�Գ�¶�ڴ��˰������϶�����������������ͷ������������ҽ�������ϸ�����ѧ�͵���ѧ�о���LA--ICP--MS �ʯ U--Pb �������������������γ��� 143 ��141 Ma��ʱ��Ϊ����������ڣ���������ǰ��Ϊ����٪����������ѧ����������ʱ�����������߼ظƼ��Թ�������ʯ��������ʯ��׼��ϡ��������߳���ϡ��������������ʽ�� ( La/Yb)N= 2. 55 �� 12. 82���������Ը� Eu �쳣��ԭʼ��ᣱ�׼��ͼ����ʾ��������ʯԪ�� ( LILE) ��b��Th��U��K��Pb �ĸ������߳�ǿԪ�� ( HFSE) Nb�� Ta��Ti��P ��ǿ�ҿ������ǿ�Դ�ҽ����������������ʯ εHf( t) = + 4. 6 �� + 10. 9�����׶� Hf ģʽ����Ϊ 501 ��905 Ma����Ӧ��Դ��������ҪΪ�������—��Ԫ�Ŵ�ʱ������������ؿ����ʡ�����ͷ�������������γ�����ɽ����չ�������������ɹ�—�����Ŀ���պϺ����ʯȦ��չ������ء�

The authors studied in detail the chronology and geochemistry of the rhyolites in Manketou'ebo For- mation from Ta'erqi area of central Greater Xing'an ��ange�� LA--ICP--MS ziron U--Pb dating revealed that the vol- canic rocks formed in 143 �� 141 Ma��which is the early Early Cretaceous rather than Late Jurassic previously�� Meanwhile��the geochemical characteristics of the rhyolites belong to high-K calc-alkaline peraluminous rocks��and the chondrite-normalized ��EE paterns indicate the volcanic rocks enriched in light rare earth elements with signifi- cant fractionation of H��EE and L��EE ( (La/Yb)N=2. 55 ��12. 82) and strong negative Eu anolies�� The primitive mantle-normalized trace element spidergram showed the volcanic rocks containing high LILE (��b��Th��U��K��Pb) and low HFSE (Nb��Ta��Ti��P)��in accord with the characteristics of crust source magma�� The rhyolitic zircon had εHf(t) values ranging from +4. 6 to +10. 9��and the two-age Hf model age was 501 ��905 Ma�� These datsuggest that the magma for these volcanic rocks derived from the newly accreted Early Paleozoic-Neoproterozoic ju- venile crustal materials�� The rhyolites of Manketou'ebo Formation formed in non orogenic intraplate environment and maybe closely related to the lithosphere extension after the closure of Mongol �� Okhotsk Ocean��