大兴安岭北端塔木兰沟组玄武质岩石的地球化学特征及构造背景

Geochemical characteristics and tectonic setting of basaltic rocks of the Tamulangou Formation at the northern end of the Da Hinggan Mountains, China

摘要: 大兴安岭北部晚侏罗世塔木兰沟组玄武质岩石具有富碱(K2O+Na2O>5.45%),高K2O(2.15%～3.75%)、K2O/Na2O(0.48～1.12)和高的Th/Ta、Ce/Nb、Ta/Nb比值,以及强烈富集大离子亲石元素(LILE)和轻稀土元素(LREE)的特征,属于钾玄质系列。现有资料分析表明,该钾玄质岩石形成于大陆板内环境。元素地球化学特征揭示,形成钾玄质岩石的原生岩浆经过强烈的结晶分异作用,并混染了前中生代的基底物质。

Abstract: Basaltic rocks of the Late Jurassic Tamulangou Formation in the northern Da Hinggan Mountains are characterized by rich alkalis (K2O+Na2O>5.45%),high K2O (2.15%- 3.75%),high ratios of K2O /Na2O (0.48- 1.12),Th /Ta,Ce/Nb and Ta/Nb and strong enrichment in large- ion lithophile elements (LILE)and light rare earth elements (LREE),belonging to the shoshonitic series. Analysis of the available data indicates that these shoshonitic rocks formed in a continental intraplate set- ting. Geochemical characteristics suggest that the primary magma of these shoshonitic rocks underwent strong crystallization dif- ferentiation and was contaminated with pre- Mesozoic basement materials.