内蒙古北山交叉沟地区变质火山岩Sm-Nd同位素研究  

Sm-Nd Isotope Study on Metamorphosed Volcano—Sedimentary Rocks of the Jiaochagou Metamorphic Complex, Beishan Mt., Inner Mongolia

作　　者：聂凤军[1] 江思宏[1] 刘妍[1] 张义[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2004年第6期807-812,共6页Acta Geologica Sinica

基　　金：国家自然科学基金项目 (编号 40 0 73 0 15 );国家地质调查项目 (编号 K1.3 .3 2 )资助的成果

摘　　要：交叉沟变质杂岩套主要由斜长角闪岩、片麻岩、长英片岩、绿片岩和条带状混合岩组成 ,为中国西北北山造山带红石山—黑鹰山地体的重要组成部分。长期以来 ,由于缺少可信的同位素年代学数据 ,该套变质岩的形成时代、成岩环境和物质来源尚不清楚。笔者等首次对交叉沟变质杂岩套代表性变质岩进行了 Sm- Nd同位素研究 ,其中斜长角闪岩 Sm- Nd同位素等时线年龄为 12 6 4± 11Ma、其 1 43Nd/ 1 44 Nd初始值为 0 .5 11375± 13,εNd(t)为 7.2 4± 0 .0 2 (2 σ)。与斜长角闪岩样品相比 ,各类片麻岩的 εNd(12 6 4 Ma)值明显偏低 ,变化范围为 1.18～ - 5 .17。依据上述Sm- Nd同位素数据 ,并且结合野外地质证据和岩相学特征 ,认为交叉沟地区斜长角闪岩的原岩为基性火成岩 ,属于幔源基性岩浆活动的产物 ,成岩时代为中元古代 ,而片麻岩的原岩则多为中酸性火成岩 ,其形成过程与古元古代或太古宙古陆壳岩层的再造作用有关。Located at northeastern part of the Kazakhstan—Beishan plate, Ejin Qi, Inner Mongolia, the Jiaochagou metamorphic complex consists mainly of migmatite, hornblende—plagioclase gneiss, K-feldspar—plagioclase gneiss, amphibolite, chlorite schist, quartzite and sericite—quartz schist. The tectonic setting of the metamorphic complex has been considered to be a uplift-related volcanic basin along the Precambrian contintental margin. Sm-Nd isotope data on amphibolite and various gneiss samples are presented in this paper. Five amphibolite samples from the metamorphic complex give a Sm-Nd isochron age of 1264±11 Ma with ε Nd (t) value of 7.24±0.02 (2σ). As the Sm-Nd isochron age is in agreement with field geological evidence, it has been suggested to be the mafic volcanic eruption time of the Jiaochagou metamorphic complex. The original rock of the amphibolite was derived from a depleted mantle source. In contrast, the ε Nd (1264 Ma) values of the gneiss samples range from 1.18～-5.17, which are much lower than those of amphibolite. Combined with other field and geological evidence, the authors believe that the contamination of magma by the continental crust was involved during the rock-forming process of the various gneiss of the Jiaochagou metamorphic complex.

关 键 词：ND同位素 斜长角闪岩 北山 片麻岩 变质杂岩 原岩 变质岩 幔源 成岩环境 火成岩 

分 类 号：P588.3[天文地球—岩石学]