青海同仁县隆务峡地区首次发现镁铁质—超镁铁质岩带

Discovery of a mafic-ultramafic belt in the Rongwoxia area,Tongren,Qinghai,China

在青海省同仁县隆务峡南段的二叠纪地层中首次发现了北西—南东向分布的镁铁质—超镁铁质岩带,命名为隆务峡镁铁质—超镁铁质岩带。该岩带的岩石组合包括纯橄岩、辉石橄榄岩、辉长岩、辉绿岩、枕状玄武岩等。从超镁铁岩—下部堆晶岩—辉绿岩—上部堆晶岩,其稀土元素总量逐渐增加,稀土元素配分型式总体一致,从超镁铁岩的Eu正异常到上部辉长岩的Eu负异常,显示了各岩石间的同源性。根据对其两侧沉积岩中化石的研究,推测该镁铁质—超镁铁质岩带的形成时代为二叠纪。该岩带位于西秦岭造山带与祁连造山带的接舍部,对于揭示秦岭和祁连接合部的大地构造演化有重要意义。

A NW-SE-trending mafic-ultramafic belt has been found in Permian strata in the southern segment of the Rongwo Gorge, Tongren County, Qinghai Province, which is named the Rongwoxia mafic-ultramafic belt in this paper. The rock association of this mafic-ultramafic belt include dunite, harzburgite, gabbro, diabase and pillow basalt. The gradual increase of the total REE content from ultramafic rocks→lower cumulates→diabase→upper cumulates, general consistent REE distribution patterns and change from Eu positive anomalies of ultramafic rocks at the base to negative anomalies of gabbro in the upper part--all these suggest the cogenesis of these rocks. Based on the study of the fossils taken from sedimentary rocks at both sides of the belt, it is inferred that this age of the belt Permian. The Rongwoxia mafic-ultramafic belt is located in the junction zone between the West Qiuling orogenic belt and Qilian orogenic belt and has great significance for revealing the exact tectonic evolution of the junction zone of the Qinling and Qilian.