大兴安岭中南段塔尔气地区满克头鄂博组火山岩地球化学特征及地质意义

THE VOLCANIC ROCKS IN MANKETOUEBO FORMATION FROM TAERQI AREA,SOUTH-CENTRAL DAXINGANLING MOUNTAINS:Geochemical Characteristics and Geological Implication

塔尔气地区满克头鄂博组火山岩主要为流纹岩、流纹质凝灰熔岩和流纹质晶屑凝灰岩,主量元素分析结果表明该火山岩具有准铝—弱过铝质(Al_2O_3=11.55%~14.76%,A/CNK=1.01~1.35)、富碱(Na_2O+K_2O=4.56%~8.79%)、贫钙镁的岩石化学特点.稀土元素分析结果表明火山岩ΣREE含量较高(平均为168.69×10^(-6)),稀土元素配分模式图均呈右倾型,LREE为轻度富集型,HREE分布相对较为平坦,铕负异常明显(δEu=0.29~0.72),岩石Rb/Sr=0.3~11.4,微量元素明显富集LILE(Rb、Ba、K)而亏损HFSE(Nb、Ta、Ti).结合地球化学特征及前人研究资料,认为塔尔气地区满克头鄂博组火山岩具有壳源岩浆的典型特征,岩浆源区有斜长石残留或岩浆经历了斜长石的分离结晶作用;满克头鄂博组火山岩属于A型火山岩,可能是蒙古-鄂霍次克洋闭合后的岩石圈伸展体制下的产物.

The volcanic rocks in Manketouebo Formation from Taerqi area are mainly rhyolite, rhyolitic tufflava and rhyolitic crystal tuff. The analysis results of major elements indicate that the volcanic rocks are characterized by quasi aluminum-weak peraluminum, with Al2O3 = 11.55% - 14.76% and MCNK = 1.01 - 1.35, rich alkali （Na2O＋K2O = 4.56% - 8.79% ） and poor calcium and magnesium. The average content of REEs in the volcanic rocks is 168.69×10^6. The distribution patterns show right-dipping curves with slight enrichment of LREEs and relatively fiat distribution of HREEs, with distinctive negative Eu anomaly （δEu=0.29 - 0.72） and Rb/Sr = 0.3 - 11.4. The trace elements are obviously enriched in LILEs such as Rb, Ba and K, but depleted in HFSEs like Nb, Ta and Ti. Combined with the geochemical characteristics and previous research data, it is thought that the volcanic rocks in Manketouebo Formation, bearing the typical characteristics of crust-derived magma, with residual plagioclase or fractional crystallization of plagioelase in the magma source area, belong to A-type, which is possibly the product of lithosphere extension tectonic system after the closure of Mongolia-Okhotsk Ocean.