Petrogenesis of Luodong mafic-ultramafic layered intrusion,Beishan region,Xinjiang

Lens shaped Luodong mafic-ultramafic intrusion lies in Beishan region of Xinjiang in Northeastern Tarim Plate and covers an area of 2.1 km2.It consists of dunite,wehrlite,plagio-lherzolite,olivine websterite,peridotite pyroxenite,troctolite,olivine gabbro,gabbro,noritegabbro and leucogabbro.The Luodong intrusion is a layered intrusion with obvious cumulus textures and rhythmics.The mainly fractional crystallized or cumulated phases are olivine and clinopyroxene,together with minor plagioclase,orthopyroxene and Cr-spinel during magma evolution.The geochemical feature indicates weak crustal contamination.The primary magma is picritic with MgO contents up to 14.7% and high crystallization temperature of 1412 ℃.OIB-like Nd,Sr isotopic compositions and high temperature picritic primary magma indicate that Luodong intrusion may have an affinity with mantle plume and be formed by partial melting of axis plume.The Early Permain mantle-derived magmatic rocks in Northeastern Tarim Plate are thus a part of Tarim Large Igneous Province.