Occurrence of Rhonite with clinopyroxene in the Kamarbon Teschenitic gabbro (Central Alborz)

In northern hillside of Central Alborz, south of the Kamarbon village, there is an outcrop of alkaline gabbro that has fine grain theralite in margins and toward the center, changes to coarse grain teschenite. In the teschenitic rocks the main minerals are diopside clinopyroxenes and rhonite. In this research, the occurrence of this mineral in Kamarbon gabbroic intrusion is reported and its mineralogical properties, paragenesis and source of magma are investigated based on whole rock and microprobe analysis data. In these rocks, rhonite has (Si, IVAl)6.02(Ti, VIAl, Fe+3, Fe+2, Mn, Mg)5.99 (Na, Ca)1.97O22 composition. This composition is similar to pervious published analysis of rhonite. Studied rhonites in teschenitic gabbroitic rocks has low values of Na+IVSi and high values of Ca+IVAl that can be primary source for this mineral. The studies indicate the stable paragenesis of rhonite and Al rich clinopyroxene. Considerable factors for crystallization of rhonites in undersaturated magmas are enrichment of Al and Ti and depletion of Si whereas associated clinopyroxenes represents enrichment of Al2O3 and TiO2 and depletion of silica. Therefore regarding to the mineralogical and chemical properties of rhonite and associated clinopyroxenes, it could be concluded that rhonite mineral may be produced from an undersaturated alkaline magma enriched in Al and Ti. Occurrence of rhonite and associated clinopyroxenes in south Kamarbon teschenitic alkaline gabbros represents the existence of an undersaturated plutonic phase in nothern part of Central Alborz.