A cathodoluminescence-assisted LA-ICP-MS study of topaz from different geological settings

ABSTRACT: In this study, the crystallization dynamics and the fingerprints of two topaz crystals from the Ouro Preto region (Brazil), two from the Eastern Brazilian Pegmatite Province (EBPP), one from the Western part of the United States (US) and one from Pakistan were characterized. The combination of scanning electron microscope-cathodoluminescence (SEM-CL) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data allowed for the characterization of these samples. Samples from the Ouro Preto region showed primary crystallization and recrystallization processes, which were demonstrated by a CL-heterogeneous core and CL-homogeneous rims in the SEM-CL images. Their fingerprint was composed of Ca, Ti, V, Cr, Mn, Fe, Cu and Zn. Samples from the EBPP showed both dark and CL-homogeneous SEM-CL images, implying slow and late-stage crystallization, typical of pegmatites. Their fingerprints were composed of Li, Nb, LREE, Ta and W, and of Ti, Nb and HREE. A sample from a Western part of the US displayed CL-heterogeneity with growth and resorption events and well-preserved growth zones, which were noticeable through the SEM-CL images. Its fingerprint was composed of Li, Ti, V, Mn, Nb, LREE, Ta and W. A sample from Pakistan showed an evident metamorphic recrystallization process, which was visible by the incipient and CL-homogeneous luminescence given by the SEM-CL images. Its fingerprint was composed of Ca, Cr, V, Zn, LREE, HREE and W.

摘要：本研究对产自巴西欧鲁普雷图地区的2颗黄玉（Topaz）晶体、巴西东部伟晶岩省（Eastern Brazilian Pegmatite Province, EBPP）的2颗黄玉晶体、美国西部的1颗黄玉晶体以及巴基斯坦的1颗黄玉晶体的结晶动力学特征与元素指纹图谱进行了系统表征。结合扫描电子显微镜-阴极发光（SEM-CL）与激光剥蚀电感耦合等离子体质谱法（LA-ICP-MS）测试数据，完成了对上述样品的表征分析。欧鲁普雷图地区的样品存在初始结晶与重结晶作用过程，该特征可通过SEM-CL图像中阴极发光非均一的核部与阴极发光均一的边部得到证实；其元素指纹由Ca、Ti、V、Cr、Mn、Fe、Cu及Zn构成。巴西东部伟晶岩省（EBPP）的样品兼具暗区与阴极发光均一的SEM-CL图像特征，暗示其结晶速率缓慢且属于晚期结晶作用，为伟晶岩的典型特征；其元素指纹分别由Li、Nb、轻稀土元素（Light Rare Earth Element, LREE）、Ta、W以及Ti、Nb、重稀土元素（Heavy Rare Earth Element, HREE）构成。美国西部的1颗样品表现出阴极发光非均质性，存在生长与溶蚀事件且保存完好的生长环带，该特征可通过SEM-CL图像清晰观测；其元素指纹由Li、Ti、V、Mn、Nb、LREE、Ta及W构成。巴基斯坦的1颗样品呈现显著的变质重结晶作用，该特征可通过SEM-CL图像中出现的初始且均一的阴极发光得到验证；其元素指纹由Ca、Cr、V、Zn、LREE、HREE及W构成。