,, + 1,,, +, Abstract

J Hot Spring Sci /3,3/ +3,*+* +, + +,, + 1,,, +, Geochemical Features and Genetic Process of Hotspring Waters Discharged from Deep Hotspring Wells in the Miyazaki Plain, Kyushu Island, Japan : Diagenetic Dehydrated Fluid as a Source Fluid of Hotspring Water +, + Shinji O HSAWA, Kazuhiro A MITA, Makoto Y AMADA, + Taketoshi MISHIMA and Kohei KAZAHAYA For identification of diagenetic dehydrated fluids as source fluids of hotspring water, we conducted chemical and isotopic analyses of waters and accompanied gases collected from hotspring wells in the Miyazaki plain in the forearc region of Kyushu Island, Japan Interpretation of systematical relationships appearing among chemical and isotope data, and geochemical estimation of hydrothermal temperatures of hot spring waters revealed two hotspring water source fluids in existing groundwaters of meteoric origin : squeezed pore water from marine sediments, and hydrothermal fluid of unidentified generation stored in sedimentary rocks Geochemical thermodynamic evaluation of the unidentified fluids using representative hot spring waters indicated a dehydrated interlayer water from clay mineral (smectite) at around +* Furthermore, comparison to + +,, Abstract 21 *3* Beppu Geothermal Research Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University, Noguchibaru, Beppu, Oita 21 *3*, Japan *+* 2/*, + + Department of Earth Science and Technology, Faculty of Engineering and Resource Science, Akita University, + + Tegatagakuencho, Akita *+* 2/*,, Japan */ 2/01 + + + Crustal fluid research group, Institute of Geology and Geoinformation, AIST, Higashi + + +, Central 1, Tsukuba, Ibaraki */ 2/01, Japan 295

results of a geochemical analysis of accompanied hydrocarbon gases and a geological consideration of genetic process of the source fluids of the hot spring waters implied their origin at di# erent stages during the burial diagenesis of marine sediments An important result obtained from comparisons of the chemical and isotopic data on some geochemical systematic diagrams is that hydrothermal fluid of hot spring waters in the Oita plain, also located in the forearc region of Kyushu, apparently have a di# erent origin and genetical process from hydrothermal fluids of the Miyazaki plain Key words : Miyazaki plain, hot spring well, hotspring water, geochemical feature, origin, diagenetic dehydrated fluid, + +*, : + +31 +32, +31 ; Takamatsu et al, +320 Giggenbach et al, +33 296

/3,*+* Static geothermal system Conductive geothermal system formation water connate water Frape and Fritz, +32 ; Motyka et al, +323 ; Pauwels et al, +33 ; Davisson et al, +33 ; Lodemann et al, +331 ; Worden et al, +333 ; Kloppmann et al,,**, +32+ ; +32/ ; +321 ; +33+ +330 + d C,**+ + DIC d C DIC CO NaCl, HCO, DIC DIC dd vs d O,**/,**3,**, kbar,**/,,+ 0* 297

km Fig + /* +332 +33* CH +33 +33 Fig + Fig + Fig + Locations of investigated hot spring wells ( ) and sampling sites of river waters ( ) with surface distribution of concerned geologic bodies in this study : Miyazaki group and Shimanto complex, and the Quaternary volcanic front (dashdotted line) and some active volcanoes ( ) 298

/3,*+* Table + Brief summary of hot spring wells Well Depth of Depth of screen Discharge Discharge rate Discharge SiO,* No well (m) head (m) form (L/min)* temp ( ) (mg/l) +, +1** +,** * pumping pumping self,/* /3 04 /4 +/41,24,,4 /,4, 2* +34 / +*** 11 self 0,/ /4* 3/43 0 1 2** +** 1++ 2*/ 2* 4 4 4/ 2 1/* 0* self, /4+ +43 3 +** ++/* pumping +* 24/*,34/ +* ++ +, ** +0** 2** self pumping ** +*,,4, nm /*4 41 43 114/ + +,** 342 04 + +*** /4*,04/ +/ +0 +** +/** pumping /* +0 4** 14 234, +1 +,** +04+ ** 12 self,41* +34 Remarks) * Data referred from the public data tables (Onsenbunsekisho), ** The measuring site is far from the well nm : not measured Table + 31* m +*** m +1** m No * m No No +0 No /, No 0, No ++, No +, +*** m, 2** m, +0** m, 2** m No +0 No + +1*+ 1 m +33*,, ph Fig + No / No 0 299

