Characteristics and significances of rapakivi in Yichun area of Xiaoxinganling, Heilongjiang Province

Abstract：Through 1∶250000 geological mapping of Hegang City, the authors discovered adamellite in Motianling area in the middle and south of the Xiaoxinganling Mountain, which has the rapakivi texture, and was formed in Late Carboniferous. The rapakivi feldspars are idiomorphism and assume mainly broad platy or broad columnar and subordinately spherical forms. The sizes of the rapakivi feldspars vary from 2 cm to 3.5cm. The core is pink alkali feldspar, and the crust is grayish white plagioclase 1-2mm in size. Some are spherical phanerocrysts without rapakivi. A study of lithofacies, petrochemical and geochemical characteristics of the Motianling raparkivi granite and the rock assemblage shows that it is different from the representative anorogenic raparkivi granite of the Precambrian orogenic belt. It is the I-type granite in the orogenic belt related to the subduction of the plate system and the active continental margin of the island.