大兴安岭中段突泉盆地玛尼吐组火山岩地球化学特征与~(40)Ar/~(39)Ar测年

大兴安岭中段突泉盆地玛尼吐组火山岩主要为一套中酸性岩石,化学成分显示其主要为粗面安山岩、粗面英安岩、英安岩与流纹岩.岩石激光全熔40Ar/39Ar测年结果显示玛尼吐组火山岩为138.0±3.0 Ma,形成于早白垩世早期.火山岩为高钾钙碱性系列岩石.岩石从中性→中酸性→酸性岩,稀土元素总含量分别平均为117×10-6、136×10-6、131×10-6;(La/Yb)N平均为6.38、7.62、6.27,轻重稀土分馏明显;δEu分别平均为0.88、0.85、0.40,具有负Eu异常.各类岩石富集大离子亲石元素Rb、Ba、Th、U、K和LREE,亏损高场强元素Nb、Ta、P、Ti;微量元素标准化配分图与地壳配分曲线接近一致,为一套壳源岩浆系列火山岩.结合大兴安岭地区玛尼吐组火山岩资料,该组火山岩的年代学、地球化学特征、岩浆成因及构造背景在不同区段具有差异性,而突泉盆地玛尼吐组火山岩可能是蒙古-鄂霍茨克洋闭合碰撞阶段加厚的造山带下地壳部分熔融的产物.

GEOCHEMICAL CHARACTERISTICS AND LASER 40Ar/39Ar DATING OF THE VOLCANICS FROM THE MANITU FORMATION OF TUQUAN BASIN IN CENTRAL DAXINGANLING

The volcanic rocks of Manitu Formation in the Tuquan Basin of Central Daxinganling region comprise a series of acid,acid-intermediate and intermediate rocks,namely,trachyandesite,andesite,dacite and rhyolite,with age of 138.0±3.0 Ma by Laser 40Ar/39Ar dating,identical to the early Early-Cretaceous.The geochemical characteristics of these rocks display a typical high-K calc-alkaline series with an average ΣREE of 117×10-6,136×10-6 and 131 ×10-6,average （La/Yb）N of 6.38,7.62 and 6.27,and average δEu of 0.88,0.85 and 0.40 for the intermediate,acid-intermediate and acid rocks,respectively.All the rocks share the similar geochemical characteristics of significant enrichment in Rb,Ba,Th,U,K （LILE） and LREE,depletion in Nb,Ta,P and Ti （HSFE）,indicating a crustal magmatic genesis.The chorology,geochemistry,magmatic genesis and tectonic background of the Manitu Formation largely distributed in Daxinganling have a remarkable variation by different areas on the ground of a great number of available information.Therefore,the volcanic rocks of the Manitu Formation in this study are most likely to be derived from partial melting of a thickened lower crust as a result of collision setting of Mongol-Okhotsk orogenic belt.