New data concerning the age and composition of intrusion complexes of the northern part of Balygychan-Sugoi rift depression (North- Eastern Russia)

Abstract

The Balagychan-Sugoi (Omsukchan) riftogeneous depression is described by different authors both as a part of the Okhotsk-Chukotka volcanic belt (OCVB) and as a separate structure. The unique Dukat gold and silver deposit and many other ore deposits including rare metal, such as Arylah, Lunnoe, Askold, Mechta, Tidid, Krasin, are associated with this structure. All mentioned objects are located in the southern part of the depression and from this point of view are connected with the OCVB structure. Evolution of the Balygychan-Sugoi depression is closely related to the stages of magmatic evolution of the region. In the article, these stages are characterized based on the data from intrusion bodies located in the northern part (Naygain depression). This part is the most outlying from the OCVB and less studied. For the first time, the U-Pb zircon and baddeleyite dating as well as the description of petrographic and geochemical composition have been carried out for Mandychan gabbro-diorite and Nayahan gabbro leucogranite intrusion complexes from the northern part of the depression and for the Omsukchan leucogranite complex. The Late Jurassic — Early Cretaceous intrusions of the Mandychansk complex dated as 143–139 Ma marks the beginning of the rift depression formation. The intrusion of granitoids of the Nayahan and Omsukchan complexes dated as 84–85 and 81–82 Ma correspondently is related with the new stage of magmatic activity, synchronous to the OCVB formation. The petrographic and geochemical compositions of these granitoids indicate their belonging to the I-type granites, which are typical for extension environments, whereas leucogranites of the Omsukchan complex have some features corresponding to A-type granites.