摘要
Extraterrestrial particles have higher 3He/4He ratios than those of terrestrial sediments ( > 100 Ra versus < 0.03 Ra, where Ra is the 3He/4He ratio normalized to the atmospheric value of 1.4×10?6). The inter- planetary dust particles (IDPs), which are very rich in 3He, continuously bombard the Earth and can accumulate in deposits. IDPs sedimentation rate changes can significantly influence 3He concentration in the Earth surface sediments. Since IDPs are not easy to detect in terrestrial deposits, measuring helium isotopes is a helpful approach to examine changes in IDPs. Helium concentration and helium isotopic composition magnetic substances and the quartz particles were examined for helium concen- tration and helium isotopic ratio. Results show that the 3He/4He ratio and the 3He concentrations of the magnetic substances are clearly higher than those of the bulk samples and the quartz particles, and, the 3He/4He ratio of the extracted magnetic substances is also higher than that of the average level of the Earth’s crust. The higher helium content in the magnetic fractions can be explained by an influx of IDPs.
Extraterrestrial particles have higher ^3He/^4He ratios than those of terrestrial sediments （ 〉 100 Ra versus 〈 0.03 Ra, where Ra is the ^3He/^4He ratio normalized to the atmospheric value of 1.4×10^-6）. The interplanetary dust particles （IDPs）, which are very rich in ^3He, continuously bombard the Earth and can accumulate in deposits. IDPs sedimentation rate changes can significantly influence ^3He concentration in the Earth surface sediments. Since IDPs are not easy to detect in terrestrial deposits, measuring helium isotopes is a helpful approach to examine changes in IDPs. Helium concentration and helium isotopic composition magnetic substances and the quartz particles were examined for helium concentration and helium isotopic ratio. Results show that the ^3He/^4He ratio and the ^3He concentrations of the magnetic substances are clearly higher than those of the bulk samples and the quartz particles, and, the ^3He/^4He ratio of the extracted magnetic substances is also higher than that of the average level of the Earth＇s crust. The higher helium content in the magnetic fractions can be explained by an influx of IDPs.
作者
DU XueQing1,6, WANG YongHong2, REN JianGuo3, YE XianRen4 & LU HuaYu5,1 1 State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China
2 College of Marine Geosciences, Ocean University of China, Qingdao 266003, China
3 National Natural Science Foundation of China, Beijing 100085, China
4 Lanzhou Research Center for Petroleum and Natural Gas Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China
5 Key Laboratory of Coast and Island Development, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210093, China
6 Graduate University of Chinese Academy of Sciences, Beijing 100049, China
基金
Supported by the National Natural Science Foundation of China (Grant Nos. 40173006 and 40325007)
Key Research Project of Ministry of Education, China (Grant No. 03106)
National Basic Research Program of China (Grant No. 2004CB720506)
关键词
中国
黄土高原
古土壤
氦同位素
行星际尘埃颗粒
反方向磁化
interplanetary dust particles （IDPs）, helium composition and isotope, Loess-paleosol sequence at Luochuan, Chinese Loess Plateau
