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粒径小于10μm的宇宙尘含有较地表沉积物高的稀有气体同位素3He/4He比值和3He浓度,地表物质平均3He/4He比值不足0.1RA(RA即airratio,是大气中3He/4He比值,RA=1.4×10?6),而宇宙尘的3He/4He比值却大于100RA.因此,沉积物中宇宙尘的加入可以从3He/4He比值反映出来.本文以典型的洛川黄土剖面为研究对象,对磁性地层B/M和M/G界线附近的样品进行了氦同位素测试,以探索黄土堆积的宇宙尘纪录.对8个样品的原岩样、提取的磁性矿物和石英颗粒分别进行了测试,发现磁性矿物的3He/4He比值较陆壳的值高出了一个数量级,3He和4He含量也均明显偏高,特别是磁性矿物的3He浓度比石英颗粒高出了2～3个数量级,比全岩部分高出了1～2个数量级.这些结果表明,洛川黄土中磁性矿物的高比率3He/4He可能是由于宇宙尘的注入引起的.
The cosmic dust with particle size less than 10μm contains isotopes of 3He / 4He and 3He which are higher than the surface sediments, and the average 3He / 4He ratio of the surface material is less than 0.1RA (RA is the airratio, which is the 3He / 4He ratio in the atmosphere, RA = 1.4 × 10 6), while the 3He / 4He ratio of cosmic dust is greater than 100RA. Therefore, the addition of cosmic dust in the sediments can be reflected by the 3He / 4He ratio.In this paper, the typical Luochuan loess section is taken as the research object, Helium isotope tests were performed on helium isotope samples near the B / M and M / G boundaries of the magnetic stratigraphy to explore the cosmic dust record of loess accumulation. The original samples of 8 samples, the extracted magnetic minerals and quartz particles were tested and found The 3He / 4He ratio of magnetic minerals is one order of magnitude higher than that of the continental crust, and the 3He and 4He contents are also significantly higher. In particular, 3He concentration of magnetic minerals is 2 to 3 orders of magnitude higher than that of quartz grains, Partly higher than 1 ~ 2 orders of magnitude.These results show that the high ratio of 3He / 4He to magnetic minerals in Luochuan loess may be caused by the injection of cosmic dust.