碎屑锆石U-Pb年龄有效性初探

碎屑锆石U-Pb 年代学是限定沉积地层年龄、追踪沉积物源、揭示区域构造演化历史等重要的手段，在地质学和地理学领域应用广泛。近年来，单颗粒碎屑锆石数据获取技术日渐成熟，数据量激增，然而，部分邻近甚至相同地区不同研究组获得的原始数据存在差异甚至相互矛盾。如何高效严谨地获取及处理数据，并挖掘其中所蕴涵的丰富的地质信息，越来越受到研究者的重视，但目前相关方面的研究较少。以青藏高原东北缘酒西盆地新生代疏勒河组砂岩碎屑锆石为例，采用标准实验流程，通过试验数据之间的横向和纵向对比，确定合理的碎屑锆石颗粒测试数量，利用碎屑锆石颗粒外部形态与内部结构特征相结合的方法，选择有效的测试点，发现单颗粒锆石阴极发光（CL）图像在数据测试、分析和应用方面极具前景。具体取得如下认识:1）碎屑锆石U-Pb测年前处理时需采用标准的重矿物分选流程，以保持所采集的碎屑样品中单颗粒锆石分布的全貌，避免引起年龄组分丢失或偏差；制作样品靶及选择测年颗粒时，需将全部锆石单颗粒在体视显微镜及扫描电镜下的特征紧密结合，得到最优有效数量的单颗粒年龄，提高效率及数据的准确性、完整性；2）数据处理、分析及应用中，必须结合单颗粒锆石CL图像，修正或剔除异常数据，避免由于激光剥蚀点或离子束跨越特征不同的生长环带产生无意义的“混合年龄”。该研究为碎屑锆石U-Pb年代学大数据处理及应用提供了基础技术支撑，且为有效甄别U-Pb测年数据质量进而合理、准确地应用于地学研究提供了新的视角。

Preliminary Study of Validity of Detrital Zircon U-Pb Dating: A case study of Jiuxi Basin,NE Tibetan Plateau

Inductively coupled plasma mass spectrometry （ICP-MS） U-Pb detrital zircon geochronology is an important means of determining the age of sedimentary strata and trace the source of sediments， and also reveal the history of regional tectonic evolution， and is widely used in geological and geographical work. In recent years the development of single-grain detrital zircon dating has doubled the amount of data available. However， there are differences or contradictions between the original data obtained by different research groups in adjacent areas， or even within the same area. How to obtain and process the data efficiently and rigorously and reveal the rich geological information contained in the data is attracting increased research attention， but few studies have been conducted on related aspects. This study considered the example of sandstone detrital zircons of the Cenozoic Shulehe Formation in the Jiuxi Basin on the NE Tibetan Plateau. A horizontal and vertical comparison of a reasonable number of zircon particles （“zircons”） in the test data was conducted using standard experimental procedures. The test points were selected by combining the external morphologies and internal structures of the zircons. Single-particle cathodoluminescence （CL） imaging of the zircons was found to have appreciable potential for data testing， analysis and application. The specific approach is as follows: （1） Standard heavy mineral sorting procedures should be adopted for pre-processing zircons for U-Pb dating， to maintain the complete distribution of individual zircons in the collected detrital sample and avoid the loss or deviation of age components. When selecting particles for dating， the characteristics of all the zircon grains examined under stereomicroscope and scanning electron microscope should be closely combined to obtain the optimal effective number of ages of individual zircons in order to improve the efficiency， accuracy and integrity of the data. （2） During data processing， analysis and application， it is necessary to correct， or eliminate， abnormal data in combination with the CL image of the individual zircon， in order to avoid meaningless “mixed ages” caused when the laser ablation point or ion beam crosses different growth zones. The study provides basic technical support for the processing and application of “big data” procedures in detrital zircon U-Pb geochronology， and provides a new perspective for effectively discriminating the quality of U-Pb data and applying it to geoscientific research reasonably and accurately.