Crystal chemistry of monazite and xenotime from Saxothuringian-Moldanubian metapelites, NE Bavaria, Germany

EPMA results are given for monazite and xenotime from a series of metapelites and metapsammites with major and trace element composition characteristic of volcanic arc sediments. The grain size and shape of the phosphates indicates their continuous growth from greenschist to granulite-facies T. The whole-rock REE distribution pattern for garnet-poor assemblages is dominated by these accessory phases. Monazite incorporates the LREE La-Sm as major elements and the HREE in minor or trace amounts; an increase in YPO (sub 4) was noted with increasing metamorphic T. The brabantite component, CaTh(PO (sub 4) ) (sub 2) , is an important constituent. Xenotime is essentially a solid solution between YPO (sub 4) and HREEPO (sub 4) , with minor LREE and an important coffinite component, USiO (sub 4) . Gd is preferentially incorporated into xenotime; U and Th strongly fractionate into monazite and xenotime, respectively.