Crystal-structure refinement of Na-bearing clinopyroxenes from mantle-derived eclogite xenoliths
Crystal-structure refinement of Na-bearing clinopyroxenes from mantle-derived eclogite xenoliths
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幔源榴辉岩捕虏体中含钠单斜辉石的晶体结构精修
DOI：
10.2138/am.2007.2654
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发表时间：
2007
影响因子：
3.1
通讯作者：
T. B. Ballaran
中科院分区：
文献类型：
--
作者：
F. Nestola;M. Longo;C. McCammon;T. B. Ballaran
摘要采用单晶X射线衍射、电子探针、穆斯堡尔谱和红外光谱等方法，对产于乌达奇纳亚和扎加多奇纳亚含金刚石金伯利岩中的9个绿辉石单斜辉石进行了研究。结合化学分析和穆斯堡尔谱数据的限制，晶体结构的改进显示，在三个样品中，M2位点的空位浓度很高。非化学计量样品的晶胞体积低于化学计量透辉石-翡翠组合物定义的线性趋势，其中偏离线性趋势与空位浓度呈正相关。电荷平衡似乎主要是通过取代Mg 2+的M1网站，这会导致收缩的M1网站的体积相比，化学计量单斜辉石具有相同的组合物的Al 3+。空缺与OH无关。掺入，因为具有最高浓度的空位的样品仅含有89 ppm（wt）H2O。基于低的Fe 3+浓度，排除了在上升期间通过铁氧化的显著氢损失。金伯利岩中绿辉石样品中的氢含量可以作为测定金刚石形成过程中fH-O的灵敏工具。
Abstract Nine omphacitic clinopyroxenes with a jadeitic content between 25% and 57% from the Udachnaya and Zagadochnaya diamond-bearing kimberlites were investigated using single-crystal X-ray diffraction, electron microprobe analysis, and Mössbauer and infrared spectroscopy. Crystal-structure refinements, incorporating constraints from chemical analyses and Mössbauer data, show a significant concentration of vacancies at the M2 site in three of the samples. The cell volumes of the non-stoichiometric samples plot below the linear trend defined by stoichiometric diopside-jadeite compositions, where the deviation from the linear trend is positively correlated with the concentration of vacancies. Charge-balance appears to be achieved primarily through substitution of Al3+ for Mg2+ on the M1 site, which causes a contraction of the M1 site volume compared to stoichiometric clinopyroxenes with the same composition. Vacancies are not associated with OH. incorporation, as the sample with the highest concentration of vacancies contains only 89 ppm (wt) H2O. Significant hydrogen loss through iron oxidation during ascent is ruled out based on the low Fe3+ concentrations. H content in omphacite samples from kimberlites could provide a sensitive tool for determining fH₂O during diamond formation.