大兴安岭中段塔尔气地区中酸性火山岩成因及构造背景

为探讨大兴安岭中段塔尔气地区中酸性火山岩成因及构造背景，深化大兴安岭中生代火山岩带的对比研究，对该地区满克头鄂博组、白音高老组火山岩开展了锆石U-Pb定年、岩石地球化学及Hf同位素分析.满克头鄂博组年龄为154±2 Ma和154±3 Ma，白音高老组年龄为132±2 Ma.样品富碱质，贫镁和钙，为弱过铝质.富K、Rb、Zr、Hf，贫Eu、Ba、Sr、P、Ti等元素，具有中等到较强的Eu负异常.锆石饱和温度平均值分别为915℃和841℃，表现出A型流纹岩的特点.样品ε_Hf（t）值分别介于+6.9~+8.4和+6.7~+7.9，t_DM2分别介于624~670 Ma和611~682 Ma，指示岩浆来源于新元古代亏损地幔增生年轻地壳物质.本地区满克头鄂博组形成于蒙古-鄂霍茨克洋闭合后伸展早期阶段，白音高老组则形成于蒙古-鄂霍茨克洋闭合后岩石圈伸展及拆沉作用，同时受到太平洋板块俯冲引发的弧后伸展作用叠加的影响. 

Petrogenesis and Tectonic Setting of Intermediate-Felsic Volcanics in Ta'erqi Area,Central Great Xing'an Range

In order to study the petrogenesis and tectonic setting of intermediate-felsic volcanics in Ta'erqi area, central Great Xing'an Range and promote the comparative study of Mesozoic volcanics in this region, in this paper it presents a synthesis study of zircon U-Pb chronology, geochemistry and Hf isotopes of volcanics from Manketouebo and Baiyingaolao formations. Zircon U-Pb dating yielded weighted mean ages of 154±2 Ma and 154±3 Ma of Manketouebo Formation and 132±2 Ma of Baiyingaolao Formation.The samples are weak peraluminous with high alkali, low Mg and Ca contents, while existing the enrichment of Rb, K, Zr, Hf and depletion of Eu, Sr, Ba, P, Ti with moderate to strong negative Eu anomalies. The average zirconium saturation temperature are 915 ℃ and 841 ℃, respectively, showing the characteristics of A-type rhyolite. The ε_Hf(t) values range from +6.9 to +8.4 and +6.7 to +7.9, while the t_DM2 values range from 624 Ma to 670 Ma and 611 Ma to 682 Ma, indicating that the magma originated from the the partial melting of Neoproterozoic young crust accreted from the depleted mantle. Manketouebo Formation in Ta'erqi area formed in the early stage of extensional tectonic setting after the closure of Mongolia-Okhotsk ocean, while Baiyingaolao Formation was caused by the lithosphere extension and delamination after the closure of the Mongolia-Okhotsk Ocean and the back-arc extension induced by the subduction of the paleo-Pacific plate to Eurasia.