The Genesis and Evolution of Alpine‐Type Ultrabasic Rocks in Western Junggar, Xinjiang

Abstract

Abstract The alpine‐type ultrabasic rocks of the studied area have undergone plastic deformation under a temperature about 800–1200°C, a pressure about 0.9–1.68 GPa and differential stress of 0.2–0.35 GPa in relatively dry conditions, forming ultrabasic mylonite with porphyroclastic and mylonitic textures. Primary crystallized silicate melt inclusions and melt‐fluid inclusions are discovered in porphyroclastic minerals and ore‐forming chrome spinel. These rocks are formed under relatively stable physico‐chemical conditions through liquid immiscibility of silicate melts, at 1200°– 1300° C and 1.1–1.38 GPa, equivalent to a depth of 40–50 km. No inclusion has been found in recrystallized secondary olivine and pyroxene, indicating that the plastic deformation happened after the formation of the rocks.