Rb and Sr partitioning between haplogranitic melts and aqueous solutions
Rb and Sr partitioning between haplogranitic melts and aqueous solutions
复制标题
DOI：
10.1016/j.gca.2009.10.033
复制
发表时间：
2010-02
影响因子：
5
通讯作者：
M. Borchert;M. Wilke;C. Schmidt;K. Rickers
中科院分区：
文献类型：
--
作者：
M. Borchert;M. Wilke;C. Schmidt;K. Rickers
在750-950℃和0.2-1.4 Gpa条件下，进行了单晶花岗岩熔体和水溶液(水或1.16-3.56M(NaC l+KCl)±HCl)之间的Rb和Sr分配实验，研究了熔体和流体组成、压力和温度对Rb和Sr分配的影响。此外，我们还研究了应用的技术(快速和缓慢淬火，以及现场测定流体中的痕量元素浓度)是否对获得的数据有影响。对于氯化物溶液，不同技术得到的数据有很好的一致性，而冷却时流体与熔体之间的反向反应对水实验结果有很大影响。RB流体-熔体分配系数对熔体组成和温度没有明显的依赖关系。对于氯离子溶液，它是∼0.4，与压力无关。在水的实验中，它会降低一到两个数量级，并随着压力的增加而增加。锶的流融分配系数不受温度的影响。在无氯实验中，它随着压力的增加而略有增加。在氯化流体中，锶的分配系数急剧增加，氧化铝饱和指数从0.003.8时的0.8增加到1.05时的最大值0.3。在较高的ASI时，它略有下降到0.2，ASI为1.6。与在H2O实验中发现的相比，在氯化流体中发现的温度要高出一到两个数量级。与金属铝熔体平衡的非氯化溶液中的Rb/Sr比值随压力增大而增大，而氯化流体中的Rb/Sr比值与压力无关，随流体盐度的升高而减小。得到的流体-熔体分配系数与天然同生流体和熔体包裹体的数据吻合较好。数值模拟表明，尽管残余熔体中的Rb/Sr比对分离结晶程度特别敏感，但在大多数花岗岩类结晶过程中，流体相的出溶和伴生的流体-熔体分配并不是控制残余熔体中Rb和Sr浓度的重要因素。
Rubidium and strontium partitioning experiments between haplogranitic melts and aqueous fluids (water or 1.16–3.56m (NaCl+KCl)±HCl) were conducted at 750–950°C and 0.2–1.4 GPa to investigate the effects of melt and fluid composition, pressure, and temperature. In addition, we studied if the applied technique (rapid and slow quench, and in-situ determination of trace element concentration in the fluid) has a bearing on the obtained data. There is good agreement of the data from different techniques for chloridic solutions, whereas back reactions between fluid and melt upon cooling have a significant effect on results from the experiments with water. The Rb fluid–melt partition coefficient shows no recognizable dependence on melt composition and temperature. For chloridic solutions, it is ∼0.4, independent of pressure. In experiments with water, it is one to two orders of magnitude lower and increases with pressure. The strontium fluid–melt partition coefficient does not depend on temperature. It increases slightly with pressure in Cl free experiments. In chloridic fluids, there is a sharp increase in the Sr partition coefficient with the alumina saturation index (ASI) from 0.003 at an ASI of 0.8 to a maximum of 0.3 at an ASI of 1.05. At higher ASI, it decreases slightly to 0.2 at an ASI of 1.6. It is one to two orders of magnitude higher in chloridic fluids compared to those found in H2O experiments. The Rb/Sr ratio in non-chloridic solutions in equilibrium with metaluminous melts increases with pressure, whereas the Rb/Sr ratio in chloridic fluids is independent of pressure and decreases with fluid salinity. The obtained fluid–melt partition coefficients are in good agreement with data from natural cogenetic fluid and melt inclusions. Numerical modeling shows that although the Rb/Sr ratio in the residual melt is particularly sensitive to the degree of fractional crystallization, exsolution of a fluid phase, and associated fluid–melt partitioning is not a significant factor controlling Rb and Sr concentrations in the residual melt during crystallization of most granitoids.