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1 No pp Chemical Composition of Phenocrysts in Products of the Last Eruption of Nikko-Nantai Volcano, Central Japan, and Its Implications for the Processes in Magma Chamber Kohei HIRANO and Masaki TAKAHASHI Received November, 2005 Eruptive products of the last stage of Nikko- Nantai volcano consist of three serieses, the Imaichi, Shirogake and Misawa, based on stratigraphy and whole- rock major element chemistry. The Imaichi- series is composed of the Imaichi pumice- fall, Shizu scoria- flow and Takanosu scoria-fall. The phenocryst of Imaichi- series comprises plagioclase, olivine, orthopyroxene and clinopyroxene; its total content is 0.8 to 15 vol The core composition of plagioclase of Imaichiseries shows bimodal distribution of An= and An=. The content of An= plagioclase decreases with decreasing whole- rock SiO 2 content. The compositional of phenocryst and crystal clot are similar, and plagioclase, orthopyroxene and clinopyroxene show reversed zoning. Orthopyroxene and clinopyroxene are not equilibrium with olivine on the basis of the Fe- Mg distribution between both minerals. The Imaichi-series is formed by magma mixing between mafic magma with An= plagioclase and olivine and high temperature poorly phyric felsic magma with An= plagioclase and pyroxenes. The Shirogake- and Misawa- series is composed of the Shichihonzakura pumice- fall, Shirogake and Ryuzunotaki pumice- flows, and Misawa lava flow. The Shirogake- and Misawa-series can be unified as the Shichihonzakura- series, because whole- rock chemical compositions of felsic member of Shirogake- and Misawa-series are the same. The phenocryst of Shichihonzakura- series is composed of plagioclase, quartz, olivine, orthopyroxene, clinopyroxene and hornblende, showing disequilibrium mineral assemblage; the compositions of phenocryst and crystal clot are similar. The Shichihonzakura- series is enriched in phenocryst; its total content is 15 to vol Pyroxenes and dusty plagioclase are reversely zoned. Orthopyroxene and clinopyroxene are not equilibrium with olivine on the basis of the Fe- Mg distribution between both minerals. The Shichihonzakura- series are produced by magma mixing between mafic magma with An= plagioclase and olivine and low temperature phyric felsic magma with An= plagioclase, quartz, pyroxenes and hornblende. It is concluded that the Imaichi-, Shirogake- and Misawa- series were derived from different magma chambers, and the magma plumbing system beneath the Nikko- Nantai volcano consists of a multiple magma chamber system. Keywords: Nikko-Nantai Volcano, mineral chemistry, phenocryst, crystal clot, magma mixing, magma chamber, magmatic plumbing system 1 20ka 12ka ka : Graduate school of integrated basic sciences, Nihon University: Sakurajosui Setagaya-ku, Tokyo, 156- Japan Department of Geosystem Sciences, College of Humanities and Sciences, Nihon University: Sakurajosui Setagaya-ku, Tokyo, 156- Japan

2 Lava Dome Nikko-Nantai Volcano Nikko-Shirane Volcano Orokura Sannoboshi Taro Komanago Nyoho-Akanagi Volcano Fukushima Pref. Mitsudake Volcano Nikko-Nantai Volcano Omanago 36 Gunma Pref. Tochigi Pref. 0 5km Lake Chuzenjiko Tanze Fig. 1 Map showing the distribution of volcanic edifices in Nikko volcano group. Arasawa lava Nantai-minami lava Kegon Lava Konagi stratovolcano Nantai-kita stratovolcano Onagi lava Furunagi stratovolcano Nantai-nishi lava Shizu scoria-flow Shirogake pumice-flow Misawa lava Altered zone 1km Fig. 2 Geologic sketch map of the Nikko-Nantai volcano. 2 Fig. 1 0ka 100ka ka ka 20ka 12ka 12ka 124

3 Fig. 2 12ka ka 12ka 2 10cm 19 12ka 0.74km SiO Fig SiO 2 67wt SiO 2 67wt 58wt SiO 2 67wt SiO 2 54wt SiO 2 SiO 2 58wt 67 wt 67 54wt SiO 2 53wt Al 2 O 3 MgO P 2 O 5 T io 2 K 2 O Na 2 O CaO FeO FeO /MgO SiO 2 67 Na 2 O MnO P 2 O 5 T io 2 FeO FeO /MgO Al 2 O 3 CaO MgO K 2 O

