Fluorine and Chlorine Contents in the Products of the Large-Scale Pyroclastic Activity of Aira Caldera

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1 /, (,**1), 23 +*-,**0 -,2,**0 +,,/ Fluorine and Chlorine Contents in the Products of the Large-Scale Pyroclastic Activity of Aira Caldera Minoru YOSHIDA and Mineharu OSHIMA Fluorine (F) and chlorine (Cl) have been determined for the products of a series of large-scale pyroclastic eruptions that produced the Aira caldera at the northern end of Kagoshima bay in southern Kyushu. It started with a Plinian pumice eruption (Osumi pumice fall, 32 km - ) followed by the Tsumaya pyroclastic flow (+- km - ). After a short pose, a violent explosive eruption occurred to form the Ito pyroclastic flow (,/* km - ) accompanied by the Aira-Tn ash fall (/* km - ). Pumice blocks, pumice grains, no welding matrices and welded tu#s sampled from the deposits of the Osumi pumice fall, the Tsumaya pyroclastic flow and the Ito pyroclastic flow are analyzed. Their F and Cl contents varied in the course of the eruptions. The Osumi pumice fall samples have uniform F and Cl contents and show the highest average values among those deposits. Fluorine contents of the Ito pyroclastic flow samples are distinctly lower than the Osumi pumice samples in order of grain size : fine-grained matrices coarse-grained matrices pumice grains pumice blocks. The Tsumaya pyroclastic samples are divided into two groups according to their F contents. The lower-layer deposits show F contents nearly the same as those of the Osumi pumices, while the higher-layer deposits near to the Ito samples. The variation of F contents from the Osumi pumices to the Ito pyroclastic deposits is thought to be caused by the change of distribution of F between silicate melt and aqueous phases before and after the first Plinian eruption. The variation among the Ito deposits can be explained by the reaction between gases and silicates after the eruption. Chlorine contents in pumices and no welding matrices of both pyroclastic flows show wide range, but the highest values are almost the same as that of the Osumi pumices. Welded tu# samples show the lowest Cl contents and the highest F/Cl ratio. These results can be explained by release of Cl after deposition of the flows. Key words : fluorine, chlorine, Aira caldera, large-scale pyroclastic deposits, pumice fall deposit + Yoshida, +30- ; +31/ ; Yoshida, +33* F Cl +/, 2//+, +, + Faculty of Science, Tokyo Institute of Technology, Ookayama, +, +, Meguro-ku, Tokyo +/, 2//+, Japan.,1, *2,0 + / +0 Present address. Mama + / +0, Ichikawa,1, *2,0, Japan. +3/1 ; Aramaki and Yamasaki, +30- F Cl +12- Yoshida and Tsuchiya,,**. ++*2 (Yoshida and Aoyagi,,**.) F Cl --0 *3,- +/./. /*1 Present address. Oomagi +/./. /*1, Saitama --0 *3,-, Japan. Corresponding author: Minoru Yoshida

2 90 F Cl (+301) A Cl F Cl +*** + (+301) F Cl +33/ F Cl F/Cl Cl F/Cl Cl H,O( ) Cl (+301) Cl H,O( ) F F F/Cl ++*2 (Yoshida and Aoyagi,,**.) +12- (Yoshida and Tsuchiya,,**.) F/Cl, - 32 km - (Kobayashi et al., +32-) (+- km - ) +32- ; Aramaki, +32.,/* km - (Aramaki, +32.) Tn /* km * F/Cl,,,,,*** B.P. Tn,.,***,/,*** B.P.,0,***,3,*** B.P.,**- ;,**,

3 91 (Fig. +) Tn (Os ; PF) Os + Os - (Os.) (Fig.,) Os +, Os. Os,, Os- (Ito) Os. (Ito 2 ; Fig.,) Ito +, Ito,, Ito- ; Ito,, (Ito., Ito /, Ito0) (Ito 1) (Fig. -) Ts; Ito + Ts + Ts. (Fig. -) (PB) / -* cm + (Ito. PB-,) H,O( ) F Cl Aramaki, +32. ; +33* F, Cl F/Cl *.1+ mm Ts + + mm,. mm handpicking Fig. +. Index map of sampling areas : +. the Kanoya area,,. the Kokubu-Krishima area. Fig.,. Sampling locations in the Kanoya area. (Osumi pumice fall and Ito pyroclastic flow)

