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

独居石作为变质作用过程中流体活动时间和类型的敏感指标

• 批准号: 0126020
• 负责人: John Ayers
• 金额: $ 19.55万
• 依托单位: Vanderbilt University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-01 至 2005-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0126020&HistoricalAwards=false
• 关键词: Monazite; Sensitive; Indicator; Timing; Type

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.

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得的年龄具有重要意义。 为了完善解释，设计了补充实验室和野外实验，以识别和表征花岗岩类和相关岩石中的独居石重结晶和蚀变。 独居石的溶解度将被测量为压力，温度和流体组成的函数，使用双胶囊法，以确定导致增强的溶解度和重结晶的条件和流体组成。 在400-600摄氏度和0.1-0.2 GPa的冷密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体atidified条件下运行，以表征重结晶的速率和蚀变对晶内分带和元素及氧同位素组成的影响。 在天然独居石中观察到的重复分带样式和氧同位素系统学将在独居石蚀变和流体之间建立牢固的联系，建立蚀变发生的条件，并大大增加解释独居石年龄的信心。野外研究旨在验证独居石中蚀变带的年龄对应于流体流入时间的假设，并检验这些领域特有的重要假设。 在接触变质晕中，岩浆流体渗入含独居石的围岩中，将研究温度变化、流体成分和流体/岩石比对先存独居石的影响：内华达州南部的Ireteba岩体、白色山脉的Birch Creek岩体。和中国东南部广东省北方的红山钨锡存款。 大别山中部超高压带独居石和锆石的年代学研究成果将扩展到神秘的北方大别杂岩，以确定超高压变质作用的范围，并确定北方大别的扬子地块或中朝地块归属。