��������λ��С�˰��붫�϶Σ�����ʯ���Ϊ���������ҺͶ��������ҡ����ⶨ��Ʒ�е��ʯ���������������������Th /U ��ֵ��������Щ�ʯΪ�ҽ�����LA--ICP MS U--Pb ��������ʾ�����γ�ʱ���ֱ�Ϊ432. 8 ± 1. 2 Ma ��431. 9 ± 1. 7 Ma������־��������������ĵ���ѧ������ʾ�������ڸ߼ظƼ���ϵ�У�ACNK ֵΪ1. 16 �� 1. 40�����ڹ����ʻ�����; ΢��Ԫ�ر��ֳ�������������ʯԪ��( Rb��Ba��U ��Th) ����ϡ��Ԫ�أ�����߳�ǿԪ��( Nb��Ta��Ti) ��P��Sr �Լ���ϡ��Ԫ�ء���������ѧ������ʾ����Ҫ��Դ���µؿ����ʵIJ������ڣ���Ʒ�Ĺ�����������ʾ���γ���½�ǼӺ񻷾������ǰ���о��ɹ�����Ϊ���������γ������۵ؿ�ͼ�ľ˹�ؿ����ײƴ�ϻ����������۵ؿ�ͼ�ľ˹�ؿ��������־������ײƴ�ϡ�

Chenming pluton is located in the southeastern Xiao Hinggan mountains��composed of monzonitic granite and granodiorite�� Combined with the Th /U ratios of zircons in all samples which possess oscillatory growth ring��it suggests that these zircons are magmatic in origin�� LA--ICP MS U--Pb dating results show that the forming age is 432. 8 ± 1. 2 and 431. 9 ± 1. 7 Ma��which indicates the Early Silurian�� According to its geochemical characteristics�� the Chenming pluton belongs to high potassium calc--alkaline series in category�� Its ACNK value is ranging between 1. 16 �� 1. 40��which indicates to be peraluminous granite in nature�� The trace elements are enriched by LILE ( Rb��Ba��U and Th) and LREE��with loss of HFSE ( Nb��Ta��Ti) ��P��Sr and HREE��which impliesthat the Chenming pluton originated mainly from the partial melting of lower crust material��and its peraluminous characteristics suggested its forming in the environment of continental crust thickening�� Combined with the results of previous researches��the Chenming pluton formed in the collision backgroud of Songnen massif with Jiamusi massif�� that means the collision of Songnen massif and Jiamusi massif may occur in the Early Silurian��