Hf-Sr-Nd-Pb isotopes and petrogeochemistry of the Huangshandong sulfide-bearing mafic-ultramafic intrusion in the Central Asian Orogenic Belt,NW China

摘要

Several sizable magmatic sulfide deposits have been found in north China within the Central Asian Orogenic Belt (CAOB).The Huangshandong mafic–ultramafic intrusion is one of many important sulfide-bearing mafic-ultramafic intrusions in the Chinese Tianshan orogenic belt which is located in the southern part of the CAOB in north Xinjiang,NW China.The Huangshandong intrusion is intruded into the Mesoproterozoic metamorphic rocks,lens-shaped on the surface with an areal extent of about 2.8 km2,is a multiple intrusion composed by peridotite phase,norite phase,gabbro phase and diorite phase.The calculated εNd(t) and εHf(t) values (t=274 Ma) of the Huangshandong intrusion rocks range from 6.6 to 10.5 and from 15.38 to 19.91 respectively,the initial 87Sr/86Sr values between 0.7028 and 0.7038,206Pb/204Pb (17.698- 18.110),207Pb/204Pb (15.397-15.508),and 208Pb/204Pb (37.138-37.795) indicate that the Huangshandong intrusion derived from depleted source mantle.The high La/Sm ratios (1.06–3.03),La/Nb ratios (0.16–4.19),Th/Ta ratios and lower Nb/U ratios suggesting some crustal contamination.The positive εHf values of zircon and the mixing calculations of (87Sr/86Sr)i and (143Nd/144Nd)i show that ～5％ lower crustal contamination.