Zircon U-Pb geochronology and petrogenesis of Middle Eocene monzonitic plutons in NE Turkey: constraints for generation of post-collisional I-type shoshonitic magmas

We present U - Pb zircon geochronology and whole-rock Sr-Nd-Pb isotopic compositions of monzonitic plutons from NE Turkey to elucidate their genesis and provide significant insights into the generation of post-collisional I-type shoshonitic magmas. Zircon U - Pb dating of the monzonitic plutons yielded an emplacement of the Middle Eocene (44-39 Ma). Geochemically, the monzonitic plutons are I-type, metaluminous, and shoshonitic in composition, and have high contents of total alkalis and LILE, high ratios of LREE/HREE and LREE/HFSE, and show negative Nb-Ta-Ti and Eu (Eu-N/Eu* = 0.69-0.84) anomalies. The monzonitic plutons have homogeneous and moderately low initial Sr-87/Sr-86 (0.70464-0.70495), positive epsilon Nd-(t) values (0.33 to 1.28), and narrow variation of the initial Pb isotope contents with Pb-206/Pb-204 (18.74-18.82), Pb-207/Pb-204 (15.64-15.65), and Pb-207/Pb-204 (38.81-38.90). The combined use of whole-rock trace elements and isotopic compositions with regional geology suggests that parental magmas of the monzonitic plutons were generated from mainly melt-metasomatized sub-continental lithospheric mantle source and lesser crustal components in an extensional orogenic setting, and then monzonitic magmas have evolved by dominantly fractional crystallization in crustal levels.

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