Thermodynamic Model for the Effect of Post-entrapment Crystallization on the H2O–CO2 Systematics of Vapor-saturated, Silicate Melt Inclusions
Thermodynamic Model for the Effect of Post-entrapment Crystallization on the H2O–CO2 Systematics of Vapor-saturated, Silicate Melt Inclusions
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包埋后结晶对蒸气饱和硅酸盐熔融包裹体的 H2O-CO2 系统影响的热力学模型
DOI：
10.1093/petrology/egr052
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发表时间：
2011
影响因子：
3.9
通讯作者：
R. Bodnar
中科院分区：
文献类型：
--
作者：
M. Steele‐MacInnis;Rosario Esposito;R. Bodnar
熔融包裹体（MI）是有关岩浆喷发前挥发分含量的最佳信息来源。如果捕获的熔体富含挥发性物质，则捕获MI后可能会产生含有从熔体中逸出的挥发性物质的蒸汽泡。蒸汽饱和钠长石成分（NaAlSi 3 O 8）MI的热力学模型表明，MI中熔体相的CO2含量对少量的包埋后结晶（PEC）敏感，而熔体中的H2O含量对PEC不太敏感。在PEC过程中，CO2从熔体转移到气相，气泡可能包含MI中大量的CO2（如果不是大部分的话）。PEC过程中H2O和CO2的对比行为导致H2O^CO2趋势与岩浆上升和减压过程中开放系统脱气预测的趋势相似。因此，如果（1）蒸汽饱和的MI被捕获在岩浆上升路径沿着不同深度，或（2）具有相同挥发物含量的MI都被捕获在相同深度，但捕获后经历不同的PEC量，则可能产生类似的H2O^CO2趋势。仅根据MI挥发性数据无法区分这两种对比解释。然而，通过在结晶或岩浆演化进程的其他地球化学监测器的背景下检查挥发性趋势，有可能确定挥发性趋势是否是沿着脱气路径产生的，或者它们是否反映了原始均质熔体包裹体组合中的PEC的不同数量。本研究中所描述的MI的PEC产生的挥发性趋势直接适用于富硅（花岗岩）MI被困在非铁镁基质相中，并且仅定性地适用于更多的镁铁质熔体组合物和/或基质相，这是由于Fe交换与基质和后捕获再平衡过程的修改。
Melt inclusions (MI) represent the best source of information concerning the pre-eruptive volatile contents of magmas. If the trapped melt is enriched in volatile species, following trapping the MI may generate a vapor bubble containing volatiles that have exsolved from the melt.Thermodynamic modeling of vapor-saturated albitic composition (NaAlSi3O8) MI shows that the CO2 content of the melt phase in the MI is sensitive to small amounts of post-entrapment crystallization (PEC), whereas the H2O content of the melt is less sensitive to PEC. During PEC, CO2 is transferred from the melt to the vapor phase and the vapor bubble may contain a significant amount, if not most, of the CO2 in the MI.The contrasting behaviors of H2O and CO2 during PEC lead to H2O^CO2 trends that are similar to those predicted for open-system degassing during magma ascent and decompression.Thus, similar H2O^CO2 trends may be produced if (1) vapor-saturated MI are trapped at various depths along a magmatic ascent path, or (2) MI having the same volatile content are all trapped at the same depth, but undergo different amounts of PEC following trapping. It is not possible to distinguish between these two contrasting interpretations based on MI volatile data alone. However, by examining the volatile trends within the context of other geochemical monitors of crystallization or magma evolution progress, it may be possible to determine whether the volatile trends were generated along a degassing path or if they reflect various amounts of PEC in an originally homogeneous melt inclusion assemblage. The volatile trends resulting from PEC of MI described in this study are directly applicable to silica-rich (granitic) MI trapped in non-ferromagnesian host phases, and are only qualitatively applicable to more mafic melt compositions and/or host phases owing to modifications resulting from Fe exchange with the host and to post-entrapment re-equilibration processes.
影响因子：
5.8
作者：
Collins, S. J.;Pyle, D. M.;Maclennan, J.
通讯作者：
Maclennan, J.