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首页> 外文期刊>Contributions to Mineralogy and Petrology >NanoSIMS mapping and LA-ICP-MS chemical and U-Th-Pb data in monazite from a xenolith enclosed in andesite (Central Slovakia Volcanic Field)
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NanoSIMS mapping and LA-ICP-MS chemical and U-Th-Pb data in monazite from a xenolith enclosed in andesite (Central Slovakia Volcanic Field)

机译：NanoSIMS制图以及独山石包裹在安山岩中的异种岩中独居石中的LA-ICP-MS化学和U-Th-Pb数据（斯洛伐克中部火山场）

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In this study, we use NanoSIMS element and isotope ratio mapping and LA-ICP-MS trace element measurements to elucidate the origins of monazites from a restitic xenolith enclosed in a 13.5 +/- 0.3 Ma andesitic lava (Slovakia). The xenolith/lava interaction is mainly characterized by the growth of a plagioclase-bearing corona around the xenolith and magmatic garnet overgrowths on primary metamorphic garnets within the xenolith. NanoSIMS images (Y-89, La-139, Pb-208, Th-232 and U-238) and trace element analyses indicate that variations of HREE, Y and Eu contents in the monazite are correlated with the resorption and the following overgrowth of garnet and plagioclase in the xenolith. Three domains are distinguished in the monazite grains: the inherited Variscan core at ca. 310 Ma (M1 domain) characterized by low Y and HREE contents and a weak negative Eu anomaly; the inner rim (M2 domain) crystallized during the growth of the plagioclase magmatic corona (large negative Eu anomaly) and the resorption of metamorphic garnet (high HREE and Y contents); and the external rim (M3 domain) crystallized during the growth of the plagioclase corona (large negative Eu anomaly) and during the crystallization of magmatic garnet (low Y, HREE contents) at similar to 13 Ma, i.e. the age of the andesitic lava. The age and chemical zonation of the monazites attest to the preservation of primary monazite in the xenolith despite the interaction with the andesite lava. NanoSIMS imaging provides high-quality sub-mu m scale images of the monazite that reveals chemical domains that were not distinguishable on WDS X-ray maps, especially for depleted elements such as U and Pb. Owing to its small size, the M2 domain could not be accurately dated by the LA-ICP-MS method. However, NanoSIMS isotopic maps reveal that the M2 domain has similar Pb-208/Th-232 isotope ratios to the M3 domain and thus similar ages. These results support the hypothesis that melt-assisted partial dissolution-precipitation in monazite efficiently records chemical and mineralogical changes during xenolith/lava interaction.
机译：在这项研究中，我们使用NanoSIMS元素和同位素比率图以及LA-ICP-MS痕量元素测量来阐明独居石的起源，该独居石来自封闭在13.5 +/- 0.3 Ma的安山岩熔岩（斯洛伐克）中的重晶异岩。异岩/熔岩相互作用的主要特征在于，在异岩周围有斜长石的日冕的生长和岩浆石榴石在异岩内初级变质石榴石上的过度生长。 NanoSIMS图像（Y-89，La-139，Pb-208，Th-232和U-238）和痕量元素分析表明，独居石中HREE，Y和Eu含量的变化与重金属的吸收和随后的过度生长相关eno石中的石榴石和斜长石。独居石的晶粒区分出三个区域：大约在的继承的Variscan核。 310 Ma（M1域），其Y和HREE含量低，负Eu异常弱;内缘（M2域）在斜长石岩浆电晕（大的负Eu异常）生长和变质石榴石的吸收（高HREE和Y含量）过程中结晶;在斜长石日冕的生长过程中（大的负Eu异常）和岩浆石榴石的结晶过程（Y，HREE含量低）在约13 Ma时结晶，即安山岩熔岩的年龄。尽管与安山岩熔岩相互作用，独居石的年龄和化学区划证明了异岩中原生独居石的保存。 NanoSIMS成像提供了独居石的高质量亚微米级图像，揭示了WDS X射线图上无法区分的化学域，特别是对于贫化元素（如U和Pb）。由于M2域较小，因此无法通过LA-ICP-MS方法准确标出日期。然而，NanoSIMS同位素图显示，M2域与M3域具有相似的Pb-208 / Th-232同位素比率，因此具有相似的年龄。这些结果支持以下假说：独居石中熔融辅助的部分溶解-沉淀有效地记录了异石/熔岩相互作用期间的化学和矿物学变化。

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