4 L ;c <¼ 92 Fig. -. Sampling locations in the Kokubu-Kirishima area. (Tsumaya and Ito pyroclastic ﬂows) (PG)! " Ito 0, Ito 2 #$%&'( ) *+,-+./01 23 (LF) B=9 <= >?@ A 4? C 0) 456+ L M %NO$ P H Q =9 RSFR T U V W XY ZC3 [ \1 1 2 c ug 2 2 R 34 =b Philips $ a & " H,O( ) ++*,. h DE2F1 G (+33/)?H I J2K 1 C: PW+.*. z X 52 C wjl 456+ (WT) : ; &, sug2 1 /?0 0 L? ]!^ 3 _`ab=9,-" _ cd +32, 2ef..ῌ FeO +**ῌ (FeOª) 2«C: 1h : Table + Y Z8 /0:C1h Aramaki, +32. ; 3 c±9 +33* ²³ \ 0 4,-" *.1+ mm µ Ito,- + Ito,-, Ts - #$%&'( h1ijklm& 2T Table + F)01h *.-/ mm µ jmno# pq(r$s%t& ug _' h1v I#$%&'( C:²³ (lq&`(w xyzz)& cl,**/ 2¹ / *.-/ *.1+ mm #Ng Tsuchiya et al. (+32/) { } *~ 1 ug + 7u #$%&'( d #$%&'( º g sug2 2, sug : C?:G)0 / SiO, K,O?@ Al,O- CaO FeOª MgO? C SiO, C: f» 0 - :C1 sug? P.

5 93 Table +. Major chemical compositions of the deposits of the Aira pyroclastic eruption. Weight : normalized to +** on the water-free base. species size mm SiO, TiO, Al,O - FeO* MnO MgO CaO Na,O K,O P,O / Os + Os, Os - Os. Ts - Ts - Ts - Ts - Ts - Ts - Ts - Ito + Ito, Ito,-+ Ito,-+ Ito,-+ Ito,-+ Ito,-+ Ito,-+ Ito,-, Ito,-, Ito,-, Ito,-, Ito,-, Ito,-, Ito. Ito. Ito / Ito 0 Ito 1 Ito 1 PF PF PF PF PG-+ PG-, PB PB PG PG PB PG-+ PG-, PB-+ PB-, PB PB WT-+ WT--,-.,-. *.-/-*.1+ *.,/-*.-/ *.+.3-*.+11,-*.+.3,,-. *.-/-*.1+** *.,/-*.-/** *.+.3-*.+11,-*.+.3**,**,-. *.-/-*.1+ *.,/-*.-/ *.+11-*.,/,-*.+.3,,-.,-. *.-/-*.1+ *.,/-*.-/ *.+.3-*.+11,-*.+.3, *.++ *.+* *.+* *.*3 1/ *. 1/ * 1/.*3 1/.,1 01.,0 1*.+1 1, ,..1 1/ * ,/ 1/../ 1/./ /../ 1+.1/ 1..3, 1/.., 10.* /.01 1/.-/ 1../3 1+../ 1-./. 1..,2 1..1, 1,.1-1/./* /..* 1..,2 1-.-/ 1,.*- *.+2 *.+3 *.,* *.,, *.,- *.,- *.-3 *..+ *..* *.-+ *.-* *.+3 *.-- *.-+ *.-+ *.,/ *.,+ *.,1 *.,3 *.-+ *.,0 *.+3 *.,+ *.,* *.,3 *.-+ *.-. *.,1 *.,3 *.+3 *.,* *.+3 *.,* *.,0 *., ,/ /../ ,, / , /, /.,- +-../ +-.+/ +-.*2 +..** /. +/../ +..,1 +..* / , / , *3,.0,,.3+,.* ,./2,.,-,.*-,./, +.22,.2*,..*, /, , +.10,.3/,.1.,.0/,.-3,.31 +./3 +.1/ ,.+2,..2 *.,, *.,1 *.-2 *.,1 *.-+ +.,2 +.*3 *.1, *..3 *... *.,2 *.-1 *.3, *./1 *.-. *.,2 *.-, *.11 *..3 *..* *.,1 *.,/ *.,/ *.,/ *.2, *.0+ *..- *.-, *.-2 *.,/ *.,2 *.,3 *.,3 *./, *./0 +.1* / ,., ,.*/ , / , +.// -.+/ * / +./, , , +.3, ,./-, * -./- -.0, / * / / /, /1 -./1 -./ /- -./ * -./ * * , *3, , ,.,3,.11 -.** -.*., * -.+-,.*0, / -.+1,.+*,.2* -.*. -.,3 -., ,. -.*1,.*,,.01 -.*3 -., / -.+-,.01,.03 *.*- *.*, *.*- * Calculated total FeasFeO. ** These samples are not analyzed for F, Cl and H,O. 1, *.-/ *.1+ mm Aramaki (+32.) (+33*) *.-/ mm Ts - *.,/ *.-/ mm SiO,

