sout westjapan ng p ase relations at high pressures- Eα71え P如“鉱 Sc乙 ,1. 乙8比,60 317 ‐ . ,305 Tsuchiya bata ,T. ,Shi , N‐ .H. ,owada ,Y. ,Koide , M- ,E‐ ,Goto ,Takasawa ,j ,Y. ,Choi ,Terada , S‐ Y d H i 1 9 8 9 M l l i ( f k ) j t l b a n a a r a o r e e m e n a n ayss o roc sampes y X‐ y, ‐ ray , ・ f luorescencespectrometry usings do び”カー candi um anodetube . Z Eαc .Sメリ 嵐陳 腐Z , seれ 4 22 48 9 0 2 5 , , ‐ . Wrada 1991 ) Mixing and evolution of maglnas at Me‐akan volcano, eastem Hokkaido, , K‐( ** 1apan 78 2メーSoc ‐ くめα“,36 ‐お“”-”◇如7 ‐′ ‐ ,61 Wratanabe 1988 ) K-Ar ages of Miocene Volcanic rocks and the 1d Yamagichi , Y. ar , S‐( l l the Nayoro-Asahikawa region northen1 Hokka tectonics i ido 々” i α z z 8 , ・ C力茨夕” ぞこ. 本* i 99 (Ea【h Sc ) ene ‐ ‐ ,42 ,91 Wアatanabe Y h i U i S d 1991 l ) K‐AragesofNeogenebasa t tami Green si n Ki , . , c mm, - ,an Uto ,K.( * Tuf f Region h H Z k k i d t G s t 9 7 1 4 6 6 e a s 入 n o r 工 o a B O o c ‐ o 物” 形 , . ‐ ‐ , . * i njapanese ホ* i 1 i th Eng tract nJapanese Wi sh abs. “率 i i njapaneseand Engl sh. ( 45).

(13)

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