Type of Garnet Zoning in Skarns of Ghohroud Intrusion, south of Kashan

Next to the Ghohroud granitic intrusive body in the south of Kashan, skarns are outcropped, of which some contain garnet crystals with obvious zoning. In order to investigate characteristics of this zonation, garnet crystals were analyzed from core to rim by EDX point analysis, using scanning electron microscope. Obtained data show that garnet crystals belong to grandite (grassolar-andradite) series and oscillatory and complex zoning are widespread. Variation of Al and Fe from center to rim of analyzed crystal indicates sharp variation in XGras in grandite solid solution series. Therefore, garnet zoning formed during crystal growth and diffusion has an insignificant effect. However, based on the BSE images, oscillatory zoning has been disturbed by fluid infiltration next to fractures. Pattern of variation on XGras from core to rim indicates that the main factor on formation of oscillatory zonings was immiscibility in grandite series which followed by changes in hydrothermal solution composition. Sharp micron-scale boundaries in zonation and preservation of zoned garnet reveal that skarns have not experienced thermal overprint after formation and emplacement of pluton and formation of skarns were not followed by further thermal geological event like regional metamorphism in the area.