【摘要】 本文对西乌珠穆沁旗迪彦庙-达青俯冲增生杂岩带内的斜长花岗岩开展了岩石地球化学、锆石U-Pb年代学和锆石Hf同位素研究。该区斜长花岗岩主要由斜长石、石英和少量黑云母组成,具有较高的SiO₂（68. 24%～79. 34%）、低Al（Al₂O₃为11. 33%～15. 23%）、低Ti（TiO₂为0. 270%～0. 773%）、低MgO（Mg#值为11～47）和富Na贫K（Na₂O/K₂O为4. 90～24. 25）的特征。稀土元素总量为14. 15×10^-6～189. 04×10^-6,稀土元素球粒陨石标准化配分曲线为轻稀土弱富集、重稀土平坦的配分模式。微量元素原始地幔标准化蛛网图中,Nb、Ta和Ti为负异常。LA-ICP-MS锆石U-Pb测年结果显示:样品DYM17-006的锆石U-Pb谐和年龄为330. 1±3. 2 Ma,样品DQ17-007的锆石U-Pb谐和年龄为316. 5±2. 4 Ma,分别代表了迪彦庙和达青地区斜长花岗岩的形成年龄。锆石Hf同位素组成显示具有高的(¹⁷⁶Hf/¹⁷⁷Hf)_t比值以及正的ε_Hf（t）值（9. 387～16. 251）,反映其岩浆源自于亏损地幔。综合分析认为,迪彦庙-达青俯冲增生杂岩带内斜长花岗岩应属于结晶分异型花岗岩,由起源于亏损地幔源区的洋脊玄武质岩浆结晶分异形成。迪彦庙-达青一带存在一个长期演化的大洋,在石炭纪处于洋盆扩张阶段,伴随着古亚洲洋的俯冲消减及洋陆转换,最终构成了中亚造山带的一部分。更多还原

【Abstract】 This paper presents a study on petrogeochemistry,U-Pb chronology of zircon and Hf isotope of the plagiogranite in the Diyanmiao-Daqing subduction accretionary complex belt in West Ujimqin,Inner Monglia. The plagiogranite is composed predominantly of plagioclase,quartz and a small amount of biotite,with high SiO₂（ 68. 24% ～ 79. 34%）,low Al（ Al₂O₃ is 11. 33% ～ 15. 23%）,low Ti（ TiO₂ is 0. 270% ～ 0. 773%）,high MgO（ Mg#value 11 ～ 47）,rich Na and poor K（ Na₂O/K₂O 4. 90 ～ 24. 25）. The total amount of rare earth elements is 14. 15 × 10^-6～ 189. 04 × 10^-6. The distribution curve of rare-earth elements standardized by chondrites displays a distribution model of weakly enriched LREE and flat HREE. Nb,Ta and Ti are negative anomalies in the spider diagram of trace elements normalized by the original mantle. According to LA-ICP-MS zircon U-Pb dating results,the concordant ages of the zircons from samples DYM17-006 and DQ17-007 are 330. 1 ± 3. 2 Ma and 316. 5 ± 2. 4 Ma,respectively,which represent the formation ages of the plagoclagic granite in the Diyanmiao and Daqin areas,respectively. The Hf isotopic composition of zircons shows a high(¹⁷⁶ Hf/¹⁷⁷ Hf)_t ratio and a positive ε_Hf（ t） value（ 9. 387 ～ 16. 251）,indicating that the magma was originated from the depleted mantle. Comprehensive analysis suggests that the plagiogranites in the Diyanmiao-Daqing subduction accretionary complex belt should be attributed to crystalline heterogeneous granite,which were formed by the crystallzation and differentiation of oceanic ridge basaltic magma originating from a depleted mantle source area. It implies that the Diyanmiao-Daqin area had a long period of evolution,which was in the stage of ocean basin expansion in the Middle Carboniferous,followed by subduction of the Paleo-Asian Ocean and ocean-continent transition,and finally became part of the Central Asian orogenic belt.更多还原