4 TiO CaO Al2O3 FeO* Na2O K2O 2.4 high-k low-k MnO MgO SiO 2(wt%) SiO2(wt%) P 2O SiO2(wt%) CA FeO*/MgO TH Misawa lava Mafic Inclusion Ryuzunotaki pumic-flow Shirogake pumice-flow Shichihonzakura pumice-fall Takanosu scoria-fall (Hanatatezawa) Takanosu scoria-fall (Arasawa) Shizu scoria-flow Imaichi scoria-fall (Misawa) Imaichi scoria-fall (Arasawa) Imaichi scoria-fall (Kiyotaki) Fig. 3 SiO 2 variation diagrams for eruptive products of the last eruption of Nikko Nantai volcano

6 6 1 1 0.3 vol 3 mm 2 4 vol 1.6 mm 1 mm 0.6 mm 3 15vol 6 2 1 A.

4 Back scattering images of plagioclase phenocryst in the

A, B and C show that patchy or mottled core is surrounded by

D shows sieve texture along the rim of plagioclase grain; thin

5 vol 3 mm 2 4 vol 1.6 mm 1 mm 0.6 mm 3 15vol A. B. C. D. Fig. 4 Back scattering images of plagioclase phenocryst in the eruptive products of Shichihonzakura-series. A, B and C show that patchy or mottled core is surrounded by oscillatory and normally zoned margin. D shows sieve texture along the rim of plagioclase grain; thin rim with high An content grows around the margin with sieve texture. Light colored portions indicate high An domain and dark colored parts represent low An domain

6 15vol 5 mm Fig. 4 1 mm 3 mm 2 4 mm 2.6 mm 1.8 mm 0.8 mm Fig. 5 G and H 44vol vol 4 mm Fig. 5 C and D Fig. 5 E and F 3 mm 2.6 mm 2 mm 1.4 mm 0.15 mm SiO 2 64wt SiO 2 64wt vol 3 Fig.5 A Fig.5 B 7 1 EPMA

7 日光男体火山最末期噴出物の斑晶鉱物化学組成とマグマ溜りプロセス A. B. C. D. E. F. G. H. Fig.5 Phenocryst in eruptive products of Shichihonzakura-series. A: olivine (Ol) coexisting with quartz (Qtz); B: quartz phenocryst surrounded by reaction rim of pyroxene; C: sieved plagioclase phenocryst (open nichol); D: sieved plagioclase phenocryst (crossed nichol); E: honey-comb plagioclase phenocryst (open nichol); F: honey-comb plagioclase phenocryst (crossed nichol); G: reaction rim of hornblende phenolcryst (open nichol); H: reaction rim of hornblende phenocryst (hbl) (crossed nichol) 129

8 # 220 # 0 # 0 # mm # 0 # m EPMA Electron Probe Micro Analyzer JX kv 12nA Fig. 6 Fig. 7 Fig. 8 Fig. 9 1 A 1111C 1 SiO wt An 88 An 78 Fig. 6a An 62 An 88 Fig. 6a Mg# 68 Fig. 7a Mg# 73 Fig. 8a B 1113A 6 SiO 2.97wt An An Fig. 6b An 81 An 82 Fig. 6b Mg# 68 Mg# 68 Mg# 68 Mg# Fig. 7b Mg# 73 Mg# Fig. 8b C B 2 SiO 2 64.wt. An 88 Fig. 6c An 88 An 88 An 76 An Fig. 6c Mg# Mg# 69 Mg# 76 Mg# Fig. 7c Mg# 71 Mg# 67 Fig. 7c Mg# Fig. 8c Mg# Mg# 66 Fig. 8c Mg# Mg# 74 Fig. 9a Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig A SiO wt An An 45 Fig. 6d An 76 An 63 An Fig.6d 56 1

9 Rim(An) a. b. c. d. Core(An) phenocryst (clear pl) phenocryst (honey-comb pl) crystal clot (pl+opx) crystal clot (pl+cpx) crystal clot (pl+opx+cpx) Rim(An) e. f. g. h. Core(An) a. Imaichi scoria-fall (1111C-1 SiO 2=67.08wt%) b. Imaichi scoria-fall (1113A-6 SiO2=.97wt%) c. Imaichi scoria-fall (112201B-2 SiO 2=64.wt%) d. Shizu scoria-flow ( SiO2=64.46wt%) e. Shizu scoria-flow ( SiO2=63.78wt%) f. Takanosu scoria-fall (112202A1a SiO 2=62.83wt%) g. Takanosu scoria-fall (112202A2 SiO2=.03wt%) h. Takanosu scoria-fall (112201A1 SiO 2=58.87wt%) Fig. 6 Diagram showing the relationship between core and rim compositions of plagioclase phenocryst in the eruptive products of Imaichi- series

