华北板块北缘中段中元古代晚期花岗岩类特征及其构造意义

Characteristics and Their Tectonic Environment of Late Mesoproterozoic Granitoids in the Middle Segment of North Margin of the North China Plate

华北板块北缘出露的中元古代晚期花岗岩主要为黑云母花岗岩和二长花岗岩,化学上富SiO2和K2O,贫FeO、CaO、MgO和TiO2,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,其(La/Yb)N=6.61～64.31,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,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。

Granitoids in the late stage of the Mesoproterozoic along the north margin of the North China plate, are composed of biotite granites, tonalites, granodiorites and monzonitic granites. They exhibit the features of peraluminous granites, A/CNK〉1.1, and are characterized by higher SiO2, K2O and low FeO, MgO, CaO, TiO2, also higher Rb, K, Ta, Nd, Hf and low Nb, St, P, Ti in trace and minor elements. They have strong differentiation between LREE and HREE （La/Yb）N=6.61-54.63）. REE patterns have middle negative Eu anomalies. The granitoid belt is approximately EW-trenging and parallel to Mesoproterozoic island arc belt of Bainaimiao group and Weijiagou rock group and ophiolite mélanges belt of Kaiyuan rock group. The new geochemical data suggest that the Mesoproterozoic granitoids in middle segment of north margin of the North China Plate belong to syn-collisional S-type granitoids.They were produced during processes of subduction and collision between the North China Plate and Xiberia Plate in the late stage of Mesoproterozoic. This collisional event in the North China Plate may provide an essential constraint to the aggregation between the plate and others of supercontinental Rodinia.