Five biotites of Himalayan Period from southern Xizang platean have been irradiated and determined using reactor No. 901 in Qinghua University as fast neutron source(neutron flux 1.17× 10^13n/cm^2·s, fast ne...Five biotites of Himalayan Period from southern Xizang platean have been irradiated and determined using reactor No. 901 in Qinghua University as fast neutron source(neutron flux 1.17× 10^13n/cm^2·s, fast neutron - 25%, duration of irradiation 18 hours) and MMhb-1 hornblende from USA as standard. Most of the samples were also determined by Ar^36 isotope dilation method, and good agreement has been obtained for the results between the two approaches. This shows that Ar^40/Ar^39 dating is capable to distinguish clearly the order of intrusion among the multiphase intrnsions with respect to the young granites of Himalayan Period. Powder sample of CaF2 and K2SO4 were irradiated and ratios of (Ar^36/Ar^37)Ca. and(Ar^39/Ar^37)Ca and (Ar^40/Ar^39)x have been measured, which are of the same magnitutc of order as reported from other reac-tors in the world. For the ZBH-2506 biotite standard of China, Ar^40/Ar^39 age (130.9--131.9my)agrees with the age of 131±2.6 my as determined by dilution method. Plateau age obtained by step-wise heating (131±0.8my) is similar with the data obtained from total fusion and dilution methods.展开更多
文摘Five biotites of Himalayan Period from southern Xizang platean have been irradiated and determined using reactor No. 901 in Qinghua University as fast neutron source(neutron flux 1.17× 10^13n/cm^2·s, fast neutron - 25%, duration of irradiation 18 hours) and MMhb-1 hornblende from USA as standard. Most of the samples were also determined by Ar^36 isotope dilation method, and good agreement has been obtained for the results between the two approaches. This shows that Ar^40/Ar^39 dating is capable to distinguish clearly the order of intrusion among the multiphase intrnsions with respect to the young granites of Himalayan Period. Powder sample of CaF2 and K2SO4 were irradiated and ratios of (Ar^36/Ar^37)Ca. and(Ar^39/Ar^37)Ca and (Ar^40/Ar^39)x have been measured, which are of the same magnitutc of order as reported from other reac-tors in the world. For the ZBH-2506 biotite standard of China, Ar^40/Ar^39 age (130.9--131.9my)agrees with the age of 131±2.6 my as determined by dilution method. Plateau age obtained by step-wise heating (131±0.8my) is similar with the data obtained from total fusion and dilution methods.
