Ocean crust vein mineral deposition: Rb/Sr ages, U-Th-Pb geochemistry, and duration of circulation at DSDP sites 261, 462 and 516
Ocean crust vein mineral deposition: Rb/Sr ages, U-Th-Pb geochemistry, and duration of circulation at DSDP sites 261, 462 and 516
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DOI：
10.1016/0016-7037(86)90224-3
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发表时间：
1986-12
影响因子：
5
通讯作者：
S. Hart;H. Staudigel
中科院分区：
文献类型：
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作者：
S. Hart;H. Staudigel
阳离子交换实验（醋酸铵和阳离子树脂）从三个DSDP孔的绿松石-蒙皂石脉矿物表现出选择性去除常见的Sr相对于Rb和放射性Sr。这种技术增加了Rb/Sr比的2.3至22的因素，而不显着改变矿物的年龄，允许更容易和更精确的定年等脉矿物。该技术测定的年龄（261-121.4 ± 1.6万年; 462 A站为105.1 ± 2.8百万年;研究中心516 F-69.9 ± 2.4百万年）分别为34、54和18百万年。在462 A号地点，年轻的年龄显然与块状岩床/流复合体在洋脊外就位有关。在其他地点，要么热液循环系统比正常地壳持续时间更长（10-15百万年），与玄武岩前体相比，绿松石的U、Pb含量和Pb同位素组成变化不大，Th含量明显降低。因此，青瓷具有异常高的碱/U、Th比值和低的Th/U比值。如果这种绿鳞岩蚀变特征在整个洋壳上有显著的印记，那么对于任何含有古老俯冲再循环洋壳成分的热点岩浆，都将产生非常独特的Pb同位素特征。（绿土，绿松石，沸石，方解石）介于原生玄武岩值和现代海水值之间，表明在海水主导的系统下形成，岩石比为20-200。
Cation exchange experiments (ammonium acetate and cation resin) on celadonite-smectite vein minerals from three DSDP holes demonstrate selective removal of common Sr relative to Rb and radiogenic Sr. This technique increases the Rb/Sr ratio by factors of 2.3 to 22 without significantly altering the age of the minerals, allowing easier and more precise dating of such vein minerals. The ages determined by this technique (site 261—121.4 ±1.6m.y.; site 462A—105.1 ±2.8m.y.; site 516F—69.9 ±2.4m.y.) are 34, 54 and 18 m.y. younger, respectively, than the age of crust formation at the site; in the case of site 462A, the young age is clearly related to off-ridge emplacement of a massive sill/flow complex. At the other sites, either the hydrothermal circulation systems persisted longer than for normal crust (10–15 m.y.), or were reactivated by off-ridge igneous activity.Celadonites show U and Pb contents and Pb isotopic compositions little changed from their basalt precursors, while Th contents are significantly lower. Celadonites thus have unusually high alkali/U,Th ratios and low Th/U ratios. If this celadonite alteration signature is significantly imprinted on oceanic crust as a whole, it will lead to very distinctive Pb isotope signatures for any hot spot magmas which contain a component of aged subducted recycled oceanic crust.Initial Sr isotope ratios of ocean crust vein minerals (smectite, celadonite, zeolite, calcite) are intermediate between primary basalt values and contemporary sea water values and indicate formation under seawaterdominated systems with effective water/rock ratios of 20–200.