Petrogensis and tectonomagmatic setting of Moghanlu Granitoid (NW of Iran)

The Moghanlu granitoid was located in the northwest of central Iranian structural zone with a Precamberian age. Based on field observations and microscopic studies, this body includes tonalite, monzogranite and granodiorite. Based on geochemical studies, tonalites are I-type, calc-alkaline, and weakly peraluminous. Based on isotopic studies [(87Sr/86Sr (i) and εNd (i) values equal to 0.710544, -7.01 respectively)], low values of La/Yb, Sr/Y , Nb/Ta, Ni and Cr, low fractionated patterns (flat pattern) of rare earth elements (REE) and negative anomaly of Eu, it can be concluded that they were resulted from melting of amphibolitic thickened mafic crust or under plate basalts (in the stability field of plagioclase) in low pressures and low depth in volcanic arc granitic area. Monzogranites are S-type, peraluminous and calc-alkaline, which are plotted in collision zone. These rocks are enriched in LILE and LREE and also depleted in HFSE, which represent negative anomaly of Ba, Ti, Nb, Sr with Mg number about 11-20. On the basis of this result, it can be concluded that the granitoids were generated from melting of crustal rocks (melt derived from pelitic rocks with high plagioclase content). Granodiorite are I-type, calc-alkaline and peraluminous. They have 87Sr/86Sr (i) and εNd(i) values of 0.71713, -10.55, Mg number between 31-33, negative anomaly of Sr and Nb, and also positive anomaly of La and Th, which represent that these rocks were generated from partial melting of lower to middle crust. These granodiorites were formed because of thickening and shorting due to continental- continental collision (collision of Iranian-Arabian plates). With respect to geographical location of Moghanlu body and the age of this units, it seems that these granitoide rocks formed on active continental margin during convergence of Central Iran and Alborz-Azarbayjan plates to Arabian platform during Precambrian.