鄂尔多斯盆地东北部早白垩世玄武岩地球化学特征

Geochemical characteristics of basalts in the northeastern Ordos Basin

白垩纪是我国区域构造演化的重要时期。鄂尔多斯盆地内白垩纪侵入岩的研究为华北克拉通西部块体早白垩世构造-热演化提供了重要的依据。本次工作以鄂尔多斯东北部杭锦旗下白垩统内黑石头沟玄武岩和榆林中侏罗统内大柳塔玄武岩为研究对象。通过地球化学特征的分析,本次工作探讨了白垩纪玄武岩源区特征及其所反映的区域动力学背景。主量元素特征分析表明,杭锦旗黑石头沟玄武岩为粗面玄武岩,属于钾玄岩系列。大柳塔玄武岩属于低钾(拉斑)系列。微量和稀土元素特征均表现为右倾的特征,轻重稀土分馏较弱。黑石头沟玄武岩来自于富集地幔,无地壳混染作用;大柳塔玄武岩具有活动大陆边缘和地壳混染特征。区域动力学背景分析表明,古太平洋板块斜向俯冲作用下的深部残留体,导致了华北克拉通西部板块(鄂尔多斯)东部及大兴安岭-太行山重力梯度带深部岩石圈的失稳,进一步造成了鄂尔多斯盆地东北部及邻区玄武岩的发育。

The Cretaceous is the significant transition stage for the tectonic evolution of China. As the basin with multiple energy resources, the research on the Cretaceous intrusions in the Ordos Basin has supplied the important evidences for the tectono-thermal evolution of the western part of the North China Craton. In this work,the Hangjinqi Heishitougou basalt in the Early Cretaceous successions and Yulin Daliuta basalt in the Middle Jurassic successions in the northeastern Ordos Basin are taken as the research objects. For these rocks, their geochemical characteristics was analyzed and the regional dynamic background was further discussed. The analysis of major elements shows that the Hangjinqi Heitongshigou basalt belongs to the series of potassium basalt. Yulin Daliuta basalt belongs to the low potassium(Tholeiitic) series. The characteristics of trace and rare earth elements are right-inclined with a low grade fractionation of light REE/heavy REE. Heidonggou basalt is regarded to come from the enriched mantle without crustal mixing. While, the Daliuta basalt has the characteristics of active continental margin with crustal mixing. Regional dynamic background analysis indicates that the deep residual body under the oblique subduction of the paleo-Pacific plate caused the instability of the deep lithosphere in the eastern margin of the western North China Craton(Ordos) and the Daxing’anling-Taihang Gravity Gradient Belt. The development of basalts in the northeastern and adjacent areas of the Ordos Basin were believed to be the result of these tectono-thermal activities.