Hf-Nd Isotoptic Characteristics of the Huangshandong Mafic-ultramafic Intrusion, Eastern Xinjiang, and Their Geological Implications

The Huangshandong mafic-ultramafic intrusion,is located at the centre segment of Tudun-Huangshan-Jing'erquan-Tulaergen mafic-ultramafic rock belt,the northern of the East Tianshan,controlled by the Kangurtag-Huangshan ductile sheer zone,and it is a multiple intrusion formed by at least three pulses of magmas with different compositions,and composes of lherzolite,olivine gabbro,gabbro norite,and gabbro diorite.Sulfide mineralization is associated with the second (gabbronorite) and third (plagioclase-bearing lherzolite-wehrlite) intrusive phases that are volumetrically minor in the intrusion.The ¹⁷⁶Hf/¹⁷⁷Hf ratios of the Huangshandong zircons range from 0.283 037 to 0.283 165 with an average of 0.283 098; ¹⁷⁶Yb/¹⁷⁷Hf ratios range from 0.013 590 to 0.046 774 with an average of 0.030 491,that these ratios are all less than 0.05 indicates that little radiogenic Hf has accumulated in these zircons; ¹⁷⁶Lu/¹⁷⁷Hf ratios range from 0.000 700 to 0.002 094 and average 0.001 318; the εHf_(t) (t=274 Ma) values range from 15.38 to 19.91 and average 17.57; εHf_(O) values range from 9.50 to 14.30 with an average of 11.78.The calculated εNd_(t) values and initial ⁸⁷Sr/⁸⁶Sr values (t=274 Ma) of the Huangshandong intrusive rocks between 6.6 and 8.3,and between 0.703 1 and 0.703 8,respectively.The Hf and Sr-Nd isotopic compositions of the Huangshandong intrusion are significantly different from that of the Tarim basalts and coeval mafic-ultramafic dykes in the Tarim basin,similarly with the volcanic arc basalts and consistent with the mid-ocean basalts (MORB).The results of mixing calculations using Sr-Nd isotopes show that crustal contamination is 2% in the Huangshandong parental magmas.