海底多金属结核和富钴结壳的He同位素对比研究

A Comparative Study of Helium Isotope of Polymetallic Nodules and Cobalt Crust

对东太平洋海盆C- C 区海底多金属结核及西太平洋马绍尔地区富钴结壳的He 同位素组成进行了对比研究。发现结核的3He/4He 比值普遍较高,为(1.73 ～13 .26) ×10- 5 。所有结核样品的3 He/4 He 比值均高于MORB 的平均3 He/4 He 比值,有些样品的3 He/4 He 比值甚至高于地幔热柱的值。磁性部分相对非磁性部分3 He/4He 比值和4 He 含量均明显偏高。结壳的3 He/4 He 比值相对较低,变化范围为6 .05 ×10 - 8 ～8 .08 ×10 - 5 。在3 He- 4He 图上大部分结壳的He 同位素数据点均位于MORB 和地幔热柱的He 同位素分布区及其附近。粒径小于10μm 的宇宙尘含有极高的3 He/4 He 比值和4 He 含量,微量宇宙尘的加入即可造成地内物质的3 He/4 He 比值明显偏高。在3 He- 3 He/4 He 图上,结核、结壳及深海沉积物的He 同位素数据点均沿着宇宙尘与陆壳物质的混合曲线分布。表明海底多金属结核和富钴结壳的He 同位素异常均是由宇宙尘注入引起的。结核中宇宙尘的含量相对较高,约1 ×10- 6 ;结壳中宇宙尘的含量相对较低,且分布不均匀,约为(80 ～800) ×10- 9 。

A comparative study of helium isotope for polymetallic nodules from C-C zone of the east Pacific basin and cobalt crusts from Marshall Island was reported. The nodules from C-C zone of the east Pacific basin all have extraordinarily high 3He/ 4He ratios, from 1.7×10 -5 to 13.3×10 -5 . The 3He/ 4He ratios of all nodule samples are higher than the MORB average level, some even higher than the hot point level. The 3He/ 4He ratios and 4He concentrations of magnetic fractions are obviously higher than those of bulk. The 3He/ 4He ratios of cobalt crust are lower than those of nodules, and vary in a wide range, from 6.05×10 -8 to 8.08×10 -5 . In the 3He- 4He figure, most data points of cobalt crust fall into the helium isotope range of MORB and mantle plume. The micrometeorite interplanetary dust particles (IDPs) smaller than 10μm in diameter have extraordinarily high 3He/ 4He ratios and abundant helium. Trace of IDPs can result in extraordinarily high 3He/ 4He ratios in terrestrial material. In the 3He- 3He/ 4He figure, all data points of nodules, cobalt crusts and sediments sit in or close to the mixing curve between the micrometeorite interplanetary dust particles (IDPs) and the terrigenous sediments. It is considered that, just as those of pelagic sediments,the anomalous helium isotope ratios of nodules and crust can be attributed to IDPs. The concentration of IDPs in nodules is about 1×10 -6 ,and that in cobalt crust is lower, from 80×10 -9 to 800 ×10 -9 .