Juvenile crust and mantle sources for the Nasrand intrusive rocks, the central Urumieh-Dokhtar magmatic arc, Iran: Insights from elemental and isotopic geochemistry

The Oligocene Nasrand intrusive rocks (NIRs), located in the central part of the Urumieh-Dokhtar magmatic arc, are mainly composed of granite and subordinate diorite and gabbro. These rocks are characterized by the enrichment of light rare earth elements (LREEs), Nb-Ta negative anomalies, and high LILE/HFSE, suggesting a subduction-related origin. The felsic rocks with granite compositions have high SiO2 content (69.77-77.88 wt.%), low Mg# (0.02-0.43), low Nb/Ta, and Zr/Hf (Avg: 12.53, and 33.08, respectively). The initial Sr-87/Sr-86 ratio and epsilon Nd-(t) values in felsic rocks range from 0.70577 to 0.70576 and 0.4 to -0.3, respectively. These data suggest that these felsic rocks originated from juvenile crust by heat rising from basaltic magmas in an orogenic setting. The mafic-intermediate rocks and dikes are gabbro, gabbroic diorite, and monzodiorite, with low SiO2 content (48.08-56.11 wt.%) and high Mg# (0.37-0.68), with average ratios of Nb/Ta and Zr/Hf are 27.88 and 39.84, respectively. The initial Sr-87/Sr-86 ratio and epsilon Nd-(t) values for mafic-intermediate rocks and dikes are 0.70583 to 0.70476 and -0.1 to +2.6, respectively. These characteristics indicate magma from a mantle source that had undergone minor mixing with juvenile crust. It seems mantle-derived juvenile magma underplating played an important role in the crustal growth in the Urumieh-Dokhtar magmatic belt during the Ediacaran to Early Cambrian, relative to other time frames.