Trace element partitioning between plagioclase and silicate melt: The importance of temperature and plagioclase composition, with implications for terrestrial and lunar magmatism
Trace element partitioning between plagioclase and silicate melt: The importance of temperature and plagioclase composition, with implications for terrestrial and lunar magmatism
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DOI：
10.1016/j.gca.2017.03.003
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发表时间：
2017-06
影响因子：
5
通讯作者：
Chenguang Sun;M. Graff;Yan Liang
中科院分区：
文献类型：
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作者：
Chenguang Sun;M. Graff;Yan Liang
在0.6 GPa和1350-1400 °C下，对月球高钛苦橄玻璃和大洋中脊玄武岩（MORB）中微量元素在斜长岩斜长石和玄武质熔体之间的分配系数（D）进行了实验测定。斜长石98摩尔%和86摩尔%的钙长石产生在月球苦橄质熔体和MORB熔体，分别。基于新的实验分配数据和那些从文献中选择的，我们开发了参数化的晶格应变模型的一价（Na，K，Li），二价（Ca，Mg，Ba，Sr，Ra）和三价（REE和Y）阳离子斜长石和硅酸盐熔体之间的分配。通过新的模型，我们表明，这些微量元素在斜长石中的分配取决于温度，压力，以及斜长石中的Ca和Na的丰度。斜长石中的Na含量主要控制二价元素的配分，而温度和斜长石中的Ca含量是斜长石中REE配分的主导因素。从这些模型中，我们还推导出了一个新的表达式DRa/DBa，可用于火山斜长石斑晶的Ra-Th定年，和斜长石熔体稀有气体分配的新模型。将这些分配模型应用于MORB和月球岩浆海洋（LMO）的分离结晶研究表明：（1）在MORB分异过程中，温度和斜长石成分的竞争效应导致斜长石-熔体DREE的微小变化，但（2）在LMO凝固过程中，温度效应尤其显著，可以使钙长石-熔体DREE的变化超过一个数量级。温度和斜长石成分时，必须考虑建模的镁铁质长英质岩浆的化学分异斜长石。
Trace element partition coefficients between anorthitic plagioclase and basaltic melts (D) have been determined experimentally at 0.6 GPa and 1350–1400 °C in a lunar high-Ti picritic glass and a mid-ocean ridge basalt (MORB). Plagioclases with 98 mol% and 86 mol% anorthite were produced in the lunar picritic melt and MORB melt, respectively. Based on the new experimental partitioning data and those selected from the literature, we developed parameterized lattice strain models for the partitioning of monovalent (Na, K, Li), divalent (Ca, Mg, Ba, Sr, Ra) and trivalent (REE and Y) cations between plagioclase and silicate melt. Through the new models we showed that the partitioning of these trace elements in plagioclase depends on temperature, pressure, and the abundances of Ca and Na in plagioclase. Particularly, Na content in plagioclase primarily controls divalent element partitioning, while temperature and Ca content in plagioclase are the dominant factors for REE partitioning in plagioclase. From these models, we also derived a new expression forDRa/DBathat can be used for Ra-Th dating on volcanic plagioclase phenocrysts, and a new model for plagioclase-melt noble gas partitioning. Applications of these partitioning models to fractional crystallization of MORB and lunar magma ocean (LMO) indicate that (1) the competing effect of temperature and plagioclase composition leads to small variations of plagioclase-meltDREEduring MORB differentiation, but (2) the temperature effect is especially significant and can vary anorthite-meltDREEby over one order of magnitude during LMO solidification. Temperature and plagioclase composition have to be considered when modeling the chemical differentiation of mafic to felsic magmas involving plagioclase.