华北北部武川-康保地区中元古代晚期花岗岩类基本特征及其构造意义

The characteristics and tectonic significance of Meso-Proterozoic late stage granitoids in Wucuan-Kangbao

华北板块北缘武川-康保地区出露的中元古代晚期花岗岩主要为黑云母花岗岩类和二长花岗岩类,化学成分富SiO_2、K_2O,贫FeO、CaO、MgO,TiO_2,A/CNK平均大于1.1,具过铝质花岗岩特征。微量元素Nb、Sr、P、Ti相对亏损,而Rb、K、Ta、Nd相对富集;轻重稀土较强分馏(La/Yb)_N=6.61～54.63,负铕异常明显,具有碰撞成因S型花岗岩特征。花岗岩呈东西向带状展布,并与北侧白乃庙(白乃庙群)和阜新旧庙(魏家沟岩群)中元古代古岛弧链及开原蛇绿混杂岩带平行,这表明该区中元古代晚期存在一个强烈的俯冲碰撞造山过程,同碰撞花岗岩带的存在无疑是该区中元古代造山带的重要标志,这一碰撞造山事件为华北板块在Rodinia超大陆的拼合模式提供了最基本的制约条件。

Mesoproterozoic late stage granitoids occurred in Wucuan-Kangbao of Central Inner Mongolia, mainly consist of biotite granites and monzonitic granites. Two types of granites are peraluminous granite having high SiO2 K2O and low FeO, MgO, CaO, TiO2, A/CNK > 1.1; trace elements have high Rb, K, Ta, Nd, Hf and low Nb, Sr, P, Ti; Two types of granites have strong contrast between LREE and HREE (La/Yb = 6.61 similar to 54.63), REE models have middle negative Eu abnormality. The granitoids belt is approximately EW-trenging and parallel with Mesoproterozoic island arc belt of Bainaimiao group and Weijiagou rock group and ophiolite melanges belt of Kaiyuan rock group. Our research suggests thant Wucuan-Kangbao granitoids belts belong to syn-collisional granitoids(S-type). They were produced during processes of Mesoproterozoic late stage subduction and collision between the North China Plate and Xiboliya Plate. The correlation of North China Plate with other Plates of the world on Mesoproterocoic tectonics will provide important constraints for reconstruction of Rodinia.