Qaidamshan granite is one of the biggest intrusions in the northern margin of Qaidam Basin.To determine the genesis of Qaidamshan granite and its relationship with the Early Paleozoic orogenic movement in northern Qaidam,the authors apphed LAICP-MS tcchnique to conducting zircon U-Pb dating and Hf isotope compositions measuring.Augen granite and granodiorite of Qaidamshan intrusion have weighted average 206Pb/238U age of 436.9Ma±2.8Ma and 440.8Ma±7.3Ma respectively,with their Th/U ratios both lower than 0.2,which represent the magmatic formation age.Augen granite and granodiorite have similar zircon Hf isotope geochemical characteristics:of the 35 zircon Hf isotope measurements,32 zircons have the data 176Lu/177Hf =0.000735～0.002786,176Hf/177Hf=0.282264～0.282439,εHf(t)=-8.5～-2.5,and TDM2=1.44～1.77Ga.It is shown that the Qaidamshan granite was formed in 437～446Ma,had multi-phase emplacement characteristics,and its protolith came from Qaidam plate basement.In combination with the Paleozoic tectonic evolution characteristics of northern Qaidam margin,the authors hold that the Qaidamshan intrusion was produced by continent-continent collision.%柴达木山岩体是柴北缘地区最大的岩体之一.为确定柴达木山岩体成因及其与柴北缘早古生代造山作用的关系,采用LA-ICP-MS方法对柴达木山眼球状花岗岩和花岗闪长岩中的锆石进行了U-Th-Pb同位素及Hf同位素研究.柴达木山眼球状花岗岩及花岗闪长岩206pb/238U年龄加权平均值分别为436.9Ma±2.8Ma及440.8Ma±7.3Ma,Th/U值均大于0.2,代表了岩浆的形成年龄.眼球状花岗岩和花岗闪长岩锆石Hf同位素地球化学特征相近,45个锆石Hf同位素分析值中42个锆石176Lu/77Hf值均介于0.000735～0.002786之间,176Hf/177Hf值变化范围为0.282264～0.282439,εHf(t)变化于-8.5～-2.5之间,Hf同位素两阶段模式年龄为1.44～1.77Ga.研究表明,柴达未山岩体形成于437～446Ma,具有多期侵位特点,其原岩来自柴达木板块基底下地壳；结合柴北地区缘早古生代构造演化特点认为,柴达木山岩体为陆陆碰撞的产物.
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