Hydrothermal experiments for the reconstruction of REE phosphates of Precambrian paleosols

Abstract

Precipitation of monazite on original rhabdophane occurred by hydrothermal experiments of basalt and weathered granite containing rhabdophane and churchite (which had been already altered to xenotime) at 200 °C. The occurrences of monazite and xenotime found in the 2.5-Ga Pronto paleosol can be explained as follows: rhabdophane and churchite were formed at the time of weathering and altered to monazite and xenotime, respectively, by later metasomatism and metamorphism. Because Ce, like the other LREEs, is inherited only from rhabdophane to monazite, the compositions of monazite reflect atmospheric oxygen at the time of weathering.