南天山南缘下二叠统小提坎立克组英安岩的地球化学和同位素地质年代学特征

摘要

Along the southern margin of South Tianshan occurs a 300-km-long EW-trending volcanic rock belt consisting of mafic, intermediate and acidic rocks of the lower Permian Xiaotikanlike Formation. Dacites outcropping near the Tiereke hot spring are characterized by calc-lkaline (8=1. 37～ 1. 69) and metaluminous-peraluminous (A/CNK = 0. 89-1. 36) , enrichment in LREE (La/Yb=10. 45～12. 77) and elements such as Th, Hf, Zr, Tb, Gd, Rb,U, and depletion in elements such as P, Ti ,Nb, Ta, Sr and Ba. They have a medium negative Eu anomaly (δEu = 0. 57 ～0. 62), with εNd(288 Ma) = -6. 77, εSr(288 Ma) = 117. 78, TDM=1. 47 Ga. U-Pb LA-ICP-MS dating on zircon yields a weighted 206pb/238U age of 288. 4 + 3. 0 Ma (MSWD = 2. 7). Combined with regional geological data, the dacites are likely the result of partial melting of mid-lower crust in the Tianshan orogenic belt, and formed in an post-collsional extension settings in early Permian.%南天山南缘发育一条东西向延伸近300 km的下二叠统小提坎立克组基性、中性和酸性火山岩带.拜城县铁热克温泉西侧下二叠统小提坎立克组的英安岩具有钙碱性(里特曼指数δ=1.37～1.69)和准铝—过铝质特征(A/CNK=0.89～1.36).轻稀土富集(La/Yb=10.45～12.77),具有中等铕负异常(δEu=0.57～0.62)；微量元素富集Th、Hf、Zr、Tb、Gd、Rb、U,亏损P、Ti、Nb、Ta、Sr、Ba.εNd(288Ma)=—6.35,εSr(288 Ma)=117.78,模式年龄(TDM)为1.47 Ga.LA-ICP MS锆石U-Pb定年获得了206 pb/238U加权平均年龄288.4±3.0 Ma (MSWD=2.7).结合区域地质资料表明,该英安岩很可能源自天山造山带中—下地壳的部分熔融,形成于早二叠世南天山造山带碰撞后伸展背景.