THE OCCURRENCE AND ORIGIN OF ATOLL GARNET IN HORNBLENDE SCHISTS FROM THE CONTACT AUREOLE OF THE MASHHAD GRANITE, NE IRAN

The formation of atoll garnet in hornblende schists from the contact aureole of Mashhad granite, NE Iran, is discussed using textural and chemical data. These data suggest the possibility of incipient replacement of pre-existing idioblastic garnet from the core. In addition, the presence of chlorite and calcite in the core of atoll garnet reveal the retrograde nature of atoll formation.