Physicochemical properties and tectonic setting of the basic intrusive rocks from south of the Germi (Ardabil): based on amphibole and plagioclase crystals chemistry.

Eocene- Oligocene intrusive stock of basic bodies of south Germi are intruded into and cropped out in Eocene basaltic lavas. Studied gabroic intrusive rocks generally show granular texture with assemblages characterized by Cpx + Pl + Bi + Amph. Pyroxenes have augitic composition, plagioclase have labradoritic and amphiboles have pargasitic compositions. The studied amphiboles show (Na+K)A ≥ 0.5 with variable amount (0.57 - 0.99), Fe+3 content ranges from 0.00 to 1.17, also AlVI ranges from 0.00 to 0.68 and AlVI<Fe+3. Chemical composition of amphibole can be used in determination of magma genesis. Results of thermobarometric studies indicate that the amphiboles formed at temperature range of 750oC -885 oC and pressure range of 5.96 – 8.36 Kb, that coincide with depth of 18.5 – 25.9 km. Also using the amphiboles and coexisting plagioclases thermometer shows temperature range from 758 oC to 865oC. Chemical composition of amphibole minerals with Fe2+/(Fe2++Mg) ratio from 0.11 to 0.32, variable oxygen fugacity (-5.83 - -6.34) and water content (3.09 – 4.16%) shows that they formed from sub-alkaline magma. Chemical studies of amphibole crystals indicate that they formed during a subduction related magmatic activity.