南天山拜城县波孜果尔A型花岗岩类锆石U-Pb定年及其Lu-Hf同位素组成

Zircon LA-ICP-MS U-Pb dating and Lu-Hf isotopic system of A-type granitoids in South Tianshan,Baicheng County,Xinjiang

新疆拜城县波孜果尔A型花岗岩类岩体位于塔里木地台北缘及邻区的近东西向碱性侵入岩带上，主要岩石类型为霓石钠闪石英碱长正长岩、霓石钠闪碱长花岗岩、黑云母碱长正长岩。全岩SiO2：68．97％～74．14％，Na20＋K20=9．67％～11．19％，A1，O，=13．72％～15．26％，Fe20，=0．18％～1．41％，FeO=0．91％-1．51％，CaO=0．35％-0．63％。稀土元素总量较高，∑REE=298×10～-1286×10～，平均706×10～，轻稀土富集，重稀土亏损，强烈的Eu负异常，呈“右倾海鸥型”的稀土元素配分模式。富Nb、Ta、Zr、Hf等高场强元素，亏损Ba、K、sr等大离子亲石元素，zr＋Nb＋ce＋Y=936×10-6 —3684×10-6，平均1813×10-6。为A1型花岗岩。岩体形成于早二叠纪。锆石LA—ICP-MSU—Pb年龄为287．7～291．6Ma，平均289．8Ma，岩体形成后，在279．1～282Ma左右经历了后期热液流体的改造。锆石εHf（t）值为-6．3—9．0，两阶段模式年龄（trj。）跨越古元古代晚期．新元古代中期，主要集中在中元古代。岩浆平均温度832～839℃，形成于非造山的板内构造环境，且具高温、无水、低氧逸度的成岩特点。该岩体具有壳幔混源的特点。

The Boziguoer A-type granitoids in Baicheng County, Xinjiang, belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks. The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite, an aegirine or arfvedsonite alkali feldspar granite, and a biotite alkali feldspar syenite. The chemical composition of the alkaline granitoids show that SiO2 varies from 68. 97% to 74. 14%, Na20 ＋ K20 is 9. 67% ~ 11.19%, Al2O3 ranges from 13.72% to 15.26%, Fe203 is0. 18% -1.41%, FeO is between 0. 91% and 1.51%, and CaO is 0.35% ~0.63%. The REE content is high and the total Y. REE is 298 × 10 -6 ~ 1286 x 10-6 （ mean = 706 × 10-6 ）, showing LREE enrichment HREE depletion with strong negative Eu anomalies. In addition, the chondrite-normalized REE patterns of the alkaline granitoids belong to the ＂seagull＂ pattern of the right-type. The Zr ＋ Nb ＋ Ce ＋ Y content is 936 ×10 -6 ~ 3684 × 10 -6 with a mean of 1813 × 10 -6. Furthermore, the alkaline granitoids have high HFSE （Nb, Ta, Zr, and Hf） content and low LILE （Ba, K, and Sr） content. The zircons from samples llCL901 ~ 11CL904 show a black core-white rim structure with a ^206 pb/nS U age of 287. 7 ~ 291.6Ma （Early Permian）, in addition, the granites experienced reworking by late-stage hydrothermal fluid 279. 1 ~ 282Ma ago. The Hf isotope systematics of samples 11 C1.901 ~ 11CL904 show that εHf（t） = -6. 3 ~9. 0 with positive and negative values indicating that the magma source mixed with continental crust and mantle materials. Two-stage Hf model ages （tDra ） covered the Late Paleoproterozoic and Middle Neoproterozoic, and mainly concentrated in the Mesoproterozoic. The Boziguoer A-type granitoids share similar features with Al-type granites. The average temperature of the granitic magma was estimated at 832 ~ 839℃. The Boziguoer A-type granitoids show crust-mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature, anhydrous, and low oxygen fugacity conditions.