Mineralogical and mineral-chemical changes in a fractionation-dominated diorite-monzodiorite-monzonite sequence; evidence from cathodoluminescence

CL investigations on these rocks from Freital in the Meissen plutonic complex NW of Dresden revealed complex growth patterns in apatite, plagioclase and K-feldspar. In apatites from monzonites violet and yellow luminescing zones are caused by variations in abundance of Sm (super 3+) , Dy (super 3+) , Eu (super 2+) , Ce (super 3+) and Mn (super 2+) ; the apatite compositions in diorite and monzodiorite suggest alkaline affinities for their parental melt. The dioritic plagioclase luminesces bluish green, characterized by the Mn (super 2+) and Fe (super 3+) peaks at 560 and 750 nm, respectively; an increase in the 750 nm peak in monzonitic plagioclases generates a brownish CL, indicating higher Fe (super 3+) . The successive enrichment of mainly blue luminescing K-feldspar may result from fractional crystallization of the basic magma. Late K-feldspar shows increasing Fe (super 3+) -induced red luminescence suggesting metasomatic influences.