10 a. Imaichi-series Orthopyroxnene e. b. f. c. g. d. h. Core(Mg#) Core(Mg#) phenocryst crystal clot (pl+opx) crystal clot (pl+opx+cpx) a. Imaichi scoria-fall (1111C-1 SiO2=67.08wt%) b. Imaichi scoria-fall (1113A-6 SiO2=.97wt%) c. Imaichi scoria-fall (112201B-2 SiO2=64.wt%) d. Shizu scoria-flow ( SiO2=64.46wt%) e. Shizu scoria-flow ( SiO 2=63.78wt%) f. Takanosu scoria-fall (112202A1a SiO2=62.83wt%) g. Takanosu scoria-fall (112202A2 SiO 2=.03wt%) h. Takanosu scoria-fall (112201A1 SiO 2=58.87wt%) Fig. 7 Diagram showing the relationship between core and rim compositions of orthopyroxene phenocryst in the eruptive products of Imaichi-series

11 a. e. b. f. c. g. d. h. Core(Mg#) Core(Mg#) phenocryst crystal clot (pl+cpx) crystal clot (pl+opx+cpx) a. Imaichi scoria-fall (1111C-1 SiO2=67.08wt%) b. Imaichi scoria-fall (1113A-6 SiO2=.97wt%) c. Imaichi scoria-fall (112201B-2 SiO 2=64.wt%) d. Shizu scoria-flow ( SiO 2=64.46wt%) e. Shizu scoria-flow ( SiO2=63.78wt%) f. Takanosu scoria-fall (112202A1a SiO2=62.83wt%) g. Takanosu scoria-fall (112202A2 SiO2=.03wt%) h. Takanosu scoria-fall (112201A1 SiO2=58.87wt%) Fig. 8 Diagram showing the relationship between core and rim compositions of clinopyroxene phenocryst in the eruptive products of Imaichi-series

12 a. b. Core(Mg#) phenocryst c. d. Core(Mg#) a.imaichi scoria-fall (112201B-2 SiO2=64.wt%) b.shizu scoria-flow ( SiO2=64.46wt%) c.takanosu scoria-fall (112202A2 SiO2=.03wt%) d.takanosu scoria-fall (112201A1 SiO2=58.87wt%) Fig. 9 Diagram showing the relationship between core and rim compositions of olivine phenocryst in the eruptive products of Imaichi-series. Mg# 68 Mg# Fig. 7d Mg# Mg# Fig. 7d Mg# 68 Mg# Fig. 7d Mg# 73 Fig. 8d Mg# 68 Mg# 74 Fig. 8d Mg# Mg# 72 Fig. 9b Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig. 10 B SiO wt An 61 An Fig. 6e Mg# Mg# Fig. 7e Mg# Mg# Fig. 8e 134

13 Opx(Mg#) Cpx(Mg#) 3 A A 1a SiO wt An Fig. 6f Mg# Mg# Fig. 7f Mg# 73 Fig. 8f B A 2 SiO 2.03wt Olivine(Mg#) Imaichi scoria-fall (112201B-2 SiO2=64.wt%) Shizu scoria-flow ( SiO2=64.46wt%) Takanosu scoria-fall (112202A2 SiO2=.03wt%) Takanosu scoria-fall (112201A1 SiO2=58.87wt%) Fig. 10 Mg-Fe partition between olivine and orthopyroxene phenocrysts in eruptive products of Imaichi-series. Marks denote the average compositions, and bars represent the range of compositional variation of the core of orthopyroxene and olivine phenocrysts. An An Fig. 6g Mg# Mg# Fig. 7g Mg# Fig. 8g Mg# 76 Mg# 76 Fig. 9c Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig. 10 C A 1 SiO wt An An 88 Fig. 6 h An An 82 An 86 Fig. 6 h Mg# Mg# Fig. 7h Mg# Mg# 72 Fig. 7h Mg# Mg# 72 Fig. 8h Mg# 67 Mg# 73 Fig. 8h Mg# 72 Mg# 73 Fig. 9d Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig Fig. 11 An An

