(Table 1) Boron analyses from ODP Sites 186-1150 and 186-1151

Interstitial pore waters from Ocean Drilling Program (ODP) Sites 1150 and 1151, both penetrating ca. 1200 m of sub-seafloor sediment from the upper Japan Trench forearc, were analyzed for B concentrations and d11B isotopes. B concentrations cover a wide range from 329 to 3920 µM (0.8-9.3* seawater) and vary isotopically from +20 to +46 per mil (relative to SRM 951). In general, B concentrations increase more or less steadily with depth. At both sites, the B enrichment and isotopic changes seem to be related to a deep fluid influence, possibly coupled with alteration of volcanic products. Silica diagenesis does not affect the B geochemistry of the waters, as is evident from intact diatom tests and high opal-A contents throughout the holes.

The B enrichment is more pronounced at Site 1150 in the seismic portion of the forearc. Here, a large positive anomaly in d11B values is observed, which corresponds with abundant fracturing and two prominent shear zones. At about the same depth range at Site 1151, the d11B values show a negative shift, attesting to an enrichment in 10B in the fluid as a result of B desorption from clay due to burial and tectonic stress. We conclude that B release from clay minerals is the major contributor to pore fluid anomalies, and that fluid flow through permeable out-of-sequence thrust (like the shear zones at Site 1150) may be an efficient mechanism for B backflux from the forearc into the hydrosphere.

采自大洋钻探计划（Ocean Drilling Program, ODP）1150与1151站位的孔隙水，两个站位均钻穿日本海沟弧前上部约1200米的海底以下沉积物，被开展了硼浓度与δ¹¹B同位素组成分析。硼浓度范围为329~3920 μM，相当于海水浓度的0.8~9.3倍，同位素组成介于+20‰至+46‰之间（相对于标准参考物质SRM 951）。总体而言，硼浓度随深度大致呈稳步上升趋势。两个站位的硼富集现象与同位素变化均似乎与深部流体影响相关，可能伴随火山产物的蚀变作用。硅质成岩作用并未对孔隙水的硼地球化学特征产生影响，该结论可从钻孔全程完整的硅藻壳体以及高含量蛋白石-A（opal-A）得到佐证。
在位于弧前地震探测区段的1150站位，硼富集现象更为显著。该站位观测到δ¹¹B值存在显著正异常，该异常与大量断裂发育以及两处显著剪切带相对应。在1151站位的相近深度区间内，δ¹¹B值呈现负偏移，表明流体中¹⁰B发生富集，其成因是埋藏作用与构造应力导致硼从黏土矿物中解吸。本研究得出结论：黏土矿物释硼是孔隙流体异常的主要贡献源，而流体通过渗透性失序逆冲断层（out-of-sequence thrust，如1150站位的剪切带）的运移，或是硼从弧前区反向回流至水圈的高效机制。