摘要
黄河和长江流域泛滥平原细粒沉积物的 Sr同位素组成存在较大差异。前者的 87Sr/86Sr变化范围较小，为 0.712 868～ 0.718 860，平均值为 0.715 474；后者变化范围较大，为 0.713 035～ 0.736 502，平均值为 0.721 438。黄河流域中、上游细粒沉积物的 87Sr/86Sr低于下游；而长江流域细粒沉积物的 87Sr/86Sr中游高于上、下游，且南侧高于北侧。由 NW向 SE， 87Sr/86Sr逐渐增加。 87Sr/86Sr这种空间变化规律明显受各汇水盆地内地壳岩石平均组成、年龄和化学风化作用强度的制约：岩石的 Rb/Sr比值越大、年代越老、化学风化作用越强， 87Sr/86Sr比值就越大。 87Sr/86Sr比值是识别中国边缘海黄河、长江输运物质的有效参数，其端员值分别为 0.719 269和 0.724 312。
There is clear difference of strontium isotopic compositions between fine-grained sediments from the overbanks of the Yellow River’ s watershed and those of the Yangtze River’ s watershed. The range of 87Sr/86Sr of the former is from 0.712 868 to 0.718 860, with an average of 0.715 474, which is lower than that of the latter, whose range is from 0.713 035 to 0.736 502, with an average of 0.721 438. In the Yellow River’ s watershed, the 87Sr/86Sr ratios of the fine-grained sediment from the overbanks of the middle and upper reaches are lower than those of the lower reach are. While in the Yangtze River’ s watershed, the 87Sr/86Sr ratios of the fine-grained sediments from the overbanks of the middle reach are higher than those of the upper and lower reaches are, and higher in the south than in the north. Both in the fountainheads and lower reaches, 87Sr/86Sr ratios of the Yellow River’ s watershed are approximately equal to those of the Yangtze River’ s watershed. The difference of 87Sr/86Sr in the fine-grained sediments between the Yellow River’ s watershed and the Yangtze River’ s watershed merely exists in each middle and upper reaches. Therefore, in the whole area, the 87Sr/86Sr ratios increase gradually from the northwest to the southeast. The spatial variation of 87Sr/86Sr ratios is clearly related to the chemical composition of the fine-grained sediments in each catchment basin: the greater Rb/Sr, the greater 87Sr/86Sr; and the lower concentrations of CaCO3, Na2O, CaO, and MgO in the fine-grained sediments, the greater 87Sr/86Sr. These relationships implicate that spatial variation of 87Sr/86Sr is controlled by chemical compositions and ages of crust rocks in each catchment basin, as well as by the strength of chemical weathering, i.e., the greater Rb/Sr of the rocks, or the older rocks, or the stronger chemical weathering, the greater 87Sr/86Sr ratio. The flux of particulates entering marginal China Sea, driven respectively by the Yellow River and the Yangtze River, is mainly controlled by middle and upper reaches, each of Yellow River and Yangtze River. Therefore, it is due to the difference of 87Sr/86Sr, existing in the middle and upper reaches, between Yellow River’ s watershed and Yangtze River’ s watershed that makes it be an useful tool for recognizing the Yellow River-driven matters or Yangtze River-driven matters from sediments of the marginal China Sea. According to effect of chemical averaging during the surficial action, two 87Sr/86Sr of ratios of suspended particulate matter (treated by 0.25 mol/L HCl) each from master stream of the Yellow River and Yangtze River, not affected by tide, but nearest to mouths, are used to represent endmember values (0.719 269 and 0.724 312, respectively).
出处
《地球化学》
CAS
CSCD
北大核心
2000年第6期562-569,共8页
Geochimica
基金
国家自然科学基金资助项目!(49706068)
关键词
平原
沉积物
同位素示踪
黄河
长江
锶同位素
overbank sediments
strontium isotope tracing
Yellow River’ s watersheds
Yangtze River’ s watersheds
