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)

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1 No pp 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 KONO, Maya YASUI and Tatsuo KANAMARU Accepted November 30, 2017 The whole-rock chemistry for the radial dike rocks of Komochi volcano, Central Japan, is studied based on newly obtained analytical data of 102 dikes. On the basis of major element chemistry of dike rocks, the radial dikes are classified into the six compositional groups; they are (1) basalt (SiO 2 <53wt.%), (2) high MgO mafic andesite (53wt.%<SiO 2 <56wt.%), (3) low MgO mafic andesite (53wt.%<SiO 2 <56wt.%), (4) andesite (56wt.%<SiO 2 <58wt.%), (5) felsic andesite (58wt.%<SiO 2 <61wt.%), (6) dacite (SiO 2 >62wt.%). The felsic andesite magma is difficult to be derived from the basalt magma by simple crystallization differentiation, because the ratios of incompatible elements of basalt and felsic andesite are considerably different. The mafic andesite is probably produced by magma mixing between the basalt and felsic end-member magmas, as its incompatible elements ratios vary in wide range. However, the felsic end-member magma is not the felsic andesite or dacite magmas, for their chemical compositions are not plotted on the extension of linear compositional trends of mafic andesite and andesite in the SiO 2 variation diagrams. It is probable that the high MgO mafic andesite magma is formed by accumulation of mafic phenocrysts such as olivine and pyroxenes in the low MgO mafic andesite magma. The dacite magma cannot be produced by simple crystallization differentiation of felsic andesite magma, because the contents of incompatible elements are lower in the dacite than the felsic andesite. There is not relationship between the spatial distribution of compositional groups in the radial dikes and the distances or directions from the central vent, although the felsic andesite is exclusively distributed in the western half of the radial dikes. The wholerock major element chemistry of radial dikes of Komochi volcano is different from that of the Haruna volcano and similar to that of the Akagi volcano, but the radial dike rocks mostly belong to the tholeiitic rock-series and lacking in the calcalkalic andesite which is abundant in the Akagi volcano. Keywords : Komochi volcano, radial dikes, whole-rock chemistry, basalt, andesite, dacite 1 10 km 1290 m 9km 7.5km Fig Geshi, : : Department of Earth and Environmental Sciences, College of Humanities and Sciences, Nihon University: Sakurajosui, Setagaya-ku, Tokyo, , Japan Department of Geosystem Sciences, College of Humanities and Sciences, Nihon Unversity: , Sakurajosui, Setagaya-ku, Tokyo, Japan Numata Prefectural Senior High School: , Kuyaharamachi, Numata City, Gunma, Japan present address 77 61

N Fig.1 Map showing the location of Komochi volcano (open star).

Hasegawa, 2007). Numerals denote the depth in km.

3 9 150 1996 K-Ar Alluvium Terrace deposits 2km 1 2 3 4 5 6 Fig.2 Geologic sketch map of the Komochi volcano after Iizuka (1996).

2 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) and Philippine sea plate (solid lines) (Nakajima and Hasegawa, 2007). Numerals denote the depth in km. open star: Asama volcano; solid circle: Quaternary volcano; VF: volcanic front; SAT: Sagami trough; SUT: Suruga trough K-Ar Alluvium Terrace deposits 2km Fig.2 Geologic sketch map of the Komochi volcano after Iizuka (1996). 1: late stage lava (lava dome forming stage); 2: late stage lava (stratovolcano forming stage, Ma); 3: debris avalanche deposit; 4: late stage lava (stratovolcano forming stage, Ma); 5: early stage lava; 6: Ayado lavas; 7: volcanic neck (Daikokuiwa lava) Fig.2 1 6Ma Ma Ma Ma Ma Ma Ma

3 m m 150 m 100 m km Fig m 3 5m Geshi 2008 L-type V-type L-type V-type L-type SiO 2 >55wt. V-type SiO 2 <55wt. MgO>4.0wt vol vol. Fig.4 SiO 2 10vol. Fig Rb Sr Ba Y, Zr, Nb, Ni, Cr 5-1 2mm g 0.01g g 5 Li 2 B 4 O 7 N 300m Fig.3 Map showing the distribution of radial dikes of Komochi volcano after Kubo (1983). A grey circle is the central vent consisting of volcanic neck (Daikokuiwa lava)

4 Fig.4 Phenocryst contents vs. SiO 2 for the radial dikes of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite 2.0 X PW2400 SiO 2 = 0.153% TiO 2 = 0.009% Al 2 O 3 = % FeO = 0.065% MnO= 0.004% MgO= 0.093% CaO= 0.050% Na 2 O= 0.025% K 2 O= 0.024% P 2 O 5 = 0.003% Rb= 1.5ppm, Ba= 8.8ppm, Sr= 5.7ppm, Y= 1.9ppm, Zr= 6.5ppm, Nb= 1.3ppm, Ni= 2.2ppm, Cr= 11.6ppm 5-2 SiO 2 51wt. 62wt. SiO 2 54wt. 56wt. Fig.5 SiO 2 Al 2 O 3 CaO FeO MgO P 2 O 5 Na 2 O K 2 O Figs.6 and 7 TiO 2 MnO Fig.6 FeO /MgO SiO 2 Fig.8 Fig.5 Histogram showing the whole-rock SiO 2 content of radial dike rocks. Frequency indicates the number of samples

