【摘要】 在鄂尔多斯地块西南缘的六盘山断裂带内出露铁马河辉绿岩。铁马河辉绿岩相对贫CaO、MgO和K₂O;富集FeOT、TiO₂和Na₂O。轻稀土相对富集,重稀土平坦,不显示Eu异常,稀土配分曲线显示右倾型;高场强元素无异常,大离子亲石元素K、Rb、Ba相对富集,显示富集地幔源的地球化学特征。对辉绿岩样品进行LA-ICP-MS锆石U-Pb测年,获得上交点年龄2018±16Ma,说明岩体形成于古元古代。样品具有低的(⁸⁷Sr/⁸⁶Sr)i值（07003～07064）和正的εNd（t）值（+514～+433）,Nd同位素一阶段模式年龄（约20Ga）与LA-ICP-MS锆石U-Pb年龄基本一致,暗示其来源于软流圈地幔的部分熔融。结合区域地质资料的研究表明,华北克拉通西部地块（鄂尔多斯地块）在20Ga期间的伸展背景与东部陆块一致,暗示整个华北克拉通在20Ga左右存在广泛的裂解事件。更多还原

【Abstract】 The Tiemahe diabase is exposed in Longxian County,Shaanxi Province,at the southwestern margin of the Ordos Block.It’s geotectonic location belongs to the southwestern part of the North China Craton and the southern part of the Liupanshan tectonic belt.Zircons from the diabase yield a U-Pb upper intercept age of 2018 Ma,which belongs to Paleoproterozoic.The diabase is characterized by high FeOT,TiO₂ and Na₂O,depleted in CaO,MgO and K₂O,and it has enriched light rare earth element（LREE）with a flat heavy rare earth element（HREE） pattern and an insignificant Eu anomaly.Trends in trace element abundances show that the gabbro is depleted in high field strength elements and slightly enriched in large ion lithophile element K,Rb and Ba.Geochemical features show that it is from enriched mantle sources.The samples show low(⁸⁷Sr/⁸⁶Sr)i values（0.7003～0.7064） and positiveεNd（t） values（+5.14～+4.33）,with a tDM of Nd about 2.0 Ga which is similar to the zircon U-Pb age,indicating that the magma material is directly derived from the mantle and there was a period of crustal growth events during 2.0 Ga.The geochemical and Sr-Nd isotopes of the diabase show that its magma came from the asthenosphere mantle that have not been contaminated by the crustal material or slightly altered.Thr-ough the analysis of the formation temperature and pressure conditions of the diabase,it is shown that the lithosphere and the crust of the study area was in a thinning state when the Tiemahe diabase was formed,which may suggest a mature continental rift environment.Compared with the North China Craton,the stretching tectonic background of the Ordos Block at 2.0 Ga is coincidental with that of the Eastern Block,indicating that the whole North China Craton has a wide range of cracking event during the period of 2.2～2.0 Ga.更多还原