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首页> 外文期刊>Geochimica et Cosmochimica Acta: Journal of the Geochemical Society and the Meteoritical Society >Evidence for basaltic Sr in midocean ridge-flank hydrothermal systems and implications for the global oceanic Sr isotope balance
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Evidence for basaltic Sr in midocean ridge-flank hydrothermal systems and implications for the global oceanic Sr isotope balance

机译：中海脊脊热液系统玄武质锶的证据及其对全球海洋锶同位素平衡的影响

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摘要

Previous models and calculations of the global mass balance of Sr in the oceans have shown that the input of unradiogenic basaltic basaltic Sr from on-axis midocean ridge hydrothermal systems is much less than needed to balance the input of radiogenic Sr delivered to the oceans by rivers. The implication is that either the oceans are far from steady state with respect to Sr isotope balance (and that the ~(87)Sr/~(86)Sr ratio of seawater is increasing at unprecedented rates) or that there is a significant missing source of basaltic Sr. It has long been recognized that off-axis hydrothermal fluxes might significantly affect the mass and isotopic balance of Sr and other elements in the oceans, but nearly all previous work has concluded that the ~(87)Sr/~(86)Sr ratio of pore fluids in ridge-flank hydrothermal areas is virtually indistinguishable from the seawater ratio or is dominated by authigenic carbonates. In contrast, we report here the ~(87)Sr/~(86)Sr ratios of warm springs, sediment pore fluids, and basement reservoir fluid with a clear basaltic signature from the eastern flank of the Juan de Fuca ridge (JFR). Fluids venting from Ocean Drilling Program Hole 1026B on the Juan de Fuca east flank have relatively stable Sr isotope and major element composition for the 3 yr following drilling. These results and similar results recently reported by Elderfield et al. (1999) indicate that low-temperature ridge-flank hydrothermal circulation has an important effect on the Sr isotope balance in the oceans. If published values for the other major sources of Sr input to the oceans (rivers and axial hydrothermal flux) are accurate, then the rate of increase of the ~(87)Sr/~(86)Sr ratio in seawater (～0.000054 per million years) can be accommodated if ridge flanks on a global scale deliver fluids to the ocean with Δ(~(87)Sr/~(86)Sr)/heat ratios one third to one half of the ratio found in warm JFR basement fluids. Based on published Sr and O isotope signatures of calcite veins in the uppermost basaltic ocean crust, the average Δ(~(87)Sr/~(86)Sr)/heat ratio of low-temperature fluids is in the range required to balance the oceanic Sr isotope budget. Although the ~(87)Sr/~(86)Sr ratios of the JFR flank fluids in this study overlap with fluid properties inferred from some calcite veins in the upper oceanic crust, the magnitudes of the Δ(~(87)Sr/~(86)Sr)/heat ratios of nearly all of the JFR flank fluids are too large to be representative of the average global flank fluid flux; the same has been argued on the basis of the extremely high implied Mg flux.
机译：先前对海洋中Sr的全球质量平衡的模型和计算表明，轴心中洋脊热液系统的非放射性玄武质玄武岩Sr的输入量远远不足于平衡河流向海洋输送的放射性Sr的输入量。 。这意味着，要么海洋在Sr同位素平衡方面远未达到稳定状态（海水的〜（87）Sr /〜（86）Sr之比正以前所未有的速度增加），要么存在大量缺失源长期以来人们已经认识到，离轴热液通量可能会显着影响海洋中Sr和其他元素的质量和同位素平衡，但几乎所有先前的工作都得出结论，〜（87）Sr /〜（86脊侧面热液区的孔隙流体的锶比实际上与海水比没有区别，或由自生碳酸盐控制。相比之下，我们在这里报告了来自胡安德富卡海岭（JFR）东翼的具有清晰玄武岩特征的暖泉，沉积物孔隙流体和基底储层流体的〜（87）Sr /〜（86）Sr比。从胡安·德·富卡东翼上的海洋钻探计划孔1026B排放的流体在钻探后的3年中具有相对稳定的Sr同位素和主要元素组成。这些结果和Elderfield等人最近报道的类似结果。 （１９９９）指出，低温脊侧面热液循环对海洋中Sr同位素的平衡有重要影响。如果其他输入到海洋的主要Sr来源（河流和轴向热液通量）的公布值是准确的，那么海水中〜（87）Sr /〜（86）Sr比的增加率（〜0.000054 /百万如果全球范围内的脊侧面以Δ（〜（87）Sr /〜（86）Sr）/热比率将温暖的JFR地下流体中的比率的三分之一至一半提供给海洋，则可以容纳10年。根据已公布的玄武岩最上层地壳中方解石脉的Sr和O同位素特征，低温流体的平均Δ（〜（87）Sr /〜（86）Sr）/热比处于平衡平衡所需的范围内。大洋Sr同位素预算。尽管本研究中JFR侧面流体的〜（87）Sr /〜（86）Sr比值与根据大洋地壳中某些方解石脉推断的流体性质重叠，但Δ（〜（87）Sr /〜的大小几乎所有JFR侧面流体的（86）Sr）/热比都太大，无法代表平均整体侧面流体通量;在极高的隐含镁通量的基础上也提出了同样的观点。

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