6 94 Table,a. F, Cl and H,O( ) contents of the samples of the Osumi pumice fall. *.+,/ *.,/ mm, mm *.1+ mm., F, Cl, H,O( ) Table,a,,b,,c F Cl.** mg g + +* mg g + -., + H,O( ) H,O( ), *./ H,O( ), mm H,O( ) Aramaki and Lipman, +30/ ; +300 Na,O, SiO, H,O( ) Na,O SiO, H,O( ): Na,O (r) *./.* : -- + SiO, *.-/ mm SiO, H,O( ): SiO, r*..*1 :,3 / H,O( ) H,O( ): Cl H, O( ): F Cl +33/ H,O( ): Cl r*.+10 : /. / Cl SiO,,Na,O H,O( ): F r*./++ : /. + F H,O( ) F F +31/ ; Yoshida, +33* F.,, F, Cl F Cl Fig.. *.-/ mm Cl F

7 95 Table,b. F, Cl and H,O( ) contents of the samples of the Tsumaya pyroclastic flow. Cl F Cl F t +) F / + + *.+,) (, mm) (, *.1+ mm) /

8 96 Table,c. F, Cl and H,O( ) contents of the samples of the Ito pyroclastic flow. + +* + -) F (Ts +, Ts,) +* (Ts -, Ts.) + (, mm) (, *.1+ mm)

9 97 Table,c. Continued. F F, Cl +3/1b; Iwasaki et al., +302 ; Yoshida et al., +31+ t Cl Fig.. F Cl Fig.. t +) Cl / / +* +*,) (, *.1+ mm) (, mm) / (, *.1+ mm) +* /

10 98 Fig... F-Cl insol. variation patterns for the samples of the Aira pyroclastic eruptions: Osumi pumice fall, Ito, pumice block, Ito, pumice grain (,. mm), Tsumaya, pumice grain (,. mm), upper layer, Ito, no welding matrix, coarse-grained fractions (, *.1+ mm), Ito, no welding matrix, fine-grained fraction (, mm), Tsumaya, no welding matrix, lower layer, Tsumaya, no welding matrix, upper layer, Ito welded tu#. Samples whose symbols are parenthesized have main chemical compositions di#erent from the others. +* -) Cl +*.) + Cl., - F, Cl F, Cl Yoshida and Tsuchiya (,**.) Yoshida and Aoyagi (,**.) F, Cl Cl Cl Cl Cl H,O F +) F,) F Cl Cl F (Yoshida, +30- ; Yoshida, +33*)

11 99 F Cl +),), +) F, F F +32- ; Aramaki, +32. F, (+33*),,) F Cl H,O F F Cl Aramaki (+31+) (+33.) 11* 12*, kbar (+33*) 12*,* - / kbar Shinohara et al.(+323) Cl 2+*, *.0 0.* kbar,., kbar Cl Cl,., kbar Cl Cl +33* Cl Cl Cl Shinohara et al. (+323),., kbar Cl Cl Cl 1** +*** mg g + Webster (,**.) Cl F F F +312 ; White, +3/1 F Cl White, +3/1 ; +32/ F, -) F +/.,,) F F F (+33*) +/.

12 100 F 2** F (Iwasaki et al., +30, ; Yoshida, +33*) F F Cl HCl NaCl F F F F +3/1a; +3/2 ;,**. *.-/ mm Cl F,,),,) F, -) F F ; Yoshida et al., +31+ F +,2 : -*, mg g + (,1* --* mg g + ) F Ts +,, +/* mg g + F F F, -).,. Cl., - Cl Cl +32- ; Aramaki, +32. Cl Ito + Ito 0, / + Ito + Ito 0 3* +** m Table,c Cl insol. /** mg g + Ito + Ito, Ito 0 0** mg g + Cl insol. Ito + Ito 0 Cl insol. Cl insol. Ito 2 0** mg g + Cl insol. Cl Cl (Aramaki, +32.) +32- Ito 2

13 101., / F, Cl +33/ Cl F/Cl +- Table - F/Cl..,1 /0 Cl, ; Yoshida et al., ,2 F Cl (m [log (F/Cl)] *./,) (s [log (F/Cl)] *./0) + Cl F/Cl F, Cl F/Cl,.1,.2 Table - + Cl + Cl Table - Cl insol. +** mg g + ++* +0* mg g + 2** Cl F / 0** 1** F +31/ ; Yoshida, +33* F (Weyl, +3/*)., 0,. mm, F, Cl F F, Cl (Fuge, +31. ; Koritnig, +31,) F Cl / F, Cl F, Cl F, Cl F, Cl F F F F F Cl Cl Cl F/Cl X

14 102 Table -. F, Cl contents of welded tu# samples taken from several large-scale pyroclastic flows in Japan. (+3/1)Pyroclastic flow +.1 /1. Aramaki, S. (+31+) Hydrothermal determination of temperature and water pressure of the magma of Aira caldera, Japan. Am. Mineral., /0, +10* (+32-) / 2-3,. Aramaki, S. (+32.) Formation of the Aira caldera, southern Kyushu,,,,*** years ago. J. Geophys. Res., 23, 2.2/ 2/*+. Aramaki S and Yamasaki, M. (+30-) Pyroclastic flow in Japan. Bull. Volcanol.,,0, Aramaki, S. and Lipman, P. W. (+30/)Possible leaching of Na,O during hydration of volcanic glasses. Proc. Jap. Academy,.+,.0/ 1*.

