AGE OF GRANITOIDS OF THE BEKCHIUL PLUTON (LOWER AMUR REGION)

Abstract

The Bekchiul pluton is located in the Lower Amur region and is a large granitoid body of complex structure within the Zhuravlevka-Amur terrain of the Sikhote-Alin orogenic belt. On the northwestern flank of the Bekchiul pluton there is the Mnogovershinnoe gold-silver deposit. To determine the formation time of this pluton, U/Pb dating was performed on zircons from the second-phase granodiorite of the Bekchiul complex and the third-phase granite. Granodiorite yielded U-Pb age of 73.8±0.4 Ma, and granite – 66.2±0.3 Ma. Some zircon grains found in granite have a U-Pb age of 75.6±0.6 Ma which is close to that of granodiorites. Magmatic pulses of about 76–73 Ma and about 66 Ma are synchronous with the stages of ore formation of the Mnogovershinnoe deposit, corresponding to earlier-obtained K-Ar age of adularia from ore zones. The formation of granitoids and the associated mineralization probably occurred due to subduction of the Izanagi Plate beneath the continental margin.

Keywords

• bekchiul pluton
• sikhote-alin orogenic belt
• zhuravlevka-amur terrain
• granitoids
• u-pb zircon dating
• late cretaceous