14 Rim (An) Plagioclase Core (An) Rim (Mg#) Olivine Core (Mg#) Orthopyroxene Clinopyroxene Rim (Mg#) Core (Mg#) phenocryst phenocryst (honey-comb pl) Core (Mg#) crystal clot (pl+opx) crystal clot (pl+cpx) crystal clot (pl+opx+cpx) Fig. 11 Diagram showing the summar y of relationships between core and rim compositions of phenocrysts in the eruptive products of Imaichi-series. An Fig. 12 An 88 An 82 2 SiO 2 Mg# Mg# Mg# Mg# Mg# Mg# 72 Fe Mg Fig A 1111F SiO wt

15 Fig. 12 Histograms showing the chemical composition of core of phenocrysts and crystal clots. A: plagioclase (Imaichi-series); B: orthopyroxene (Imaichi-series); C: clinopyroxene (Imaichi-series); D: olivine (Imaichi-series); E: plagioclase (Shichihonzakura-series); F: orthopyroxene (Shichihonzakura-series); G: clinopyroxene (Shichihonzakura-series); H: olivine (Shichihonzakura-series) An 42 An An Fig. 13 a An An 72 An 44 An 45 An 88 An 59 An 52 An 45 An 88 Mg# Mg# 64 Fig. 14a Mg# Mg# Mg# Mg# 74 Fig. 15a 2 A 1112B 6 SiO 2 66.wt

16 Rim(An) a. Rim(An) e. b. f. c. d. g. Core(An) phenocryst (clear pl) phenocryst (dusty pl) phenocryst (honey-comb pl) crystal clot (pl+opx) crystal clot (pl+cpx) crystal clot (pl+opx+cpx) Core(An) a. Shichihonzakura pumice-fall (1111F SiO2=67.00wt%) b. Shirogake pumice-flow (1112B-6 SiO2=66.wt%) c. Ryuzunotaki pumice-flow ( SiO2=63.42wt%) d. Misawa lava (1017A SiO2=67.19wt%) e. Misawa lava (1018 SiO2=66.46wt%) f. Misawa lava ( SiO2=.61wt%) g. Misawa lava (0311 SiO2=.51wt%) Fig. 13 Diagram showing the relationship between core and rim compositions of plagioclase phenocryst in the eruptive products of the Shirogake- and Misawa- series

17 a. e. b. f. c. g. d. Core(Mg#) phenocryst crystal clot (pl+opx) crystal clot (pl+opx+cpx) crystal clot (opx+cpx) Core(Mg#) a. Shichihonzakura pumice-fall (1111F SiO2=67.00wt%) b. Shirogake pumice-flow (1112B-6 SiO2=66.wt%) c. Ryuzunotaki pumice-flow ( SiO2=63.42wt%) d. Misawa lava (1017A SiO2=67.19wt%) e. Misawa lava (1018 SiO2=66.46wt%) f. Misawa lava ( SiO2=.61wt%) g. Misawa lava (0311 SiO2=.51wt%) Fig. 14 Diagram showing the relationship between core and rim compositions of orthopyroxene phenocryst in the eruptive products of Shirogake- and Misawa- series. 139

18 a. e. b. f. c. g. d. Core(Mg#) phenocryst crystal clot (pl+cpx) crystal clot (pl+opx+cpx) crystal clot (opx+cpx) Core(Mg#) a. Shichihonzakura pumice-fall (1111F SiO2=67.00wt%) b. Shirogake pumice-flow (1112B-6 SiO2=66.wt%) c. Ryuzunotaki pumice-flow ( SiO2=63.42wt%) d. Misawa lava (1017A SiO2=67.19wt%) e. Misawa lava (1018 SiO2=66.46wt%) f. Misawa lava ( SiO2=.61wt%) g. Misawa lava (0311 SiO2=.51wt%) Fig. 15 Diagram showing the relationship between core and rim compositions of clinopyroxene phenocryst in the eruptive products of Shirogake- and Misawa- series. 66 1

