Sr‐Nd isotope systematics in 14–28 Ma low‐temperature altered mid‐ocean ridge basalt from the Australian Antarctic Discordance, Ocean Drilling Program Leg 187
Sr‐Nd isotope systematics in 14–28 Ma low‐temperature altered mid‐ocean ridge basalt from the Australian Antarctic Discordance, Ocean Drilling Program Leg 187
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DOI：
10.1029/2004gc000802
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发表时间：
2005-01
期刊：
影响因子：
3.7
通讯作者：
Sylwia Królikowska-Ciągło;F. Hauff;K. Hoernle
中科院分区：
文献类型：
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作者：
Sylwia Królikowska-Ciągło;F. Hauff;K. Hoernle
在大洋钻探计划（ODP）第187航次从澳大利亚南极不一致性中回收的14-28 Ma洋中脊玄武岩中，通过对比原始玻璃和相关的蚀变玄武岩，研究了低温蚀变对Rb-Sr和Sm-Nd同位素系统的影响。Nd和Sm在低温蚀变过程中都是不动的，143 Nd/144 Nd即使在严重蚀变的样品中也显示地幔值。相比之下，87 Sr/86 Sr和Rb浓度在海水-岩石相互作用期间增加，这在具有宏观分区蚀变域的单个样品中尤其明显。87 Sr/86 Sr的增加大致与可见的蚀变程度相关，表明在蚀变更严重的样品中海水/岩石比率更高。锶浓度，但是，不系统地增加蚀变程度的增加，最有可能反映在蒙脱石层间网站的锶交换。澳大利亚南极不整合面最上层洋壳的蚀变程度与地壳年龄无关。与年轻和古老的蚀变洋壳的文献数据比较表明，大多数低温蚀变发生在洋壳形成后的几百万年内，这可能反映了由于海脊附近较高的渗透性和增加的流体循环，在其早期历史中通过地壳的流体流量更大。
The effects of low‐temperature alteration on the Rb‐Sr and Sm‐Nd isotope systems were investigated in 14–28 Ma mid‐ocean ridge basalts recovered during Ocean Drilling Program (ODP) Leg 187 from the Australian Antarctic Discordance through comparison of pristine glass and associated variably altered basalts. Both Nd and Sm are immobile during low‐temperature alteration, and 143Nd/144Nd displays mantle values even in heavily altered samples. In contrast, 87Sr/86Sr and Rb concentrations increase during seawater‐rock interaction, which is especially apparent in single samples with macroscopically zoned alteration domains. The increase in 87Sr/86Sr roughly correlates with the visible degree of alteration, indicating a higher seawater/rock ratio in the more altered samples. Sr concentrations, however, do not systematically increase with increasing degree of alteration, most likely reflecting exchange of Sr in smectite interlayer sites. The degree of alteration in the uppermost oceanic crust of the Australian Antarctic Discordance is independent of crustal age. A comparison with literature data for young and old altered oceanic crust suggests that most low‐temperature alteration occurs within a few million years after formation of the oceanic crust, probably reflecting greater fluid flux through the crust during its early history as a result of higher permeability and increased fluid circulation near the ridge.