Olivine compositional mapping of mafic-ultramafic complexes in eastern Xinjiang (NW China): Implications for Cu-Ni mineralization and tectonic dynamics

Abstract

Early Permian mafic-ultramafic complexes in eastern Xinjiang (新疆) are mainly distributed in the Beishan (北山) area, Mid-Tianshan (天山) massif and Jueluotage (觉罗塔格) belt. Systematic compositional mapping of olivines from these Early Permian mafic-ultramafic complexes demonstrates that an apparently spatial distribution and heterogeneous partial melting in the mantle source exists from the Beishan area, across the Mid-Tianshan massif, to the Jueluotage belt from the south to the north. This is probably consistent with the spatial evolutional differences and tectonic features of these three belts. The decreasing degree of partial melting, as revealed by decreasing Fo contents of olivines, from south to north and from east to west reflects the southward subduction of the Paleo-Asian Ocean and the south location of the indistinct mantle plume in the Permian. Simultaneously, NiO and Fo-mapping in olivine also indicates that sulfide segregation before olivine crystallization played an important role in Ni-Cu mineralization in the mafic-ultramafic complexes. Olivines with the compositional range of Fo (77–86) and NiO (less than 0.22 wt.%) are more favorable for Ni-Cu sulfide mineralization.