西准噶尔玛依拉山组志留纪玄武岩的地球化学特征及构造意义  

Geochemistry of the Basalts from the Silurian Maylashan Formation in the West Junggar and its Tectonic Implications

作　　者：杨高学[1] 李永军[1] 刘振伟[1] 杨宝凯[1] 张洪伟[2] 佟丽莉[1] 

机构地区：[1]长安大学地球科学与资源学院,西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [2]新疆维吾尔自治区地质矿产勘查开发局第七地质大队,新疆乌苏833000

出　　处：《大地构造与成矿学》2012年第1期127-136,共10页Geotectonica et Metallogenia

基　　金：中央高校基本科研业务费专项资金(CHD2010ZY005);国土资源大调查项目(XJZBKD2008-04,XJQDZ2009-03)联合资助

摘　　要：西准噶尔地区中-上志留统玛依拉山组主要分布于玛依拉山一带,以玛依勒蛇绿岩的围岩产出,两者为断层接触,主要组成为灰绿-暗灰绿色凝灰质粉-细砂岩,砂岩和砂砾岩组合,夹硅质岩和玄武岩。对玄武岩进行详细的岩石地球化学研究表明,SiO2含量中等(47.1%～53.92%),高Fe2O3T(12.54%～17.82%)、Al2O3(13.3%～15.7%)、Na2O(3.84%～8.02%),低TiO2(0.45%～1.48%)、MgO(3.28%～5.77%,Mg#=27.01～41.96)、K2O(0.36%～0.7%),全碱K2O+Na2O含量为4.4%～8.39%,属于亚碱性拉斑玄武岩系列。稀土元素总量较低(∑REE=27.16×10-6～54.41×10-6),轻、重稀土分馏较为明显((La/Yb)N=1.53～2.74),无明显Eu异常(Eu/Eu*=0.96～1.16),稀土配分模式类似于E-MORB。相对富集LILE(如Rb、Ba、Th和K),亏损HFSE(如Zr、Ti),明显的Nb和Ta负异常,具有岛弧玄武岩的地球化学特征。综合研究认为玛依拉山组玄武岩形成于俯冲带上的弧后盆地环境,与玛依拉山蛇绿岩的形成环境不同,其岩浆来源于尖晶石二辉橄榄岩2%～10%的部分熔融,并有少量俯冲流体的参与。结合前人研究资料,认为西准噶尔在志留纪-石炭纪处在洋内弧演化阶段。The Maylashan area is situated in the southern part of the West Junggar, NW China. The Middle-Upper Silurian Maylasha Formation consists of grayish green tuffaceous siltstone and fine-grained sandstone, sandstone and conglomerate, with intercalated beds of chert and basalt, and fault contacts with the Maylashan ophiolitic mélange. The basalts are of sub-alkaline tholeiitic showing geochemical characteristics similar to those of island arc basalt （IAB）, with low TiO2 （0.45%-1.48%）, MgO （3.28%-5.77%, Mg#=27.01-41.96）, K2O （0.36%-0.7%） and total alkaline （K2O＋Na2O=4.4%-8.39%）, medium SiO2 （47.1%-53.92%）, high Fe2OT3（12.54%-17.82%）, Al2O3 （13.3%-15.7%） and Na2O （3.84%-8.02%）. The basalts are lower in REE （∑REE=27.16×10^-6-54.41×10^-6）, and exhibit slightly flat REE patterns, with （La/Yb）N=1.53-2.74, weak or no Eu anomaly （Eu/Eu＊=0.96-1.16）, which are similar to those of E-MORB. Moreover, the basalts are enriched in LILEs （ e.g. Rb, Ba, Th and K） and depleted in HFSEs （e.g. Ti and Zr） with pronounced negative Nb-Ta anomalies. It can be deduced that the volcanic rocks were derived from partial melting of spinel iherzolite mantle source （2%-10% partial melting） with the participation of small amount of subducted fluid, under back-arc basin setting different from that of the Maylashan ophiolitic mélange. Thus, an intra-oceanic subduction model was proposed for the Silurian-Carboniferous evolution of the West Junggar.

关 键 词：玄武岩 弧后盆地 玛依拉山组 地球化学 西准噶尔 

分 类 号：P595[天文地球—地球化学]