Chemical evolution of major and minor minerals in rocks of the Arbarastakh complex (Aldan shield, Republic of Sakha, Yakutia)

Abstract

The alkaline-ultrabasic carbonatite complex Arbarastakh is located in the southwestern part of the Siberian craton. In addition to ultrabasic rocks such as pyroxenites and ijolites, various types of carbonatite dikes, phoscorites, and aillikites are present in the massif. Based on their modal and compositional characteristics, as well as the chemical composition of minerals, the rocks of the Arbarastakh complex have been divided into three groups: "aillikite," "phoscorite", and "alkaline-silicate and carbonatite" groups. The chemical compositions of olivines, phlogopites and spinellides indicate that aillikites are the least differentiated rocks in the complex. The compositional differences of micas from the "phoscorite" and "alkaline-silicate and carbonatite" groups support the liquation of the aillikite melt into two immiscible silicates and CPIO (carbonate-phosphate/iron-oxide-rich) melts. After liquation, for the "phoscorite" and "alkaline-silicate and carbonatite" groups, evolution follows fractional crystallization. Pyroxene-phlogopite-calcite and calcite carbonatites probably resulted from metasomatic alteration of silicate phases by apatite-dolomite carbonatites, which is confirmed by structural-textural features and the overlapping compositions of phlogopites, apatites and pyroxenes from calcite carbonatites and those from pyroxenites and ijolites.