新疆贝勒库都克岩体的锆石SHRIMP U-Pb年龄及其地质意义

SHRIMP U-Pb zircon dating of the Beilekuduk pluton in Xinjiang and its geological implications.

贝勒库都克正长花岗岩体位于东准噶尔贝勒库都克富碱花岗岩带中,该带由正长花岗岩、钠铁闪石花岗岩、钠闪石花岗岩体组成。通过对贝勒库都克正长花岗岩体锆石SHRIMP U-Pb年龄测定,获得306±5 Ma的^(206)pb/^(238)U年龄,表明岩体侵位时代为晚石炭世末。结合前人的年龄数据限定了贝勒库都克富碱花岗岩带形成时代为晚石炭世末-早二叠世初(307～290 Ma)。岩石地球化学表明,贝勒库都克正长花岗岩具有富硅、碱、REE、Rb、Th、Ce、Nd、Hf元素,贫Ba、Sr、P、Ti、Eu、Nb、Zr元素,富集轻稀土,强负铕异常,(Ga/Al)×10~4=4～4.1,具有A_2型花岗岩特征。贝勒库都克富碱花岗岩的形成是紧随造山运动之后发生,形成于后碰撞阶段的张性构造环境中。

The Beilekuduk syenogranite pluton is located in the Beilekuduke alkali-rich granite belt, East Junggar. This alkali-rich granite belt is composed of syenogranite, arfvedsonit granite and riebeckite granite plutons. SHRIMP U-Pb dating for zircons from the Beilekuduk syenogranite pluton yielded a (206)Pb/(238)U age of 306 +/- 5 Ma, suggesting that the emplacement of the pluton occurred at the end of the Late Carboniferous. On the basis of this new SHRIMP zircon U-Pb age, combined with the zircon U-Pb ages of the granite belt reported in the literature, the Beilekuduk alkali-rich granite belt is determined to be terminal Late Carboniferous to initial Early Permian (307 similar to 290 Ma) in age. Geochemically, the Beilekuduk syenogranite is enriched in silica, alkalis, REE, Rb, Th, Ce, Nd and Hf and depleted in Ba, Sr, P, Ti, Eu, Nb and Zr and exhibits LREE enrichment and a strong Eu negative anomaly, with (Ga/Al) x 10(4) = 4 to 4.1, showing the features of an A(2)-type granite. It formed in an extensional environment during the post-collision stage, immediately following the orogenic movement.