塔里木北山地区橄榄岩—辉石岩的微量元素地球化学特征及其深部过程

Trace element geochemistry and plutonic process of peridotite and pyroxenite in the Beishan, Tarium Area

橄榄岩-辉石岩是塔里木北山地区镁铁-超镁铁岩体中非常重要的岩石类型．橄榄岩-辉石岩的主元素特征表明其主要为准铝质岩石,同时存在过碱质系列岩石．在稀土元素CI标准化配分图上,表现为LREE富集,HREE配分曲线平坦;在微量元素N-MORB标准化的蛛网图上,表现为Cs,U, Pb等大离子低场强元素强烈富集,Nb,Ta,Zr,Ti等高场强元素明显亏损;w(Sm)／w(Nd)值特征表明研究区橄榄-辉石岩源于地幔源区．微量元素地球化学研究表明,塔里木北山地区橄榄岩-辉石岩形成于活动大陆边缘弧后张裂构造环境,为构造应力释放阶段的产物．本文及前期研究结果表明:橄榄岩、辉石岩和辉长岩的地球化学特征研究在解决深部地质过程方面具有较大潜力．

Both peridotite and pyroxenite are the most important types of mafic and ultramafic rocks in the Beishan region. Major elemental characteristics show that sub-aluminium rocks dominate these two types of rock, and some over-alkalic magmatites existed in this region at the same time. These rocks show a diagram of LREE-enriched and HREE flat CI normalized REE patterns and an obvious pinnacle of LILE of Cs, U, Pb and low-trough of HFSE of Nb, Ta, Zr and Ti in N-MORB normalized spider diagram. The ratio of Sm vs Nd !ndicates that these peridotites and pyroxenites were derived from the mantle sources. All the trace elements geochemical characteristics show that they were formed in the back-arc tensional tectonics at the active-continental-margin in the Beishan, Tarim Area hence the products of stress release stage. In addition, great potentials for peridotite, pyroxenite and gabbro are revealed in the plutonic process study through this paper and in our previous research.