Lithium: sources in pore fluids of Peru slope sediments and implications for oceanic fluxes
Lithium: sources in pore fluids of Peru slope sediments and implications for oceanic fluxes
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DOI：
10.1016/0025-3227(91)90012-s
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发表时间：
1991-12
期刊：
影响因子：
2.9
通讯作者：
Jonathan B. Martin;M. Kastner;H. Elderfield
中科院分区：
文献类型：
--
作者：
Jonathan B. Martin;M. Kastner;H. Elderfield
在秘鲁收敛边缘斜坡沉积物的孔隙流体中观察到高Li含量，最高可达1155μM。在大洋钻探计划第683和685点(∼9°S)，Li的浓度深度梯度是第682和688点(∼11°S)的两倍。在沉积物中，最重要的锂来源是铝硅酸盐矿物。生物源蛋白石-A含少量锂，从而稀释了块状沉积物的锂浓度。在9°和11°S的沉积组成和热状态相似，表明北部孔隙流体中观察到的高Li含量有额外的非沉积来源。在S温度为9°时，~(87)Sr/~(86)Sr比值达到最大值0.709958。观测到的孔隙流体中放射性成因的~(87)Sr/~(86)Sr值支持额外Li可能来自与下伏陆壳的交换反应的说法。11°S的高Li含量可能来自中-高温玄武岩蚀变，这些孔隙流体中的非放射性成因87Sr/86Sr比值最低可达0.707218。根据(1)秘鲁和其他几个边缘斜坡沉积物中孔隙流体中Li的浓度，以及(2)对大陆边缘流入海洋的流体通量的近似估计，大陆边缘向海洋提供了约1-3×10~(10)分子Li/a。这一以前没有考虑过的海洋锂的来源，与一些热液和河流锂通量的估计具有相同的量级，并可能对海洋锂同位素收支产生重要影响。对于这个新发现的可能是大的锂来源，水槽是未知的，但它可能是比先前估计的更普遍的大洋基底的低温蚀变，或者是矿物相的埋藏，如自生粘土矿物，或可能富锂的金属氢氧化物。
High Li concentrations, up to a maximum of 1155 μM are observed in the pore fluids of the Peru convergent margin slope sediments. At Ocean Drilling Program Sites 683 and 685 (∼9°S), the Li concentration depth gradients are twice as steep as at Site 682 and 688 (∼11°S). Within the sediments, the most important Li sources are from aluminosilicate minerals. Biogenic opal-A contains little Li and thus dilutes the Li concentration of the bulk sediments. The sediment compositions and the thermal regimes are similar at 9° and 11°S, suggesting there is an additional, non-sedimentary source for the observed high Li concentrations in the northern pore fluids. At 9°S, the87Sr/86Sr ratios reach a maximum value of 0.709958. The observed radiogenic87Sr/86Sr values in the pore fluids support the suggestion that the additional Li may derive from exchange reactions with underlying continental crust. The high concentrations of Li at 11°S may derive from basalt alteration at moderate to high temperatures, as suggested by the non-radiogenic87Sr/86Sr ratios in these pore fluids, which reach a minimum value of 0.707218.Based on (1) Li concentrations in the pore fluids in slope sediments from Peru and several other margins, and (2) an approximate estimate of fluid flux from continental margins into the ocean, continental margins provide an estimated 1 to 3 × 1010moles Li/yr to the ocean. This source of oceanic Li, which has not been considered previously, is of the same order of magnitude as some estimates of hydrothermal and river Li fluxes and may have important consequences for the oceanic Li isotope budget. The sink is unknown for this newly discovered and possibly large Li source, but it may be more pervasive low-temperature alteration of oceanic basement than previously estimated, or burial of mineral phases, such as authigenic clay minerals, or metal oxyhydroxides which may be Li-rich.