鄂尔多斯盆地早白垩世构造-热事件与铀成矿的关系——来自玄武岩锆石U-Pb年代学的约束

The Relationship Between Early Cretaceous Tectonic-Thermal Event and Uranium Mineralization in the Ordos Basin:Constraint From UPb Geochronology of Basalt Zircon

鄂尔多斯盆地北部纳岭沟铀矿床以北,大营及巴音青格利铀矿床以东的黑石头沟发育一层玄武岩,为探讨这期玄武岩与鄂尔多斯盆地北部铀成矿的关系,文章对该玄武岩进行了地球化学与年代学的分析。该玄武岩切穿下白垩统东胜组,SiO_(2)含量较低(46.99%),里特曼指数σ为8.69,显示出碱性玄武岩的特征;其锆石U-Pb定年结果为(126.7±2.4) Ma,表明黑石头沟玄武岩形成于早白垩世,反映鄂尔多斯地块在早白垩世发生了一次构造-岩浆-热事件,与大区域的华北地区乃至中国东部在早白垩世发生的较普遍的构造-岩浆-热事件具有一致性。结合前人的研究成果,这次构造-岩浆-热事件是由于岩石圈地幔减薄造成的。该事件使地下深部热流体上涌及板内运移,导致早白垩世古地温梯度增高,这一过程为铀元素在鄂尔多斯盆地北部的迁移、沉淀、富集成矿创造了条件。

Basalt was found in Heishigougou,northern of the Nalinggou uranium deposit and eastern of the Daying and Bayinqinggeli uranium deposits of the northern Ordos Basin.To explore the relationship between the basalt and uranium mineralization in northern ordos basin,the geochemistry and chronology of the basalt were analyzed in this paper.This basalt cuts through the Lower Cretaceous Dongsheng Formation and is of low SiO_(2) content(46.99%).The Ritman indexσis 8.69,showing the characteristics of alkaline basalt.U-Pb dating result of zircons from the basalt is(126.7±2.4)Ma,indicating that the basalt in Heishitougou was formed in the Early Cretaceous,reflecting that a tectonic-magmatic-thermal event occurred in the Ordos block in the Early Cretaceous,which is consistent with the common tectonic-magmatic-thermal events that occurred in the Early Cretaceous in North China and even eastern China.Combined with the research results of other researchers,this tectonic-magmatic-thermal event was believed to be caused by the thinning of the lithospheric mantle.This thinning event resulted in upwelling and intra-plate migration of deep underground hot fluids,which resulted in an increase of paleotemporal gradient in the Early Cretaceous.This process created conditions for the migration,precipitation and enrichment of uranium in the northern Ordos Basin.