鄂尔多斯地块早白垩世构造-热事件:杭锦旗玄武岩的Ar-Ar年代学证据

在鄂尔多斯地块北部杭锦旗黑石头沟,于下白垩统砂岩之上发现了一层玄武岩。其SiO2(46.93%)较低而碱含量(K2O+Na2O=6.21%)较高,组合指数σ=8.0,含标准矿物Ne,属于碱性橄榄玄武岩。Ar-Ar激光阶段加热定年结果表明,该玄武岩具有126.2±0.4Ma的Ar-Ar年龄。年龄数据表明杭锦旗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,这与华北、乃至整个中国东部在早白垩世发生了较普遍的构造-岩浆-热事件具有一致性。这次构造-岩浆-热事件可能引起深部流体自地下深部上涌及在地块内部运移,为各种成矿元素的迁移、沉淀、富集和成矿创造了合适条件。

CRETACEOUS TECTONO-THERMAL EVENT IN THE ORDOS BLOCK: AN AR-AR CHRONOLOGICAL EVIDENCE FROM BASALT AT HANGJIN BANNER, INNER MONGOLIA, NORTH CHINA CRATON

The Ordos Block is considered as a stable relict of the North China Craton which was later strongly activated and reformed since the Mesozoic.The Meso-Cenozoic igneous rocks within the Ordos Block have not been reported until now.A basalt layer overlying on sandstone of the Lower Cretaceous at Heishitougou,Hangjin Banner,Inner Mongolia in the Ordos Block was found in recent years.The basalt belongs to the alkali olivine basalt series with normative mineral Ne.It is characterized by lower SiO2(46.93%)and higher alkali contents(K2O+Na2O=6.21%),with the serial index σ being 8.0.The result of Ar-Ar laser step-heating dating indicates that the basalt was formed in 126.2±0.4 Ma.The chronological datum shows that a tectonic-magma-thermal event once occurred in the Ordos Block during the early Cretaceous.It coincided with the early Cretaceous giant igneous event in the North China and even throughout eastern China.This tectonic-magma-thermal event could result in the deep-seated fluid ascending and diffusing,driving various minerogenic elements to be transported,concentrated,deposited and mineralized in the block.