西藏蒙亚啊铅锌矿区花岗斑岩年代学、地球化学及Hf同位素组成特征

Geochronology,Geochemistry and Hf Isotopic Compositions of the Granite Porphyry in the Mengya′a Pb-Zn Deposit,Tibet

蒙亚啊铅锌矿床位于冈底斯铅锌成矿带东段,矿区发育大量的花岗斑岩体.本文通过LA-ICP-MS锆石U-Pb年代学、主量元素、微量元素地球化学和锆石Hf同位素组成探讨了花岗斑岩体侵位时序、岩石成因、成岩物质源区及其与成矿之间的关系.锆石U-Pb年代学测试结果表明,花岗斑岩体侵位时代为13.18～13.57 Ma,系中新世岩浆作用的产物.花岗斑岩富硅,富碱,A/CNK为1.04～1.15;稀土元素呈轻稀土富集的配分模式,发育明显的Eu负异常;微量元素中富集Rb、Th、U、K、Pb等大离子亲石元素,而Ba、Sr及高场强元素Nb、Ta、Ce、P、Zr、Ti则有不同程度的亏损.主量、微量元素综合研究结果显示花岗斑岩为高分异的S型花岗岩.花岗斑岩εHf（t）值为-9.0～1.6之间,平均值为-2.0;两阶段模式年龄为996～1673Ma,平均值为1225Ma.花岗斑岩亏损高场强元素及锆石Hf同位素组成特征指示岩浆物质源区为念青唐古拉群结晶基底.

The Mengya＇a Pb-Zn deposit with lots of granite porphyries developing is located in the eastern section of the Gangdese Pb-Zn metallogenic belt.On the basis of study on LA-ICP-MS zircon U-Pb dating,geochemistry,and Hf isotopes of the granite porphyry,the emplacement sequence,petrogenesis,sources of diagenetic materials,and the relation between the Pb-Zn mineralization and granite porphyry have been discussed.Zircon U-Pb geochronology results show that the granite porphyries were formed during 13.18 to 13.57 Ma,and they were formed during the same stage of magmatism of the Miocene.Major elements of the granite porphyries have characteristics of enrichment in silicon and alkali and the parameter of A/ CNK ranges from 1.04 to 1.15.Rare earth elements have the pattern of light REE enrichment with strong negative Eu abnormality.Rare elements compositions show that granite porphyries are rich in LILE such as Rb,Th,U,K and Pb and poor in Ba,Sr and the HFSE such as Nb,Ta,Ce,P,Zr and Ti.Geochemistry results show granite porphyries in the Mengya＇a deposit are highly fractionated S type granite.εHf（t） values and two-stage model ages of zircons are-9.0～1.6 and 996～1673 Ma respectively,with the average values of-2.0 and 1225 Ma,which indicates that the magma sources of the granite porphyries in the Mengya＇a deposit were from the remelting of the Nyainqentanglha Group basement.