Altered oceanic crust as an inorganic record of paleoseawater Sr concentration
Altered oceanic crust as an inorganic record of paleoseawater Sr concentration
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DOI：
10.1029/2008gc002341
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发表时间：
2009-04
期刊：
影响因子：
3.7
通讯作者：
L. A. Coogan
中科院分区：
文献类型：
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作者：
L. A. Coogan
海水Sr含量最低值为90-95 Ma，是根据当时被热液蚀变的洋壳席状岩墙复合体的Sr含量和Sr同位素组成，根据简单的质量和热量平衡确定的。当这种方法应用于被现代海水热液蚀变的席状岩墙复合体时，计算出流体Sr的最小含量<3 μg g−1。这大大低于现代海洋Sr含量1.78 μg g−1，支持了该方法提供了地壳形成时海洋Sr含量的最低值的论点。将同样的方法应用于白垩纪特罗多斯和阿曼蛇绿岩中的席状岩墙复合体，得出此时海洋的最小Sr含量分别为27和38 μg g−1。这些值与以前的研究生物矿化的碳酸盐，这表明在这个时候，在海水中较高的Sr/Ca和流体包裹体分析，这表明在这个时候在海洋中较高的钙含量是一致的。海洋中的钙含量一定在流体包裹体分析所建议的范围的上限（≥30 mmol kg−1）。90-95 Ma海水中高Ca和Sr含量至少部分是由于海底热液循环增强，从玄武岩地壳中浸出Sr，因为它与海水87 Sr/86 Sr低的时间相一致。此时Sr含量升高可能影响了分泌SrSO 4骨架的珊瑚虫的进化和/或生物地球化学作用。
The minimum Sr content of seawater at 90–95 Ma is determined from the Sr content and Sr isotopic composition of the sheeted dike complex of oceanic crust that was hydrothermally altered at this time on the basis of simple mass and heat balances. When this approach is applied to sheeted dike complexes that were hydrothermally altered by modern seawater a minimum fluid Sr content of <3 μg g−1 is calculated. This is substantially less than the modern ocean Sr content of ∼7.8 μg g−1 supporting the arguments that the approach provides a robust minimum Sr content of the ocean at the time of crust formation. Applying the same approach to the sheeted dike complexes in the Cretaceous Troodos and Oman ophiolites gives minimum Sr contents for the ocean at this time of 27 and 38 μg g−1, respectively. These values are consistent with previous studies of biomineralized carbonate that suggest higher Sr/Ca in seawater at this time and fluid inclusion analyses that suggest higher Ca contents in the ocean at this time. The Ca content of the ocean must have been at the upper end of the range suggested by fluid inclusion analyses (≥30 mmol kg−1). The high Ca and Sr content of seawater at 90–95 Ma was, at least partially, due to enhanced submarine hydrothermal circulation which leaches Sr from the basaltic crust because it coincides with a time of low seawater 87Sr/86Sr. Elevated Sr contents at this time may have impacted the evolution and/or biogeochemical role of the Acantharians which secrete a SrSO4 skeleton.