Magma evolution of Huangshannan mafic-ultramafic intrusion in East Tianshan region : Indication from mineralogy and Sr, Nd isotopic characteristics

The Huangshannan mafic-ultramafic intrusion, located in the Jueluotage tectonic zone, East Tianshan orogenic belt, belongs to the Tudun-Huangshan-Tulaergen mafic-ultramafic rock belt. Based on previous research work, the mineral compositions of olivines and pyroxenes of this intrusion, as well as its whole rock Sr-Nd isotopic characteristics were studied in this paper. Further more, by comparison with typical intrusions in the same region, such as the Huangshan, the Huangshandong and the Xiangshan, we try to find its magma source, and to detect the properties and the evolutionary process of its parental magma. The results of Sr-Nd isotopic characteristics of the Huangshannan intrusion indicate that its source comes from a slightly depleted mantle, which is a more enriched mantle source compared with those for the Huangshan, the Huangshandong and the Xiangshan intrusions. All of the olivines from the Huangshannan intrusion are chrysolite. The orthopyroxenes are mainly composed of broncite, with small amount of amblystegite. The clinopyroxenes mainly consist of augite and diopside. The compositions of clinopyroxene and olivine indicate that the parental magma of the Huangshannan intrusion is tholeiitic basalt magma with a low evolution degree, with High Mg and Ni contents. The calculated contents of the parental magma of the Huangshannan intrusion is as follows : FeOT = 13. 20% , MgO = 16. 96% , Ni = 377.2 x 10(-6). We also realize that the parental magma doesn' t experience a sufficient sulfide segregation process, which dominantly lead to the high Ni content in its parental magma and poor metallogenetic potentiality of the Huangshannan intrusion.