Geochemical Characteristics and Geologic Implications of Halaqiaola Mafic Intrusion,Southeast Altai,Xinjiang

Halaqiaola mafic intrusion lies in the southeast margin of the Altai orogenic belt in Xinjiang,northwestern China.The main rock types are gabbros,gabbro norite,plagioclase-bearing pyroxenite,olivine gabbro and troctolite.Halaqiaola intrusion has low contents of TiO2(0.09%-1.28%) and alkali(Na2O+K2O=0.37%-0.78%),and belongs to tholeiitic series;the intrusion is rich in large ion lithophile elements and light rare earth elements and depleted in high field elements(such as Nb,Ta).The eNd(t) and the eSr(t) values range from-2.62 to-0.78 and 37.49 to 45.28 respectively.Element geochemistry and Nd-Sr isotopic composition shows that the magma was derived from the dehydration of subducted plate and metasomatismed enriched lithosphere mantle.The primary magma of the intrusion is basaltic magma.During the process of magma evolution,the primary magma has experienced fractional crystallization of olivine,clinopyroxene and plagioclase,with ilmenite-precipitation in the late period.