SURVEY OF MINERAL CHEMISTRY OF SOUTH AMLASH CLINOPYROXENE, NORTH OF IRAN: AN EVIDENCE OF BI MODAL GABBRO

South Amlash Gabbroic bodies in eastern of Giulan provenance, according to geological subdivision of Iran is located in Gorgan-Rasht zone. The gabbroic rocks texturally are homogenous and minerallogically and geochemically divided in two distinctive group with two different origin: 1) In Alkaline type the dominant mineralogy is plagioclase, Clinipyroxen (titan-augite) and apatite which are also enriched from LREE and HFSE such as Nb and Ti, virtually shows the characteristic of typical oceanic island basalt. 2) Subalkaline types also have plagioclase and clinopyroxene, with negative anomaly of Nb and Zr suggested the rocks which formed in an island arc. According to microprobe data, clinopyroxene in Alkaline gabbros are enriched of Ti and show alkaline affinity. Occurrence of high Ti clinopyroxene in conjunction with their geochemical characteristics, suggested that this group of gabbros are similar to the basaltic rocks which formed in an enriched-source like as oceanic island. #Mg, high content of Al2O3 and amount of Cr and Ti of these clinopyroxenes indicate that they are crystallized from an enriched basaltic source in low pressure and high Oxygen fugacity. clinopyroxene of sub-alkaline gabbros are Diopside type and #Mg and Ti and Na content equivalent with island arc gabbros. According to their clinopyroxene characteristics, it seems that these gabbros are sourced from a suprasubduction zone and from melting of a mantle which metasomatized with subducted slab fluids.