Geochemistry of Major Constituents, Boron and Boron Isotopes in Pore Waters from ODP Site 1202, Okinawa Trough

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 sensitive 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 1.16mM compared to that of 0.42mM in seawater. The δ^(11)B values, however, vary considerably from ~32.7 to 50.9‰ relative to the seawater value of 39.5‰. 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 calcium carbonate, fluid advection through high-porosity permeable sandy horizons, interaction with terrigenous sediments and/or ash alteration may also modify the B and 3δ^(11)B distributions.

並列關鍵字

B isotopes ； Pore waters ； Sedimentary B-desorption ； Okinawa Trough

國際替代計量

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