Sr-Nd isotopic characteristic, U-Pb zircon geochronology, and petrogenesis of Najmabad Granodiorite batholith, Eastern Iran

Abstract

The study area is located south of Ghonabad in Eastern Iran. This area is situated between two major faults, Darouneh to the north and Dashtbyaz to the south. The movements of these faults cased major dislocation of this block. Najmabad granodiorite to granite batholith is elongated trending east-west 2×8 Km2. Mineralization is associated with granite and monzonite. Alteration zones are: propylitic, sericitic, argillic and silicification. Chemically, granite-granodiorite is met-aluminous,, spider diagram normalized to lower continental crust show enrichment of LILE such as Rb, Cs, K and LREE (La, Ce) , depletion of Ti, Sr, Ta, Nb, Ba, Cs. Based on low values of magnetic susceptibility [(5 to 11) × 10-5 SI], therefore it is classified as belonging to the ilmenite-series (reduced type). The result of U-Pb zircon age dating of granodiorite is 161.85 Ma (Middle Jurassic, Callovian time). Based on Initial εNd isotope values for granodiorite is -6.51, initial 87Sr/86Sr and 143Nd/144Nd ratios for granodiorite is (0.70913 and 0.512095), the magma for granite and granodiorite originated from the continental crust. During Middle Jurassic (Callovian) due to continental collision, Upper Triassic to Lower Jurassic rocks is regionally metamorphosed. During the continental collision, Middle Jurassic (164-162Ma) reduced type granitoid magma (Ilmenite series, continental crust melting) formed and intruded these regional metamorphosed rock in Najmabad, Shah Kuh and Sorkh Kuh area.

Keywords

• Najmabad
• Granite
• zircon
• continental collision
• magma