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柯坪玄武岩位于塔里木板块西缘,产于下二叠统库普库兹曼组和开派兹雷克组中。岩石化学组成以富集TFeO、TiO2、P2O5和SiO2不饱和为特征。大部分样品属碱性玄武岩系列,个别属拉斑玄武岩系列。它们的稀土元素和微量元素显示了板内拉张环境玄武岩的地球化学特征。εNd(t)=-1.73--3.69,εSr(t)=+27.56-+56.87,206Pb／204Pb=17.87-18.02,207Pb／204Pb=15.45-15.53,208Pb／204Pb=38.22-38.49。Nd、Sr、Pb同位素组成证明柯坪玄武岩源自于前寒武纪的富集型大陆岩石圈地幔。而且,这种情况在塔里木盆地及周缘地区十分发育的镁铁质岩浆岩中具有广泛的代表性。据此,可以将新疆南部和北部划分为两个明显不同的同位素地球化学省。南部省以富集型地幔的同位素组成为特征,而北部省以亏损型地幔的同位素组成为特征。分属于这两个省的古生代晚期阶段岩浆岩有可能不是同一个地质过程的产物。
Keping basalts are located on the western margin of the Tarim plate and are produced in the Lower Permian Kupfuzman and Kaipuzile groups. The rock chemistry is characterized by enrichment of unsaturated TFeO, TiO2, P2O5 and SiO2. Most of the samples are alkaline basalt series, some are basalt series. Their rare earth elements and trace elements show the geochemical characteristics of the basalt within the extensional environment. εNd (t) = - 1.73 - 3.69, εSr (t) = + 27.56- + 56.87, 206Pb / 204Pb = 17.87-18.02, 207Pb / 204Pb = 15.45-15.53, 208Pb / 204Pb = 38.22-38.49. The Nd, Sr and Pb isotopic compositions confirm that Keping basalts originate from Precambrian enrichment continental lithospheric mantle. Moreover, this situation is extensively represented in the mafic magmatic rocks, which are well-developed in the Tarim Basin and its peripheral areas. Accordingly, southern and northern Xinjiang can be divided into two distinctly different isotope geochemical provinces. The southern province is characterized by the isotopic composition of the enriched mantle, while the northern province is characterized by the isotopic composition of the depleted mantle. The magmatic rocks belonging to the late Paleozoic belonged to these two provinces may not be the product of the same geological process.