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Petrologic Study and Fission-track Age of Middle Pleistocene Hirano Volcanic Ash
in Northern Nomura Town, Southwestern Shikoku, Japan῍,
Masayuki SAKAKIBARA῍, Chisato NAKAMURA῍, Hitomi IWASAKI, Michiharu IKEDA῍
Sakae SANO῍῍῍ and Tohru DANHARA῍῍῍῍The Hirano volcanic ash in Nomura Town, southwestern Shikoku, Japan, has been characterized bypetrography, refractive index and geochemical composition of volcanic glass (major and trace elements), andﬁssion-track age of zircon. The Hirano volcanic ash has abundant vesicular glass shards and phenocrysts of biotite,
hornblende and orthopyroxene. The volcanic glass has a rhyolitic composition. LREE (Light Rare EarthElement) proﬁles of the volcanic glass are steep with La/SmN /.*ῌ/.- and those of HREE (Heavy Rare EarthElement) are ﬂat with Gd/YbN +.,ῌ+.-. They have a weakly developed Eu anomaly. The Hirano volcanic ash
has similar values of some incompatible trace element ratios, such as La/Y, Ba/La and Nb/Zr, with the Yufugawa
pyroclastic ﬂow deposit in the Ooita Prefecture. The ﬁssion-track age of *..0*.*3 Ma (+s) was obtained forzircons from the Hirano volcanic ash. The Hirano volcanic ash can be correlated to the Yufugawa pyroclastic ﬂow
deposit based on petrographical, geochemical and geochronological data.
Key words : Hirano volcanic ash, Middle Pleistocene, Yufugawa pyroclastic ﬂow deposit, Nomura Town, southwestern Shikoku+ῌ ῐ ῎ ῑ ῏

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Department of Earth Sciences, Graduate School of
Science and Engineering, Ehime University, Matsuyama
13*-2/11, Japan.
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Shikoku Research Institute Inc., Takamatsu 10+ῌ*+3,,
Japan.
78 

Department of Geology, Faculty of Education, Ehime
University, Matsuyama 13*ῌ2/11, Japan.
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Kyoto Fission-Track Co. Ltd., ..ῌ. Omiyaminamitajiri-cho, Kita-ku, Kyoto 0*-ῌ22-,, Japan.
Corresponding author : Masayuki Sakakibara
e-mail : sakakiba@sci.ehime-u.ac.jp  242  

Fig. +. Map showing the study area. (a) locality of the study area ; (b) topographical map
around the outcrop. Original map is a part of + : ,/,*** topographic map of Nomura
published by Geographical Survey Institute of Japan.

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245

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246

Table -. Major element composition of volcanic glasses fromthe Hirano volcanic ash and Yufugawa pyroclastic ﬂow
deposit. SD : standard deviation.

Fig. -. Histgrams of refractive index of volcanic
glass from the Hirano volcanic ash. Yfg data
are from Machida and Arai (,**-). Yfg :Yufugawa pyroclastic ﬂow deposit.

Fig. ..

Harker diagrams of the volcanic glass shards from the Hirano volcanic ash.

 (Fig. .)!

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247

Table .. Trace element composition of volcanic glasses
from the Hirano volcanic ash and others. K-Ah :Kikai-Akahoya tephra, AT : Aira-Tanzawa tephra,Yfg p.f.d : Yufugawa pyroclastic ﬂow deposits.

Fig. /. Spiderdiagram showing the compositional di#erence of volcanic glass among the Hirano volcanicash, Yufugawa pyroclastic ﬂow deposit, K-Ah andAT tephras.

 K-Ah :;< AT :;<=>?@ABCDE

FG70+H<IJK LMN
OP=>?@AQRS

T Gd U# Lu 0+H<IVWX Y#UZ[\ ]^ "!# 0H<IV_`X Eu abcNde.ῌ. 

fghi H-H0 jkl+Tmno`^ 0p Mg#  *.1+῍*.13  Deer et al.

(+331) n?  qD<T`rstuq Mg#  *.02῍*.13 



 

CEvh wvh x34H<Imyz{  0 Ca  Leake (+312)   ferroan
pargasite  pargasite n?

! | edenite }~ !  "!# Mg#  *.01῍*.1. CEvh34H<Imyz{  An/+ Ab.1

Or,An,- Ab1. Or-  7 

#!S CEwvh total FeO21.-22., wt.
ῌ TiO,0.,0.3 wt.ῌ TiO,  FeO `Xa

m{
/ FT



kl +  (H-/) U#`^ (Fig. ,) E (+333) X^ kl *./ kg U

Fig. 0. Chondrite normalized REE patterns of volcanic
glass from the Hirano volcanic ash, Yufugawa pyroclastic ﬂow deposit, and K-Ah and AT tephras. CIchondrite value data are from Sun and Mcdonough(+323).

,-.  /0  1 2

248

Table /.

- !

Results of ﬁssion-track dating.

r. and N : density and total number of counted tracks, respectively ; Analyses were made by the external detector
method applying to external surfaces of zircon (ED, method : Gleadow, +32+) ; Age was calculated using adosimeter glass NIST-SRM0+, and age calibration factor zED,-/, . (+s) (Danhara et al., ,**-) ; P(c,),
probability of obtaining the c, value for n degrees of freedom (nnumber of cristals-+) (Galbraith, +32+) ; r :correlation coe$cient between rs and ri ; U : uranium content (Iwano et al., ,***) ; Zircon grains were irradiatedwith thermal neutrons in the pneumatic tube of the JRR-. unit of the Japan Atomic Energy Research Institute(JAERI) reactor with NIST-SRM0+, dosimeter.

