The compositional variability of eudialyte-group minerals
The compositional variability of eudialyte-group minerals
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DOI：
10.1180/minmag.2011.075.1.87
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发表时间：
2011-02
影响因子：
2.7
通讯作者：
J. Schilling;F. Wu;C. McCammon;T. Wenzel;M. Marks;K. Pfaff;D. E. Jacob-;G. Markl
中科院分区：
文献类型：
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作者：
J. Schilling;F. Wu;C. McCammon;T. Wenzel;M. Marks;K. Pfaff;D. E. Jacob-;G. Markl
摘要/ Abstract摘要：易溶基团矿物（EGM）是人体透析系统中最重要的指标矿物。本文介绍了EPMA、Mössbauer光谱和LA-ICP-MS联合研究的结果，并比较了在硅过饱和和欠饱和体系中不同母熔体和矿物组合在不同分馏阶段结晶的EGM。成分变异性与结构密切相关，允许重建局部作用的岩浆-热液过程。早期岩浆期EGM始终以铁为主，而热液期EGM几乎不含铁，形成纯Mn端元。因此，Mn/Fe比是最合适的分馏指标，尽管晶体化学效应和共晶相在Fe和Mn掺入EGM中起次要作用。Mössbauer对3个矿点的EGM光谱分析表明，Fe3+/∑Fe比值由EGM的水化状态决定，而不是由共存熔体的氧逸度决定。负Eu异常局限于碱性玄武岩母质熔体结晶的EGM，而辉白云岩母质熔体结晶的EGM总是缺乏负Eu异常。即使经过很长的分异间隔，EGM也能反映出它们各自的母熔体的性质，以及斜长石和其他矿物（如铁钛氧化物、角闪洞和硫化物）的分异。
Abstract Eudialyte-group minerals (EGM) represent the most important index minerals of persodic agpaitic systems. Results are presented here of a combined EPMA, Mössbauer spectroscopy and LA-ICP-MS study and EGM which crystallized in various fractionation stages from different parental melts and mineral assemblages in silica over- and undersaturated systems are compared. Compositional variability is closely related to texture, allowing for reconstruction of locally acting magmatic to hydrothermal processes. Early-magmatic EGM are invariably dominated by Fe whereas hydrothermal EGM can be virtually Fe-free and form pure Mn end-members. Hence the Mn/Fe ratio is the most suitable fractionation indicator, although crystal chemistry effects and co-crystallizing phases play a secondary role in the incorporation of Fe and Mn into EGM. Mössbauer spectroscopy of EGM from three selected occurrences indicates the Fe3+/∑Fe ratio to be governed by the hydration state of EGM rather than by the oxygen fugacity of the coexisting melt. Negative Eu anomalies are restricted to EGM that crystallized from alkali basaltic parental melts while EGM from nephelinitic parental melts invariably lack negative Eu anomalies. Even after extensive differentiation intervals, EGM reflect properties of their respective parental melts and the fractionation of plagioclase and other minerals such as Fe-Ti oxides, amphibole and sulphides.