ͨ�� LA- - ICP- - MS �ʯ U- - Pb �������ʯ��ѧ�������о��˼���ʡ�����������㲱���������ص�������γ����������ѧ�������γɻ�������ʯ����ѧ������ʾ�㲱������Ϊ�������������壬��ص�����Ϊ���������塣��������ļ�Ȩƽ������ֱ�Ϊ 262. 3 ± 3. 1 Ma �� 244. 5 ± 1. 9 Ma���Ƕ�����ĩ�������ͳ��������塣�㲱������ĺ���ָ�� A/CNK =0. 88 ��0. 94��������ָ�� σ =2. 09 ��2. 45��Na 2 O/K 2 O =1. 45 ��1. 69; ��ص�����ĺ���ָ�� A/CNK = 0. 902 �� 1. 001��σ = 2. 15 �� 2. 55�� Na 2 O/K 2 O =0. 99 ��1. 12������ѧ�����������߾�����׼���ʵ� I �ͻ����ң�Դ�����п�Դ���ʣ��ǹ��������鸩������ص��������������������������� 224 Ma ± ��δ�պϡ�

The geochronology��geochemical characteristics and tectonic setting of Yanboling and Zhundundian plutons from Tadong iron deposit area are studied with zircon LA - -ICP - -MS dating�� Geochemical characteristics suggest that Yanboling pluton is of granodiorite and Zhundundian pluton is of granite�� The weighted mean ages of the two plutons are 262. 3 ±3. 1 Ma and 244. 5 ±1. 9 Ma��indicating the intrusions are the Late Permian to the Ear- ly Triassic in ages��respectively�� The Na 2 O/K 2 O ratios of Yanboling pluton are 1. 45 ��1. 69��A/CNK values are 0. 88 ��0. 94��while ��ittmann index σ as 2. 09 ��2. 45�� Zhundundian pluton has Na 2 O/K 2 O ratios of 0. 99 ��1. 12�� A/CNK values of 0. 902 ��1. 001����ittmann index σ as 2. 15 ��2. 55�� The geochemical features indicate that Yan- boling and Zhundundian plutons are metaluminous I- type granites and they both have the characteristics of crust source��which were producted by the subduction of the Paleo- - Asian Ocean plate�� The instrusion age of the Yanbol- ing pluton signify the Paleo- - Asian ocean not closed in ca�� 244 Ma��