青海泽库赛日迪印支期中基性岩体地球化学特征及构造背景

青海泽库东南赛日迪附近产出的印支期中基性岩体前人研究较少.对该岩体进行地球化学、构造背景及岩浆演化方面研究,结果表明,赛日迪岩体硅量中等、高镁铁、低铝、低钾钠,属准铝质钙碱性系列.富集Rb,K,Pb等大离子亲石元素(LILE)和Th,U,Ta,Nb,Hf等高场强元素(HFSE).普遍贫Ba,Sr等大离子亲石元素(LILE)和P,Zr,Ti等高场强元素(HFSE).稀土元素含量较低,轻稀土元素相对富集,轻稀土元素较重稀土元素分馏明显.Eu略显负异常,表现为同源岩浆成分特征.LREE与SiO2相关性不强,Nb/U、Nb/La远低于全球MORB、OIB值,Nb/Ta和Zr/Hf与原始地幔值相当,低Sm/Yb值,La/Nb和La/Ta指数指示赛日迪中基性岩可能为地幔源,岩浆经历部分熔融岩浆演化过程,上升过程中未受地壳物质混染.构造环境判别赛日迪中基性岩为钙碱性玄武岩,形成于板内环境,与板块碰撞作用有一定联系.

Geochemical Charateristics of Indosinian Basaltic-Intermediate Magatism From Sairidi area,Zeku County,Qinghai Province and their Tectonic Setting

The Sairidi Indosinian basaltic-intermediate magmatism lies in Zeku county,Qinghai province.This paper discuss on the geochemical characteristics,tectonic setting and the magma evolution.It shows that the Sairidi intrusion belongs to low Si,high Mg and Fe,low Al,low K and Na,metaluminous and calcium-alkaline.It enrich in big ion lithophile element such as Rb,K,Pb and high field elements such as Th,U,Ta,Nb,Hf and poor in big ion lithophile element such as Ba,Sr and high field elements such as P,Zr,Ti.The capacity of rare earth is relatively lower.Light REEs are rich and the fraction of LREE is higher than HREE.The magmatism has negative Eu anomalies which show that all the sample comes from the same source.There is no correlation between LREE and SiO2.The value of Nb/U and Nb/La are far lower than MORB and OIB’s.The value of Nb/Ta and Zr/Hf and Sm/Yb、La/Nb、La/Ta is close to the primitive mantle.The maga is undergoing partial melting phase and that there is no crustal assimilation during the ascend.We sugested that the Sairidi intrusion is relate to the plate collusion and is within plate tholeiite(WPT)and calc-alkaline basalts through the tectonic discrimination diagrams.