Alteration of the oceanic crust: Processes and timing
Alteration of the oceanic crust: Processes and timing
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DOI：
10.1016/0012-821x(81)90186-2
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发表时间：
1981-02
影响因子：
5.3
通讯作者：
H. Staudigel;S. Hart;S. H. Richardson
中科院分区：
文献类型：
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作者：
H. Staudigel;S. Hart;S. H. Richardson
87Sr/86Sr 比率、Sr、K、Rb 和 Cs 含量以及从 DSDP 站点 332B、417A、417D 和 418A 深层基底钻探中回收的玄武岩和次生相的岩石学特征表明，洋壳在四个不同阶段发生变化，其特征是形成菱角石、蒙脱石和方解石（分别为阶段 I、II 和 III）。第四阶段代表地壳的最终压实，包括地壳脱水但没有重大化学变化。 Hart 和 Staudigel [11] 以及 Richardson 等人进行的同位素年龄测定。 [13]表明，至少对于大西洋型地壳状态，第一阶段和第二阶段最多持续3米，第三阶段持续超过第一阶段和第二阶段，但可能在明显小于10米的时间内完成。第四阶段寿命较长，可能在 100 米时仍然活跃。第一阶段和第二阶段，即铜解阶段，包括第二层上部 500 m 的海水和玄武岩之间具有地球化学意义的相互作用，并且涉及含有大量玄武岩成分的大量海水。第三阶段解决方案显示出海水与玄武岩相互作用较少的证据，至少在 500 m 的深度；从这些溶液中沉积的方解石的 Sr 同位素比接近海水值；但也具有非常低的 Sr/Ca 比率，表明溶液中存在大量玄武岩 Ca 成分。蒙脱石的形成是海水和玄武岩相互作用的结果。蒙脱石的初始 87 Sr/ 86 Sr 比率代表形成蒙脱石时溶液的Sr同位素组成。此后，可以按照水合能降低的顺序(Cs比Rb更富集，Rb比K更富集)连续地将碱添加到蒙皂石中的层间位置。后来形成的碳酸盐具有非常低的碱浓度，并且87Sr/86Sr比率与同期海水相同。因此，由于整个岩石样品中的碱浓度受到不同蚀变过程的影响，碱浓度本身并不能作为蚀变程度的可靠指标。
87Sr/86Sr ratios, Sr, K, Rb and Cs contents and the petrology of basalts and secondary phases recovered from deep basement drilling at DSDP Sites 332B, 417A, 417D and 418A show that the oceanic crust alters in four distinct stages characterized by formation of palagonite, smectite and calcite (Stages I, II and III, respectively). Stage IV represents the final compaction of the crust, including a dehydration of the crust without major chemical changes. Isotopic age determinations by Hart and Staudigel [11] and Richardson et al. [13], show that, at least for Atlantic-type crustal regimes, Stage I and II last for a maximum of 3 m.y., and Stage III lasts beyond Stage I and II, but is probably completed in significantly less than 10 m.y. Stage IV is long-lived and may still be active at 100 m.y. Stages I and II, the phase of halmyrolysis, include geochemically significant interactions between seawater and basalt for the upper 500 m of layer II and involve volumes of seawater containing a large basaltic component. Stage III solutions show evidence of less seawater-basalt interaction, at least to depths of 500 m; calcites deposited from these solutions have Sr isotopic ratios close to seawater values; but also have very low Sr/Ca ratios indicating a large basalt Ca component in the solutions.Smectite formation is the result of the interaction of seawater and basalt. The initial87Sr/86Sr ratios of smectites represent the Sr isotopic composition of the solution when the smectite is being formed. Thereafter, alkalies may be continuously added to interlayer positions in the smectite in order of decreasing hydration energy (Cs is more enriched than Rb, Rb more than K). The later-formed carbonates have very low alkali concentrations, and87Sr/86Sr ratios identical to contemporaneous seawater. Therefore, since the alkali concentrations in a whole rock sample are affected by different alteration processes, the alkali concentrationsaloneare not reliable indicators of the degree of alteration.