Li B HCO Na, K, Mg, Ca, Cl, SO Li B H +33/ HCO ph + dd d O The stable isotope Laboratory, GNS Science Limited dd d O +* * + No ++ No +/ Cl JIS,*+ CH C H CO, N, O CH N *+ O CO **+ CH + * **+ CH, CH, CO d C *, 2,,,,,,, 0, Table, Table Table, Analytical results of collected hot spring waters and estimated underground temperatures of hot spring waters Well Na K Mg Ca Li Cl HCO SO B dd d O q NaKCa* ph No (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) ( ) ( ) ( ) +, 14 142 3,*,* 14 +/43 +42,+4 300 241,4* *401 3/* 03* 3 1 nd 42 24 +41 +,4/,34* *4* 4*+ 32 2 14 12* 24, +4,+ 43 10/*,*4, +43,+41 4** +** 240,+1* 34+ nd *4 4 +1,*,11* nd,,4, *41 +43* +*/ / 0 143 24+,3/*,*0*,41 +*42 34,4*,14, ++4,4/ +4+ 2/*,,** ++0* +/3* nd nd +/* 1041 +141,,4 *41 +41, +*3 3, 1 2 141 24 * +/+*,343,42 *4* nd ++ /40,4+ *401 01* +//* 01 +,** nd nd +/*,*40 +*41 +40,431 4/* 31 0* 3 24/ +0* 43 nd 142 +4+ +13* +,** nd *41 +4 4, 00 +* 142 30/*,4+ 3/41,/ +4, +0** +/0 nd 43 4* *43/ 02 ++ na na na na na na,* na na na,/4,4/ +, + 14 14/ * /* 0/4*,242 ++4/ +4* 0341,34* /4*,42 /3* +1+*,3,*,*,* nd nd +33 242 +4/,/4 +43,,4, +3 +,1 + 143 3* 140 343 1,4* *41 1*1, nd 34 241 /431 +* +/ na na na na na na /*2* na na na 342 40 +0 +1 14/ 14 3/* +*/**,14 2+4/ 4* +/, +40 /+ 04+ +4/,* /** 0+1*,, +// nd,20 ++4+ 04, 04 4* +43 +, +*0 14 //,*,4 04/, 4, 2***, nd 40 +/4 41 33 Remarks) Sampling date ; Nos + : Feb ++,,**, Nos / ++ : Feb +,,,**, Nos +, +0 : Feb +,,**, No +1 : Feb +/,,**, No : Nov +,,**1, nd : not detected, na : not analyzed, * : derived from the NaKCa geochemical thermometer mentioned in Nicholson ( +33) 300

/3,*+* Table Results of isotopic and chemical analyses of surface waters collected from rivers No a b c d Name of river Hitotsuse Hirowatari Kiyotake Ohyodo dd d O Cl ( ) ( ) (mg/l) 042 141 +42 +4* 04/3 /42 +4+ 040*,34, 41 043 ++40 Remarks) Sampling date ; No a : Feb ++,,**, Nos b and c : Feb +,,**, No d : Feb +,,** Table Results of chemical and isotopic analyses of gases accompanied with hot spring waters Well CO N O CH C H C H + d C CO + d C CH + d C C H No ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ),,,, 0 2,, 0 / +4*+ 24, *423 2342 *4*, nd /4+ /4,,04 0 +4+0 4 *4,3 34*3 *4*, nd 04 24,41 Remarks) Sampling date ; Nov +,,**1 for chemical composition and carbon isotopes, nd : not detected + Fig, No + No + Na, K SO Cl HCO HCO Cl 32 Na NaCl NaCl, HCO Fig HCO Cl TDS Fig + +313 NaCl No +* No +1 HCO NaCl, HCO HCO Cl + HCO Cl TDS No +, No,, No, No 1, No No +* No +1 301