5 Fig.6 SiO 2 variation diagrams for TiO 2, P 2 O 5, Al 2 O 3, CaO, FeO, MnO, MgO and Na 2 O contents of the radial dike rocks of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite 81 65

6 Fig.7 K 2 O vs.sio 2 diagram for the radial dike rocks of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite; high-k: high-k series; med-k: medium-k series; low-k: low-k series Fig.8 FeO /MgO vs. SiO 2 diagram for the radial dike rocks of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite; TH: tholeiitic rock-series; CA: calcalkalic rock series 6 1 SiO 2 <53wt. 2 53wt. <SiO 2 <56wt. MgO>4.0wt. MgO MgO 3 53wt. <SiO 2 <56wt. MgO<4.0wt. MgO MgO 4 56wt. <SiO 2 <58wt. 5 58wt. <SiO 2 <61wt. 6 SiO 2 >62wt. Figs.6, 7 and 8 MgO MgO MgO Al 2 O 3 CaO Fig.6 P 2 O 5 K 2 O medium-k SiO 2 Fig.6 and 7 Fig.6 and 7 SiO 2 vs. FeO /MgO MgO 5-3 SiO 2 Rb Ba Y Zr Nb Sr Fig.9 Ni Cr 66 82

7 Fig.9 SiO 2 variation diagrams for Rb, Sr, Ba, Y, Zr and Nb contents of the radial dike rocks of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite 83 67

8 53wt. <SiO 2 <56wt MgO Fig.10 Rb Ba Y Zr Nb MgO MgO Rb Ba Y Zr Nb Ni, Cr MgO Sr MgO Figs.9 and Rb/Ba, Rb/Y, Rb/ Zr,Rb/Nb, Ba/Y, Zr/Y, Nb/Y Figs.11 and 12 Ba/ Zr, Ba/Nb, Nb/Zr Fig.12 Fig.10 SiO 2 variation diagrams for Ni and Cr contents of the radial dike rocks of the Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite 68 84

9 30 30 Rb (ppm) Rb (ppm) Ba (ppm) Y (ppm) Rb (ppm) Rb (ppm) Zr (ppm) Nb (ppm) Fig.11 Rb vs. Ba, Rb vs. Y, Rb vs. Zr Rb vs.nb diagrams for the radial dike rocks of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite 85 69

10 Ba (ppm) Zr (ppm) Y (ppm) Y (ppm) Ba (ppm) Nb (ppm) Zr (ppm) Y (ppm) Ba (ppm) Nb (ppm) Nb (ppm) Zr (ppm) Fig.12 Ba vs. Y, Ba vs. Zr, Ba vs. Nb, Zr vs. Y, Nb vs. Y and Nb vs. Zr diagrams for the radial dike rocks of Komochi volcano. 1: basalt, low MgO mafic andesite and andesite; 2: high MgO mafic andesite; 3: felsic andesite; 4: dacite 70 86

11 Daikokuiwa volcanic neck N m Fig.13 Map showing the distribution of dike groups based on the whole-rock chemistry. 1: basalt (SiO 2 <53wt.%); 2: high-mgo mafic andesite (53wt.%<SiO 2 <56wt.%; MgO>4.0wt.%); 3: low-mgo mafic andesite; (53wt.%<SiO 2 <56wt.%; MgO<4.0wt.%); 4: andesite (56wt.%<SiO 2 <58wt.%); 5: felsic andesite (58wt.%<SiO 2 <62wt.%); 6: dacite(sio 2 >62wt.%) Rb/Ba, Rb/Y, Rb/Zr,Rb/Nb, Ba/Y, Zr/Y, Nb/Y 2 MgO MgO MgO Ni Cr MgO Al 2 O 3 CaO Sr Geshi 2008 MgO MgO MgO Ni Cr Al 2 O 3 CaO Sr Rb Ba Y Zr Nb Rb/Ba, Rb/Y, Rb/Zr,Rb/Nb, Ba/Y, Zr/Y, Nb/Y 3 Rb/Ba, Rb/Y, Rb/Zr, Rb/Nb, Ba/Y, Zr/Y, Nb/Y 87 71

12 Fig.14 SiO 2 variation diagrams for TiO 2, P 2 O 5, Al 2 O 3, CaO, FeO, MnO, MgO and Na 2 O contents of the radial dike rocks of Komochi volcano, together with those of the volcanic rocks of Haruna and Akagi volcanoes. 1: radial dike rocks of the Komochi volcano; 2: eruptive products of the Haruna volcano; 3: eruptive products of the Akagi volcano 72 88

