CLINOPYROXENES OF NEPHELINE SYENITES FROM THE TAMAZEGHT (HIGH-ATLAS, MOROCCO)

Within the southern part of the Tamazeght alkaline complex, five types of nepheline syenites were recognized: amphibole malignites, biotite malignites, zircon syenites, lavenite syenites and eudialyte syenites. The compositional pyroxene trend shows a two-stage development separa ted by a compositional gap, firstly from diopside to hedenbergite, las tly to aegyrine, representing the successive stages of crystallization from the same parental magma. The compositional gap, studied from zon ed crystals, is the result from changes of substitution sites in pyrox enes, related to the increase of alkaline saturation of magma, and to the break in magnetite crystallization.