�����������������ľ��������� LA--ICP--MS �ʯ U--Pb ���ꡢ����Ԫ�ء�ϡ��Ԫ�غ�΢��Ԫ�ز��Է�������������������������Ϊ 235. 1 ± 3. 2 Ma��������������������и� SiO2���� K2O���� CaO���� TiO2��������ǿ�ҿ��� Sr��Ba��Ti��P ��Ԫ�أ����� K����b��Th ����ʯԪ�أ��������� “��Ÿ��”������ʯ��׼��ϡ�������ʽ��ǿ�ҵĸ����쳣���ص㡣A/CNK = 0. 77 �� 1. 19��A/NK = 1. 26 ��1. 64��������ľ���������ƫ���� A �ͻ����ҵ����������нϸߵ� Y/Nb ֵ ( 2. 31 �� 3. 00 �� 1. 2) ����ʾ�� A2�ͻ����ҵ�������˵�������γ�����ɽ�����չ������

The zircon U--Pb ages and geochemical characteristics of Amuwu pluton in Sonid Zuoqi area were determined by the method of LA--ICP--MS zircon U--Pb dating as well as major��trace and ��EE elements analysis�� The results showed that the 206Pb/238U age was 235. 1 ±3. 2 Ma��formed in Middle Triassic�� The granite was char- acterized by high SiO2and K2O��low CaO and TiO2��strongly depleted in Sr��Ba��Ti��P��and enriched in K����b�� Th�� The pluton showed particularly intensive Eu negative anomalies and with a seagull shape to rightward in chon- drite-normalized ��EE pattern�� The A/CNK and A/NK values were 0. 77 ��1. 193 and 1. 26 ��1. 64��respectively�� belonging to A-type granite�� According to the high Y/Nb value (2. 31 ��3. 00 ��1. 2)��the pluton shows the charac- teristics of granite type A2��which formed in the extensional environment of post-orogenic��