盐池北山碱长花岗岩岩体位于白音乌拉-东乌旗岩浆岩带与燕山期大兴安岭岩浆岩带的叠加部位,岩体内存在结构演化序列.本次采用LA-ICP-MS锆石U-Pb法对3件碱长花岗岩样品进行了年代学研究,测定岩体成岩年龄为283.5 ± 2.1Ma、277.6 ± 2.5Ma和298.7 ± 2.3Ma,属早二叠世.地球化学显示,该岩体具高硅、高碱、低铝、低铁镁钙、高钾钙碱性特征.岩石具有较高的稀土元素总量,∑REE为(200.56~316.70) ×10 -6,平均含量为252.52 ×10 -6,∑LREE为(183.60 ~275.01) ×10 -6,∑HREE=(16.95 ~41.69) ×10 -6.岩石 ω(LREE)/ω(HREE)为6.10~10.83,总体表现为轻稀土中等富集的右倾V字配分形式.微量元素结果表明盐池北山碱长花岗岩可能为造山后伸展体制下岩浆作用的产物,标志着兴蒙造山带晚古生代构造演化处于后造山构造阶段.%The Yanchi Beishan alkali-feldspar granite rock mass is situated in the superimposition region of Bayan Ula-Dong Ujimqin magmatite belt and Yanshanian Da Hinggan Ling magmatite belt,within the rock mass existed structural evolutionary series. The LA-ICP-MS zircon U-Pb method has been used on 3 alkali-feldspar granite samples dating in this study,determined rock mass age of diagenesis is 283.5 ± 2.1Ma,277.6 ± 2.5Ma and 298.7 ± 2.3Ma, belongs to early Permian. The geochemistry has shown that the rock mass has high-silica,high-alkali,low-alumina and low Fe,Mg,Ca characteristics with high potassium calc-alkaline char-acteristics. The rock has higher ΣREE of(200.56~316.70) ×10 -6, average 252.52×10 -6; ΣLREE(183.60~275.01) ×10 -6;ΣHREE(16.95~41.69) ×10 -6. ω(LREE)/ω(HREE) is 6.10~10.83,the overall performance is LREE medium enriched right V-type partition form. The trace element results have shown that Yanchi Beishan alkali-feldspar granite may be a result of postorogen-ic extensional system magmatism,indicated the Hinggan-Mongolian orogenic belt had been in postorogenic phase of late Paleozoic tec-tonic evolution.
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