13 Fig.15 K 2 O vs. SiO 2 diagram for the radial dike rocks of Komochi volcano, together with those of the volcanic rocks of Haruna and Akagi volcanoes. 1: radial dike rocks of the Komochi volcano; 2: eruptive products of the Haruna volcano; 3: eruptive products of the Akagi volcano Rb/Ba, Rb/Y, Rb/ Zr,Rb/Nb, Ba/Y, Zr/Y, Nb/Y P 2 O 5, K 2 O, Rb, Ba, Y, Zr, Nb SiO 2 Fig.16 FeO /MgO vs. SiO 2 diagram for the radial dike rocks of Komochi, together with those of the volcanic rocks of Haruna and Akagi volcanoes. 1: radial dike rocks of the Komochi volcano; 2: eruptive products of the Haruna volcano; 3: eruptive products of the Akagi volcano 4 1 SiO 2 K 2 O, P 2 O 5, Rb, Ba, Y, Zr, Nb 89 73

14 6-2 Geshi 2008 MgO Vtype MgO MgO Geshi 2008 Fig ; 2016 Figs.14, 15 and 16 TiO 2 SiO 2 P 2 O 5 SiO 2 Al 2 O 3 SiO 2 Fig.14 CaO FeO MnO MgO Na 2 O Fig.14 K 2 O SiO 2 low-k medium-k Fig.15 SiO 2 K 2 O low-k K 2 O FeO /MgO vs. SiO 2 Fig.16 TiO 2 P 2 O SiO 2 <53wt. 2 53wt. <SiO 2 <56wt. MgO>4.0wt. MgO MgO 3 53wt. <SiO 2 <56wt. MgO< 4.0wt. MgO MgO 4 56wt. <SiO 2 <58wt. 5 58wt. <SiO 2 <61wt. 6 SiO 2 >62wt SiO 2 4 MgO MgO MgO TiO 2 P 2 O

15 Geshi, N. (2008) Vertical and lateral propagation of radial dikes infered from the flow-direction analysis of the radial dike swarm in Komochi Volcano, Central Japan. J.Volcanol. Geotherm.Res., 173, Nakajima, J. and Hasegawa, A. (2007): Subduction of the Phil- ippine sea plate beneath southwestern Japan: Slab geometry and its relationship to arc magmatism. J.Geophys.Res., 112, B08306, doi: /2006jb p

16 Table 1 Major element chemistry for the radial dike rocks of Komochi volcano. basalt:18, 61, 76, 89, 90; high MgO mafic andesite: 3, 15, 17, 55, 58, 60, 65, 67, 69, 80, 84, 85, 86, 87, 98: low MgO mafic andesite: 1, 7, 9, 10, 11, 12, 13, 14, 19, 22, 23, 24, 26, 27, 30, 36, 41, 42, 43, 46, 49, 52, 53, 56, 57, 59, 64, 68, 70, 71, 73, 74, 77, 81, 82, 83, 88, 91, 92, 94, 99; andesite: 2, 4, 5, 6, 33, 34, 37, 47, 48, 50, 51, 62, 63, 66, 72, 75, 78, 93, 95, 96, 97, 100, 101, 102; felsic andesite: 16, 20, 21, 25, 28, 29, 31, 32, 38, 39, 40, 35, 44, 45, 54, 79; dacite: 8 Sample No. Dike No. SiO 2 TiO 2 Al 2 O 3 FeO MnO MgO CaO Na 2 O K 2 O P 2 O 5 TOTAL phenocryst content

17 Sample No. Dike No. SiO 2 TiO 2 Al 2 O 3 FeO MnO MgO CaO Na 2 O K 2 O P 2 O 5 TOTAL phenocryst content

18 Table 2 Trace element chemistry for the radial dike rocks of Komochi volcano. basalt:18, 61, 76, 89, 90; high MgO mafic andesite: 3, 15, 17, 55, 58, 60, 65, 67, 69, 80, 84, 85, 86, 87, 98: low MgO mafic andesite: 1, 7, 9, 10, 11, 12, 13, 14, 19, 22, 23, 24, 26, 27, 30, 36, 41, 42, 43, 46, 49, 52, 53, 56, 57, 59, 64, 68, 70, 71, 73, 74, 77, 81, 82, 83, 88, 91, 92, 94, 99; andesite: 2, 4, 5, 6, 33, 34, 37, 47, 48, 50, 51, 62, 63, 66, 72, 75, 78, 93, 95, 96, 97, 100, 101, 102; felsic andesite: 16, 20, 21, 25, 28, 29, 31, 32, 38, 39, 40, 35, 44, 45, 54, 79; dacite: 8 Sample No. Dike No. Sc V Cr Ni Ga Rb Y Sr Zr Nb Ba

19 Sample No. Dike No. Sc V Cr Ni Ga Rb Y Sr Zr Nb Ba

20 m N Appendix Map showing the number of radial dikes used for the chemical analysis 80 96

09-.n R38-V412

09-.n R38-V412 No.38 (23) pp.117-166 847 1 2 2 3 4 3 2 1 Whole - Rock Chemistry for Eruptive Products of Fuji Volcano, Central Japan: Summary of Aanalytical Data of 847 Samples. Masaki TAKAHASHI 1, Masanaga KOMINAMI