鱼洞子群变质岩年龄及秦岭造山带太古宙基底

On the Age of Metamorphic Rocks of the Yudongzi Group and the Archean Crystalline Basement of the Qinling Orogen

秦岭是横亘我国中部狭持于中朝克拉通华北陆块和扬子克拉通陆块间的著名大陆碰撞造山带,其形式和演化历史受到重视。本文报道了位于秦岭造山带西南鱼洞子群变质岩的Sm-Nd、Rb-Sr同位素分析结果和侵入其中的TTG岩类的锆石U-Pb同位素分析结果,讨论了秦岭造山带太古宙结晶基底。采自陕西省略阳县鱼洞子—阁老岭块体的13个鱼洞子群变质岩样品的Sm-Nd同位素分析结果给予的等时年龄为2688±100(2σ)Ma,I_(Nd)=0.50913±7(2σ),ε_(Nd)(t)=-0.4,MSWD3.62。Rb-Sr同位素结果分散,不构成等时线。侵入鱼洞子群变质岩的花岗岩的锆石U-Pb不一致线上交点年龄为2693±9(2σ),下交点年龄为702±58(2σ)Ma。鱼洞子群变质岩Nd同位素特征与崆岭群变质杂岩类似,它的原岩可能是扬子克拉通基底碎片。

The Qinling Mountains in central China are the joint orogenic zone between the Sino-Korean (North China) block and the Yangtze (South China) era ton block, which are the two major tectonic units of eastern Asia. Their generation and evolution history have been noted by geologists. This paper reports the Sm-Nd and Rb-Sr isotopic analytical results for the metamorphic rocks of the Yudongzi Group in the southwest Qinling oro-gen and the zircon U-Pb isotopic data for the late TTG rocks in the metamorphic rocks and discusses the Archaean crystalline basement of the Qinling orogen. A good isochron of t=2688 ± 100(2σ)Ma, corresponding to INd = 0. 50913±7(2σ), εNd(t)=-0. 4 and MSWD 3. 62, was given by Sm-Nd results of 13 rock samples of the Yudongzi Group from the Yudongzi-Gelaoling massif in Lueyang County, Shaanxi Province. However, their Rb-Sr results are quite scattered. The zircon U-Pb isotopic data of the granites intruding into metamorphic rocks of the Yudongzi Group yield an upper intercept age of 2693 ±7 (2σ) Ma and a lower intercept age of 702 ±58(2σ) Ma. The Nd isotopic characteristics of the metamorphic rocks show similarities to those of the Kongling metamorphic complex, which indicates that their protoliths are possibly fragments of the basement of the Yangtze craton.