75 TAO, Vol. 16, No. 1, 75-93, March 2005 Geochemistry of Major Constituents, Boron and Boron Isotopes in Pore Waters from ODP Site 1202, Okinawa Trough Kuo-Fang Huang 1 , Chen-Feng You 1, *, Min-Lin Shen 1 , and Hui-Ling Lin 2 (Manuscript received 16 March 2004, in final form 8 November 2004) ABSTRACT 1 Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan, ROC 2 Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, Kaohsiung,Taiwan, ROC * Corresponding author address: Prof. Chen-Feng You, Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan, ROC;E-mail: cfy20@mail.ncku.edu.tw Forty-one interstitial water samples recovered from ODP Site 1202, Okinawa Trough, were analyzed for major constituents, B and δ 11 B. The geochemical results show that major constituents and boron content varied largely in pore fluids and possibly were affected by sulfate reduction, re- crystallization of biogenic carbonate or silica, ash alteration, and organic matter degradation. Mixing of fluids along high-porosity sandy layers or fracture zones also changes the pore water chemical compositions significantly. The down-core distribution of B and δ 11 B in the pore waters are sensi- tive tracers for assessing fluid migration and water/sediment interaction at various depths. Pore water B content at Site 1202 falls in a range between 0.25 and 1.16 mM compared to that of 0.42 mM in seawater. The δ 11 B values, however, vary considerably from ~32.7 to 50.9 0 00 relative to the seawater value of 39.5 0 00 . The δ 11 B vs. 1/B plot indicates that sedimentary B released from clays is the most important source to pore waters, resulting in elevated B with low δ 11 B. Other processes including precipitation of cal- cium carbonate, fluid advection through high-porosity permeable sandy horizons, interaction with terrigenous sediments and/or ash alteration may also modify the B and δ 11 B distributions. (Key words: B isotopes; Pore waters; Sedimentary B-desorption; Okinawa Trough) 1. INTRODUCTION The chemical concentration and isotopic composition of boron in interstitial waters often provide useful diagnostic tools to assess possible solute migration, geochemical interactions, <Back to Index>