辽宁西部中生代火山岩的基本特征

Essential Characteristics of Mesozoic Volcanic Rocks in Western Liaoning

辽西中生代火山岩主要分布于燕辽台褶带,由兴隆沟、兰旗和义县旋回构成。火山岩的岩石化学特征为SiO_2平均60.2%、富Na_2O、介于钙碱性和弱碱性系列之间。稀土总量低,铕的负异常弱,Isr在0.70546—0.70653之间。其特征与源区基底太古代建平群变质岩十分相似,反映了它们之间的成因联系。将太古代建平群变质岩和亏损地幔作为端员组分,由G.Faure二元混合模拟公式求得辽西中生代火山岩由65.8%—82.1%的源区物质——建平群变质岩和34.2%—7.9%的亏损地幔混合组成,表明辽西中生代火山岩主要是由源区物质——晚太古代建平群变质岩经部分熔融后形成的,成因上属于典型的不成熟地壳重熔类型。

The Mesozoic volcanic rocks in western Liaoning Province which inclndethose of the Xinglonggou cycle, the Lanqi cycle and tbe Yixian cycle, aremainly distributed in the Yan-Liao platformal fold belt. These rocks chara-cterized by having SiO_2 of 60.2% (average), standard alumina and highNa_2O content plot in the range between the alkali-lime series and the weak-alkali series. In addition, their REE total. contents (∑REE+Y) and europiumnegative anomaly are lower and I_sr is from 0.70546 to 0.70653. From thepetrochemical point of view, these rocks are similar the Archean metamor-phic rocks of the Jianping Group, which are their basement and source area.So it can be said that there is a genetic connection between them. Theresults calculated using the binary mixed formula proposed by G. Faure, inwhich the Archean metamorphic rocks of the Jianping Group and depletedmantle are thought to be the end members, show that the Mesozoic volcanicrocks in western Liaoning are derived from the metamorphic rocks of theJianping Group (65.8%--82.1%) and depleted mantle (34.2%--17.9%).Therefore, we shall come to the conclusion that the volcanic rocks wetemainly formed by partial melting of source materials-the Iate Archean meta-morphic rocks of the Jianping Group, and belong genetically to the unmatu-red crust remelting type.