Geochemical Aspects of Na-Metasomatism in Sargaz Granitic Intrusion (South of Kerman Province, Iran)

The Sargaz granitic intrusion has been emplaced in Sargaz ophiolitic suite, south-east of Sanandaj-Sirjan metamorphic zone, south of Kerman province. The central part of the intrusive body contains pinkish coarse-grained granite, but the fractured northern part, neighboring Chah-Mazraeh fault, has been subjected to pervasive Na-metasomatism and related subsolidus reactions. In the northern altered rocks, the primary magmatic textures have been changed into a new generation of albite along with chlorite, epidote and sericite. Petrographically, in Sargaz altered rocks, albite occurs as overgrowth, crack-filling, vug-filling and interstitial forms. The first form has been replaced the primary plagioclase, and/or alkali feldspars by a coupled dissolution-reprecipitation mechanism, while, the other forms have been crystallized from Na-rich alkali fluids during Na-metasomatism. In Sargaz unaltered granites, primary feldspars contain oligoclase (An23.8-An10.6) and K-feldspar (kf70-kf95.9), while, metasomatic feldspars are entirely albite (An8.4-An0.3) without any chemical zonation. Na-metasomatism in these rocks resulted obvious mass changes in rock composition, as the altered rock are enriched in Na, La, Y, Yb, Hf and Th and depleted in K, Fe, Mg, Ca, Sr, Co and Zn. Si, P, Rb, Ti, Al and Zr possibly acted as immobile elements during Na-metasomatism. Evidences in Sargaz intrusion show that alkali Na-rich fluids caused Na-metasomatism as dissolution of primary quartz and then, crystallization of albite. Microcracks facilitated infiltration of fluids. During the metasomatism, enough quartz grains were dissolved, thereby releasing silica for the formation of different forms of new albites, thus, the role of quartz dissolution, is more important than those expected earlier.