Origin of Arima-Type Deep thermal Water from Hot Spring Wells in Oita Plain, eastern Kyushu, Japan

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1 64 * : * +1 0,. +1 3, Origin of Arima-Type Deep thermal Water from Hot Spring Wells in Oita Plain, eastern Kyushu, Japan Kazuhiro AMITA, Shinji OHSAWA, Jianguo DU* and Makoto YAMADA Beppu Geothermal Research Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University (* Present a$liation : Institute of Earthquake Prediction, China Seismological Bureau) Abstract Chemical and isotopic compositions : concentrations of major and trace dissolved constituents, ddandd +2 Oofwater and d +- Cofdissolved inorganic carbon (DIC), of hot and cold waters of Na-Cl, HCO - type collected from deep s and natural s in the Oita plain, eastern Kyushu, Japan are reported and the origins of the waters are discussed. Most dd andd +2 Odata of the water samples are plotted near the local meteoric water line in the diagram of d +2 O versus dd, but two of them scatter far away the line and near the point of Arima-type deep thermal water. The two water samples have very high Cl concentration (,.,*** mg/l and +3,*** mg/l) and extremely high dd andd +2 O values (,,.,,,1.+ and,.1, +.3, respectively). Such high values in water isotope composition imply that these saline waters are originated from andesitic magmatic steam or metamorphic water. Concentrations and d +- Cvalues of DIC in the two heavy waters are,.,*** mg/l, +3,*** mg/l and -.2, -.,, respectively. Reciprocals of concentrations and d +- Cvalues of DIC of all the hot and cold water samples including the two heavy water samples display a linear relationship, and, consequently, DIC in the hot and cold waters is a gradual mixture of soil CO, and deep-originated CO, (magmatic or mantle-derived), and the greater part of the DIC in the heavy waters consists of the deep-originated CO,. Therefore, it is appropriate that the saline thermal waters having high dd andd +2 Owith high-d +- CCO, found in the Oita plain are derived from the Earth s interior. dd values of the hot and cold water samples are in direct proportion to respective concentrations of Li and B. These relations also express that the formation of the hot and cold waters in the Oita plain can be explained by the mixture model of two end-members ; one is groundwater of meteoric origin having low dd and low Li and B concentrations, and the other is deep-originated thermal water having high dd and high Li and B concentrations. The latter is likely to

2 //,**/ 65 be the fluid devolatilized from the subducting oceanic plate as pieced together from the various accounts, and, furthermore, its formation should have no relation to magma generation, because the Oita plain is located in fore-arc region. In addition, good liner relations between Li and Cl concentrations and between B and Cl concentrations of the hot and cold water samples suggest that Cl as a major constituent of the deep-originated thermal water of Na-Cl, HCO - type in the Oita plain also comes together with the devolatilized fluid of the slab. Key words : Oita plain, Arima-type deep thermal water, Isotope, slab-derived fluid : + Na-Cl Na-Cl - Na-Cl dd d +2 O dd +33+ ; +330, /* gl dd -* d +2 O 2.* +32+ He - He. He 3.,+* * 0 He Wakita et al., +321,*** a;,*** b 0*/* km

3 66, km * 0** m2** m +32/ -*// gl CO, +32+ d +- C,**+ CO, CO, Na-Cl, HCO - CO, Na-Cl, HCO - NEDO He. He 2.1+* 0 2.*+* 0 -,**- ++ +, 0**2** m +333 mgl

//,**/ 67 Fig. + Map showing locations of water sampling in the Oita plain. Closed squares, gray hatched crosses and open circles show sampling points at hot (), cold and, respectively. Fig. + ph Na, K, Ca, Mg, NH.

4 //,**/ 67 Fig. + Map showing locations of water sampling in the Oita plain. Closed squares, gray hatched crosses and open circles show sampling points at hot (), cold and, respectively. Fig. + ph Na, K, Ca, Mg, NH.,Cl,SO. Li B H DIC : dissolved inorganic carbonco,aqhco, - CO - H, SO. CO,aq DIC +- C +, C Sr OH, SrCO - CO,, H + H +2 O +0 O H, CO, Rafter Stable Isotope Laboratory, Institute of Geological and Nuclear Sciences dd, d +2 O, d +- C; Na, K, Ca, Mg, NH.,Cl,SO.,Li,B Table + DIC CO, d d +2 d +- C DIC Table,..+ dd-d +2 O Fig., MWL : meteoric water line andesitic magmatic steam ; Giggenbach, +33,

