Evolution of High-Magnesium Melts During Crystallization of Rocks in Ultramafic Massifs, Siberian Platform

Abstract

The results of study of primary melt inclusions in accessory Cr–spinelides from dunite have revealed features of the chemical compositions of high-magnesium picrite–basalt melts that formed ultramafic massifs of the Siberian Platform. Computational modeling (with the PETROLOG and PLUTON software) using the inclusion compositions allowed determination of the crystallization temperatures of olivines from dunites of the Guli (1520–1420°С), Konder (1545–1430°С), Inagli (1530–1430°С), and Chad (1460–1420°C) massifs. The Cr–spinellids from the same complexes crystallized at Guli (1410–1370°С), Konder (1420–1380°С), Inagli (up to 1430°С), and Chad (1430–1330°С). Overall, computational modeling has revealed two types of trends of high-Mg melt evolution on the Siberian Platform. The first type is characteristic of the Guli Pluton, with the following rock sequence: dunite–pyroxenite–alkalic rocks. The second type occurs in the Konder massif, with a different sequence: dunite–kosvite–pyroxenite and olivine–diopside rocks.