The refractory nature of zircon to temperature and pressure allows even a single zircon grain to preserve a rich history of magmatic, metamorphic, and hydrothermal processes. Isotopic dating of micro-domains exposed in cross-sections of zircon grains allows us to interrogate this history. Unfortunately, our ability to select the zircon grains in a heavy mineral concentrate that records the most geochronologic information is limited by our inability to predict internal zonation from observations of whole grains. Here we document the use of a petrographic microscope to observe and image the photoluminescence (PL) response of whole zircon grains excited under ultraviolet (UV) light, and the utility of this PL response in selecting grains for geochronology. While zircon fluorescence has long been known, there is limited documentation of its utility for and application to geochronologic studies. Our observations of zircon from an un-metamorphosed igneous rock, two meta-igneous rocks, and a placer deposit show that variations in the PL color are readily observable in real-time, both among grains in a population of zircons and within single grains. Analyses of cross-sections of the same grains demonstrate that the changes in PL correlate with zoning in backscattered electron (BSE) and cathodoluminescence (CL) images as well as with changes in U + Th concentration and spectroscopic proxies for radiation damage. In other words, the whole grain PL provides a low-resolution preview of the U + Th zoning expected in a cross-sectioned grain. We demonstrate the usefulness of this “preview” in identifying and selecting the subset of zircon grains in a heavy mineral separate that has metamorphic rims of sufficient width to date by secondary ionization mass spectrometry (SIMS). The data are also used to place preliminary constraints on the age and U + Th concentrations at which a yellow PL response is observed in natural samples. The PL response of zircon is well-known among spectroscopists, and these simple applications demonstrate several ways in which the response might be more effectively used by geochronologists.

中文翻译：

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石油相显微镜上的整个锆石晶粒的光致发光成像-地质学研究的未充分利用的助手

锆石对温度和压力的耐火性质甚至允许单个锆石颗粒保留丰富的岩浆，变质和热液过程历史。锆石横断面中暴露的微区的同位素定年使我们可以探究这一历史。不幸的是，我们无法从记录最丰富的年代学信息的重矿物精矿中选择锆石晶粒的能力受到我们无法根据全谷物观察结果预测内部区域划分的限制。在这里，我们记录了使用岩石显微镜观察和成像在紫外线（UV）激发下的整个锆石晶粒的光致发光（PL）响应，以及该PL响应在选择用于年代学的晶粒中的实用性。锆石荧光早已为人所知，关于它的实用性和在地质年代研究中的应用的文献有限。我们从未变质的火成岩，两个变质火成岩和砂矿中观察到的锆石表明，无论是在锆石种群中的晶粒间还是在单个晶粒内，PL色的变化都易于实时观察到。对相同晶粒横截面的分析表明，PL的变化与背向散射电子（BSE）和阴极发光（CL）图像中的分区以及U + Th浓度和光谱损伤的辐射损伤相关。换句话说，整个颗粒PL提供了横截面颗粒中预期的U + Th分区的低分辨率预览。我们通过二次电离质谱法（SIMS）证明了这种“预览”在识别和选择重矿物分离区中锆石晶粒的子集的有用性，重矿物分离区具有足够宽的变质边缘。数据还用于对年龄和U + Th浓度进行初步限制，在自然样品中观察到黄色PL反应。锆石的PL响应在光谱学家中是众所周知的，这些简单的应用展示了地球年代学家可以更有效地使用响应的几种方法。