Fig, Major cation and anion compositions of collected hot spring waters in Fig + with modern seawater Fig Relation between TDS (total dissolved substance) and HCO /Cl ratio of hot spring waters with brine waters at Sadowara area and modern seawater For the location of Sadowara area, blackstar ( ) in Fig + 302

/3,*+*, dd vs d O Fig HCO Cl TDS No +, No,, No, No 1, No No +* No +1 HCO NaCl, HCO HCO Cl TDS No +, No,, No, No 1, No No, No /, No 0, No 2, No 3, No ++, No +,, No +, No +, No +/, No +0 d O dd dd vs Cl Fig dd vs d O No, No 1 dd vs Cl No +* No +1 HCO Cl TDS No +, No,, No, No 1, No d O dd Fig Relationships of dd vs d O and dd vs Cl of hot spring waters in Miyazaki with modern seawater, river waters in the study area, ranges of pore waters of marine sediments and andesitic volcanic steam For data points shown by open diamond (Nos +,,,, 1 and ), see text or refer Fig Ranges circled by dotted lines indicate formation waters shown by Kato and Kajiwara ( +320) 303

B Li Cl Soluble group species, Cl Giggenbach and Goguel, +323 BCl +333 BCl Fig / BCl dd BCl Cl +** mgl BCl *+ *+ **+ **+ dd vs BCl dd vs d O dd vs Cl HCO Cl TDS Cl No +, No,, No, No 1, No, Fig 0 BLiCl No +* No +1 Cl Fig / Relation between dd and B/Cl ratio of hot spring waters with modern seawater Discrimination for origins of hot spring waters by B/Cl ratio shown on Yaxis is done by means of an authorized geochemical method described in Inuyama et al ( +333) For data points shown by open diamond (Nos +,,,, 1 and ), see text or refer Figs and 304

/3,*+* Fig 0 Relative BLiCl compositions of hot spring waters with modern seawater These elements are classified into Soluble group species recognized in Geothermal geochemistry (eg Nicholson, +33 ) For data points shown by open diamond (Nos +,,,, 1 and ), see text or refer Figs, and / No /, No 0, No 2, No 3, No +,, No +, No +, No +0 No B Fig / No +, No,, No 1 B Cl No No Li No Li 305

Nicholson, +33 NaKCa Table, dd Fig 1 Fig 1 Fig 1 Relation between dd and the NaKCa geochemical temperature of whole the hot spring waters (upper) and systematical relationships between them of selected hot spring waters (Nos /, 0, 2, 3, +0 and Nos +,, +, + ) by previous data analyses in this study (lower) For the data analyses and the selection, see text 306

/3,*+* dd Fig 1 Fig +, +312 ; +32+ No +,, No +, No + No /, No 0, No 2, No 3, No +0 dd +** +* No +, No +0 + +, O D B Mud volcano Geopressured hydrothermal system, Smectite Dia et al, +333 ; You et al,,** ; Xu et al,,**0 ;,**3 ;,**3 0* +/* Illite Dählmann and De Lange,,** Fig 2 O D,**3 Brown et al,,**+ ; Dählmann and De Lange,,** ; Haese et al,,**0 ; You et al,,** Dählmann and De Lange,** Clay membrane ion filtration, Ash particle alteration, Bigogenic opal recrystallization, Anaerobic methane oxidation 307

Fig 2 A modified schematic crosssection of smectite and illite showing the crystallographic sites that hold Li, B and H O originally illustrated by Williams and Hervig (,**/), Cl O D Cl + +** 0* +/* Stability diagram, No +, No +0 K Mg Na H, Nasmectite + K */2 Mg +13 OH, illite *,3 quartz *10 Na *20 H O, NaKCa Aoyagi and Kazama, +32* ; +321 ; +33+ +** +33+ ; Kyser and Hiatt,,** NaKCa Fig 3 No +, NaKCa +3 +, No +0 NaKCa +, ++ +*, 308

