Trace-element distributions in silicates during prograde metamorphic reactions: implications for monazite formation

摘要: To assess the petrogenetic relationship between monazite and major silicates during prograde metamorphism, REE were measured across coexisting zoned in garnet through kyanite-grade pelitic schists from Great Smoky Mountains, western Blue Ridge terrane, southern Appalachians, to establish concentrations distributions before after monazite-in isograd, identify role play formation of monazite. Results indicate significant scavenging light rare-earth elements (LREE) isograd reaction; however, absolute concentration LREE hosted was insufficient produce quantity observed these schists. Monazite must have formed mainly either dissolution allanite or some other source concentrated (possibly adsorbed onto grain boundaries), even though direct evidence for is lacking a majority samples. Laser-ablation ICP-MS analyses theoretical thermodynamic calculations show that may as result contributions both silicates. Allanite breakdown initially monazite, production drew liberated allanite, possibly crystal boundaries. In many rocks reaction further promoted by staurolite-in reaction, allowing rapid, isogradic growth.