新生代後期におけるグローバルストロンチウム循環と風化作用の関係

抄録

A computational model of global strontium cycle in the late Cenozoic (Neogene) has been built up. It is used for evaluating the influence of the weathering in the HTP (Himalayan and Tibetan Plateau) region due to the uplift and denudation and that in high-latitude area due to the glaciation on the increase in seawater ⁸⁷Sr/⁸⁶Srr in the late Cenozoic. The results indicate that (1) approximately 30% of the increase in ⁸⁷Sr/⁸⁶Srr of seawater can be explained by the HTP weathering, which is substantially influential as compared to its small area;(2) however, the ⁸⁷Sr/⁸⁶Srr fluctuations of silicate weathering in the region except the HTP region could be partially attributed to the weathering in high latitude especially the Antarctica;(3) the correlation between this ⁸⁷Sr/⁸⁶Srr variation and δ¹⁸O variation is identified in from the late Oligocene to the early Miocene and the Pliocene to the present, whereas the correlation is not confirmed in from the middle to late Miocene.
This discrepancy may be partially derived from uncertainty of estimation of the HTP uplift and the ⁸⁷Sr/⁸⁶Srr variation in the region except the HTP and high-latitude areas. The critical problems in attributing the increase in seawater ⁸⁷Sr/⁸⁶Srr to the weathering in high-latitude area might be low temperature and water availability. The former could be overcome by the previous studies of dependence of weathering rate and temperature, but the water availability in high latitude might have varied with time. Because low water availability has been presumed since late Miocene by previous studies, the above disagreement in from the middle to the late Miocene might be identified.