Monazite as a Sensitive Indicator of the Timing and Type of Fluid Activity During Metamorphism

Ayers和MillerEAR-0126020独居石对流体诱导重结晶的敏感性对于解释电子或离子探针原位测量的年龄具有重要意义。为了完善解释，设计了补充的实验室和野外实验，以识别和表征花岗岩类和伴生岩石中的独居石重结晶和蚀变。独居石的溶解度将使用双胶囊方法作为压力、温度和流体组成的函数进行测量，以确定导致溶解和重结晶增强的条件和流体组成。在400-600摄氏度和0.1-0.2 GPA的冷封压力容器中进行的实验将表征潜在络合配体F、Cl和OH的不同浓度的影响。然后将大的天然晶体在高溶解度的流态化条件下运行，以表征再结晶速度和蚀变对晶内分带和元素和氧同位素组成的影响。重复在天然独居石中观察到的分带样式和氧同位素系统，将在独居石蚀变与流体之间建立牢固的联系，建立发生蚀变的条件，并极大地增加独居石年龄解释的可信度。野外研究旨在检验独居石中蚀变带的年龄与流体流入时间相对应的假设，并检验针对这些野外区域的重要假设。在岩浆流体渗入独居石围岩的接触变质光环中，将研究温度、流体成分和流体/岩石比的变化对原有独居石的影响：内华达州南部的Ireteba岩体，怀特山的Birch Creek岩体。位于加利福尼亚州中东部，以及位于广东省北部的红山钨锡矿床，位于中国东南部。大别山中央超高压(超高压)带独居石和锆石的年代学研究成果将延伸到神秘的大别北部杂岩，以确定超高压变质作用的面积范围和大别北部与扬子地块或中朝地块的归属。

Ayers and MillerEAR-0126020The susceptibility of monazite to fluid-induced recrystallization has important implications for interpretation of ages measured in-situ by electron or ion microprobe. To refine interpretations, complementary laboratory and field experiments havebeen designed to identify and characterize monazite recrystallization and alteration in granitoids and associated rocks. The solubility of monazite will be measured as a function of pressure, temperature and fluid composition using the double-capsule method to identify the conditions and fluid compositions that lead to enhanced solubility and recrystallization. Experiments run in cold-seal pressure vessels at 400-600 degrees C and 0.1-0.2 GPa will characterize the effects of varying concentrations of potential complexing ligands F, Cl and OH. Large natural crystals will then be run in fluid atidentified conditions of high solubility to characterize the rate of recrystallization and the effect of alteration on intracrystalline zoning and elemental and oxygen isotopic composition. Duplication of zoning styles and oxygen isotope systematics observed in natural monazites will create a firm link between monazite alteration and fluids, establish the conditions under which alteration occurs, and greatly increase confidence in interpretations of monazite ages.Field studies are designed to test the hypothesis that the ages of altered zones in monazites correspond to the timing of fluid influx, and to test important hypotheses specific to those field areas. The effects of changing temperature, fluid composition, and fluid/rock ratio on preexisting monazite will be examined in contact metamorphic aureoles in which magmatic fluids infiltrate monazite-bearing country rocks: the Ireteba pluton in southern Nevada, the Birch Creek pluton in the White Mts. of east-central California, and the Red Hill W-Sn deposit in northern Guangdong Province, Southeast China. Fruitful geochronological studies of monazite and zircon in the Dabie Shan central UHP (ultra-high pressure) zone will be extended to the enigmatic northern Dabie complex to determine the areal extent of UHP metamorphism and the assignment of the northern Dabie to the Yangtze or Sino-Korean blocks.