Five manganese nodules collected from the Northern Mid - Pacific have been analysed for their U and Th isotopes.lt is found that the enrichment of thorium compared to uranium is universal in deep- sea manganese, nodul...Five manganese nodules collected from the Northern Mid - Pacific have been analysed for their U and Th isotopes.lt is found that the enrichment of thorium compared to uranium is universal in deep- sea manganese, nodules and in the top sides of the nodules there are large excesses of Th and Pa decreasing exponentially with depth. For each of the nodules, the concordant growth rates are obtained from three different methods: 230Thex 230Thex/232Th and 231Paex.The growth rates of manganese nodules are closely related to the chemical compositions of the nodules and the types of the underlying sediments. The growth rates of five nodules are determined to be in the range of 0.79-7.4 mm/106a, in agreement with those predicted from the chemical compositions of the nodules. By the comparison of the extrapolated 230Thex,230Thex/232 Th and 231PaeX data from the top and bottom surfaces of the nodule from Site M21 yields, the nodule turnover time is (9.83-13.7)×104a.展开更多
文摘Five manganese nodules collected from the Northern Mid - Pacific have been analysed for their U and Th isotopes.lt is found that the enrichment of thorium compared to uranium is universal in deep- sea manganese, nodules and in the top sides of the nodules there are large excesses of Th and Pa decreasing exponentially with depth. For each of the nodules, the concordant growth rates are obtained from three different methods: 230Thex 230Thex/232Th and 231Paex.The growth rates of manganese nodules are closely related to the chemical compositions of the nodules and the types of the underlying sediments. The growth rates of five nodules are determined to be in the range of 0.79-7.4 mm/106a, in agreement with those predicted from the chemical compositions of the nodules. By the comparison of the extrapolated 230Thex,230Thex/232 Th and 231PaeX data from the top and bottom surfaces of the nodule from Site M21 yields, the nodule turnover time is (9.83-13.7)×104a.
