Timing of chlorine-rich fluid infiltration and behavior of REE-bearing minerals in high-temperature metamorphic terrane

Abstract

Pelitic gneisses with Cl-rich biotite included in garnet are linearly distributed for 200 km long in the Sor Rondane Mountains. The condition of Cl-rich fluid infiltration is estimated to be ca. 800 oC, 8 kbar at 600 Ma. Garnet in this sample has core-rim boundary defined by P-zoning, rim formation being contemporaneous with the Cl-rich fluid infiltration. The garnet core includes monazite, and the rim includes xenotime and coarse-grained zircon. This suggests that originally LREE-rich mineral assemblage changed to HREE- and Zr-rich ones, because of Cl-rich fluid infiltration. Further study is needed to account for the mechanism of this process.