华北克拉通南缘豫西下汤地区2.3Ga岩浆作用和1.94Ga变质作用——锆石U-Pb定年和Hf同位素组成及全岩地球化学研究

2.3 Ga Magmatism and 1.94 Ga Metamorphism in the Xiatang Area,Southern Margin of the North China Craton

本文报道了华北克拉通南缘豫西鲁山下汤地区古元古代片麻状花岗岩和黑云角闪斜长片麻岩的全岩地球化学和锆石SHRIMP U-Pb年龄和Hf同位素组成。岩石呈包体形式存在于中元古代花岗岩中。片麻状花岗岩具深熔特征,岩浆锆石年龄为2.30Ga;岩石高SiO2和K2O,低ΣFeO、MgO和CaO,具稀土总量较高(ΣREE=165.8×10-6)、轻重稀土分离较强[(La/Yb)n=37.8]及弱负铕异常(Eu/Eu*=0.76)的稀土模式;εNd(t)(t=2.30Ga)=-0.75;tDM(Nd)=2.66Ga。黑云角闪斜长片麻岩变质原岩为辉长闪长岩,捕获锆石年龄为2.25Ga;岩石低SiO2和MgO,高Al2O3和P2O5,具稀土总量高(ΣREE=373.4×10-6)、轻重稀土分离不强[(La/Yb)n=9.4]及较强负铕异常(Eu/Eu*=0.44)的稀土模式;εNd(t)(t=2.25Ga)=-1.21;tDM(Nd)=2.75Ga。片麻状花岗岩和黑云角闪斜长片麻岩都记录了1.94Ga变质锆石年龄。片麻状花岗岩的岩浆锆石组成域的εHf(t)(t=2.30Ga)=-6.71～0.38,tDM1(Hf)=2627～2910Ma,tDM2(CC)(Hf)=2823～3255Ma。黑云角闪斜长片麻岩的捕获锆石组成域的εHf(t)(t=2.25Ga)=-19.58～-1.73,tDM1(Hf)=2664～3360Ma,tDM2(CC)(Hf)=2968～4011Ma。结合前人资料,得出如下结论:华北克拉通南缘豫陕晋结合部地区存在一规模较大的约2.3Ga地质体分布区;华北克拉通南缘很可能存在规模巨大的>2.7Ga基底;中部造山带与孔兹岩带具有类似的古元古代晚期构造热事件演化历史。

This paper reports whole-rock geochemistry and zircon geochronology and Hf isotope of gneissic granite and biotite-amphibole-plagioclase gneiss from the Xiatang area, southern margin of the North China Craton. They occur in Mesoproterozoic granite as enclaves. The gneissic granite shows anatectic features. SHRIMP dating of magmatic zircons yielded an upper intercept age of 2.30 ± 0.02 Ga. The rock is high in SiO2 and K2O and low in ∑FeO, MgO and CaO, with a EREE content, （La/Yb） n and Eu/Eu^＊ values being 165.8 × 10^-6, 37.8 and 0.76, respectively. It has εNd（t） （ t = 2. 30 Ga） of - 0. 75 and tDM （Nd） of 2.66 Ga. The biotite- amphibole--plagioclase gneiss is considered to be meta-gabbroic diorite. It contains captured zircons of 2.25 Ga with no magmatic zircons having been determined. The rock is high in Al2O3 and P2O5and low in SiO2 and MgO, showing a high EREE content （ 373.4 × 10^-6 ） and low （ La/Yb ） n ratio （ 9.4 ） and obvious negative Eu/Eu^＊ anomaly （0. 44） , with εNd（t） （t =2. 30 Ga） and toM（Nd） being - 1.21 and 2.75 Ga, respectively. Combined with early researches, the conclusions can be arrived at that 1 ） there is a huge about 2.3 Ga rock distribution area in western Henan, southern margin of the North China Craton, and 2） the Trans-North China Orogen shared similar late Paleoproteorzoic tectono-thermal evolution to the Khondalite Belt in the northwestern North China Craton.