Material composition of the Mesozoic igneous rocks of the Mikhailovsky massif and small bodies of the Evotinskiy ore district (Southern Yakutia, Aldan-Stanovoi shield)

Abstract

The petrographic and geochemical characteristics of the Mesozoic igneous rocks of the Mikhailovsky massif, including the sills and dikes of the Evotinsky ore district located in the central part of the Nimnyr terrane of the Aldan-Stanovoy shield, were examined. This study revealed for the first time that the Mikhailovsky Massif is composed of  quartz monzonites, while the sills and dikes are composed of quartz syenites. These rocks are geochemically close to the shoshonite-latite series of island arc rocks and are enriched in LREE and depleted in HREE, characterized by aweak negative Eu-anomaly. The sequence of magmatism development in the Mesozoic has been established: the formation of rocks of the Mikhailovsky massif and most small bodies occurred in the post-collision period, followed by the intrusion of quartzsyenite dike bodies in theanorogenicstages of territorial development.The study suggeststhat all the studied igneous rocks of the northeastern part of the Evotinsky region are characterized by a duality of geochemical composition,which indicates either intense mantle-crustal interactionor the existence of two sources of both mantle and crustal originat that time.