19 An An An Fig. 13b An An 86 An Mg# Fig. 14b Mg# 68 Mg# Fig. 15b Mg# B SiO wt An An 72 Fig. 13c An 45 An Mg# Mg# 62 Fig. 14c Mg# 57 Mg# 78 Mg# 73 Fig. 15c A 1017A SiO wt An An Fig. 13d An An Mg# 63 Mg# Fig. 14d Mg# 74 Fig. 15d magnesio-hornblende actinolitic hornblende Fig.16 B 1018 SiO wt An An Fig. 13e Tsch 2.0 Par Tr-Ho Mag-Ho Act-Ho 7 6. Al(IV) 1.0 Ed Mg/(Mg+Fe+Mn) Na+K Tr 0 Si Misawa Lava (1018 SiO 2 =66.46wt%) Core Rim Misawa Lava (1017A SiO 2 =67.19wt%) Core Rim Fig. 16 Diagram showing the core and rim compositions of hornblende phenocryst in the eruptive products of the Misawa series

20 An 58 An An An 68 An 82 An Mg# Mg# 62 Fig. 14e Mg# 74 Fig. 15e magnesio- hornblende actinolitic hornblende Fig. 16 C SiO 2.61wt An An 39 Fig. 13 f An 64 An 82 An 42 An An Mg# 63 Fig. 14f Mg# 74 Mg# 72 Fig. 15f D 0311 SiO 2.51wt An 45 An 58 An An An Fig. 13g An 79 An 52 An An An An 68 An An An An Mg# 62 Fig. 14g Mg# Mg# Mg# Mg# Fig. 17 Diagram showing the relationship between core and rim compositions of olivine phenocr yst in the eruptive products of Shirogake-and Misawa-series. Fig. 15g Mg# 82 Mg# Fig. 17 Core(Mg#) Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig phenocryst Fig. 19 An An 38 An An An An An An An An 4 Mg# Mg# Mg# Mg# Mg# 82 Mg#

21 Opx (Mg#) Cpx(Mg#) Olivine (Mg#) Misawa lava (0311 SiO2=.51wt%) Mafic inclusion (1012I-1 SiO2=53.88wt%) Mafic inclusion (06a SiO2=54.96wt%) Fig.18 Mg- Fe partition between olivine and clinopyroxene phenocrysts in eruptive products of Shichihonzakuraseries. Marks denote the average compositions, and bars represent the range of compositional variation of the core of clinopyroxene and olivine phenocrysts. 3 A 06a SiO wt An An 86 An Fig. 20a An An An An Mg# 63 Mg# Fig. 21a Mg# Mg# Mg# Mg# Fig. 22a Mg# 77 Mg# 81 Mg# Fig. 23a Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig. 18 B 1012I 1 SiO wt An An 84 Fig. 20b An An Mg# Mg# Fig. 21b Mg# Fig. 22b Mg# Mg# 77 Fig. 23b Fe Mg Opx Mg# vs. Ol Mg# Cpx Mg# vs. Ol Mg# 1 1 Fig Fig.24 An An An 89 An

22 Rim (An) Plagioclase Core (An) Rim (Mg#) Olivine Core (Mg#) Orthopyroxene Clinopyroxene Rim (Mg#) Core (Mg#) Core (Mg#) phenocryst phenocryst (dusty pl) phenocryst (honey-comb pl) crystal clot (pl+opx) crystal clot (pl+cpx) crystal clot (pl+opx+cpx) crystal clot (opx+cpx) Fig.19 Diagram showing the summary of relationships between core and rim compositions of phenocrysts in the eruptive products of Shichihonzakura- series. Mg# Mg# Mg# Mg# Mg# 81 Mg# Lindsley Fig

23 Rim(An) a. b. Core(An) Mafic Inclusion Plagioclase a.mafic inclusion (06a SiO 2 =54.96wt%) b.mafic inclusion ( SiO 2 =53.88wt%) phenocryst (clear pl) phenocryst (dusty pl) phenocryst (honey-comb pl) crystal clot (pl+opx+cpx) a. b. Core (Mg#) Mafic Inclusion Clinopyroxene a.mafic inclusion (06a SiO2=54.96wt%) b.mafic inclusion ( SiO2=53.88wt%) phenocryst crystal clot (pl+opx+cpx) crystal clot (opx+cpx) Fig. 20 Diagram showing the relationship between core and rim compositions of plagioclase phenocryst in mafic inclusions of the Misawa lava. Fig. 22 Diagram showing the relationship between core and rim compositions of clinopyroxene phenocryst in mafic inclusions of the Misawa lava. a. Mafic Inclusion Orthopyroxene a. Mafic inclusion Olivine b. Core(Mg#) a.mafic inclusion (06a SiO 2 =54.96wt%) b.mafic inclusion ( SiO 2 =53.88wt%) phenocryst crystal clot (pl+opx+cpx) crystal clot (opx+cpx) b. Core(Mg#) a.mafic inclusion (06a SiO2=54.96wt%) b.mafic inclusion ( SiO2=53.88wt%) phenocryst Fig. 21 Diagram showing the relationship between core and rim compositions of orthopyroxene phenocryst in mafic inclusions of the Misawa lava. Fig. 23 Diagram showing the relationship between core and rim compositions of olivine phenocr yst in mafic inclusions of the Misawa lava Fig. 12 solidification front Marsh 1996 rigid crust solidification front

