扎兰屯地区白音高老组火山岩特征及成因

Baiyingaolao Group Volcanic Rock Characteristics and Genesis in Zhalantun Region

通过对扎兰屯地区硅酸盐、重砂等样品的采集、化验与分析,w（SiO2）为70.10%~75.97%,w（Al2O3）为12.50%~15.60%,属于酸性岩石且SiO2、Al2O3过饱和,样品以亚碱性岩石为主,w（K2O）为4.20%~5.77%,平均为5.03%;w（Na2O＋K2O）为7.56%~9.95%,平均为8.62%。富集大离子亲石元素（LILE）K、Rb、Sr,高场强元素（HFSE）Nb、Ta、P、Ti和重稀土元素（HREE）相对亏损,在原始地幔蛛网图解中明显异常。经CIPW标准矿物重量百分比计算,δEu为0.05~0.68,平均为0.38;δCe为0.88~1.02,平均为0.98。通过等离子质谱（LA-ICP-MS）技术对火山岩样品进行同位素测年分析,并根据年龄谐和图与权重图发现区内的火山岩年龄为125~135 Ma,属于早白垩世白音高老组。综合考虑其研究区内火山岩特征并结合他人研究成果,认为扎兰屯地区白音高老组火山岩形成于古亚洲洋或与蒙古—鄂霍次克洋闭合有关的受流体交代的地幔及其结晶分异作用。

Samples such as silicate and heavy sand in Zhalantun region are collected, tested and analyzed. Among these, w （ SiO2 ） is from 70.10% to 75.97 %, and w （ Al2O3 ） is from 12.50% to 15.60% , which belong to the acid rocks and SiO2, Al2O3 are over saturated. Sub-alkaline rocks are the main component of the samples ,w（ K2O） is from 4.20% to 5.77% with average of 4.05% ,and w（ Na2O ＋ K2O） is from 7.56% to 9.95% with average of 8.62%. The samples are enriched in LILE such as Rb, Ba 、 Sr, but the HFSE such as Nb 、Ta、 P, Ti and HREE are less relatively. So, anomaly is obviously in the primitive mantle spider diagram. Based on calculation method of the CIPW standard mineral percentage by weight,SEu is from 0.05 to 0.68 with average of 0.38 ;SCe is from 0.88 to 1.02 with average of 0. 98. The volcanic rocks samples are conducted to make isotopic dating analysis by means of LA-CIP-MS technology. According to the age harmonic graph and weighted graph, age of the volcanic rocks in the Zhalantun region is from 125 to 135 Ma,so the volcanic rocks belong to the early Cretaceous Baiyin- gaolao formation. Comprehensively analyzing the characteristics of the Zhalantun volcanic rocks and combined with the research results of other people,it is found that the early Cretaceous Baiyingaolao formation in Zhalantun region was formed in ancient Asia or mantle with fluid metasomatism and crystallization differentiation related by Mongolia-Okhotsk ocean close.