/3,*+* Fig 3 Comparison between estimated hydrothermal temperatures by various geochemical thermometers using chemical data of hot spring waters (Nos +, and +0) closely related to a source hydrothermal fluid inferred to be derived from dehydrated interlayer water from clay mineral (smectite) +** +* +* Stability diagram Fig +* mixedlayer clay mineral No +, No +0 +* BLiCl B Fig 2 309

Fig +* An evaluation of hot spring waters (Nos +, and +0) closely related to a source hydrothermal fluid inferred to be derived from dehydrated interlayer water from clay mineral (smectite) on a stability diagram of smectite and illite at the estimated hydrothermal temperature : +* and stability boundaries of smectite and illite at,** and ** B BOH HO, Li K Cl BLiCl B, No / No 0 Table + Bernard CH d C CH C H C H, 0 2 Fig ++ Igari and Sakata, +323 ; +330 Bernard No / No 0 Thermo genic Microbial Table + CO d C CH, No / No 0 Fig ++ Microbial 310

/3,*+* + Fig ++ Relation between d C of CH and CH /(C, H0CH 2) ratio of accompanied gases of hot spring waters expressed on the Bernard plot, which is generally used for discrimination of origin of CH and interpretation of undergoing physical and chemical processes of hydrocarbon gases Data of Sadowara, Shintomi and Nichinan are cited from Igari and Sakata ( +323 ) and Igari ( +330) CH CH CH Claypool and Kvenvolden, +32 ; Judd,,**, squeezed pore water from marine sediments CH dehydrated interlayer water from clay mineral : smectite CH, re lease of water from pores and hydrous minerals ; Kyser and Hiatt,,** Fig +,, No +* No +1 No +, No +0 NaKCa CH 311

Fig +, Estimated hydrothermal temperatures of hot spring waters of Nos +, and +0 ( ) and hot spring waters of Nos +* and +1 ( ) closely related to source fluids inferred to be derived from dehydrated interlayer water from clay mineral (smectite) and squeezed pore water of marine sediments, respectively, roughly connected to temperature ranges of smectiteillite transformation and CH generation, and average changes with burial depth on porosity and geothermal temperature in the Neogene argillaceous sediments of Japan with presentday geothermal gradients at Miyazaki and Nichinan areas CH CH CH No +, No +0 No +* No +1 02 +*0 CH /* 0* No +* No +1 ** m, +1** m ; Table + +32+,/ 0,, Fig dd vs d O dd vs Cl +320 312

/3,*+* formation water,**/ O D + d C B Li dd Fig + dd vs d O D,**/,**3 dd Fig + dd vs Cl Cl / + Cl dd d O Fig + Comparison between water isotope compositions ( dd vs d O) of hot spring waters in Miyazaki (in this study) and Oita plain (by Amita et al,,**/) with modern seawater and ranges of source fluids of hot spring waters recognized in this study and metamorphic fluids 313

Fig + Comparison between hot spring waters in Miyazaki (in this study) and Oita plain (by Amita et al,,**/) on the correlation diagram of dd vs Cl with modern seawater and ranges of source fluids of hot spring waters recognized in this study Cl Cl Cl BLiCl Fig +/ Fig 0 BLiCl,**/ BLi ClB,,**/ Oita* Oita* Oita+, Fig + dd vs Cl Fig + BLi LiB LiB dd Li BLiCl,**3 ; Sengen et al, in prep BLi,**/ BLi 314

/3,*+* Fig +/ Relative BLiCl compositions of hot spring waters in the Oita plain (by Amita et al,,**/) compared with modern seawater and ranges of source fluids of hot spring waters in the Miyazaki plain The attached figure shows relation between dd and Li/B ratio for hot spring waters in Oita having relatively high B and Li contents Grayish thick long allow presumably shows a compositional change path on generated fluids from diagenesis to metamorphism,**3 Oita*+ Oita*, +302 +33, /, : +* +330 ;,** ;,**/ ;,**/ ;,**1 ;,**3 ;,**3 315

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