�����ױ��ǻ��ֹȵ�����״�����ҽ���ϵͳ�ĵ���ѧ�� Sr--Nd ͬλ���о�����������ʯ���򼰹���������������ۡ�����������ð�״������Ϊ�߼ظƼ���—������ϵ�е�׼���ʻ�����; ��ʯ�����ϡ���� ��b��Th��U��K��Pb �ȴ�������ʯԪ�أ�ƶ Nb��Ta��Ti��Zr��Hf �ȸ߳�ǿԪ�أ������е����쳣����ʯ�ȳ�ʼֵΪ 0. 715 61 ��0. 722 07��εNd( t) Ϊ ��13. 9 �� ��12. 7��Nd ͬλ��ģʽ����Ϊ2 025 ��2 153 Ma����ʾ���ֹȵ�����״������Ϊͬ��ײ S �ͻ����ң���Ҫ��Դ�ڹ��ϵؿ����ʵ����ۣ��� Kalahari ����ͨ�� Congo ����ͨ��ײ��ɽ�IJ��

The authors studied the geochemical characteristic and Sr-Nd isotope of the porphyritic granites in the Gaudeanmus area��Namibia and discussed the petrogenesis and tectonic significance�� The results indicate the porphyritic granites showing the characteristics of metaluminous��belonging to high-K calc-alkaline to shoshonite se- ries�� The granites contained high alkali and rare eatth elements (��EE)��enriched in large-ion lithopile elements (��b��Th��U��K��Pb)��and depleted in high field-strength elements (Nb��Ta��Ti��Zr��Hf)��with medium negative Eu anomalies�� These rocks have high initial 87Sr/86Sr ratios (0. 715 61 ��0. 722 07)��low intial εNd(t) values ( ��13. 9 �� ��12. 7) and ancient Nd isotope crust model ages (2 025 ��2 153 Ma)�� Such geochemical signa- ture showed that the porphyritic granites were syn-collision S-type granite in characteristics and derived from partial melting of ancient crustal rocks during the main periods collision of Kalahari and Congo craton��