An Experimental Study of Chlorine Incorporation In Amphibole Synthesized Along the Pargasite–Ferro-Pargasite Join
An Experimental Study of Chlorine Incorporation In Amphibole Synthesized Along the Pargasite–Ferro-Pargasite Join
复制标题
氯掺入角闪石中沿帕格石-铁-帕格石连接合成的实验研究
DOI：
10.3749/canmin.1600082
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发表时间：
2017
影响因子：
0.9
通讯作者：
D. Jenkins
中科院分区：
文献类型：
--
作者：
Benjamin P. Campanaro;D. Jenkins
摘要了解钙角闪石和环境流体之间的氯分配，可以用来推断在广泛的地质过程，如高级变质作用，沉积的经济矿物，氯交代作用，海水-海洋地壳相互作用的流体中的氯含量。在钙闪石中观察到的最常见的相关性之一是氯浓度随Fe 2+ /（Fe 2+ + Mg）（= Fe#）的增加而增加。为了量化这种依赖性，在浓度从1摩尔（m）NaCl到岩盐饱和度的NaCl盐水中，合成了沿着钠钙石-铁钠钙石[NaCa 2（Mg 4Al）（Al 2Si 6）O22（Cl，OH）2 -NaCa 2（Fe 4Al）（Al 2Si 6）O22（Cl，OH）2 ]连接的具有预期组成的角闪石。合成温度为700-950 °C，压力为0.2- 0.5GPa，氧逸度（fO 2）为46-576 h。当Fe 3+ /（Fe 2+ + Fe 3+）比值为0.18时，角闪石的组成随Fe#的增加而变化。最常见的附加相是斜长石和富钙单斜辉石，在某些合成中含有少量的davyne。在任何给定的整体组成下，角闪石的Cl含量随着盐水浓度的增加而增加，在NaCl的摩尔分数约为0.1-0.2（X NaCl，或5-15 m NaCl）的盐水中达到平台。在盐水中合成的角闪石低于岩盐饱和度表现出相当线性的增加，从基本上0.0至0.11原子每式单元（apfu），随着铁含量的增加，氯含量。在盐水以上的岩盐饱和度的合成显示出一个明显的跳跃氯含量高达0.14-0.30 apfu的两个最富铁的散装组合物。用等NaCl浓度等值线拟合了所有数据，并对在1 mNaCl卤水中合成的角闪石Cl/OH比值与卤水中H2O/HCl活度比值的关系进行了热化学分析。比较合成角闪石与天然角闪石的Cl含量表明，即使是最高的Cl含量，也仅为某些地区角闪石中Cl含量的20%左右。这项研究的主要含义是，有非常有限的Cl吸收角闪石在这个化学系统中的存在下，在水盐水的高度可变的浓度，即使是最富铁的角闪石。在自然组合中观察到的高Cl含量可能是由盐水，或卤化物或硅酸盐熔体化学，或晶体化学因素（例如，K含量）比闪石的Fe#产生更强的影响。
Abstract Understanding how chlorine partitions between calcium amphiboles and an ambient fluid can be used to deduce the chlorine content of fluids involved in a wide range of geological processes, such as in high-grade metamorphism, deposition of economic minerals, chlorine metasomatism, and seawater-oceanic crust interactions. One of the most common correlations that is observed in calcium amphiboles is the increase in chlorine concentration with increasing Fe 2+ /(Fe 2+ + Mg) (= Fe#). To quantify this dependence, amphiboles with intended compositions along the pargasite–ferro-pargasite [NaCa 2 (Mg 4 Al)(Al 2 Si 6 )O 22 (Cl,OH) 2 –NaCa 2 (Fe 4 Al)(Al 2 Si 6 )O 22 (Cl,OH) 2 ] join were synthesized in the presence of NaCl brines ranging in concentration from 1 molal ( m ) NaCl to halite saturation. Syntheses were made over the range 700–950 °C and 0.2–0.5 GPa at oxygen fugacities ( f O 2 ) near the Co-CoO buffer and for durations of 46–576 h. The observed amphibole compositions varied between pargasite and hastingsite with increasing Fe# for an assumed constant Fe 3+ /(Fe 2+ + Fe 3+ ) ratio of 0.18. The most common additional phases were plagioclase and Ca-rich clinopyroxene with minor davyne in some syntheses. At any given bulk composition, amphiboles increase in Cl content with increasing brine concentrations, reaching a plateau in brines of about 0.1–0.2 mole fraction of NaCl ( X NaCl , or 5–15 m NaCl). Amphiboles synthesized in brines below halite saturation showed a fairly linear increase in Cl content from essentially 0.0 to 0.11 atoms per formula unit ( apfu ) with increasing Fe content. Syntheses in brines above halite saturation showed a distinct jump in Cl contents up to 0.14–0.30 apfu for the two most Fe-rich bulk compositions. Isopleths of constant NaCl concentration have been fitted to all of the data, and a thermochemical analysis of the dependence of the Cl/OH ratio of amphibole to the activity ratio of H 2 O/HCl in the brine has been offered for amphiboles synthesized in the 1 m NaCl brines. Comparison of the Cl contents of synthetic amphiboles made here with natural pargasitic amphiboles shows that even the highest Cl contents observed here are only about 20% of the maximum Cl contents found in amphiboles from some localities. The main implication of this study is that there is very limited Cl uptake in amphiboles made in this chemical system in the presence of aqueous brines of highly variable concentrations, even for the most Fe-rich amphiboles. The high Cl contents observed in natural assemblages are likely controlled by brine, or perhaps halide or silicate melt chemistry, or crystal-chemical factors ( e.g ., K content) that exert a stronger effect than just the Fe# of the amphibole.
影响因子：
3.9
作者：
Kusebauch, Christof;John, Timm;Austrheim, Hakon O.
通讯作者：
Austrheim, Hakon O.