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鞍子山蛇绿杂岩位于秦岭勉略带东段,它由蛇纹石化变质橄榄岩和MORB型变质镁铁质岩组成。蛇纹石化变质橄榄岩主要是方辉橄榄岩和少量二辉橄榄岩,代表了古洋幔的上部岩石;变质镁铁质岩为斜长角闪岩,其原岩是基性火成岩类,它多以亏损LREE元素和具有很高的~(143)Nd/~(144)Nd值为特征,类似于现代洋壳中的洋中脊玄武岩(MORB),代表了古洋壳的残余部分。这表明鞍子山蛇绿杂岩是勉略混杂岩带中又一个典型的蛇绿岩块,其可能形成在一个孤后盆地或小洋盆的扩张洋脊环境。然而,鞍子山蛇绿杂岩的Pb、Nd同位紊体系明显不同于勉略带西段的三岔子蛇绿岩,它们来源于两个不同的同位素地幔储源库,鞍子山蛇绿杂岩的形成时代可能比西段古洋壳更老,这意味着勉略带应有更复杂的构造演化历史。
The Anszishan ophiolite complex is located in the eastern segment of the Mian Luan zone in the Qinling Mountains. It consists of serpentinizational metamorphic peridotites and MORB-type metamorphic mafic rocks. Serpentinite metamorphic peridotites are mainly harzburgites and a small amount of lherzolites, representing the upper rock of the ancient mantle; metamorphic mafic rocks are amphibolite, the protolith is a basic igneous rock, it It is characterized by a depleted LREE element and a high ~ (143) Nd / ~ (144) Nd value, similar to the mid-ocean ridge basalts (MORB) in the modern oceanic crust, representing the remnants of the paleo-oceanic crust. This indicates that the Anszishan ophiolite complex is another typical ophiolite block in the Mianlue melange zone, which may be formed in an open ocean ridge environment in an orphan basin or a small oceanic basin. However, the Pb and Nd isotopic systems of the Ansiziyama ophiolite are obviously different from the Sanchazi ophiolite in the western segment of the Mianleo zone, which originated from two different isotopic mantle reservoir reservoirs and the Anszishan ophiolite complex The formation age may be older than the western segment of the ancient oceanic crust, which means that the Mulao zone should have a more complicated history of tectonic evolution.