Major-trace elements geochemical characterization, geochronology and radiogenic isotopesg of Eocene magmatic rocks in Anique, Qaradagh pluton, NW Iran

Abstract

The Qaradagh batholith straddles the border between Armenia and NW Iran and is a constituent of the Arasbaran Magmatic Belt (AMB). The Qaradagh batholith is composed of several distinct basic to intermediate and felsic intrusions, cross cut by various dykes.

⁴⁰Ar/³⁹Ar biotite step-heating plateau ages of 40.52 ± 0.44 Ma for a granodiorite intrusion indicate that intrusive activity is of early Eocene age. These intrusions are generally biotite, amphibole, magnetite, and titanite-bearing oxidized I-type and can be determined as magnetite series Cordilleran granitoids. They are enriched in LILE, relatively enriched in LREE, depleted in some HFS elements specially Ti, Nb, Ta (TNT) and P, and relatively depleted in HREE. They also have distinctly low Rb/Sr ratios (mainly 0.08-0.525), consistent with derivation from mantle wedge materials and limited contribution from crustal materials. The granitoids have arc-like signatures and the relatively flat HREE patterns (Sm/Yb = 1.08 - 5.29). The restricted range of initial ⁸⁷Sr/⁸⁶Sr (0.7043 to 0.7050) and positive εNd_i values (+3.1 to +2.5) suggest depleted mantle- derived magmas were the primary source of these granitoids. Based on the chronology results, the Anique granitoids were the earliest bodies intruding the AMB which took place during the early stages of subduction evolution. These magmatic units were emplaced along the ocean-ward portion of the AMB continental arc. The major and trace element, and Sr-Nd isotope geochemistry indicates that these granitoids have mantle- dominated characteristics, which suggests accretion of new continental crust in the Early Cenozoic in this part of the northwestern Iranian Micro-Continent.