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La/Y-Ba/La 

La/Y-Ba 

WXY Nb-Zr (W) '=>?-./=K0

123456789:;1  FT <=>?@ABCDE

249

Fig. 1. Comparison of major elements of volcanic glass compositions among the Hirano volcanic
ash and other Middle Pleistocene tephras.

Fig. 3. Nb-Zr diagram of volcanic glasses from the
Hirano volcanic ash, Yufugawa pyroclastic ﬂow
deposit, and K-Ah and AT tephras.

Fig. 2. La/Y-Ba/La diagrams of volcanic glass fromthe Hirano volcanic ash and other Middle
Pleistocene tephras.

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250
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   I )*+  6  J (+300) K ,  - L
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 6  (+333) A_`a$    L l M
NOP QRmSTU gnD<EFD5
qmD [/\ ..ῌ//
Danhara, T., Iwano, H., Yoshioka, T. and Tsuruta, T.
(,**-) Zeta calibration values for ﬁssion track datingwith a diallyl phthalate detector. J. Geol. Soc. Japan, +*3,00/ῌ002.
Deer, W. A., Howie, R. A. and Zussman, J. (+331) RockForming Minerals. Volume ,B, Double-Chain Silicates.
Geol. Soc., London, ,nd edition, 10. p.
Eggins, S. M., Woodhead, J. D., Kinsley, L. P. J.,
Mortimer, G. E., Sylvester, P., McCulloch, M. T., Hergt,
J. M. and Handler, M. R. (+331) A simple method forthe precise determination of.* trace elements ingeological samples by ICPMS using enriched isotope
internal standardisation. Chem. Geo., +-., -++ῌ-,0.
Fisher, R. V. and Schmincke, H. U. (+32.) Pyroclastic
Rocks. Springer -Verlag, Berlin, .1, p.
Galbraith, R. F.(+32+)On statistical models for ﬁssion
track counts. Math. Geol., +-, .1+ῌ.22.
Gleadow, A. J. W. (+32+) Fission-track dating methods :what are the real alternatives? Nucl. Tracks, /, -ῌ+..
Hart, S. R., Blusztajn, J., Dick, H. J. B., Meyer, P. S. andMuehlenbachs, K. (+333) The ﬁngerprint of seawater
circulation in a /**-meter section of ocean crust gabbros.
Geochim. Cosmochim. Acta, 0-, .*/3ῌ.*2*.
~  (+322) I
5 z 56 5 z 56  D  /   + 56
  56¡ +-+ pp
Hurford, A. J. (+33*a) Standardization of ﬁssion track
dating calibration : recommendation by the Fission Track
Working Group of the I.U.G.S. Subcommission of Geochronology. Chem. Geol., 2*, +1+ῌ+12.
Hurford, A. J. (+33*b) International Union of Geological
Sciences Subcommission on Geochronology recommendation for the standardization of ﬁssion track dating
calibration and data reporting. Nucl. Tracks Rad. Meas.,+1, ,--ῌ,-0.
8¦§ S6  (,***) A_`a$ !"#$%&' :^EF`@¨jk. . A_`a$ «¬F­GF +- +ῌ+*
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! (,**.)  EDS "#
*+,"-.#/   '! 3 +* 3ῌ+/?$% (+330) @&)"9 AB'C()D*"-.#-H5 A&./;IJ"KL-H5?$% 3O4 (+330) 5 P6Q *.2,
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&ab cde (,**2) ;AfgHCgH
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tu (,**,) %&5;"x#  yz)*[ ( `a 1/ 3 //-ῌ/1*
&e (+333) }fDEG29gQ hiS +.1 pp
Leake B. E (+312) Nomenclature of amphiboles Amer.
Mineral., 0-, +*,-ῌ+*/,Y _ {jk (+33,) 289l$
U6 pq ,10 p
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 {  ? $  % [\] @ (+33+)     X
 . q ,*  + X³N5 2´µ¶·Kº 20 p
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251

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789 (+33+) :"#"";<=0>+, EPMA EFG +.+ +- +03ῌ+17  89 (+33-) 01 MN EPMA 2 (WDS)  %'R72 89%'S: +11ῌ+23
Pearce, J. A. and Parkinson, I. J. (+33-) Trace element
models for mantle melting : application to volcanic arc
petrogenesis : In Magmatic Processes and Plate Tectonics(Prichard, H. M. et al. eds.), Geol. Soc. Spec. Pub., 10,-1-ῌ.*-.
Sakakibara M. and Isono Y. (+330) Middle Miocene thermal metamorphism due to the inﬁltration of hightemperature ﬂuid in the Sanbagawa metamorphic belt
southwest Japan. Contrib Mineral Petrol, +,/, -.+ῌ-/2.
KoPL Qp (,**2)
R3STqGrs
sVGrs G+, %' .1
+/ῌ,1
<{N (,***) \?]$^_"DEF 89_]|_"DEF%'bAc_}~d %' -, +3ῌ,1Sun, S. S. and McDonough, W. F. (+323) In Magmatism in
the Ocean Basins. Spec. Pub. Geol. Soc. Lond., .,, -+-ῌ-./mn   (+33-) Jo&Z> 2   -2 0-ῌ00
r  (+330) jV]$"x#RsjGr s
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