Trace element zoning and incipient metamictization in a lunar zircon: Application of three microprobe techniques
Trace element zoning and incipient metamictization in a lunar zircon: Application of three microprobe techniques
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月球锆石中的微量元素分带和初期变晶化：三种微探针技术的应用
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
D. T. Kremser
中科院分区：
文献类型：
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作者：
B. Wopenka;B. Jolliff;E. Zinner;D. T. Kremser
本文测定了阿波罗14号地点采集的14161、7069号月球样品中200μm锆石的主量元素（Si、Zr、Hf）、次量元素（Al、Y、Fe、P）和微量元素（Ca、Sc、Ti、Ba、REE、Th、U）含量及拉曼光谱。用离子微探针、电子微探针和激光拉曼微探针在薄切片上进行原位分析。锆石颗粒在双折射方面呈光学环带，反映了U和Th浓度环带化导致的可变（不完全）变质作用。U和Th浓度的变化与其他高场强微量元素的变化以及拉曼光谱参数的变化密切相关。铀和钍的浓度范围分别为21至55 ppm和6至31 ppm，并与较低的拉曼峰强度，较宽的拉曼峰，和移位的Si-O峰位置。重稀土元素的浓度范围超过三到四倍，并与荧光峰的强度相关。微量元素浓度的相关变化反映了母体熔体~ 4b.y的原始岩浆分异作用。前锆石结构的退化，如所观察到的拉曼光谱参数所反映的，已经发生在该样品中的α衰变事件剂量范围从~5.2 × 10 ~（14）到1.4 × 10 ~（15）衰变事件/毫克锆石，根据U和Th浓度计算。该剂量远低于导致完全变晶化的每毫克累积剂量~1016个事件，并表明激光拉曼微探针光谱是一种对锆石中的辐射诱导损伤非常敏感的分析技术。
Abstract We have determined major (Si, Zr, Hf), minor (Al, Y, Fe, P), and trace element (Ca, Sc, Ti, Ba, REE, Th, U) concentrations and Raman spectra of a zoned, 200μm zircon grain in lunar sample 14161,7069, a quartz monzodiorite breccia collected at the Apollo 14 site. Analyses were obtained on a thin section in situ with an ion microprobe, an electron microprobe, and a laser Raman microprobe. The zircon grain is optically zoned in birefringence, a reflection of variable (incomplete) metamictization resulting from zo- nation in U and Th concentrations. Variations in the concentrations of U and Th correlate strongly with those of other high-field-strength trace elements and with changes in Raman spectral parameters. Concentrations of U and Th range from 21 to 55 ppm and 6 to 31 ppm, respectively, and correlate with lower Raman peak intensities, wider Raman peaks, and shifted Si-O peak positions. Concentrations of heavy rare earth elements range over a factor of three to four and correlate with intensities of fluorescence peaks. Correlated variations in trace element concentrations reflect the original magmatic differentiation of the parental melt ~4 b.y. ago. Degradation of the zircon structure, as reflected by the observed Raman spectral parameters, has occurred in this sample over a range of α-decay event dose from ~5.2 × 1014 to 1.4 × 1015 decay events per milligram of zircon, as calculated from the U and Th concentrations. This dose is well below the ~1016 events per milligram cumulative dose that causes complete metamictization and indicates that laser Raman microprobe spectroscopy is an analytical technique that is very sensitive to the radiation-induced damage in zircon.