U and Pb distribution in eclogites: implications for in-situ U-Pb dating of high-pressure metamorphism through rock-forming minerals

了解和量化共存的变质矿物之间的主元素和微量元素分布是非常有意义的，因为它们被用作许多地质过程的示踪剂。激光烧蚀ICPMS领域的最新仪器进步和技术发展提高了灵敏度，使我们能够更详细地研究俯冲带过程和反应。因此，出现了新的研究领域，例如低铀矿物的地质年代学。变质低铀矿物的U-Pb定年仍处于起步阶段，但与传统的溶解技术相比，快速的数据采集、数据处理和高空间分辨率代表了巨大的优势。由于主要矿物相的快速生长在很大程度上取决于含水矿物的分解，对这些不同区域的分析和定年以及将它们与特定变质反应联系起来的可能性将可能为我们提供一个更完整的俯冲各个阶段的时间框架。因此，研究俯冲带变质作用期间控制铀和铅（再）分布及其与主要造岩矿物结合的过程，将是在理解这些元素的活动方面向前迈出的重要一步，这将是对岩石年代学的重要贡献，而岩石年代学是将岩石学和地质年代学数据联系起来的跨学科方法。本研究的主要目的是获得有关榴辉岩主要成岩矿物中U和Pb分布的新信息，并随后获得其对低U矿物相（即，石榴石、单斜辉石、角闪石）。在这个项目的过程中，我们将调查来自三个地质区域的各种榴辉岩，这些榴辉岩记录了i）低温变质作用（500-550 ºC，As Sifah榴辉岩，阿曼），ii）中温矿物组合（约100 - 100 º C）。800 ºC，西班牙卡波奥尔特加尔复合体）和iii）高温共生（>850 ºC，捷克共和国摩尔达努比亚区）。这将使我们能够i）确定各种P-T历史的天然岩石中的实际U和Pb分布，ii）评估原岩整体成分对矿物U和Pb含量的影响，iii）研究除石榴石外的其他主要相的定年的可能性，以及iv）预测哪些是主要矿物U-Pb定年的最佳岩性。最后，我们将对三个地点的石榴子石进行测年，这将有助于解开每个地区高压岩石中不同事件的地质历史。

Understanding and quantifying the major and trace-element distribution between co-existing metamorphic minerals are of great interest as they are used as tracers of many geological processes. Recent instrumental advances and technical developments in the field of laser-ablation ICPMS have improved the sensitivity, allowing us to investigate subduction-zone processes and reactions in much greater detail. As a consequence, new research fields have emerged as the geochronology of low-U minerals for example. The U-Pb dating of metamorphic low-U minerals is still in its infancy, but the rapid data acquisition, data processing and high spatial resolution represent a huge benefit as compared to conventional dissolution techniques. As the prograde growth of major mineral phases largely depends on the breakdown of hydrous minerals, the analysis and dating of these distinct domains and the possibility to link them with a specific metamorphic reaction will likely give us a much more complete time frame of the various stages of subduction. Thus, the study of the processes controlling the (re)distribution of U and Pb and their incorporation in the major rock-forming minerals during subduction-zone metamorphism will represent a significant step forward in the understanding the mobilization of those elements, which will be an important contribution to petrochronology, the interdisciplinary approach linking petrological and geochronological data. The major aim of this study is to gain new information about U and Pb distribution in major eclogite-forming minerals and subsequently, its constraints for the U-Pb geochronology of low-U mineral phases (i.e., garnet, clinopyroxene, amphibole). In the course of this project, we will investigate a variety of eclogites from three geological areas that record i) low-temperature metamorphism (500–550 ºC, As Sifah eclogites, Oman), ii) medium-temperature mineral assemblages (ca. 800 ºC, Cabo Ortegal complex, Spain) and iii) high-temperature paragenesis (>850 ºC, Moldanubian Zone, Czech Republic). This will allow us to i) determine the practical U and Pb distribution in natural rocks of various P–T histories, ii) evaluate the influence of the protolith bulk composition in the U and Pb content of minerals, iii) study the possibility of dating other major-phases apart from garnet, and iv) predict which are the best lithologies for U-Pb dating of major-minerals. Finally, we will date garnet from the three localities, which will help to unravel the geological history of different events in the high-pressure rocks of each area.