俯冲型和碰撞型含矿斑岩地球化学组成的差异  

Geochemical differences between the subduction-and collisional-type ore-bearing porphyric rocks

作　　者：陈建林[1] 许继峰[1] 任江波[1,2] 王保弟[3] 余红霞[1,2] 

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广州510640 [2]中国科学院研究生院,北京100039 [3]成都地质矿产研究所,成都610081

出　　处：《岩石学报》2011年第9期2733-2742,共10页Acta Petrologica Sinica

基　　金：国家973项目(2009CB421004);中科院知识创新项目(KZCX2-YW-Q04-2);国家自然科学基金项目(40872055;40930316;41073033)联合资助

摘　　要：Cu-Mo-Au含矿斑岩不仅可以形成于与洋壳俯冲相联系的弧环境,而且也产于碰撞造山带内。通过对比俯冲型和碰撞型含矿斑岩的地球化学特征,发现它们特别在微量元素上具有较大差别,暗示它们有着不同的物源区组成或形成机制。同冈底斯带碰撞型含矿斑岩相比,太平洋东岸俯冲型含矿斑岩有着明显高的HREE和Y含量,低的Sr/Y、(La/Yb)N以及(Dy/Yb)N比值,表明其物质源区不含或含有少量的石榴子石并可能以角闪石组成为主。统计发现这些俯冲型含矿斑岩部分样品具有埃达克岩地球化学特征,但大部分样品却显示出具有与正常岛弧系列火山岩相似的特征,它们很可能是板片释放流体交代地幔楔形成的熔体并在后期经历MASH过程的产物。冈底斯带碰撞型含矿斑岩具有典型埃达克岩地球化学特征,指示其形成条件达到了石榴子石相变,可能形成于增厚的下地壳,其物质源区很可能与前期的洋壳俯冲有着密切的联系。普朗-雪鸡坪含矿斑岩具有与俯冲型含矿斑岩十分相似的地球化学特征,它们有可能是西向俯冲的甘孜-理塘洋发生断离,进而诱发前期俯冲流体交代的富集地幔楔发生部分熔融的产物,而并非是俯冲洋壳直接发生部分熔融的产物。Porphyry Cu-Mo-Au deposits occur not only in an arc setting,but also in a collisional belt.These ore-bearing porphyries in different tectonic settings have distinctly different geochemistry in trace elements,implying that they have different compositions in source or dynamic mechanisms.Comparing with collisional-type ore-bearing porphyries,the subduction-type rocks have obviously high HREE and Y concentrations,low Sr/Y,（La/Yb）N and（Dy/Yb）N ratios,suggesting that their source are mainly consisted of amphibole but less or no garnet.Although some of subduction-type ore-bearing porphyric rocks have somewhat adakitic geochemical signature,most samples show characteristics similar to the normal arc volcanic rocks,which are likely the product of mantle wedge,metasomatically enriched during slab subduction,through MASH（melting-assimilation-storage-homogenization） process.The collisional-type ore-bearing porphyric rocks clearly have characteristics of typical adakites,which be likely related to the earlier episodes of subduction in their source.The geochemistry of major and trace elements of ore-bearing porphyric rocks in Pulang-Xuejipin is similar to that of the subduction-type.They are likely the products by partial melting of metasomatized mantle wedge by subduction fluid or sediment,trigged by slab break-off of westward-subduction of Ganzi-Litang Ocean,instead of by direct partial melt of an oceanic slab.

关 键 词：俯冲型 碰撞型 含矿斑岩 普朗-雪鸡坪 地球化学 

分 类 号：P588.13[天文地球—岩石学]