5 68 Table + Concentrations of major constituents and trace elements (Li and B) of water samples collected No. Sampling date Type Depth of (m) Temp. () ph Na NH. K Oita-*+ Oita-*, Oita-*- Oita-*. Oita-*/ Oita-*0 Oita-*1 Oita-*2 Oita-*3 Oita-+* Oita-++ Oita-+, Nov.,0,,**- Nov.,0,,**- Nov.,2,,**- Nov.,2,,**- Nov.,2,,**- Nov.,2,,**- Dec.,,,**- Dec.,,,**- Dec.,,,**- Dec.,,,**- Dec. -,,**- Dec. -,,**- 2** 2** 1+* /1/ 2** 3** 2** +04/ +/ ,41 -.4* / , 24-24* / * +/ /* ,// -1,+ +,,+- -1*, +/2+- +/1/ 0,4* /042-24/ -, , //42 204*,21 3* ,4, ,/ 1,4-,+/ 012,..,-+ +/4* OitaR-*+ OitaR-*, OitaR-*- OitaR-*. OitaR-*/ OitaR-*0 Nov.,0,,**- Dec.,,,**- Dec.,,,**- Dec.,,,**- Dec. -,,**- Dec. -,,** , ,40 +,4. 14/ * / +,4+ 04, 041 * *4/ +41,4. *41 *4/ [Rem] : not detected metamorphic water +311 NEDO, +323, Oita-*3 Oita-++, Oita-*3 Oita-++ +2,0** mgl,,-,3** mgl dd,1.+,,., d +2 O +.3,.1, Cl /*,*** mgl, dd -* d +2 O2 : +33+ Cl +2,2** mgl, dd/-.- d +2 O-.1 ;Takamatsu et al., +320 Cl +.,2** mgl, dd.,.3 d +2 O,.* ;Matsubaya et al., +31- MWL : dd2d +2 O+* d +2 O

6 //,**/ 69 from s (hot s), cold s and s in the Oita plain. Mg Ca Cl NO - SO. Li B (mg/l),4* +/- +3/ /, , +3/ 12. +,/ +*., -/4, 3+4/ +1/4. -14* * +,/ / 1140,2,4* /,42,,20,-0*,0-. +2*1-3,,*+2.,.-.-/ ,+-/,-212,01/ +*4. 34* *4, * / 14, +04/ /+42, / *4+, , ,.+4, 1/4+ +./ /*43,12 /4.,* * /40.43 / /4/ , /4*.40, , ,4/ -41,43 24* 041 /4/ * d +2 O. 3,-.* mgl ;,**+., Table, DIC d +- C DIC Fig /,**+,,**+ DIC

7 70 Table, dd and d +2 O of water, and d +- C and concentration of dissolved inorganic carbon (DIC) of water samples from s (hot s), cold, and in the Oita plain. No. Type dd H,O d +2 O H,O d +- C DIC DIC (mg/l) () Oita-*+ Oita-*, Oita-*- Oita-*. Oita-*/ Oita-*0 Oita-*1 Oita-*2 Oita-*3 Oita-+* Oita-++ Oita-+, /-43 /-4- /14* /341.14/.14+, ,,4, /34. 04, / 14-24/ 34* /42.4, +43 /4-, ,43 +.4/ +-4/ / 14/ /4* -4, * +*.* ++2 -,*,-.* 22, -*,*,22* -12* +-+*.-,*,**.242 /*40 /+42 /-4* /*4..-4/ OitaR-*+ OitaR-*, OitaR-*- OitaR-*. OitaR-*/ OitaR-* , [Rem] : not analyzed CO, Fig. - NEDO, +323 mixing line,**+ d +- C DIC DIC DIC, CO, deep-originated thermal water CO, normal groundwater.. + Oita-*3 Oita-++ Oita-*3 Oita-++ DIC -,12* mgl,.,-,* mgl Na-Cl Na-Cl, HCO - d +- C DIC Oita-*3 Oita-++ CO, *.+

8 //,**/ 71 Fig., dd-d +2 O plots of water samples from hot and cold s (closed circles) and from s (gray squares) collected in this study. Open circles show hot water samples collected and measured by NEDO (+323). Open circle with dot in center indicates the Arima-type deep thermal water (Sakai and Matsubatya, +31.). Dashed line box shows the range of dd and d +2 O values of andesitic magmatic steam (Giggenbach, +33,). Bold line box shows the range of d-values of metamorphic water (Sasaki, +311). Solid straight line labeled with MWL expresses meteoric water line : dd2 d +2 O+*. *.3 ;,*** -/ CO, /0 ; +330 CO, NEDO, +323 CO, dd +33/ ;,**- +331

9 72 Fig. - Plots of d +- C versus reciprocal of concentration of dissolved inorganic carbon (DIC). Closed circles show the obtained data in this study and open diamonds are cited from Ohsawa (,**+). Two closed asterisks show saline waters found in the Oita plain which are classified into the Arima-type deep thermal water. Solid straight line is the regression line calculated using data obtained by NEDO by Ohsawa (,**+) and represents the mixing relation between deep-originated CO, (magmatic or mantle origins) and soil CO,. For detail, see text.,1 CO, NaCl +33. ; Touret,,**+ NaCl CO, N, NaCl Scambelluri and Philippot,,**+ Na-Cl, HCO - Fluid-mobile elements Li, Rb, Cs B, Pb Li B Scambelluri et al.,,**. ; Savov et al.,,**/ ;Zack et al.,,**- ;Moriguti et al.,,**. NEDO, +323

