中国东北地区中生代火山岩与板块构造环境

MESOZOIC VOLCANIC ROCKS AND PLATE TECTONIC ENVIRONMENTS IN NORTHEASTERN CHINA

中国东北地区大面积分布着中生代（侏罗纪～白垩纪）火山岩，主要为钙碱性系列与碱性系列。钙碱性系列主要分布在东带和中带，碱性系列主要分布在西带：ＳｉＯ＿２％频率直方图，ｌｏｇσ－ｌｏｇｒ图解和球粒陨石标准化稀土元素分布模式说明中生代东北地区属活动大陆边缘。用Ｋ＿２Ｏ含量计算的俯冲带深度显示中生代东北大陆壳下存在双重俯冲带。西带、中带火山岩源于内侧俯冲带，东带火山岩主要源于外侧俯冲带。

Abstract Large amounts of volcanic rocks in Northeastern China belong to different volcanicrock stuite, main alkalic suite and calc一alkalic suite and can be divided into three zones:West Zone,Middle Zone and East Zone. The alkalic suite is mainly located in WestZone,the calc-alkalic mainly Middle Zone and East Zone. In addition, maps of frequen-cy distrlbution of SiO_2%,logσ-logτ diagrams and chondrodite-normalized REE patternsshow that volcanic rocks in Northeastern China are situated at active continental mar-gin.The volcanic activities in the three zones came to an end in turn,stopping earlier in West Zone than in East Zone . The depths of Benioff Zone calculated with K_2O%at 57.5% SiO_2 and 60% SiO_2 indicate there are two subduction zones under the Northeastern China in Mesozoic. SUBJECT TERMS:volcanic rocks,active continental margin,double subduction belts