K- and Si-Metasomatism, Mineral Transformation and Formation of Granitoids from Basic Rocks in Qooshchi Area, NW Iran: A Mineralogical Context

The Qooshchi area lies to northwest of Orumieh Lake in western Azerbaijan, NW Iran. A basement metamorphic complex, consisting of Precambrian schists and gneisses, has been intruded by gabbros and diorites. Granitoids are grouped into five suites according to their mineralogy, texture and exposed features. The main body, pink Qooshchi granite, and apophyse-like, myrmekite-bearing grani toids are discussed in this paper. On the basis of field observations and micros copic studies, an intensive metasomatism has overprinted the country rocks, espe cially gabbros, transforming them into a more felsic composition. A prior ev ent of intensive deformation and cataclasis preceded the metasomatism, allowing the introduction of hydrothermal fluids. K-metasomatism converted plagioclase into K-feldspar (microcline), myrmekite, and sodic plagioclase as Si-metasomati sm replaced the ferromagnesian silicates by quartz. Apophyse like bodies within gabbros, called leucometasomatites, are formed during this process.