���ɹ�׼��˳�������������ʯ��������--�����Σ����о��ȵ������������ͽϸߵ� Th/U ��ֵ (0. 67 ��1. 26)����ʾ���ҽ�����������LA--ICP--MS �ʯ U--Pb �������������� 206 Pb/ 238 U ��Ȩƽ������Ϊ (433 ±2) Ma (��־����)������������˻��������ҵĽᾧ���䡣�������ѧ������� SiO₂ Ϊ 62.74% �� 64. 50%���� CaO (4.47% �� 6.44%)���� Al ₂ O ₃ (16.51% �� 17.22%)���� K 2 O (1.51% �� 2.02%)��Na 2 O (2.21% ��3.54%)�����ڸƼ���ϵ�У���ʯ������������ʯԪ�� (�� K����b��Ba��Sr)������߳�ǿԪ�� (�� Nb��Ta��Hf��Zr��Ti)��ϡ������������㡣�� Mg # ֵ (Mg # = 39 ��43 ��45)���͵�����Ԫ�غ��� (Cr��Ni �����ֱ�Ϊ 3. 12 × 10 ^��6 �� 24. 6 × 10 ^��6 ��5. 57 × 10 ^��6 ��11. 6 × 10��6 )����ʾ����Դ�ص㡣�ۺ�����ͬʱ������ҵ��о��ɹ�����Ϊ׼��˳�����������γ��ڹ������󸩳������ĵ��������С�

Zircons in Zhungashun granodiorites are all euhedral to subhedral in shape with homogeneous oscillatory growth bands and high Th/U ratio (0. 67 ��1. 26)��which suggests their magmatic origin�� LA--ICP--MS zir- con U--Pb dating shows the weighted age of (433 ±2) Ma with MSDW =0. 44��indicating the intrusion formed in Early Silurian�� The rocks have a SiO 2 content variety from 62. 74% to 64. 50%��high CaO (4. 47% ��6. 44%) and Al 2 O 3 (16. 51% ��17. 22%)��low K 2 O (1. 51% ��2. 02%) and Na 2 O (2. 21% ��3. 54%)��belonging to calc-alkaline series�� The rocks are characterized by enrichment in LILE (such as K����b��Ba and Sr) and rela- tively depleting in HFSE (such as Nb��Ta��Hf��Zr and Ti)��and the chondrite-normalized ��EE patterns exhibit a right-dipping type�� Low Mg # values (39 ��43 ��45) and compatible elements like Cr (3. 12 × 10 ^��6 �� 24. 6 × 10^��6 ) and Ni (5. 57 ×10 ^��6 ��11. 6 ×10 ^��6 ) suggest that the primary magma was derived from lower crust�� Combined with the data of igneous rocks of the same age��the authors conclude that the formation of Zhungashun grano- diorites were related to the subduction of the Paleo-Asian oceanic plate��