赣东北蛇绿岩中的埃达克型花岗岩——地球化学和Nd同位素证据  

Adakitic Granites within the NE Jiangxi Ophiolites,South China——Geochemical and Nd Isotopic Evidence

作　　者：李武显[1] 李献华[1] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640

出　　处：《高校地质学报》2004年第2期199-208,共10页Geological Journal of China Universities

基　　金：中科院知识创新工程项目 (KZCX2 - 10 2 ) ;国家自然科学基金重点项目 (40 0 32 0 10 -B)资助

摘　　要：报道了赣东北蛇绿岩中西湾钠长花岗岩的地球化学和Nd同位素研究结果 ,它的许多特征与现代环太平洋地区的埃达克岩 (Adakite)极为相似 ,包括高Al2 O3(15 %～ 17% ) ,Sr (383× 10 - 6 ～92 0× 10 - 6 )和Sr/Y (16 6～ 4 44) ,低HREE(Yb =0 .14× 10 - 6 ～ 0 .2 1× 10 - 6 )和Y(1.6 6× 10 - 6 ～ 2 .81×10 - 6 )以及高εNd(t)值 (+ 4 .9～ + 6 .9)。与现代典型埃达克岩的差异仅在西湾钠长花岗岩具有异常高的Na2 O/K2 O(12～ 37) ,Na2 O/CaO(2 .7～ 3.6 )比值和异常低的MREE(Sm =0 .6× 10 - 6 ～ 1.2×10 - 6 )和HREE含量。上述地球化学特征表明 ,西湾钠长花岗岩为俯冲的细碧岩化的洋壳玄武岩(MORB)在高压条件下小比例部分熔融形成 ,源区残留矿物相有较大比例的角闪石和石榴石 ,而缺少斜长石。这种形成过程类似于现代的埃达克岩的成因。The geochemistry and Nd isotope compositions of Xiwan albite grnaites within NE Jiangxi opholites were reported in this paper. The granites share some geochemical similarities with modern adakite,including high Al_2O_3 (15%～17%),Sr (383×10 -6 ～920×10 -6 ),Sr/Y (166～444) and high ε_ Nd ( t ) values (+4.9～+6.0). Compared with the typical adakites,these granites are lower in HREE (Yb=0.14×10 -6 ～0.21×10 -6 ),MREE (Sm=0.6×10 -6 ～1.2×10 -6 ) and Y (1.66×10 -6 ～2.81×10 -6 ) contents but higher in Na_2O/K_2O (12～37) and Na_2O/CaO (2.7～3.6) ratios. Geological and geochemical features suggest that they were generated by lower degree of partial melting of subducting spillitized oceanic crust at pressure high enough to stabilize garnet and amphibole but the plagioclase absent. The scenario is similar to the formation of the modern adakite in circum-Pacific margin.

关 键 词：埃达克岩 西湾钠长花岗岩 岩石地球化学 赣东北蛇绿岩 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学]