Laboratory and Field Investigations of Monazite Paragenesis, Growth Kinetics, Textural Development, and U-Th-Pb Chronometry in Igneous and High-Grade Metamorphic Rocks

9873626 ayers火成岩和高级变质岩中的独居石颗粒通常包含多个生长带，这些生长带产生的U，Th-Pb日期对应于岩石历史上的多个事件。提出的实验室和现场实验旨在表征独居石的生长和再结晶。从具有良好历史特征的地区（内华达州南部的一个岩体，北卡罗来纳州和加利福尼亚州的变质地体）收集的天然独居石的结构特征、年龄和生长带组成的原位测量将有助于确定独居石生长的时间和条件。在类似条件下进行的实验室实验将量化生长机制和速率，并证实天然独居石分带的结构解释。由于生长和再结晶往往与流体流入有关，因此对含独居石和流体的岩石进行实验将有助于确定热液生长和再结晶的特征结构特征，包括晶体尺寸分布、分带模式、包裹体/主体关系和润湿角度。这些特征对流体组成、寄主粒度和粗化速率以及温度的依赖性也将进行研究，以确定天然独居石的生长条件。研究结果将有助于解释天然独居石的结构和分带，以及测量的U、Th-Pb独居石年龄与特定地球化学和构造事件的相关性。

9873626AyersMonazite grains in igneous and high-grade metamorphic rocks often contain multiple growth zones that yield U,Th-Pb dates corresponding to multiple events in the history of a rock. The proposed lab and field experiments are designed to characterize monazite growth and recrystallization. In-situ measurements of textural features, ages, and compositions of growth zones in natural monazites collected from regions with well-characterized histories (a pluton in southern Nevada, metamorphic terranes in North Carolina and California) will help to establish the timing and conditions of monazite growth. Lab experiments conducted undersimilar conditions will quantify growth mechanisms and rates and corroborate textural interpretations of zoning in natural monazites. Because growth and recrystallization often appears to be related to fluid influx, experiments on rocks containing monazite and fluid will help to identify characteristic textural features of hydrothermal growth and recrystallization including crystal size distributions, zoning patterns, inclusion/host relations, and wetting angles. The dependence of these features on fluid composition, host grain size and coarsening rate, and temperature will also be investigated to identify conditions of growth of natural monazites. Results will refine interpretations of texture and zoning in natural monazites and the correlation of measured U,Th-Pb monazite ages with specific geochemical and tectonic events.