Collaborative Research: Improved Geochronology-Based Sediment Provenance Analysis Through Physico-Mechanical Characterization of Zircon Transport

风和水流对沉积物的产生和移动是数十亿年来塑造地球表面的基本地质过程。通过这些过程，由于风化和侵蚀从高海拔地区移走的物质被机械地运送到低海拔地区（即盆地），从而平整地形高处（如山脉）。以定量的方式研究和理解这些过程为地球科学家提供了关于地理、演化、人类迁移、气候、构造和经济上重要的沉积盆地发展的基本信息。研究现代和古代沉积系统（如河流、沙漠）中沉积物运输的最可靠的方法之一是测量含有放射性母同位素和子同位素的锆石等耐风化矿物的地质年龄。通过研究远行锆石的年龄模式，地球科学家可以绘制出具有可比年龄的潜在源区之间的联系，并重建古代沉积物路线系统。学生们将接受研究方法方面的培训，作为项目的一部分，将为本科生开设一门新的创造性探究课程。通过碎屑矿物的年龄测定来研究沉积物的迁移并非没有复杂性和潜在的偏差。尽管一个多世纪以来，由牵引流携带的颗粒的机械分选和分选已经成为沉积学中众所周知的过程，但我们对沉积物运输如何影响碎屑锆石种群和影响U-Pb年龄谱的了解仍然严重不足。利用河流系统作为自然实验室，本项目将量化锆石的物理特征（如粒度、形态和累积辐射损伤）在运输过程中对碎屑锆石年龄谱的系统偏置的影响。本项目将：1)收集碎屑锆石在输运过程中分馏的可靠年龄和物理性质信息；2)应用统计推断方法量化这些物理特征对观测年龄谱偏差的潜在影响。这些见解将使地球科学家能够进行更多的“地质信息”样本间比较，提高构造重建的准确性，定量物源模型，以及从碎屑锆石U-Pb数据中得出的沉积物运输路径。开发的代码将是用户友好的，并可供其他研究人员使用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The generation and movement of sediments by wind and water currents are fundamental geologic processes that have shaped the surface of our planet for billions of years. Through these processes, material removed from higher elevation areas by weathering and erosion is mechanically transported to lower elevation regions (i.e., basins), thereby leveling topographic highs (e.g., mountains). Studying and understanding these processes in a quantitative way provides Earth Scientists with fundamental information about geography, evolution, human migration, climate, tectonics, and the development of economically important sedimentary basins. One of the most robust ways to study sediment transport in modern and ancient sedimentary systems (e.g., rivers, deserts), is by measuring the geologic ages of weathering-resistant minerals such as zircon that contain radioactive parent and daughter isotopes. By studying the age patterns of far-travelled zircons, Earth Scientists can draw linkages to potential source areas with comparable ages and reconstruct ancient sediment routing systems. Students will be trained in the research methods and a new Creative Inquiry course for undergraduates will be developed as part of the project.Studying sediment transport through age-dating of detrital minerals is not without complexities and potential biases. Although the mechanical sorting and fractionation of particles carried by tractive currents have been well-known processes in sedimentology for well over a century, our knowledge of how sediment transport affects detrital zircon populations and influences U-Pb age spectra remains critically inadequate. Using fluvial systems as natural laboratories, this project will quantify the effects that the physical characteristics of zircon, such as grain size, morphology, and accumulated radiation damage, have in systematically biasing detrital zircon age spectra during transport. This project will: 1) collect robust age and physical-properties information of detrital zircon fractionation during transport, and 2) apply methods of statistical inference to quantify the latent effects these physical characteristics have in biasing the observed age spectra. These insights will allow Earth Scientists to perform more ‘geologically informed’ inter-sample comparisons, enhancing the accuracy of tectonic reconstructions, quantitative provenance models, and sediment-transport pathways derived from detrital zircon U-Pb data. The code developed will be user friendly and available to other researchers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.