10 //,**/ 73 Fig.. Plots of dd versus Li concentration and dd versus B concentration of the hot and cold waters collected from the Oita plain (left side) and Arima area (right side). Solid lines are regression lines. Closed circle show present sea water and open triangles show brines accompanied by natural gas from Miyazaki and Chiba areas. Closed asterisks are saline waters found in the Oita plain in this study. Thick allow indicates the estimated dd value of devolatilized fluid from subducting oceanic plate (Kazahaya, +331). For detail, see text. Li B dd Fig.. Li dd B dd R,,, dd Li B dd Li B dd //.-/- ; Table, Fig.. Oita-*3 Oita-++ dd,1 ; +331 :Fig.. dd Li, B Fig.. Masuda et al. +32/

11 74 Fig. / Plots of Li versus Cl concentrations and B versus Cl concentrations of the hot and cold waters collected from the Oita plain (left side) and Arima area (right side). Closed asterisks are saline waters found in the Oita plain in this study. Fig.. ; +33+ ; LiB Cl Na-Cl, HCO - d, d +- C DIC, Li B Cl

12 //,**/ 75 NEDO, +323 Masuda et al., +32/ Li Cl B Cl Fig. / Fig. /.. - Li-Cl B-Cl -, - Philippot et al Cl Cl Li B / +/,*** mgl DIC d +- C DIC CO, CO,, Li, B dd dd Li dd B dd Li B dd Li B,1 Li, B Cl Li B Li, B, Cl - Cl Oita-*3 /1/ m, Oita-++ 3** m

13 76 Rafter Stable Isotope Laboratory, Institute of Geological and Nuclear Sciences +33+ :.,,,-.. Giggenbach, W.F. (+33,) : Isotopic shifts in waters from geothermal and volcanic system along convergent plate boundaries and their origin, Earth Planet. Sci. Lett., ++-,.3//+*.,*** : /* 203-.,**- : -3,,**+ : /, /30, :,1 +*/ / : -0 ++,. Masuda, H., Sakai, H., Chiba, H. and Tsurumaki, M. (+32/) : Geochemical Characteristics of Na-Ca-Cl-HCO - type waters in Arima and its vicinity in the western Kinki district, Japan, Geochemical Journal, +3, +.3+0,. Matsubaya, O., Sakai, H., Kusachi, I. and Satake, H. (+31-) : Hydrogen and oxygen isotopic ratios and major element chemistry of Japanese thermal water systems, Geochemical Hournal, 1, +,-+/ : -+.1/ : :,/0 +33/ : +,-+.0 Moriguti, T., Shibata, T. and Nakamura, E. (,**.) : Lithium, boron and lead isotope and trace element systematics of Quaternary basaltic volcanic rocks in northeastern Japan : mineralogical controls on slab-derived fluid composition, Chemical Geology,,+,, 2++**.

14 //,**/ : -1-2/*. NEDO +323 : -,-0.,*** a :.3,*1,+0.,*** b : /* : -,.-//.,**+ : /,,+,0. Philippot, P., Agrinier, P. and Scambelluri, M. (+332) Chlorine cycling during subduction of altered crust, Earth Planet. Sci. Lett., +0+, : Sano, Y. and Wakita, H. (+32/) :Geographical distribution of - He/. He ratios in Japan : implications for arc tectonics and incipient magmatism, J. Geophys. Res., 3*, 21, : 113/ Savov, I.P., Guggino, S., Ryan, J.G., Fryer, P. and Mottl, M. J. (,**/) : Geochemistry of Serpentinite muds and metamorphic rocks from the Mariana forearc, ODP sites +,** and , south Chamorro and Conical seamounts, Proceedings of the Ocean Drilling Program, Scientific Results Volume +3/. Scambelluri, M., Müntener, O., Ottolini, L., Pettke, T.T. and Vannucci, R. (,**.) : The fate of B, Cl and Li in the subducted oceanic mantle and in the antigorite breakdown fluids, Earth and Planetary Science Letters,,,,,,+1,-.. Scambelluri, M.and Philippot, P. (,**+) :Deep fluids in subduction zones, Lithos, //,,+-,,1. Takamatsu, N., Imahashi, M., Kamimura, K. and Tsutsumi, M. (+320) : Geochemical implication of the lithium content of saline waters in Japan.,Geochemical Journal,,*, +.-+/+. +33/ : +20 Touret, J.L.R. (,**+) :Fluids in metamorphic rocks, Lithos, //, +,/ : BrCl Wakita, H., Sano, Y. and Mizoue, M. (+321) :High - He emanation and seismic swarms observed in a nonvolcanic, forearc region, Journal of Geophysical Research, 3,, +,/-3+,/.0. Zack, T., Tomascak, P.B., Rudnick, R.L., Dalpe, C. and McDonough, W.F. (,**-) : Extremely light Li in orogenic eclogites : The role of isotope fractionation during dehydration in subducted oceanic crust, Earth and Planetary Science Letters,,*2,,13,3*.

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