Partitioning of Ba, La, Yb and Y between haplogranitic melts and aqueous solutions: An experimental study
Partitioning of Ba, La, Yb and Y between haplogranitic melts and aqueous solutions: An experimental study
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DOI：
10.1016/j.chemgeo.2010.06.009
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发表时间：
2010-09-01
期刊：
影响因子：
3.9
通讯作者：
Tucoulou, Remi
中科院分区：
文献类型：
--
作者：
Borchert, Manuela;Wilke, Max;Tucoulou, Remi
在750 ~ 950℃、0.2 ~ 1 GPa的条件下，对饱和单长花岗岩熔体和水溶液进行了钡、镧、镱和钇的分配实验，研究了熔体和流体组成、压力和温度的影响。采用不同的实验方法确定了分割系数。一方面进行了淬火实验，另一方面利用热液金刚石砧池和同步辐射x射线荧光k线微量分析直接测定了水溶液中微量元素的含量。由于激发所研究元素的k线所需的高能量，后者需要50键的高激发能。在含氯溶液中，这两种方法的结果一致，而在Ba的情况下，淬火对仅用水的实验结果有显著影响。在无cl实验中，淬火液中镧和钇的微量元素含量甚至低于检测极限，而在类似的原位实验中检测到的浓度很小。这种明显的差异很可能是由于冷却时流体和熔体之间的反反应。各元素的分配数据与温度无关，与压力的关系较小。相反，分配受到启动流体和熔体组成的强烈影响。对于含氯流体，Ba、La、Y和Yb分配系数随氧化铝饱和指数（ASI）的增大而急剧增大。Ba分配系数由ASI为0.8时的0.002增加到ASI为1.07时的0.55。在较高的ASI时，它略微下降到0.2，而ASI与1.3相似。同样，在含氯流体中，它比在水实验中发现的要高一到两个数量级。La和Y的流体熔体分配系数从接近0.8的ASI时的0.002增加到接近1.2 ASI时的0.1。在相同的ASI范围内，Yb分配系数增大到最大值为0.02。即使在高盐度条件下，所有的元素也会分解到熔体中。配分数据的组分依赖性表明，熔体组分和流体组分对微量元素的配位行为和Ba的配位都有较大的影响。流体中的稀土和钇不仅受流体中Cl-存在的控制。相反，这些元素很可能与溶解在流体中的主要熔体组分相互作用。(C) 2010 Elsevier B.V.版权所有
Barium, lanthanum, ytterbium, and yttrium partitioning experiments between fluid-saturated haplogranitic melts and aqueous solutions were conducted at 750 to 950 degrees C and 0.2 to 1 GPa to investigate the effects of melt and fluid composition, pressure, and temperature. Partition coefficients were determined using different experimental methods. On one hand quenched experiments were performed, and on the other hand, trace element contents in the aqueous fluid were determined directly using a hydrothermal diamond-anvil cell and synchrotron radiation X-ray fluorescence microanalysis of K-lines. The latter required a high excitation energy of 50 key due to the high energies necessary to excite the K-lines of the studied elements. The data from these two techniques showed good agreement for chloridic solutions, whereas quenching had a significant effect on results of the experiments with only water in the case of Ba. In Cl-free experiments, lanthanum and yttrium, trace element contents were even below detection limit in the quenched fluids, whereas small concentrations were detected in comparable in-situ experiments. This distinct difference is likely due to back reactions between fluid and melt upon cooling.The partitioning data of all elements show no dependence on the temperature and only small dependence on pressure. In contrast, the partitioning is strongly influenced by the composition of the starting fluid and melt. For chloridic fluids, there was a sharp increase in the Ba, La, Y and Yb partition coefficients with the alumina saturation index (ASI). The Ba partition coefficient increased from 0.002 at an ASI of 0.8 to 0.55 at an ASI of 1.07. At higher ASI, it decreased slightly to 0.2 at an ASI of similar to 1.3. Likewise, it was one to two orders of magnitude higher in chloridic fluids compared to those found in H2O experiments. Fluid-melt partition coefficients of La and Y increased from 0.002 at an ASI of similar to 0.8 to similar to 0.1 at an ASI of 1.2. In the same ASI range, the Yb partition coefficient increased to a maximum value of 0.02. Even at high salinities all elements fractionate into the melt. The compositional dependence of the partitioning data imply that both melt composition and fluid composition have a strong influence on trace element behavior and that complexation of Ba. REE and Y tin the fluid is not only controlled by the presence of Cl- in the fluid. Instead, interaction of these elements with major melt components dissolved in the fluid is very likely. (C) 2010 Elsevier B.V. All rights reserved.