Zircon U-Pb ages, geochemical characteristics and geological significance of Luohe pluton in Duobaoshan area, Heilongjiang Province

Petrology, geochronology and geochemistry of Luohe pluton in the connecting areas between Great Xinganling and Lesser Khingan Mountains were studied to intensify the knowledge of the tectonic evolution in the middle part of Xingmeng orogenic belt and discuss the Jurassic tectonomagmatic evolution in Duobaoshan area. The results show that Luohe pluton is mainly composed of medium fine-grained granodiorite and fine-grained granodiorite, with a small amount of granodiorite porphyry developed in the middle of the pluton. The zircon U-Pb ages of the granodiorite is (168.09 ± 0.95) Ma, indicating that it is emplaced during the Middle Jurassic. The granodiorite is characterized by high Na, high K, low Ti and low P in major elements, and low Sr and high Yb in trace elements, with depleted HREE. And weakly negative Eu anomaly is in REE distribution, which makes the granodiorite belonging to the high-K calcium alkaline series I-type granite. The Triassic and Early Jurassic sedimentary in the study area and Great Hinggan Mountains were deficient according to the discrimination diagram of tectonic setting, which means that the granodiorite of Luohe pluton belongs to the post-collision granite. Combined with the characteristics of the early-middle Jurassic intrusive rocks around the study area, the Luohe pluton is considered to be formed in the post collisional tectonic environment after the closure of Mongolia Okhotsk ocean.