MINERALOGY OF THE OXIDE MINERALS IN THE BUCK CREEK MAFIC-ULTRAMAFIC COMPLEX, NORTH CAROLINA
Metadunite is composed of Mg-rich olivine and chromite. Unaltered chromite is brown or oqaque in PPL. The unaltered chromite is a Al (cr# = 100xCr/Cr+Al = 31-68) Mg (mg# = 100xMg/Mg+Fe) chromite. Progressive hydration alters the chromite to chromian clinochlore and lowers the Al content of the relict chromite (cr# = 42-96). Replacement of the chromite takes place along the (111) directions giving the grains a lattice appearance. A late-stage meshwork of serpentine alters the olivine and contains magnetite.
Metatroctolite contains complex coronal textures between olivine and plagioclase grains. A brown chromite (cr# = 4-41; mg# = 49-81) is included within the metatroctolite fabric and a Al-rich green spinel (pleonaste, cr# = 7, mg# = 74) is part of the symplectite intergrowths in the coronal texture. Green spinel also rims some of the brown chromite.
The edenite margarite schist is a bright green rock with pink grains of corundum and brown chromite. The chromite is Fe-rich (mg# = 17-21) with high Al contents (cr# = 31-48). A vein edenite margarite corundum occurs in a metadunite that contains green spinel (cr# = 4, mg# = 76).
The complex pattern of variation in oxide minerals in the Buck Creek complex mimics the history of crystallization and recrystallization in the corona assemblages.