The evolution of the Earth surface sulfur reservoir
The evolution of the Earth surface sulfur reservoir
复制标题
DOI：
10.2475/ajs.304.10.839
复制
发表时间：
2004-12-01
影响因子：
2.9
通讯作者：
Canfield, DE
中科院分区：
文献类型：
--
作者：
Canfield, DE
地表硫化物储集层与地幔密切接触。在很长的时间尺度上，与地幔的交换影响了地表储集层的大小，可能还影响了其同位素组成。将硫从地幔输送到地球表面的过程包括火山放气、热液输入和洋壳风化。由于热液硫酸盐还原作用而固定在洋壳中的硫化物，以及沉积硫化物的俯冲作用，代表了硫返回地幔的途径。这些不同途径在影响地表硫库大小方面的重要性取决于海洋和大气化学的特殊性。在海洋含有溶解铁的带状铁形成时期，海底热液活动中的硫化物在海底沉淀，然后俯冲回地幔，因此对表层硫磺储藏量影响很小。在硫化物海底水条件下，大量的硫化物被俯冲到地幔中，这可能发生在中元古代和新元古代的很长一段时间。当海洋被氧化时，硫化物俯冲并不重要，而另一个来源，海洋地壳风化，将硫输送到地球表面。物质平衡模拟表明，地表硫库的规模可能在中元古代早期达到顶峰，新元古代降至最低，并在显生界增加到现在的规模。地幔与地表环境之间的硫交换也会影响地表储集层的同位素组成。模拟结果表明，S-34贫硫通过中元古代俯冲到新元古代晚期，可显着增加地表储集层的平均三角洲(34)S。新元古代保存的同位素记录很不平衡，硫酸盐和硫化物的平均增量(34)S都超过了现代地壳平均水平。这种不平衡是可以解释的，至少部分可以解释，如果地壳平均比现在更富含S-34，就像这里提供的模型所表明的那样。
The surface sulfur reservoir is in intimate contact with the mantle. Over long time scales, exchange with the mantle has influenced the surface reservoir size and possibly its isotopic composition. Processes delivering sulfur to the Earth surface from the mantle include volcanic outgassing, hydrothermal input, and ocean crust weathering. The sulfide fixed in ocean crust as a consequence of hydrothermal sulfate reduction, and subduction of sedimentary sulfides, represent return pathways of sulfur to the mantle. The importance of these different pathways in influencing the size of the surface sulfur reservoir depends on the particulars of ocean and atmosphere chemistry. During times of banded iron formation when the oceans contained dissolved iron, sulfide from submarine hydrothermal activity was precipitated on the seafloor and subsequently subducted back into the mantle and, therefore, had little impact on the surface sulfur reservoir size. With sulfidic ocean bottom water conditions, which may have occurred through long stretches of the Mesoproterozoic and Neoproterozoic, significant amounts of sulfide is subducted into the mantle. When the oceans are oxic, sulfide subduction is unimportant, and an additional source, ocean crust weathering, delivers sulfur to the Earth surface. Thus, under oxic conditions the surface environment accumulates sulfur, and probably has for most of the last 700 million years.Mass balance modeling suggests that the surface sulfur reservoir may have peaked in size in the early Mesoproterozoic, declined to a minimum in the Neoproterozoic, and increased to its present size through the Phanerozoic. The exchange of sulfur between the mantle and the surface environment can also influence the isotopic composition of the surface reservoir. Modeling shows that the subduction of S-34- depleted sulfur through the Mesoproterzoic could have significantly increased the average delta(34)S of the surface reservoir into the late Neoproterozoic. The preserved isotope record through the Neoproterozoic is well out of balance, with the average delta(34)S for sulfate and sulfide both exceeding the modem crustal average. This imbalance could be explained, at least partly, if the crustal average was more S-34-enriched than at present, as the modeling presented here suggests.