15 103 (+300) Na,O 1, Fuge, R. (+31.) Chlorine, Abundance in common sedimentary rock types. In Handbook of Geochemistry (Wedepohl, K. H., Correns, C.W., Shaw, D. M., Turekian, K. K. and Zemann, J. eds.), +1-K-+ +1-K-2, Springer- Verlag, Berlin. (+301) A +, + +*. (+3/1a) -, +*+ +*/. (+3/1b).+ 12, ,. Iwasaki, I., Ozawa, T., Yoshida, M., Katsura, T., Iwasaki, B., Kamada, M. and Hirayama, M. (+30,) Volcanic gases in Japan. Bull. Tokyo Inst. Technol., no..1, + /.. Iwasaki, I., Katsura, T., Ozawa, T., Yoshida, M. and Iwasaki, B. (+302) Chlorine content of volcanic rocks and migration of chlorine from the mantle to the surface of the Earth. In The crust and upper mantle of the Pacific area (Knopo#, L., Drake, C. L. and Hart, P. J. eds.),.,-.,1, Geophys. Monograph +,, American Geophys. Union, Washington D. C. (+3/2) /. Kobayashi, T., Hayakawa, Y. and Aramaki, S. (+32-) Thickness and grain-size distribution of the Osumi pumice fall deposit from the Aira caldera.,2 +, Koritnig, S. (+31,) Fluorine, Abundance in common sedimentary rock types. In Handbook of Geochemistry (Wedepohl, K. H., Correns, C.W., Shaw, D. M., Turekian, K. K. and Zemann, J. eds.), 3-K-+ 3-K-2, Springer-Verlag, Berlin. (+310) Tn (,**-) --0p. (+33.) SIMS +33. p.++-. (,**.) no..1 B, 10/ 11+. (,**,) -.+,,/,-0. (+32,) / + 2*p (+33/) /,p. (,**/) (GSJ) /*,.-,.0 (+312).2.+ /,. Shinohara, H., Iiyama, J. T. and Matsuo, S. (+323) Partition of chlorine compounds between silicate melt and hydrothermal solutions: Partition of NaCl-KCl. Geochim. Cosmochim. Acta, /-,,0+1,0-*. Tsuchiya, K., Imagawa, T., Yamaya, K. and Yoshida, M. (+32/) Separation of microamounts of fluoride coexisting with large amounts of aluminum and silica by improved trimethylsilylating distillation. Anal. Chim. Acta, +10, +/+ +/3. (+33*) -/,-+,.2. Webster, J. D. (,**.) The exsolution of magmatic hydrosaline chloride liquids. Chem. Geol.,,+*, Weyl, W. A. (+3/*) Fluorine compounds in glass technology and ceramics. In Fluorine Chemistry.. (Simons, J. H. ed.), //- /1., Academic Press, New York. White, D. E. (+3/1) Thermal waters of volcanic origin. Bull. Geol. Soc. Am., 02, /2. Yoshida, M. (+30-) The volatilization of chlorine and fluorine compounds from igneous rocks on heating. Bull. Chem. Soc. Japan, -0, 11-12,. (+31/) +31/..3./.. (+32/), (.) Yoshida, M. (+33*) Fractionation of fluorine and chlorine through the volcanic process. In Geochemistry of gaseous elements and compounds (Durance, E. M., Galimov, E. M., Hinkle, M. E., Reimer, G. M., Sugisaki, R. and Augustithis, S. S. eds.), , Theophrastus Publications, S. A., Athens. Yoshida, M. and Aoyagi, R. (,**.) Fluorine and chlorine contents in the products of the ++*2 (Tennin) eruption of Asama volcano..3, Yoshida, M. and Tsuchiya, K. (,**.) Fluorine and chlorine contents in the products of the +12- (Temmmei) eruption of Asama volcano..3, 0/ 1,. Yoshida, M., Takahashi, K., Yonehara, N., Ozawa, T. and Iwasaki, I. (+31+) The fluorine, chlorine, bromine, and iodine contents of volcanic rocks in Japan. Bull. Chem. Soc. Japan,.., /*.

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