24 suspension 2 EPMA A An An B An An C An An D An An Rim (An) Plagioclase Core (An) 4 4 mottled core An An Fig. 4 An 93 An Fig. 26 A B Fig. 5 E F Mafic Inclusion Rim (Mg#) An Olivine Core (Mg#) Orthopyroxene Clinopyroxene Rim (Mg#) Core (Mg#) phenocryst phenocryst (dusty pl) phenocryst (honey-comb pl) Core (Mg#) crystal clot (pl+opx) crystal clot (pl+cpx) crystal clot (pl+opx+cpx) crystal clot (opx+cpx) Fig.24 Diagram showing the summary of relationships between the core and rim compositions of phenocrysts in mafic inclusions of the Misawa lava

A B An An C D An An An Fig. 4D Fig. 5 C D Fig. 26 A C 4 2 3 1 2 3 An An SiO 2 An An An Mg# 72 77 An 1000 1100 SiO 2 67wt 57wt 4 1 2 3 An An 4 An An 5 6 Fig. 5 A B 6 Fig.

25 A B An An C D An An An Fig. 4D Fig. 5 C D Fig. 26 A C An An SiO 2 An An An Mg# An SiO 2 67wt 57wt An An 4 An An 5 6 Fig. 5 A B 6 Fig. 5 G H Clinopyroxene Imaichi-series phenocryst Shichihonzakura-series phenocryst Imaichi-series crystal clot Shichihonzakura-series crystal clot Orthopyroxene Fig. 25 Pyroxene thermometry by Lindsley (1983). The solvus of pyroxenes at 5kb is presented

26 2 3 1 cross section Zoning pattern of plagioclase low An core / low An rim high An core / low An rim contact with mafic end member magma 4. 67wt 53wt 5 SiO 2 67wt An An 15vol SiO 2 An SiO 2 58wt SiO 2 67wt crystallization front rigid crust Sieve texture is formed in low An rim and high An rim overgrows Fig. 26 Cartoon showing the complex compositional zoning of plagioclase phenocryst in the eruptive products of Shichihonzakura-series. The relationships between core and rim compositions depend upon the position of cross section. 1: mottled core and rim with low An content; 2: oscillatory zoned margin with medium An content; 3: patchy core with high An content; 4: sieve texture. An An 0 0 An SiO 2 SiO 2 58wt An SiO 2 67wt An SiO wt SiO 2 SiO wt SiO 2 67wt SiO 2 58wt SiO 2 53wt

27 SiO 2 14 vol An 0 0 crystallization front rigid crust crystallization front MgO mingling Mg# 81 An SiO 2 67wt 2 SiO 2 67wt 58wt SiO 2 67wt 53wt 3 4 MgO 5 6 An SiO 2 67wt 15vol An SiO 2 58wt SiO 2 67wt 14 vol SiO 2 53wt MgO

28 MgO 1979 pp ka Lindsley, D. H Pyroxene Thermometr y. Am. Mineral., 68, Marsh, B. D Solidification fronts and magmatic evolution. Mineralogical Magazine,, pp p

N Fig.1 Map showing the location of Komochi volcano (open star). The contours show the depth of upper surface of subducting Pacific plate (grey lines)

N Fig.1 Map showing the location of Komochi volcano (open star). The contours show the depth of upper surface of subducting Pacific plate (grey lines) No.53 2018 pp.77 96 102 Whole-rock Chemistry for Radial Dike Rocks in the Komochi Volcano, Central Japan: Summary of Analytical Data of 102 Dikes Masaki TAKAHASHI, Seiji KUBO, Naoaki TAKASUGI, Tamotsu