Chlorine incorporation in amphiboles synthesized along the magnesio-hastingsite–hastingsite compositional join
Chlorine incorporation in amphiboles synthesized along the magnesio-hastingsite–hastingsite compositional join
复制标题
沿镁黑斯汀位点-黑斯汀位点组成连接合成的角闪石中的氯掺入
DOI：
10.1127/ejm/2017/0029-2606
复制
发表时间：
2017
影响因子：
2.1
通讯作者：
M. Dyar
中科院分区：
文献类型：
--
作者：
Bailey L. Mueller;David M. Jenkins;M. Dyar
黑斯廷石角闪石在陆地和陨石样品中都含有高含量的氯，然而，为角闪石提供氯的溶液或熔体，以及宿主角闪石的晶体化学控制，还没有很好的理解。研究了沿着镁铁锰矿-镁铁锰矿体相组成连接NaCa 2（Mg 4Fe 3+）（Al 2Si 6）O22（OH，Cl）2 -NaCa 2（Fe 42 + Fe 3+）（Al 2Si 6）O22（OH，Cl）2合成角闪石的Fe#（= Fe 2+ /（Fe 2+ + Mg））与Cl接受性之间的关系。样品由试剂级起始材料的混合物制成，所述试剂级起始材料沿着组成接合处以约20摩尔%增量制备，并在700-850 ℃和0.2-0.4 GPa下合成3-4天，其中氧逸度被广泛地限制在低于Co-CoO和高于浮氏体-磁铁矿氧缓冲层。Cl的来源是FeCl 2。虽然角闪石的合成名义上是无水的，但一些水分不可避免地被吸湿的FeCl 2吸收，并可能产生Cl（= X Cl）摩尔分数为0.58至0.91的盐水，假设这样的盐水浓度低于FeCl 2的饱和度。用穆斯堡尔谱测定了合成角闪石的三价铁含量。沿沿着这一成分连接形成的角闪石通常在富镁端附近缺乏Fe 3+，在富铁端附近缺乏Na，产生的角闪石分别被归类为角闪石和亚铁或亚铁铁角闪石，而不是黑斯廷石角闪石。观察到Cl含量与Fe#之间总体正相关，但在Fe#为0.69 ± 0.04时出现明显的最大值，其中Cl达到0.42 ± 0.06个原子/化学式单位（apfu）或1.5 ± 0.2wt% Cl，并在Fe#为1.0时降至0.20 Cl apfu。这一观察结果表明，除Fe#外，还有一个因素更为重要，即Fe 2+的比例（=Fe 2+ /（Fe 2+ +Fe 3+））。与自然界中其他富Cl的部分气化角闪石相比，本研究中观察到的最大Cl apfu为0.42，仍然比天然样品中观察到的最大值低2 - 3倍。研究结果表明，Cl含量最高的角闪石是Fe 2+含量最高的角闪石，Fe 3+含量最低的角闪石，同时也是T Al含量最高的角闪石，K含量最高的角闪石。
Hastingsitic amphiboles can contain high Cl contents in both terrestrial and meteorite samples; however, the solutions or melts providing Cl to the amphibole, as well as the crystal-chemical controls of the host amphibole, are not well understood. This study focuses on the correlation between the Fe# (= Fe 2+ /(Fe 2+ + Mg)) and the acceptance of Cl for amphiboles synthesized along the magnesio-hastingsite–hastingsite bulk compositional join, NaCa 2 (Mg 4 Fe 3+ )(Al 2 Si 6 )O 22 (OH,Cl) 2 –NaCa 2 (Fe 4 2+ Fe 3+ )(Al 2 Si 6 )O 22 (OH,Cl) 2 . Samples were made from mixtures of reagent-grade starting materials prepared along the compositional join at approximately 20 mol% increments and synthesized at 700–850 °C and 0.2–0.4 GPa for 3–4 days, where the oxygen fugacity was broadly constrained to lie below the Co–CoO and above the wustite–magnetite oxygen buffers. The source of Cl was FeCl 2 . Although the amphibole syntheses were nominally anhydrous, some moisture was inevitably absorbed by the hygroscopic FeCl 2 and could have produced brines with mole fractions of Cl (= X Cl ) of 0.58 to 0.91, assuming such brine concentrations are below saturation in FeCl 2 . Ferric iron contents of the synthetic amphiboles were determined by Mossbauer spectroscopy. Amphiboles formed along this compositional join were generally deficient in Fe 3+ near the Mg-rich end and deficient in Na near the Fe-rich end, yielding amphiboles that are classified as pargasite and ferro- or ferro-ferri-hornblende, respectively, rather than hastingsitic amphiboles. An overall positive correlation was observed between Cl content and the Fe#, but with a distinct maximum at Fe# of 0.69 ± 0.04 where the Cl reaches 0.42 ± 0.06 atoms per formula unit (apfu) or 1.5 ± 0.2 wt% Cl, and decreases to 0.20 Cl apfu at Fe# of 1.0. This observation points to a factor other than Fe# as being more important, namely the proportion of Fe 2+ (=Fe 2+ /(Fe 2+ +Fe 3+ ). In comparison to other Cl-rich pargasitic amphiboles in nature, the maximum of 0.42 Cl apfu observed in this study is still about a factor of two to three lower than the maximum observed in natural samples. The implications of this study are that the amphiboles most likely to host the highest Cl contents are those with the highest proportion of Fe 2+ , and conversely the lowest proportion of Fe 3+ , as well as having significant T Al and most likely K.
影响因子：
3.9
作者：
Kusebauch, Christof;John, Timm;Austrheim, Hakon O.
通讯作者：
Austrheim, Hakon O.